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Current papers in developmental biology and gene function





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Monday, August 31st, 2015

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Lewis, L.P., Siju, K.P., Aso, Y., Friedrich, A.B., Bulteel, A.J., Rubin, G.M. and Grunwald Kadow, I.C. (2015). A higher brain circuit for immediate integration of conflicting sensory information in Drosophila. Curr Biol [Epub ahead of print]. PubMed ID: 26299514
Summary:
Animals continuously evaluate sensory information to decide on their next action. Different sensory cues, however, often demand opposing behavioral responses. How does the brain process conflicting sensory information during decision making? This study shows that flies use neural substrates attributed to odor learning and memory, including the mushroom body (MB), for immediate sensory integration and modulation of innate behavior. Drosophila melanogaster must integrate contradictory sensory information during feeding on fermenting fruit that releases both food odor and the innately aversive odor CO2. Using this framework, this study examined the neural basis for this integration. A local circuit consisting of specific glutamatergic output and PAM dopaminergic input neurons with overlapping innervation in the MB-β'2 lobe region was identified, which integrates food odor and suppresses innate avoidance. Activation of food odor-responsive dopaminergic neurons reduces innate avoidance mediated by CO2-responsive MB output neurons. The study hypothesizes that the MB, in addition to its long recognized role in learning and memory, serves as the insect's brain center for immediate sensory integration during instantaneous decision making.

Rohwedder, A., Selcho, M., Chassot, B. and Thum, A. S. (2015). Neuropeptide F neurons modulate sugar reward during associative olfactory learning of Drosophila larvae. J Comp Neurol [Epub ahead of print]. PubMed ID: 26234537
Summary:
All organisms continuously have to adapt their behavior according to changes in the environment in order to survive. Experience-driven changes in behavior are usually mediated and maintained by modifications in signaling within defined brain circuits. Given the simplicity of the larval brain of Drosophila and its experimental accessibility on the genetic and behavioral level, this study has analyzed if neuropeptide F (dNPF) neurons are involved in classical olfactory conditioning. dNPF is an ortholog of the mammalian neuropeptide Y, a highly conserved neuromodulator that stimulates food-seeking behavior. This study provides a comprehensive anatomical analysis of the dNPF neurons on the single cell level. Artificial activation of dNPF neurons inhibits appetitive olfactory learning by modulating the sugar reward signal during acquisition. No effect is detectable for the retrieval of an established appetitive olfactory memory. The modulatory effect is based on the joint action of three distinct cell types that, if tested on single cell level, inhibit and invert the conditioned behavior. Taken together, this work describes anatomically and functionally a new part of the sugar reinforcement signaling pathway for classical olfactory conditioning in Drosophila larvae.

Volkenhoff, A., Weiler, A., Letzel, M., Stehling, M., Klambt, C. and Schirmeier, S. (2015). Glial glycolysis is essential for neuronal survival in Drosophila. Cell Metab [Epub ahead of print]. PubMed ID: 26235423
Summary:
Neuronal information processing requires a large amount of energy, indicating that sugars and other metabolites must be efficiently delivered. However, reliable neuronal function also depends on the maintenance of a constant microenvironment in the brain. Therefore, neurons are efficiently separated from circulation by the blood-brain barrier, and their long axons are insulated by glial processes. At the example of the Drosophila brain, this study addressed how sugar is shuttled across the barrier to nurture neurons. Glial cells of the blood-brain barrier specifically take up sugars and that their metabolism relies on glycolysis, which, surprisingly, is dispensable in neurons. Glial cells secrete alanine and lactate to fuel neuronal mitochondria, and lack of glial glycolysis specifically in the adult brain causes neurodegeneration. This work implies that a global metabolic compartmentalization and coupling of neurons and glial cells is a conserved, fundamental feature of bilaterian nervous systems independent of their size.

Kim, A. J., Fitzgerald, J. K. and Maimon, G. (2015). Cellular evidence for efference copy in Drosophila visuomotor processing. Nat Neurosci 18: 1247-1255. PubMed ID: 26237362
Summary:
Each time a locomoting fly turns, the visual image sweeps over the retina and generates a motion stimulus. Classic behavioral experiments suggested that flies use active neural-circuit mechanisms to suppress the perception of self-generated visual motion during intended turns. Direct electrophysiological evidence, however, has been lacking. This study found that visual neurons in Drosophila receive motor-related inputs during rapid flight turns. These inputs arrived with a sign and latency appropriate for suppressing each targeted cell's visual response to the turn. Precise measurements of behavioral and neuronal response latencies supported the idea that motor-related inputs to optic flow-processing cells represent internal predictions of the expected visual drive induced by voluntary turns. Motor-related inputs to small object-selective visual neurons could reflect either proprioceptive feedback from the turn or internally generated signals. The results in Drosophila echo the suppression of visual perception during rapid eye movements in primates, demonstrating common functional principles of sensorimotor processing across phyla.

Sunday, August 30th

Gáliková, M., Diesner, M., Klepsatel, P., Hehlert, P., Xu, Y., Bickmeyer, I., Predel, R. and Kühnlein, R.P. (2015). Energy homeostasis control in Drosophila Adipokinetic hormone mutants. Genetics [Epub ahead of print]. PubMed ID: 26275422
Summary:
Maintenance of biological functions under negative energy balance depends on mobilization of storage lipids and carbohydrates in animals. In mammals, glucagon and glucocorticoid signaling mobilizes energy reserves, whereas Adipokinetic hormones (AKHs) play a homologous role in insects. Numerous studies based in AKH injections and correlative studies in a broad range of insect species have established the view that AKH acts as master regulator of energy mobilization during development, reproduction, and stress. In contrast to AKH, the second peptide, which is processed from the Akh encoded prohormone - termed Adipokinetic hormone precursor related peptide (APRP) - is functionally orphan. APRP is discussed as ecdysiotropic hormone or as scaffold peptide during AKH prohormone processing. However, as in the case of AKH, final evidence for APRP functions requires genetic mutant analysis. This study employed CRISPR/Cas9-mediated genome engineering to create AKH and AKH plus APRP-specific mutants in the model insect Drosophila melanogaster. Lack of APRP did not affect any of the tested steroid-dependent processes. Similarly, Drosophila AKH signaling is dispensable for ontogenesis, locomotion, oogenesis, and homeostasis of lipid or carbohydrate storage until up to the end of metamorphosis. During adulthood, however, AKH regulates body fat content and the hemolymph sugar level as well as nutritional and oxidative stress responses. Finally, the study provides evidence for a negative auto-regulatory loop, in Akh gene regulation.

Mosher, J., Zhang, W., Blumhagen, R. Z., D'Alessandro, A., Nemkov, T., Hansen, K. C., Hesselberth, J. R. and Reis, T. (2015). Coordination between Drosophila Arc1 and a specific population of brain neurons regulates organismal fat. Dev Biol 405: 280-290. PubMed ID: 26209258
Summary:
The brain plays a critical yet incompletely understood role in regulating organismal fat. This study performed a neuronal silencing screen in Drosophila larvae to identify brain regions required to maintain proper levels of organismal fat. When used to modulate synaptic activity in specific brain regions, the enhancer-trap driver line E347 elevated fat upon neuronal silencing, and decreased fat upon neuronal activation. Unbiased sequencing revealed that Arc1 mRNA levels increase upon E347 activation. Arc1 mutations have been previously demonstrated in a high-fat screen. This study revealed metabolic changes in Arc1 mutants consistent with a high-fat phenotype and an overall shift toward energy storage. Arc1-expressing cells neighbor E347 neurons, and manipulating E347 synaptic activity alters Arc1 expression patterns. Elevating Arc1 expression in these cells decreased fat, a phenocopy of E347 activation. Finally, loss of Arc1 prevented the lean phenotype caused by E347 activation, suggesting that Arc1 activity is required for E347 control of body fat. Importantly, neither E347 nor Arc1 manipulation altered energy-related behaviors. These results support a model wherein E347 neurons induce Arc1 in specific neighboring cells to prevent excess fat accumulation.

Tachibana, S., Touhara, K. and Ejima, A. (2015). Modification of male courtship motivation by olfactory habituation via the GABAA receptor in Drosophila melanogaster. PLoS One 10: e0135186. PubMed ID: 26252206
Summary:
A male-specific component, 11-cis-vaccenyl acetate (cVA) works as an anti-aphrodisiac pheromone in Drosophila melanogaster. The presence of cVA on a male suppresses the courtship motivation of other males and contributes to suppression of male-male homosexual courtship, while the absence of cVA on a female stimulates the sexual motivation of nearby males and enhances the male-female interaction. However, little is known how a male distinguishes the presence or absence of cVA on a target fly from either self-produced cVA or secondhand cVA from other males in the vicinity. This study demonstrates that male flies have keen sensitivity to cVA; therefore, the presence of another male in the area reduces courtship toward a female. This reduced level of sexual motivation, however, could be overcome by pretest odor exposure via olfactory habituation to cVA. Real-time imaging of cVA-responsive sensory neurons using the neural activity sensor revealed that prolonged exposure to cVA decreased the levels of cVA responses in the primary olfactory center. Pharmacological and genetic screening revealed that signal transduction via GABAA receptors contributed to this olfactory habituation. It was also found that the habituation experience increased the copulation success of wild-type males in a group. In contrast, transgenic males, in which GABA input in a small subset of local neurons was blocked by RNAi, failed to acquire the sexual advantage conferred by habituation. Thus, this study illustrates a novel phenomenon in which olfactory habituation positively affects sexual capability in a competitive environment.

Wu, Y., Baum, M., Huang, C. L. and Rodan, A. R. (2015). Two inwardly rectifying potassium channels, Irk1 and Irk2, play redundant roles in Drosophila renal tubule function. Am J Physiol Regul Integr Comp Physiol: ajpregu 00148 02015. PubMed ID: 26224687
Summary:
Inwardly rectifying potassium channels play essential roles in renal physiology across phyla. Barium-sensitive K+ conductances are found on the basolateral membrane of a variety of insect Malpighian (renal) tubules, including Drosophila melanogaster. This study found that barium decreases the lumen-positive transepithelial potential difference in isolated perfused Drosophila tubules, and decreases fluid secretion and transepithelial K+ flux. In those insect species in which it has been studied, transcripts from multiple genes encoding inwardly rectifying K+ channels are expressed in the renal (Malpighian) tubule. In Drosophila melanogaster, this includes transcripts of the Irk1, Irk2 and Irk3 genes. The role of each of these gene products in renal tubule function is unknown. Simultaneous knockdown of Irk1 and Irk2 in the principal cell of the fly tubule decreases transepithelial K+ flux, with no additive effect of Irk3 knockdown, and decreases barium sensitivity of transepithelial K+ flux by approximately 50%. Knockdown of any of the three inwardly rectifying K+ channels individually has no effect, nor does knocking down Irk3 simultaneously with Irk1 or Irk2. Irk1/Irk2 principal cell double knockdown tubules remain sensitive to the kaliuretic effect of cAMP. Inhibition of the Na+/K+-ATPase with ouabain and Irk1/Irk2 double knockdown have additive effects on K+ flux, and 75% of transepithelial K+ transport is due to Irk1/Irk2 or ouabain-sensitive pathways. In conclusion, Irk1 and Irk2 play redundant roles in transepithelial ion transport in the Drosophila melanogaster renal tubule, and are additive to Na+/K+-ATPase-dependent pathways.

Saturday, August 29th

Clowney, E.J., Iguchi, S., Bussell, J.J., Scheer, E. and Ruta, V. (2015). Multimodal chemosensory circuits controlling male courtship in Drosophila. Neuron [Epub ahead of print]. PubMed ID: 26279475
Summary:
Throughout the animal kingdom, internal states generate long-lasting and self-perpetuating chains of behavior. In Drosophila, males instinctively pursue females with a lengthy and elaborate courtship ritual triggered by activation of sexually dimorphic P1 interneurons. Gustatory pheromones are thought to activate P1 neurons but the circuit mechanisms that dictate their sensory responses to gate entry into courtship remain unknown. This study uses circuit mapping and in vivo functional imaging techniques to trace gustatory and olfactory pheromone circuits to their point of convergence onto P1 neurons and reveals how their combined input underlies selective tuning to appropriate sexual partners. Inhibition was identified, even in response to courtship-promoting pheromones, as a key circuit element that tunes and tempers P1 neuron activity. These results suggest a circuit mechanism in which balanced excitation and inhibition underlie discrimination of prospective mates and stringently regulate the transition to courtship in Drosophila.

Kayser, M. S., Mainwaring, B., Yue, Z. and Sehgal, A. (2015). Sleep deprivation suppresses aggression in Drosophila. Elife 4. PubMed ID: 26216041
Summary:
Sleep disturbances negatively impact numerous functions and have been linked to aggression and violence. However, a clear effect of sleep deprivation on aggressive behaviors remains unclear. This study found that acute sleep deprivation profoundly suppresses aggressive behaviors in the fruit fly, while other social behaviors are unaffected. This suppression is recovered following post-deprivation sleep rebound, and occurs regardless of the approach to achieve sleep loss. Genetic and pharmacologic approaches suggest octopamine signaling transmits changes in aggression upon sleep deprivation, and reduced aggression places sleep-deprived flies at a competitive disadvantage for obtaining a reproductive partner. These findings demonstrate an interaction between two phylogenetically conserved behaviors, and suggest that previous sleep experiences strongly modulate aggression with consequences for reproductive fitness.

Carazo, P., Perry, J.C., Johnson, F., Pizzari, T. and Wigby, S. (2015). Related male Drosophila melanogaster reared together as larvae fight less and sire longer lived daughters. Ecol Evol 14: 2787-2797. PubMed ID: 26306167
Summary:
Competition over access to reproductive opportunities can lead males to harm females. However, recent work has shown that, in Drosophila melanogaster, male competition and male harm of females are both reduced under conditions simulating male-specific population viscosity (i.e., in groups where males are related and reared with each other as larvae). This study investigated whether male population viscosity can have repercussions for the fitness of offspring in the next generation. It was shown that groups of unrelated-unfamiliar (i.e., unrelated individuals raised apart) males fight more intensely than groups of related-familiar males (i.e., full siblings raised together as larvae), supporting previous findings, and that exposure to a female is required to trigger these differential patterns of male-male competition. Importantly, it was shown that differences in male-male competition can be associated with transgenerational effects: the daughters of females exposed to unrelated-unfamiliar males suffer higher mortality than the daughters of females exposed to related-familiar males. Collectively, these results suggest that population structure (i.e., variation in the relatedness and/or larval familiarity of local male groups) can modulate male-male competition with important transgenerational consequences. 

Chippindale, A.K., Berggren, M., Alpern, J.H. and Montgomerie, R. (2015). Does kin selection moderate sexual conflict in Drosophila? Proc Biol Sci 282(1813). PubMed ID: 26269501
Summary:
Two recent studies provide provocative experimental findings about the potential influence of kin recognition and cooperation on the level of sexual conflict in Drosophila melanogaster. In both studies, male fruit flies apparently curbed their mate-harming behaviours in the presence of a few familiar or related males, suggesting some form of cooperation mediated by kin selection. In one study, the reduction in agonistic behaviour by brothers apparently rendered them vulnerable to dramatic loss of paternity share when competing with an unrelated male. If these results are robust and generalizable, fruit flies could be a major new focus for the experimental study of kin selection and social evolution. The authors maintain, however, that the restrictive conditions required for male cooperation to be adaptive in this species make it unlikely to evolve. These phenomena were then investigated in two different populations of D. melanogaster using protocols very similar to those in the two previous studies. No evidence was seen for a reduction in mate harm based upon either relatedness or familiarity between males, and no reduction was found in male reproductive success when two brothers are in the presence of an unfamiliar, unrelated, 'foreign' male. Thus, the reduction of sexual conflict owing to male cooperation does not appear to be a general feature of the species, at least under domestication, and these contrasting results call for further investigation: in new populations, in the field and in the laboratory populations in which these phenomena have been reported.

Friday, August 28th

Liu, T. Y., Bian, X., Romano, F. B., Shemesh, T., Rapoport, T. A. and Hu, J. (2015). Cis and trans interactions between Atlastin molecules during membrane fusion. Proc Natl Acad Sci U S A 112: E1851-1860. PubMed ID: 25825753
Summary:
Atlastin (ATL), a membrane-anchored GTPase that mediates homotypic fusion of endoplasmic reticulum (ER) membranes, is required for formation of the tubular network of the peripheral ER. How exactly ATL mediates membrane fusion is only poorly understood. This study shows that fusion is preceded by the transient tethering of ATL-containing vesicles caused by the dimerization of ATL molecules in opposing membranes. Tethering requires GTP hydrolysis, not just GTP binding, because the two ATL molecules are pulled together most strongly in the transition state of GTP hydrolysis. Most tethering events are futile, so that multiple rounds of GTP hydrolysis are required for successful fusion. Supported lipid bilayer experiments show that ATL molecules sitting on the same (cis) membrane can also undergo nucleotide-dependent dimerization. These results suggest that GTP hydrolysis is required to dissociate cis dimers, generating a pool of ATL monomers that can dimerize with molecules on a different (trans) membrane. In addition, tethering and fusion require the cooperation of multiple ATL molecules in each membrane. A comprehensive model is proposed for ATL-mediated fusion that takes into account futile tethering and competition between cis and trans interactions.

Deivasigamani, S., Basargekar, A., Shweta, K., Sonavane, P., Ratnaparkhi, G. S. and Ratnaparkhi, A. (2015). A pre-synaptic regulatory system acts trans-synaptically via Mon1 to regulate Glutamate receptor levels in Drosophila. Genetics [Epub ahead of print]. PubMed ID: 26290519
Summary:
Mon1 is an evolutionarily conserved protein involved in the conversion of Rab5 positive early endosomes to late endosomes through the recruitment of Rab7. This study has identified a role for Drosophila Mon1 in regulating glutamate receptor levels at the larval neuromuscular junction. Mutants were generated in Dmon1 through P-element excision. These mutants are short-lived with strong motor defects. At the synapse, the mutants show altered bouton morphology with several small supernumerary or satellite boutons surrounding a mature bouton; a significant increase in expression of GluRIIA and reduced expression of Bruchpilot. Neuronal knockdown of Dmon1 is sufficient to increase GluRIIA levels suggesting its involvement in a pre-synaptic mechanism that regulates post-synaptic receptor levels. Ultrastructural analysis of mutant synapses reveals significantly smaller synaptic vesicles. Overexpression of vglut suppresses the defects in synaptic morphology and also downregulates GluRIIA levels in Dmon1 mutants suggesting that homeostatic mechanisms are not affected in these mutants. It is proposed that DMon1 is part of a pre-synaptically regulated trans-synaptic mechanism that regulates GluRIIA levels at the larval neuromuscular junction.

Lin, C. H., Li, H., Lee, Y. N., Cheng, Y. J., Wu, R. M. and Chien, C. T. (2015). Lrrk regulates the dynamic profile of dendritic Golgi outposts through the golgin Lava lamp. J Cell Biol 210: 471-483. PubMed ID: 26216903
Summary:
Constructing the dendritic arbor of neurons requires dynamic movements of Golgi outposts (GOPs), the prominent component in the dendritic secretory pathway. GOPs move toward dendritic ends (anterograde) or cell bodies (retrograde), whereas most of them remain stationary. This study shows that Leucine-rich repeat kinase (Lrrk), the Drosophila melanogaster homologue of Parkinson's disease-associated Lrrk2, regulates GOP dynamics in dendrites. Lrrk localized at stationary GOPs in dendrites and suppressed GOP movement. In Lrrk loss-of-function mutants, anterograde movement of GOPs was enhanced, whereas Lrrk overexpression increased the pool size of stationary GOPs. Lrrk interacts with the golgin Lava lamp and inhibits the interaction between Lva and dynein heavy chain, thus disrupting the recruitment of dynein to Golgi membranes. Whereas overexpression of kinase-dead Lrrk causes dominant-negative effects on GOP dynamics, overexpression of the human LRRK2 mutant G2019S with augmented kinase activity promotes retrograde movement. This study reveals a pathogenic pathway for LRRK2 mutations causing dendrite degeneration.

Matsubayashi, Y., Coulson-Gilmer, C. and Millard, T. H. (2015). Endocytosis-dependent coordination of multiple actin regulators is required for wound healing. J Cell Biol 210: 419-433. PubMed ID: 26216900
Summary:
The ability to heal wounds efficiently is essential for life. After wounding of an epithelium, the cells bordering the wound form dynamic actin protrusions and/or a contractile actomyosin cable, and these actin structures drive wound closure. Despite their importance in wound healing, the molecular mechanisms that regulate the assembly of these actin structures at wound edges are not well understood. This paper, using Drosophila embryos, demonstrates that Diaphanous, SCAR, and WASp play distinct but overlapping roles in regulating actin assembly during wound healing. Moreover, that endocytosis was shown to be essential for wound edge actin assembly and wound closure. Adherens junctions (AJs) were identified as a key target of endocytosis during wound healing, and it is proposed that endocytic remodeling of AJs is required to form 'signaling centers' along the wound edge that control actin assembly. It is concluded that coordination of actin assembly, AJ remodeling, and membrane traffic is required for the construction of a motile leading edge during wound healing.

Siebert, M., et al. (2015). A high affinity RIM-binding protein/Aplip1 interaction prevents the formation of ectopic axonal active zones. Elife 4 [Epub ahead of print]. PubMed ID: 26274777
Summary:
Synaptic vesicles (SVs) fuse at active zones (AZs) covered by a protein scaffold, at Drosophila synapses comprised of ELKS family member Bruchpilot (BRP) and RIM-binding protein (RBP). This study demonstrates axonal co-transport of BRP and RBP using intravital live imaging, with both proteins co-accumulating in axonal aggregates of several transport mutants. RBP, via its C-terminal Src-homology 3 (SH3) domains, binds Aplip1/JIP1, a transport adaptor involved in kinesin-dependent SV transport. RBP C-terminal SH3 domains were shown in atomic detail to bind a proline-rich (PxxP) motif of Aplip1/JIP1 with submicromolar affinity. Point mutating this PxxP motif provoked formation of ectopic AZ-like structures at axonal membranes. Direct interactions between AZ proteins and transport adaptors seem to provide complex avidity and shield synaptic interaction surfaces of pre-assembled scaffold protein transport complexes, thus, favouring physiological synaptic AZ assembly over premature assembly at axonal membranes.

Pradhan-Sundd, T. and Verheyen, E. M. (2015). The Myopic-Ubpy-Hrs nexus enables endosomal recycling of Frizzled. Mol Biol Cell [Epub ahead of print]. PubMed ID: 26224310
Summary:
Endosomal trafficking of signaling proteins plays an essential role in cellular homeostasis. The seven-pass transmembrane protein, Frizzled (Fz) is a critical component of the Wnt signaling. Although Wnt signaling is proposed to be regulated by endosomal trafficking of Fz, the molecular events that enable this regulation are not completely understood. This study shows that the endosomal protein Myopic (Mop) regulates Fz trafficking in the Drosophila wing disk by inhibiting the ubiquitination and degradation of Hrs. Deletion of Mop or Hrs results in endosomal accumulation of Fz and therefore reduced Wnt signaling. The in situ Proximity Ligation Assay revealed a strong association between Mop and Hrs in the Drosophila wing disk. Overexpression of Hrs rescues the trafficking defect caused by mop knockdown. Mop aids in the maintenance of Ubpy which deubiquitinates (and thus stabilizes) Hrs. In the absence of the ubiquitin ligase Cbl, Mop is dispensable. These findings support a previously unknown role for Mop in endosomal trafficking of Fz in Wnt-receiving cells.

