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Current papers in developmental biology and gene function





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Tuesday, May 31st, 2016

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Galletta, B.J., Jacobs, K.C., Fagerstrom, C.J. and Rusan, N.M. (2016). Asterless is required for centriole length control and sperm development. J Cell Biol [Epub ahead of print]. PubMed ID: 27185836
Summary:
Centrioles are the foundation of two organelles, centrosomes and cilia. Centriole numbers and functions are tightly controlled, and mutations in centriole proteins are linked to a variety of diseases, including microcephaly. Loss of the centriole protein Asterless (Asl), the Drosophila melanogaster orthologue of Cep152, prevents centriole duplication, which has limited the study of its nonduplication functions. This study identifies populations of cells with Asl-free centrioles in developing Drosophila tissues, allowing the assessment of its duplication-independent function. A role for Asl was found in controlling centriole length in germline and somatic tissue, functioning via the centriole protein Cep97. It was also found that Asl is not essential for pericentriolar material recruitment or centrosome function in organizing mitotic spindles. Lastly, Asl is required for proper basal body function and spermatid axoneme formation. Insights into the role of Asl/Cep152 beyond centriole duplication could help shed light on how Cep152 mutations lead to the development of microcephaly.

Stormo, B. M. and Fox, D. T. (2016). Distinct responses to reduplicated chromosomes require distinct Mad2 responses. Elife 5 [Epub ahead of print]. PubMed ID: 27159240
Summary:
Duplicating chromosomes once each cell cycle produces sister chromatid pairs, which separate accurately at anaphase. In contrast, reduplicating chromosomes without separation frequently produces polytene chromosomes, a barrier to accurate mitosis. Chromosome reduplication occurs in many contexts, including: polytene tissue development, polytene tumors, and following treatment with mitosis-blocking chemotherapeutics. However, mechanisms responding to or resolving polyteny during mitosis are poorly understood. This study, using Drosophila, uncovered two distinct reduplicated chromosome responses. First, when reduplicated polytene chromosomes persist into metaphase, an anaphase delay prevents tissue malformation and apoptosis. Second, reduplicated polytene chromosomes can also separate prior to metaphase through a spindle-independent mechanism termed Separation-Into-Recent-Sisters (SIRS). Both reduplication responses require the spindle assembly checkpoint protein Mad2. While Mad2 delays anaphase separation of metaphase polytene chromosomes, Mad2's control of overall mitotic timing ensures efficient SIRS. These results pinpoint mechanisms enabling continued proliferation after genome reduplication, a finding with implications for cancer progression and prevention.

Blattner, A. C., Chaurasia, S., McKee, B. D. and Lehner, C. F. (2016). Separase is required for homolog and sister disjunction during Drosophila melanogaster male meiosis, but not for biorientation of sister centromeres. PLoS Genet 12: e1005996. PubMed ID: 27120695
Summary:
Spatially controlled release of sister chromatid cohesion during progression through the meiotic divisions is of paramount importance for error-free chromosome segregation during meiosis. Cohesion is mediated by the cohesin protein complex and cleavage of one of its subunits by the endoprotease separase removes cohesin first from chromosome arms during exit from meiosis I and later from the pericentromeric region during exit from meiosis II. Separase-mediated removal of centromeric cohesin during exit from meiosis I might explain sister centromere individualization which is essential for subsequent biorientation of sister centromeres during meiosis II. To characterize a potential involvement of separase in sister centromere individualization before meiosis II, meiosis was studied in Drosophila males where homologs are not paired in the canonical manner. Meiosis does not include meiotic recombination and synaptonemal complex formation in these males. Instead, an alternative homolog conjunction system keeps homologous chromosomes in pairs. This study demonstrated that separase is required for the inactivation of this alternative conjunction at anaphase I onset. Mutations that abolish alternative homolog conjunction therefore result in random segregation of univalents during meiosis I also after separase depletion. Interestingly, these univalents become bioriented during meiosis II, suggesting that sister centromere individualization before meiosis II does not require separase.

