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Sunday, May 31st, 2015

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Choi, S., Lim, D.S. and Chung, J. (2015). Feeding and fasting signals converge on the LKB1-SIK3 pathway to regulate lipid metabolism in Drosophila. PLoS Genet 11: e1005263. PubMed ID: 25996931
Summary:
LKB1 plays important roles in governing energy homeostasis by regulating AMP-activated protein kinase (AMPK) and other AMPK-related kinases, including the salt-inducible kinases (SIKs). However, the roles and regulation of LKB1 in lipid metabolism are poorly understood. This study shows that Drosophila LKB1 mutants display decreased lipid storage and increased gene expression of brummer, the Drosophila homolog of adipose triglyceride lipase (ATGL). These phenotypes were consistent with those of SIK3 mutants and were rescued by expression of constitutively active SIK3 in the fat body, suggesting that SIK3 is a key downstream kinase of LKB1. Using genetic and biochemical analyses, HDAC4, a class IIa histone deacetylase, was identified as a lipolytic target of the LKB1-SIK3 pathway. Interestingly, it was found that the LKB1-SIK3-HDAC4 signaling axis was modulated by dietary conditions. In short-term fasting, the adipokinetic hormone (AKH) pathway, related to the mammalian glucagon pathway, inhibited the kinase activity of LKB1 as shown by decreased SIK3 Thr196 phosphorylation, and consequently induced HDAC4 nuclear localization and brummer gene expression. However, under prolonged fasting conditions, AKH-independent signaling decreased the activity of the LKB1-SIK3 pathway to induce lipolytic responses. It was also identified that the Drosophila insulin-like peptides (DILPs) pathway, related to mammalian insulin pathway, regulated SIK3 activity in feeding conditions independently of increasing LKB1 kinase activity. Overall, these data suggest that fasting stimuli specifically control the kinase activity of LKB1 and establish the LKB1-SIK3 pathway as a converging point between feeding and fasting signals to control lipid homeostasis in Drosophila.

Eriksson, A., et al. (2015). Implication of coronin 7 in body weight regulation in humans, mice and flies. BMC Neurosci 16: 13. PubMed ID: 25887538
Summary:
Obesity is a growing global concern with strong associations with cardiovascular disease, cancer and type-2 diabetes. Although various genome-wide association studies have identified more than 40 genes associated with obesity, these genes cannot fully explain the heritability of obesity, suggesting there may be other contributing factors, including epigenetic effects. This study performed genome wide DNA methylation profiling comparing normal-weight and obese 9-13 year old children to investigate possible epigenetic changes correlated with obesity. Of note, obese children had significantly lower methylation levels at a CpG site located near coronin 7 (CORO7), which encodes a tryptophan-aspartic acid dipeptide (WD)-repeat containing protein most likely involved in Golgi complex morphology and function. Anatomical profiling of coronin 7 (Coro7) mRNA expression in mice revealed that it was highly expressed in appetite and energy balance regulating regions, including the hypothalamus, striatum and locus coeruleus, the main noradrenergic brain site. Interestingly, food deprivation in mice downregulated hypothalamic Coro7 mRNA levels, and injecting ethanol, an appetite stimulant, increased the number of Coro7 expressing cells in the locus coeruleus. Finally, by employing the genetically-tractable Drosophila melanogaster model they were able to demonstrate an evolutionarily conserved metabolic function for the CORO7 homologue pod1. Knocking down the pod1 in the Drosophila adult nervous system increased their resistance to starvation. Furthermore, feeding flies a high-calorie diet significantly increased pod1 expression. The study concludes that coronin 7 is involved in the regulation of energy homeostasis and this role stems, to some degree, from the effect on feeding for calories and reward.

Waterson, M. J., Chan, T. P. and Pletcher, S. D. (2015). Adaptive physiological response to perceived scarcity as a mechanism of sensory modulation of life span. J Gerontol A Biol Sci Med Sci. PubMed ID: 25878032
Summary:
Chemosensation is a potent modulator of organismal physiology and longevity. In Drosophila, loss of recognition of diverse tastants has significant and bidirectional life-span effects. Recently published results revealed that when flies were unable to taste water, they increased its internal generation, which may have subsequently altered life span. To determine whether similar adaptive responses occur in other contexts, this study explored the impact of sensory deficiency of other metabolically important molecules. Trehalose is a major circulating carbohydrate in the fly that is recognized by the gustatory receptor Gr5a. Gr5a mutant flies are short lived, and this study found that they specifically increased whole-body and circulating levels of trehalose, but not other carbohydrates, likely through upregulation of de novo synthesis. dILP2 transcript levels were increased in Gr5a mutants, a possible response intended to reduce hypertrehalosemia, and likely a contributing factor to their reduced life span. Together, these data suggest that compensatory physiological responses to perceived environmental scarcity, which are designed to alleviate the ostensive shortage, may be a common outcome of sensory manipulation. It is suggested that future investigations into the mechanisms underlying sensory modulation of aging may benefit by focusing on direct or indirect consequences of physiological changes that are designed to correct perceived disparity with the environment.

Ugrankar, R., Berglund, E., Akdemir, F., Tran, C., Kim, M.S., Noh, J., Schneider, R., Ebert, B. and Graff, J.M. (2015). Drosophila glucome screening identifies Ck1alpha as a regulator of mammalian glucose metabolism. Nat Commun 6: 7102. PubMed ID: 25994086
Summary:
Circulating carbohydrates are an essential energy source, perturbations in which are pathognomonic of various diseases, diabetes being the most prevalent. Yet many of the genes underlying diabetes and its characteristic hyperglycaemia remain elusive. This study uses physiological and genetic interrogations in D. melanogaster to uncover the 'glucome', the complete set of genes involved in glucose regulation in flies. Partial genomic screens of ∼1,000 genes yielded ∼160 hyperglycaemia 'flyabetes' candidates that were classify using fat body- and muscle-specific knockdown and biochemical assays. The results highlighted the minor glucose fraction as a physiological indicator of metabolism in Drosophila. Loss of Ck1alpha in both fat body and muscle of third instar larvae produced significant haemolymph glucose elevations 100% of the time This gene may have conserved functions in mammalian glucose homeostasis, as heterozygous and homozygous mutants of Ck1alpha in the murine adipose lineage, developed diabetes. These findings demonstrate that glucose has a role in fly biology and that genetic screenings carried out in flies may increase our understanding of mammalian pathophysiology.

Saturday, May 30th

Byri, S., Misra, T., Syed, Z.A., Bätz, T., Shah, J., Boril, L., Glashauser, J., Aegerter-Wilmsen, T., Matzat, T., Moussian, B., Uv, A. and Luschnig, S. (2015). The triple-repeat protein Anakonda controls epithelial tricellular junction formation in Drosophila. Dev Cell [Epub ahead of print]. PubMed ID: 25982676
Summary:
In epithelia, specialized tricellular junctions (TCJs) mediate cell contacts at three-cell vertices. TCJs are fundamental to epithelial biology and disease, but only a few TCJ components are known, and how they assemble at tricellular vertices is not understood. This study describes a transmembrane protein, Anakonda (Aka), which localizes to TCJs and is essential for the formation of tricellular, but not bicellular, junctions in Drosophila. Loss of Aka caused epithelial barrier defects associated with irregular TCJ structure and geometry, suggesting that Aka organized cell corners. Aka was necessary and sufficient for accumulation of Gliotactin at TCJs, suggesting that Aka initiated TCJ assembly by recruiting other proteins to tricellular vertices. Aka's extracellular domain had an unusual tripartite repeat structure that might mediate self-assembly, directed by the geometry of tricellular vertices. Conversely, Aka's cytoplasmic tail was dispensable for TCJ localization. Thus, extracellular interactions, rather than TCJ-directed intracellular transport, appear to mediate TCJ assembly.

Vanderploeg, J. and Jacobs, R. (2015). Talin is required to position and expand the luminal domain of the Drosophila heart tube. Dev Biol [Epub ahead of print]. PubMed ID: 25958089
Summary:
Fluid- and gas-transporting tubular organs are critical to metazoan development and homeostasis. Tubulogenesis involves cell polarization and morphogenesis to specify the luminal, adhesive, and basal cell domains and to establish an open lumen. This study explores a requirement for Talin, a cytoplasmic integrin adaptor, during Drosophila melanogaster embryonic heart tube development. Talin marked the presumptive luminal domain and was required to orient and develop an open luminal space within the heart. Genetic analysis demonstrated that loss of zygotic or maternal-and-zygotic Talin disrupted heart cell migratory dynamics, morphogenesis, and polarity. Talin was essential for subsequent polarization of luminal determinants Slit, Robo, and Dystroglycan as well as stabilization of extracellular and intracellular integrin adhesion factors. In the absence of Talin function, mini-lumens enriched in luminal factors formed in ectopic locations. Rescue experiments performed with mutant Talin transgenes suggested actin-binding was required for normal lumen formation, but not for initial heart cell polarization. The study proposes that Talin provides instructive cues to position the luminal domain and coordinate the actin cytoskeleton during Drosophila heart lumen development.

Saias, L., Swoger, J., D'Angelo, A., Hayes, P., Colombelli, J., Sharpe, J., Salbreux, G. and Solon, J. (2015). Decrease in cell volume generates contractile forces driving dorsal closure. Dev Cell [Epub ahead of print]. PubMed ID: 25982674
Summary:
Biological tissues must generate forces to shape organs and achieve proper development. Such forces often result from the contraction of an apical acto-myosin meshwork. This study describes an alternative mechanism for tissue contraction, based on individual cell volume change. It was shown that during Drosophila dorsal closure (DC), a wound healing-related process, the contraction of the amnioserosa (AS) was associated with a major reduction of the volume of its cells, triggered by caspase activation at the onset of the apoptotic program of AS cells. Cell volume decrease resulted in a contractile force that promoted tissue shrinkage. Estimating mechanical tensions with laser dissection and using 3D biophysical modeling, it was shown that the cell volume decrease acted together with the contraction of the actin cable surrounding the tissue to govern DC kinetics. The study identifies a mechanism by which tissues generate forces and movements by modulating individual cell volume during development.

Klomp, J., Athy, D., Kwan, C. W., Bloch, N. I., Sandmann, T., Lemke, S. and Schmidt-Ott, U. (2015). A cysteine-clamp gene drives embryo polarity in the midge Chironomus. Science [Epub ahead of print]. PubMed ID: 25953821
Summary:
In the common fruit fly Drosophila, head formation is driven by a single gene, bicoid, which generates head-to-tail polarity of the main embryonic axis. Bicoid deficiency results in embryos with tail-to-tail polarity and no head. However, most insects lack bicoid, and the molecular mechanism for establishing head-to-tail polarity is poorly understood. A gene has been identified that establishes head-to-tail polarity of the mosquito-like midge, Chironomus riparius. This gene, named panish, encodes a cysteine-clamp DNA binding domain and operates through a different mechanism than bicoid. This finding, combined with the observation that the phylogenetic distributions of panish and bicoid are limited to specific families of flies, reveals frequent evolutionary changes of body axis determinants and a remarkable opportunity to study gene regulatory network evolution.

Friday, May 29th

Wagner, N., Laugks, U. Heckmann, M., Asan, E. and Neuser, K. (2015) . Aging Drosophila melanogaster display altered pre- and postsynaptic ultrastructure at adult neuromuscular junctions. J Comp Neurol [Epub ahead of print]. PubMed ID: 25940748
Summary:
While age-related changes in synaptic plasticity are an important focus within neuroscience, little is known about ultrastructural changes of synaptic morphology during aging. This study reports how aging affects synaptic ultrastructure using fluorescence and electron microscopy at the adult Drosophila neuromuscular junction (NMJ) of ventral abdominal muscles. Mainly four striking morphological changes of aging NMJs were revealed: (1) Bouton size increased with proportionally rising number of active zones (AZs). (2) Synaptic vesicle (SV) density at AZs was increased in old flies. (3) Late endosomes, cisternae and multivesicular bodies (MVBs) accumulated in the presynaptic terminal and vesicles accumulated between membranes of the terminal bouton and the subsynaptic reticulum. (4) The electron-dense pre- and postsynaptic apposition was expanded in aging NMJs, accompanied by an expansion of the postsynaptic glutamate receptor fields. These findings suggest that aging is possibly accompanied by impaired synaptic vesicle release and recycling, and a potentially compensatory, expansion of active zones and postsynaptic densities.

Li, T., Tan, Y., Li, Q., Chen, H., Lv, H., Xie, W. and Han, J. (2015). The Neurexin-NSF interaction regulates short-term synaptic depression. J Biol Chem. [Epub ahead of print]. PubMed ID: 25953899
Summary:
Although Neurexins, which are cell adhesion molecules localized predominately to the presynaptic terminals, are known to regulate synapse formation and synaptic transmission, their role in the regulation of synaptic vesicle release during repetitive nerve stimulation is unknown. This study shows that Drosophila neurexin mutant synapses exhibit rapid short-term synaptic depression upon tetanic nerve stimulation. Moreover, the intracellular region of Neurexin was demonstrated to be essential for synaptic vesicle release upon tetanic nerve stimulation. Using a yeast two-hybrid screen, it was found that the intracellular region of Neurexin interacts with N-ethylmaleimide sensitive factor (NSF), an enzyme that mediates soluble NSF attachment protein receptor (SNARE) complex disassembly and plays an important role in synaptic vesicle release. The binding sites of each molecule were mapped, and it was demonstrated that the Neurexin-NSF interaction is critical for both the distribution of NSF at the presynaptic terminals and SNARE complex disassembly. These results reveal a previously unknown role of Neurexin in the regulation of short-term synaptic depression upon tetanic nerve stimulation and provide new mechanistic insights into the role of Neurexin in synaptic vesicle release.

Kim, J. H., Ren, Y., Ng, W. P., Li, S., Son, S., Kee, Y. S., Zhang, S., Zhang, G., Fletcher, D. A., Robinson, D. N. and Chen, E. H. (2015). Mechanical tension drives cell membrane fusion. Dev Cell 32: 561-573. PubMed ID: 25684354
Summary:
Membrane fusion is an energy-consuming process that requires tight juxtaposition of two lipid bilayers. Little is known about how cells overcome energy barriers to bring their membranes together for fusion. Previous studies have shown that cell-cell fusion is an asymmetric process in which an 'attacking' cell drills finger-like protrusions into the 'receiving' cell to promote cell fusion. This study shows that the receiving cell mounts a Myosin II (MyoII)-mediated mechanosensory response to its invasive fusion partner. MyoII acts as a mechanosensor, which directs its force-induced recruitment to the fusion site, and the mechanosensory response of MyoII is amplified by chemical signaling initiated by cell adhesion molecules. The accumulated MyoII, in turn, increases cortical tension and promotes fusion pore formation. It is proposed that the protrusive and resisting forces from fusion partners put the fusogenic synapse under high mechanical tension, which helps to overcome energy barriers for membrane apposition and drives cell membrane fusion. A preview of this article is available: Myoblast Fusion: Playing Hard to Get

Valdez, C., Scroggs, R., Chassen, R. and Reiter, L. T. (2015). Variation in Dube3a expression affects neurotransmission at the Drosophila neuromuscular junction. Biol Open [Epub ahead of print]. PubMed ID: 25948754
Summary:
Changes in UBE3A expression levels in neurons can cause neurogenetic disorders ranging from Angelman syndrome (AS) (decreased levels) to autism (increased levels). This study investigated the effects on neuronal function of varying UBE3A levels using the Drosophila neuromuscular junction. Stimulations that evoked excitatory junction potentials (EJPs) at 1 Hz intermittently failed to evoke EJPs at 15 Hz in a significantly higher proportion of Dube3a over-expressors relative to controls. However, in the Dube3a over-expressing larval neurons with no failures, there was no difference in EJP amplitude at the beginning of the train, or the rate of decrease in EJP amplitude over the course of the train compared to controls. In the absence of tetrodotoxin (TTX), spontaneous EJPs were observed in significantly more over-expression larva compared to controls. In the presence of TTX, spontaneous and evoked EJPs were completely blocked and mEJP amplitude and frequency did not differ among genotypes. These data suggest that over-expression of wild type Dube3a, but not a ubiquitination defective protein, compromises the ability of motor neuron axons to support closely spaced trains of action potentials, while at the same time increasing excitability. Effects could not be recapitulated using knockdown of Dube3a in muscle or neurons alone, suggesting more global developmental defects contribute to this phenotype. These data suggest that reduced UBE3A expression levels may cause global changes that affect resting membrane potential and neurotransmitter release from motorneurons at the NMJ.

Thursday, May 28th

Byri, S., Misra, T., Syed, Z.A., Bätz, T., Shah, J., Boril, L., Glashauser, J., Aegerter-Wilmsen, T., Matzat, T., Moussian, B., Uv, A. and Luschnig, S. (2015).. The triple-repeat protein Anakonda controls epithelial tricellular junction formation in Drosophila.. Dev Cell [Epub ahead of print]. PubMed ID: 25982676
Summary:
In epithelia, specialized tricellular junctions (TCJs) mediate cell contacts at three-cell vertices. TCJs are fundamental to epithelial biology and disease, but only a few TCJ components are known, and how they assemble at tricellular vertices is not understood. This study describes a transmembrane protein, Anakonda (Aka), which localizes to TCJs and is essential for the formation of tricellular, but not bicellular, junctions in Drosophila. Loss of Aka caused epithelial barrier defects associated with irregular TCJ structure and geometry, suggesting that Aka organized cell corners. Aka was necessary and sufficient for accumulation of Gliotactin at TCJs, suggesting that Aka initiated TCJ assembly by recruiting other proteins to tricellular vertices. Aka's extracellular domain had an unusual tripartite repeat structure that might mediate self-assembly, directed by the geometry of tricellular vertices. Conversely, Aka's cytoplasmic tail was dispensable for TCJ localization. Thus, extracellular interactions, rather than TCJ-directed intracellular transport, appear to mediate TCJ assembly.

Vanderploeg, J. and Jacobs, R. (2015). Talin is required to position and expand the luminal domain of the Drosophila heart tube. Dev Biol [Epub ahead of print]. PubMed ID: 25958089
Summary:
Fluid- and gas-transporting tubular organs are critical to metazoan development and homeostasis. Tubulogenesis involves cell polarization and morphogenesis to specify the luminal, adhesive, and basal cell domains and to establish an open lumen. This study explores a requirement for Talin, a cytoplasmic integrin adaptor, during Drosophila melanogaster embryonic heart tube development. Talin marked the presumptive luminal domain and was required to orient and develop an open luminal space within the heart. Genetic analysis demonstrated that loss of zygotic or maternal-and-zygotic Talin disrupted heart cell migratory dynamics, morphogenesis, and polarity. Talin was essential for subsequent polarization of luminal determinants Slit, Robo, and Dystroglycan as well as stabilization of extracellular and intracellular integrin adhesion factors. In the absence of Talin function, mini-lumens enriched in luminal factors formed in ectopic locations. Rescue experiments performed with mutant Talin transgenes suggested actin-binding was required for normal lumen formation, but not for initial heart cell polarization. The study proposes that Talin provides instructive cues to position the luminal domain and coordinate the actin cytoskeleton during Drosophila heart lumen development.

Klomp, J., Athy, D., Kwan, C. W., Bloch, N. I., Sandmann, T., Lemke, S. and Schmidt-Ott, U. (2015). A cysteine-clamp gene drives embryo polarity in the midge Chironomus.Science. PubMed ID: 25953821
Summary:
In the common fruit fly Drosophila, head formation is driven by a single gene, bicoid, which generates head-to-tail polarity of the main embryonic axis. Bicoid deficiency results in embryos with tail-to-tail polarity and no head. However, most insects lack bicoid, and the molecular mechanism for establishing head-to-tail polarity is poorly understood. This study has identified a gene that establishes head-to-tail polarity of the mosquito-like midge, Chironomus riparius. This gene, named panish, encodes a cysteine-clamp DNA binding domain and operates through a different mechanism than bicoid. This finding, combined with the observation that the phylogenetic distributions of panish and bicoid are limited to specific families of flies, reveals frequent evolutionary changes of body axis determinants and a remarkable opportunity to study gene regulatory network evolution.

Saias, L., Swoger, J., D'Angelo, A., Hayes, P., Colombelli, J., Sharpe, J., Salbreux, G. and Solon, J. (2015). . Decrease in cell volume generates contractile forces driving dorsal closure. Dev Cell [Epub ahead of print]. PubMed ID: 25982674
Summary:
Biological tissues must generate forces to shape organs and achieve proper development. Such forces often result from the contraction of an apical acto-myosin meshwork. This study describes an alternative mechanism for tissue contraction, based on individual cell volume change. It was shown that during Drosophila dorsal closure (DC), a wound healing-related process, the contraction of the amnioserosa (AS) was associated with a major reduction of the volume of its cells, triggered by caspase activation at the onset of the apoptotic program of AS cells. Cell volume decrease resulted in a contractile force that promoted tissue shrinkage. Estimating mechanical tensions with laser dissection and using 3D biophysical modeling, it was shown that the cell volume decrease acted together with the contraction of the actin cable surrounding the tissue to govern DC kinetics. The study identifies a mechanism by which tissues generate forces and movements by modulating individual cell volume during development.

Wednesday, May27th

Sapiro, A. L., Deng, P., Zhang, R. and Li, J. B. (2015). Cis regulatory effects on A-to-I RNA editing in related Drosophila species. Cell Rep [Epub ahead of print]. PubMed ID: 25921533
Summary:
Adenosine-to-inosine RNA editing modifies maturing mRNAs through the binding of adenosine deaminase acting on RNA (Adar) proteins to double-stranded RNA structures in a process critical for neuronal function. Editing levels at individual editing sites span a broad range and are mediated by both cis-acting elements (surrounding RNA sequence and secondary structure) and trans-acting factors. This study aimed to determine the roles that cis-acting elements and trans-acting factors play in regulating editing levels. Using two closely related Drosophila species, D. melanogaster and D. sechellia, and their F1 hybrids, the effects were dissected of cis sequences from trans regulators on editing levels by comparing species-specific editing in parents and their hybrids. This study reports that cis sequence differences are largely responsible for editing level differences between these two Drosophila species. This study presents evidence for cis sequence and structure changes as the dominant evolutionary force that modulates RNA editing levels between these Drosophila species.

Lerner, I., Bartok, O., Wolfson, V., Menet, J. S., Weissbein, U., Afik, S., Haimovich, D., Gafni, C., Friedman, N., Rosbash, M. and Kadener, S. (2015). Clk post-transcriptional control denoises circadian transcription both temporally and spatially. Nat Commun 6: 7056. PubMed ID: 25952406
Summary:
The transcription factor CLOCK (CLK) is essential for the development and maintenance of circadian rhythms in Drosophila. However, little is known about how CLK levels are controlled. This study shows that Clk mRNA is strongly regulated post-transcriptionally through its 3' UTR. Flies expressing Clk transgenes without normal 3' UTR exhibit variable CLK-driven transcription and circadian behaviour as well as ectopic expression of CLK-target genes in the brain. In these flies, the number of the key circadian neurons differs stochastically between individuals and within the two hemispheres of the same brain. Moreover, flies carrying Clk transgenes with deletions in the binding sites for the miRNA bantam have stochastic number of pacemaker neurons, suggesting that this miRNA mediates the deterministic expression of CLK. Overall these results demonstrate a key role of Clk post-transcriptional control in stabilizing circadian transcription, which is essential for proper development and maintenance of circadian rhythms in Drosophila.

Duff, M.O., Olson, S., Wei, X., Garrett, S.C., Osman, A., Bolisetty, M., Plocik, A., Celniker, S.E. and Graveley, B.R. (2015). Genome-wide identification of zero nucleotide recursive splicing in Drosophila. Nature [Epub ahead of print]. PubMed ID: 25970244
Summary:
Recursive splicing is a process in which large introns are removed in multiple steps by re-splicing at ratchet points-5' splice sites recreated after splicing. Recursive splicing was first identified in the Drosophila Ultrabithorax (Ubx) gene and only three additional Drosophila genes have since been experimentally shown to undergo recursive splicing. This study identifies 197 zero nucleotide exon ratchet points in 130 introns of 115 Drosophila genes from total RNA sequencing data generated from developmental time points, dissected tissues and cultured cells. The sequential nature of recursive splicing was confirmed by identification of lariat introns generated by splicing to and from the ratchet points. The study also showed that recursive splicing was a constitutive process, that depletion of U2AF inhibited recursive splicing, and that the sequence and function of ratchet points were evolutionarily conserved in Drosophila. Finally, they identified four recursively spliced human genes, one of which was also recursively spliced in Drosophila. Together, these results indicate that recursive splicing is commonly used in Drosophila, occurs in humans, and provides insight into the mechanisms by which some large introns are removed.