Thursday, August 28th

Price, D.C., Egizi, A. and Fonseca, D.M. (2015). The ubiquity and ancestry of insect doublesex. Sci Rep 5: 13068. PubMed ID: 26278009
Summary:
The doublesex (dsx) gene functions as a molecular switch at the base of the insect sex determination cascade, and triggers male or female somatic sexual differentiation in Drosophila. To understand the evolution of this integral gene relative to other arthropods, this study tested for the presence of dsx within public EST and genome sequencing projects representative of all 32 hexapod orders. dsx was found to be ubiquitous, with putative orthologs recovered from 30 orders. Additionally, both alternatively spliced and putative paralogous dsx transcripts were recovered from several orders of hexapods, including basal lineages, indicating the likely presence of these characteristics in the hexapod common ancestor. Of note, other arthropods such as chelicerates and crustaceans express two dsx genes, both of which are shown to lack alternative splicing. Furthermore, a large degree of length heterogeneity was discovered in the common region of dsx coding sequences within and among orders, possibly resulting from lineage-specific selective pressures inherent to each taxon. This work serves as a valuable resource for understanding the evolution of sex determination in insects. 

Singh N.D., Criscoe, D.R., Skolfield, S., Kohl, K.P., Keebaugh, E.S. and Schlenke, T.A. (2015). Fruit flies diversify their offspring in response to parasite infection. Science 349: 747-750. Direct link
Summary:
The evolution of sexual reproduction is often explained by Red Queen dynamics: Organisms must continually evolve to maintain fitness relative to interacting organisms, such as parasites. Recombination accompanies sexual reproduction and helps diversify an organism's offspring, so that parasites cannot exploit static host genotypes. This study shows that Drosophila melanogaster plastically increases the production of recombinant offspring after infection. The response is consistent across genetic backgrounds, developmental stages, and parasite types but is not induced after sterile wounding. Furthermore, the response appears to be driven by transmission distortion rather than increased recombination. This study extends the Red Queen model to include the increased production of recombinant offspring and uncovers a remarkable ability of hosts to actively distort their recombination fraction in rapid response to environmental cues. 

Cooper, B.S., Burrus, C.R., Ji, C., Hahn, M.W. and Montooth, K.L. (2015). Similar efficiencies of selection shape mitochondrial and nuclear genes in both Drosophila melanogaster and Homo sapiens. G3 (Bethesda) [Epub ahead of print]. PubMed ID: 26297726
Summary:
Deleterious mutations contribute to polymorphism even when selection effectively prevents their fixation. The efficacy of selection in removing deleterious mitochondrial mutations from populations depends on the effective population size (Ne) of the mtDNA, and the degree to which a lack of recombination magnifies the effects of linked selection. Using complete mitochondrial genomes from Drosophila melanogaster and nuclear data available from the same samples, this study re-examines the hypothesis that non-recombining animal mtDNA harbor an excess of deleterious polymorphisms relative to the nuclear genome. No evidence was found of recombination in the mitochondrial genome, and the much-reduced level of mitochondrial synonymous polymorphism relative to nuclear genes is consistent with a reduction in Ne. Nevertheless, it was found that the neutrality index (NI), a measure of the excess of nonsynonymous polymorphism relative to the neutral expectation, is only weakly significantly different between mitochondrial and nuclear loci. This difference is likely the result of the larger proportion of beneficial mutations in X-linked relative to autosomal loci, and little to no difference was found between mitochondrial and autosomal NI. Reanalysis of published data from Homo sapiens reveals a similar lack of a difference between the two genomes, though previous studies suggest a strong difference in both species. Thus, despite a smaller Ne, mitochondrial loci of both flies and humans appear to experience similar efficacies of purifying selection as do loci in the recombining nuclear genome.

Shinomiya, K., Takemura, S. Y., Rivlin, P. K., Plaza, S. M., Scheffer, L. K. and Meinertzhagen, I. A. (2015). A common evolutionary origin for the ON- and OFF-edge motion detection pathways of the Drosophila visual system. Front Neural Circuits 9: 33. PubMed ID: 26217193
Summary:
Two candidate pathways for ON- and OFF-edge motion detection in the visual system act via circuits that use respectively either T4 or T5, two cell types of the fourth neuropil, or lobula plate (LOP), that exhibit narrow-field direction-selective responses and provide input to wide-field tangential neurons. T4 or T5 both have four subtypes that terminate one each in the four strata of the LOP. Representatives are reported in a wide range of Diptera, and both cell types exhibit various similarities in: (1) the morphology of their dendritic arbors; (2) their four morphological and functional subtypes; (3) their cholinergic profile in Drosophila; (4) their input from the pathways of L3 cells in the first neuropil, or lamina (LA), and by one of a pair of LA cells, L1 (to the T4 pathway) and L2 (to the T5 pathway); and (5) their innervation by a single, wide-field contralateral tangential neuron from the central brain. Progenitors of both also express the gene atonal early in their proliferation from the inner anlage of the developing optic lobe, being alone among many other cell type progeny to do so. Yet T4 receives input in the second neuropil, or medulla (ME), and T5 in the third neuropil or lobula (LO). This study suggests that these two cell types were originally one, that their ancestral cell population duplicated and split to innervate separate ME and LO neuropils, and that a fiber crossing-the internal chiasma-arose between the two neuropils.

Wednesday, August 26th

Bai, H., Post, S. Kang, P. and Tatar, M. (2015). Drosophila longevity assurance conferred by reduced insulin receptor substrate Chico partially requires d4eBP. PLoS One 10: e0134415. PubMed ID: 26252766
Summary:
Mutations of the insulin/IGF signaling (IIS) pathway extend Drosophila lifespan. Based on genetic epistasis analyses, this longevity assurance is attributed to downstream effects of the FOXO transcription factor. However, as reported FOXO accounts for only a portion of the observed longevity benefit. One candidate is target of rapamycin complex 1 (TORC1). Reduced TORC1 activity is reported to slow aging, whereas reduced IIS is reported to repress TORC1 activity. The eukaryotic translation initiation factor 4E binding protein (4E-BP) is repressed by TORC1, and activated 4E-BP is reported to increase Drosophila lifespan. This study uses genetic epistasis analyses to test whether longevity assurance mutants of chico, the Drosophila insulin receptor substrate homolog, require Drosophila d4eBP to slow aging. In chico heterozygotes, which are robustly long-lived, d4eBP is required but not sufficient to slow aging. Remarkably, d4eBP is not required or sufficient for chico homozygotes to extend longevity. Likewise, chico heterozygote females partially require d4eBP to preserve age-dependent locomotion, and both chico genotypes require d4eBP to improve stress-resistance. It thus appears that altered IRS function within the IIS pathway of Drosophila appears to have partial, conditional capacity to regulate aging through an unconventional interaction with 4E-BP. 

Yadav, S., Garner, K., Georgiev, P., Li, M., Gomez-Espinosa, E., Panda, A., Mathre, S., Okkenhaug, H., Cockcroft, S. and Raghu, P. (2015). RDGBα, a PI-PA transfer protein regulates G-protein coupled PtdIns(4,5)P2 signalling during Drosophila phototransduction. J Cell Sci. PubMed ID: 26203165
Summary:
Many membrane receptors activate phospholipase C (PLC) during signalling, triggering changes in the levels of several plasma membrane (PM) lipids including PtdIns, PtdOH and PtdIns4,5P2. It is widely believed that exchange of lipids between the PM and endoplasmic reticulum (ER) is required to restore lipid homeostasis during PLC signalling, yet the mechanism remains unresolved. RDGB is a multi-domain protein with a PITP domain (RDGB-PITPd). In vitro, RDGB-PITPd binds and transfers both PtdOH and PtdIns. In Drosophila photoreceptors that experience high rates of PLC activity, RDGB function is essential for phototransduction. Binding of PtdIns to RDGB-PITPd is essential for normal phototransduction; yet this property is insufficient to explain in vivo function since another Drosophila PITP (vib) that also binds PtdIns cannot rescue the phenotypes of RDGB deletion. In RDGB mutants, PtdIns4,5P2 resynthesis at the PM following PLC activation is delayed and PtdOH levels elevate. Thus RDGB couples the turnover of both PtdIns and PtdOH, key lipid intermediates during G-protein coupled PtdIns(4,5)P2 turnover.

Ho, D. M., Pallavi, S. K. and Artavanis-Tsakonas, S. (2015). The Notch-mediated hyperplasia circuitry in Drosophila reveals a Src-JNK signaling axis. Elife 4. PubMed ID: 26222204
Summary:
Notch signaling controls a wide range of cell fate decisions during development and disease via synergistic interactions with other signaling pathways. Through a genome-wide genetic screen in Drosophila, this study uncovered a highly complex Notch-dependent genetic circuitry that profoundly affects proliferation and consequently hyperplasia. A novel synergistic relationship is reported between Notch and either of the non-receptor tyrosine kinases Src42A and Src64B to promote hyperplasia and tissue disorganization resulting in cell cycle perturbation, JAK/STAT signal activation, and differential regulation of Notch targets. Significantly, the JNK pathway is responsible for the majority of the phenotypes and transcriptional changes downstream of Notch-Src synergy. It has been reported that Notch-Mef2 also activates JNK, indicating that there are commonalities within the Notch-dependent proliferation circuitry; however, the current data indicate that Notch-Src accesses JNK in a significantly different fashion than Notch-Mef2.

Icreverzi, A., de la Cruz, A. F., Walker, D. W. and Edgar, B. A. (2015). Changes in neuronal CycD/Cdk4 activity affect aging, neurodegeneration, and oxidative stress. Aging Cell [Epub ahead of print]. PubMed ID: 26219626
Summary:
Mitochondrial dysfunction has been implicated in human diseases, including cancer, and proposed to accelerate aging. The Drosophila Cyclin-dependent protein kinase complex cyclin D/cyclin-dependent kinase 4 (CycD/Cdk4) promotes cellular growth by stimulating mitochondrial biogenesis. This study examine the neurodegenerative and aging consequences of altering CycD/Cdk4 function in Drosophila. Pan-neuronal loss or gain of CycD/Cdk4 was found to increase mitochondrial superoxide, oxidative stress markers, and neurodegeneration and decreases lifespan. RNAi-mediated depletion of the mitochondrial transcription factor, Tfam, can abrogate CycD/Cdk4's detrimental effects on both lifespan and neurodegeneration. This indicates that CycD/Cdk4's pathological consequences are mediated through altered mitochondrial function and a concomitant increase in reactive oxygen species. In support of this, CycD/Cdk4 activity levels in the brain were shown to affect the expression of a set of 'oxidative stress' genes. These results indicate that the precise regulation of neuronal CycD/Cdk4 activity is important to limit mitochondrial reactive oxygen species production and prevent neurodegeneration.

Tuesday, August 25th

Lovick, J. K., Kong, A., Omoto, J. J., Ngo, K. T., Younossi-Hartenstein, A. and Hartenstein, V. (2015). Patterns of growth and tract formation during the early development of secondary lineages in the Drosophila larval brain. Dev Neurobiol. PubMed ID: 26178322
Summary:
The Drosophila brain consists of a relatively small number of invariant, genetically determined lineages which provide a model to study the relationship between gene function and neuronal architecture. This article focuses on the secondary phase of lineage morphogenesis, from the reactivation of neuroblast proliferation in the first larval instar to the time when proliferation ends and secondary axon tracts have fully extended in the late third larval instar. The location and projection of secondary lineages were reconstructed at close (4 h) intervals and a detailed map was produced in the form of confocal z-projections and digital three-dimensional models of all lineages at successive larval stages. Based on these reconstructions, it was possible to compare the spatio-temporal pattern of axon formation and morphogenetic movements of different lineages in normal brain development. In addition to wild type, lineage morphology was reconstructed in two mutant conditions. (1) Expressing the construct UAS-p35 which rescues programmed cell death it could be systematically determine which lineages normally lose hemilineages to apoptosis. (2) so-Gal4-driven expression of dominant-negative EGFR ablated the optic lobe, which led to a conclusion that the global centrifugal movement normally affecting the cell bodies of lateral lineages in the late larva is causally related to the expansion of the optic lobe, and that the central pattern of axonal projections of these lineages is independent of the presence or absence of the optic lobe.

Lin, T. Y., Luo, J., Shinomiya, K., Ting, C. Y., Lu, Z., Meinerzhagen, I. A. and Lee, C. H. (2015). Mapping chromatic pathways in the Drosophila visual system. J Comp Neurol. PubMed ID: 26179639
Summary:
In Drosophila, color vision and wavelength-selective behaviors are mediated by the compound eye's narrow-spectrum photoreceptors, R7 and R8, and their downstream neurons, Tm5a/b/c and Tm20, in the second optic neuropil, or medulla. These chromatic Tm neurons project axons to a deeper optic neuropil, the lobula, which in insects has been implicated in processing and relaying color information to the central brain. The synaptic targets of the chromatic Tm neurons in the lobula are not known, however. Using a modified GRASP (GFP reconstitution across synaptic partners) method to probe connections between the chromatic Tm neurons and 28 known and novel types of lobula neurons, the visual projection neurons LT11 and LC14, and the lobula intrinsic neurons Li3 and Li4, were identified anatomically as synaptic targets of the chromatic Tm neurons. Single-cell GRASP analyses revealed that Li4 receives synaptic contacts from over 90% of all four types of chromatic Tm neurons while LT11 is postsynaptic to the chromatic Tm neurons with only modest selectivity and at a lower frequency and density. To visualize synaptic contacts at the ultrastructural level, a 'two-tag' double labeling method was developed and applied to label LT11's dendrites and the mitochondria in Tm5c's presynaptic terminals. Serial electron microscopic reconstruction confirmed that LT11 receives direct contacts from Tm5c. This method would be generally applicable to map the connections of large complex neurons in Drosophila and other animals.

Ammer, G., Leonhardt, A., Bahl, A., Dickson, B. J. and Borst, A. (2015). Functional specialization of neural input elements to the Drosophila ON motion detector. Curr Biol [Epub ahead of print]. PubMed ID: 26234212
Summary:
The neural apparatus for detecting the direction of visual movement consists of two spatially separated input lines that are asymmetrically filtered in time and then interact in a nonlinear way. However, the cellular implementation of this computation remains elusive. Recent connectomic data of the Drosophila optic lobe has suggested a neural circuit for the detection of moving bright edges (ON motion) with medulla cells Mi1 and Tm3 providing spatially offset input to direction-selective T4 cells, thereby forming the two input lines of a motion detector. Electrophysiological characterization of Mi1 and Tm3 revealed different temporal filtering properties and proposed them to correspond to the delayed and direct input, respectively. This hypothesis was tested by silencing either Mi1 or Tm3 cells and using electrophysiological recordings and behavioral responses of flies as a readout. It was shown that Mi1 is a necessary element of the ON pathway under all stimulus conditions. In contrast, Tm3 is specifically required only for the detection of fast ON motion in the preferred direction. This study thereby provides first functional evidence that Mi1 and Tm3 are key elements of the ON pathway and uncover an unexpected functional specialization of these two cell types. The results thus require an elaboration of the currently prevailing model for ON motion detection and highlight the importance of functional studies for neural circuit breaking.

Jeibmann, A., Halama, K., Witte, H. T., Kim, S. N., Eikmeier, K., Koos, B., Klambt, C. and Paulus, W. (2015). Involvement of CD9 and PDGFR in migration is evolutionarily conserved from Drosophila glia to human glioma. J Neurooncol [Epub ahead of print]. PubMed ID: 26224160
Summary:
Platelet-derived growth factor receptor (PDGFR) signaling plays an important role in the biology of malignant gliomas. To investigate mechanisms modulating PDGFR signaling in gliomagenesis, a Drosophila glioma model and genetic screen were used to identify genes interacting with Pvr, the fly homolog of PDGFRs. Glial expression of constitutively activated Pvr (λPvr) led to glial over migration and lethality at late larval stage. Among 3316 dsRNA strains crossed against the tester strain, 128 genes shifted lethality to pupal stage, including tetraspanin 2A (tsp2A). In a second step knockdown of all Drosophila tetraspanins was investigated. Of all tetraspanin dsRNA strains only knockdown of tsp2A partially rescued the Pvr-induced phenotype. Human CD9 (TSPAN29/MRP-1), a close homolog of tsp2A, was found to be expressed in glioma cell lines A172 and U343MG as well as in the majority of glioblastoma samples. Furthermore, in situ proximity ligation assay revealed close association of CD9 with PDGFR α and β. In U343MG cells, knockdown of CD9 blocked PDGF-BB stimulated migration. In conclusion, modulation of PDGFR signaling by CD9 is evolutionarily conserved from Drosophila glia to human glioma and plays a role in glia migration.

Moris-Sanz, M., Estacio-Gómez, A., Sánchez-Herrero, E and Díaz-Benjumea, F.J. (2015). The study of the Bithorax-complex genes in patterning CCAP neurons reveals a temporal control of neuronal differentiation by Abd-B. Biol Open [Epub ahead of print]. PubMed ID: 26276099
Summary:
During development, HOX genes play critical roles in the establishment of segmental differences. In the Drosophila central nervous system, these differences are manifested in the number and type of neurons generated by each neuroblast in each segment. HOX genes can act either in neuroblasts or in postmitotic cells, and either early or late in a lineage. Additionally, they can be continuously required during development or just at a specific stage. Moreover, these features are generally segment-specific. Lately, it has been shown that contrary to what happens in other tissues, where HOX genes define domains of expression, these genes are expressed in individual cells as part of the combinatorial codes involved in cell type specification. This study analyzes the role of the Bithorax-complex genes - Ultrabithorax, abdominal-A and Abdominal-B - in sculpting the pattern of crustacean cardioactive peptide (CCAP)-expressing neurons. These neurons are widespread in invertebrates, express CCAP, Bursicon and MIP neuropeptides and play major roles in controlling ecdysis. There are two types of CCAP neuron: interneurons and efferent neurons. Results indicate that Ultrabithorax and Abdominal-A are not necessary for specification of the CCAP-interneurons, but are absolutely required to prevent the death by apoptosis of the CCAP-efferent neurons. Furthermore, Abdominal-B controls by repression the temporal onset of neuropeptide expression in a subset of CCAP-efferent neurons, and a peak of ecdysone hormone at the end of larval life counteracts this repression. Thus, Bithorax complex genes control the developmental appearance of these neuropeptides both temporally and spatially.

Jindra, M., Uhlirova, M., Charles, J. P., Smykal, V. and Hill, R. J. (2015). Genetic evidence for function of the bHLH-PAS Protein Gce/Met as a juvenile hormone receptor. PLoS Genet 11: e1005394. PubMed ID: 26161662
Summary:
Juvenile hormones (JHs) play a major role in controlling development and reproduction in insects and other arthropods. Synthetic JH-mimicking compounds such as methoprene are employed as potent insecticides against significant agricultural, household and disease vector pests. However, a receptor mediating effects of JH and its insecticidal mimics has long been the subject of controversy. The bHLH-PAS protein Methoprene-tolerant (Met), along with its Drosophila melanogaster paralog Germ cell-expressed (Gce), has emerged as a prime JH receptor candidate, but critical evidence that this protein must bind JH to fulfill its role in normal insect development has been missing. This study shows that Gce binds a native D. melanogaster JH, its precursor methyl farnesoate, and some synthetic JH mimics. Conditional on this ligand binding, Gce mediates JH-dependent gene expression and the hormone's vital role during development of the fly. Any one of three different single amino acid mutations in the ligand-binding pocket that prevent binding of JH to the protein block these functions. Only transgenic Gce capable of binding JH can restore sensitivity to JH mimics in D. melanogaster Met-null mutants and rescue viability in flies lacking both Gce and Met that would otherwise die at pupation. Similarly, the absence of Gce and Met can be compensated by expression of wild-type but not mutated transgenic D. melanogaster Met protein. This genetic evidence definitively establishes Gce/Met in a JH receptor role, thus resolving a long-standing question in arthropod biology.

Monday, August 24th

Lovato, T. L., Sensibaugh, C. A., Swingle, K. L., Martinez, M. M. and Cripps, R. M. (2015). The Drosophila transcription factors Tinman and Pannier activate and collaborate with Myocyte enhancer factor-2 to promote heart cell fate. PLoS One 10: e0132965. PubMed ID: 26225919
Summary:
Expression of the MADS domain transcription factor Myocyte Enhancer Factor 2 (MEF2) is regulated by numerous and overlapping enhancers which tightly control its transcription in the mesoderm. To understand how Mef2 expression is controlled in the heart, this study has identified a late stage Mef2 cardiac enhancer that is active in all heart cells beginning at stage 14 of embryonic development. This enhancer is regulated by the NK-homeodomain transcription factor Tinman, and the GATA transcription factor Pannier through both direct and indirect interactions with the enhancer. Since Tinman, Pannier and MEF2 are evolutionarily conserved from Drosophila to vertebrates, and since their vertebrate homologs can convert mouse fibroblast cells to cardiomyocytes in different activator cocktails, tests were performed to see whether over-expression of these three factors in vivo could ectopically activate known cardiac marker genes. Mesodermal over-expression of Tinman and Pannier resulted in approximately 20% of embryos with ectopic Hand and Sulphonylurea receptor (Sur) expression. By adding MEF2 alongside Tinman and Pannier, a dramatic expansion in the expression of Hand and Sur was observed in almost all embryos analyzed. Two additional cardiac markers were also expanded in their expression. These results demonstrate the ability to initiate ectopic cardiac fate in vivo by the combination of only three members of the conserved Drosophila cardiac transcription network, and provide an opportunity for this genetic model system to be used to dissect the mechanisms of cardiac specification.
Jain, D., Baldi, S., Zabel, A., Straub, T. and Becker, P. B. (2015). Active promoters give rise to false positive 'Phantom Peaks' in ChIP-seq experiments. Nucleic Acids Res [Epub ahead of print]. PubMed ID: 26117547
Summary:
Chromatin immunoprecipitation (ChIP) is widely used to identify chromosomal binding sites. Chromatin proteins are cross-linked to their target sequences in living cells. The purified chromatin is sheared and the relevant protein is enriched by immunoprecipitation with specific antibodies. The co-purifying genomic DNA is then determined by massive parallel sequencing (ChIP-seq). This study applied ChIP-seq to map the chromosomal binding sites for two ISWI-containing nucleosome remodeling factors, ACF and RSF, in Drosophila embryos. Employing several polyclonal and monoclonal antibodies directed against their signature subunits, ACF1 and RSF-1, robust profiles were obtained indicating that both remodelers co-occupied a large set of active promoters. Further validation included controls using chromatin of mutant embryos that do not express ACF1 or RSF-1. Surprisingly, the ChIP-seq profiles were unchanged, suggesting that they were not due to specific immunoprecipitation. Conservative analysis lists about 3000 chromosomal loci, mostly active promoters that are prone to non-specific enrichment in ChIP and appear as 'Phantom Peaks'. These peaks are not obtained with pre-immune serum and are not prominent in input chromatin. Mining the modENCODE ChIP-seq profiles identifies potential Phantom Peaks in many profiles of epigenetic regulators. These profiles and other ChIP-seq data featuring prominent Phantom Peaks must be validated with chromatin from cells in which the protein of interest has been depleted.