Varadarajan, R., Ayeni, J., Jin, Z., Homola, E. and Campbell, S. D. (2016). Myt1 inhibition of Cyclin A/Cdk1 is essential for fusome integrity and pre-meiotic centriole engagement in Drosophila spermatocytes. Mol Biol Cell [Epub ahead of print]. PubMed ID: 27170181
Summary:
Regulation of cell cycle arrest in pre-meiotic G2 phase coordinates germ cell maturation and meiotic cell division with hormonal and developmental signals by mechanisms that control Cyclin B synthesis and inhibitory phosphorylation of the M phase kinase, Cdk1. This study investigated how inhibitory phosphorylation of Cdk1 by Myt1 kinase regulates pre-meiotic G2 phase of Drosophila male meiosis. Immature spermatocytes lacking Myt1 activity exhibit two distinct defects: disrupted intercellular bridges (fusomes) and premature centriole disengagement. As a result the myt1 mutant spermatocytes enter meiosis with multipolar spindles. These myt1 defects could be suppressed by depletion of Cyclin A activity or ectopic expression of Wee1 (a partially redundant Cdk1 inhibitory kinase) and phenocopied by expression of a Cdk1F mutant defective for inhibitory phosphorylation. It is therefore concluded that Myt1 inhibition of Cyclin A/Cdk1 is essential for normal fusome behavior and centriole engagement during pre-meiotic G2 arrest of Drosophila male meiosis. These novel meiotic functions that were discovered for Myt1 kinase are spatially and temporally distinct from previously described functions of Myt1 as an inhibitor of Cyclin B/Cdk1 to regulate G2/MI timing.

Monday, May 30th

Zimmer, C. T., Garrood, W. T., Puinean, A. M., Eckel-Zimmer, M., Williamson, M. S., Davies, T. G. and Bass, C. (2016). A CRISPR/Cas9 mediated point mutation in the α 6 subunit of the nicotinic acetylcholine receptor confers resistance to spinosad in Drosophila melanogaster. Insect Biochem Mol Biol 73: 62-69. PubMed ID: 27117524
Summary:
Spinosad, a widely used and economically important insecticide, targets the nicotinic acetylcholine receptor (nAChRs) of the insect nervous system. Several studies have associated loss of function mutations in the insect nAChR α6 subunit with resistance to spinosad. More recently a single non-synonymous point mutation, that does not result in loss of function, was identified in spinosad resistant strains of three insect species that results in an amino acid substitution (G275E) of the nAChR α6 subunit. This study used the CRISPR/Cas9 gene editing platform to introduce the G275E mutation into the nAChR α6 subunit of Drosophila melanogaster. This mutation does not disrupt the normal splicing of the two exons in close vicinity to the mutation site. A marked decrease in sensitivity to spinosad (66-fold) was observed in mutant flies. Although the resistance levels observed are 4.7-fold lower than exhibited by a fly strain with a null mutation of Dα6, they are nevertheless predicated to be sufficient to result in resistance to spinosad at recommended field rates. Reciprocal crossings with susceptible fly strains followed by spinosad bioassays revealed G275E is inherited as an incompletely recessive trait, thus resembling the mode of inheritance described for this mutation in the western flower thrips, Frankliniella occidentalis. This study both resolves a debate on the functional significance of a target-site mutation and provides an example of how recent advances in genome editing can be harnessed to study insecticide resistance.

Remnant, E. J., Williams, A., Lumb, C., Yang, Y. T., Chan, J., Duchene, S., Daborn, P. J., Batterham, P. and Perry, T. (2016). Evolution, expression, and function of non-neuronal ligand-gated chloride channels in Drosophila melanogaster. G3 (Bethesda) [Epub ahead of print]. PubMed ID: 27172217
Summary:
Ligand-gated chloride channels have established roles in inhibitory neurotransmission in the nervous systems of vertebrates and invertebrates. Paradoxically, expression databases in Drosophila melanogaster have revealed that three uncharacterized ligand-gated chloride channel subunits, CG7589, CG6927 and CG11340, are highly expressed in non-neuronal tissues. Furthermore, subunit copy number varies between insects, with some orders containing one ortholog, whereas other lineages exhibit copy number increases. This study shows that the Dipteran lineage has undergone two gene duplications followed by expression-based functional differentiation. Promoter-GFP expression analysis, RNA-sequencing and in situ hybridization was used to examine cell-type and tissue specific localization of the three D. melanogaster subunits. CG6927 is expressed in the nurse cells of the ovaries. CG7589 is expressed in multiple tissues including salivary gland, ejaculatory duct, malpighian tubules and early midgut. CG11340 is found in malpighian tubules, and the copper cell region of the midgut. Overexpression of CG11340 increased sensitivity to dietary copper, and RNAi and ends-out knockout of CG11340 resulted in copper tolerance, providing evidence for a specific non-neuronal role for this subunit in D. melanogaster Ligand-gated chloride channels are important insecticide targets and this study highlights copy number and functional divergence in insect lineages, raising the potential that order-specific receptors could be isolated within an effective class of insecticide targets.