Kelly, S.M., Bienkowski, R., Banerjee, A., Melicharek, D.J., Brewer, Z.A., Marenda, D.R., Corbett, A.H. and Moberg, K.H. (2015). The Drosophila ortholog of the ZC3H14 RNA binding protein acts within neurons to pattern axon projection in the developing brain. Dev Neurobiol [Epub ahead of print]. PubMed ID: 25980665
Summary:
The dNab2 polyadenosine RNA binding protein is the D. melanogaster ortholog of the vertebrate ZC3H14 protein, which is lost in a form of inherited intellectual disability (ID). Human ZC3H14 can rescue D. melanogaster dNab2 mutant phenotypes when expressed in all neurons of the developing nervous system, suggesting that dNab2/ZC3H14 performs well-conserved roles in neurons. However, the cellular and molecular requirements for dNab2/ZC3H14 in the developing nervous system have not been defined in any organism. This study shows that dNab2 is autonomously required within neurons to pattern axon projection from Kenyon neurons into the mushroom bodies, which are required for associative olfactory learning and memory in insects. Mushroom body axons lacking dNab2 projected aberrantly across the brain midline and also showed evidence of defective branching. Coupled with the prior finding that ZC3H14 is highly expressed in rodent hippocampal neurons, this requirement for dNab2 in mushroom body neurons suggested that dNab2/ZC3H14 has a conserved role in supporting axon projection and branching. Consistent with this idea, loss of dNab2 impairs short-term memory in a courtship conditioning assay. Taken together these results reveal a cell-autonomous requirement for the dNab2 RNA binding protein in mushroom body development and provide a window into potential neurodevelopmental functions of the human ZC3H14 protein.

Tuesday, May 26th

Bouzaiane, E., Trannoy, S., Scheunemann, L., Plaçais, P.Y. and Preat, T. (2015). Two independent mushroom body output circuits retrieve the six discrete components of Drosophila aversive memory. Cell Rep [Epub ahead of print]. PubMed ID: 25981036
Summary:
Understanding how the various memory components are encoded and how they interact to guide behavior requires knowledge of the underlying neural circuits. Currently, aversive olfactory memory in Drosophila is behaviorally subdivided into four discrete phases. Among these, short- and long-term memories rely, respectively, on the γ and α/β Kenyon cells (KCs), two distinct subsets of the ∼2,000 neurons in the mushroom body (MB). Whereas V2 efferent neurons retrieve memory from α/β KCs, the neurons that retrieve short-term memory are unknown. This study identified a specific pair of MB efferent neurons, named M6, that retrieve memory from γ KCs. Moreover, network analysis revealed that six discrete memory phases actually existed, three of which had been conflated in the past. At each time point, two distinct memory components separately recruited either V2 or M6 output pathways. Memory retrieval thus features a dramatic convergence from KCs to MB efferent neurons.

Nesterov, A., Spalthoff, C., Kandasamy, R., Katana, R., Rankl, N. B., Andres, M., Jahde, P., Dorsch, J. A., Stam, L. F., Braun, F. J., Warren, B., Salgado, V. L. and Gopfert, M. C. (2015). TRP channels in insect stretch receptors as insecticide targets. Neuron 86: 665-671. PubMed ID: 25950634
Summary:
Defining the molecular targets of insecticides is crucial for assessing their selectivity and potential impact on environment and health. Two commercial insecticides are now shown to target a transient receptor potential (TRP) ion channel complex that is unique to insect stretch receptor cells. Pymetrozine and pyrifluquinazon disturbed Drosophila coordination and hearing by acting on chordotonal stretch receptor neurons. This action required the two TRPs Nanchung (Nan) and Inactive (Iav), which co-occur exclusively within these cells. Nan and Iav together sufficed to confer cellular insecticide responses in vivo and in vitro, and the two insecticides were identified as specific agonists of Nan-Iav complexes that, by promoting cellular calcium influx, silence the stretch receptor cells. This establishes TRPs as insecticide targets and defines specific agonists of insect TRPs. It also shows that TRPs can render insecticides cell-type selective and puts forward TRP targets to reduce side effects on non-target species.

Xiao, N. and Venton, B. J. (2015). Characterization of dopamine releasable and reserve pools in Drosophila larvae using ATP/P2X -mediated stimulation. J Neurochem. PubMed ID: 25951875
Summary:
Dopaminergic signaling pathways are conserved between mammals and Drosophila, but the factors important for maintaining the functional pool of synaptic dopamine are not fully understood in Drosophila. This study characterized the releasable and reserve dopamine pools in Drosophila larvae using ATP/ P2X2 -mediated stimulation. Dopamine release was stable with stimulations performed at least every 5 min but decayed with stimulations performed 2 min apart or less, indicating the replenishment of the releasable pool occurred on a time scale between 2 and 5 min. Dopamine synthesis or uptake were pharmacologically inhibited with 3-iodotyrosine and cocaine, respectively, to evaluate their contributions to maintaining the releasable dopamine pool. Both synthesis and uptake were needed to maintain the releasable dopamine pool, with synthesis playing a major part in long-term replenishment and uptake being more important for short-term replenishment. These effects of synthesis and uptake on different time scales in Drosophila are analogous to mammals. However, unlike in mammals, cocaine did not activate a reserve pool of dopamine in Drosophila when using P2X2 stimulations. This study shows that both synthesis and uptake replenish the releasable pool, providing a better understanding of dopamine regulation in Drosophila.

Chadha, A., Kaneko, M. and Cook, B. (2015). NOMPC-dependent mechanotransduction shapes the dendrite of proprioceptive neurons. Neurosci Lett [Epub ahead of print]. PubMed ID: 25916878
Summary:
Animal locomotion depends on proprioceptive feedback which is generated by mechanosensory neurons. The evolutionarily conserved stumble (stum) gene is essential for mechanical transduction in a group of proprioceptive neurons in Drosophila leg joints. A specialized dendritic ending of the stum-expressing neurons is stretched by changes in joint position, suggesting that the dendritic site is specifically tuned for joint proprioception. This study showed that the stum-expressing neurons express the mechanosensory channel NOMPC. In nompC mutants responses to joint position were abolished, indicating that NOMPC is the mechanosensitive channel in stum-expressing neurons. The NOMPC protein had a similar subcellular distribution as STUM, being located specifically at the dendritic site that is stretched by joint motions, thus validating that this site is a specialized sensory compartment. In the absence of NOMPC the sensory portion of the dendrite was misshapen, generating membrane protrusions. Thus, this study has shown that mechanical responsiveness at a specialized dendritic site is essential for determination of the fine dendritic structure. The abnormal morphology at the sensory compartment of non-active neurons suggests that the dendrite samples for a responsive anchoring site and stabilizes the structure that elicits the effective mechanotransduction.

Monday, May 25th

Kiparaki, M., Zarifi, I. and Delidakis, C. (2015). bHLH proteins involved in Drosophila neurogenesis are mutually regulated at the level of stability. Nucleic Acids Res 43(5): 2543-59.. PubMed ID: 25694512
Summary:
Drosophila Sc is a prototypical proneural activator that heterodimerizes with the E-protein Daughterless (Da) and is antagonized by, among others, the E(spl) repressors. This study determined parameters that regulate Sc stability in Drosophila S2 cells. Sc was a very labile phosphoprotein and its turnover took place via at least three proteasome-dependent mechanisms. (1) When Sc was in excess of Da, its degradation was promoted via its transactivation domain (TAD). (2) In a DNA-bound Da/Sc heterodimer, Sc degradation was promoted via an SPTSS phosphorylation motif and the AD1 TAD of Da; Da was spared in the process. (3) When E(spl)m7 was expressed, it complexed with Sc or Da/Sc and promoted their degradation in a manner that required the corepressor Groucho and the Sc SPTSS motif. Da/Sc reciprocally promoted E(spl)m7 degradation. Since E(spl)m7 is a direct target of Notch, the mutual destabilization of Sc and E(spl) may contribute in part to the highly conserved anti-neural activity of Notch. Sc variants lacking the SPTSS motif were dramatically stabilized and were hyperactive in transgenic flies. These results propose a novel mechanism of regulation of neurogenesis, involving the stability of key players in the process.

Lhamo, T. and Ismat, A. (2015). The extracellular protease stl functions to inhibit migration of v'ch1 sensory neuron during Drosophila embryogenesis. Mech Dev [Epub ahead of print]. PubMed ID: 25953091
Summary:
Proper migration of cells through the dense and complex extracellular matrix (ECM) requires constant restructuring of the ECM to allow cells to move forward in a smooth manner. This restructuring can occur through the action of extracellular enzymes. Among these extracellular enzymes is the ADAMTS (A Disintegrin And Metalloprotease with ThromboSpondin repeats) family of secreted extracellular proteases. Drosophila stall (stl) encodes an ADAMTS protease expressed in and around the peripheral nervous system (PNS) during embryogenesis. The absence of stl displayed one specific neuron, the v'ch1 sensory neuron, migrating to its target sooner than in wild type. During normal development, the v'ch1 sensory neuron migrated dorsally at the same time it was extending an axon ventrally toward the CNS. Surprisingly, in the absence of stl, the v'ch1 neuron migrated further dorsally as compared to the wild type at stage 15, but did not migrate past its correct target at stage 16, suggesting a novel role for this extracellular protease in inhibiting migration of this neuron past a certain point.

Burow, D. A., Umeh-Garcia, M. C., True, M. B., Bakhaj, C. D., Ardell, D. H. and Cleary, M. D. (2015). Dynamic regulation of mRNA decay during neural development. Neural Dev 10: 11. PubMed ID: 25896902
Summary:
Gene expression patterns are determined by rates of mRNA transcription and decay. While transcription is known to regulate many developmental processes, the role of mRNA decay is less extensively defined. A critical step toward defining the role of mRNA decay in neural development is to measure genome-wide mRNA decay rates in neural tissue. This study developed a technique that allows genome-wide mRNA decay measurements in intact Drosophila embryos, across all tissues and specifically in the nervous system. The approach revealed neural-specific decay kinetics, including stabilization of transcripts encoding regulators of axonogenesis and destabilization of transcripts encoding ribosomal proteins and histones. Correlations were identified between mRNA stability and physiologic properties of mRNAs; mRNAs that are predicted to be translated within axon growth cones or dendrites have long half-lives while mRNAs encoding transcription factors that regulate neurogenesis have short half-lives. A search for candidate cis-regulatory elements identified enrichment of the Pumilio recognition element (PRE) in mRNAs encoding regulators of neurogenesis. Decreased expression of the RNA-binding protein Pumilio was found to stabilized predicted neural mRNA targets, and a PRE was found to be necessary to trigger reporter-transcript decay in the nervous system. In conclusion it was found that differential mRNA decay contributes to the relative abundance of transcripts involved in cell-fate decisions, axonogenesis, and other critical events during Drosophila neural development. Neural-specific decay kinetics and the functional specificity of mRNA decay suggest the existence of a dynamic neurodevelopmental mRNA decay network. Pumilio was found to be one component of this network, revealing a novel function for this RNA-binding protein.

Golubyatnikov, V. P., Bukharina, T. A. and Furman, D. P. (2015). A model study of the morphogenesis of D. melanogaster mechanoreceptors: The central regulatory circuit. J Bioinform Comput Biol 13: 1540006. PubMed ID: 25666652
Summary:
Macrochaetes (large bristles) are sensor organs of the Drosophila peripheral nervous system with a function of mechanoreceptors. An adult mechanoreceptor comprises four specialized cells: shaft (trichogen), socket (tormogen), neuron, and glial cell (thecogen). All these cells originate from a single cell, the so-called sensor organ precursor (SOP) cell. Separation of the SOP cell from the encompassing cells of the imaginal disc initiates a multistage process of sensory organ development. A characteristic feature of the SOP cell is presence of the highest amount of the proneural proteins AS-C as compared with the encompassing ectodermal cells. The accumulation of proneural proteins and maintenance of their amount in the SOP cell at a necessary level is provided by the gene network with the achaete-scute gene complex (AS-C) as its key component. The activity of this complex is controlled by the central regulatory circuit (CRC). The CRC comprises the genes hairy, senseless (sens), charlatan (chn), scratch (scrt), daughterless (da), extramacrochaete (emc), and groucho (gro), coding for the transcription factors involved in the system of direct links and feedbacks and implementation of activation-repression relationships between the CRC components. The gene phyllopod (phyl), involved in degradation of the AS-C proteins, is also associated with the CRC functioning. This paper proposes a mathematical model for the CRC functioning as a regulator of the amount of proneural AS-C proteins in the SOP cell taking into account their degradation. The modeling has demonstrated that a change in the amount of proneural proteins in the SOP cell is stepwise rather than strictly monotonic. This prediction can be tested experimentally.

Sunday, May 24th

Voigt, S., Laurent, S., Litovchenko, M. and Stephan, W. (2015). Positive selection at the Polyhomeotic locus led to decreased thermosensitivity of gene expression in temperate Drosophila melanogaster. Genetics [Epub ahead of print]. PubMed ID: 25855066
Summary:
For insects, which are mostly ectotherms, ambient temperature plays a major role in their ability to colonize new habitats. Chromatin-based gene regulation is known to be sensitive to temperature. Ambient temperature leads to changes in the activation of genes regulated in this manner. One such regulatory system is the Polycomb group (PcG) whose target genes are more expressed at lower temperatures than at higher ones. Therefore, a greater range in ambient temperature in temperate environments may lead to greater variability (plasticity) in the expression of these genes. This might have detrimental effects, such that positive selection acts to lower the degree of the expression plasticity. This study provides evidence in Drosophila for this process in a genomic region that harbors two PcG-regulated genes, polyhomeotic proximal (ph-p) and CG3835. A signature of positive selection was found in this gene region in European populations of D. melanogaster, and the region was investigated by means of reporter gene assays. The target of selection is located in the intergenic fragment between the two genes. It overlaps with the promoters of both genes and an experimentally validated Polycomb response element (PRE). This fragment harbors five sequence variants that are highly differentiated between European and African populations. The African alleles confer a temperature-induced plasticity in gene expression, which is typical for PcG-mediated gene regulation, whereas thermosensitivity is reduced for the European alleles.

Vicoso, B. and Bachtrog, D. (2015). Numerous transitions of sex chromosomes in Diptera. PLoS Biol 13: e1002078. PubMed ID: 25879221
Summary:
Many species groups, including mammals and many insects, determine sex using heteromorphic sex chromosomes. Diptera flies, which include the model Drosophila melanogaster, generally have XY sex chromosomes and a conserved karyotype consisting of six chromosomal arms (five large rods and a small dot), but superficially similar karyotypes may conceal the true extent of sex chromosome variation. This study used whole-genome analysis in 37 fly species belonging to 22 different families of Diptera and uncovered tremendous hidden diversity in sex chromosome karyotypes among flies. Over a dozen different sex chromosome configurations were identified, and the small dot chromosome is repeatedly used as the sex chromosome, which presumably reflects the ancestral karyotype of higher Diptera. However, species were identified with undifferentiated sex chromosomes, others in which a different chromosome replaced the dot as a sex chromosome or in which up to three chromosomal elements became incorporated into the sex chromosomes, and others yet with female heterogamety (ZW sex chromosomes). Transcriptome analysis shows that dosage compensation has evolved multiple times in flies, consistently through up-regulation of the single X in males. However, X chromosomes generally show a deficiency of genes with male-biased expression, possibly reflecting sex-specific selective pressures. These species thus provide a rich resource to study sex chromosome biology in a comparative manner and show that similar selective forces have shaped the unique evolution of sex chromosomes in diverse fly taxa.

Ober, U., Huang, W., Magwire, M., Schlather, M., Simianer, H. and Mackay, T. F. (2015). Accounting for genetic architecture improves sequence based genomic prediction for a Drosophila fitness trait. PLoS One 10: e0126880. PubMed ID: 25950439
Summary:
The ability to predict quantitative trait phenotypes from molecular polymorphism data will revolutionize evolutionary biology, medicine and human biology, and animal and plant breeding. Efforts to map quantitative trait loci have yielded novel insights into the biology of quantitative traits, but the combination of individually significant quantitative trait loci typically has low predictive ability. Utilizing all segregating variants can give good predictive ability in plant and animal breeding populations, but gives little insight into trait biology. This study used the Drosophila Genetic Reference Panel to perform both a genome wide association analysis and genomic prediction for the fitness-related trait chill coma recovery time. Substantial total genetic variation was found for chill coma recovery time, with a genetic architecture that differs between males and females, a small number of molecular variants with large main effects, and evidence for epistasis. Although the top additive variants explained 36% (17%) of the genetic variance among lines in females (males), the predictive ability using genomic best linear unbiased prediction and a relationship matrix using all common segregating variants was very low for females and zero for males. It was hypothesized that the low predictive ability was due to the mismatch between the infinitesimal genetic architecture assumed by the genomic best linear unbiased prediction model and the true genetic architecture of chill coma recovery time. Indeed, it was found that the predictive ability of the genomic best linear unbiased prediction model is markedly improved when quantitative trait locus mapping was combined with genomic prediction by only including the top variants associated with main and epistatic effects in the relationship matrix. This trait-associated prediction approach has the advantage that it yields biologically interpretable prediction models.

Sharma, P. P., Tarazona, O. A., Lopez, D. H., Schwager, E. E., Cohn, M. J., Wheeler, W. C. and Extavour, C. G. (2015). A conserved genetic mechanism specifies deutocerebral appendage identity in insects and arachnids. Proc Biol Sci 282. PubMed ID: 25948691
Summary:
The segmental architecture of the arthropod head is one of the most controversial topics in the evolutionary developmental biology of arthropods. The deutocerebral (second) segment of the head is putatively homologous across Arthropoda, as inferred from the segmental distribution of the tripartite brain and the absence of Hox gene expression of this anterior-most, appendage-bearing segment. While this homology statement implies a putative common mechanism for differentiation of deutocerebral appendages across arthropods, experimental data for deutocerebral appendage fate specification are limited to winged insects. Mandibulates (hexapods, crustaceans and myriapods) bear a characteristic pair of antennae on the deutocerebral segment, whereas chelicerates (e.g. spiders, scorpions, harvestmen) bear the eponymous chelicerae. In such hexapods as the fruit fly, Drosophila melanogaster, and the cricket, Gryllus bimaculatus, cephalic appendages are differentiated from the thoracic appendages (legs) by the activity of the appendage patterning gene homothorax (hth). This study shows that embryonic RNA interference against hth in the harvestman Phalangium opilio results in homeonotic chelicera-to-leg transformations, and also in some cases pedipalp-to-leg transformations. In more strongly affected embryos, adjacent appendages undergo fusion and/or truncation, and legs display proximal defects, suggesting conservation of additional functions of hth in patterning the antero-posterior and proximo-distal appendage axes. Expression signal of anterior Hox genes labial, proboscipedia and Deformed is diminished, but not absent, in hth RNAi embryos, consistent with results previously obtained with the insect G. bimaculatus. These results substantiate a deep homology across arthropods of the mechanism whereby cephalic appendages are differentiated from locomotory appendages.

Ullastres, A., Petit, N. and Gonzalez, J. (2015). Exploring the phenotypic space and the evolutionary history of a natural mutation in Drosophila melanogaster. Mol Biol Evol. PubMed ID: 25862139
Summary:
A major challenge of modern Biology is elucidating the functional consequences of natural mutations. Although there is a good understanding of the effects of laboratory-induced mutations on the molecular- and organismal-level phenotypes, the study of natural mutations has lagged behind. This work explored the phenotypic space and the evolutionary history of a previously identified adaptive transposable element insertion. Several tests that capture different signatures of selection were combined to show that there is evidence of positive selection in the regions flanking FBti0019386 insertion. Several phenotypes were explored related to known phenotypic effects of nearby genes, and having plausible connections to fitness variation in nature. Flies with FBti0019386 insertion were found to have a shorter developmental time and were more sensitive to stress, which are likely to be the adaptive effect and the cost of selection of this mutation, respectively. Interestingly, these phenotypic effects are not consistent with a role of FBti0019386 in temperate adaptation as has been previously suggested. Indeed, a global analysis of the population frequency of FBti0019386 showed that climatic variables explain well the FBti0019386 frequency patterns only in Australia. Finally, although FBti0019386 insertion could be inducing the formation of heterochromatin by recruiting HP1a (Heterochromatin Protein 1a) protein, the insertion is associated with upregulation of sra in adult females. Overall, this integrative approach shed light on the evolutionary history, the relevant fitness effects, and the likely molecular mechanisms of an adaptive mutation and highlights the complexity of natural genetic variants.

Svetec, N., Zhao, L., Saelao, P., Chiu, J. C. and Begun, D. J. (2015). Evidence that natural selection maintains genetic variation for sleep in Drosophila melanogaster. BMC Evol Biol 15: 41. PubMed ID: 25887180Summary:
Drosophila melanogaster often shows correlations between latitude and phenotypic or genetic variation on different continents, which suggests local adaptation with respect to a heterogeneous environment. Previous phenotypic analyses of latitudinal clines have investigated mainly physiological, morphological, or life-history traits. This paper studied latitudinal variation in sleep in D. melanogaster populations from North and Central America. In parallel, RNA-seq was used to identify interpopulation gene expression differences. In D. melanogaster this study found the average nighttime sleep bout duration exhibits a latitudinal cline such that sleep bouts of equatorial populations are roughly twice as long as those of temperate populations. Interestingly, this pattern of latitudinal variation is not observed for any daytime measure of activity or sleep. Evidence was found for geographic variation for sunrise anticipation. The RNA-seq experiment carried out on heads from a low and high latitude population identified a large number of gene expression differences, most of which were time dependent. Differentially expressed genes were enriched in circadian regulated genes and enriched in genes potentially under spatially varying selection. These results are consistent with a mechanistic and selective decoupling of nighttime and daytime activity. Furthermore, the present study suggests that natural selection plays a major role in generating transcriptomic variation associated with circadian behaviors. Finally, genomic variants were found that were plausibly causally associated with the observed behavioral and transcriptomic variation.

Dembeck, L. M., Huang, W., Magwire, M. M., Lawrence, F., Lyman, R. F. and Mackay, T. F. (2015). Genetic architecture of abdominal pigmentation in Drosophila melanogaster. PLoS Genet 11: e1005163. PubMed ID: 25933381
Summary:
Pigmentation varies within and between species and is often adaptive. The amount of pigmentation on the abdomen of Drosophila melanogaster is a relatively simple morphological trait, which serves as a model for mapping the genetic basis of variation in complex phenotypes. This study assessed natural variation in female abdominal pigmentation in 175 sequenced inbred lines of the Drosophila melanogaster Genetic Reference Panel, derived from the Raleigh, NC population. The proportion of melanization on the two most posterior abdominal segments, tergites 5 and 6 (T5, T6), was quantified. Significant genetic variation was found in the proportion of melanization and high broad-sense heritabilities for each tergite. Genome-wide association studies identified over 150 DNA variants associated with the proportion of melanization on T5 (84), T6 (34), and the difference between T5 and T6 (35). Several of the top variants associated with variation in pigmentation are in tan, ebony, and bric-a-brac1, genes known to affect D. melanogaster abdominal pigmentation. Mutational analyses and targeted RNAi-knockdown showed that 17 out of 28 (61%) novel candidate genes implicated by the genome-wide association study affected abdominal pigmentation. Several of these genes are involved in developmental and regulatory pathways, chitin production, cuticle structure, and vesicle formation and transport. These findings show that genetic variation may affect multiple steps in pathways involved in tergite development and melanization. Variation in these novel candidates may serve as targets for adaptive evolution and sexual selection in D. melanogaster.