Van Bortle, K., Peterson, A. J., Takenaka, N., O'Connor, M. B. and Corces, V. G. (2015). CTCF-dependent co-localization of canonical Smad signaling factors at architectural protein binding sites in D. melanogaster. Cell Cycle: [Epub ahead of print]. PubMed ID: 26125535
Summary:
The transforming growth factor beta (TGF-beta) and bone morphogenic protein (BMP) pathways transduce extracellular signals into tissue-specific transcriptional responses. During this process, signaling effector Smad proteins translocate into the nucleus to direct changes in transcription, but how and where they localize to DNA remain important questions. This study has mapped Drosophila TGF-beta signaling factors Mad, dSmad2, Medea and Schnurri genome-wide in Kc cells and find that numerous sites for these factors overlap with the architectural protein CTCF Depletion of CTCF by RNAi results in the disappearance of a subset of Smad sites, suggesting Smad proteins localize to CTCF binding sites in a CTCF-dependent manner. Sensitive Smad binding sites are enriched at low occupancy CTCF peaks within topological domains, rather than at the physical domain boundaries where CTCF may function as an insulator. In response to Decapentaplegic, CTCF binding is not significantly altered, whereas Mad, Medea, and Schnurri are redirected from CTCF to non-CTCF binding sites. These results suggest that CTCF participates in the recruitment of Smad proteins to a subset of genomic sites and in the redistribution of these proteins in response to BMP signaling.

Sloutskin, A., Danino, Y. M., Orenstein, Y., Zehavi, Y., Doniger, T., Shamir, R. and Juven-Gershon, T. (2015). ElemeNT: a computational tool for detecting core promoter elements. Transcription 6: 41-50. PubMed ID: 26226151
Summary:
Core promoter elements play a pivotal role in the transcriptional output, yet they are often detected manually within sequences of interest. This study presents 2 contributions to the detection and curation of core promoter elements within given sequences. First, the Elements Navigation Tool (ElemeNT) is a user-friendly web-based, interactive tool for prediction and display of putative core promoter elements and their biologically-relevant combinations. Second, the CORE database summarizes ElemeNT-predicted core promoter elements near CAGE and RNA-seq-defined Drosophila melanogaster transcription start sites (TSSs). ElemeNT's predictions are based on biologically-functional core promoter elements, and can be used to infer core promoter compositions. ElemeNT does not assume prior knowledge of the actual TSS position, and can therefore assist in annotation of any given sequence. These resources, facilitate the identification of core promoter elements as active contributors to gene expression.

Sunday, August 23

Jia, D., Soylemez, M., Calvin, G., Bornmann, R., Bryant, J., Hanna, C., Huang, Y. C. and Deng, W. M. (2015). A large-scale in vivo RNAi screen to identify genes involved in Notch-mediated follicle cell differentiation and cell cycle switches. Sci Rep 5: 12328. PubMed ID: 26205122
Summary:
During Drosophila oogenesis, follicle cells sequentially undergo three distinct cell-cycle programs: the mitotic cycle, endocycle, and gene amplification. Notch signaling plays a central role in regulating follicle-cell differentiation and cell-cycle switches; its activation is essential for the mitotic cycle/endocycle (M/E) switch. Cut, a linker between Notch signaling and cell-cycle regulators, is specifically downregulated by Notch during the endocycle stage. To determine how signaling pathways coordinate during the M/E switch and to identify novel genes involved in follicle cell differentiation, an in vivo RNAi screen was performed through induced knockdown of gene expression and examination of Cut expression in follicle cells. 2205 RNAi lines were screened, and 33 genes were found regulating Cut expression during the M/E switch. These genes were confirmed with the staining of two other Notch signaling downstream factors, Hindsight and Broad, and validated with multiple independent RNAi lines. Gene ontology software was applied to find enriched biological meaning, and the results were compared with other publications to find conserved genes across tissues. Specifically, earlier endocycle entry in anterior follicle cells was found than those in the posterior, the insulin-PI3K pathway was found to participate in the precise M/E switch, and Nejire was suggested as a cofactor of Notch signaling during oogenesis.
Chatterjee, R. N., Chatterjee, P., Kuthe, S., Acharyya-Ari, M. and Chatterjee, R. (2015). Intersex (ix) mutations of Drosophila melanogaster cause nonrandom cell death in genital disc and can induce tumours in genitals in response to decapentaplegic (dppdisk) mutations. J Genet 94: 207-220. PubMed ID: 26174668
Summary:
In Drosophila melanogaster, the mediator complex protein intersex (ix) is a terminally positioned gene in somatic sex determination hierarchy and functions with the female specific product of doublesex to implement female sexual differentiation. The null phenotype of ix is to transform diplo-X individuals into intersexes while leaving haplo-X animals unaffected. This study on the effect of different intersex mutations on genital disc development provides the following major results: (1) similar range of a characteristic array of morphological structures (from almost double sex terminalia to extreme reduction of terminal appendages) was displayed by the terminalia of ix flies; (2) an increased number of apoptotic cells were found to occur in a localized manner in mature third instar larval genital discs of ix individuals; (3) ix mutations can induce high frequency of neoplastic tumours in genitals in the presence of decapentaplegic mutations; and (iv) heteroallelic combinations of dpp mutations can also induce tumours in intersex genitals with variable expressivity. On the basis of these findings, it is suggested that: (1) loss of function of ix causes massive cell death in both male and female genital primordia of genital discs, resulting phenotype mimicking in male and female characteristics in genitals; and (2) at the discs, the apoptotic cells persist as 'undead' cells that can induce oncogenic transformation in the neighbouring disc cells when dpp signalling is blocked or reduced by dpp) mutations.

Ayyub, C., Banerjee, K. K. and Joti, P. (2015). Reduction of Cullin-2 in somatic cells disrupts differentiation of germline stem cells in the Drosophila ovary. Dev Biol. [Epub ahead of print] PubMed ID: 26206612
Summary:
Signaling from a niche consisting of somatic cells is essential for maintenance of germline stem cells (GSCs) in the ovary of Drosophila. Decapentaplegic (Dpp), a type of bone morphogenetic protein (BMP) signal, emanating from the niche, is the most important signal for this process. Cullin proteins constitute the core of a multiprotein E3-ligase important for their functions viz. degradation or modification of proteins necessary for different cellular processes. This study has found that a Cullin protein called Cullin-2 (Cul-2) expresses in both somatic and germline cells of the Drosophila ovary. Reduction of Cul-2 in somatic cells causes upregulation of Dpp signal and produces accumulation of extra GSC-like cells inside germarium, the anteriormost structure of the ovary. These results suggest that Cullin-2 protein present in the somatic cells is involved in a non cell-autonomous regulation of the extent of Dpp signaling and thus controls the differentiation of GSCs to cystoblasts (CBs).

Romani, P., Gargiulo, G. and Cavaliere, V. (2015). The ecdysone receptor signalling regulates microvilli formation in follicular epithelial cells. Cell Mol Life Sci [Epub ahead of print]. PubMed ID: 26223269
Summary:
Epithelial morphogenesis contributes greatly to the development and homeostasis of the organs and body parts. This study analysed the consequences of impaired Ecdysone receptor (EcR) signalling in the Drosophila follicular epithelium. Besides governing cell growth, the three EcR isoforms act redundantly in controlling follicle cell positioning. Flattening of the microvilli and an aberrant actin cytoskeleton arise from defective EcR signalling in follicle cells, and these defects impact on the organisation of the oocyte membrane. This signalling was found to govern a complex molecular network since its impairment affects key molecules as atypical protein kinase C and activated Moesin. Interestingly, the activity of the transcription factor Tramtrack69 isoform is required for microvilli and their actin core morphogenesis as well as for follicle cell positioning. In conclusion, these findings provide evidence of novel roles for EcR signalling and Tramtrack69 transcription factor in controlling stage-specific differentiation events that take place in the follicular epithelium.

Saturday, August 22nd

Fischer, P., La Rosa, M.K., Schulz, A., Preiss, A. and Nagel, A.C. (2015). Cyclin G functions as a positive regulator of growth and metabolism in Drosophila. PLoS Genet 11: e1005440. PubMed ID: 26274446
Summary:
In multicellular organisms, growth and proliferation is adjusted to nutritional conditions by a complex signaling network. The Insulin receptor/target of rapamycin (InR/TOR) signaling cascade plays a pivotal role in nutrient dependent growth regulation in Drosophila and mammals alike. This study identifies Cyclin G (CycG) as a regulator of growth and metabolism in during larval development in Drosophila. CycG mutants have a reduced body size and weight and show signs of starvation accompanied by a disturbed fat metabolism. InR/TOR signaling activity is impaired in cycG mutants, combined with a reduced phosphorylation status of the kinase Akt1 and the downstream factors S6-kinase and eukaryotic translation initiation factor 4E binding protein (4E-BP). Moreover, the expression and accumulation of Drosophila insulin like peptides (dILPs) is disturbed in cycG mutant brains. Using a reporter assay, it was shown that the activity of one of the first effectors of InR signaling, Phosphoinositide 3-kinase (PI3K92E), is unaffected in cycG mutants. However, the metabolic defects and weight loss in cycG mutants are rescued by overexpression of Akt1 specifically in the fat body and by mutants in widerborst (wdb), the B'-subunit of the phosphatase PP2A, known to downregulate Akt1 by dephosphorylation. Together, these data suggest that CycG acts at the level of Akt1 to regulate growth and metabolism via PP2A in Drosophila.

Xie, X. J., et al. (2015). CDK8-Cyclin C Mediates Nutritional Regulation of Developmental Transitions through the Ecdysone Receptor in Drosophila. PLoS Biol 13: e1002207. PubMed ID: 26222308
Summary:
EcR-dependent transcription, and thus, developmental timing in Drosophila, is regulated by CDK8 and its regulatory partner Cyclin C (CycC), and the level of CDK8 is affected by nutrient availability. cdk8 and cycC mutants resemble EcR mutants and EcR-target genes are systematically down-regulated in both mutants. Indeed, the ability of the EcR-Ultraspiracle (USP) heterodimer to bind to polytene chromosomes and the promoters of EcR target genes is also diminished. Mass spectrometry analysis of proteins that co-immunoprecipitate with EcR and USP identified multiple Mediator subunits, including CDK8 and CycC. Consistently, CDK8-CycC interacts with EcR-USP in vivo; in particular, CDK8 and Med14 can directly interact with the AF1 domain of EcR. These results suggest that CDK8-CycC may serve as transcriptional cofactors for EcR-dependent transcription. During the larval-pupal transition, the levels of CDK8 protein positively correlate with EcR and USP levels, but inversely correlate with the activity of sterol regulatory element binding protein (SREBP), the master regulator of intracellular lipid homeostasis. Likewise, starvation of early third instar larvae precociously increases the levels of CDK8, EcR and USP, yet down-regulates SREBP activity. Conversely, refeeding the starved larvae strongly reduces CDK8 levels but increases SREBP activity. Importantly, these changes correlate with the timing for the larval-pupal transition. Taken together, these results suggest that CDK8-CycC links nutrient intake to developmental transitions (EcR activity) and fat metabolism (SREBP activity) during the larval-pupal transition.

Mansilla, A., Martín, F.A., Martín, D. and Ferrús, A. (2015). Ligand-independent requirements of steroid receptors EcR and USP for cell survival. Cell Death Differ [Epub ahead of print]. PubMed ID: 26250909
Summary:
The steroid hormone ecdysone 20-hydroxyecdysone (20E) binds the heterodimer EcR/USP nuclear receptor to regulate target genes that elicit proliferation, cell death and differentiation during insect development. This study shows that the prothoracic gland (PG), the major steroid-producing organ of insect larvae, requires EcR and USP to survive in a critical period previous to metamorphosis, and that this requirement is 20E-independent. The cell death induced by the downregulation of these receptors involves the activation of the JNK-encoding basket gene and it can be rescued by upregulating EcR isoforms which are unable to respond to 20E. Also, while PG cell death prevents ecdysone production, blocking hormone synthesis or secretion in normal PG does not lead to cell death, demonstrating further the ecdysone-independent nature of the receptor-deprivation cell death. In contrast to PG cells, wing disc or salivary glands cells do not require these receptors for survival, revealing their cell and developmental time specificity. For exploring the potential use of this feature of steroid receptors in cancer, tumor overgrowth induced by altered yorkie signaling was assayed. This overgrowth is suppressed by EcR downregulation in PG, but not in wing disc, cells. The mechanism of all these cell death features is based on the transcriptional regulation of reaper. These novel and context-dependent functional properties for EcR and USP receptors may help to understand the heterogeneous responses to steroid-based therapies in human pathologies.

Ghosh, A.C., Shimell, M., Leof, E.R., Haley, M.J. and O'Connor, M.B. (2015). UPRT, a suicide-gene therapy candidate in higher eukaryotes, is required for Drosophila larval growth and normal adult lifespan. Sci Rep 5: 13176. PubMed ID: 26271729
Summary:
Uracil phosphoribosyltransferase (UPRT) is a pyrimidine salvage pathway enzyme that catalyzes the conversion of uracil to uridine monophosphate (UMP). The enzyme is highly conserved from prokaryotes to humans and yet phylogenetic evidence suggests that UPRT homologues from higher-eukaryotes, including Drosophila, are incapable of binding uracil. Purified human UPRT also do not show any enzymatic activity in vitro, making microbial UPRT an attractive candidate for anti-microbial drug development, suicide-gene therapy, and cell-specific mRNA labeling techniques. Nevertheless, the enzymatic site of UPRT remains conserved across the animal kingdom indicating an in vivo role for the enzyme. This study finds that the Drosophila UPRT homologue, krishah (kri), codes for an enzyme that is required for larval growth, pre-pupal/pupal viability and long-term adult lifespan. These findings suggest that UPRT from all higher eukaryotes is likely enzymatically active in vivo and challenges the previous notion that the enzyme is non-essential in higher eukaryotes and cautions against targeting the enzyme for therapeutic purposes. These findings also suggest that expression of the endogenous UPRT gene will likely cause background incorporation when using microbial UPRT as a cell-specific mRNA labeling reagent in higher eukaryotes.

Friday, August 21st

Ishizu, H., Iwasaki, Y. W., Hirakata, S., Ozaki, H., Iwasaki, W., Siomi, H. and Siomi, M. C. (2015). Somatic primary piRNA biogenesis driven by cis-acting RNA elements and trans-acting Yb. Cell Rep 12: 429-440. PubMed ID: 26166564
Summary:
Primary piRNAs in Drosophila ovarian somatic cells arise from piRNA cluster transcripts and the 3' UTRs of a subset of mRNAs, including Traffic jam (Tj) mRNA. However, it is unclear how these RNAs are determined as primary piRNA sources. This study identified a cis-acting 100-nt fragment in the Tj 3' UTR that is sufficient for producing artificial piRNAs from unintegrated DNA. These artificial piRNAs were effective in endogenous gene transcriptional silencing. Yb, a core component of primary piRNA biogenesis center Yb bodies, directly binds the Tj-cis element. Disruption of this interaction markedly reduces piRNA production. Thus, Yb is the trans-acting partner of the Tj-cis element. Yb-CLIP revealed that Yb binding correlates with somatic piRNA production but Tj-cis element downstream sequences produced few artificial piRNAs. It is thus proposed that Yb determines primary piRNA sources through two modes of action: primary binding to cis elements to specify substrates and secondary binding to downstream regions to increase diversity in piRNA populations.

Clemente, P., Pajak, A., Laine, I., Wibom, R., Wedell, A., Freyer, C. and Wredenberg, A. (2015). SUV3 helicase is required for correct processing of mitochondrial transcripts. Nucleic Acids Res 43(15):7398-413. PubMed ID: 26152302
Summary:
Mitochondrial gene expression is largely regulated by post-transcriptional mechanisms that control the amount and translation of each mitochondrial mRNA. Despite its importance for mitochondrial function, the mechanisms and proteins involved in mRNA turnover are still not fully characterized. Studies in yeast and human cell lines have indicated that the mitochondrial helicase SUV3, together with the polynucleotide phosphorylase, PNPase, composes the mitochondrial degradosome. To further investigate the in vivo function of SUV3, the homolog of SUV3 was disrupted in Drosophila melanogaster (Dm). Loss of dmsuv3 led to the accumulation of mitochondrial mRNAs, without increasing rRNA levels, de novo transcription or decay intermediates. Furthermore, a severe decrease was observed in mitochondrial tRNAs accompanied by an accumulation of unprocessed precursor transcripts. These processing defects lead to reduced mitochondrial translation and a severe respiratory chain complex deficiency, resulting in a pupal lethal phenotype. In summary, these results propose that SUV3 is predominantly required for the processing of mitochondrial polycistronic transcripts in metazoan and that this function is independent of PNPase.

Verma, P. and Cohen, S. M. (2015). miR-965 controls cell proliferation and migration during tissue morphogenesis in the abdomen. Elife 4. PubMed ID: 26226636
Summary:
Formation of the Drosophila adult abdomen involves a process of tissue replacement in which larval epidermal cells are replaced by adult cells. The progenitors of the adult epidermis are specified during embryogenesis and, unlike the imaginal discs that make up the thoracic and head segments, they remain quiescent during larval development. During pupal development, the abdominal histoblast cells proliferate and migrate to replace the larval epidermis. This study provides evidence that the microRNA, miR-965, acts via string and wingless to control histoblast proliferation and migration. Ecdysone signaling downregulates miR-965 at the onset of pupariation, linking activation of the histoblast nests to the hormonal control of metamorphosis. Replacement of the larval epidermis by adult epidermal progenitors involves regulation of both cell-intrinsic events and cell communication. By regulating both cell proliferation and cell migration, miR-965 contributes to the robustness of this morphogenetic system.

Trcek, T., Grosch, M., York, A., Shroff, H., Lionnet, T. and Lehmann, R. (2015). Drosophila germ granules are structured and contain homotypic mRNA clusters. Nat Commun 6: 7962. PubMed ID: 26242323
Summary:
Germ granules, specialized ribonucleoprotein particles, are a hallmark of all germ cells. In Drosophila, an estimated 200 mRNAs are enriched in the germ plasm, and some of these have important, often conserved roles in germ cell formation, specification, survival and migration. How mRNAs are spatially distributed within a germ granule and whether their position defines functional properties is unclear. This study, using single-molecule FISH and structured illumination microscopy, a super-resolution approach, shows that mRNAs are spatially organized within the granule whereas core germ plasm proteins are distributed evenly throughout the granule. Multiple copies of single mRNAs organize into 'homotypic clusters' that occupy defined positions within the center or periphery of the granule. This organization, which is maintained during embryogenesis and independent of the translational or degradation activity of mRNAs, reveals new regulatory mechanisms for germ plasm mRNAs that may be applicable to other mRNA granules.

Jeske, M., Bordi, M., Glatt, S., Muller, S., Rybin, V., Muller, C. W. and Ephrussi, A. (2015). The crystal structure of the Drosophila germline inducer Oskar identifies two domains with distinct Vasa helicase- and RNA-binding activities. Cell Rep 12: 587-598. PubMed ID: 26190108
Summary:
In many animals, the germ plasm segregates germline from soma during early development. Oskar protein is known for its ability to induce germ plasm formation and germ cells in Drosophila. However, the molecular basis of germ plasm formation remains unclear. This study shows that Oskar is an RNA-binding protein in vivo, crosslinking to nanos, polar granule component, and germ cell-less mRNAs, each of which has a role in germline formation. Furthermore, high-resolution crystal structures are presented of the two Oskar domains. RNA-binding maps in vitro to the C-terminal domain, which shows structural similarity to SGNH hydrolases. The highly conserved N-terminal LOTUS domain forms dimers and mediates Oskar interaction with the germline-specific RNA helicase Vasa in vitro. These findings suggest a dual function of Oskar in RNA and Vasa binding, providing molecular clues to its germ plasm function.

Norvell, A., Wong, J., Randolph, K. and Thompson, L. (2015). Wispy and Orb cooperate in the cytoplasmic polyadenylation of localized gurken mRNA. Dev Dyn [Epub ahead of print]. PubMed ID: 26214278
Summary:
In Drosophila, the dorsal-ventral (D-V) axis of the oocyte is dependent on Gurken (Grk) protein distribution. This is achieved through the cytoplasmic localization of grk mRNA and regulation of its translation. As females carrying mutations in the gene encoding the CPEB protein Orb lay ventralized eggs due to insufficient Grk levels, it seemed likely that cytoplasmic polyadenylation of grk transcripts may play a role in their translational regulation. This study has found that grk is polyadenylated throughout oogenesis, with poly(A) tails of approximately 30-50 A residues. Hyperadenylated grk transcripts, with poly(A) tails of 50-90 As, are detected in late stage egg chambers, but they fail to accumulate in oocytes deficient in Orb or the poly(A) polymerase Wispy (Wisp). wisp females also lay weakly ventralized eggs, demonstrating that they produce inadequate amounts of Grk. Finally, unlocalized grk transcripts are also not appropriately hyperadenylated. It is concluded that localized cytoplasmic polyadenylation of grk mRNA by Wisp and Orb is necessary to achieve appropriate Grk protein accumulation in the D/A corner of the oocyte during mid to late oogenesis.

Thursday, August 20th

Pinto, P.B., Espinosa-Vázquez, J.M., Rivas, M.L. and Hombría, J.C. (2015). JAK/STAT and Hox dynamic interactions in an organogenetic gene cascade. PLoS Genet 11: e1005412. PubMed ID: 26230388
Summary:
This study analyzes in detail how a Hox protein induces during early embryogenesis a simple organogenetic cascade that matures into a complex gene network through the activation of feedback and feed forward interaction loops. To address how the network organization changes during development and how the target genes integrate the genetic information it provides, this study analyzed the induction of posterior spiracle organogenesis in Drosophila by the Hox gene Abdominal-B (Abd-B). Initially, Abd-B activates in the spiracle primordium a cascade of transcription factors and signalling molecules including the JAK/STAT signalling pathway. At later stages STAT activity was found to feed back directly into Abd-B, initiating the transformation of the Hox cascade into a gene-network. Focusing on crumbs, a spiracle downstream target gene of Abd-B, the study analyzed how a modular cis regulatory element integrates the dynamic network information set by Abd-B and the JAK/STAT signalling pathway during development. It was shown that a Hox induced genetic cascade transforms into a robust gene network during organogenesis due to the repeated interaction of Abd-B and one of its targets, the JAK/STAT signalling cascade. These results show that in this network STAT functions not just as a direct transcription factor, but also acts as a "counter-repressor", uncovering a novel mode for STAT directed transcriptional regulation.