Barry, W.E. and Thummel, C.S. (2016). The Drosophila HNF4 nuclear receptor promotes glucose-stimulated insulin secretion and mitochondrial function in adults. Elife 5. PubMed ID: 27185732
Summary:
Although mutations in HNF4A were identified as the cause of Maturity Onset Diabetes of the Young 1 (MODY1) two decades ago, the mechanisms by which this nuclear receptor regulates glucose homeostasis remain unclear. This study reports that loss of Drosophila HNF4 recapitulates hallmark symptoms of MODY1, including adult-onset hyperglycemia, glucose intolerance and impaired glucose-stimulated insulin secretion (GSIS). These defects are linked to a role for dHNF4 in promoting mitochondrial function as well as the expression of Hex-C, a homolog of the MODY2 gene Glucokinase. dHNF4 is required in the fat body and insulin-producing cells to maintain glucose homeostasis by supporting a developmental switch toward oxidative phosphorylation and GSIS at the transition to adulthood. These findings establish an animal model for MODY1 and define a developmental reprogramming of metabolism to support the energetic needs of the mature animal. 

Shen, R., Wang, B., Giribaldi, M.G., Ayres, J., Thomas, J.B. and Montminy, M. (2016). Neuronal energy-sensing pathway promotes energy balance by modulating disease tolerance. Proc Natl Acad Sci U S A [Epub ahead of print]. PubMed ID: 27208092
Summary:
The starvation-inducible coactivator cAMP response element binding protein (CREB)-cAMP-regulated transcription coactivator (Crtc) has been shown to promote starvation resistance in Drosophila by up-regulating CREB target gene expression in neurons, although the underlying mechanism is unclear. This study found that Crtc and its binding partner CREB enhance energy homeostasis by stimulating the expression of short neuropeptide F (sNPF), an ortholog of mammalian neuropeptide Y, which was shown to be a direct target of CREB and Crtc. Neuronal sNPF was found to promote energy homeostasis via gut enterocyte sNPF receptors, which appear to maintain gut epithelial integrity. Loss of Crtc-sNPF signaling disrupts epithelial tight junctions, allowing resident gut flora to promote chronic increases in antimicrobial peptide (AMP) gene expression that compromised energy balance. Growth on germ-free food reduces AMP gene expression and rescues starvation sensitivity in Crtc mutant flies. Overexpression of Crtc or sNPF in neurons of wild-type flies dampens the gut immune response and enhances starvation resistance. These results reveal a previously unidentified tolerance defense strategy involving a brain-gut pathway that maintains homeostasis through its effects on epithelial integrity.

Sunday, May 29th

O'Neill, R.S. and Clark, D.V. (2016). Partial functional diversification of Drosophila melanogaster septins Sep2 and Sep5. G3 (Bethesda) [Epub ahead of print]. PubMed ID: 27172205
Summary:
The septin family of hetero-oligomeric-complex-forming proteins can be divided into subgroups, and subgroup members are interchangeable at specific positions in the septin complex. Drosophila melanogaster has five septin genes, including the two SEPT6 subgroup members Sep2 and Sep5. It has been previously shown that Sep2 has a unique function in oogenesis, which is not performed by Sep5. This study finds that Sep2 is uniquely required for follicle cell encapsulation of female germline cysts, and that Sep2 and Sep5 are redundant for follicle cell proliferation. The five D. melanogaster septins localize similarly in oogenesis, including as rings flanking the germline ring canals. Pnut fails to localize in Sep5; Sep2 double mutant follicle cells, indicating that septin complexes fail to form in the absence of both Sep2 and Sep5. It was also found that mutations in septins enhance the mutant phenotype of bazooka, a key component in the establishment of cell polarity, suggesting a link between septin function and cell polarity. Overall, this work suggests Sep5 has undergone partial loss of ancestral protein function, and demonstrates redundant and unique functions of septins.