Kurmangaliyev, Y. Z., Favorov, A. V., Osman, N. M., Lehmann, K. V., Campo, D., Salomon, M. P., Tower, J., Gelfand, M. S. and Nuzhdin, S. V. (2015). Natural variation of gene models in Drosophila melanogaster. BMC Genomics 16: 198. PubMed ID: 25888292
Summary:
Variation within splicing regulatory sequences often leads to differences in gene models among individuals within a species. Two alleles of the same gene may express transcripts with different exon/intron structures and consequently produce functionally different proteins. Matching genomic and transcriptomic data allows identification of putative regulatory variants associated with changes in splicing patterns. This study analyzed natural variation of splicing patterns in the transcriptomes of 81 natural strains of Drosophila melanogaster with known genotypes. Dozens of genotype-specific splicing patterns were identified associated with putative cis-splicing quantitative trait loci (sQTL). The majority of changes can be explained by mutations in splice sites. Allelic-imbalance in splicing patterns confirmed that the majority are regulated mainly by cis-genetic effects. Remarkably, allele-specific splicing changes often lead to qualitative changes in gene models, yielding many isoforms not previously annotated. The observed alterations are typically outside protein-coding regions or affect only very short protein segments. Overall, the sets of gene models appear to be flexible within D. melanogaster populations. The observed variation in splicing patterns are predicted to have limited effects on the encoded protein sequences. This is considered to be the first sQTL mapping study in Drosophila (Kurmangaliyev, 2015).

Halberg, K. A., Terhzaz, S., Cabrero, P., Davies, S. A. and Dow, J. A. (2015). Tracing the evolutionary origins of insect renal function. Nat Commun 6: 6800. PubMed ID: 25896425
Summary:
Knowledge on neuropeptide receptor systems is integral to understanding animal physiology. Yet, obtaining general insight into neuropeptide signalling in a clade as biodiverse as the insects is problematic. This study applied fluorescent analogues of three key insect neuropeptides to map renal tissue architecture across systematically chosen representatives of the major insect Orders, to provide an unprecedented overview of insect renal function and control. In endopterygote insects, such as Drosophila, two distinct transporting cell types receive separate neuropeptide signals, whereas in the ancestral exopterygotes, a single, general cell type mediates all signals. Intriguingly, the largest insect Order Coleoptera (beetles) has evolved a unique approach, in which only a small fraction of cells are targets for neuropeptide action. In addition to demonstrating a universal utility of this technology, these results reveal not only a generality of signalling by the evolutionarily ancient neuropeptide families but also a clear functional separation of the types of cells that mediate the signal.

Zhao, L., Wit, J., Svetec, N. and Begun, D. J. (2015). Parallel gene expression differences between low and high latitude populations of Drosophila melanogaster and D. simulans. PLoS Genet 11: e1005184. PubMed ID: 25950438
Summary:
This study investigated low and high latitude populations of Drosophila melanogaster and its sister species, D. simulans, to determine whether the two species show similar patterns of population differentiation. The whole male transcriptome was compared of D. melanogaster and D. simulans sampled from Panama City (Panama) and Maine (USA). A significant excess of genes exhibiting differential expression in both species, consistent with parallel adaptation to heterogeneous environments. Moreover, the majority of genes showing parallel expression differentiation showed the same direction of differential expression in the two species and the magnitudes of expression differences between high and low latitude populations were correlated across species, further bolstering the conclusion that parallelism for expression phenotypes results from spatially varying selection. However, the species also exhibited important differences in expression phenotypes. For example, the genomic extent of genotype x environment interaction was much more common in D. melanogaster. Highly differentiated SNPs between low and high latitudes were enriched in the 3' UTRs and CDS of the geographically differently expressed genes in both species, consistent with an important role for cis-acting variants in driving local adaptation for expression-related phenotypes.

Saturday, May 23rd

Tiebe, M., Lutz, M., De La Garza, A., Buechling, T., Boutros, M. and Teleman, A. A. (2015). REPTOR and REPTOR-BP regulate organismal metabolism and transcription downstream of TORC1. Dev Cell 33: 272-284. PubMed ID: 25920570
Summary:
TORC1 (see Drosophila Tor) regulates growth and metabolism, in part, by influencing transcriptional programs. This study has identified REPTOR and REPTOR-BP, both leucine zipper DNA-binding proteins, as transcription factors downstream of TORC1 that are required for approximately 90% of the transcriptional induction that occurs upon TORC1 inhibition in Drosophila. Thus, REPTOR and REPTOR-BP are major effectors of the transcriptional stress response induced upon TORC1 inhibition, analogous to the role of FOXO downstream of Akt.When TORC1 is active, it phosphorylates REPTOR on Ser527 and Ser530, leading to REPTOR cytoplasmic retention. Upon TORC1 inhibition, REPTOR becomes dephosphorylated in a PP2A-dependent manner, shuttles into the nucleus, joins its partner REPTOR-BP to bind target genes, and activates their transcription. In vivo functional analysis using knockout flies reveals that REPTOR and REPTOR-BP play critical roles in maintaining energy homeostasis and promoting animal survival upon nutrient restriction.

Enomoto, M., Kizawa, D., Ohsawa, S. and Igaki, T. (2015). JNK signaling is converted from anti- to pro-tumor pathway by Ras-mediated switch of Warts activity. Dev Biol [Epub ahead of print]. PubMed ID: 25967126
Summary:
The c-Jun N-terminal kinase (JNK) pathway is a dual-functional oncogenic signaling that exerts both anti- and pro-tumor activities. However, the mechanism by which JNK switches its oncogenic roles depending on different cellular contexts has been elusive. Using the Drosophila genetics, this study shows that hyperactive Ras acts as a signaling switch that converts JNK's role from anti- to pro-tumor signaling through the regulation of Hippo signaling activity. In the normal epithelium, JNK signaling antagonized the Hippo pathway effector Yorkie (Yki) through elevation of Warts activity, thereby suppressing tissue growth. In contrast, in the presence of hyperactive Ras, JNK signaling enhanced Yki activation by accumulating F-actin through the activity of the LIM domain protein Ajuba, thereby promoting tissue growth. They also fond that the epidermal growth factor receptor (EGFR) signaling used this Ras-mediated conversion of JNK signaling to promote tissue growth. These observations suggest that Ras-mediated switch of the JNK pathway from anti- to pro-tumor signaling could play crucial roles in tumorigenesis as well as in normal development.

Teixeira, F. K., Sanchez, C. G., Hurd, T. R., Seifert, J. R., Czech, B., Preall, J. B., Hannon, G. J. and Lehmann, R. (2015). ATP synthase promotes germ cell differentiation independent of oxidative phosphorylation. Nat Cell Biol 17: 689-696. PubMed ID: 25915123
Summary:
The differentiation of stem cells is a tightly regulated process essential for animal development and tissue homeostasis. Through this process, attainment of new identity and function is achieved by marked changes in cellular properties. Intrinsic cellular mechanisms governing stem cell differentiation remain largely unknown, in part because systematic forward genetic approaches to the problem have not been widely used. Analysing genes required for germline stem cell differentiation in the Drosophila ovary, this study found that the mitochondrial ATP synthase plays a critical role in this process. Unexpectedly, the ATP synthesizing function of this complex was not necessary for differentiation, as knockdown of other members of the oxidative phosphorylation system did not disrupt the process. Instead, the ATP synthase acted to promote the maturation of mitochondrial cristae during differentiation through dimerization and specific upregulation of the ATP synthase complex. Taken together, these results suggest that ATP synthase-dependent crista maturation is a key developmental process required for differentiation independent of oxidative phosphorylation.

Baker, R.P. and Urban, S. (2015). Cytosolic extensions directly regulate a rhomboid protease by modulating substrate gating. Nature [Epub ahead of print]. PubMed ID: 25970241
Summary:
Intramembrane proteases catalyse the signal-generating step of various cell signalling pathways, and continue to be implicated in diseases ranging from malaria infection to Parkinsonian neurodegeneration. Despite playing such decisive roles, it remains unclear whether or how these membrane-immersed enzymes might be regulated directly. To address this limitation, this study characterized a rhomboid protease that harbours calcium-binding EF-hands. Calcium was found to potently stimulate proteolysis by endogenous rhomboid-4 in Drosophila cells, and, remarkably, when rhomboid-4 was purified and reconstituted in liposomes. Interestingly, deleting the amino-terminal EF-hands activated proteolysis prematurely, while residues in cytoplasmic loops connecting distal transmembrane segments mediated calcium stimulation. Rhomboid regulation was not orchestrated by either dimerization or substrate interactions. Instead, calcium increased catalytic rate by promoting substrate gating. Substrates with cleavage sites outside the membrane could be cleaved but lost the capacity to be regulated. These observations indicate substrate gating is not an essential step in catalysis, but instead evolved as a mechanism for regulating proteolysis inside the membrane. Moreover, these insights provide new approaches for studying rhomboid functions by investigating upstream inputs that trigger proteolysis.

Takeuchi, T., Suzuki, M., Fujikake, N., Popiel, H. A., Kikuchi, H., Futaki, S., Wada, K. and Nagai, Y. (2015). Intercellular chaperone transmission via exosomes contributes to maintenance of protein homeostasis at the organismal level. Proc Natl Acad Sci U S A. PubMed ID: 25918398
Summary:
This study reports that proteostasis can be maintained by molecular chaperones not only in a cell-autonomous manner but also in a non-cell-autonomous manner. Elevated expression of molecular chaperones, such as Hsp40 and Hsp70, in a group of cells improves proteostasis in other groups of cells, both in cultured cells and in Drosophila expressing aggregation-prone polyglutamine proteins. Hsp40, as well as Hsp70 and Hsp90, is physiologically secreted from cells via exosomes, and the J domain at the N terminus is responsible for its exosome-mediated secretion. Addition of Hsp40/Hsp70-containing exosomes to the culture medium of the polyglutamine-expressing cells results in efficient suppression of inclusion body formation, indicating that molecular chaperones non-cell autonomously improve the protein-folding environment via exosome-mediated transmission. This study reveals that intercellular chaperone transmission mediated by exosomes is a novel molecular mechanism for non-cell-autonomous maintenance of organismal proteostasis that could functionally compensate for the imbalanced state of the HSR among different cells, and also provides a novel physiological role of exosomes that contributes to maintenance of organismal proteostasis.

Wittkorn, E., Sarkar, A., Garcia, K., Kango-Singh, M. and Singh, A. (2015). The Hippo pathway effector Yki downregulates Wg signaling to promote retinal differentiation in the Drosophila eye. Development [Epub ahead of print]. PubMed ID: 25977365
Summary:
The evolutionarily conserved Hippo signaling pathway is known to regulate cell proliferation and maintain tissue homeostasis during development. This study found that activation of Yorkie (Yki), the effector of the Hippo signaling pathway, causes separable effects on growth and differentiation of the Drosophila eye. It presented evidence supporting a role for Yki in suppressing eye fate by downregulation of the core retinal determination genes. Other upstream regulators of the Hippo pathway mediated this effect of Yki on retinal differentiation. The study showed that in the developing eye, Yki could prevent retinal differentiation by blocking morphogenetic furrow (MF) progression and R8 specification. The inhibition of MF progression was due to ectopic induction of Wingless (Wg) signaling and Homothorax (Hth), the negative regulators of eye development. Modulating Wg signaling could modify Yki-mediated suppression of eye fate. Furthermore, ectopic Hth induction due to Yki activation in the eye was dependent on Wg. Last, using Cut (Ct), a marker for the antennal fate, it was shown that suppression of eye fate by hyperactivation of yki did not change the cell fate (from eye to antenna-specific fate). In summary, this study provides the genetic mechanism by which yki plays a role in cell fate specification and differentiation - a novel aspect of Yki function that is emerging from multiple model organisms.

Friday, May 22nd

Kang, K., Ryoo, H.D., Park, J.E., Yoon, J.H. and Kang, M.J. (2015). A Drosophila reporter for the translational activation of ATF4 marks stressed cells during development. PLoS One 10: e0126795. PubMed ID: 25978358
Summary:
Eukaryotic cells have evolved signaling pathways that help to restore cellular homeostasis in response to various physiological or pathological conditions. ATF4 is a transcription factor whose mRNA translation is stimulated in response to stress-activated eIF2alpha kinases. Established conditions that activate eIF2alpha phosphorylation and ATF4 translation include excessive stress in the endoplasmic reticulum (ER) and amino acid deprivation. ATF4 is activated through a unique translational activation mechanism that involves multiple upstream open reading frames (uORFs) in the 5'-untranslated region (UTR), which is conserved from yeast to mammals. Taking advantage of this, this study developed a translational activation reporter of ATF4 in Drosophila, in which the dsRed reporter coding sequence was placed downstream of the Drosophila ATF4 5' UTR. This reporter remained inactive in most tissues under normal conditions, but showed dsRed expression when starved, or when challenged with conditions that imposed ER stress. In normally developing flies, a small number of cell types showed reporter expression even without exogenous stress, which included the salivary gland, gut, the male reproductive organ, and the photoreceptor cells, suggestive of inherent stress during the normal development of these cell types. These results establish a new tool to study ATF4-mediated stress response in Drosophila development and disease.

Bieli, D., Kanca, O., Gohl, D., Denes, A., Schedl, P., Affolter, M. and Muller, M. (2015). The Drosophila melanogaster mutants apblot and apXasta affect an essential apterous wing enhancer. G3 (Bethesda) [Epub ahead of print]. PubMed ID: 25840432
Summary:
The selector gene apterous (ap) plays a key role during the development of the Drosophila melanogaster wing as it governs the establishment of the dorsal-ventral (D-V) compartment boundary. The D-V compartment boundary is known to serve as an important signaling center that is essential for the growth of the wing. The role of Ap and its downstream effectors have been studied extensively. However, very little is known about the transcriptional regulation of ap during wing disc development. This study presents a first characterization of an essential wing-specific ap enhancer. First, an 874 bp fragment about 10 kb upstream of the ap transcription start was defined that faithfully recapitulates the expression pattern of ap in the wing imaginal disc. Analysis of deletions in the ap locus covering this element demonstrated that it is essential for proper regulation of ap and formation of the wing. Moreover, the mutations apblot and apXasta were shown to directly affect the integrity of this enhancer leading to characteristic wing phenotypes. Furthermore, an in vivo rescue system was engineered at the endogenous ap gene locus, allowing investigation of the role of enhancer fragments in their native environment. Using this system, it was possible to demonstrate that the essential wing enhancer alone is not sufficient for normal wing development. The in vivo rescue system will allow characterization of the ap regulatory sequences in great detail at the endogenous locus.

Baeza, M., Viala, S., Heim, M., Dard, A., Hudry, B., Duffraisse, M., Rogulja-Ortmann, A., Brun, C. and Merabet, S. (2015). Inhibitory activities of short linear motifs underlie Hox interactome specificity in vivo. Elife 4. PubMed ID: 25869471
Summary:
Hox proteins are well-established developmental regulators that coordinate cell fate and morphogenesis throughout embryogenesis. In contrast, knowledge of their specific molecular modes of action is limited to the interaction with few cofactors. This study shows that Hox proteins are able to interact with a wide range of transcription factors in the live Drosophila embryo. In this context, specificity relies on a versatile usage of conserved short linear motifs (SLiMs), which, surprisingly, often restrain the interaction potential of Hox proteins. This novel buffering activity of SLiMs was observed in different tissues and found in Hox proteins from cnidarian to mouse species. For example AbdA is the Hox protein establishing the highest number of interactions, which is consistent with the fact that it served as a bait protein in the starting competition screen. However, the observation that Hox proteins do not interact systematically with the same set of cofactors shows their specificity. Interestingly, this specificity is not only occurring at the DNA-binding level since the loss of AbdA DNA-binding activity did not affect all interactions (18 interactions of 31 were affected). Although these interactions remain to be analysed in the context of endogenous Hox regulatory activities, these observations challenge the traditional role assigned to SLiMs and provide an alternative concept to explain how Hox interactome specificity could be achieved during the embryonic development.

Carl, S. H. and Russell, S. (2015). Common binding by redundant group B Sox proteins is evolutionarily conserved in Drosophila. BMC Genomics 16: 292. PubMed ID: 25887553
Summary:
Group B Sox proteins are a highly conserved group of transcription factors that act extensively to coordinate nervous system development in higher metazoans while showing both co-expression and functional redundancy across a broad group of taxa. In Drosophila melanogaster, the two group B Sox proteins Dichaete and SoxNeuro show widespread common binding across the genome. While some instances of functional compensation have been observed in Drosophila, the function of common binding and the extent of its evolutionary conservation is not known. This study used DamID-seq to examine the genome-wide binding patterns of Dichaete and SoxNeuro in four species of Drosophila. Through a quantitative comparison of Dichaete binding, the rate of binding site turnover was evaluated across the genome as well as at specific functional sites. The presence of Sox motifs was examined within binding intervals, along with the correlation between sequence conservation and binding conservation. To determine whether common binding between Dichaete and SoxNeuro is conserved, a detailed analysis was performed of the binding patterns of both factors in two species. This study found that, while the regulatory networks driven by Dichaete and SoxNeuro are largely conserved across the drosophilids studied, binding site turnover is widespread and correlated with phylogenetic distance. Nonetheless, binding is preferentially conserved at known cis-regulatory modules and core, independently verified binding sites. The strongest binding conservation was observed at sites that are commonly bound by Dichaete and SoxNeuro, suggesting that these sites are functionally important. This analysis provides insights into the evolution of group B Sox function, highlighting the specific conservation of shared binding sites and suggesting alternative sources of neofunctionalisation between paralogous family members.

Thursday, May 21st

Suzuki, Y., Ikeda, H., Miyamoto, T., Miyakawa, H., Seki, Y., Aonishi, T. and Morimoto, T. (2015). Noise-robust recognition of wide-field motion direction and the underlying neural mechanisms in Drosophila melanogaster. Sci Rep 5: 10253. PubMed ID: 25974721
Summary:
Appropriate and robust behavioral control in a noisy environment is important for the survival of most organisms. Understanding such robust behavioral control has been an attractive subject in neuroscience research. This study investigated the processing of wide-field motion with random dot noise at both the behavioral and neuronal level in Drosophila melanogaster. The head yaw optomotor response (OMR) and the activity of motion-sensitive neurons of the lobula plate termed the horizontal system (HS) cells, were measured with in vivo whole-cell patch clamp recordings at various levels of noise intensity. It was found that flies had a robust sensation of motion direction under noisy conditions, while membrane potential changes of HS cells were not correlated with behavioral responses. By applying signal classification theory to the distributions of HS cell responses, however, it was found that motion direction under noise could be clearly discriminated by HS cells, and that this discrimination performance was quantitatively similar to that of OMR. Furthermore, HS cell activity in response to noisy motion stimuli with a local motion detector model including a spatial filter and threshold function was successfully reproduced. This study provides evidence for the physiological basis of noise-robust behavior in a tiny insect brain.

Buchanan, S. M., Kain, J. S. and de Bivort, B. L. (2015). Neuronal control of locomotor handedness in Drosophila. Proc Natl Acad Sci U S A [Epub ahead of print]. PubMed ID: 25953337
Summary:
Genetically identical individuals display variability in their physiology, morphology, and behaviors, even when reared in essentially identical environments, but there is little mechanistic understanding of the basis of such variation. This study investigated whether Drosophila melanogaster displays individual-to-individual variation in locomotor behaviors. A new high-throughout platform was developed capable of measuring the exploratory behavior of hundreds of individual flies simultaneously. With this approach, it was found that, during exploratory walking, individual flies exhibit significant bias in their left vs. right locomotor choices, with some flies being strongly left biased or right biased. This idiosyncrasy was present in all genotypes examined, including wild-derived populations and inbred isogenic laboratory strains. The biases of individual flies persist for their lifetime and are nonheritable: i.e., mating two left-biased individuals does not yield left-biased progeny. This locomotor handedness is uncorrelated with other asymmetries, such as the handedness of gut twisting, leg-length asymmetry, and wing-folding preference. Using transgenics and mutants, it was found that the magnitude of locomotor handedness is under the control of columnar neurons within the central complex, a brain region implicated in motor planning and execution. When these neurons are silenced, exploratory laterality increases, with more extreme leftiness and rightiness. This observation intriguingly implies that the brain may be able to dynamically regulate behavioral individuality.

Kim, A.J., Lazar, A.A. and Slutskiy, Y.B. (2015). Projection neurons in Drosophila antennal lobes signal the acceleration of odor concentrations. Elife [Epub ahead of print]. PubMed ID: 25974217
Summary:
Temporal experience of odor gradients is important in spatial orientation of animals. The fruit fly Drosophila melanogaster exhibits robust odor-guided behaviors in an odor gradient field. In order to investigate how early olfactory circuits process temporal variation of olfactory stimuli, this study subjected flies to precisely defined odor concentration waveforms and examined spike patterns of olfactory sensory neurons (OSNs) and projection neurons (PNs). A significant temporal transformation between OSN and PN spike patterns, manifested by the PN output strongly signaling the OSN spike rate and its rate of change. A simple two-dimensional model admitting the OSN spike rate and its rate of change as inputs closely predicted the PN output. When cascaded with the rate-of-change encoding by OSNs, PNs primarily signal the acceleration and the rate-of-change of dynamic odor stimuli to higher brain centers, thereby enabling animals to reliably respond to the onsets of odor concentrations.

Agrawal, T. and Hasan, G. (2015). Maturation of a central brain flight circuit in Drosophila requires Fz2/Ca signaling. Elife 4 [Epub ahead of print]. PubMed ID: 25955970
Summary:
The final identity of a differentiated neuron is determined by multiple signaling events, including activity dependent calcium transients. Non-canonical Frizzled2 (Fz2) signaling generates calcium transients that determine neuronal polarity, neuronal migration and synapse assembly in the developing vertebrate brain. This study demonstrates a requirement for Fz2/Ca2+ signaling in determining the final differentiated state of a set of central brain dopaminergic neurons in Drosophila, referred to as the PAM cluster. Knockdown or inhibition of Fz2/Ca2+ signaling during maturation of the flight circuit in pupae reduces Tyrosine Hydroxylase (TH) expression in the PAM neurons and affects maintenance of flight. Thus this study demonstrates that Fz2/Ca2+ transients during development serve as a pre-requisite for normal adult behavior. These results support a neural mechanism where PAM neuron send projections to the α' and β' lobes of a higher brain centre, the mushroom body, and function in dopaminergic re-inforcement of flight.

Ohyama, T., Schneider-Mizell, C. M., Fetter, R. D., Aleman, J. V., Franconville, R., Rivera-Alba, M., Mensh, B. D., Branson, K. M., Simpson, J. H., Truman, J. W., Cardona, A. and Zlatic, M. (2015). A multilevel multimodal circuit enhances action selection in Drosophila. Nature 520: 633-639. PubMed ID: 25896325
Summary:
Natural events present multiple types of sensory cues, each detected by a specialized sensory modality. Combining information from several modalities is essential for the selection of appropriate actions. Key to understanding multimodal computations is determining the structural patterns of multimodal convergence and how these patterns contribute to behaviour. Modalities could converge early, late or at multiple levels in the sensory processing hierarchy. This study shows that combining mechanosensory and nociceptive cues synergistically enhances the selection of the fastest mode of escape locomotion in Drosophila larvae. In an electron microscopy volume that spans the entire insect nervous system, the multisensory circuit was reconstructed supporting the synergy and spanning multiple levels of the sensory processing hierarchy. The wiring diagram revealed a complex multilevel multimodal convergence architecture. Using behavioural and physiological studies, functionally connected circuit nodes were identified that trigger the fastest locomotor mode, and others were identified that facilitate it. Evidence is provided evidence that multiple levels of multimodal integration contribute to escape mode selection. It is proposed that the multilevel multimodal convergence architecture may be a general feature of multisensory circuits enabling complex input-output functions and selective tuning to ecologically relevant combinations of cues.

Nagy, V., Cole, T., Van Campenhout, C., Khoung, T. M., Leung, C., Vermeiren, S., Novatchkova, M., Wenzel, D., Cikes, D., Polyansky, A. A., Kozieradzki, I., Meixner, A., Bellefroid, E. J., Neely, G. G. and Penninger, J. M. (2015). The evolutionarily conserved transcription factor PRDM12 controls sensory neuron development and pain perception. Cell Cycle: [Epub ahead of print]. PubMed ID: 25891934
Summary:
PR homology domain-containing member 12 (PRDM12) belongs to a family of conserved transcription factors implicated in cell fate decisions. This study show that PRDM12 is a key regulator of sensory neuronal specification in Xenopus. Modeling of human PRDM12 mutations that cause hereditary sensory and autonomic neuropathy (HSAN) revealed remarkable conservation of the mutated residues in evolution. Expression of wild-type human PRDM12 in Xenopus induced the expression of sensory neuronal markers, which was reduced using various human PRDM12 mutants. In Drosophila, Hamlet as identified was the functional PRDM12 homologue that controls nociceptive behavior in sensory neurons. Furthermore, expression analysis of human patient fibroblasts with PRDM12 mutations uncovered possible downstream target genes. Knockdown of several of these target genes including thyrotropin-releasing hormone degrading enzyme (TRHDE) in Drosophila sensory neurons resulted in altered cellular morphology and impaired nociception. These data show that PRDM12 and its functional fly homologue Hamlet are evolutionary conserved master regulators of sensory neuronal specification and play a critical role in pain perception. These data also uncover novel pathways in multiple species that regulate evolutionary conserved nociception.