Gallach, M. (2015). 1.688 g/cm satellite-related repeats: a missing link to dosage compensation and speciation. Mol Ecol [Epub ahead of print]. PubMed ID: 26224418
Summary:
Despite the important progress that has been made on dosage compensation (DC), a critical link in understanding of the X chromosome recognition mechanisms is still missing. Recent studies in Drosophila indicate that the missing link could be a family of DNA repeats populating the euchromatin of the X chromosome. This opinion article discusses how these findings add a new fresh twist on the DC problem. Understanding of DC in Drosophila and integrate these recent discoveries into knowledge of the X chromosome recognition problem is discussed. Previous studies tested RNA from these repeats for a role in dosage compensation (Menon, 2014) and found that ectopic expression of single-stranded RNAs from 1.688(X) repeats enhanced the male lethality of mutants with defective X recognition. In contrast, expression of double-stranded hairpin RNA from a 1.688(X) repeat generated abundant siRNA and dramatically increased male survival. Consistent with improved survival, X localization of the MSL complex was largely restored in these males (Menon, 2014). A model is introduced according to which, 1.688 g/cm3 satellite-related (SR) repeats would be the primary recognition elements for the dosage compensation complex. Contrary to the current belief, it is suggested that the DC system in Drosophila is not conserved and static, but it is continuously co-evolving with the target SR repeats. The potential role of the SR repeats in hybrid incompatibilities and speciation is also discussed.

Crona, F., Holmqvist, P.H., Tang, M., Singla, B., Vakifahmetoglu-Norberg, H., Fantur, K. and Mannervik, M. (2015). The Brakeless CO-regulator can directly activate and repress transcription in early Drosophila embryos. Dev Biol [Epub ahead of print]. PubMed ID: 26260775
Summary:
Previous studies have shown that Brakeless can function as a transcriptional co-repressor. This study performs transcriptional profiling of brakeless mutant embryos. Unexpectedly, the majority of affected genes are down-regulated in brakeless mutants. It was demonstrated that genomic regions in close proximity to some of these genes are occupied by Brakeless, that over-expression of Brakeless causes a reciprocal effect on expression of these genes, and that Brakeless remains an activator of the genes upon fusion to an activation domain. Together, these results show that Brakeless can both repress and activate gene expression. A yeast two-hybrid screen identifies the Mediator complex subunit Med19 as interacting with an evolutionarily conserved part of Brakeless. Both down- and up-regulated Brakeless target genes are also affected in Med19-depleted embryos, but only down-regulated targets are influenced in embryos depleted of both Brakeless and Med19. These data provide support for a Brakeless activator function that regulates transcription by interacting with Med19.

Campbell, K. and Casanova, J. (2015). A role for E-cadherin in ensuring cohesive migration of a heterogeneous population of non-epithelial cells. Nat Commun 6: 7998. PubMed ID: 26272476
Summary:
Collective cell migration is a key process underlying the morphogenesis of many organs as well as tumour invasion, which very often involves heterogeneous cell populations. This study investigates how such populations can migrate cohesively in the Drosophila posterior midgut, comprised of epithelial and mesenchymal cells and shows a novel role for the epithelial adhesion molecule E-cadherin (E-Cad) in mesenchymal cells. Despite a lack of junctions at the ultrastructure level, reducing E-Cad levels causes mesenchymal cells to detach from one another and from neighbouring epithelial cells; as a result, coordination between the two populations is lost. Moreover, Bazooka and recycling mechanisms are also required for E-Cad accumulation in mesenchymal cells. These results indicate an active role for E-Cad in mediating cohesive and ordered migration of non-epithelial cells, and discount the notion of E-Cad as just an epithelial feature that has to be switched off to enable migration of mesenchymal cells. 

Wednesday, August 19th

Scialo, F., Sriram, A., Naudí, A., Ayala, V., Jové, M., Pamplona, R. and Sanz, A. (2015). Target of rapamycin activation predicts lifespan in fruit flies. Cell Cycle [Epub ahead of print]. PubMed ID: 26259964
Summary:
Aging and age-related diseases are one of the most important health issues that the world will confront during the 21st century. Only by understanding the proximal causes will it be possible to find treatments to reduce or delay the onset of degenerative diseases associated with aging. Currently, the prevalent paradigm in the field is the accumulation of damage. However, a new theory that proposes an alternative explanation is gaining momentum. The hyperfunction theory proposes that aging is not a consequence of a wear and tear process, but a result of the continuation of developmental programs during adulthood. This study uses Drosophila melanogaster, where evidence supporting both paradigms has been reported, to identify which parameters that have been previously related with lifespan best predict the rate of aging in wild type flies cultured at different temperatures. It was found that mitochondrial function and mitochondrial reactive oxygen species (mtROS) generation correlates with metabolic rate, but not with the rate of aging. Importantly, it was found that activation of nutrient sensing pathways (i.e. insulin-PI3K/Target of rapamycin (Tor) pathway) correlates with lifespan, but not with metabolic rate. These results, dissociate metabolic rate and lifespan in wild type flies and instead link nutrient sensing signalling with longevity as predicted by the hyperfunction theory.

Na, J., Sweetwyne, M. T., Park, A. S., Susztak, K. and Cagan, R. L. (2015). Diet-induced podocyte dysfunction in Drosophila and Mammals. Cell Rep 12: 636-647. PubMed ID: 26190114
Summary:
Diabetic nephropathy is a major cause of end-stage kidney disease. Characterized by progressive microvascular disease, most efforts have focused on injury to the glomerular endothelium. Recent work has suggested a role for the podocyte, a highly specialized component of the glomerular filtration barrier. This study demonstrates that the Drosophila nephrocyte, a cell analogous to the mammalian podocyte, displays defects that phenocopy aspects of diabetic nephropathy in animals fed chronic high dietary sucrose. Through functional studies, an OGT-Polycomb-Knot-Sns pathway was identified that links dietary sucrose to loss of the Nephrin ortholog Sticks and stones (Sns). Reducing OGT through genetic or drug means is sufficient to rescue loss of Sns, leading to overall extension of lifespan. Upregulation of the Knot ortholog EBF2 is demonstrated in glomeruli of human diabetic nephropathy patients and a mouse ob/ob diabetes model. Furthermore, rescue was demonstrated of Nephrin expression and cell viability in ebf2-/- primary podocytes cultured in high glucose. Therefore, this study provides evidence for a pathway that includes flux through the hexosamine biosynthetic pathway and the Polycomb gene complex, which in turn regulates the transcription factor Knot to regulate Sns expression. In cultured mouse primary podocytes, the Knot ortholog EBF2 similarly mediated response by Nephrin to high dietary sucrose. Finally, it was demonstrated how a chemical inhibitor of hexosamine flux can improve the whole-animal response to high dietary sucrose, providing a guideline for candidate therapeutics.

Huang, C.W., Wang, H.D., Bai, H., Wu, M.S., Yen, J.H., Tatar, M., Fu, T.F. and Wang, P.Y. (2015). Tequila regulates insulin-like signaling and extends lifespan in Drosophila melanogaster. J Gerontol A Biol Sci Med Sci [Epub ahead of print]. PubMed ID: 26265729
Summary:
The aging process is a universal phenomenon shared by all living organisms. The identification of longevity genes is important in that the study of these genes is likely to yield significant insights into human senescence. This study identified Tequila as a novel candidate gene involved in the regulation of longevity in Drosophila melanogaster. It was found that a hypomorphic mutation of Tequila (Teq f01792), as well as cell-specific downregulation of Tequila in insulin-producing neurons of the fly, significantly extends lifespan. Tequila deficiency-induced lifespan extension is likely to be associated with reduced insulin-like signaling, because Tequila mutant flies display several common phenotypes of insulin dysregulation, including reduced circulating Drosophila insulin-like peptide 2 (Dilp2), reduced Akt phosphorylation, reduced body size, and altered glucose homeostasis. These observations suggest that Tequila may confer life-span extension by acting as a modulator of Drosophila insulin-like signaling.

Zhikrevetskaya, S., Peregudova, D., Danilov, A., Plyusnina, E., Krasnov, G., Dmitriev, A., Kudryavtseva, A., Shaposhnikov, M. and Moskalev, A. (2015). Effect of low doses (5-40 cGy) of gamma-irradiation on lifespan and stress-related genes expression profile in Drosophila melanogaster. PLoS One 10: e0133840. PubMed ID: 26248317
Summary:
Studying of the effects of low doses of γ-irradiation is a crucial issue in different areas of interest, from environmental safety and industrial monitoring to aerospace and medicine. The goal of this work is to identify changes of lifespan and expression stress-sensitive genes in Drosophila melanogaster, exposed to low doses of γ-irradiation (5 - 40 cGy) on the imaginal stage of development. Although some changes in life extensity in males were identified (the effect of hormesis after the exposure to 5, 10 and 40 cGy) as well as in females (the effect of hormesis after the exposure to 5 and 40 cGy), they were not caused by the organism "physiological" changes. This means that the observed changes in life expectancy are not related to the changes of organism physiological functions after the exposure to low doses of ionizing radiation. The identified changes in gene expression are not dose-dependent, there is not any proportionality between dose and its impact on expression. These results reflect nonlinear effects of low dose radiation and sex-specific radio-resistance of the postmitotic cell state of Drosophila melanogaster imago.

Tuesday, August 18th

Kim, A.J., Fitzgerald, J.K. and Maimon, G. (2015). Cellular evidence for efference copy in Drosophila visuomotor processing. Nat Neurosci [Epub ahead of print]. PubMed ID: 26237362
Summary:
Each time a locomoting fly turns, the visual image sweeps over the retina and generates a motion stimulus. Classic behavioral experiments have suggested that flies use active neural-circuit mechanisms to suppress the perception of self-generated visual motion during intended turns. Direct electrophysiological evidence, however, has been lacking. This study found that visual neurons in Drosophila receive motor-related inputs during rapid flight turns. These inputs arrive with a sign and latency appropriate for suppressing each targeted cell's visual response to the turn. Precise measurements of behavioral and neuronal response latencies support the idea that motor-related inputs to optic flow-processing cells represent internal predictions of the expected visual drive induced by voluntary turns. Motor-related inputs to small object-selective visual neurons could reflect either proprioceptive feedback from the turn or internally generated signals. These results in Drosophila echo the suppression of visual perception during rapid eye movements in primates, demonstrating common functional principles of sensorimotor processing across phyla.

Mauss, A. S., Pankova, K., Arenz, A., Nern, A., Rubin, G. M. and Borst, A. (2015). Neural circuit to integrate opposing motions in the visual field. Cell 162: 351-362. PubMed ID: 26186189
Summary:
When navigating in their environment, animals use visual motion cues as feedback signals that are elicited by their own motion. Such signals are provided by wide-field neurons sampling motion directions at multiple image points as the animal maneuvers. Each one of these neurons responds selectively to a specific optic flow-field representing the spatial distribution of motion vectors on the retina. This study describes the discovery of a group of local, inhibitory interneurons in the fruit fly Drosophila key for filtering these cues. Using anatomy, molecular characterization, activity manipulation, and physiological recordings, this study demonstrates that these interneurons convey direction-selective inhibition to wide-field neurons with opposite preferred direction and provides evidence for how their connectivity enables the computation required for integrating opposing motions. The results indicate that, rather than sharpening directional selectivity per se, these circuit elements reduce noise by eliminating non-specific responses to complex visual information.

Das, A., Holmes, T. C. and Sheeba, V. (2015). dTRPA1 modulates afternoon peak of activity of fruit flies Drosophila melanogaster. PLoS One 10: e0134213. PubMed ID: 26226013
Summary:
Circadian rhythms in Drosophila under semi-natural conditions (or SN) have received much recent attention. One of the striking differences in the behaviour of wild type flies under SN is the presence of an additional peak of activity in the middle of the day. This is referred to as the afternoon peak (A-peak) and is absent under standard laboratory regimes using gated light and temperature cues. Although previous reports identified the physical factors that contribute towards the A-peak there is no evidence for underlying molecular mechanisms or pathways that control A-peak. This study reports that the A-peak is mediated by thermosensitive TRPA1 (Transient Receptor Potential A1) ion channels as this peak is absent in TRPA1 null mutants. Further, when natural cycles of light and temperature are simulated in the lab, the amplitude of the A-peak was found to be TRPA1-dependent. Although a few circadian neurons express TRPA1, modulation of A-peak is primarily influenced by non-CRY TRPA1 expressing neurons. Hence, it is proposed that A-peak of activity observed under SN is a temperature sensitive response in flies that is elicited through TRPA1 receptor signalling.

Newland, P.L., Al Ghamdi, M.S., Sharkh, S., Aonuma, H. and Jackson, C.W. (2015). Exposure to static electric fields leads to changes in biogenic amine levels in the brains of Drosophila. Proc Biol Sci 282(1812). PubMed ID: 26224706
Summary:
Natural and anthropogenic static electric fields are commonly found in the environment and can have both beneficial and harmful effects on many animals. This study investigated how the fruitfly responds to these fields and what the consequences of exposure are on the levels of biogenic amines in the brain. When given a choice in a Y-tube bioassay, Drosophila avoids electric fields, and the greater the field strength the more likely Drosophila are to avoid it. By comparing wild-type flies, flies with wings surgically removed and vestigial winged flies, it was found that the presence of intact wings is necessary to produce avoidance behaviour. It was also shown that Coulomb forces produced by electric fields physically lift excised wings, with the smaller wings of males being raised by lower field strengths than larger female wings. An analysis of neurochemical changes in the brains showed that a suite of changes in biogenic amine levels occurs following chronic exposure. Taken together, the study concludes that physical movements of the wings are used by Drosophila in generating avoidance behaviour and are accompanied by changes in the levels of amines in the brain, which in turn impact on behaviour. 

Monday, August 17th

Wingert, L. and DiNardo, S. (2015). Traffic jam functions in a branched pathway from Notch activation to niche cell fate. Development 142: 2268-2277. PubMed ID: 26092848
Summary:
The niche directs key behaviors of its resident stem cells, and is thus crucial for tissue maintenance, repair and longevity. However, little is known about the genetic pathways that guide niche specification and development. The male germline stem cell niche in Drosophila houses two stem cell populations and is specified within the embryonic gonad, thus making it an excellent model for studying niche development. The hub cells that form the niche are specified early by Notch activation. Over the next few hours, these individual cells then cluster together and take up a defined position before expressing markers of hub cell differentiation. This timing suggests that there are other factors for niche development yet to be defined. This study has identified a role for the large Maf transcription factor Traffic jam (Tj) in hub cell specification downstream of Notch. Tj downregulation is the first detectable effect of Notch activation in hub cells. Furthermore, Tj depletion is sufficient to generate ectopic hub cells that can recruit stem cells. Surprisingly, ectopic niche cells in tj mutants remain dispersed in the absence of Notch activation. This led th the uncovering of a branched pathway downstream of Notch in which Bowl functions to direct hub cell assembly in parallel to Tj downregulation.

Schardt, L., Ander, J. J., Lohmann, I. and Papagiannouli, F. (2015). Stage-specific control of niche positioning and integrity in the Drosophila testis. Mech Dev. PubMed ID: 26226434
Summary:
This study addressed the complex question of how complex structures are maintained after their initial specification by studying the Drosophila male stem cell niche, called the hub. Once specified, the hub cells need to maintain their position and architectural integrity through embryonic, larval and pupal stages of testis organogenesis and during adult life. The Hox gene Abd-B, in addition to its described role in male embryonic gonads, maintains the architecture and positioning of the larval hub from the germline by affecting integrin localization in the neighboring somatic cyst cells. The AbdB-Boss/Sev cascade affects integrin independent of Talin, while genetic interactions depict integrin as the central downstream player in this system. Focal adhesion and integrin-adaptor proteins within the somatic stem cells and cyst cells, such as Paxillin, Pinch and Vav, also contribute to proper hub integrity and positioning. During adult stages, hub positioning is controlled by Abd-B activity in the outer acto-myosin sheath, while Abd-B expression in adult spermatocytes exerts no effect on hub positioning and integrin localization. The data point at a cell- and stage-specific function of Abd-B and suggest that the occurrence of new cell types and cell interactions in the course of testis organogenesis made it necessary to adapt the whole system by reusing the same players for male stem cell niche positioning and integrity in an alternative manner.

Ayyub, C., Banerjee, K.K. and Joti, P. (2015). Reduction of Cullin-2 in somatic cells disrupts differentiation of germline stem cells in the Drosophila ovary. Dev Biol [Epub ahead of print]. PubMed ID: 26206612
Summary:
Signaling from a niche consisting of somatic cells is essential for maintenance of germline stem cells (GSCs) in the ovary of Drosophila. Decapentaplegic (Dpp), a type of bone morphogenetic protein (BMP) signal, emanating from the niche, is the most important signal for this process. Cullin proteins constitute the core of a multiprotein E3-ligase important for their functions viz. degradation or modification of proteins necessary for different cellular processes. This study found that a Cullin protein called Cullin-2 (Cul-2) is expressed in both somatic and germline cells of the Drosophila ovary. Reduction of Cul-2 in somatic cells causes upregulation of Dpp signal and produces accumulation of extra GSC-like cells inside germarium, the anteriormost structure of the ovary. These results suggest that Cullin-2 protein present in the somatic cells is involved in a non cell-autonomous regulation of the extent of Dpp signaling and thus controls the differentiation of GSCs to cystoblasts (CBs).

Antonello, Z. A., Reiff, T., Ballesta-Illan, E. and Dominguez, M. (2015). Robust intestinal homeostasis relies on cellular plasticity in enteroblasts mediated by miR-8-Escargot switch. EMBO J [Epub ahead of print]. PubMed ID: 26077448
Summary:
This study used tracing methods that allow simultaneously capturing the dynamics of intestinal stem and committed progenitor cells (called enteroblasts) and intestinal cell turnover with spatiotemporal resolution. Intestinal stem cells (ISCs) divide 'ahead' of demand during Drosophila midgut homeostasis. Their newborn enteroblasts, on the other hand, take on a highly polarized shape, acquire invasive properties and motility. They extend long membrane protrusions that make cell-cell contact with mature cells, while exercising a capacity to delay their final differentiation until a local demand materializes. This cellular plasticity is mechanistically linked to the epithelial-mesenchymal transition (EMT) programme mediated by escargot, a snail family gene. Activation of the conserved microRNA miR-8/miR-200 in "pausing" enteroblasts in response to a local cell loss promotes timely terminal differentiation via a reverse MET by antagonizing escargot. These findings unveil that robust intestinal renewal relies on hitherto unrecognized plasticity in enteroblasts and reveal their active role in sensing and/or responding to local demand.

Sunday, August 16th

Bonchuk, A., Maksimenko, O., Kyrchanova, O., Ivlieva, T., Mogila, V., Deshpande, G., Wolle, D., Schedl, P. and Georgiev, P. (2015). Functional role of dimerization and CP190 interacting domains of CTCF protein in Drosophila melanogaster. BMC Biol 13: 63. PubMed ID: 26248466
Summary:
This study analyzed the CTCF, one of the few insulator proteins conserved from flies to man. The study focused on the identification and characterization of two CTCF protein interaction modules. The first mediates CTCF multimerization, while the second mediates CTCF-CP190 interactions. The multimerization domain maps in the N-terminus of the CTCF protein and likely mediates the formation of tetrameric complexes. The CP190 interaction module encompasses a sequence ~200 amino acids long that spans the C-terminal and mediates interactions with the N-terminal BTB domain of the CP190 protein. CTCF protein lacking sequences critical for CP190 interactions is almost as effective as wild type in rescuing the phenotypic effects of a CTCF null allele. The mutation does, however, affect CP190 recruitment to specific insulator elements and has a modest effect on CTCF chromatin association. A protein lacking the N-terminal CTCF multimerization domain incompletely rescues the zygotic and maternal effect lethality of the null and does not rescue the defects in Abd-B regulation evident in surviving adult CTCF mutant flies. Elimination of maternally contributed CTCF at the onset of embryogenesis has quite different effects on development and Abd-B regulation than is observed when the homozygous mutant animals develop in the presence of maternally derived CTCF activity. These results indicate that CTCF-CP190 interactions are less critical for the in vivo functions of the CTCF protein than the N-terminal CTCF-CTCF interaction domain. Also, that the phenotypic consequences of CTCF mutations differ depending upon when and how CTCF activity is lost.

Liu, J., Zimmer, K., Rusch, D. B., Paranjape, N., Podicheti, R., Tang, H. and Calvi, B. R. (2015). DNA sequence templates adjacent nucleosome and ORC sites at gene amplification origins in Drosophila. Nucleic Acids Res [Epub ahead of print]. PubMed ID: 26227968
Summary:
Eukaryotic origins of DNA replication are bound by the origin recognition complex (ORC), which scaffolds assembly of a pre-replicative complex (pre-RC) that is then activated to initiate replication. Both pre-RC assembly and activation are strongly influenced by developmental changes to the epigenome, but molecular mechanisms remain incompletely defined. The activation of origins responsible for developmental gene amplification was examined in Drosophila. At a specific time in oogenesis, somatic follicle cells transition from genomic replication to a locus-specific replication from six amplicon origins. Previous evidence indicated that these amplicon origins are activated by nucleosome acetylation, but how this affects origin chromatin is unknown. This study examine nucleosome position in follicle cells using micrococcal nuclease digestion with Ilumina sequencing. The results indicate that ORC binding sites and other essential origin sequences are nucleosome-depleted regions (NDRs). Nucleosome position at the amplicons was highly similar among developmental stages during which ORC is or is not bound, indicating that being an NDR is not sufficient to specify ORC binding. Importantly, the data suggest that nucleosomes and ORC have opposite preferences for DNA sequence and structure. It is proposed that nucleosome hyperacetylation promotes pre-RC assembly onto adjacent DNA sequences that are disfavored by nucleosomes but favored by ORC

Pengelly, A. R., Kalb, R., Finkl, K. and Muller, J. (2015). Transcriptional repression by PRC1 in the absence of H2A monoubiquitylation. Genes Dev 29: 1487-1492. PubMed ID: 26178786
Summary:
Histone H2A monoubiquitylation (H2Aub) is considered to be a key effector in transcriptional repression by Polycomb-repressive complex 1 (PRC1). Drosophila was analyzed with a point mutation in the PRC1 subunit Sex combs extra (Sce) that abolishes its H2A ubiquitylase activity or with point mutations in the H2A and H2Av residues ubiquitylated by PRC1. H2Aub is essential for viability and required for efficient histone H3 Lys27 trimethylation by PRC2 early in embryogenesis. However, H2Aub-deficient animals fully maintain repression of PRC1 target genes and do not show phenotypes characteristic of Polycomb group mutants. PRC1 thus represses canonical target genes independently of H2Aub.

Pascual-Garcia, P., Jeong, J. and Capelson, M. (2014). Nucleoporin Nup98 associates with Trx/MLL and NSL histone-modifying complexes and regulates Hox gene expression. Cell Rep 9: 433-442. PubMed ID: 25310983
Summary:
The nuclear pore complex is a transport channel embedded in the nuclear envelope and made up of 30 different components termed nucleoporins (Nups). In addition to their classical role in transport, a subset of Nups has a conserved role in the regulation of transcription via direct binding to chromatin. The molecular details of this function remain obscure, and it is unknown how metazoan Nups are recruited to their chromatin locations or what transcription steps they regulate. This study demonstrates genome-wide and physical association between Nup98 and histone-modifying complexes MBD-R2/NSL and Trx/MLL. Importantly, a requirement was identified for MBD-R2 in recruitment of Nup98 to many of its genomic target sites. Consistent with its interaction with the Trx/MLL complex, Nup98 is shown to be necessary for Hox gene expression in developing fly tissues. These findings introduce roles of Nup98 in epigenetic regulation that may underlie the basis of oncogenicity of Nup98 fusions in leukemia.