Luo, J., Wang, H., Kang, D., Guo, X., Wan, P., Wang, D. and Chen, J. (2016). Dlg5 maintains apical polarity by promoting membrane localization of Crumbs during Drosophila oogenesis. Sci Rep 6: 26553. PubMed ID: 27211898
Summary:
Apical-basal polarity plays critical roles in the functions of epithelial tissues. However, the mechanisms of epithelial polarity establishment and maintenance remain to be fully elucidated. This study shows that the membrane-associated guanylate kinase (MAGUK) family protein Dlg5 is required for the maintenance of apical polarity of follicle epithelium during Drosophila oogenesis. Dlg5 localizes at the apical membrane and adherens junction (AJ) of follicle epithelium in early stage egg chambers. Specifically, the major function of Dlg5 is to promote apical membrane localization of Crumbs, since overexpression of Crumbs but not other major apical or AJ components can rescue epithelial polarity defects resulting from loss of Dlg5. Furthermore, by performing a structure-function analysis of Dlg5, it was found that the C-terminal PDZ3 and PDZ4 domains are required for all Dlg5's functions as well as its ability to localize to apical membrane. The N-terminal coiled-coil motif can be individually targeted to the apical membrane, while the central linker region can be targeted to AJ. Lastly, the MAGUK core domains of PDZ4-SH3-GUK can be individually targeted to apical, AJ and basolateral membranes. 

Cheng, B., Kuppanda, N., Aldrich, J.C., Akbari, O.S. and Ferree, P.M. (2016). Male-killing spiroplasma alters behavior of the dosage compensation complex during Drosophila melanogaster embryogenesis. Curr Biol [Epub ahead of print]. PubMed ID: 27161498
Summary:
Numerous arthropods harbor maternally transmitted bacteria that induce the preferential death of males. This sex-specific lethality benefits the bacteria because males are "dead ends" regarding bacterial transmission, and their absence may result in additional resources for their viable female siblings who can thereby more successfully transmit the bacteria. Although these symbionts disrupt a range of developmental processes, the underlying cellular mechanisms are largely unknown. It has previously been shown that mutations in genes of the dosage compensation pathway of Drosophila melanogaster suppress male killing caused by the bacterium Spiroplasma. This suggests that dosage compensation is a target of Spiroplasma. However, it remains unclear how this pathway is affected, and whether the underlying interactions require the male-specific cellular environment. This study investigated the cellular basis of male embryonic lethality in D. melanogaster induced by Spiroplasma. It was found that the dosage compensation complex (DCC), which acetylates X chromatin in males, becomes mis-localized to ectopic regions of the nucleus immediately prior to the killing phase. This effect is accompanied by inappropriate histone acetylation and genome-wide mis-regulation of gene expression. Artificially induced formation of the DCC in infected females, through transgenic expression of the DCC-specific gene msl-2, results in mis-localization of this complex to non-X regions and early Spiroplasma-induced death, mirroring the killing effects in males. These findings strongly suggest that Spiroplasma initiates male killing by targeting the dosage compensation machinery directly and independently of other cellular features characteristic of the male sex.

Barton, L. J., Lovander, K. E., Pinto, B. S. and Geyer, P. K. (2016). Drosophila male and female germline stem cell niches require the nuclear lamina protein Otefin. Dev Biol. [Epub ahead of print] PubMed ID: 27174470
Summary:
The nuclear lamina is an extensive protein network that underlies the inner nuclear envelope. This network includes the LAP2-emerin-MAN1-domain (LEM-D) protein family, proteins that share an association with the chromatin binding protein Barrier-to-autointegration factor (BAF). Loss of individual LEM-D proteins causes progressive, tissue-restricted diseases, known as laminopathies. Mechanisms associated with laminopathies are not yet understood. This study describes one of the Drosophila nuclear lamina LEM-D proteins, Otefin (Ote), a homologue of emerin. Previous studies have shown that Ote is autonomously required for the survival of female germline stem cells (GSCs). This study demonstrates that Ote is also required for survival of somatic cells in the ovarian niche, with loss of Ote causing a decrease in cap cell number and altered signal transduction. Germ cell-restricted expression of Ote rescues these defects, revealing a non-autonomous function for Ote in niche maintenance and emphasizing that GSCs contribute to the maintenance of their own niches. Further, the requirement of Ote in the male fertility was investigated. ote mutant males become prematurely sterile as they age. Parallel to observations in females, this sterility is associated with GSC loss and changes in somatic cells of the niche, phenotypes that are largely rescued by germ cell-restricted Ote expression. Taken together, these studies demonstrate that Ote is required autonomously for survival of two stem cell populations, as well as non-autonomously for maintenance of two somatic niches. Finally, the data add to growing evidence that LEM-D proteins have critical roles in stem cell survival and tissue homeostasis.