Wednesday, May 20th

Kacsoh, B.Z., Bozler, J., Ramaswami, M. and Bosco, G. (2015). Social communication of predator-induced changes in Drosophila behavior and germline physiology. Elife [Epub ahead of print]. PubMed ID: 25970035
Summary:
Behavioral adaptation to environmental threats and subsequent social transmission of adaptive behavior has evolutionary implications. In Drosophila, exposure to parasitoid wasps leads to a sharp decline in oviposition. This study shows that exposure to predator elicits both an acute and learned oviposition depression, mediated through the visual system. However, long-term persistence of oviposition depression after predator removal required neuronal signaling functions, a functional mushroom body, and neurally driven apoptosis of oocytes through effector caspases. Strikingly, wasp-exposed flies (teachers) could transmit egg-retention behavior and trigger ovarian apoptosis in naive, unexposed flies (students). Acquisition and behavioral execution of this socially learned behavior by naive flies required all of the factors needed for primary learning. The ability to teach did not require ovarian apoptosis. This work provides new insight into genetic and physiological mechanisms that underlie an ecologically relevant form of learning and mechanisms for its social transmission.

Kimura, K., Sato, C., Koganezawa, M and Yamamoto, D. (2015). Drosophila ovipositor extension in mating behavior and egg deposition involves distinct sets of brain interneurons. PLoS One 10: e0126445. PubMed ID: 25955600
Summary:
Oviposition is a female-specific behavior that directly affects fecundity, and therefore fitness. If a fertilized female encounters another male that she has evaluated to be of better quality than her previous mate, it would be beneficial for her to remate with this male rather than depositing her eggs. Females who decided not to remate exhibited rejection behavior toward a courting male and engaged in oviposition. Although recent studies of Drosophila melanogaster identified sensory neurons and putative second-order ascending interneurons that mediate uterine afferents affecting female reproductive behavior, little is known about the brain circuitry that selectively activates rejection versus oviposition behaviors. This study identified the sexually dimorphic pC2l and female-specific pMN2 neurons, two distinct classes of doublesex (dsx)-expressing neurons that can initiate ovipositor extension associated with rejection and oviposition behavior, respectively. pC2l interneurons, which induced ovipositor extrusion for rejection in females, had homologues that controlled courtship behavior in males. Activation of these two classes of neurons appeared to be mutually exclusive and each governed hierarchical control of the motor program in the VNC either for rejection or oviposition, contributing centrally to the switching on or off of the alternative motor programs.

Dweck, H.K., Ebrahim, S.A., Thoma, M., Mohamed, A.A., Keesey, I.W., Trona, F., Lavista-Llanos, S., Svatos;, A., Sachse, S., Knaden, M. and Hansson, B.S. (2015). Pheromones mediating copulation and attraction in Drosophila. Proc Natl Acad Sci U S A 112(21): E2829-35. PubMed ID: 25964351
Summary:
Intraspecific olfactory signals known as pheromones play important roles in insect mating systems. In the model Drosophila melanogaster, a key part of the pheromone-detecting system has remained enigmatic through many years of research in terms of both its behavioral significance and its activating ligands. This study shows that Or47b-and Or88a-expressing olfactory sensory neurons (OSNs) detect the fly-produced odorants methyl laurate (ML), methyl myristate, and methyl palmitate. Fruitless (fruM)-positive Or47b-expressing OSNs detected ML exclusively, and Or47b- and Or47b-expressing OSNs were required for optimal male copulation behavior. In addition, activation of Or47b-expressing OSNs in the male was sufficient to provide a competitive mating advantage. Further, the vigorous male courtship displayed toward oenocyte-less flies was attributed to an oenocyte-independent sustained production of the Or47b ligand, ML. In addition, Or88a-expressing OSNs responded to all three compounds, and that these neurons were necessary and sufficient for attraction behavior in both males and females. Beyond the OSN level, information regarding the three fly odorants was transferred from the antennal lobe to higher brain centers in two dedicated neural lines. Finally, both Or47b- and Or88a-based systems and their ligands were remarkably conserved over a number of drosophilid species. Taken together, these results close a significant gap in the understanding of the olfactory background to Drosophila mating and attraction behavior; while reproductive isolation barriers between species are created mainly by species-specific signals, the mating enhancing signal in several Drosophila species is conserved.

Ayroles, J. F., Buchanan, S. M., O'Leary, C., Skutt-Kakaria, K., Grenier, J. K., Clark, A. G., Hartl, D. L. and de Bivort, B. L. (2015). Behavioral idiosyncrasy reveals genetic control of phenotypic variability. Proc Natl Acad Sci U S A. PubMed ID: 25953335
Summary:
Quantitative genetics has primarily focused on describing genetic effects on trait means and largely ignored the effect of alternative alleles on trait variability, potentially missing an important axis of genetic variation contributing to phenotypic differences among individuals. To study the genetic effects on individual-to-individual phenotypic variability (or intragenotypic variability), Drosophila inbred lines were used and the spontaneous locomotor behavior of flies walking individually in Y-shaped mazes was measured, focusing on variability in locomotor handedness, an assay optimized to measure variability. It was discovered that some lines had consistently high levels of intragenotypic variability among individuals, whereas lines with low variability behaved as although they tossed a coin at each left/right turn decision. The degree of variability is itself heritable. Using a genome-wide association study (GWAS) for the degree of intragenotypic variability as the phenotype across lines, several genes expressed in the brain were identified that affect variability in handedness without affecting the mean. One of these genes, Ten-a, implicates a neuropil in the central complex of the fly brain as influencing the magnitude of behavioral variability, a brain region involved in sensory integration and locomotor coordination. These results were validated using genetic deficiencies, null alleles, and inducible RNAi transgenes. This study reveals the constellation of phenotypes that can arise from a single genotype and shows that different genetic backgrounds differ dramatically in their propensity for phenotypic variabililty. Because traditional mean-focused GWASs ignore the contribution of variability to overall phenotypic variation, current methods may miss important links between genotype and phenotype.

Tuesday, May 19th

Comoglio, F., Schlumpf, T., Schmid, V., Rohs, R., Beisel, C. and Paro, R. (2015). High-resolution profiling of Drosophila replication start sites reveals a DNA shape and chromatin signature of metazoan origins. Cell Rep [Epub ahead of print]. PubMed ID: 25921534
Summary:
At every cell cycle, faithful inheritance of metazoan genomes requires the concerted activation of thousands of DNA replication origins. However, the genetic and chromatin features defining metazoan replication start sites remain largely unknown. This study delineates the origin repertoire of the Drosophila genome at high resolution. They addressed the role of origin-proximal G-quadruplexes and suggested that they transiently stall replication forks in vivo. By dissecting the chromatin configuration of replication origins, this study identified a rich spatial organization of chromatin features at initiation sites. DNA shape and chromatin configurations, not strict sequence motifs, mark and predict origins in higher eukaryotes. The link between transcription and origin firing was further examined, and it was revealed that modulation of origin activity across cell types was intimately linked to cell-type-specific transcriptional programs. This study unravels conserved origin features and provides unique insights into the relationship among DNA topology, chromatin, transcription, and replication initiation across metazoa.

Tritto, P., Palumbo, V., Micale, L., Marzulli, M., Bozzetti, M.P., Specchia, V., Palumbo, G., Pimpinelli, S. and Berloco, M. (2015). Loss of Pol32 in Drosophila melanogaster causes chromosome instability and suppresses variegation. PLoS One 10: e0120859. PubMed ID: 25826374
Summary:
Pol32 is an accessory subunit of the replicative DNA Polymerase δ and of the translesion Polymerase ζ. Pol32 is involved in DNA replication, recombination and repair. Pol32's participation in high- and low-fidelity processes, together with the phenotypes arising from its disruption, imply multiple roles for this subunit within eukaryotic cells, not all of which have been fully elucidated. Using pol32 null mutants and two partial loss-of-function alleles pol32rd1 and pol32rds in Drosophila melanogaster, this study shows that Pol32 plays an essential role in promoting genome stability. Pol32 was essential to ensure DNA replication in early embryogenesis and it participated in the repair of mitotic chromosome breakage. In addition pol32 mutants suppressed position effect variegation, suggesting a role for Pol32 in chromatin architecture.

Liu, Y. and Zhang, D. (2015). HP1a/KDM4A is involved in the autoregulatory loop of the oncogene gene c-Jun. Epigenetics[Epub ahead of print]. PubMed ID: 25945750
Summary:
The proto-oncogene c-Jun plays crucial roles in tumorigenesis, and its aberrant expression has been implicated in many cancers. Previous studies have shown that the c-Jun gene is positively autoregulated by its product. Notably, it has also been reported that c-Jun proteins are enriched in its gene body region. However, the role of c-Jun proteins in its gene body region has yet to be uncovered. HP1a is an evolutionarily conserved heterochromatin-associated protein, which plays an essential role in heterochromatin-mediated gene silencing. Interestingly, accumulating evidence shows that HP1a is also localized to euchromatic regions to positively regulate gene transcription. However, the underlying mechanism has not been defined. This study demonstrates that HP1a is involved in the positive autoregulatory loop of the Jra gene, the KDM4A complex to its gene body region upon osmotic stress to reduce H3K36 methylation levels and disrupt H3K36 methylation-dependent histone deacetylation, resulting in high levels of histone acetylation in the Jra gene body region, thus promoting gene transcription. These results not only expand our knowledge towards the mechanism of c-Jun regulation, but also reveal the mechanism by which HP1a exerts its positive regulatory function in gene expression.

Cabrera, J. R., Olcese, U. and Horabin, J. I. (2015). A balancing act: heterochromatin protein 1a and the Polycomb group coordinate their levels to silence chromatin in Drosophila. Epigenetics Chromatin 8: 17. PubMed ID: 25954320
Summary: Early in Drosophila development, Heterochromatin protein 1a (HP1a) collaborates with the Polycomb/trithorax groups of proteins to regulate gene expression and that the two chromatin systems do not act separately as convention describes. This study shows that HP1a affects the levels of both the Polycomb complexes and RNA polymerase II at promoters, as assayed by chromatin immunoprecipitation analysis. Deposition of both the repressive (H3K27me3) and activating (H3K4me3) marks promoted by the Polycomb/trithorax group genes at gene promoters is affected. Additionally, depending on which parent contributes the null mutation of the HP1a gene, the levels of the H3K27me3 and H3K9me3 silencing marks at both promoters and heterochromatin are different. Changes in levels of the H3K27me3 and H3K9me3 repressive marks show a mostly reciprocal nature. The time around the mid-blastula transition, when the zygotic genome begins to be actively transcribed, appears to be a transition/decision point for setting the levels. This study finds that HP1a affects the generation of the epigenetic marks of the Polycomb/trithorax groups of proteins, chromatin modifiers which are key to maintaining gene expression in euchromatin. At gene promoters, deposition of both the repressive H3K27me3 and activating H3K4me3 marks of histone modifications shows a dependence on HP1a. Around the mid-blastula transition, when the zygotic genome begins to be actively transcribed, a pivotal decision for the level of silencing appears to take place. This is also when the embryo organizes its genome into heterochromatin and euchromatin. A balance between the HP1a and Polycomb group silencing systems appears to be set for the chromatin types that each system will primarily regulate.

Monday, May 18th

Siegenthaler, D., Enneking, E. M., Moreno, E. and Pielage, J. (2015). L1CAM/Neuroglian controls the axon-axon interactions establishing layered and lobular mushroom body architecture. J Cell Biol 208: 1003-1018. PubMed ID: 25825519
Summary:
This study demonstrates that the Drosophila melanogaster L1CAM homologue Neuroglian mediates adhesion between functionally distinct mushroom body axon populations to enforce and control appropriate projections into distinct axonal layers and lobes essential for olfactory learning and memory. This study addressed the regulatory mechanisms controlling homophilic Neuroglian-mediated cell adhesion by analyzing targeted mutations of extra- and intracellular Neuroglian domains in combination with cell type-specific rescue assays in vivo. Independent and cooperative domain requirements were demonstrated: intercalating growth depends on homophilic adhesion mediated by extracellular Ig domains. For functional cluster formation, intracellular Ankyrin2 association is sufficient on one side of the trans-axonal complex whereas Moesin association is likely required simultaneously in both interacting axonal populations. Together, these results provide novel mechanistic insights into cell adhesion molecule-mediated axon-axon interactions that enable precise assembly of complex neuronal circuits.

Arthur, A. L., Yang, S. Z., Abellaneda, A. and Wildonger, J. (2015). Dendrite arborization requires the dynein cofactor NudE. J Cell Sci [Epub ahead of print]. PubMed ID: 25908857
Summary:
The microtubule-based molecular motor dynein is essential for proper neuronal morphogenesis. Dynein activity is regulated by cofactors whose role(s) in shaping neuronal structure are still being elucidated. Using Drosophila melanogaster, this study revealed that the loss of the dynein cofactor NudE results in abnormal dendrite arborization. The data show that NudE associates with Golgi outposts, which mediate dendrite branching, suggesting NudE normally influences dendrite patterning by regulating Golgi outpost transport. Neurons lacking NudE also have increased microtubule dynamics, reflecting a change in microtubule stability that likely also contributes to abnormal dendrite growth and branching. These defects in dendritogenesis are rescued by elevating Lis1, another dynein cofactor that interacts with NudE as part of a tripartite complex. These data further show that the NudE C-terminus is dispensable for dendrite morphogenesis and likely modulates NudE activity. It is proposed that a key function of NudE is to enhance an interaction between Lis1 and dynein that is critical for motor activity and dendrite architecture.

Stewart, S., Koh, T. W., Ghosh, A. C. and Carlson, J. R. (2015). Candidate ionotropic taste receptors in the Drosophila larva. Proc Natl Acad Sci U S A 112: 4195-4201. PubMed ID: 25825777
Summary:
This paper examines in Drosophila a group of approximately 35 ionotropic receptors (IRs), the IR20a clade, about which remarkably little is known. Of 28 genes analyzed, GAL4 drivers representing 11 showed expression in the larva. Eight drivers labeled neurons of the pharynx, a taste organ, and three labeled neurons of the body wall that may be chemosensory. Expression was not observed in neurons of one taste organ, the terminal organ, although these neurons express many drivers of the Gr (Gustatory receptor) family. For most drivers of the IR20a clade, expression was observed in a single pair of cells in the animal, with limited coexpression, and only a fraction of pharyngeal neurons are labeled. The organization of IR20a clade expression thus appears different from the organization of the Gr family or the Odor receptor (Or) family in the larva. A remarkable feature of the larval pharynx is that some of its organs are incorporated into the adult pharynx, and several drivers of this clade are expressed in the pharynx of both larvae and adults. Different IR drivers show different developmental dynamics across the larval stages, either increasing or decreasing. Among neurons expressing drivers in the pharynx, two projection patterns can be distinguished in the CNS. Neurons exhibiting these two kinds of projection patterns may activate different circuits, possibly signaling the presence of cues with different valence. Taken together, the simplest interpretation of these results is that the IR20a clade encodes a class of larval taste receptors.

Shih, C. T., Sporns, O., Yuan, S. L., Su, T. S., Lin, Y. J., Chuang, C. C., Wang, T. Y., Lo, C. C., Greenspan, R. J. and Chiang, A. S. (2015). Connectomics-based analysis of information flow in the Drosophila brain. Curr Biol [Epub ahead of print]. PubMed ID: 25866397
Summary:
Understanding the overall patterns of information flow within the brain has become a major goal of neuroscience. The current study produced a first draft of the Drosophila connectome at the mesoscopic scale, reconstructed from 12,995 images of neuron projections collected in FlyCircuit (version 1.1). Neuron polarities were predicted according to morphological criteria, with nodes of the network corresponding to brain regions designated as local processing units (LPUs). The weight of each directed edge linking a pair of LPUs was determined by the number of neuron terminals that connected one LPU to the other. The resulting network showed hierarchical structure and small-world characteristics and consisted of five functional modules that corresponded to sensory modalities (olfactory, mechanoauditory, and two visual) and the pre-motor center. Rich-club organization was present in this network and involved LPUs in all sensory centers, and rich-club members formed a putative motor center of the brain. Major intra- and inter-modular loops were also identified that could play important roles for recurrent and reverberant information flow. The present analysis revealed whole-brain patterns of network structure and information flow. Additionally, it is proposed that the overall organizational scheme showed fundamental similarities to the network structure of the mammalian brain.

Sunday, May 17th

Kim, A. Y., Seo, J. B., Kim, W. T., Choi, H. J., Kim, S. Y., Morrow, G., Tanguay, R. M., Steller, H. and Koh, Y. H. (2015). The pathogenic human Torsin A in Drosophila activates the unfolded protein response and increases susceptibility to oxidative stress. BMC Genomics 16: 338. PubMed ID: 25903460
Summary:
Dystonia1 (DYT1) dystonia is caused by a glutamic acid deletion (DeltaE) mutation in the gene encoding Torsin A in humans (HTorA). To investigate the unknown molecular and cellular mechanisms underlying DYT1 dystonia, an unbiased proteomic analysis was performed. The amount of proteins and transcripts of an Endoplasmic reticulum (ER) resident chaperone Heat shock protein cognate 3 (HSC3; Drosophila homolog Heat shock 70-kDa protein cognate 3) and a mitochondria chaperone Heat Shock Protein 22 (HSP22; Drosophila homolog - HSP22) were found to be significantly increased in the HTorA(DeltaE)- expressing brains compared to the normal HTorA (HTorA(WT)) expressing brains. The physiological consequences included an increased susceptibility to oxidative and ER stress compared to normal HTorA(WT) flies. The alteration of transcripts of Inositol-requiring enzyme-1 (IRE1)-dependent spliced X box binding protein 1(Xbp1), several ER chaperones, a nucleotide exchange factor, Autophagy related protein 8b (ATG8b) and components of the ER associated degradation (ERAD) pathway and increased expression of the Xbp1-enhanced Green Fluorescence Protein (eGFP) in HTorA(DeltaE) brains strongly indicated the activation of the unfolded protein response (UPR). In addition, perturbed expression of the UPR sensors and inducers in the HTorA(DeltaE) Drosophila brains resulted in a significantly reduced life span of the flies. Furthermore, the types and quantities of proteins present in the anti-HSC3 positive microsomes in the HTorA(DeltaE) brains were different from those of the HTorA(WT) brains. Taken together, these data show that HTorA(DeltaE) in Drosophila brains may activate the UPR and increase the expression of HSP22 to compensate for the toxic effects caused by HTorA(DeltaE) in the brains.

Papadopoulos, C., Orso, G., Mancuso, G., Herholz, M., Gumeni, S., Tadepalle, N., Jungst, C., Tzschichholz, A., Schauss, A., Honing, S., Trifunovic, A., Daga, A. and Rugarli, E. I. (2015). Spastin binds to lipid droplets and affects lipid metabolism. PLoS Genet 11: e1005149. PubMed ID: 25875445
Summary:
Mutations in SPAST, encoding spastin, are the most common cause of autosomal dominant hereditary spastic paraplegia (HSP). HSP is characterized by weakness and spasticity of the lower limbs, owing to progressive retrograde degeneration of the long corticospinal axons. Spastin is a conserved microtubule (MT)-severing protein, involved in processes requiring rearrangement of the cytoskeleton in concert to membrane remodeling, such as neurite branching, axonal growth, midbody abscission, and endosome tubulation. Two isoforms of spastin are synthesized from alternative initiation codons (M1 and M87). This study shows that spastin-M1 can sort from the endoplasmic reticulum (ER) to pre- and mature lipid droplets (LDs). A hydrophobic motif comprised of amino acids 57 through 86 of spastin was sufficient to direct a reporter protein to LDs, while mutation of arginine 65 to glycine abolished LD targeting. Increased levels of spastin-M1 expression reduced the number but increased the size of LDs. Expression of a mutant unable to bind and sever MTs caused clustering of LDs. Consistent with these findings, ubiquitous overexpression of Dspastin in Drosophila led to bigger and less numerous LDs in the fat bodies and increased triacylglycerol levels. In contrast, Dspastin overexpression increased LD number when expressed specifically in skeletal muscles or nerves. Downregulation of Dspastin and expression of a dominant-negative variant decreased LD number in Drosophila nerves, skeletal muscle and fat bodies, and reduced triacylglycerol levels in the larvae. Moreover, reduced amount of fat stores were found in intestinal cells of worms in which the spas-1 homologue was either depleted by RNA interference or deleted. Taken together, these data uncovers an evolutionarily conserved role of spastin as a positive regulator of LD metabolism and open up the possibility that dysfunction of LDs in axons may contribute to the pathogenesis of HSP.

Burnouf, S., Gorsky, M. K., Dols, J., Gronke, S. and Partridge, L. (2015). Aβ is neurotoxic and primes aggregation of Aβ in vivo. Acta Neuropathol. PubMed ID: 25862636
Summary:
The involvement of Amyloid-β (Aβ; see Drosophila &beta amyloid protein precursor-like) in the pathogenesis of Alzheimer's disease (AD) is well established. However, it is becoming clear that the amyloid load in AD brains consists of a heterogeneous mixture of Aβ peptides, implying that a thorough understanding of their respective role and toxicity is crucial for the development of efficient treatments. Besides the well-studied Aβ40 and Aβ42 species, recent data have raised the possibility that Aβ43 peptides might be instrumental in AD pathogenesis, because they are frequently observed in both dense and diffuse amyloid plaques from human AD brains and are highly amyloidogenic in vitro. However, whether Aβ43 is toxic in vivo is currently unclear. Using Drosophila transgenic models of amyloid pathology, this study showed that Aβ43 peptides are mainly insoluble and highly toxic in vivo, leading to the progressive loss of photoreceptor neurons, altered locomotion and decreased lifespan when expressed in the adult fly nervous system. In addition, it was demonstrated that Aβ43 species are able to trigger the aggregation of the typically soluble and non-toxic Aβ40, leading to synergistic toxic effects on fly lifespan and climbing ability, further suggesting that Aβ43 peptides could act as a nucleating factor in AD brains. Altogether, this study demonstrates high pathogenicity of Aβ43 species in vivo and supports the idea that Aβ43 contributes to the pathological events leading to neurodegeneration in AD.
Kim, Y., Park, H., Nah, J., Moon, S., Lee, W., Hong, S. H. and Jung, Y. K. (2015). Essential role of POLDIP2 in Tau aggregation and neurotoxicity via autophagy/proteasome inhibition. Biochem Biophys Res Commun. PubMed ID: 25930997
Summary:
In Alzheimer's disease and other tauopathy, abnormal Tau proteins form intracellular aggregates and Tau filaments. However, the mechanisms that regulate Tau aggregation are not fully understood. This paper shows that POLDIP2 is a novel regulator of Tau aggregation. From a cell-based screening using cDNA expression library, POLDIP2, which increased Tau aggregation, was isolated. Expression of POLDIP2 was increased in neuronal cells by the multiple stresses, including Aβ, TNF-alpha and H2O2. Accordingly, ectopic expression of POLDIP2 enhanced the formation of Tau aggregates without affecting Tau phosphorylation, while down-regulation of POLDIP2 alleviated ROS-induced Tau aggregation. Interestingly, it was found that POLDIP2 overexpression induced impairments of autophagy activity and partially proteasome activity and this activities were retained in DUF525 domain of POLDIP2. In a Drosophila model of human tauopathy, knockdown of the Drosophila POLDIP2 homolog, CG12162, attenuated rough eye phenotype induced by Tau overexpression. Further, the lifespan of neural-TauR406W transgenic files were recovered by CG12162 knockdown. Together, these observations indicate that POLDIP2 plays a crucial role in Tau aggregation via the impairment of autophagy activity, providing insight into Tau aggregation in Tau pathology.