Chakraborty, R., Li, Y., Zhou, L. and Golic, K.G. (2015). Corp regulates P53 in Drosophila melanogaster via a negative feedback loop. PLoS Genet 11: e1005400. PubMed ID: 26230084
Summary:
The tumor suppressor P53 is a critical mediator of the apoptotic response to DNA double-strand breaks through the transcriptional activation of pro-apoptotic genes. This mechanism is evolutionarily conserved from mammals to lower invertebrates, including Drosophila melanogaster. P53 also transcriptionally induces its primary negative regulator, Mdm2, which has not been found in Drosophila. This study identified the Drosophila gene companion of reaper (corp) as a gene whose overexpression promotes survival of cells with DNA damage in the soma but reduces their survival in the germline. These disparate effects are shared by p53 mutants, suggesting that Corp may be a negative regulator of P53. Confirming this supposition, it was found that corp negatively regulates P53 protein level. It has been previously shown that P53 transcriptionally activates corp; thus, Corp produces a negative feedback loop on P53. It was further found that Drosophila Corp shares a protein motif with vertebrate Mdm2 in a region that mediates the Mdm2:P53 physical interaction. In Corp, this motif mediates physical interaction with Drosophila P53. These findings implicate Corp as a functional analog of vertebrate Mdm2 in flies.

Mansilla, A., Martín, F.A., Martín, D. and Ferrús, A. (2015). Ligand-independent requirements of steroid receptors EcR and USP for cell survival. Cell Death Differ [Epub ahead of print]. PubMed ID: 26250909
Summary:
The active form of the Drosophila steroid hormone ecdysone, 20-hydroxyecdysone (20E), binds the heterodimer EcR/USP nuclear receptor to regulate target genes that elicit proliferation, cell death and differentiation during insect development. This study shows that the prothoracic gland (PG), the major steroid-producing organ of insect larvae, requires EcR and USP to survive in a critical period previous to metamorphosis, and that this requirement is 20E-independent. The cell death induced by the downregulation of these receptors involves the activation of the JNK-encoding basket gene. Also, while PG cell death prevents ecdysone production, blocking hormone synthesis or secretion in normal PG does not lead to cell death, demonstrating further the ecdysone-independent nature of the receptor-deprivation cell death. In contrast to PG cells, wing disc or salivary glands cells do not require these receptors for survival, revealing their cell and developmental time specificity. For exploring the potential use of this feature of steroid receptors in cancer, tumor overgrowth induced by altered yorkie signaling was assayed. This overgrowth is suppressed by EcR downregulation in PG, but not in wing disc, cells. The mechanism of all these cell death features is based on the transcriptional regulation of reaper. These novel and context-dependent functional properties for EcR and USP receptors may help to understand the heterogeneous responses to steroid-based therapies in human pathologies.

Garcia-Hughes, G., Link, N., Ghosh, A. B. and Abrams, J. M. (2015). Hid arbitrates collective cell death in the Drosophila wing. Mech Dev [Epub ahead of print]. PubMed ID: 26226435
Summary:
Elimination of cells and tissues by apoptosis is a highly conserved and tightly regulated process. In Drosophila, the entire wing epithelium is completely removed shortly after eclosion. The cells that make up this epithelium are collectively eliminated through a highly synchronized form of apoptotic cell death, involving canonical apoptosome genes. This study presents evidence that collective cell death does not require cell-cell contact and shows that transcription of the IAP antagonist, head involution defective, is acutely induced in wing epithelial cells prior to this process. hid mRNAs accumulate to levels that exceed a component of the ribosome and likewise, Hid protein becomes highly abundant in these same cells. hid function is required for collective cell death, since loss of function mutants show persisting wing epithelial cells and, furthermore, silencing of the hormone Bursicon in the CNS produced collective cell death defective phenotypes manifested in the wing epithelium. Taken together, these observations suggest that acute induction of Hid primes wing epithelial cells for collective cell death and that Bursicon is a strong candidate to trigger this process, possibly by activating the abundant pool of Hid protein already present.

Caputa, G., Zhao, S., Criado, A. E., Ory, D. S., Duncan, J. G. and Schaffer, J. E. (2015). RNASET2 is required for ROS propagation during oxidative stress-mediated cell death. Cell Death Differ. PubMed ID: 26206090
Summary:
RNASET2 is a ubiquitously expressed acidic ribonuclease that has been implicated in diverse pathophysiological processes including tumorigeneis, vitiligo, asthenozoospermia, and neurodegeneration. Prior studies indicate that RNASET2 is induced in response to oxidative stress and that overexpression of RNASET2 sensitizes cells to reactive oxygen species (ROS)-induced cell death through a mechanism that is independent of catalytic activity. This study reports a loss-of-function genetic screen that identified RNASET2 as an essential gene for lipotoxic cell death. Haploinsufficiency of RNASET2 confers increased antioxidant capacity and generalized resistance to oxidative stress-mediated cell death in cultured cells. This function is critically dependent on catalytic activity. Furthermore, knockdown of RNASET2 in the Drosophila fat body confers increased survival in the setting of oxidative stress inducers. Together, these findings demonstrate that RNASET2 regulates antioxidant tone and is required for physiological ROS responses.

Friday, August 14th

Sun, D. and Buttitta, L. (2015). Protein phosphatase 2A promotes the transition to G0 during terminal differentiation in Drosophila. Development [Epub ahead of print]. PubMed ID: 26253406
Summary:
Protein phosphatase type 2A complex (PP2A) has been known as a tumor suppressor for over two decades, but it remains unclear exactly how it suppresses tumor growth. This study provides data indicating a novel role for PP2A in promoting the transition to quiescence upon terminal differentiation in vivo. Using Drosophila eyes and wings as a model, it was found that compromising PP2A activity during the final cell cycle prior to a developmentally controlled cell cycle exit leads to extra cell divisions and delays entry into quiescence. By systematically testing the regulatory subunits of Drosophila PP2A, it was found that the B56 family member widerborst (wdb) is required for the role of PP2A in promoting the transition to quiescence. Cells in differentiating tissues with compromised PP2A retain high Cdk2 activity when they should be quiescent, and genetic epistasis tests demonstrate that ectopic CyclinE/Cdk2 activity is responsible for the extra cell cycles caused by PP2A inhibition. The loss of wdb/PP2A function cooperates with aberrantly high Cyclin E protein, allowing cells to bypass a robust G0 late in development. This provides an example of how loss of PP2A can cooperate with oncogenic mutations in cancer. The study proposes that the wdb/PP2A complex plays a novel role in differentiating tissues to promote developmentally controlled quiescence through the regulation of CyclinE/Cdk2 activity.

Alexander, J. L., Barrasa, M. I. and Orr-Weaver, T. L. (2015). Replication fork progression during re-replication requires the DNA damage checkpoint and double-strand break repair. Curr Biol 25: 1654-1660. PubMed ID: 26051888
Summary:
Replication origins are under tight regulation to ensure activation occurs only once per cell cycle. Origin re-firing in a single S phase leads to the generation of DNA double-strand breaks (DSBs) and activation of the DNA damage checkpoint. If the checkpoint is blocked, cells enter mitosis with partially re-replicated DNA that generates chromosome breaks and fusions. It has been proposed that fork instability and DSBs formed during re-replication are the result of head-to-tail collisions and collapse of adjacent replication forks. This study utilized the Drosophila ovarian follicle cells, which exhibit re-replication under precise developmental control, to model the consequences of re-replication at actively elongating forks. Re-replication occurs from specific replication origins at six genomic loci, termed Drosophila amplicons in follicle cells (DAFCs). Precise developmental timing of DAFC origin firing permits identification of forks at defined points after origin initiation. This study shows that DAFC re-replication causes fork instability and generates DSBs at sites of potential fork collisions. Immunofluorescence and ChIP-seq demonstrate the DSB marker γH2Av is enriched at elongating forks. Fork progression is reduced in the absence of DNA damage checkpoint components and nonhomologous end-joining (NHEJ), but not homologous recombination. NHEJ appears to continually repair forks during re-replication to maintain elongation.

Rodrigues, N. T., Lekomtsev, S., Jananji, S., Kriston-Vizi, J., Hickson, G. R. and Baum, B. (2015). Kinetochore-localized PP1-Sds22 couples chromosome segregation to polar relaxation. Nature [Epub ahead of print]. PubMed ID: 26168397
Summary:
Cell division requires the precise coordination of chromosome segregation and cytokinesis. This coordination is achieved by the recruitment of an actomyosin regulator, Ect2, to overlapping microtubules at the centre of the elongating anaphase spindle. Ect2 then signals to the overlying cortex to promote the assembly and constriction of an actomyosin ring between segregating chromosomes. By studying division in proliferating Drosophila and human cells this study demonstrates the existence of a second, parallel signalling pathway, which triggers the relaxation of the polar cell cortex at mid anaphase. This is independent of furrow formation, centrosomes and microtubules and, instead, depends on PP1 phosphatase and its regulatory subunit Sds22. As separating chromosomes move towards the polar cortex at mid anaphase, kinetochore-localized PP1-Sds22 helps to break cortical symmetry by inducing the dephosphorylation and inactivation of ezrin/radixin/moesin proteins at cell poles. This promotes local softening of the cortex, facilitating anaphase elongation and orderly cell division. In summary, this identifies a conserved kinetochore-based phosphatase signal and substrate, which function together to link anaphase chromosome movements to cortical polarization, thereby coupling chromosome segregation to cell division.

Richens, J.H., Barros, T.P., Lucas, E.P., Peel, N., Pinto, D.M., Wainman, A. and Raff, J.W. (2015). The Drosophila Pericentrin-like-protein (PLP) cooperates with Cnn to maintain the integrity of the outer PCM. Biol Open [Epub ahead of print]. PubMed ID: 26157019
Summary:
Centrosomes comprise a pair of centrioles surrounded by a matrix of pericentriolar material (PCM). In vertebrate cells, Pericentrin plays an important part in mitotic PCM assembly, but the Drosophila Pericentrin-like protein (PLP) appears to have a more minor role in mitotic fly cells. This study investigates the function of PLP during the rapid mitotic cycles of the early Drosophila embryo. Unexpectedly, it was found that PLP is specifically enriched in the outer-most regions of the PCM, where it largely co-localizes with the PCM scaffold protein Cnn. In the absence of PLP the outer PCM appears to be structurally weakened, and it rapidly disperses along the centrosomal MTs. As a result, centrosomal MTs are subtly disorganized in embryos lacking PLP, although mitosis is largely unperturbed and these embryos develop and hatch at near-normal rates. Y2H analysis reveals that PLP can potentially form multiple interactions with itself and with the PCM recruiting proteins Asl, Spd-2 and Cnn. A deletion analysis suggests that PLP participates in a complex network of interactions that ultimately help to strengthen the PCM.

Thursday, August, 13th

Panneton, V., Nath, A., Sader, F., Delaunay, N., Pelletier, A., Maier, D., Oh, K. and Hipfner, D. R. (2015). Regulation of catalytic and non-catalytic functions of the Drosophila Ste20 kinase Slik by activation segment phosphorylation. J Biol Chem [Epub ahead of print]. PubMed ID: 26170449
Summary:
Protein kinases carry out important functions in cells both by phosphorylating substrates and by means of regulated non-catalytic activities. Such non-catalytic functions have been ascribed to many kinases, including some members of the Ste20 family. The Drosophila Ste20 kinase Slik phosphorylates and activates Moesin in developing epithelial tissues to promote epithelial tissue integrity. It also functions non-catalytically to promote epithelial cell proliferation and tissue growth. A structure-function analysis was carried out to determine how these two distinct activities of Slik are controlled. The conserved C-terminal coiled-coil domain (CCD) of Slik, which is necessary and sufficient for apical localization of the kinase in epithelial cells, is not required for Moesin phosphorylation but is critical for the growth-promoting function of Slik. Slik is auto- and trans-phosphorylated in vivo. Phosphorylation of at least two of three conserved sites in the activation segment is required for both efficient catalytic activity and non-catalytic signaling. Slik function is thus dependent upon proper localization of the kinase via the CCD and activation via activation segment phosphorylation, which enhances both phosphorylation of substrates like Moesin and engagement of effectors of its non-catalytic growth-promoting activity.

Shi, J., Liu, Y., Xu, X., Zhang, W., Yu, T., Jia, J. and Liu, C. (2015). Deubiquitinase USP47/UBP64E regulates β-Catenin ubiquitination and degradation and plays a positive role in wnt signaling. Mol Cell Biol [Epub ahead of print]. PubMed ID: 26169834
Summary:
Wnt signaling plays important roles in development and tumorigenesis. A central question in the Wnt pathway is the regulation of β-catenin (see Drosophila Armadillo). Phosphorylation of β-catenin by CK1α and GSK3 (see Drosophila CK1α and Shaggy) promotes β-catenin binding to β-TrCP (see Drosophila Slimb), leading β-catenin degradation through the proteasome. Phosphorylation and ubiquitination of β-catenin have been well characterized, however it is unknown whether and how a deubiquitinase is involved. By screening RNAi libraries, this study identified USP47 as a deubiquitinase that prevents β-catenin ubiquitination. Inactivation of USP47 by RNAi increased β-catenin ubiquitination, attenuated Wnt signaling and repressed cancer cell growth. Furthermore, USP47 deubiquitinates itself, whereas β-TrCP promotes USP47 ubiquitination through interaction with an atypical motif in USP47. Finally, in vivo studies in Drosophila wing suggest that UBP64E, the USP47 counterpart in Drosophila, is required for Armadillo stabilization and plays a positive role in regulating Wnt target gene expression.

Williams, M. J., et al. (2015). The obesity-linked gene Nudt3 Drosophila homolog Aps is associated with insulin signalling. Mol Endocrinol: ME20151077. PubMed ID: 26168034
Summary:
Several genome wide association studies have linked the Nudix hydralase family member Nucleoside Diphosphate-Linked Moiety X Motif 3 (NUDT3) to obesity. However, the manner of NUDT3 involvement in obesity is unknown and NUDT3 expression, regulation and signalling in the central nervous system (CNS) has not been studied. This study performed an extensive expression analysis in mice, as well as knocked down the Drosophila NUDT3 homolog Aps in the nervous system to determine its effect on metabolism. Detailed in situ hybridization studies in the mouse brain revealed abundant Nudt3 mRNA and protein expression throughout the brain, including reward and feeding related regions of the hypothalamus and amygdala; while Nudt3 mRNA expression was significantly up-regulated in the hypothalamus and brain stem of food-deprived mice. Knocking down Aps in the Drosophila CNS, or a subset of median neurosecretory cells, known as the insulin-producing cells (IPCs), induces hyperinsulinemia-like phenotypes, including a decrease in circulating trehalose levels, as well as significantly decreasing all carbohydrate levels under starvation conditions. Moreover, lowering Aps IPC expression leads to a decreased ability to recruit these lipids during starvation. Also, loss of neuronal Aps expression caused a starvation susceptibility phenotype, while inducing hyperphagia. Finally, loss of IPC Aps lowered the expression of Akh, Ilp6 and Ilp3, genes known to be inhibited by insulin signalling. These results point towards a role for this gene in the regulation of insulin signalling which could explain the robust association to obesity in humans.

Wei, Z., Li, Y., Ye, F. and Zhang, M. (2015). Structural basis for the phosphorylation-regulated interaction between the cytoplasmic tail of cell polarity protein crumbs and the actin-binding protein moesin. J Biol Chem 290: 11384-11392. PubMed ID: 25792740
Summary:
The type I transmembrane protein Crumbs (Crb) plays critical roles in the establishment and maintenance of cell polarities in diverse tissues. As such, mutations of Crb can cause different forms of cancers. The cell intrinsic role of Crb in cell polarity is governed by its conserved, 37-residue cytoplasmic tail (Crb-CT) via binding to moesin and protein associated with Lin7-1 (PALS1). However, the detailed mechanism governing the Crb.moesin interaction and the balance of Crb in binding to moesin and PALS1 are not well understood. This paper reports the 1.5 A resolution crystal structure of the moesin protein 4.1/ezrin/radixin/moesin (FERM).Crb-CT complex of mouse, revealing that both the canonical FERM binding motif and the postsynaptic density protein-95/Disc large-1/Zonula occludens-1 (PDZ) binding motif of Crb contribute to the Crb.moesin interaction. It was further demonstrated that phosphorylation of Crb-CT by atypical protein kinase C (aPKC) disrupts the Crb.moesin association but has no impact on the Crb.PALS1 interaction. The above results indicate that, upon the establishment of the apical-basal polarity in epithelia, apical-localized aPKC can actively prevent the Crb.moesin complex formation and thereby shift Crb to form complex with PALS1 at apical junctions. Therefore, Crb may serve as an aPKC-mediated sensor in coordinating contact-dependent cell growth inhibition in epithelial tissues.

Wednesday, August 12th

Hallier, B., Hoffmann, J., Roeder, T., Tögel, M., Meyer, H. and Paululat, A. (2015). The bHLH transcription factor Hand regulates the expression of genes critical to heart and muscle function in Drosophila melanogaster. PLoS One 10: e0134204. PubMed ID: 26252215
Summary:
Hand proteins belong to the highly conserved family of basic Helix-Loop-Helix transcription factors that are critical to distinct developmental processes, including cardiogenesis and neurogenesis in vertebrates. In Drosophila melanogaster a single orthologous hand gene is expressed with absence of the respective protein causing semilethality during early larval instars. Surviving adult animals suffer from shortened lifespan associated with a disorganized myofibrillar structure being apparent in the dorsal vessel, the wing hearts and in midgut tissue. Based on these data, the major biological significance of Hand seems to be related to muscle development, maintenance or function; however, up to now the physiological basis for Hand functionality remains elusive. Thus, the identification of genes whose expression is, directly or indirectly, regulated by Hand has considerable relevance with respect to understanding its biological functionality in flies and vertebrates. Beneficially, hand mutants are viable and exhibit affected tissues, which renders Drosophila an ideal model to investigate up- or downregulated target genes by a comparative microarray approach focusing on the respective tissues from mutant specimens. This study reveals for the first time that Drosophila Hand regulates the expression of numerous genes of diverse physiological relevancy, including distinct factors required for proper muscle development and function such as Zasp52 or Msp-300. These results relate Hand activity to muscle integrity and functionality and may thus be highly beneficial to the evaluation of corresponding hand phenotypes.

Lu, Q., Schafer, D. A. and Adler, P. N. (2015). The Drosophila planar polarity gene multiple wing hairs directly regulates the actin cytoskeleton. Development 142: 2478-2486. PubMed ID: 26153232
Summary:
The evolutionarily conserved frizzled/starry night (fz/stan) pathway regulates planar cell polarity (PCP) in vertebrates and invertebrates. This pathway has been extensively studied in the Drosophila wing, where it is manifested by an array of distally pointing cuticular hairs. Using in vivo imaging this study has found that, early in hair growth, cells have multiple actin bundles and hairs that subsequently fuse into a single growing hair. The downstream PCP gene multiple wing hairs (mwh) plays a key role in this process and acts to antagonize the actin cytoskeleton. In mwh mutants hair initiation is not limited to a small region at the distal edge of pupal wing cells as in wild type, resulting in multiple hairs with aberrant polarity. Extra actin bundles/hairs are formed and do not completely fuse, in contrast to wild type. As development proceeded additional hairs continued to form, further increasing hair number. This study identified a fragment of Mwh with in vivo rescue activity and has found that it bound and bundled F-actin filaments and inhibited actin polymerization in in vitro actin assays. The loss of these activities can explain the mwh mutant phenotype. The data suggest a model whereby, prior to hair initiation, proximally localized Mwh inhibits actin polymerization resulting in polarized activation of the cytoskeleton and hair formation on the distal side of wing cells. During hair growth Mwh is found in growing hairs, where it is suggested to function to promote the fusion of actin bundles and inhibit the formation of additional actin bundles that could lead to extra hairs.

Ray, R. P., Matamoro-Vidal, A., Ribeiro, P. S., Tapon, N., Houle, D., Salazar-Ciudad, I. and Thompson, B. J. (2015). Patterned anchorage to the apical extracellular matrix defines tissue shape in the developing appendages of Drosophila. Dev Cell [Epub ahead of print]. PubMed ID: 26190146
Summary:
How tissues acquire their characteristic shape is a fundamental unresolved question in biology. While genes have been characterized that control local mechanical forces to elongate epithelial tissues, genes controlling global forces in epithelia have yet to be identified. This study describes a genetic pathway that shapes appendages in Drosophila by defining the pattern of global tensile forces in the tissue. In the appendages, shape arises from tension generated by cell constriction and localized anchorage of the epithelium to the cuticle via the apical extracellular-matrix protein Dumpy (Dp). Altering Dp expression in the developing wing results in predictable changes in wing shape that can be simulated by a computational model that incorporates only tissue contraction and localized anchorage. Three other wing shape genes, narrow, tapered, and lanceolate, encode components of a pathway that modulates Dp distribution in the wing to refine the global force pattern and thus wing shape.

Takahara, B. and Takahashi, K. H. (2015). Genome-wide association study on male genital shape and size in Drosophila melanogaster. PLoS One 10: e0132846. PubMed ID: 26182199
Summary:
Male genital morphology of animals with internal fertilization and promiscuous mating systems have been one of the most diverse and rapidly evolving morphological traits. This study used highly inbred whole genome sequenced strains of D. melanogaster to perform genome wide association analysis on posterior lobe morphology. The first and second principal components (PC1 and PC2) obtained from Fourier analysis explained approximately 88% of the total variation of the posterior lobe shape. The association was examined between the principal component scores and posterior lobe size and 1902142 single nucleotide polymorphisms (SNPs). As a result, 15, 14 and 15 SNPs were obtained for PC1, PC2 and posterior lobe size with P-values smaller than 10-5. Based on the location of the SNPs, 13, 13 and six protein coding genes were identified as potential candidates for PC1, PC2 and posterior lobe size, respectively. In addition to the previous findings showing that the intraspecific posterior shape variation are regulated by multiple QTL with strong effects, the present study suggests that the intraspecific variation may be under polygenic regulation with a number of loci with small effects. Further studies are required for investigating whether these candidate genes are responsible for the intraspecific posterior lobe shape variation.