Gross, C., et al. (2015). Increased expression of the PI3K enhancer PIKE mediates deficits in synaptic plasticity and behavior in Fragile X syndrome. Cell Rep [Epub ahead of print]. PubMed ID: 25921541
Summary:
The PI3K enhancer PIKE links PI3K catalytic subunits to group 1 metabotropic glutamate receptors (mGlu1/5) and activates PI3K signaling. The roles of PIKE in synaptic plasticity and the etiology of mental disorders are unknown. This study shows that increased PIKE expression is a key mediator of impaired mGlu1/5-dependent neuronal plasticity in mouse and fly models of the inherited intellectual disability fragile X syndrome (FXS). Normalizing elevated PIKE protein levels in FXS mice reversed deficits in molecular and cellular plasticity and improved behavior. Notably, PIKE reduction rescued PI3K-dependent and -independent neuronal defects in FXS. Further, PI3K signaling was increased in a fly model of FXS and that genetic reduction of the Drosophila ortholog of PIKE, CenG1A rescued excessive PI3K signaling, mushroom body defects, and impaired short-term memory in these flies. These results demonstrate a crucial role of increased PIKE expression in exaggerated mGlu1/5 signaling causing neuronal defects in FXS.

Pearce, M. M., Spartz, E. J., Hong, W., Luo, L. and Kopito, R. R. (2015). Prion-like transmission of neuronal huntingtin aggregates to phagocytic glia in the Drosophila brain. Nat Commun 6: 6768. PubMed ID: 25866135
Summary:
The brain has a limited capacity to self-protect against protein aggregate-associated pathology, and mounting evidence supports a role for phagocytic glia in this process. This study has established a Drosophila model to investigate the role of phagocytic glia in clearance of neuronal mutant huntingtin (Htt; see Drosophila Huntingtin) aggregates associated with Huntington disease. Glia were found to regulate steady-state numbers of Htt aggregates expressed in neurons through a clearance mechanism that requires the glial scavenger receptor Draper and downstream phagocytic engulfment machinery. Remarkably, some of these engulfed neuronal Htt aggregates effect prion-like conversion of soluble, wild-type Htt in the glial cytoplasm. Genetic evidence is provided that this conversion depends strictly on the Draper signalling pathway, unveiling a previously unanticipated role for phagocytosis in transfer of pathogenic protein aggregates in an intact brain. These results suggest a potential mechanism by which phagocytic glia contribute to both protein aggregate-related neuroprotection and pathogenesis in neurodegenerative disease.

Saturday, May 16th

Clemmons, A.W., Lindsay, S.A. and Wasserman, S.A. (2015). An effector Peptide family required for Drosophila toll-mediated immunity. PLoS Pathog 11: e1004876. PubMed ID: 25915418
Summary:
A family of twelve genes - the Bomanins (Boms) - has been identified that are specifically induced by Toll and that encode small, secreted peptides of unknown biochemical activity. Using targeted genome engineering, ten of the twelve Bom genes were deleted. Remarkably, inactivating these ten genes decreased survival upon microbial infection to the same extent, and with the same specificity, as does eliminating Toll pathway function. Toll signaling, however, appeared unaffected. Assaying bacterial load post-infection in wild-type and mutant flies, evidence was provided that the Boms were required for resistance to, rather than tolerance of, infection. In addition, by generating and assaying a deletion of a smaller subset of the Bom genes, it was found that there was overlap in Bom activity toward particular pathogens. Together, these studies deepen our understanding of Toll-mediated immunity and provide a new in vivo model for exploration of the innate immune effector repertoire.

Merkling, S. H., Bronkhorst, A. W., Kramer, J. M., Overheul, G. J., Schenck, A. and Van Rij, R. P. (2015). The epigenetic regulator g9a mediates tolerance to RNA virus infection in Drosophila. PLoS Pathog 11: e1004692. PubMed ID: 25880195
Summary:
Little is known about the tolerance mechanisms that reduce the negative effects of microbial infection on host fitness. This study demonstrates that the histone H3 lysine 9 methyltransferase G9a regulates tolerance to virus infection by shaping the response of the evolutionary conserved Jak-Stat pathway in Drosophila. G9a-deficient mutants are more sensitive to RNA virus infection and succumb faster to infection than wild-type controls, which was associated with strongly increased Jak-Stat dependent responses, but not with major differences in viral load. Genetic experiments indicate that hyperactivated Jak-Stat responses are associated with early lethality in virus-infected flies. These results identify an essential epigenetic mechanism underlying tolerance to virus infection.

Yamamoto-Hino, M., Muraoka, M., Kondo, S., Ueda, R., Okano, H. and Goto, S. (2015). Dynamic regulation of innate immune responses in Drosophila by Senju-mediated glycosylation. Proc Natl Acad Sci U S A. PubMed ID: 25901322
Summary:
The innate immune system is the first line of defense encountered by invading pathogens. Delayed and/or inadequate innate immune responses can result in failure to combat pathogens, whereas excessive and/or inappropriate responses cause runaway inflammation. Therefore, immune responses are tightly regulated from initiation to resolution and are repressed during the steady state. It is well known that glycans presented on pathogens play important roles in pathogen recognition and the interactions between host molecules and microbes; however, the function of glycans of host organisms in innate immune responses is less well known. This study shows that innate immune quiescence and strength of the immune response are controlled by host glycosylation involving a novel UDP-galactose transporter called Senju (CG14040). In senju mutants, reduced expression of galactose-containing glycans resulted in hyperactivation of the Toll signaling pathway in the absence of immune challenges. Genetic epistasis and biochemical analyses revealed that Senju regulates the Toll signaling pathway at a step that converts Toll ligand Spatzle to its active form. Interestingly, Toll activation in immune-challenged wild type (WT) flies reduced the expression of galactose-containing glycans. Suppression of the degalactosylation by senju overexpression resulted in reduced induction of Toll-dependent expression of an antimicrobial peptide, Drosomycin, and increased susceptibility to infection with Gram-positive bacteria. These data suggest that Senju-mediated galactosylation suppresses undesirable Toll signaling activation during the steady state; however, Toll activation in response to infection leads to degalactosylation, which raises the immune response to an adequate level and contributes to the prompt elimination of pathogens.

Newton, I. L., Savytskyy, O. and Sheehan, K. B. (2015). Wolbachia utilize host actin for efficient maternal transmission in Drosophila melanogaster. PLoS Pathog 11: e1004798. PubMed ID: 25906062
Summary:
Wolbachia pipientis is a ubiquitous, maternally transmitted bacterium that infects the germline of insect hosts. Estimates are that Wolbachia infect nearly 40% of insect species on the planet, making it the most prevalent infection on Earth. The bacterium, infamous for the reproductive phenotypes it induces in arthropod hosts, has risen to recent prominence due to its use in vector control. Wolbachia infection prevents the colonization of vectors by RNA viruses, including Drosophila C virus and important human pathogens such as Dengue and Chikungunya. This study presents data indicating that Wolbachia utilize the host actin cytoskeleton during oogenesis for persistence within and transmission between Drosophila melanogaster generations. Phenotypically wild type flies heterozygous for cytoskeletal mutations in Drosophila profilin chic or villin quail either clear a Wolbachia infection, or result in significantly reduced infection levels. This reduction of Wolbachia is supported by PCR evidence, Western blot results and cytological examination. This phenotype is unlikely to be the result of maternal loading defects, defects in oocyte polarization, or germline stem cell proliferation, as the flies are phenotypically wild type in egg size, shape, and number. Importantly, however, heterozygous mutant flies exhibit decreased total G-actin in the ovary, compared to control flies and chic heterozygous mutants exhibit decreased expression of profilin. Additionally, RNAi knockdown of profilin during development decreases Wolbachia titers. Evidence in support of alternative theories was analyzed to explain this Wolbachia phenotype and it was concluded that the results support the hypothesis that Wolbachia utilize the actin skeleton for efficient transmission and maintenance within Drosophila.

Vanha-Aho, L.M., Anderl, I., Vesala, L., Hultmark, D., Valanne, S and Rämet, M. (2015). Edin expression in the fat body is required in the defense against parasitic wasps in Drosophila melanogaster. PLoS Pathog 11: e1004895. PubMed ID: 25965263
Summary:
The cellular immune response against parasitoid wasps in Drosophila involves the activation, mobilization, proliferation and differentiation of different blood cell types. This study has assessed the role of Edin (elevated during infection) in the immune response against the parasitoid wasp Leptopilina boulardi in Drosophila melanogaster larvae. Blast search revels that edin is a novel gene confined to dipteran species. The expression of edin is induced within hours after a wasp infection in larval fat bodies. Tissue-specific RNAi showed that Edin is an important determinant of the encapsulation response. Although edin expression in the fat body is required for the larvae to mount a normal encapsulation response, it is dispensable in hemocytes. Edin expression in the fat body is not required for lamellocyte differentiation, but it is needed for the increase in plasmatocyte numbers and for the release of sessile hemocytes into the hemolymph. The study concludes that edin expression in the fat body affects the outcome of a wasp infection by regulating the increase of plasmatocyte numbers and the mobilization of sessile hemocytes in Drosophila larvae

Friday, May 16th

Bajgar, A., Kucerova, K., Jonatova, L., Tomcala, A., Schneedorferova, I., Okrouhlik, J. and Dolezal, T. (2015). Extracellular adenosine mediates a systemic metabolic switch during immune response. PLoS Biol 13: e1002135. PubMed ID: 25915062
Summary:
Immune defense is energetically costly, and thus an effective response requires metabolic adaptation of the organism to reallocate energy from storage, growth, and development towards the immune system. The natural infection of Drosophila with a parasitoid wasp was used to study energy regulation during immune response. To combat the invasion, the host must produce specialized immune cells (lamellocytes) that destroy the parasitoid egg. A significant portion of nutrients are allocated to differentiating lamellocytes when they would otherwise be used for development. This systemic metabolic switch is mediated by extracellular adenosine released from immune cells. The switch is crucial for an effective immune response. Preventing adenosine transport from immune cells or blocking adenosine receptor precludes the metabolic switch and the deceleration of development, dramatically reducing host resistance. Adenosine thus serves as a signal that the "selfish" immune cells send during infection to secure more energy at the expense of other tissues.
Seelig, J. D. and Jayaraman, V. (2013). Neural dynamics for landmark orientation and angular path integration. Nature 521: [Epub ahead of print]. Nature
Summary:
Many animals navigate using a combination of visual landmarks and path integration. In mammalian brains, head direction cells integrate these two streams of information by representing an animal's heading relative to landmarks, yet maintaining their directional tuning in darkness based on self-motion cues. This study used two-photon calcium imaging in head-fixed Drosophila melanogaster walking on a ball in a virtual reality arena to demonstrate that landmark-based orientation and angular path integration are combined in the population responses of neurons whose dendrites tile the ellipsoid body, a toroidal structure in the centre of the fly brain. The neural population encodes the fly's azimuth relative to its environment, tracking visual landmarks when available and relying on self-motion cues in darkness. When both visual and self-motion cues are absent, a representation of the animal's orientation is maintained in this network through persistent activity, a potential substrate for short-term memory. Several features of the population dynamics of these neurons and their circular anatomical arrangement are suggestive of ring attractors, network structures that have been proposed to support the function of navigational brain circuits. See Online videos

Owald, D., Felsenberg, J., Talbot, C. B., Das, G., Perisse, E., Huetteroth, W. and Waddell, S. (2015). Activity of defined mushroom body output neurons underlies learned olfactory behavior in Drosophila. Neuron 86: 417-427. PubMed ID: 25864636
Summary:
During olfactory learning in fruit flies, dopaminergic neurons assign value to odor representations in the mushroom body Kenyon cells. This study identified a class of downstream glutamatergic mushroom body output neurons (MBONs) called M4/6, or MBON-β2β'2a, MBON-β'2mp, and MBON-γ5&beta'2a, whose dendritic fields overlap with dopaminergic neuron projections in the tips of the β, β', and γ lobes. This anatomy and their odor tuning suggests that M4/6 neurons pool odor-driven Kenyon cell synaptic outputs. Like that of mushroom body neurons, M4/6 output is required for expression of appetitive and aversive memory performance. Moreover, appetitive and aversive olfactory conditioning bidirectionally alters the relative odor-drive of M4β' neurons (MBON-β'2mp). Direct block of M4/6 neurons in naive flies mimics appetitive conditioning, being sufficient to convert odor-driven avoidance into approach, while optogenetically activating these neurons induces avoidance behavior. It is therefore proposed that drive to the M4/6 neurons reflects odor-directed behavioral choice. See Three Pairs of Glutamatergic Output Neurons Innervate the Tips of the Horizontal Mushroom Body Lobes

Tastekin, I., Riedl, J., Schilling-Kurz, V., Gomez-Marin, A., Truman, J. W. and Louis, M. (2015). Role of the subesophageal zone in sensorimotor control of Orientation in Drosophila larva. Curr Biol. PubMed ID: 25959970
Summary:
In the Drosophila melanogaster larva, chemotaxis mainly consists of an alternation of distinct behavioral modes: runs and directed turns. During locomotion, turns are triggered by the integration of temporal changes in the intensity of the stimulus. While the anatomy of the peripheral olfactory circuits is reasonably well documented, the neural circuits connecting the sensory neurons to the motor neurons remain unknown. This study combined a loss-of-function behavioral screen with optogenetics-based clonal gain-of-function manipulations to identify neurons that are necessary and sufficient for the initiation of reorientation maneuvers in odor gradients. The results indicate that a small subset of neurons residing in the subesophageal zone controls the rate of transition from runs to turns-a premotor function compatible with observations made in other invertebrates. After having shown that this function pertains to the processing of inputs from different sensory modalities (olfaction, vision, thermosensation), it is concluded that the subesophageal zone operates as a general premotor center that regulates the selection of different behavioral programs based on the integration of sensory stimuli. The present analysis paves the way for a systematic investigation of the neural computations underlying action selection in a miniature brain amenable to genetic manipulations.

Gepner, R., Mihovilovic Skanata, M., Bernat, N. M., Kaplow, M. and Gershow, M. (2015). Computations underlying photo-taxis, odor-taxis, and multi-sensory integration. Elife 4 [Epub ahead of print]. PubMed ID: 25945916
Summary:
To better understand how organisms make decisions on the basis of temporally varying multi-sensory input, this study identified computations made by Drosophila larvae responding to visual and optogenetically induced fictive olfactory stimuli. The larva's navigational decision to initiate turns was modeled as the output of a Linear-Nonlinear-Poisson cascade. Reverse-correlation was used to fit parameters to this model; the parameterized model predicted larvae's responses to novel stimulus patterns. For multi-modal inputs, it was found that larvae linearly combine olfactory and visual signals upstream of the decision to turn. This prediction was verified by measuring larvae's responses to coordinated changes in odor and light. Other navigational decisions were studied, and it was found that larvae integrated odor and light according to the same rule in all cases. These results suggest that photo-taxis and odor-taxis are mediated by a shared computational pathway.

Yoshii, T., Hermann-Luibl, C., Kistenpfennig, C., Schmid, B., Tomioka, K. and Helfrich-Forster, C. (2015). Cryptochrome-dependent and -independent circadian entrainment circuits in Drosophila. J Neurosci 35: 6131-6141. PubMed ID: 25878285
Summary:
Entrainment to environmental light/dark (LD) cycles is a central function of circadian clocks. In Drosophila, entrainment is achieved by Cryptochrome (Cry) and input from the visual system. During activation by brief light pulses, Cry triggers the degradation of Timeless and subsequent shift in circadian phase. This is less important for LD entrainment, leading to questions regarding light input circuits and mechanisms from the visual system. Recent studies show that different subsets of brain pacemaker clock neurons, the morning (M) and evening (E) oscillators, have distinct functions in light entrainment. However, the role of Cry in M and E oscillators for entrainment to LD cycles is unknown. This study addresses this question by selectively expressing Cry in different subsets of clock neurons in a cry-null (cry0) mutant background. It was possible to rescue the light entrainment deficits of cry0 mutants by expressing Cry in E oscillators but not in any other clock neurons. Par domain protein 1 molecular oscillations in the E, but not M, cells of cry0 mutants still responded to the LD phase delay. This residual light response was stemming from the visual system because it disappeared when all external photoreceptors were ablated genetically. It is concluded that the E oscillators are the targets of light input via Cry and the visual system and are required for normal light entrainment.

Bushey, D., Tononi, G. and Cirelli, C. (2015). Sleep- and wake-dependent changes in neuronal activity and reactivity demonstrated in fly neurons using in vivo calcium imaging. Proc Natl Acad Sci U S A 112: 4785-4790. PubMed ID: 25825756
Summary:
Sleep in Drosophila shares many features with mammalian sleep, but it remains unknown whether spontaneous and evoked activity of individual neurons change with the sleep/wake cycle in flies as they do in mammals. This study used calcium imaging to assess how the Kenyon cells in the fly mushroom bodies change their activity and reactivity to stimuli during sleep, wake, and after short or long sleep deprivation. As before, sleep was defined as a period of immobility of >5 min associated with a reduced behavioral response to a stimulus. Calcium levels in Kenyon cells were found to decline when flies fall asleep and increase when they wake up. Moreover, calcium transients in response to two different stimuli are larger in awake flies than in sleeping flies. The activity of Kenyon cells is also affected by sleep/wake history: in awake flies, more cells are spontaneously active and responding to stimuli if the last several hours (5-8 h) before imaging were spent awake rather than asleep. By contrast, long wake (>/=29 h) reduces both baseline and evoked neural activity and decreases the ability of neurons to respond consistently to the same repeated stimulus. The latter finding may underlie some of the negative effects of sleep deprivation on cognitive performance and is consistent with the occurrence of local sleep during wake as described in behaving rats. Thus, calcium imaging uncovers new similarities between fly and mammalian sleep: fly neurons are more active and reactive in wake than in sleep, and their activity tracks sleep/wake history. See: Identification of sleep and wake states during calcium imaging

Thursday, May 14th

Irizarry, J. and Stathopoulos, A. (2015). FGF signaling supports Drosophila fertility by regulating development of ovarian muscle tissues. Dev Biol [Epub ahead of print]. PubMed ID: 25958090
Summary:
The thisbe (ths) gene encodes a Drosophila FGF, and mutant females are viable but sterile suggesting a link between FGF signaling and fertility. Ovaries exhibit abnormal morphology including lack of epithelial sheaths, muscle tissues that surround ovarioles. This study investigated how FGF influences Drosophila ovary morphogenesis. Heartless (Htl) FGF receptor was found expressed within somatic cells at the larval and pupal stages, and phenotypes were uncovered using RNAi. Differentiation of terminal filament cells was affected, but this effect did not alter ovariole number. In addition, proliferation of epithelial sheath progenitors, the apical cells, was decreased in both htl and ths mutants, while ectopic expression of the Ths ligand led to these cells' over-proliferation suggesting that FGF signaling supports ovarian muscle sheath formation by controlling apical cell number in the developing gonad. Additionally, live imaging of adult ovaries was used to show that htl RNAi mutants, hypomorphic mutants in which epithelial sheaths were present, exhibited abnormal muscle contractions. Collectively, these results demonstrate that proper formation of ovarian muscle tissues is regulated by FGF signaling in the larval and pupal stages through control of apical cell proliferation and is required to support fertility.

Ma, X., Chen, Y., Xu, W., Wu, N., Li, M., Cao, Y., Wu, S., Li, Q. and Xue, L. (2015). Impaired Hippo signaling promotes Rho1-JNK-dependent growth.Proc Natl Acad Sci U S A 112: 1065-1070. PubMed ID: 25583514
Summary:
The Hippo and c-Jun N-terminal kinase (JNK) pathways both regulate growth and contribute to tumorigenesis when dysregulated. Whereas the Hippo pathway acts via the transcription coactivator Yki/YAP to regulate target gene expression, JNK signaling, triggered by various modulators including Rho GTPases, activates the transcription factors Jun and Fos. This study shows that impaired Hippo signaling induces JNK activation through Rho1. Blocking Rho1-JNK signaling suppresses Yki-induced overgrowth in the wing disk, whereas ectopic Rho1 expression promotes tissue growth when apoptosis is prohibited. Furthermore, Yki directly regulates Rho1 transcription via the transcription factor Sd. Thus, these results have identified a novel molecular link between the Hippo and JNK pathways and implicated the essential role of the JNK pathway in Hippo signaling-related tumorigenesis.
Wang, Z. H., Rabouille, C. and Geisbrecht, E. R. (2015). Loss of a Clueless-dGRASP complex results in ER stress and blocks integrin exit from the perinuclear endoplasmic reticulum in Drosophila larval muscle. Biol Open. PubMed ID: 25862246
Summary:
Drosophila Clueless (Clu) and its conserved orthologs are known for their role in the prevention of mitochondrial clustering. This study uncovered a new role for Clu in the delivery of integrin subunits in muscle tissue. In clu mutants, αPS2 integrin (Inflated), but not βPS integrin, abnormally accumulates in a perinuclear endoplasmic reticulum (ER) subdomain, a site that mirrors the endogenous localization of Clu. Loss of components essential for mitochondrial distribution do not phenocopy the clu mutant alphaPS2 phenotype. Conversely, RNAi knockdown of the Drosophila Golgi reassembly and stacking protein GRASP55/65 recapitulates clu defects, including the abnormal accumulation of αPS2 and larval locomotor activity. Both Clu and dGRASP proteins physically interact and loss of Clu displaces dGRASP from ER exit sites, suggesting that Clu cooperates with dGRASP for the exit of alphaPS2 from a perinuclear subdomain in the ER. This study also found that Clu and dGRASP loss of function leads to ER stress and that the stability of the ER exit site protein Sec16 is severely compromised in the clu mutants, thus explaining the ER accumulation of αPS2. Remarkably, exposure of clu RNAi larvae to chemical chaperones restores both αPS2 delivery and functional ER exit sites. It is proposed that Clu together with dGRASP prevents ER stress and therefore maintains Sec16 stability essential for the functional organization of perinuclear early secretory pathway. This, in turn, is essential for integrin subunit αPS2 ER exit in Drosophila larval myofibers.

Slade, J. D. and Staveley, B. E. (2015). Compensatory growth in novel Drosophila Akt1 mutants. BMC Res Notes 8: 77. PubMed ID: 25889856
Summary:
The insulin receptor signalling pathway with its central component, the Akt1 kinase, and endpoint regulator, the transcription factor Foxo, plays a significant role in the control of growth. Imprecise excision of a PZ P-element inserted in the upstream region of Akt1 generated several mutations that lead to small, viable flies that presented with delays in development. Suppression of this phenotype by the directed expression of Akt1- indicates that the phenotypes observed are Akt1 dependent. Somatic clones of the eyes, consisting of homozygous tissue in otherwise heterozygous organisms that develop within a standard timeframe, signify that more severe phenotypes are masked by an extension in the time of development of homozygous mutants. Generation of flies having the hypomorphic Akt1 alleles and a null allele of the downstream target foxo result in a phenotype very similar to that of the foxo mutant and do not resemble the Akt1 mutants. It is concluded that developmental delay of these novel Akt1 hypomorphs results in a latent phenotype uncovered by generation of somatic clones. The compensatory growth occurring during the extended time of development appears to be implemented through alteration of foxo activity. Production of clones is an effective and informative way to observe the effects of mutations that result in small, viable, developmentally delayed flies.

Wednesday, May 13th

Means, J.C., et al. (2015). Drosophila Spaghetti and Doubletime link the circadian clock and light to caspases, apoptosis and tauopathy. PLoS Genet 11: e1005171. PubMed ID: 25951229
Summary:
While circadian dysfunction and neurodegeneration are correlated, the mechanism for this is not understood. This study shows that the knock-down of a regulator (spag) of the circadian kinase Dbt in circadian cells lowers Dbt levels abnormally, lengthens circadian rhythms and causes expression of activated initiator caspase (Dronc) in the optic lobes during the middle of the day or after light pulses at night. Likewise, reduced Dbt activity lengthened circadian period and caused expression of activated Dronc, and a loss-of-function mutation in Clk also lead to expression of activated Dronc in a light-dependent manner. Genetic epistasis experiments placed Dbt downstream of Spag in the pathway, and Spag-dependent reductions of Dbt were shown to require the proteasome. Importantly, activated Dronc expression due to reduced Spag or Dbt activity occurred in cells that did not express the spag RNAi or dominant negative Dbt and required PDF neuropeptide signaling from the same neurons that support behavioral rhythms. Furthermore, reduction of Dbt or Spag activity lead to Dronc-dependent Drosophila Tau cleavage and enhanced neurodegeneration produced by human Tau in a fly eye model for tauopathy. Aging flies with lowered Dbt or Spag function showed markers of cell death as well as behavioral deficits and shortened lifespans, and even old wild type flies exhibited Dbt modification and activated caspase at particular times of day. These results suggest that circadian clock defects confer sensitivity to expression of activated Dronc in response to prolonged light. This study has established a link between the circadian clock factors, light, cell death pathways and Tau toxicity.

Shi, Q., Li, S., Li, S., Jiang, A., Chen, Y. and Jiang, J. (2014). Hedgehog-induced phosphorylation by CK1 sustains the activity of Ci/Gli activator.Proc Natl Acad Sci U S A 111: E5651-5660. PubMed ID: 25512501
Summary:
Hedgehog (Hh) signaling governs many developmental processes by regulating the balance between the repressor (CiR/GliR) and activator (CiA/GliA) forms of Cubitus interruptus (Ci)/glioma-associated oncogene homolog (Gli) transcription factors. Although much is known about how CiR/GliR is controlled, the regulation of CiA/GliA remains poorly understood. This study, carried out in larval wing discs demonstrates that Casein kinase 1 (CK1) sustains Hh signaling downstream of Costal2 and Suppressor of fused (Sufu) by protecting CiA) from premature degradation. Hh stimulates Ci phosphorylation by CK1 at multiple Ser/Thr-rich degrons to inhibit its recognition by the Hh-induced MATH and BTB domain containing protein (HIB), a substrate receptor for the Cullin 3 family of E3 ubiquitin ligases. In Hh-receiving cells, reduction of CK1 activity accelerated HIB-mediated degradation of CiA, leading to premature loss of pathway activity. Evidence that GliA is regulated by CK1 in a similar fashion and that CK1 acts downstream of Sufu to promote Sonic hedgehog signaling. Taken together, this study not only reveals an unanticipated and conserved mechanism by which phosphorylation of Ci/Gli positively regulates Hh signaling but also provides the first evidence that substrate recognition by the Cullin 3 family of E3 ubiquitin ligases is negatively regulated by a kinase.

Wong, H. W., Shaukat, Z., Wang, J., Saint, R. and Gregory, S. L. (2014). JNK signaling is needed to tolerate chromosomal instability. Cell Cycle 13: 622-631. PubMed ID: 24335260
Summary:
Chromosomal instability (CIN), as a common feature of tumors, represents a potential therapeutic target if ways can be found to specifically cause apoptosis in unstably dividing cells. Previous studies has shown that if signaling through the JNK pathway is reduced, apoptosis is triggered in models of chromosomal instability induced by loss of the spindle checkpoint (reducing Mad2 in adult flies by RNAi). This study identified components upstream and downstream of JNK that are able to mediate this effect, and tested the involvement of p53 and DNA damage in causing apoptosis when JNK signaling is reduced in CIN cells. Cell cycle progression timing has shown to have a strong effect on the apoptosis seen when JNK signaling is reduced in genetically unstable cells: a shortened G 2 phase enhances the apoptosis, while lengthening G 2 rescues the JNK-deficient CIN cell death phenotype. These findings suggest that chromosomal instability represents a significant stress to dividing cells, and that without JNK signaling, cells undergo apoptosis because they lack a timely and effective response to DNA damage.

Andersen, D. S., et al. (2015). The Drosophila TNF receptor Grindelwald couples loss of cell polarity and neoplastic growth. Nature [Epub ahead of print]. PubMed ID: 25874673
Summary:
Disruption of epithelial polarity is a key event in the acquisition of neoplastic growth. JNK signalling is known to play an important part in driving the malignant progression of many epithelial tumours, although the link between loss of polarity and JNK signalling remains elusive. In a Drosophila genome-wide genetic screen designed to identify molecules implicated in neoplastic growth, this study identified grindelwald (grnd; CG10176), a gene encoding a transmembrane protein with homology to members of the tumour necrosis factor receptor (TNFR) superfamily. This study shows that Grnd mediates the pro-apoptotic functions of Eiger (Egr), the unique Drosophila TNF, and that overexpression of an active form of Grnd lacking the extracellular domain is sufficient to activate JNK signalling in vivo. Grnd also promotes the invasiveness of RasV12/scrib-/- tumours through Egr-dependent Matrix metalloprotease-1 (Mmp1) expression. Grnd localizes to the subapical membrane domain with the cell polarity determinant Crumbs (Crb) and couples Crb-induced loss of polarity with JNK activation and neoplastic growth through physical interaction with Veli (also known as Lin-7). Therefore, Grnd represents the first example of a TNFR that integrates signals from both Egr and apical polarity determinants to induce JNK-dependent cell death or tumour growth.

Tuesday, May 12th

Beehler-Evans, R. and Micchelli, C. A. (2015). Generation of enteroendocrine cell diversity in# #Drosophila #midgut #stemcell #lineages. Development 142: 654-664. PubMed ID: 25670792
Summary:
The endocrine system mediates long-range peptide hormone signaling to broadcast changes in metabolic status to distant target tissues via the circulatory system. In many animals, the diffuse endocrine system of the gut is the largest endocrine tissue, with the full spectrum of endocrine cell subtypes not yet fully characterized. This study combine molecular mapping, lineage tracing and genetic analysis in the adult fruit fly to gain new insight into the cellular and molecular mechanisms governing enteroendocrine cell diversity. Neuropeptide hormone distribution was used as a basis to generate a high-resolution cellular map of the diffuse endocrine system. These studies show that cell diversity is seen at two distinct levels: regional and local. Class I and class II enteroendocrine cells can be distinguished locally by combinatorial expression of secreted neuropeptide hormones. Cell lineage tracing studies demonstrate that class I and class II cells arise from a common stem cell lineage and that peptide profiles are a stable feature of enteroendocrine cell identity during homeostasis and following challenge with the enteric pathogen Pseudomonas entomophila. Genetic analysis shows that Notch signaling controls the establishment of class II cells in the lineage, but is insufficient to reprogram extant class I cells into class II enteroendocrine cells. Thus, one mechanism by which secretory cell diversity is achieved in the diffuse endocrine system is through cell-cell signaling interactions within individual adult stem cell lineages.

Hasan, S., Hétié, P. and Matunis, E.L. (2015). Niche signaling promotes stem cell survival in the Drosophila testis via the Jak-STAT target DIAP1. Dev Biol [Epub ahead of print]. PubMed ID: 25941003
Summary:
Tissue-specific stem cells are thought to resist environmental insults better than their differentiating progeny, but this resistance varies from one tissue to another, and the underlying mechanisms are not well-understood. This study uses the Drosophila testis as a model system to study the regulation of cell death within an intact niche. This niche contains sperm-producing germline stem cells (GSCs) and accompanying somatic cyst stem cells (or CySCs). Although many signals are known to promote stem cell self-renewal in this tissue, including the highly conserved JAK-STAT pathway, the response of these stem cells to potential death-inducing signals, and factors promoting stem cell survival, have not been characterized. The study found that both GSCs and CySCs resisted cell death better than their differentiating progeny, under normal laboratory conditions and in response to potential death-inducing stimuli such as irradiation or starvation. To ask what might be promoting stem cell survival, the study characterized the role of the anti-apoptotic gene Drosophila inhibitor of apoptosis 1 (diap1) in testis stem cells. DIAP1 protein was enriched in the GSCs and CySCs and was a Jak-STAT target. diap1 was necessary for survival of both GSCs and CySCs, and ectopic up-regulation of DIAP1 in somatic cyst cells was sufficient to non-autonomously rescue stress-induced cell death in adjacent differentiating germ cells (spermatogonia). Altogether, these results show that niche signals can promote stem cell survival by up-regulation of highly conserved anti-apoptotic proteins, and suggest that this strategy may underlie the ability of stem cells to resist death more generally.

Ren, W., Zhang, Y., Li, M., Wu, L., Wang, G., Baeg, G.H., You, J., Li, Z. and Lin, X. (2015). Windpipe controls Drosophila intestinal homeostasis by regulating JAK/STAT pathway via promoting receptor endocytosis and lysosomal degradation. PLoS Genet 11: e1005180. PubMed ID: 25923769
Summary:
The adult intestinal homeostasis is tightly controlled by proper proliferation and differentiation of intestinal stem cells. The JAK/STAT (Janus Kinase/Signal Transducer and Activator of Transcription) signaling pathway is essential for the regulation of adult stem cell activities and maintenance of intestinal homeostasis. Currently, it remains largely unknown how JAK/STAT signaling activities are regulated in these processes. This study has identified windpipe (wdp) as a novel component of the JAK/STAT pathway. Wdp was positively regulated by JAK/STAT signaling in Drosophila adult intestines. Loss of wdp activity resulted in the disruption of midgut homeostasis under normal and regenerative conditions. Conversely, ectopic expression of Wdp inhibited JAK/STAT signaling activity. Importantly, Wdp interacted with the receptor Domeless (Dome), and promoted its internalization for subsequent lysosomal degradation. Together, these data led the study to propose that Wdp acts as a novel negative feedback regulator of the JAK/STAT pathway in regulating intestinal homeostasis.

Wang, L., Ryoo, H.D., Qi, Y. and Jasper, H. (2015). PERK limits Drosophila lifespan by promoting intestinal stem cell proliferation in response to ER stress. PLoS Genet 11: e1005220. PubMed ID: 25945494
Summary:
Intestinal homeostasis requires precise control of intestinal stem cell (ISC) proliferation. In Drosophila, this control declines with age largely due to chronic activation of stress signaling and associated chronic inflammatory conditions. An important contributor to this condition is the age-associated increase in endoplasmic reticulum (ER) stress. This study shows that the PKR-like ER kinase (PERK) integrates both cell-autonomous and non-autonomous ER stress stimuli to induce ISC proliferation. In addition to responding to cell-intrinsic ER stress, PERK was also specifically activated in ISCs by JAK/Stat signaling in response to ER stress in neighboring cells. The activation of PERK was required for homeostatic regeneration, as well as for acute regenerative responses, yet the chronic engagement of this response became deleterious in aging flies. Accordingly, knocking down PERK in ISCs was sufficient to promote intestinal homeostasis and extend lifespan. These studies highlight the significance of the PERK branch of the unfolded protein response of the ER (UPRER) in intestinal homeostasis and provide a viable strategy to improve organismal health- and lifespan.

Monday, May 11th

Bozzetti, M.P., Specchia, V., Cattenoz, P., Laneve, P., Geusa, A., Sahin, H.B., Di Tommaso, S., Friscini, A., Massari, S., Diebold, C. and Giangrande, A. (2015). The Drosophila Fragile X Mental Retardation Protein participates in the piRNA pathway. J Cell Sci [Epub ahead of print]. PubMed ID: 25908854
Summary:
RNA metabolism controls multiple biological processes and a specific class of small RNAs, called piRNAs, act as genome guardians by silencing the expression of transposons and repetitive sequences in the gonads. Defects in the piRNA pathway affect genome integrity and fertility. The possible implications in physiopathological mechanisms of human diseases have made the piRNA pathway the object of intense investigation and recent work calls for a role of this pathway in somatic processes including synaptic plasticity. The RNA-binding Fragile X Mental Retardation Protein (FMRP) controls translation and its loss triggers the most frequent syndromic form of mental retardation as well as gonadal defects in humans. This study demonstrates for the first time that germline as well as somatic expression of dFmr1, the Drosophila ortholog of FMRP, are necessary in a pathway mediated by piRNAs. Moreover, dFmr1 interacted genetically and biochemically with Aubergine, an Argonaute protein and a key player in this pathway. These data open novel perspectives for understanding the phenotypes observed in Fragile X patients and support the view that piRNAs may be at work in the nervous system.

Antic, S., Wolfinger, M.T., Skucha, A., Hosiner, S. and Dorner, S. (2015). General and miRNA-mediated mRNA degradation occurs on ribosome complexes in Drosophila cells. Mol Cell Biol [Epub ahead of print]. PubMed ID: 25918245
Summary:
The translation and degradation of mRNAs are two key steps in gene expression that are highly regulated and targeted by many factors including miRNAs. While it is well established that translation and mRNA degradation are tightly coupled, it is still not entirely clear where in the cell mRNA degradation takes place. This study has investigated the possibility of mRNA degradation on the ribosome in Drosophila cells. Using polysome profiles and ribosome affinity purification, the co-purification of various deadenylation and decapping factors with ribosome complexes was demonstrated. Also AGO1 and GW182, two key factors in the miRNA-mediated mRNA degradation pathway, were associated with ribosome complexes. Their co-purification was dependent on intact mRNAs suggesting the association of these factors with the mRNA rather than the ribosome itself. Furthermore, decapped mRNA degradation intermediates were isolated from ribosome complexes, and HiSeq analysis was performed. Interestingly, 93 % of decapped mRNA fragments (approx. 12,000) could be detected with the same relative abundance on ribosome complexes as in cell lysates. In summary, these findings strongly indicate the association of the majority of bulk mRNAs but also mRNAs targeted by miRNAs with the ribosome during their degradation.

Roy, C. K., Olson, S., Graveley, B. R., Zamore, P. D. and Moore, M. J. (2015). Assessing long-distance RNA sequence connectivity via RNA-templated DNA-DNA ligation. Elife 4. PubMed ID: 25866926
Summary:
Many RNAs, including pre-mRNAs and long non-coding RNAs, can be thousands of nucleotides long and undergo complex post-transcriptional processing. Multiple sites of alternative splicing within a single gene exponentially increases the number of possible spliced isoforms, with most human genes currently estimated to express at least ten. To understand the mechanisms underlying these complex isoform expression patterns, methods are needed that faithfully maintain long-range exon connectivity information in individual RNA molecules. This study describes SeqZip, a methodology that uses RNA-templated DNA-DNA ligation to retain and compress connectivity between distant sequences within single RNA molecules. Using this assay, proposed coordination between distant sites of alternative exon utilization in mouse Fn1 was tested and the extraordinary exon diversity of Drosophila melanogaster Dscam1 was characterized. Consistent with previous reports, it is concluded that individual Dscam1 isoforms are produced via stochastic alternative splicing.

Matsumoto, N., Sato, K., Nishimasu, H., Namba, Y., Miyakubi, K., Dohmae, N., Ishitani, R., Siomi, H., Siomi, M. C. and Nureki, O. (2015). Crystal structure and activity of the endoribonuclease domain of the piRNA pathway factor Maelstrom. Cell Rep 11: 366-375. PubMed ID: 25865890
Summary:
PIWI-interacting RNAs (piRNAs) protect the genome from transposons in animal gonads. Maelstrom (Mael) is an evolutionarily conserved protein, composed of a high-mobility group (HMG) domain and a MAEL domain, and is essential for piRNA-mediated transcriptional transposon silencing in various species, such as Drosophila and mice. However, its structure and biochemical function have remained elusive. This study reports the crystal structure of the MAEL domain from Drosophila melanogaster Mael, at 1.6 A resolution. The structure reveals that the MAEL domain has an RNase H-like fold but lacks canonical catalytic residues conserved among RNase H-like superfamily nucleases. The biochemical analyses reveal that the MAEL domain exhibits single-stranded RNA (ssRNA)-specific endonuclease activity. Cell-based analyses further indicate that ssRNA cleavage activity appears dispensable for piRNA-mediated transcriptional transposon silencing in Drosophila. These findings provide clues toward understanding the multiple roles of Mael in the piRNA pathway.

Sinha, N. K., Trettin, K. D., Aruscavage, P. J. and Bass, B. L. (2015). Drosophila Dicer-2 cleavage is mediated by helicase- and dsRNA termini-dependent states that are modulated by Loquacious-PD. Mol Cell. PubMed ID: 25891075
Summary:
Previous studies have shown that the helicase domain of Drosophila Dicer-2 (dmDcr-2) governs substrate recognition and cleavage efficiency, and that dsRNA termini are key to this discrimination. This study now provides a mechanistic basis for these observations. Discrimination of termini was shown to occur during initial binding. Without ATP, dmDcr-2 binds 3' overhanging, but not blunt, termini. By contrast, with ATP, dmDcr-2 binds both types of termini, with highest-affinity binding observed with blunt dsRNA. In the presence of ATP, binding, cleavage, and ATP hydrolysis are optimal with blunt termini compared to 3'overhang termini. Limited proteolysis experiments suggest the optimal reactivity of blunt dsRNA is mediated by a conformational change that is dependent on ATP and the helicase domain. dmDcr-2's partner protein, Loquacious-PD, alters termini dependence, enabling dmDcr-2 to cleave substrates normally refractory to cleavage, such as dsRNA with blocked, structured, or frayed ends.

Herter, E. K., Stauch, M., Gallant, M., Wolf, E., Raabe, T. and Gallant, P. (2015). snoRNAs are a novel class of biologically relevant Myc targets. BMC Biol 13: 25. PubMed ID: 25888729
Summary:
Myc proteins are essential regulators of animal growth during normal development, and their deregulation is one of the main driving factors of human malignancies. They function as transcription factors that (in vertebrates) control many growth- and proliferation-associated genes, and in some contexts contribute to global gene regulation. This study combined ChIPseq and RNAseq approaches in Drosophila tissue culture cells to identify a core set of less than 500 Myc target genes, whose salient function resides in the control of ribosome biogenesis. Among these genes, the non-coding snoRNA genes were found to be a large novel class of Myc targets. All assayed snoRNAs are affected by Myc, and many of them are subject to direct transcriptional activation by Myc, both in Drosophila and in vertebrates. The loss of snoRNAs impairs growth during normal development, whereas their overexpression increases tumor mass in a model for neuronal tumors. This work shows that Myc acts as a master regulator of snoRNP biogenesis. In addition, in combination with recent observations of snoRNA involvement in human cancer, it raises the possibility that Myc's transforming effects are partially mediated by this class of non-coding transcripts.

Sunday, May 9th

Spencer, A.K., Siddiqui, B.A. and Thomas, J.H. (2015). Cell shape change and invagination of the cephalic furrow involves reorganization of F-actin. Dev Biol [Epub ahead of print]. PubMed ID: 25929228
Summary:
Invagination of epithelial sheets to form furrows is a fundamental morphogenetic movement and is found in a variety of developmental events including gastrulation and vertebrate neural tube formation. The cephalic furrow is a deep epithelial invagination that forms during Drosophila gastrulation. In the first phase of cephalic furrow formation, the initiator cells that will lead invagination undergo apicobasal shortening and apical constriction in the absence of epithelial invagination. In the second phase of cephalic furrow formation, the epithelium starts to invaginate, accompanied by both basal expansion and continued apicobasal shortening of the initiator cells. The cells adjacent to the initiator cells also adopt wedge shapes, but only after invagination is well underway. Myosin II did not appear to drive apical constriction in cephalic furrow formation. However, cortical F-actin was increased in the apices of the initiator cells and in invaginating cells during both phases of cephalic furrow formation. These findings suggest that a novel mechanism for epithelial invagination is involved in cephalic furrow formation.

Biersmith, B., Wang, Z. H. and Geisbrecht, E. R. (2015). Fine-tuning of the actin cytoskeleton and cell adhesion during Drosophila development by guanine nucleotide exchange factors Myoblast city and Sponge. Genetics [Epub ahead of print]. PubMed ID: 25908317
Summary:
The evolutionarily conserved Dock proteins function as unconventional guanine nucleotide exchange factors (GEFs). Upon binding to Engulfment and cell motility (ELMO) proteins, Dock-ELMO complexes activate the Rho family of small GTPases to mediate a diverse array of biological processes. Both in vertebrate and invertebrate systems, the actin dynamics regulator, Rac, is the target GTPase of the Dock-A subfamily. However, it remains unclear whether Rac or Rap1 are the in vivo downstream GTPases of the Dock-B subfamily. Drosophila melanogaster is an excellent genetic model organism to understand Dock protein function as its genome encodes one ortholog per subfamily: Myoblast city (Mbc; Dock-A) and Sponge (Spg; Dock-B). This study shows that the roles of Spg and Mbc are not redundant in the Drosophila somatic muscle or the dorsal vessel (dv). Moreover, this study confirms the in vivo role of Mbc upstream of Rac and provides evidence that Spg functions in concert with Rap1, possibly to regulate aspects of cell adhesion. Together these data show that Mbc and Spg can have different downstream GTPase targets. These findings predict that the ability to regulate downstream GTPases is dependent on cellular context and allows for the fine-tuning of actin cytoskeletal or cell adhesion events in biological processes that undergo cell morphogenesis.

Babic, M., Russo, G. J., Wellington, A. J., Sangston, R. M., Gonzalez, M. and Zinsmaier, K. E. (2015). Miro's N-Terminal GTPase domain is required for transport of mitochondria into axons and dendrites. J Neurosci 35: 5754-5771. PubMed ID: 25855186
Summary:
Mitochondria are dynamically transported in and out of neuronal processes to maintain neuronal excitability and synaptic function. In higher eukaryotes, the mitochondrial GTPase Miro binds Milton/TRAK adaptor proteins linking microtubule motors to mitochondria. This study shows that Drosophila Miro (dMiro), which has previously been shown to be required for kinesin-driven axonal transport, is also critically required for the dynein-driven distribution of mitochondria into dendrites. In addition, the loss-of-function mutations dMiroT25N and dMiroT460N were used to determine the significance of dMiro's N-terminal and C-terminal GTPase domains, respectively. Expression of dMiroT25N in the absence of endogenous dMiro caused premature lethality and arrested development at a pupal stage. dMiroT25N accumulated mitochondria in the soma of larval motor and sensory neurons, and prevented their kinesin-dependent and dynein-dependent distribution into axons and dendrites, respectively. dMiroT25N mutant mitochondria also were severely fragmented and exhibited reduced kinesin and dynein motility in axons. In contrast, dMiroT460N did not impair viability, mitochondrial size, or the distribution of mitochondria. However, dMiroT460N reduced dynein motility during retrograde mitochondrial transport in axons. Finally, this study showed that substitutions analogous to the constitutively active Ras-G12V mutation in dMiro's N-terminal and C-terminal GTPase domains cause neomorphic phenotypic effects that are likely unrelated to the normal function of each GTPase domain. Overall, this analysis indicates that dMiro's N-terminal GTPase domain is critically required for viability, mitochondrial size, and the distribution of mitochondria out of the neuronal soma regardless of the employed motor, likely by promoting the transition from a stationary to a motile state.

Brust-Mascher, I., Civelekoglu-Scholey, G. and Scholey, J. M. (2015). Mechanism for anaphase B: Evaluation of "slide-and-cluster" versus "slide-and-flux-or-elongate" models. Biophys J 108: 2007-2018. PubMed ID: 25902440
Summary:
Elongation of the mitotic spindle during anaphase B contributes to chromosome segregation in many cells. This study quantitatively tested the ability of two models for spindle length control to describe the dynamics of anaphase B spindle elongation using experimental data from Drosophila embryos. In the slide-and-flux-or-elongate (SAFE) model, kinesin-5 motors persistently slide apart antiparallel interpolar microtubules (ipMTs). During pre-anaphase B, this outward sliding of ipMTs is balanced by depolymerization of their minus ends at the poles, producing poleward flux, while the spindle maintains a constant length. Following cyclin B degradation, ipMT depolymerization ceases so the sliding ipMTs can push the poles apart. The competing slide-and-cluster (SAC) model proposes that MTs nucleated at the equator are slid outward by the cooperative actions of the bipolar kinesin-5 and a minus-end-directed motor, which then pulls the sliding MTs inward and clusters them at the poles. In assessing both models, it is assumed that kinesin-5 preferentially cross-links and slides apart antiparallel MTs while the MT plus ends exhibit dynamic instability. However, in the SAC model, minus-end-directed motors bind the minus ends of MTs as cargo and transport them poleward along adjacent, parallel MT tracks, whereas in the SAFE model, all MT minus ends that reach the pole are depolymerized by kinesin-13. Remarkably, the results show that within a narrow range of MT dynamic instability parameters, both models can reproduce the steady-state length and dynamics of pre-anaphase B spindles and the rate of anaphase B spindle elongation. However, only the SAFE model reproduces the change in MT dynamics observed experimentally at anaphase B onset. Thus, although both models explain many features of anaphase B in this system, the quantitative evaluation of experimental data regarding several different aspects of spindle dynamics suggests that the SAFE model provides a better fit.