Tuesday, August 11th

Jonson, M., Pokrzywa, M., Starkenberg, A., Hammarstrom, P. and Thor, S. (2015). Systematic Aβ analysis in Drosophila reveals high toxicity for the 1-42, 3-42 and 11-42 peptides, and emphasizes N- and C-Terminal residues. PLoS One 10: e0133272. PubMed ID: 26208119
Summary:
Brain amyloid plaques are a hallmark of Alzheimer's disease (AD), and primarily consist of aggregated peptides. While Aβ 1-40 and Aβ 1-42 are the most abundant, a number of other Aβ peptides have also been identified. Studies have indicated differential toxicity for these various Aβ peptides, but in vivo toxicity has not been systematically tested. To address this issue, this study generated improved transgenic Drosophila UAS strains expressing 11 pertinent Aβ peptides. UAS transgenic flies were generated by identical chromosomal insertion, hence removing any transgenic position effects, and crossed to a novel and robust Gal4 driver line. Using this improved Gal4/UAS set-up, survival and activity assays revealed that Aβ 1-42 severely shortens lifespan and reduces activity. N-terminal truncated peptides were quite toxic, with 3-42 similar to 1-42, while 11-42 showed a pronounced but less severe phenotype. N-terminal mutations in 3-42 (E3A) or 11-42 (E11A) resulted in reduced toxicity for 11-42, and reduced aggregation for both variants. Strikingly, C-terminal truncation of Aβ were non-toxic. In contrast, C-terminal extension to 1-43 resulted in reduced lifespan and activity, but not to the same extent as 1-42. Mutating residue 42 in 1-42 greatly reduced Aβ accumulation and toxicity. Histological and biochemical analysis revealed strong correlation between in vivo toxicity and brain Aβ aggregate load, as well as amount of insoluble Aβ. This systematic Drosophila in vivo and in vitro analysis reveals crucial N- and C-terminal specificity for Aβ neurotoxicity and aggregation, and underscores the importance of residues 1-10 and E11, as well as a pivotal role of A42.

Sanchez-Díaz, I., Rosales-Bravo, F., Reyes-Taboada, J.L., Covarrubias, A.A., Narvaez-Padilla, V. and Reynaud, E. (2015). The Esg gene is involved in nicotine sensitivity in Drosophila melanogaster. PLoS One 10: e0133956. PubMed ID: 26222315
Summary:
In humans, there is a strong correlation between sensitivity to substances of abuse and addiction risk. This differential tolerance to drugs has a strong genetic component. The identification of human genetic factors that alter drug tolerance has been a difficult task. For this reason and taking advantage of the fact that Drosophila responds similarly to humans to many drugs, and that genetically it has a high degree of homology (sharing at least 70% of genes known to be involved in human genetic diseases), this study looked for genes in Drosophila that alter their nicotine sensitivity. An instantaneous nicotine vaporization technique was developed that exposed flies in a reproducible way. The amount of nicotine sufficient to "knock out" half of control flies for 30 minutes was determined and this parameter was defined as Half Recovery Time (HRT). Two fly lines, L4 and L70, whose HRT was significantly longer than control´s were identified. The L4 insertion is a loss of function allele of the transcriptional factor escargot (esg), whereas L70 insertion causes miss-expression of the microRNA cluster miR-310-311-312-313 (miR-310c). It was demonstrated that esg loss of function induces nicotine sensitivity possibly by altering development of sensory organs and neurons in the medial section of the thoracoabdominal ganglion. The ectopic expression of the miR-310c also induces nicotine sensitivity by lowering Esg levels thus disrupting sensory organs and possibly to the modulation of other miR-310c targets.

El-Daher, M. T., Hangen, E., Bruyere, J., Poizat, G., Al-Ramahi, I., Pardo, R., Bourg, N., Souquere, S., Mayet, C., Pierron, G., Leveque-Fort, S., Botas, J., Humbert, S. and Saudou, F. (2015). Huntingtin proteolysis releases non-polyQ fragments that cause toxicity through dynamin 1 dysregulation. EMBO J. PubMed ID: 26165689
Summary:
Cleavage of mutant huntingtin (HTT) is an essential process in Huntington's disease (HD), an inherited neurodegenerative disorder. Cleavage generates N-ter fragments that contain the polyQ stretch and whose nuclear toxicity is well established. However, the functional defects induced by cleavage of full-length HTT remain elusive. Moreover, the contribution of non-polyQ C-terminal fragments is unknown. Using time- and site-specific control of full-length HTT proteolysis, this study shows that specific cleavages are required to disrupt intramolecular interactions within HTT and to cause toxicity in cells and flies. Surprisingly, in addition to the canonical pathogenic N-ter fragments, the C-ter fragments generated, that do not contain the polyQ stretch, induced toxicity via dilation of the endoplasmic reticulum (ER) and increased ER stress. C-ter HTT bound to dynamin 1 and subsequently impaired its activity at ER membranes. These findings support a role for HTT on dynamin 1 function and ER homoeostasis. Proteolysis-induced alteration of this function may be relevant to disease.

Ojelade, S. A., et al. (2015). Rsu1 regulates ethanol consumption in Drosophila and humans. Proc Natl Acad Sci U S A 112: E4085-4093. PubMed ID: 26170296
Summary:
Alcohol abuse is highly prevalent, but little is understood about the molecular causes. This study reports that Ras suppressor 1 (Rsu1) affects ethanol consumption in flies and humans. Drosophila lacking Rsu1 show reduced sensitivity to ethanol-induced sedation. Rsu1 is required in the adult nervous system for normal sensitivity;t it acts downstream of the integrin cell adhesion molecule and upstream of the Rac1 GTPase to regulate the actin cytoskeleton. In an ethanol preference assay, global loss of Rsu1 causes high naive preference. In contrast, flies lacking Rsu1 only in the mushroom bodies of the brain show normal naive preference but then fail to acquire ethanol preference like normal flies. Rsu1 is, thus, required in distinct neurons to modulate naive and acquired ethanol preference. In humans, polymorphisms in RSU1 are associated with brain activation in the ventral striatum during reward anticipation in adolescents and alcohol consumption in both adolescents and adults. Together, these data suggest a conserved role for integrin/Rsu1/Rac1/actin signaling in modulating reward-related phenotypes, including ethanol consumption, across phyla.

Monday, August 10th

Koles, K., Messelaar, E. M., Feiger, Z., Yu, C. J., Frank, C. A. and Rodal, A. A. (2015). The EHD protein Past1 controls postsynaptic membrane elaboration and synaptic function. Mol Biol Cell [Epub ahead of print]. PubMed ID: 26202464
Summary:
Membranes form elaborate structures that are highly tailored to their specialized cellular functions, yet the mechanisms by which these structures are shaped remain poorly understood. This study shows that the conserved membrane-remodeling C-terminal Eps15 Homology Domain (EHD) protein Past1 is required for the normal assembly of the subsynaptic muscle membrane reticulum (SSR) at the Drosophila melanogaster larval neuromuscular junction (NMJ). past1 mutants exhibit altered NMJ morphology, decreased synaptic transmission, reduced glutamate receptor levels, and a deficit in synaptic homeostasis. The membrane-remodeling proteins Amphiphysin and Syndapin colocalize with Past1 in distinct SSR subdomains, and collapse into Amphiphysin-dependent membrane nodules in the SSR of past1 mutants. These results suggest a mechanism by which the coordinated actions of multiple lipid-binding proteins lead to the elaboration of increasing layers of the SSR, and uncover new roles for an EHD protein at synapses.

Woznicka, O., Gorlich, A., Sigrist, S. and Pyza, E. (2015). BRP-170 and BRP190 isoforms of Bruchpilot protein differentially contribute to the frequency of synapses and synaptic circadian plasticity in the visual system of Drosophila. Front Cell Neurosci 9: 238. PubMed ID: 26175667
Summary:
In the first optic neuropil (lamina) of the optic lobe of Drosophila melanogaster, two classes of synapses, tetrad and feedback, show daily rhythms in the number and size of presynaptic profiles examined at the level of transmission electron microscopy (TEM). Number of tetrad presynaptic profiles increases twice a day, once in the morning and again in the evening, and their presynaptic ribbons are largest in the evening. In contrast, feedback synapses peak at night. The large scaffold protein Bruchpilot (BRP) is a major essential constituent of T-bars, with two major isoforms of 190 and 170 kD forming T-bars of the peripheral neuromuscular junctions (NMJ) synapses and in the brain. In the BRPDelta190 lacking BRP-190 there was almost 50% less tetrad synapses demonstrable than when both isoforms were present. The lack of BRP-170 and BRP-190 increased and decreased, respectively the number of feedback synapses, indicating that BRP-190 forms most of the feedback synapses. The oscillations in the number and size of presynaptic elements seem to depend on a different contribution of BRP isoforms in a presynaptic element at different time during the day and night and at various synapse types.

Maruzs, T., Lorincz, P., Szatmári, Z., Széplaki, S., Sándor, Z., Lakatos, Z., Puska, G., Juhász, G. and Sass, M. (2015). Retromer ensures the degradation of autophagic cargo via maintaining lysosome function in Drosophila. Traffic [Epub ahead of print]. PubMed ID: 26172538
Summary:
The retromer is an evolutionarily conserved coat complex that consists of Vps26, Vps29, Vps35 and a heterodimer of sorting nexin (Snx) protein in yeast. Retromer mediates the recycling of transmembrane proteins from endosomes to the trans-Golgi network, including receptors that are essential for the delivery of hydrolytic enzymes to lysosomes. Besides its function in lysosomal enzyme receptor recycling, involvement of retromer has also been proposed in a variety of vesicular trafficking events, including early steps of autophagy and endocytosis. This study shows that the late stages of autophagy and endocytosis are impaired in Vps26 and Vps35 deficient Drosophila larval fat body cells, but formation of autophagosomes and endosomes is not compromised. Accumulation of aberrant autolysosomes and amphisomes in the absence of retromer function appears to be the consequence of decreased degradative capacity, as they contain undigested cytoplasmic material. Accordingly, it was shown that retromer is required for proper cathepsin L trafficking mainly independent of LERP, the Drosophila homolog of the cation-independent mannose 6-phosphate receptor. Finally, it was found that Snx3 and Snx6 are also required for proper autolysosomal degradation in Drosophila larval fat body cells.

Johnson, A. E., Shu, H., Hauswirth, A. G., Tong, A. and Davis, G. W. (2015). VCP-dependent muscle degeneration is linked to defects in a dynamic tubular lysosomal network. Elife 4. PubMed ID: 26167652
Summary:
Lysosomes are classically viewed as vesicular structures to which cargos are delivered for degradation. This study identified a network of dynamic, tubular lysosomes that extends throughout Drosophila muscle, in vivo. Live imaging reveals that autophagosomes merge with tubular lysosomes and that lysosomal membranes undergo extension, retraction, fusion and fission. The dynamics and integrity of this tubular lysosomal network requires VCP, an AAA-ATPase that, when mutated, causes degenerative diseases of muscle, bone and neurons. Human VCP rescues the defects caused by loss of Drosophila VCP and overexpression of disease relevant VCP transgenes dismantles tubular lysosomes, linking tubular lysosome dysfunction to human VCP-related diseases. Finally, disruption of tubular lysosomes correlates with impaired autophagosome-lysosome fusion, increased cytoplasmic poly-ubiquitin aggregates, lipofuscin material, damaged mitochondria and impaired muscle function. It is proposed that VCP sustains sarcoplasmic proteostasis, in part, by controlling the integrity of a dynamic tubular lysosomal network.

Hagel, K. R., Beriont, J. and Tessier, C. R. (2015). Drosophila Cbp53E regulates axon growth at the meuromuscular junction. PLoS One 10: e0132636. PubMed ID: 26167908
Summary:
Calcium is a primary second messenger in all cells that functions in processes ranging from cellular proliferation to synaptic transmission. Proper regulation of calcium is achieved through numerous mechanisms involving channels, sensors, and buffers notably containing one or more EF-hand calcium binding domains. The Drosophila genome encodes only a single 6 EF-hand domain containing protein, Cbp53E, which is likely the prototypic member of a small family of related mammalian proteins that act as calcium buffers and calcium sensors. Like the mammalian homologs, Cbp53E is broadly though discretely expressed throughout the nervous system. Despite the importance of calcium in neuronal function and growth, nothing is known about Cbp53E's function in neuronal development. To address this deficiency, novel null alleles of Drosophila Cbp53E were generated, and neuronal development was examined at the well-characterized larval neuromuscular junction. Loss of Cbp53E resulted in increases in axonal branching at both peptidergic and glutamatergic neuronal terminals. This overgrowth could be completely rescued by expression of exogenous Cbp53E. Overexpression of Cbp53E, however, only affected the growth of peptidergic neuronal processes. These findings indicate that Cbp53E plays a significant role in neuronal growth and suggest that it may function in both local synaptic and global cellular mechanisms.

Knight, D., Iliadi, K. G., Iliadi, N., Wilk, R., Hu, J., Krause, H. M., Taylor, P., Moran, M. F. and Boulianne, G. L. (2015). Distinct regulation of transmitter release at the Drosophila NMJ by different isoforms of nemy. PLoS One 10: e0132548. PubMed ID: 26237434
Summary:
Synaptic transmission is highly plastic and subject to regulation by a wide variety of neuromodulators and neuropeptides. The present study examined the role of isoforms of the cytochrome b561 homologue called no extended memory (nemy) in regulation of synaptic strength and plasticity at the neuromuscular junction (NMJ) of third instar larvae in Drosophila. Specifically, two independent excisions of nemy were generated that differentially affect the expression of nemy isoforms. The nemy45 excision, which specifically reduces the expression of the longest splice form of nemy, leads to an increase in stimulus evoked transmitter release and altered synaptic plasticity at the NMJ. Conversely, the nemy26.2 excision, which appears to reduce the expression of all splice forms except the longest splice isoform, shows a reduction in stimulus evoked transmitter release, and enhanced synaptic plasticity. It was further shown that nemy45 mutants have reduced levels of amidated peptides similar to that observed in peptidyl-glycine hydryoxylating mono-oxygenase (PHM) mutants. In contrast, nemy26.2 mutants show no defects in peptide amidation but rather display a decrease in Tyramine beta hydroxylase activity (TbetaH). Taken together, these results show non-redundant roles for the different nemy isoforms and shed light on the complex regulation of neuromodulators.

Sunday, August 9th

Doggett, K., Turkel, N., Willoughby, L. F., Ellul, J., Murray, M. J., Richardson, H. E. and Brumby, A. M. (2015). BTB-zinc finger oncogenes are required for Ras and Notch-driven tumorigenesis in Drosophila. PLoS One 10: e0132987. PubMed ID: 26207831
Summary:
During tumorigenesis, pathways that promote the epithelial-to-mesenchymal transition (EMT) can both facilitate metastasis and endow tumor cells with cancer stem cell properties. To gain a greater understanding of how these properties are interlinked in cancers, Drosophila epithelial tumor models were used, that are driven by orthologues of human oncogenes (activated alleles of Ras and Notch) in cooperation with the loss of the cell polarity regulator, scribbled (scrib). Within these tumors, both invasive, mesenchymal-like cell morphology and continual tumor overgrowth, are dependent upon Jun N-terminal kinase (JNK) activity. Amongst the JNK-dependent changes was a significant enrichment for BTB-Zinc Finger (ZF) domain genes, including chinmo, which was upregulated by JNK within the tumors; overexpression of chinmo with either RasV12 or Nintra was sufficient to promote JNK-independent epithelial tumor formation in the eye/antennal disc, and, in cooperation with RasV12, promote tumor formation in the adult midgut epithelium. Chinmo primes cells for oncogene-mediated transformation through blocking differentiation in the eye disc, and promoting an escargot-expressing stem or enteroblast cell state in the adult midgut. BTB-ZF genes are also required for Ras and Notch-driven overgrowth of scrib mutant tissue, since, although loss of chinmo alone did not significantly impede tumor development, when loss of chinmo was combined with loss of a functionally related BTB-ZF gene, abrupt, tumor overgrowth was significantly reduced. abrupt is not a JNK-induced gene, however, Abrupt is present in JNK-positive tumor cells, consistent with a JNK-associated oncogenic role. As some mammalian BTB-ZF proteins are also highly oncogenic, this work suggests that EMT-promoting signals in human cancers could similarly utilize networks of these proteins to promote cancer stem cell states.

de Taffin, M., Carrier, Y., Dubois, L., Bataille, L., Painset, A., Le Gras, S., Jost, B., Crozatier, M. and Vincent, A. (2015). Genome-wide mapping of Collier in vivo binding sites highlights its hierarchical position in different transcription regulatory networks. PLoS One 10: e0133387. PubMed ID: 26204530
Summary:
Collier, the single Drosophila COE (Collier/EBF/Olf-1) transcription factor, is required in several developmental processes, including head patterning and specification of muscle and neuron identity during embryogenesis. To identify direct Collier (Col) targets in different cell types, ChIP-seq was used to map Col binding sites throughout the genome, at mid-embryogenesis. In vivo Col binding peaks were associated to 415 potential direct target genes. Gene Ontology analysis revealed a strong enrichment in proteins with DNA binding and/or transcription-regulatory properties. Characterization of a selection of candidates, using transgenic CRM-reporter assays, identified direct Col targets in dorso-lateral somatic muscles and specific neuron types in the central nervous system. These data brought new evidence that Col direct control of the expression of the transcription regulators apterous and eyes-absent (eya) is critical to specifying neuronal identities. They also showed that cross-regulation between col and eya in muscle progenitor cells is required for specification of muscle identity, revealing a new parallel between the myogenic regulatory networks operating in Drosophila and vertebrates. Col regulation of eya, both in specific muscle and neuronal lineages, may illustrate one mechanism behind the evolutionary diversification of Col biological roles.

Dominguez-Cejudo, M. A. and Casares, F. (2015). Antero-posterior patterning of Drosophila ocelli requires an anti-repressor mechanism within the hh-pathway mediated by the Six3 gene Optix. Development [Epub ahead of print]. PubMed ID: 26160900
Summary:
In addition to the compound eyes, most insects possess a set of three dorsal ocelli that develop at the vertices of a triangular cuticle patch, forming the ocellar complex. The wingless and hedgehog signaling pathways, together with the transcription factor encoded by orthodenticle, are known to play major roles in the specification and patterning of the ocellar complex. Specifically, hedgehog is responsible for the choice between ocellus and cuticle fates within the ocellar complex primordium. However, the interaction between signals and transcription factors known to date do not fully explain how this choice is controlled. This study shows that this binary choice depends on dynamic changes in the domains of hedgehog signaling. In this dynamics, the restricted expression of engrailed, a hedgehog-signaling target, is key because it defines a domain within the complex where hh transcription is maintained while the pathway activity is blocked. The Drosophila Six3, Optix, is expressed in and required for the development of the anterior ocellus specifically. Optix would not act as an ocellar selector, but rather as a patterning gene, limiting the en expression domain. These results indicate that, despite their genetic and structural similarity, anterior and posterior ocelli are under different genetic control.

Kolahgar, G., Suijkerbuijk, S. J., Kucinski, I., Poirier, E. Z., Mansour, S., Simons, B. D. and Piddini, E. (2015). Cell competition modifies adult stem cell and tissue population dynamics in a JAK-STAT-dependent manner. Dev Cell [Epub ahead of print]. PubMed ID: 26212135
Summary:
Throughout their lifetime, cells may suffer insults that reduce their fitness and disrupt their function, and it is unclear how these potentially harmful cells are managed in adult tissues. This question was addressed using the adult Drosophila posterior midgut as a model of homeostatic tissue and ribosomal Minute mutations to reduce fitness in groups of cells. A quantitative approach was taken, combining lineage tracing and biophysical modeling, and how cell competition affects stem cell and tissue population dynamics was addressed. Healthy cells were shown to induce clonal extinction in weak tissues, targeting both stem and differentiated cells for elimination. It was also found that competition induces stem cell proliferation and self-renewal in healthy tissue, promoting selective advantage and tissue colonization. Finally, winner cell proliferation was shown to be fueled by the JAK-STAT ligand Unpaired-3, produced by Minute-/+ cells in response to chronic JNK stress signaling.

Saturday, August 8th

Jeibmann, A., Halama, K., Witte, H.T., Kim, S.N., Eikmeier, K., Koos, B., Klämbt, C. and Paulus, W. (2015). Involvement of CD9 and PDGFR in migration is evolutionarily conserved from Drosophila glia to human glioma. J Neurooncol [Epub ahead of print]. PubMed ID: 26224160
Summary:
Platelet-derived growth factor receptor (PDGFR) signaling plays an important role in the biology of malignant gliomas. To investigate mechanisms modulating PDGFR signaling in gliomagenesis, this study employed a Drosophila glioma model and genetic screen to identify genes interacting with Pvr, the fly homolog of PDGFRs. Glial expression of constitutively activated Pvr (λPvr) leads to glial over migration and lethality at late larval stage. Among 3316 dsRNA strains crossed against the tester strain, 128 genes shift lethality to pupal stage, including tetraspanin 2A (tsp2A). In a second step knockdown of all Drosophila tetraspanins was investigated. Of all tetraspanin dsRNA strains only knockdown of tsp2A partially rescues the Pvr-induced phenotype. Human CD9 (TSPAN29/MRP-1), a close homolog of tsp2A, was found to be expressed in glioma cell lines A172 and U343MG as well as in the majority of glioblastoma samples (16/22, 73 %). Furthermore, in situ proximity ligation assay reveals close association of CD9 with PDGFR α and β. In U343MG cells, knockdown of CD9 blocks PDGF-BB stimulated migration. In conclusion, modulation of PDGFR signaling by CD9 is evolutionarily conserved from Drosophila glia to human glioma and plays a role in glia migration

Hartenstein, V., Younossi-Hartenstein, A., Lovick, J., Kong, A., Omoto, J., Ngo, K. and Viktorin, G. (2015). Lineage-associated tracts defining the anatomy of the drosophila first instar larval brain. Dev Biol [Epub ahead of print]. PubMed ID: 26141956
Summary:
Fixed lineages derived from unique, genetically specified neuroblasts form the anatomical building blocks of the Drosophila brain. Neurons belonging to the same lineage project their axons in a common tract, which is labeled by neuronal markers. This paper presents a detailed atlas of the lineage-associated tracts forming the brain of the early Drosophila larva, based on the use of global markers (anti-Neuroglian, anti-Neurotactin, Inscuteable-Gal4>UAS-chRFP-Tub) and lineage-specific reporters. Sixty-eight discrete fiber bundles are described that contain axons of one lineage or pairs/small sets of adjacent lineages. Bundles enter the neuropil at invariant locations, the lineage tract entry portals. Within the neuropil, these fiber bundles form larger fascicles that can be classified, by their main orientation, into longitudinal, transverse, and vertical (ascending/descending) fascicles. 3D digital models of lineage tract entry portals and neuropil fascicles are presented, set into relationship to commonly used, easily recognizable reference structures such as the mushroom body, the antennal lobe, the optic lobe, and the Fasciclin II-positive fiber bundles that connect the brain and ventral nerve cord. Correspondences and differences between early larval tract anatomy and the previously described late larval and adult lineage patterns are highlighted. The L1 atlas will be important for a host of ongoing work that attempts to reconstruct neuronal connectivity at the level of resolution of single neurons and their synapses.