Saturday, May 9th

O'Connell, M.D. and Reeves G.T. (2015). The presence of nuclear Cactus in the early Drosophila embryo may extend the dynamic range of the dorsal gradient. PLoS Comput Biol 11: e1004159. PubMed ID: 25879657
Summary:
In a developing embryo, the spatial distribution of a signaling molecule, or a morphogen gradient, has been hypothesized to carry positional information to pattern tissues. Recent measurements of morphogen distribution have allowed this hypothesis to be subjected to rigorous physical testing. In the early Drosophila embryo, measurements of the morphogen Dorsal, which is a transcription factor responsible for initiating the earliest zygotic patterns along the dorsal-ventral axis, have revealed a gradient that is too narrow to pattern the entire axis. This study uses a mathematical model of Dorsal dynamics, fit to experimental data, to determine the ability of the Dorsal gradient to regulate gene expression across the entire dorsal-ventral axis. Two assumptions were required for the model to match experimental data in both Dorsal distribution and gene expression patterns. First, Cactus, an inhibitor that binds to Dorsal and prevents it from entering the nuclei, must itself be present in the nuclei. And second, fluorescence measurements of Dorsal reflect both free Dorsal and Cactus-bound Dorsal. The model explains the dynamic behavior of the Dorsal gradient at lateral and dorsal positions of the embryo, the ability of Dorsal to regulate gene expression across the entire dorsal-ventral axis, and the robustness of gene expression to stochastic effects. These results have a general implication for interpreting fluorescence-based measurements of signaling molecules.

Liu, N. and Lasko, P. (2015). Analysis of RNA interference lines identifies new functions of maternally-expressed genes involved in embryonic patterning in Drosophila melanogaster. G3 (Bethesda) [Epub ahead of print]. PubMed ID: 25834215
Summary:
Embryonic patterning inhttp://www.sdbonline.org/sites/fly Drosophila melanogaster is initially established through the activity of a number of maternally expressed genes that are expressed during oogenesis. mRNAs from some of these genes accumulate in the posterior pole plasm of the oocyte and early embryo, and localize further into RNA islands, transient ring-like structures that form around the nuclei of future primordial germ cells (pole cells) at stage 3 of embryogenesis. As mRNAs from several genes with known functions in anterior-posterior patterning and/or germ cell specification accumulate in RNA islands, it was hypothesized that some other mRNAs that localize in this manner might also function in these developmental processes. To test this, the developmental functions of 51 genes whose mRNAs accumulate in RNA islands were investigated by abrogating their activity in the female germline using RNA interference. This analysis revealed requirements for ttk, pbl, Hip14, eIF5, eIF4G, and CG9977 for progression through early oogenesis. Dorsal appendage defects were observed in a proportion of eggs produced by females expressing double-stranded RNA targeting Mkrn1 or jvl, implicating these two genes in dorsal-ventral patterning. In addition, posterior patterning defects and a reduction in pole cell number were seen in the progeny of Mkrn1 females. As the mammalian orthologue of Mkrn1 acts as an E3 ubiquitin ligase, these results suggest an additional link between protein ubiquitination and pole plasm activity.

Wong, M. M., Liu, M. F. and Chiu, S. K. (2015). Cropped, Drosophila transcription factor AP-4, controls tracheal terminal branching and cell growth. BMC Dev Biol 15: 20. PubMed ID: 25888431
Summary:
Endothelial or epithelial cellular branching is vital in development and cancer progression; however, the molecular mechanisms of these processes are not clear. In Drosophila, terminal cell at the end of some tracheal tube ramifies numerous fine branches on the internal organs to supply oxygen. To discover more genes involved in terminal branching, mutants were sought with very few terminal branches using the Kiss enhancer-trap line collection. This analysis identified cropped (crp), encoding the Drosophila homolog of the transcription activator protein AP-4. Overexpressing the wild-type crp gene or a mutant that lacks the DNA-binding region in either the tracheal tissues or terminal cells led to a loss-of-function phenotype, implying that crp can affect terminal branching. Unexpectedly, the ectopic expression of crp also led to enlarged organs, and cell-counting experiments on the salivary glands suggest that elevated levels of AP-4 increase cell size and organ size. Like its mammalian counterpart, cropped is controlled by dMyc, as ectopic expression of dMyc in terminal cells increased cellular branching and the Cropped protein levels in vivo. This study has found that the branching morphogenesis of terminal cells of the tracheal tubes in Drosophila requires the dMyc-dependent activation of Cropped/AP-4 protein to increase the cell growth of terminal cells.

Sharma, R., et al. (2015). The single FGF receptor gene in the beetle Tribolium castaneum codes for two isoforms that integrate FGF8- and Branchless-dependent signals. Dev Biol [Epub ahead of print]. PubMed ID: 25864412
Summary:
In Drosophila, the FGF ligand / receptor combinations of FGF8 (Pyramus and Thisbe) / Heartless (Htl) and Branchless (Bnl) / Breathless (Btl) are required for the migration of mesodermal cells and for the formation of the tracheal network respectively with both the receptors functioning independently of each other. However, only a single fgf-receptor gene (Tc-fgfr) has been identified in the genome of the beetle Tribolium. It was therefore asked whether both the ligands Fgf8 and Bnl could transduce their signal through a common fgf-receptor in Tribolium. Indeed, it was found that the function of the single Tc-fgfr gene is essential for mesoderm differentiation as well as for the formation of the tracheal network during early development. Ligand specific RNAi for Tc-fgf8 and Tc-bnl resulted in two distinct non-overlapping phenotypes of impaired mesoderm differentiation and abnormal formation of the tracheal network in Tc-fgf8- and Tc-bnlRNAi embryos respectively. It was further shown that the single Tc-fgfr gene encodes at least two different receptor isoforms that are generated through alternative splicing. Exon-specific RNAi additionally demonstrated their distinct tissue-specific functions. Finally, the structure of the FGF-receptor gene esd discussed from an evolutionary perspective.

Friday, May 8th

Han, T.H., Dharkar, P., Mayer, M.L. and Serpe, M. (2015). Functional reconstitution of Drosophila melanogaster NMJ glutamate receptors. Proc Natl Acad Sci U S A [Epub ahead of print]. PubMed ID: 25918369
Summary:
The Drosophila larval neuromuscular junction (NMJ), at which glutamate acts as the excitatory neurotransmitter, is a widely used model for genetic analysis of synapse function and development. Despite decades of study, the inability to reconstitute NMJ glutamate receptor function using heterologous expression systems has complicated the analysis of receptor function, such that it is difficult to resolve the molecular basis for compound phenotypes observed in mutant flies. This study finds that Drosophila Neto functions as an essential component required for the function of NMJ glutamate receptors, permitting analysis of glutamate receptor responses in Xenopus oocytes. In combination with a crystallographic analysis of the GluRIIB ligand binding domain, the Serpe lab used this system to characterize the subunit dependence of assembly, channel block, and ligand selectivity for Drosophila NMJ glutamate receptors.

Sugie, A., Hakeda-Suzuki, S., Suzuki, E., Silies, M., Shimozono, M., Mohl, C., Suzuki, T. and Tavosanis, G. (2015). Molecular remodeling of the presynaptic active zone of Drosophila photoreceptors via activity-dependent feedback. Neuron [Epub ahead of print]. PubMed ID: 25892303
Summary:
Neural activity contributes to the regulation of the properties of synapses in sensory systems, allowing for adjustment to a changing environment. Little is known about how synaptic molecular components are regulated to achieve activity-dependent plasticity at central synapses. This study found that after prolonged exposure to natural ambient light the presynaptic active zone in Drosophila photoreceptors undergoes reversible remodeling, including loss of Bruchpilot, DLiprin-alpha, and DRBP, but not of DSyd-1 or Cacophony. The level of depolarization of the postsynaptic neurons is critical for the light-induced changes in active zone composition in the photoreceptors, indicating the existence of a feedback signal. In search of this signal, this study has identified a crucial role of microtubule meshwork organization downstream of the divergent canonical Wnt pathway, potentially via Kinesin-3 Imac. These data reveal that active zone composition can be regulated in vivo and identify the underlying molecular machinery.

Lee, J. and Littleton, J. T. (2015). Transmembrane tethering of synaptotagmin to synaptic vesicles controls multiple modes of neurotransmitter release. Proc Natl Acad Sci U S A 112: 3793-3798. PubMed ID: 25775572
Summary:
Synaptotagmin 1 (Syt1) is a synaptic vesicle integral membrane protein that regulates neurotransmitter release by activating fast synchronous fusion and suppressing slower asynchronous release. The cytoplasmic C2 domains of Syt1 interact with SNAREs and plasma membrane phospholipids in a Ca(2+)-dependent manner and can substitute for full-length Syt1 in in vitro membrane fusion assays. To determine whether synaptic vesicle tethering of Syt1 is required for normal fusion in vivo, this study performed a structure-function study with tethering mutants at the Drosophila larval neuromuscular junction. Transgenic animals expressing only the cytoplasmic C2 domains or full-length Syt1 tethered to the plasma membrane failed to restore synchronous synaptic vesicle fusion, and also failed to clamp spontaneous vesicle release. In addition, transgenic animals with shorter, but not those with longer, linker regions separating the C2 domains from the transmembrane segment abolished Syt1's ability to activate synchronous vesicle fusion. Similar defects were observed when C2 domain alignment was altered to C2B-C2A from the normal C2A-C2B orientation, leaving the tether itself intact. Although cytoplasmic and plasma membrane-tethered Syt1 variants could not restore synchronous release in syt1 null mutants, they were very effective in promoting fusion through the slower asynchronous pathway. As such, the subcellular localization of Syt1 within synaptic terminals is important for the temporal dynamics that underlie synchronous and asynchronous neurotransmitter release.

Wong, M. Y., Cavolo, S. L. and Levitan, E. S. (2015). Synaptic neuropeptide release by Dynamin-dependent partial release from circulating vesicles. Mol Biol Cell [Epub ahead of print]. PubMed ID: 25904335
Summary:
Neurons release neuropeptides, enzymes and neurotrophins by exocytosis of dense-core vesicles (DCVs). Peptide release from individual DCVs has been imaged in vitro with endocrine cells and at the neuron soma, growth cones, neurites, axons, and dendrites, but not at nerve terminals where peptidergic neurotransmission occurs. Here dynamin (encoded by the shibire gene) is shown to enhance activity-evoked peptide release at the Drosophila neuromuscular junction. Simultaneous photobleaching and imaging (SPAIM) demonstrates that activity depletes only a portion of a single presynaptic DCV's content. Activity initiates exocytosis within seconds, but subsequent release occurs slowly. Synaptic neuropeptide release is further sustained by DCVs undergoing multiple rounds of exocytosis. Synaptic neuropeptide release is surprisingly similar regardless of anterograde or retrograde DCV transport into boutons, bouton location and time of arrival in the terminal. Thus, vesicle circulation and bidirectional capture supplies synapses with functionally competent DCVs. These results show that activity-evoked synaptic neuropeptide release is independent of a DCV's past traffic and occurs by slow dynamin-dependent partial emptying of DCVs suggestive of kiss and run exocytosis.

Thursday, May 7th

Mannava, A. G. and Tolwinski, N. S. (2015). Membrane bound GSK-3 activates Wnt signaling through Disheveled and Arrow. PLoS One 10: e0121879. PubMed ID: 25848770
Summary:
Wnt ligands and their downstream pathway components coordinate many developmental and cellular processes. In adults, they regulate tissue homeostasis through regulation of stem cells. Mechanistically, signal transduction through this pathway is complicated by pathway components having both positive and negative roles in signal propagation. This study examined the positive role of GSK-3/Zw3 in promoting signal transduction at the plasma membrane. Targeting GSK-3 to the plasma membrane activates signaling in Drosophila embryos. This activation requires the presence of the co-receptor Arrow-LRP5/6 and the pathway activating protein Disheveled. These results provide genetic evidence for evolutionarily conserved, separable roles for GSK-3 at the membrane and in the cytosol, and are consistent with a model where the complex cycles from cytosol to membrane in order to promote signaling at the membrane and to prevent it in the cytosol.

Ricolo, D., Butí, E. and Araújo, S.J. (2015). Drosophila melanogaster Hedgehog cooperates with Frazzled to guide axons through a non-canonical signalling pathway. Mech Dev [Epub ahead of print]. PubMed ID: 25936631
Summary:
This study reports that the morphogen Hedgehog (Hh) is an axonal chemoattractant in the midline of D. melanogaster embryos. Hh is present in the ventral nerve cord during axonal guidance and overexpression of hh in the midline causes ectopic midline crossing of FasII-positive axonal tracts. In addition, Hh influenced axonal guidance via a non-canonical signalling pathway dependent on Ptc. These results reveal that the Hh pathway cooperates with the Netrin/Frazzled pathway to guide axons through the midline in invertebrates.

Swarup, S., Pradhan-Sundd, T. and Verheyen, E. M. (2015). Genome-wide identification of phospho-regulators of Wnt signaling in Drosophila. Development 142: 1502-1515. PubMed ID: 25852200
Summary:
Evolutionarily conserved intercellular signaling pathways regulate embryonic development and adult tissue homeostasis in metazoans. The precise control of the state and amplitude of signaling pathways is achieved in part through the kinase- and phosphatase-mediated reversible phosphorylation of proteins. In this study, a genome-wide in vivo RNAi screen for was performed for kinases and phosphatases that regulate the Wnt pathway under physiological conditions in the Drosophila wing disc. The analyses have identified 54 high-confidence kinases and phosphatases capable of modulating the Wnt pathway, including 22 novel regulators. These candidates were also assayed for a role in the Notch pathway, and numerous phospho-regulators were identified. Additionally, each regulator of the Wnt pathway was evaluated in the wing disc for its ability to affect the mechanistically similar Hedgehog pathway. Twenty-nine dual regulators were identifed that that have the same effect on the Wnt and Hedgehog pathways. As proof of principle, it was established that Cdc37 and Gilgamesh/CK1γ inhibit and promote signaling, respectively, by functioning at analogous levels of these pathways in both Drosophila and mammalian cells. The Wnt and Hedgehog pathways function in tandem in multiple developmental contexts, and the identification of several shared phospho-regulators serve as potential nodes of control under conditions of aberrant signaling and disease.

Sen, A., Sun, R. and Krahn, M. P. (2015). Localization and function of Pals1 associated tight junction protein in Drosophila is regulated by two distinct apical complexes. J Biol Chem [Epub ahead of print]. PubMed ID: 25847234
Summary:
The transmembrane protein Crumbs (Crb) and its intracellular adaptor protein Pals1 (Stardust, Sdt in Drosophila) play a crucial role in the establishment and maintenance of apical-basal polarity in epithelial cells in various organisms. In contrast, the multiple-PDZ-domain containing protein PATJ, which has been described to form a complex with Crb/Sdt, is not essential for apical basal polarity or for the stability of the Crb/Sdt complex in the Drosophila epidermis. This study shows that in the embryonic epidermis Sdt is essential for the correct subcellular localization of PATJ in differentiated epithelial cells but not during cellularization. Consistently, the L27-domain of PATJ is crucial for the correct localization and function of the protein. These data further indicate that the four PDZ domains of PATJ function to a large extent in redundancy regulating the proteins function. Interestingly the PATJ-Sdt heterodimer is not only recruited to the apical cell-cell contacts by binding to Crb but depends on functional Bazooka (Baz). However biochemical experiments show that PATJ associates with both complexes, the Baz-Sdt and the Crb-Sdt complex in the mature epithelium of the embryonic epidermis, suggesting a role of these two complexes for PATJs function during development of Drosophila.

Wednesday, May 6th

Sherrard, K.M. and Fehon, R.G. (2015). The transmembrane protein Crumbs displays complex dynamics during follicular morphogenesis and is regulated competitively by Moesin and aPKC. Development [Epub ahead of print]. PubMed ID: 25926360
Summary:
The transmembrane protein Crumbs (Crb) functions in apical polarity and epithelial integrity. To better understand its role in epithelial morphogenesis, this study examined Crb localization and dynamics in the late follicular epithelium of Drosophila. Crb was unexpectedly dynamic during middle-to-late stages of egg chamber development, being lost from the marginal zone (MZ) in stage 9 before abruptly returning at the end of stage 10b, then undergoing a pulse of endocytosis in stage 12. The reappearance of MZ Crb was necessary to maintain an intact adherens junction and MZ. Although Crb has been proposed to interact through its juxtamembrane domain with Moesin (Moe), a FERM domain protein that regulates the cortical actin cytoskeleton, the functional significance of this interaction is poorly understood. This study found that whereas the Crb juxtamembrane domain was not required for adherens junction integrity, it was necessary for MZ localization of Moe, aPKC and F-actin. Furthermore, Moe and aPKC functioned antagonistically, suggesting that Moe limits Crb levels by reducing its interactions with the apical Par network. Additionally, Moe mutant cells lost Crb from the apical membrane and accumulated excess Crb at the MZ, suggesting that Moe regulates Crb distribution at the membrane. Together, these studies reveal reciprocal interactions between Crb, Moe and aPKC during cellular morphogenesis.

Little, S. C., Sinsimer, K. S., Lee, J. J., Wieschaus, E. F. and Gavis, E. R. (2015). Independent and coordinate trafficking of single Drosophila germ plasm mRNAs. Nat Cell Biol. PubMed ID: 25848747
Summary:
Messenger RNA localization is a conserved mechanism for spatial control of protein synthesis, with key roles in generating cellular and developmental asymmetry. Whereas different transcripts may be targeted to the same subcellular domain, the extent to which their localization is coordinated is unclear. Using quantitative single-molecule imaging, this study analysed the assembly of Drosophila germ plasm mRNA granules inherited by nascent germ cells. The germ-cell-destined transcripts nanos, cyclin B and polar granule component travel within the oocyte as ribonucleoprotein particles containing single mRNA molecules but co-assemble into multi-copy heterogeneous granules selectively at the posterior of the oocyte. The stoichiometry and dynamics of assembly indicate a defined stepwise sequence. The data suggest that co-packaging of these transcripts ensures their effective segregation to germ cells. In contrast, compartmentalization of the germline determinant oskar mRNA into different granules limits its entry into germ cells. This exclusion is required for proper germline development.

Hsu, S.J., Plata, M.P., Ernest, B., Asgarifar, S. and Labrador, M. (2015). The insulator protein Suppressor of Hairy wing is required for proper ring canal development during oogenesis in Drosophila. Dev Biol [Epub ahead of print]. PubMed ID: 25882370
Summary:
Chromatin insulators orchestrate gene transcription during embryo development and cell differentiation by stabilizing interactions between distant genomic sites. Mutations in genes encoding insulator proteins are generally lethal, making in vivo functional analyses of insulator proteins difficult. In Drosophila, however, mutations in the gene encoding the Suppressor of Hairy wing insulator protein [Su(Hw)] are viable and female sterile, providing an opportunity to study insulator function during oocyte development. Whereas previous reports suggest that the function of Su(Hw) in oogenesis is independent of its insulator activity, many aspects of the role of Su(Hw) in Drosophila oogenesis remain unexplored. This study shows that mutations in su(Hw) result in smaller ring canal lumens and smaller outer ring diameters, which likely obstruct molecular and vesicle passage from nurse cells to the oocyte. Fluorescence microscopy revealed that lack of Su(Hw) lead to excess accumulation of Kelch (Kel) and Filament-actin (F-actin) proteins in the ring canal structures of developing egg chambers. Furthermore, misexpression of the Src oncogene at 64B (Src64B) may cause ring canal development defects as microarray analysis and real-time RT-PCR revealed there was a three fold decrease in Src64B expression in su(Hw) mutant ovaries. Restoration of Src64B expression in su(Hw) mutant female germ cells rescued the ring phenotype but did not restore fertility. The study concluded that loss of su(Hw) affects expression of many oogenesis related genes and down-regulates Src64B, resulting in ring canal defects potentially contributing to obstruction of molecular flow and an eventual failure of egg chamber organization.

Vogel, K. J., Brown, M. R. and Strand, M. R. (2015). Ovary ecdysteroidogenic hormone requires a receptor tyrosine kinase to activate egg formation in the mosquito Aedes aegypti. Proc Natl Acad Sci U S A 112: 5057-5062. PubMed ID: 25848040
Summary:
Mosquitoes are major disease vectors because most species must feed on blood from a vertebrate host to produce eggs. Blood feeding by the vector mosquito Aedes aegypti triggers the release of two neurohormones, ovary ecdysteroidogenic hormone (OEH) and insulin-like peptides (ILPs), which activate multiple processes required for oogenesis egg formation. ILPs function by binding to the insulin receptor, which activates downstream components in the canonical insulin signaling pathway. OEH in contrast belongs to a neuropeptide family called neuroparsins, whose receptor is unknown. This study demonstrated that a previously orphanized receptor tyrosine kinase (RTK) from A. aegypti encoded by the gene AAEL001915 is an OEH receptor. Phylogenetic studies indicated that the protein encoded by this gene, designated AAEL001915, belongs to a clade of RTKs related to the insulin receptor, which are distinguished by an extracellular Venus flytrap module. Knockdown of AAEL001915 by RNAi disabled OEH-mediated egg formation in A. aegypti. AAEL001915 was primarily detected in the mosquito ovary in association with follicular epithelial cells. Both monomeric and dimeric AAEL001915 were detected in mosquito ovaries and transfected Drosophila S2 cells. Functional assays further indicated that OEH bound to dimeric AAEL001915, which resulted in downstream phosphorylation of dbzhnsky/akt1-1.htmAkt. It is hypothesized that orthologs of AAEL001915 in other insects are neuroparsin receptors.

Tuesday, May 5th

Bartok, O., Teesalu, M., Ashwall-Fluss, R., Pandey, V., Hanan, M., Rovenko, B.M., Poukkula, M., Havula, E., Moussaieff, A., Vodala, S., Nahmias, Y., Kadener, S. and Hietakangas, V. (2015). The transcription factor Cabut coordinates energy metabolism and the circadian clock in response to sugar sensing. EMBO J [Epub ahead of print]. PubMed ID: 25916830
Summary:
Nutrient sensing pathways adjust metabolism and physiological functions in response to food intake. For example, sugar feeding promotes lipogenesis by activating glycolytic and lipogenic genes through the Mondo/ChREBP-Mlx transcription factor complex. Concomitantly, other metabolic routes are inhibited, but the mechanisms of transcriptional repression upon sugar sensing have remained elusive. This study characterizes cabut (cbtDrosophila. cbt was rapidly induced upon sugar feeding through direct regulation by Mondo-Mlx. CBT repressed several metabolic targets in response to sugar feeding, including both isoforms of phosphoenolpyruvate carboxykinase (pepck). Deregulation of pepck1 (CG17725) in mlx mutants underlay imbalance of glycerol and glucose metabolism as well as developmental lethality. Furthermore, cbt provided a regulatory link between nutrient sensing and the circadian clock. Specifically, a subset of genes regulated by the circadian clock were also targets of CBT. Moreover, perturbation of CBT levels led to deregulation of the circadian transcriptome and circadian behavioral patterns.

Zhang, Y., Liu, G., Yan, J., Zhang, Y., Li, B. and Cai, D. (2015). Metabolic learning and memory formation by the brain influence systemic metabolic homeostasis. Nat Commun 6: 6704. PubMed ID: 25848677
Summary:
Metabolic homeostasis is regulated by the brain, but whether this regulation involves learning and memory of metabolic information remains unexplored. This study use a calorie-based, taste-independent learning/memory paradigm to show that Drosophila form metabolic memories that help in balancing food choice with caloric intake; however, this metabolic learning or memory is lost under chronic high-calorie feeding. Loss of individual learning/memory-regulating genes causes a metabolic learning defect, leading to elevated trehalose and lipid levels. Importantly, this function of metabolic learning requires not only the mushroom body but also the hypothalamus-like pars intercerebralis, while NF-κB activation in the pars intercerebralis mimics chronic overnutrition in that it causes metabolic learning impairment and disorders. Finally, this study evaluated this concept of metabolic learning/memory in mice, suggesting that the hypothalamus is involved in a form of nutritional learning and memory, which is critical for determining resistance or susceptibility to obesity. In conclusion, these data indicate that the brain, and potentially the hypothalamus, direct metabolic learning and the formation of memories, which contribute to the control of systemic metabolic homeostasis.