Suslak, T. J., Watson, S., Thompson, K. J., Shenton, F. C., Bewick, G. S., Armstrong, J. D. and Jarman, A. P. (2015). Piezo is essential for amiloride-sensitive stretch-activated mechanotransduction in larval Drosophila dorsal bipolar dendritic sensory neurons. PLoS One 10: e0130969. PubMed ID: 26186008
Summary:
Stretch-activated afferent neurons, such as those of mammalian muscle spindles, are essential for proprioception and motor co-ordination, but the underlying mechanisms of mechanotransduction are poorly understood. The dorsal bipolar dendritic (dbd) sensory neurons are putative stretch receptors in the Drosophila larval body wall. An in vivo protocol was developed to obtain receptor potential recordings from intact dbd neurons in response to stretch. Receptor potential changes in dbd neurons in response to stretch showed a complex, dynamic profile with similar characteristics to those previously observed for mammalian muscle spindles. These profiles were reproduced by a general in silico model of stretch-activated neurons. This in silico model predicts an essential role for a mechanosensory cation channel (MSC) in all aspects of receptor potential generation. Using pharmacological and genetic techniques, the mechanosensory channel, Piezo, was identified in this functional role in dbd neurons, with TRPA1 playing a subsidiary role. It was also shown that rat muscle spindles exhibit a ruthenium red-sensitive current, but no expression evidence was found to suggest that this corresponds to Piezo activity. In summary, this study shows that the dbd neuron is a stretch receptor and demonstrates that this neuron is a tractable model for investigating mechanisms of mechanotransduction.

Gombos, R., Migh, E., Antal, O., Mukherjee, A., Jenny, A. and Mihaly, J. (2015). The formin DAAM functions as molecular effector of the planar cell polarity pathway during axonal development in Drosophila. J Neurosci 35: 10154-10167. PubMed ID: 26180192
Summary:
Recent studies established that the planar cell polarity (PCP) pathway is critical for various aspects of nervous system development and function, including axonal guidance. Although it seems clear that PCP signaling regulates actin dynamics, the mechanisms through which this occurs remain elusive. This study established a functional link between the PCP system and one specific actin regulator, the formin DAAM, which has previously been shown to be required for embryonic axonal morphogenesis and filopodia formation in the growth cone. dDAAM also plays a pivotal role during axonal growth and guidance in the adult Drosophila mushroom body, a brain center for learning and memory. By using a combination of genetic and biochemical assays, it was demonstrated that Wnt5 and the PCP signaling proteins Frizzled, Strabismus, and Dishevelled act in concert with the small GTPase Rac1 to activate the actin assembly functions of dDAAM essential for correct targeting of mushroom body axons. Collectively, these data suggest that dDAAM is used as a major molecular effector of the PCP guidance pathway. By uncovering a signaling system from the Wnt5 guidance cue to an actin assembly factor, it is proposed that the Wnt5/PCP navigation system is linked by dDAAM to the regulation of the growth cone actin cytoskeleton, and thereby growth cone behavior, in a direct way.

Friday, August 7th

Norvell, A., Wong, J., Randolph, K. and Thompson, L. (2015). Wispy and Orb cooperate in the cytoplasmic polyadenylation of localized gurken mRNA. Dev Dyn [Epub ahead of print]. PubMed ID: 26214278
Summary:
In Drosophila, the dorsal-ventral (D-V) axis of the oocyte is dependent on Gurken (Grk) protein distribution. This is achieved through the cytoplasmic localization of grk mRNA and regulation of its translation. During mid-late stages of oogenesis, grk mRNA and protein are localized to the dorsal-anterior of the oocyte, while unlocalized grk transcripts are translationally silenced. As females carrying mutations in the gene encoding the CPEB protein Orb lay ventralized eggs due to insufficient Grk levels, it seems likely that cytoplasmic polyadenylation of grk transcripts may play a role in their translational regulation. This study found that grk is polyadenylated throughout oogenesis, with poly(A) tails of approximately 30-50 A residues. Hyperadenylated grk transcripts, with poly(A) tails of 50-90 As, are detected in late stage egg chambers, but they fail to accumulate in oocytes deficient in Orb or the poly(A) polymerase Wispy (Wisp). wisp females also lay weakly ventralized eggs, demonstrating that they produce inadequate amounts of Grk. Finally, unlocalized grk transcripts are also not appropriately hyperadenylated. Thus, localized cytoplasmic polyadenylation of grk mRNA by Wisp and Orb is necessary to achieve appropriate Grk protein accumulation in the D/A corner of the oocyte during mid to late oogenesis.

Zaharieva, E., Haussmann, I. U., Brauer, U. and Soller, M. (2015). Concentration and localization of co-expressed ELAV/Hu proteins control specificity of mRNA processing. Mol Cell Biol [Epub ahead of print]. PubMed ID: 26124284
Summary:
Neuronally co-expressed ELAV/Hu proteins comprise a family of highly related RNA binding proteins, which bind to very similar cognate sequences. How this redundancy is linked to in vivo function and how gene specific regulation is achieved, has not been clear. Analysis of mutants in Drosophila ELAV/Hu family proteins ELAV, FNE and RBP9, and genetic interactions among them, indicates mostly independent roles in neuronal development and function, but convergence in the regulation of synaptic plasticity. Conversely, ELAV, FNE, RBP9 and human HuR bind ELAV target RNA in vitro with similar affinity. Likewise, all can regulate alternative splicing of ELAV target genes in non-neuronal wing-disc cells and substitute ELAV in eye development with artificially increased expression, but can also substantially restore ELAV's biological functions, when expressed under the control of the elav gene. Furthermore, ELAV related Sex-lethal can regulate ELAV targets and ELAV/Hu proteins can interfere with sexual differentiation. An ancient relationship to Sex-lethal is revealed by gonadal expression of RBP9 providing a maternal failsafe for dosage compensation. These results indicate that highly related ELAV/Hu RNA binding proteins select targets for mRNA processing based on expression levels and sub-cellular localization, but only minimally by altered RNA binding specificity.

Suh, Y. S., Bhat, S., Hong, S. H., Shin, M., Bahk, S., Cho, K. S., Kim, S. W., Lee, K. S., Kim, Y. J., Jones, W. D. and Yu, K. (2015). Genome-wide microRNA screening reveals that the evolutionary conserved miR-9a regulates body growth by targeting sNPFR1/NPYR. Nat Commun 6: 7693. PubMed ID: 26138755
Summary:
MicroRNAs (miRNAs) regulate many physiological processes including body growth. Insulin/IGF signalling is the primary regulator of animal body growth, but the extent to which miRNAs act in insulin-producing cells (IPCs) is unclear. This study generated a UAS-miRNA library of Drosophila stocks, and a genetic screen was performed to identify miRNAs whose overexpression in the IPCs inhibits body growth in Drosophila. Through this screen, miR-9a was identified as an evolutionarily conserved regulator of insulin signalling and body growth. IPC-specific miR-9a overexpression reduces insulin signalling and body size. Of the predicted targets of miR-9a, loss of miR-9a was found to enhance the level of short neuropeptide F receptor (sNPFR1). An in vitro binding assay showed that miR-9a binds to sNPFR1 mRNA in insect cells and to the mammalian orthologue NPY2R in rat insulinoma cells. These findings indicate that the conserved miR-9a regulates body growth by controlling sNPFR1/NPYR-mediated modulation of insulin signalling.

Dong, L., Li, J., Huang, H., Yin, M. X., Xu, J., Li, P., Lu, Y., Wu, W., Yang, H., Zhao, Y. and Zhang, L. (2015). Growth suppressor lingerer regulates bantam microRNA to restrict organ size. J Mol Cell Biol. PubMed ID: 26117838
Summary:
The evolutionarily conserved Hippo signaling pathway plays an important role in organ size control by regulating cell proliferation and apoptosis. This study identified Lingerer (Lig) as a growth suppressor using RNAi modifying screen in Drosophila melanogaster. Loss of lig increases organ size and promotes bantam (ban) and the expression of the Hippo pathway target genes, while overexpression of lig results in diminished ban expression and organ size reduction. Lig C-terminal exhibits dominant-negative function on growth and ban expression, and thus plays an important role in organ size control and ban regulation. In addition, evidence is provided that both Yki and Mad are essential for Lig-induced ban expression. Lig was shown to regulate the expression of the Hippo pathway target genes partially via Yorkie. Moreover, Lig was found to physically interact with and requires Salvador to restrict cell growth. Taken together, this study demonstrates that Lig functions as a critical growth suppressor to control organ size via ban and Hippo signaling.

Thursday, August 6th

Adewoye, A.B., Kyriacou, C.P. and Tauber, E. (2015). Identification and functional analysis of early gene expression induced by circadian light-resetting in Drosophila. BMC Genomics 16: 570. PubMed ID: 26231660
Summary:
The environmental light-dark cycle is the dominant cue that maintains 24-h biological rhythms. In Drosophila, light entrainment is mediated by the photosensitive protein CRYPTOCHROME. This study analyzed light-induced global transcriptional changes in the fly's head by using microarrays. Flies were subjected to a 30-min light pulse during the early night (3 h after lights-off). 200 genes were identified whose transcripts are significantly altered in response to the light pulse. Analysis suggests the involvement of at least six biological processes in light-induced delay phase shifts of rhythmic activities, include signalling, ion channel transport, receptor activity, synaptic organisation, signal transduction, and chromatin remodelling. Using RNAi, the expression of 22 genes was downregulated in the clock neurons, leading to significant effects on circadian output. For example, while continuous light normally causes arrhythmicity in wild-type flies, the knockdown of Kr-h1, Nipped-A, Thor, nrv1, Nf1, CG11155 (ionotropic glutamate receptor), and Fmr1 results in flies that are rhythmic, suggesting a disruption in the light input pathway to the clock. These analyses provides a first insight into the early responsive genes that are activated by light and their contribution to light resetting of the Drosophila clock.

Kohyama-Koganeya, A., Kurosawa, M. and Hirabayashi, Y. (2015). Differential Effects of Tissue-Specific Deletion of BOSS on Feeding Behaviors and Energy Metabolism. PLoS One 10: e0133083. PubMed ID: 26193363
Summary:
Food intake and energy metabolism are tightly controlled to maintain stable energy homeostasis and healthy states. Thus, animals detect their stored energy levels, and based on this, they determine appropriate food intake and meal size. Drosophila melanogaster putative G protein-coupled receptor, Bride of sevenless (BOSS) is a highly evolutionarily conserved protein that responds to extracellular glucose levels in order to regulate energy homeostasis. To address how BOSS regulates energy homeostasis, a boss mutant was characterized by assessing its food intake and stored energy levels. Boss mutants exhibited increased food intake but decreased stored triacylglyceride levels. Using boss-GAL4 drivers, it was found that boss is expressed in select tissues that are involved in nutrient sensing and food intake, in a subset of neurons in brain and chemosensory organs, in fat body, and in endocrine cells in gut (enteroendocrine cells). Flies with tissue-specific boss knockdowns in these tissues had abnormal stored energy levels and abnormal food intake. These results suggest that BOSS in either neurons or peripheral nutrient-sensing tissues affects energy homeostasis in ways that relate to the sensing of nutrients and regulation of food intake.

Petsakou, A., Sapsis, T.P. and Blau, J. (2015). Circadian rhythms in Rho1 activity regulate neuronal plasticity and network hierarchy. Cell [Epub ahead of print]. PubMed ID: 26234154
Summary:
Neuronal plasticity helps animals learn from their environment. However, it is challenging to link specific changes in defined neurons to altered behavior. This study focuses on circadian rhythms in the structure of the principal s-LNv clock neurons in Drosophila. By quantifying neuronal architecture, it was observed that s-LNv structural plasticity changes the amount of axonal material in addition to cycles of fasciculation and defasciculation. It was found that this is controlled by rhythmic Rho1 activity that retracts s-LNv axonal termini by increasing myosin phosphorylation and simultaneously changes the balance of pre-synaptic and dendritic markers. This plasticity is required to change clock network hierarchy and allow seasonal adaptation. Rhythms in Rho1 activity are controlled by clock-regulated transcription of Puratrophin-1-like (Pura), a Rho1 GEF. Since spinocerebellar ataxia is associated with mutations in human Puratrophin-1, these data support the idea that defective actin-related plasticity underlies this ataxia.

Kuo, S. Y., Wu, C. L., Hsieh, M. Y., Lin, C. T., Wen, R. K., Chen, L. C., Chen, Y. H., Yu, Y. W., Wang, H. D., Su, Y. J., Lin, C. J., Yang, C. Y., Guan, H. Y., Wang, P. Y., Lan, T. H. and Fu, T. F. (2015). PPL2ab neurons restore sexual responses in aged Drosophila males through dopamine. Nat Commun 6: 7490. PubMed ID: 26123524
Summary:
Male sexual desire typically declines with ageing. However, understanding of the neurobiological basis for this phenomenon is limited by knowledge of the brain circuitry and neuronal pathways controlling male sexual desire. A number of studies across species suggest that dopamine (DA) affects sexual desire. This study used genetic tools and behavioural assays to identify a novel subset of DA neurons that regulate age-associated male courtship activity in Drosophila. Increasing DA levels in a subset of cells in the PPL2ab neuronal cluster is necessary and sufficient for increased sustained courtship in both young and aged male flies. These results indicate that preventing the age-related decline in DA levels in PPL2ab neurons alleviates diminished courtship behaviours in male Drosophila. These results may provide the foundation for deciphering the circuitry involved in sexual motivation in the male Drosophila brain.

Wednesday, August 5th

Griffin, R.M., Le Gall, D., Schielzeth, H. and Friberg, U. (2015). Within-population Y-linked genetic variation for lifespan in Drosophila melanogaster. J Evol Biol [Epub ahead of print]. PubMed ID: 26230387
Summary:
The view that the Y chromosome is of little importance for phenotypic evolution stems from early studies of Drosophila melanogaster. This species' Y chromosome contains only 13 protein coding genes, is almost entirely heterochromatic, and is not necessary for male viability. Recent studies suggest that the D. melanogaster Y chromosome trans-regulates hundreds to thousands of X and autosomal genes. This finding suggests that the Y chromosome may play a far more active role in adaptive evolution than has previously been assumed. To evaluate the potential for the Y chromosome to contribute to phenotypic evolution from standing genetic variation, this study tested for Y-linked variation in lifespan within a population of D. melanogaster. Assessing variation for lifespan provides a powerful test because lifespan i) shows sexual dimorphism, which the Y is primarily predicted to contribute to, ii) is influenced by many genes, which provides the Y with many potential regulatory targets, and iii) is sensitive to heterochromatin remodelling, a mechanism through which the Y chromosome is believed to regulate gene expression. Results show a small but significant effect of the Y chromosome, and thus suggest that the Y chromosome has the potential to respond to selection from standing genetic variation. Despite its small effect size, Y-linked variation may still be important, in particular when evolution of sexual dimorphism is genetically constrained elsewhere in the genome.

Kofler, R., Nolte, V. and Schlötterer, C. (2015). Tempo and mode of transposable element activity in Drosophila. PLoS Genet 11: e1005406. PubMed ID: 26186437
Summary:
The evolutionary dynamics of transposable element (TE) insertions have been of continued interest since TE activity has important implications for genome evolution and adaptation. This study infers the transposition dynamics of TEs by comparing their abundance in natural D. melanogaster and D. simulans populations. By sequencing pools of more than 550 South African flies to at least 320-fold coverage, the genome wide TE insertion frequencies in both species was determined. The study suggests that the predominance of low frequency insertions in the two species (>80% of the insertions have a frequency <0.2) is probably due to a high activity of more than 58 families in both species. The study provides evidence for 50% of the TE families having temporally heterogenous transposition rates with different TE families being affected in the two species. While in D. melanogaster retrotransposons are more active, DNA transposons show higher activity levels in D. simulans. Moreover, the study suggests that LTR insertions are mostly of recent origin in both species, while DNA and non-LTR insertions are older and more frequently vertically transmitted since the split of D. melanogaster and D. simulans. The study proposes that the high TE activity is of recent origin in both species and a consequence of the demographic history, with habitat expansion triggering a period of rapid evolution

Jiang, P., Ludwig, M. Z., Kreitman, M. and Reinitz, J. (2015). Natural variation of the expression pattern of the segmentation gene even-skipped in melanogaster. Dev Biol [Epub ahead of print]. PubMed ID: 26129990
Summary:
The evolution of canalized traits is a central question in evolutionary biology. Natural variation in highly conserved traits can provide clues about their evolutionary potential. This study investigate natural variation in a conserved trait-even-skipped (eve) expression at the cellular blastoderm stage of embryonic development in Drosophila melanogaster. Expression of the pair-rule gene eve was quantitatively measured in three inbred lines derived from a natural population of D. melanogaster. One line showed marked differences in the spacing, amplitude and timing of formation of the characteristic seven-striped pattern over a 50-min period prior to the onset of gastrulation. These changes are larger than those previously reported between D. melanogaster and D. pseudoobscura, two species that are thought to have diverged from a common ancestor over 25 million years ago. This line harbors a rare 448 bp deletion in the first intron of knirps (kni). This finding suggested that reduced Kni levels caused the deviant eve expression, and indeed lower levels of Kni protein were observed at early cycle 14A in L2 compared to the other two lines. A second of the three lines displayed an approximately 20% greater level of expression for all seven eve stripes. The three lines are each viable and fertile, and none display a segmentation defect as adults, suggesting that early-acting variation in eve expression is ameliorated by developmental buffering mechanisms acting later in development. Canalization of the segmentation pathway may reduce the fitness consequences of genetic variation, thus allowing the persistence of mutations with unexpectedly strong gene expression phenotypes.

Chenoweth, S. F., Appleton, N. C., Allen, S. L. and Rundle, H. D. (2015). Genomic evidence that sexual selection impedes adaptation to a novel environment. Curr Biol 25: 1860-1866. PubMed ID: 26119752
Summary:
Sexual selection is widely appreciated for generating remarkable phenotypic diversity, but its contribution to adaptation and the purging of deleterious mutations is unresolved. To provide insight into the impact of sexual selection on naturally segregating polymorphisms across the genome, previous studies have evolved 12 populations of Drosophila serrata in a novel environment employing a factorial manipulation of the opportunities for natural and sexual selection. This study genotyped more than 1,400 SNPs in the evolved populations and revealed that sexual selection affected many of the same genomic regions as natural selection, aligning with it as often as opposing it. Intriguingly, more than half of the 80 SNPs showing treatment effects revealed an interaction between natural and sexual selection. For these SNPs, while sexual selection alone often caused a change in allele frequency in the same direction as natural selection alone, when natural and sexual selection occurred together, changes in allele frequency were greatly reduced or even reversed. This suggests an antagonism between natural and sexual selection arising from male-induced harm to females. Behavioral experiments showed that males preferentially courted and mated with high-fitness females, and that the harm associated with this increased male attention eliminated the female fitness advantage. During this experiment, females carrying otherwise adaptive alleles may therefore have disproportionally suffered male-induced harm due to their increased sexual attractiveness. These results suggest that a class of otherwise adaptive mutations may not contribute to adaptation when mating systems involve sexual conflict and male mate preferences.

Negre, B. and Simpson, P. (2015). The achaete-scute complex in Diptera: patterns of non-coding sequence evolution. J Evol Biol [Epub ahead of print]. PubMed ID: 26134680
Summary:
The achaete-scute complex has been a useful paradigm for the study of pattern formation and its evolution. achaete-scute genes have duplicated and evolved distinct expression patterns during the evolution of cyclorraphous Diptera. Are the expression patterns in different species driven by conserved regulatory elements? If so, when did such regulatory elements arise? Most of the achaete-scute complex of the fly Calliphora vicina (including the genes achaete, scute and lethal of scute) have been sequenced to compare non-coding sequences with known cis-regulatory sequences in Drosophila. The organization of the complex is conserved with respect to Drosophila species. There are numerous small stretches of conserved non-coding sequence that, in spite of high sequence turnover, display binding sites for known transcription factors. Synteny of the blocks of conserved non-coding sequences is maintained suggesting not only conservation of the position of regulatory elements but an origin prior to the divergence between these two species. It is proposed that some of these enhancers originated by duplication with their target genes.

Magnacca, K. N. and Price, D. K. (2015). Rapid adaptive radiation and host plant conservation in the Hawaiian picture wing Drosophila (Diptera: Drosophilidae). Mol Phylogenet Evol 92: 226-242. PubMed ID: 26151218
Summary:
The Hawaiian picture wing Drosophila are a striking example of adaptive radiation in specialist saprophages on an island system. This study use DNA sequences from five nuclear genes to provide a comprehensive phylogeny and biogeographic analysis of 90 species in the Hawaiian Drosophila picture wing clade. The analysis indicates that the evolution of the picture wing clade took place more recently than previously suggested. Biogeography and host plant analyses show two periods of rapid divergence occurred when Kauai and Oahu were the main high islands, indicating that a combination of complex topographical features of islands and development of novel host plant associations was key to the rapid diversification of these lineages. For the past 2 million years, host associations within lineages have been largely stable, and speciation has occurred primarily due to the establishment of populations on newer islands as they arose followed by divergence by isolation. The existence of several apparently relictual taxa suggests that extinction has also played a major role in assembly of the present Hawaiian Drosophila fauna.

Tuesday, August 4th

Reiff, T., Jacobson, J., Cognigni, P., Antonello, Z., Ballesta, E., Tan, K.J., Yew, J.Y., Dominguez, M. and Miguel-Aliaga, I. (2015). Endocrine remodelling of the adult intestine sustains reproduction in Drosophila. Elife 4. PubMed ID: 26216039
Summary:
The production of offspring is energetically costly and relies on incompletely understood mechanisms that generate a positive energy balance. In mothers of many species, changes in key energy-associated internal organs are common yet poorly characterized functionally and mechanistically. This study shows that in adult Drosophila females, the midgut is dramatically remodelled to enhance reproductive output. In contrast to extant models, organ remodelling does not occur in response to increased nutrient intake and/or offspring demands, but rather precedes them. By performing spatially and temporally directed manipulations, juvenile hormone (JH) was identified as an anticipatory endocrine signal released after mating. Acting through intestinal bHLH-PAS domain proteins Methoprene-tolerant (Met) and Germ cell-expressed (Gce), JH signals directly to intestinal progenitors to yield a larger organ, and adjusts gene expression and sterol regulatory element-binding protein (SREBP) activity in enterocytes to support increased lipid metabolism. These findings identify a metabolically significant paradigm of adult somatic organ remodelling linking hormonal signals, epithelial plasticity, and reproductive output. 

Senyilmaz, D., Virtue, S., Xu, X., Tan, C.Y., Griffin, J.L., Miller, A.K., Vidal-Puig, A. and Teleman, A.A. (2015). Regulation of mitochondrial morphology and function by stearoylation of TFR1. Nature 525(7567): 124-8. PubMed ID: 26214738
Summary:
Mitochondria are involved in a variety of cellular functions, including ATP production, amino acid and lipid biogenesis and breakdown, signalling and apoptosis. Mitochondrial dysfunction has been linked to neurodegenerative diseases, cancer and ageing. Although transcriptional mechanisms that regulate mitochondrial abundance are known, comparatively little is known about how mitochondrial function is regulated. This study identifies the metabolite stearic acid (C18:0), which was deficient in Elovl6 (Baldspot) mutant flies, and human transferrin receptor 1 (TFR1; also known as TFRC) as mitochondrial regulators. A signalling pathway was elucidated whereby C18:0 stearoylates TFR1, thereby inhibiting its activation of JNK signalling. This leads to reduced ubiquitination of mitofusin via HECT, UBA and WWE domain containing 1, E3 ubiquitin protein ligase (HUWE1), thereby promoting mitochondrial fusion and function. It was found that animal cells are poised to respond to both increases and decreases in C18:0 levels, with increased C18:0 dietary intake boosting mitochondrial fusion in vivo. Intriguingly, dietary C18:0 supplementation can counteract the mitochondrial dysfunction caused by genetic defects such as loss of the Parkinson's disease genes Pink or Parkin in Drosophila. This work identifies the metabolite C18:0 as a signalling molecule regulating mitochondrial function in response to diet.

Meserve, J. H. and Duronio, R. J. (2015). Scalloped and Yorkie are required in Drosophila for cell cycle re-entry of quiescent cells after tissue damage. Development [Epub ahead of print]. PubMed ID: 26160905
Summary:
Regeneration of damaged tissues typically requires a population of active stem cells. How damaged tissue is regenerated in quiescent tissues lacking a stem cell population is less well understood. This study used a genetic screen in the developing Drosophila melanogaster eye to investigate the mechanisms that trigger quiescent cells to re-enter the cell cycle and proliferate in response to tissue damage. Hippo signaling was found to regulate compensatory proliferation after extensive cell death in the developing eye. Scalloped and Yorkie, transcriptional effectors of the Hippo pathway, drive Cyclin E expression to induce cell cycle re-entry in cells that normally remain quiescent in the absence of damage. Ajuba, an upstream regulator of Hippo signaling that functions as a sensor of epithelial integrity, is also required for cell cycle re-entry. Thus, in addition to its well-established role in modulating proliferation during periods of tissue growth, Hippo signaling maintains homeostasis by regulating quiescent cell populations affected by tissue damage.

Wang, Z., Zhang, L., Liang, Y., Zhang, C., Xu, Z., Zhang, L., Fuji, R., Mu, W., Li, L., Jiang, J., Ju, Y. and Wang, Z. (2015). Cyclic AMP mimics the anti-ageing effects of calorie restriction by up-regulating Sirtuin. Sci Rep 5: 12012. PubMed ID: 26153625
Summary:
Cyclic adenosine monophosphate (cAMP) plays an important role in many biological processes as a second messenger, and cAMP treatment has been reported to extend the lifespan of wild-type Drosophila melanogaster (Tong, J. J., et al. 2007. Life extension through neurofibromin mitochondrial regulation and antioxidant therapy for neurofibromatosis-1 in Drosophila melanogaster. Nat Genet 39, 476-485). This study, carried out in mice, shows that exogenous cAMP improves ageing-related phenotypes by increasing the protein level of Sirtuins, which prevented metabolic disorders to mimic the effect of calorie restriction. Experiments in vitro showed that cAMP directly bound to SIRT1 and SIRT3 and consequently increased their activity. These findings suggest that cAMP slows the ageing process and is a good candidate to mimic calorie restriction (see Graphical Abstract for the Underlying Mechanism of the cAMP Regulatory Effect on Sirtuin). This research provides a promising therapeutic strategy to target metabolic disorder-induced ageing-related diseases.

Monday, August 3rd

Wu, C., Chen, C., Dai, J., Zhang, F., Chen, Y., Li, W., Pastor-Pareja, J.C. and Xue, L. (2015). Toll pathway modulates TNF-induced JNK-dependent cell death in Drosophila. Open Biol 5. PubMed ID: 26202785
Summary:
Signalling networks that control the life or death of a cell are of central interest in modern biology. While the defined roles of the c-Jun N-terminal kinase (JNK) pathway in regulating cell death have been well-established, additional factors that modulate JNK-mediated cell death have yet to be fully elucidated. To identify novel regulators of JNK-dependent cell death, this study performed a dominant-modifier screen in Drosophila and found that the Toll pathway participates in JNK-mediated cell death. Loss of Toll signalling suppresses ectopically and physiologically activated JNK signalling-induced cell death. Epistasis analysis suggests that the Toll pathway acts as a downstream modulator for JNK-dependent cell death. In addition, gain of JNK signalling results in Toll pathway activation, revealed by stimulated transcription of Drosomycin (Drs) and increased cytoplasm-to-nucleus translocation of Dorsal. Furthermore, the Spätzle (Spz) family ligands for the Toll receptor are transcriptionally upregulated by activated JNK signalling in a non-cell-autonomous manner, providing a molecular mechanism for JNK-induced Toll pathway activation. Finally, gain of Toll signalling exacerbates JNK-mediated cell death and promotes cell death independent of caspases. Thus, this study identifies another important function for the evolutionarily conserved Toll pathway, in addition to its well-studied roles in embryonic dorso-ventral patterning and innate immunity.

Ratliff, E.P., et al. (2015). Aging and autophagic function influences the progressive decline of adult Drosophila behaviors. PLoS One 10: e0132768. PubMed ID: 26182057
Summary:
Middle-aged wild-type flies (WT, ~4-weeks) exhibit a marked accumulation of neural aggregates that is commensurate with the decline of the autophagy pathway. However, enhancing autophagy via neuronal over-expression of Atg8a (Atg8a-OE) reduces the age-dependent accumulation of aggregates. Only modest behavioral changes occur by 4-weeks of age, with the noted exception of group-housed male flies. Male flies in same-sex social groups exhibit a progressive increase in nighttime activity. Infrared videos show aged group-housed males (4-weeks) are engaged in extensive bouts of courtship during periods of darkness, which is partly repressed during lighted conditions. Together, these nighttime courtship behaviors are nearly absent in young WT flies and aged Atg8a-OE flies. Previous studies have indicated a regulatory role for olfaction in male courtship partner choice. Coincidently, the mRNA expression profiles of several olfactory genes decline with age in WT flies; however, they are maintained in age-matched Atg8a-OE flies. Together, these results suggest that middle-aged male flies develop impairments in olfaction, which could contribute to the dysregulation of courtship behaviors during dark time periods. Combined, these results demonstrate that as Drosophila age, they develop early behavior defects that are coordinate with protein aggregate accumulation in the nervous system. In addition, the nighttime activity behavior is preserved when neuronal autophagy is maintained (Atg8a-OE flies). Thus, environmental or genetic factors that modify autophagic capacity could have a positive impact on neuronal aging and complex behaviors.

Clavier, A., Ruby, V., Rincheval-Arnold, A., Mignotte, B and Guénal, I. (2015). The Drosophila retinoblastoma protein, Rbf1, induces a debcl and drp1-dependent mitochondrial apoptosis. J Cell Sci [Epub ahead of print]. PubMed ID: 26208635
Summary:
In accordance with its tumor suppressor role, the Retinoblastoma protein pRb can ensure pro-apoptotic functions. rbf1, the Drosophila homolog of Rb, also displays a pro-apoptotic activity in proliferative cells. It has been previously shown that rbf1 pro-apoptotic activity depends on its ability to decrease the level of anti-apoptotic proteins such as the Bcl-2 family protein Buffy. Buffy often acts opposite to Debcl, the other Drosophila Bcl-2-family protein. Both proteins can localize at the mitochondrion, but the way they control apoptosis still remains unclear. This study demonstrates that debcl and the pro-fission gene drp1 are necessary downstream of buffy to trigger a mitochondrial fragmentation during rbf1-induced apoptosis. Interestingly, rbf1-induced apoptosis leads to a debcl- and drp1-dependent Reactive Oxygen Species production, which in turn activates the Jun Kinase pathway to trigger cell death. Moreover, Debcl and Drp1 can interact and Buffy inhibits this interaction. Notably, Debcl modulates Drp1 mitochondrial localization during apoptosis. These results provide a mechanism by which Drosophila Bcl-2 family proteins can control apoptosis and shed light on a link between Rbf1 and mitochondrial dynamics, in vivo.

Mauvezin, C. and Neufeld, T. P. (2015). Bafilomycin A disrupts autophagic flux by inhibiting both V-ATPase-dependent acidification and Ca-P60A/SERCA-dependent autophagosome-lysosome fusion. Autophagy: [Epub ahead of print]. PubMed ID: 26156798
Summary:
Autophagosome-lysosome fusion and autolysosome acidification constitute late steps in the autophagic process necessary to maintain functional autophagic flux and cellular homeostasis. Both of these steps are disrupted by the V-ATPase inhibitor bafilomycin A1, but the mechanisms potentially linking them are unclear. The role of lysosomal acidification in autophagosome-lysosome fusion was recently revisited, using an in vivo approach in Drosophila. Surprisingly, vesicle fusion remained active in V-ATPase-depleted cells, indicating that autophagosome-lysosome fusion and autolysosome acidification are 2 separable processes. In contrast, bafilomycin A1 inhibited both acidification and fusion, consistent with its effects in mammalian cells. Together, these results imply that this drug inhibits fusion independently of its effect on V-ATPase-mediated acidification. The ER-calcium ATPase Ca-P60A/dSERCA was identified as a novel target of bafilomycin A1. Autophagosome-lysosome fusion was defective in Ca-P60A/dSERCA-depleted cells, and bafilomycin A1 induced a significant increase in cytosolic calcium concentration and disrupted Ca-P60A/SERCA-mediated fusion. Thus, bafilomycin A1 disrupts autophagic flux by independently inhibiting V-ATPase-dependent acidification and Ca-P60A/SERCA-dependent autophagosome-lysosome fusion.

Sunday, August 2nd

Ren, G. R., et al. (2015). CCHamide-2 Is an orexigenic brain-gut peptide in Drosophila. PLoS One 10: e0133017. PubMed ID: 26168160
Summary:
The neuroendocrine peptides CCHamide-1 and CCHamide-2, encoded by the genes ccha1 and -2, are produced by endocrine cells in the midgut and by neurons in the brain of Drosophila. This study used the CRISPR/Cas9 technique to disrupt the ccha1 and -2 genes and identify mutant phenotypes with a focus on ccha-2 mutants. Both larval and adult ccha2 mutants showed a significantly reduced food intake as measured in adult flies by the Capillary Feeding (CAFE) assay (up to 72% reduced food intake compared to wild-type). Locomotion tests in adult flies showed that ccha2 mutants had a significantly reduced locomotor activity especially around 8 a.m. and 8 p.m., where adult Drosophila normally feeds (up to 70% reduced locomotor activity compared to wild-type). Reduced larval feeding is normally coupled to a delayed larval development, a process that is mediated by insulin. Accordingly, it was found that the ccha2 mutants had a remarkably delayed development, showing pupariation 70 hours after the pupariation time point of the wild-type. In contrast, the ccha-1 mutants were not developmentally delayed. It was also found that the ccha2 mutants had up to 80% reduced mRNA concentrations coding for the Drosophila insulin-like-peptide-2 and -3, while these concentrations were unchanged for the ccha1 mutants. From these experiments it is concluded that CCHamide-2 is an orexigenic peptide and an important factor for controlling developmental timing in Drosophila.

Jones, M. W., de Jonge, M. D., James, S. A. and Burke, R. (2015). Elemental mapping of the entire intact Drosophila gastrointestinal tract. J Biol Inorg Chem [Epub ahead of print]. PubMed ID: 26153547
Summary:
The main role of the animal gastrointestinal (GI) tract is the selective absorption of dietary nutrients from ingested food sources. One class of vital micronutrients are the essential biometals such as copper, zinc and iron, which participate in a plethora of biological process, acting as enzymatic or structural co-factors for numerous proteins and also as important cellular signalling molecules. To help elucidate the mechanisms by which biometals are absorbed from the diet, elemental distribution was mapped in entire, intact Drosophila larval GI tracts using synchrotron X-ray fluorescence microscopy. The results revealed distinct regions of the GI tract enriched for specific metals. Copper was found to be concentrated in the copper cell region but also in the region directly anterior to the copper cells and unexpectedly, in the middle midgut/iron cell region as well. Iron was observed exclusively in the iron cell region, confirming previous work with iron-specific histological stains. Zinc was observed throughout the GI tract with an increased accumulation in the posterior midgut region, while manganese was seen to co-localize with calcium specifically in clusters in the distal Malpighian tubules. This work simultaneously reveals distribution of a number of biologically important elements in entire, intact GI tracts. These distributions revealed not only a previously undescribed Ca/Mn co-localization, but also the unexpected presence of additional Cu accumulations in the iron cell region.

Mosher, J., Zhang, W., Blumhagen, R.Z., D'Alessandro, A., Nemkov, T., Hansen, K.C., Hesselberth, J.R. and Reis, T. (2015). Coordination between Drosophila Arc1 and a specific population of brain neurons regulates organismal fat. Dev Biol [Epub ahead of print]. PubMed ID: 26209258
Summary:
The brain plays a critical yet incompletely understood role in regulating organismal fat. This study performed a neuronal silencing screen in Drosophila larvae to identify brain regions required to maintain proper levels of organismal fat. When used to modulate synaptic activity in specific brain regions, the enhancer-trap driver line E347 elevates fat upon neuronal silencing, and decreases fat upon neuronal activation. Unbiased sequencing reveals that Arc1 mRNA levels increase upon E347 activation. Arc1 mutations have been previously identified in a high-fat screen. This study reveals metabolic changes in Arc1 mutants consistent with a high-fat phenotype and an overall shift toward energy storage. Arc1-expressing cells were found to neighbor E347 neurons, and manipulating E347 synaptic activity alters Arc1 expression patterns. Elevating Arc1 expression in these cells decreases fat, a phenocopy of E347 activation. Finally, loss of Arc1 prevents the lean phenotype caused by E347 activation, suggesting that Arc1 activity is required for E347 control of body fat. Importantly, neither E347 nor Arc1 manipulation altered energy-related behaviors. These results support a model wherein E347 neurons induce Arc1 in specific neighboring cells to prevent excess fat accumulation.

Dutta, D., Dobson, A. J., Houtz, P. L., Glasser, C., Revah, J., Korzelius, J., Patel, P. H., Edgar, B. A. and Buchon, N. (2015). Regional cell-specific transcriptome mapping reveals regulatory complexity in the adult Drosophila midgut. Cell Rep 12: 346-358. PubMed ID: 26146076
Summary:
Deciphering contributions of specific cell types to organ function is experimentally challenging. The Drosophila midgut is a dynamic organ with five morphologically and functionally distinct regions (R1-R5), each composed of multipotent intestinal stem cells (ISCs), progenitor enteroblasts (EBs), enteroendocrine cells (EEs), enterocytes (ECs), and visceral muscle (VM). To characterize cellular specialization and regional function in this organ, RNA-sequencing transcriptomes were generated of all five cell types isolated by FACS from each of the five regions, R1-R5. In doing so, transcriptional diversities were identified among cell types, and regional differences within each cell type were documented that define further specialization. Cell-specific and regional Gal4 drivers were validated; roles for transporter Smvt and transcription factors GATAe, Sna, and Ptx1 in global and regional ISC regulation were demonstrated, and the transcriptional response of midgut cells upon infection was studied. The resulting transcriptome database (http://flygutseq.buchonlab.com) will foster studies of regionalization, homeostasis, immunity, and cell-cell interactions.

Rodriguez-Vazquez, M., Vaquero, D., Parra-Peralbo, E., Mejia-Morales, J. E. and Culi, J. (2015). Drosophila lipophorin receptors recruit the lipoprotein LTP to the plasma membrane to mediate lipid uptake. PLoS Genet 11: e1005356. PubMed ID: 26121667
Summary:
Lipophorin, the main Drosophila lipoprotein, circulates in the hemolymph transporting lipids between organs following routes that must adapt to changing physiological requirements. Lipophorin receptors expressed in developmentally dynamic patterns in tissues such as imaginal discs, oenocytes and ovaries control the timing and tissular distribution of lipid uptake. Using an affinity purification strategy, this study identified a novel ligand for the lipophorin receptors, the circulating lipoprotein Lipid Transfer Particle (LTP). Specific isoforms of the lipophorin receptors mediate the extracellular accumulation of LTP in imaginal discs and ovaries. The interaction requires the LA-1 module in the lipophorin receptors and is strengthened by a contiguous region of 16 conserved amino acids. Lipophorin receptor variants that do not interact with LTP cannot mediate lipid uptake, revealing an essential role of LTP in the process. In addition, lipophorin was shown to associate with the lipophorin receptors and with the extracellular matrix through weak interactions. However, during lipophorin receptor-mediated lipid uptake, LTP is required for a transient stabilization of lipophorin in the basolateral plasma membrane of imaginal disc cells. Together, these data suggests a molecular mechanism by which the lipophorin receptors tether LTP to the plasma membrane in lipid acceptor tissues. LTP would interact with lipophorin particles adsorbed to the extracellular matrix and with the plasma membrane, catalyzing the exchange of lipids between them.

Yasukawa, T., Nakahara, Y., Hirai, J. and Inoue, Y. H. (2015). Drosophila Ogg1 is required to suppress 8-oxo-guanine accumulation following oxidative stress. Genes Genet Syst 90: 11-20. PubMed ID: 26119662
Summary:
Reactive oxygen species (ROS) generated during energy production processes are a major cause of oxidative DNA damage. A DNA glycosylase encoded by the Ogg1 gene removes oxidized guanine bases and is widely conserved. In this study a genetic analysis was performed to confirm that Ogg1 plays an essential role in the removal of 8-oxo-guanines from nuclei. Quantitative real-time PCR confirmed that Ogg1 mRNA expression was reduced by 30-55% in Ogg1 mutants and in flies expressing inducible Ogg1 dsRNA compared to control flies. Additional accumulation of 8-oxo-guanines occurred in the nuclei of epithelial midgut cells after paraquat feeding in flies with downregulated Ogg1 expression. A transposon possessing the UAS sequence was integrated in the 5'-UTR of the Ogg1 alleles, and it was oriented in the same transcriptional direction as the gene. Using the Gal4/UAS system, which enabled induction of ectopic expression in Drosophila, overexpression of Ogg1 was induced by 40-fold. A lower amount of 8-oxo-guanine was observed in the midgut epithelial cells of adults overexpressing Ogg1. These genetic data strongly suggest that Ogg1 plays an essential role in the suppression of 8-oxo-guanines, consistent with its role in other organisms. Although adult flies with reduced Ogg1 expression failed to show elevated sensitivity to paraquat, those with Ogg1 overexpression showed resistance to oxidative stress by paraquat feeding and had a significantly longer lifespan in normal feeding conditions. These observations are consistent with the hypothesis that oxidative DNA damage by ROS accumulation is a major contributor to senescence.

Saturday, August 1st

Herboso, L., et al. (2015). Ecdysone promotes growth of imaginal discs through the regulation of Thor in D. melanogaster. Sci Rep 5: 12383. PubMed ID: 26198204
Summary:
Animals have a determined species-specific body size that results from the combined action of hormones and signaling pathways regulating growth rate and duration. In Drosophila, the steroid hormone ecdysone controls developmental transitions, thereby regulating the duration of the growth period. This study shows that ecdysone promotes the growth of imaginal discs in mid-third instar larvae, since imaginal discs from larvae with reduced or no ecdysone synthesis are smaller than wild type due to smaller and fewer cells. It was shown that insulin-like peptides are produced and secreted normally in larvae with reduced ecdysone synthesis, and upstream components of insulin/insulin-like signaling are activated in their discs. Instead, ecdysone appears to regulate the growth of imaginal discs via Thor/4E-BP, a negative growth regulator downstream of the insulin/insulin-like growth factor/Tor pathways. Discs from larvae with reduced ecdysone synthesis have elevated levels of Thor, while mutations in Thor partially rescue their growth. The regulation of organ growth by ecdysone is evolutionarily conserved in hemimetabolous insects, as is the case also for Blattella germanica. In summary, these data provide new insights into the relationship between components of the insulin/insulin-like/Tor and ecdysone pathways in the control of organ growth.

Lozano, J., Kayukawa, T., Shinoda, T. and Belles, X. (2014). A role for Taiman in insect metamorphosis. PLoS Genet 10: e1004769. PubMed ID: 25356827
Summary:
Recent studies in vitro have reported that the Methoprene-tolerant (Met) and Taiman (Tai) complex is the functional receptor of juvenile hormone (JH). This study has discovered that the cockroach Blattella germanica possesses four Tai isoforms resulting from the combination of two indels in the C-terminal region of the sequence. The presence of one equivalent indel-1 in Tai sequences in T. castaneum and other species suggests that Tai isoforms may be common in insects. Concomitant depletion of all four Tai isoforms in B. germanica resulted in 100% mortality, but when only the insertion 1 (IN-1) isoforms were depleted, mortality was significantly reduced and about half of the specimens experienced precocious adult development. This shows that Tai isoforms containing IN-1 are involved in transducing the JH signal that represses metamorphosis. Reporter assays indicated that both T. castaneum Tai isoforms, one that contains the IN-1 and another that does not (DEL-1) activated a JH response element (kJHRE) in Kruppel homolog 1 in conjunction with Met and JH. The results indicate that Tai is involved in the molecular mechanisms that repress metamorphosis, at least in B. germanica, and highlight the importance of distinguishing Tai isoforms when studying the functions of this transcription factor in development and other processes.

Anais Tiberghien, M., Lebreton, G., Cribbs, D., Benassayag, C. and Suzanne, M. (2015). The Hox gene Dfd controls organogenesis by shaping territorial border through regulation of basal DE-Cadherin distribution. Dev Biol [Epub ahead of print]. PubMed ID: 26206615
Summary:
Hox genes are highly conserved selector genes controlling tissue identity and organogenesis. Recent work indicates that Hox genes also control cell segregation and segmental boundary in various species, however the underlying cellular mechanisms involved in this function are poorly understood. In Drosophila, the Hox gene Deformed (Dfd) is required for specification and organogenesis of the adult Maxillary (Mx) palp. This study demonstrates that differential Dfd expression controls Mx morphogenesis through the formation of a physical boundary separating the Mx field and the Peripodial Epithelium (PE). This boundary was shown to rely on DE-cadherin (DE-cad) basal accumulation in Mx cells controlled by differential Dfd expression. Indeed, Dfd controls boundary formation through cell autonomous basal redistribution of DE-cad which leads to subsequent fold at the Dfd expression border. Finally, the loss of Mx DE-cad basal accumulation and hence of Mx-PE folding is sufficient to prevent Mx organogenesis thus revealing the crucial role of boundaries in organ differentiation. Altogether, these results reveal that Hox coordination of tissue morphogenesis relies on boundary fold formation through the modulation of DE-cad positioning.

Zhou, B., Lindsay, S. A. and Wasserman, S. A. (2015). Alternative NF-κB isoforms in the Drosophila neuromuscular junction and brain. PLoS One 10: e0132793. PubMed ID: 26167685
Summary:
The Drosophila NF-κB protein Dorsal is expressed at the larval neuromuscular junction, where its expression appears unrelated to known Dorsal functions in embryonic patterning and innate immunity. Using confocal microscopy with domain-specific antisera, this study demonstrates that larval muscle expresses only the B isoform of Dorsal, which arises by intron retention. Dorsal B interacts with and stabilizes Cactus at the neuromuscular junction, but exhibits Cactus independent localization and an absence of detectable nuclear translocation. It was further found that the Dorsal-related immune factor Dif encodes a B isoform, reflecting a conservation of B domains across a range of insect NF-kappaB proteins. Carrying out mutagenesis of the Dif locus via a site-specific recombineering approach, it was demonstrated that Dif B is the major, if not sole, Dif isoform in the mushroom bodies of the larval brain. The Dorsal and Dif B isoforms thus share a specific association with nervous system tissues as well as an alternative protein structure.

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