May, C. M., Doroszuk, A. and Zwaan, B. J. (2015). The effect of developmental nutrition on life span and fecundity depends on the adult reproductive environment in Drosophila melanogaster. Ecol Evol 5: 1156-1168. PubMed ID: 25859322
Summary:
Both developmental nutrition and adult nutrition affect life-history traits; however, little is known about whether the effect of developmental nutrition depends on the adult environment experienced. This study used the fruit fly to determine whether life-history traits, particularly life span and fecundity, are affected by developmental nutrition, and whether this depends on the extent to which the adult environment allows females to realize their full reproductive potential. Flies on three different developmental food levels containing increasing amounts of yeast and sugar: poor, control, and rich. Development on poor or rich larval food resulted in several life-history phenotypes indicative of suboptimal conditions, including increased developmental time, and, for poor food, decreased adult weight. However, development on poor larval food actually increased adult virgin life span. In addition, the reproductive potential of the adult environment was manipulated by adding yeast or yeast and a male. This manipulation interacted with larval food to determine adult fecundity. Specifically, under two adult conditions, flies raised on poor larval food had higher reproduction at certain ages - when singly mated this occurred early in life and when continuously mated with yeast this occurred during midlife. Poor larval food is not necessarily detrimental to key adult life-history traits, but does exert an adult environment-dependent effect, especially by affecting virgin life span and altering adult patterns of reproductive investment. These findings are relevant because (1) they may explain differences between published studies on nutritional effects on life-history traits; (2) they indicate that optimal nutritional conditions are likely to be different for larvae and adults, potentially reflecting evolutionary history; and (3) they urge for the incorporation of developmental nutritional conditions into the central life-history concept of resource acquisition and allocation.

Jensen, K., McClure, C., Priest, N. K. and Hunt, J. (2015). Sex-specific effects of protein and carbohydrate intake on reproduction but not lifespan in Drosophila melanogaster. Aging Cell [Epub ahead of print]. PubMed ID: 25808180
Summary:
Modest dietary restriction extends lifespan (LS) in a diverse range of taxa and typically has a larger effect in females than males. Traditionally, this has been attributed to a stronger trade-off between LS and reproduction in females than in males that is mediated by the intake of calories. Recent studies, however, suggest that it is the intake of specific nutrients that extends LS and mediates this trade-off. This study, used the geometric framework (GF) to examine the sex-specific effects of protein (P) and carbohydrate (C) intake on LS and reproduction in Drosophila melanogaster. This study found that LS was maximized at a high intake of C and a low intake of P in both sexes, whereas nutrient intake had divergent effects on reproduction. Male offspring production rate and LS were maximized at the same intake of nutrients, whereas female egg production rate was maximized at a high intake of diets with a P:C ratio of 1:2. This resulted in larger differences in nutrient-dependent optima for LS and reproduction in females than in males, as well as an optimal intake of nutrients for lifetime reproduction that differed between the sexes. Under dietary choice, the sexes followed similar feeding trajectories regulated around a P:C ratio of 1:4. Consequently, neither sex reached their nutritional optimum for lifetime reproduction, suggesting intralocus sexual conflict over nutrient optimization. This study shows clear sex differences in the nutritional requirements of reproduction in D. melanogaster and joins the growing list of studies challenging the role of caloric restriction in extending LS.

Monday, May 4th

Ramos, C. I., Igiesuorobo, O., Wang, Q. and Serpe, M. (2015). Neto-mediated intracellular interactions shape postsynaptic composition at the Drosophila neuromuscular junction. PLoS Genet 11: e1005191. PubMed ID: 25905467
Summary:
The molecular mechanisms controlling the subunit composition of glutamate receptors are crucial for the formation of neural circuits and for the long-term plasticity underlying learning and memory. This study use the Drosophila neuromuscular junction (NMJ) to examine how specific receptor subtypes are recruited and stabilized at synaptic locations. In flies, clustering of ionotropic glutamate receptors (iGluRs) requires Neto (Neuropillin and Tolloid-like), a highly conserved auxiliary subunit that is essential for NMJ assembly and development. Drosophila neto encodes two isoforms, Neto-α and Neto-β, with common extracellular parts and distinct cytoplasmic domains. Mutations that specifically eliminate Netoβ or its intracellular domain were generated. When Neto-β is missing or is truncated, the larval NMJs show profound changes in the subtype composition of iGluRs due to reduced synaptic accumulation of the GluRIIA subunit. Furthermore, neto-β mutant NMJs fail to accumulate p21-activated kinase (PAK), a critical postsynaptic component implicated in the synaptic stabilization of GluRIIA. Muscle expression of either Neto-α or Neto-β rescued the synaptic transmission at neto null NMJs, indicating that Neto conserved domains mediate iGluRs clustering. However, only Neto-β restored PAK synaptic accumulation at neto null NMJs. Thus, Neto engages in intracellular interactions that regulate the iGluR subtype composition by preferentially recruiting and/or stabilizing selective receptor subtypes.

Stephan, R., Goellner, B., Moreno, E., Frank, C. A., Hugenschmidt, T., Genoud, C., Aberle, H. and Pielage, J. (2015). Hierarchical microtubule organization controls axon caliber and transport and determines synaptic structure and stability. Dev Cell 33: 5-21. PubMed ID: 25800091
Summary:
The dimensions of axons and synaptic terminals determine cell-intrinsic properties of neurons; however, the cellular mechanisms selectively controlling establishment and maintenance of neuronal compartments remain poorly understood. This study shows that two giant Drosophila Ankyrin2 isoforms, Ank2-L and Ank2-XL, and the MAP1B homolog Futsch form a membrane-associated microtubule-organizing complex that determines axonal diameter, supports axonal transport, and provides independent control of synaptic dimensions and stability. Ank2-L controls microtubule and synaptic stability upstream of Ank2-XL that selectively controls microtubule organization. Synergistically with Futsch, Ank2-XL provides three-dimensional microtubule organization and is required to establish appropriate synaptic dimensions and release properties. In axons, the Ank2-XL/Futsch complex establishes evenly spaced, grid-like microtubule organization and determines axonal diameter in the absence of neurofilaments. Reduced microtubule spacing limits anterograde transport velocities of mitochondria and synaptic vesicles. These data identify control of microtubule architecture as a central mechanism to selectively control neuronal dimensions, functional properties, and connectivity.

West, R. J., Lu, Y., Marie, B., Gao, F. B. and Sweeney, S. T. (2015). Rab8, POSH, and TAK1 regulate synaptic growth in a Drosophila model of frontotemporal dementia. J Cell Biol 208: 931-947. PubMed ID: 25800055
Summary:
Mutations in genes essential for protein homeostasis have been identified in frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) patients. Why mature neurons should be particularly sensitive to such perturbations is unclear. This study identified mutations in Rab8 in a genetic screen for enhancement of an FTD phenotype associated with ESCRT-III dysfunction. Examination of Rab8 mutants or motor neurons expressing a mutant ESCRT-III subunit, CHMP2B(Intron5), at the Drosophila melanogaster neuromuscular junction synapse revealed synaptic overgrowth and endosomal dysfunction. Expression of Rab8 rescued overgrowth phenotypes generated by CHMP2B(Intron5). In Rab8 mutant synapses, c-Jun N-terminal kinase (JNK)/activator protein-1 and TGF-beta signaling were overactivated and acted synergistically to potentiate synaptic growth. Novel roles were identified for endosomal JNK-scaffold POSH (Plenty-of-SH3s) and a JNK kinase kinase, TAK1, in regulating growth activation in Rab8 mutants. These data uncover Rab8, POSH, and TAK1 as regulators of synaptic growth responses and point to recycling endosome as a key compartment for synaptic growth regulation during neurodegenerative processes

Gavino, M. A., Ford, K. J., Archila, S. and Davis, G. W. (2015). Homeostatic synaptic depression is achieved through a regulated decrease in presynaptic calcium channel abundance. Elife 4. PubMed ID: 25884248
Summary:
Homeostatic signaling stabilizes synaptic transmission at the neuromuscular junction (NMJ) of Drosophila, mice, and human. It is believed that homeostatic signaling at the NMJ is bi-directional and considerable progress has been made identifying mechanisms underlying the homeostatic potentiation of neurotransmitter release. However, very little is understood mechanistically about the opposing process, homeostatic depression, and how bi-directional plasticity is achieved. This study shows that homeostatic potentiation and depression can be simultaneously induced, demonstrating true bi-directional plasticity. Next, it was shown that mutations that block homeostatic potentiation do not alter homeostatic depression, demonstrating that these are genetically separable processes. Finally, homeostatic depression was shown to be achieved by decreased presynaptic calcium channel abundance and calcium influx, changes that are independent of the presynaptic action potential waveform. Thus, this study identified a novel mechanism of homeostatic synaptic plasticity and proposes a model that can account for the observed bi-directional, homeostatic control of presynaptic neurotransmitter release.

Sunday, May 3rd

Kwon, Y., Song, W., Droujinine, I. A., Hu, Y., Asara, J. M. and Perrimon, N. (2015). Systemic organ wasting induced by localized expression of the secreted Insulin/IGF antagonist ImpL2. Dev Cell 33: 36-46. PubMed ID: 25850671
Summary:
Organ wasting, related to changes in nutrition and metabolic activity of cells and tissues, is observed under conditions of starvation and in the context of diseases, including cancers. A model for organ wasting in adult Drosophila is described, whereby overproliferation induced by activation of Yorkie, the Yap1 oncogene ortholog, in intestinal stem cells leads to wasting of the ovary, fat body, and muscle. These organ-wasting phenotypes are associated with a reduction in systemic insulin/IGF signaling due to increased expression of the secreted insulin/IGF antagonist ImpL2 from the overproliferating gut. Strikingly, expression of rate-limiting glycolytic enzymes and central components of the insulin/IGF pathway is upregulated with activation of Yorkie in the gut, which may provide a mechanism for this overproliferating tissue to evade the effect of ImpL2. Altogether, this study provides insights into the mechanisms underlying organ-wasting phenotypes in Drosophila and how overproliferating tissues adapt to global changes in metabolism.

Chen, H., Zheng, X. and Zheng, Y. (2015). Lamin-B in systemic inflammation, tissue homeostasis, and aging. Nucleus [Epub ahead of print]. PubMed ID: 25875575
Summary:
Gradual loss of tissue function (or homeostasis) is a natural process of aging and is believed to cause many age-associated diseases. In human epidemiology studies, the low-grade and chronic systemic inflammation in elderly has been correlated with the development of aging related pathologies. Although it is suspected that tissue decline is related to systemic inflammation, the cause and consequence of these aging phenomena are poorly understood. By studying the Drosophila fat body and gut, this study has uncovered a mechanism by which lamin-B loss in the fat body upon aging induces age-associated systemic inflammation. This chronic inflammation results in the repression of gut local immune response, which in turn leads to the over-proliferation and mis-differentiation of the intestinal stem cells, thereby resulting in gut hyperplasia. Implications and remaining questions are discussed in light of these new observations.

Jeon, H. J., Kim, Y. S., Park, J. S., Pyo, J. H., Na, H. J., Kim, I. J., Kim, C. M., Chung, H. Y., Kim, N. D., Arking, R. and Yoo, M. A. (2015). Age-related change in gammaH2AX of Drosophila muscle: its significance as a marker for muscle damage and longevity. Biogerontology. PubMed ID: 25860864
Summary:
Muscle aging is closely related to unhealthy late-life and organismal aging. Recently, the state of differentiated cells was shown to be critical to tissue homeostasis. Thus, understanding how fully differentiated muscle cells age is required for ensuring healthy aging. Adult Drosophila muscle is a useful model for exploring the aging process of fully differentiated cells. This study investigated age-related changes of γH2AX, an indicator of DNA strand breaks, in adult Drosophila muscle to document whether its changes are correlated with muscle degeneration and lifespan. The results demonstrate that γH2AX accumulation increases in adult Drosophila thoracic and leg muscles with age. Analyses of short-, normal-, and long-lived strains indicate that the age-related increase of γH2AX is closely associated with the extent of muscle degeneration, cleaved caspase-3 and poly-ubiquitin aggregates, and longevity. Further analysis of muscle-specific knockdown of heterochromatin protein 1a revealed that the excessive γH2AX accumulation in thoracic and leg muscles induces accelerated degeneration and decreases longevity. These data suggest a strong correlation between age-related muscle damage and lifespan in Drosophila. These findings indicate that γH2AX may be a reliable biomarker for assessing muscle aging in Drosophila.

Hine, C., Harputlugil, E., Zhang, Y., Ruckenstuhl, C., Lee, B. C., Brace, L., Longchamp, A., Trevino-Villarreal, J. H., Mejia, P., Ozaki, C. K., Wang, R., Gladyshev, V. N., Madeo, F., Mair, W. B. and Mitchell, J. R. (2015). Endogenous hydrogen sulfide production is essential for dietary restriction benefits. Cell 160: 132-144. PubMed ID: 25542313
Summary:
Dietary restriction (DR) without malnutrition encompasses numerous regimens with overlapping benefits including longevity and stress resistance, but unifying nutritional and molecular mechanisms remain elusive. In a mouse model of DR-mediated stress resistance, this study found that sulfur amino acid (SAA) restriction increased expression of the transsulfuration pathway (TSP) enzyme cystathionine gamma-lyase (CGL), resulting in increased hydrogen sulfide (H2S) production and protection from hepatic ischemia reperfusion injury. SAA supplementation, mTORC1 activation, or chemical/genetic CGL inhibition reduced H2S production and blocked DR-mediated stress resistance. In vitro, the mitochondrial protein SQR was required for H2S-mediated protection during nutrient/oxygen deprivation. Finally, TSP-dependent H2S production was observed in yeast, worm, fruit fly, and rodent models of DR-mediated longevity. Together, these data are consistent with evolutionary conservation of TSP-mediated H2S as a mediator of DR benefits with broad implications for clinical translation.

Saturday, May 2nd

Dissel, S., Angadi, V., Kirszenblat, L., Suzuki, Y., Donlea, J., Klose, M., Koch, Z., English, D., Winsky-Sommerer, R., van Swinderen, B. and Shaw, P.J. (2015). Sleep restores behavioral plasticity to Drosophila mutants. Curr Biol [Epub ahead of print]. PubMed ID: 25913403
Summary:
Given the role that sleep plays in modulating plasticity, this study hypothesized that increasing sleep would restore memory to canonical memory mutants without specifically rescuing the causal molecular lesion. Sleep was increased using three independent strategies: activating the dorsal fan-shaped body, increasing the expression of Fatty acid binding protein (dFabp), or by administering the GABA-A agonist 4,5,6,7-tetrahydroisoxazolo-[5,4-c]pyridine-3-ol (THIP). Short-term memory (STM) or long-term memory (LTM) was evaluated in rutabaga (rut) and dunce (dnc) mutants using aversive phototaxic suppression and courtship conditioning. Each of the three independent strategies increased sleep and restored memory to rut and dnc mutants. Importantly, inducing sleep also reversed memory defects in a Drosophila model of Alzheimer's disease. Together, these data demonstrate that sleep plays a more fundamental role in modulating behavioral plasticity than previously appreciated and suggest that increasing sleep may benefit patients with certain neurological disorders.

Gao, X. J., Clandinin, T. R. and Luo, L. (2015). Extremely sparse olfactory inputs are sufficient to mediate innate aversion in Drosophila. PLoS One 10: e0125986. PubMed ID: 25927233
Summary:
Innate attraction and aversion to odorants are observed throughout the animal kingdom, but how olfactory circuits encode such valences is not well understood, despite extensive anatomical and functional knowledge. In Drosophila melanogaster, ~50 types of olfactory receptor neurons (ORNs) each express a unique receptor gene, and relay information to a cognate type of projection neurons (PNs). To examine the extent to which the population activity of ORNs is required for olfactory behavior, a genetic strategy was developed to block all ORN outputs, and then to restore output in specific types. Unlike attraction, aversion was unaffected by simultaneous silencing of many ORNs, and even single ORN types previously shown to convey neutral valence sufficed to mediate aversion. Thus, aversion may rely on specific activity patterns in individual ORNs rather than the number or identity of activated ORNs. ORN activity is relayed into the brain by downstream circuits, with excitatory PNs (ePN) representing a major output. This study found that silencing the majority of ePNs did not affect aversion, even when ePNs directly downstream of single restored ORN types were silenced. The data demonstrate the robustness of olfactory aversion, and suggest that its circuit mechanism is qualitatively different from attraction.

Yang, Z., Yu, Y., Zhang, V., Tian, Y., Qi, W. and Wang, L. (2015). Octopamine mediates starvation-induced hyperactivity in adult Drosophila. Proc Natl Acad Sci U S A 112: 5219-5224. PubMed ID: 25848004
Summary:
Starved animals often exhibit elevated locomotion, which has been speculated to partly resemble foraging behavior and facilitate food acquisition and energy intake. Despite its importance, the neural mechanism underlying this behavior remains unknown in any species. This study confirmed and extended previous findings that starvation induces locomotor activity in adult fruit flies Drosophila melanogaster. This study also showed that starvation-induced hyperactivity was directed toward the localization and acquisition of food sources, because it could be suppressed upon the detection of food cues via both central nutrient-sensing and peripheral sweet-sensing mechanisms, via induction of food ingestion. It was further found that octopamine, the insect counterpart of vertebrate norepinephrine, as well as the neurons expressing octopamine, were both necessary and sufficient for starvation-induced hyperactivity. Octopamine was not required for starvation-induced changes in feeding behaviors, suggesting independent regulations of energy intake behaviors upon starvation. Taken together, these results establish a quantitative behavioral paradigm to investigate the regulation of energy homeostasis by the CNS and identify a conserved neural substrate that links organismal metabolic state to a specific behavioral output.

Schleyer, M., et al. (2015). The impact of odor-reward memory on chemotaxis in larval Drosophila. Learn Mem 22: 267-277. PubMed ID: 25887280
Summary:
How do animals adaptively integrate innate with learned behavioral tendencies? This study tackles this question using chemotaxis as a paradigm. Chemotaxis in the Drosophila larva largely results from a sequence of runs and oriented turns. Thus, the larvae minimally need to determine (1) how fast to run, (2) when to initiate a turn, and (3) where to direct a turn. The study first reported how odor-source intensities modulated these decisions to bring about higher levels of chemotactic performance for higher odor-source intensities during innate chemotaxis. The study then examined whether the same modulations were responsible for alterations of chemotactic performance by learned odor "valence" (understood throughout as level of attractiveness). Run speed (1) was neither modulated by the innate nor by the learned valence of an odor. Turn rate (2), however, was modulated by both. Likewise, turning direction (3) was modulated concordantly by innate and learned valence. Using numerical simulations, the paper showed that a modulation of both turn rate and of turning direction was sufficient to account for the empirically found differences in preference scores across experimental conditions. These results suggest that innate and learned valence organize adaptive olfactory search behavior by their summed effects on turn rate and turning direction, but not on run speed. This work should aid studies into the neural mechanisms by which memory impacts specific aspects of behavior.

Friday, May 1st

Katsuyama, T., Comoglio, F., Seimiya, M., Cabuy, E. and Paro, R. (2015). During Drosophila disc regeneration, JAK/STAT coordinates cell proliferation with Dilp8-mediated developmental delay. Proc Natl Acad Sci U S A [Epub ahead of print]. PubMed ID: 25902518
Summary:
Regeneration of fragmented Drosophila imaginal discs occurs in an epimorphic manner involving local cell proliferation at the wound site. After disc fragmentation, cells at the wound site activate a restoration program through wound healing, regenerative cell proliferation, and repatterning of the tissue. However, the interplay of signaling cascades driving these early reprogramming steps is not well-understood. This study profiled the transcriptome of regenerating cells in the early phase within 24 h after wounding. JAK/STAT signaling was found to become activated at the wound site and to promote regenerative cell proliferation in cooperation with Wingless (Wg) signaling. In addition, the expression of Insulin-like peptide 8 (dilp8), which encodes a paracrine peptide to delay the onset of pupariation, was found to be controlled by JAK/STAT signaling in early regenerating discs. These findings suggest that JAK/STAT signaling plays a pivotal role in coordinating regenerative disc growth with organismal developmental timing.

Hatfield, I., Harvey, I., Yates, E.R., Redd, J.R., Reiter, L.T. and Bridges, D. (2015). The role of TORC1 in muscle development in Drosophila. Sci Rep 5: 9676. PubMed ID: 25866192
Summary:
Myogenesis is an important process during both development and muscle repair. Previous studies suggest that mTORC1 plays a role in the formation of mature muscle from immature muscle precursor cells. This study shows that gene expression for several myogenic transcription factors including Myf5, Myog and Mef2c but not MyoD and myosin heavy chain isoforms decrease when C2C12 cells are treated with rapamycin, supporting a role for mTORC1 pathway during muscle development. To investigate the possibility that mTORC1 can regulate muscle in vivo, the essential dTORC1 subunit Raptor was ablated in Drosophila melanogaster, and it was found that muscle-specific knockdown of Raptor caused flies to be too weak to emerge from their pupal cases during eclosion. Using a series of GAL4 drivers it was also shown that muscle-specific Raptor knockdown also caused shortened lifespan, even when eclosure was unaffected. Together these results highlight an important role for TORC1 in muscle development, integrity and function in both Drosophila and mammalian cells.

Arias, C., Fussero, G., Zacharonok, M. and Macias, A. (2015). Dpp-expressing and non-expressing cells: two different populations of growing cells in Drosophila. PLoS One 10: e0121457. PubMed ID: 25798905
Summary:
There are different models that explain growth during development. One model is based on insect and amphibian regeneration studies. This model proposes that growth is directed by pattern, and growth takes place by intercalation at a growth discontinuity; therefore, proliferation should surround the discontinuity. Currently, this model, apart from regenerative studies on mostly adult patterning, has not found supporting evidence in Drosophila that shows proliferation surrounding a discontinuity. Despite this lack of evidence, the importance of discontinuities has been shown in different experiments, even under wt conditions, more specifically in the formation of the leg joints because of the occurrence of cell death at their boundaries. This study shows the existence of a sharp discontinuity in Decapentaplegic (Dpp) in the genital discs at the third larvae stage (L3), which determines the upregulation in the Jun-NH2-Terminal-Kinase (JNK) pathway, reaper (rpr), head involution defective (hid) and active caspases from its boundaries. The proliferation and cell death surrounding the discontinuity suggest that growth can proceed by intercalation and competitive death takes place in this area. Finally, the Rpr, Grim and Hid (RGH) products are a few of the factors that define the growth discontinuity because they are negative regulators of growth, a new function that is unique from their known functions in apoptosis.

Fernandes, V. M., Pradhan-Sundd, T., Blaquiere, J. A. and Verheyen, E. M. (2015). Ras/MEK/MAPK-mediated regulation of heparin sulphate proteoglycans promotes retinal fate in the Drosophila eye-antennal disc. Dev Biol [Epub ahead of print]. PubMed ID: 25848695
Summary:
The Drosophila eye-antennal imaginal disc is a well-characterised system in which to study regional specification; it is first divided into antennal and eye fates and subsequently retinal differentiation occurs within only the eye field. During development, signalling pathways and selector genes compete with and mutually antagonise each other to subdivide the tissue. Wingless (Wg) signalling is the main inhibitor of retinal differentiation; it does so by promoting antennal/head-fate via selector factors and by antagonising Hedgehog (Hh), the principal differentiation-initiating signal. Wg signalling must be suppressed by JAK/STAT at the disc posterior in order to initiate retinal differentiation. Ras/MEK/MAPK signalling has also been implicated in initiating retinal differentiation but its mode of action is not known. This study found that compromising Ras/MEK/MAPK signalling in the early larval disc results in expanded antennal/head cuticle at the expense of the compound eye. These phenotypes correspond both to perturbations in selector factor expression, and to de-repressed wg. Indeed, STAT activity is reduced due to decreased mobility of the ligand Unpaired (Upd) along with a corresponding loss in Dally-like protein (Dlp), a heparan sulphate proteoglycan (HSPG) that aids Upd diffusion. Strikingly, blocking HSPG biogenesis phenocopies compromised Ras/MEK/MAPK, while restoring HSPG expression rescues the adult phenotype significantly. This study identifies a novel mode by which the Ras/MEK/MAPK pathway regulates regional-fate specification via HSPGs during development.

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