Saturday, May 28th

Yang, C.H., Shih, M.F., Chang, C.C., Chiang, M.H., Shih, H.W., Tsai, Y.L., Chiang, A.S., Fu, T.F. and Wu, C.L. (2016). Additive expression of consolidated memory through Drosophila mushroom body subsets. PLoS Genet 12: e1006061. PubMed ID: 27195782
Summary:
Associative olfactory memory in Drosophila has two components called labile anesthesia-sensitive memory and consolidated anesthesia-resistant memory (ARM). Mushroom body (MB) is a brain region critical for the olfactory memory and comprised of 2000 neurons that can be classified into αβ, α'β', and γ neurons. It has been previously demonstrated that two parallel pathways mediate ARM consolidation: the serotonergic dorsal paired medial (DPM)-αβ neurons and the octopaminergic anterior paired lateral (APL)-α'β' neurons. This study shows that blocking the output of αβ neurons and that of α'β' neurons each impairs ARM retrieval, and blocking both simultaneously has an additive effect. Knockdown of radish and octβ2R in αβ and α'β' neurons, respectively, impairs ARM. A combinatorial assay of radish mutant background rsh1 and neurotransmission blockade confirms that ARM retrieved from α'β' neuron output is independent of radish. The MBON-β2β'2a and MBON-β'2mp were identified as the MB output neurons downstream of αβ and α'β' neurons, respectively, whose glutamatergic transmissions also additively contribute to ARM retrieval. Finally, α'β' neurons can be functionally subdivided into α'β'm neurons required for ARM retrieval, and α'β'ap neurons required for ARM consolidation. These data demonstrate that two parallel neural pathways mediating ARM consolidation in Drosophila MB additively contribute to ARM expression during retrieval.

Perisse, E., Owald, D., Barnstedt, O., Talbot, C.B., Huetteroth, W. and Waddell, S. (2016). Aversive learning and appetitive motivation toggle feed-forward inhibition in the Drosophila mushroom body. Neuron [Epub ahead of print]. PubMed ID: 27210550
Summary:
In Drosophila, negatively reinforcing dopaminergic neurons also provide the inhibitory control of satiety over appetitive memory expression. This study shows that aversive learning causes a persistent depression of the conditioned odor drive to two downstream feed-forward inhibitory GABAergic interneurons of the mushroom body, called MVP2, or mushroom body output neuron (MBON)-γ1pedc>α/β. However, MVP2 neuron output is only essential for expression of short-term aversive memory. Stimulating MVP2 neurons preferentially inhibits the odor-evoked activity of avoidance-directing MBONs and odor-driven avoidance behavior, whereas their inhibition enhances odor avoidance. In contrast, odor-evoked activity of MVP2 neurons is elevated in hungry flies, and their feed-forward inhibition is required for expression of appetitive memory at all times. Moreover, imposing MVP2 activity promotes inappropriate appetitive memory expression in food-satiated flies. Aversive learning and appetitive motivation therefore toggle alternate modes of a common feed-forward inhibitory MVP2 pathway to promote conditioned odor avoidance or approach.

Hoi, C.S., Xiong, W. and Rebay, I. (2016). Retinal axon guidance requires integration of Eya and the JAK/STAT pathway into phosphotyrosine-based signaling circuitries in Drosophila. Genetics [Epub ahead of print]. PubMed ID: 27194748
Summary:
The transcriptional coactivator and phosphatase eyes absent (Eya) is dynamically compartmentalized between the nucleus and cytoplasm. Although the nuclear transcriptional circuits within which Eya operates have been extensively characterized, understanding of its cytoplasmic functions and interactions remains limited. Previous work has showed that phosphorylation of Drosophila Eya by the Abelson tyrosine kinase can recruit Eya to the cytoplasm, and that eya-abelson interactions are required for photoreceptor axons to project to correct layers in the brain. Based on these observations, this study postulated that photoreceptor axon targeting might provide a suitable context for identifying the cytoplasmic signaling cascades with which Eya interacts. Using a dose-sensitive eya misexpression background, an RNAi-based genetic screen was performed to identify suppressors. Included among the top 10 hits are non-receptor tyrosine kinases and multiple members of the Jak/Stat signaling network (hop, Stat92E, Socs36E, and Socs44A), a pathway not previously implicated in axon targeting. Individual loss-of-function phenotypes combined with analysis of axonal projections in Stat92E null clones confirm the importance of photoreceptor autonomous Jak/Stat signaling. Experiments in cultured cells detect cytoplasmic complexes between Eya and Hop, Socs36E and Socs44A; the latter interaction requires both the Src Homology 2 motif in Socs44A and tyrosine phosphorylated Eya, suggesting direct binding and validating the premise of the screen. Taken together, these data provide new insight into the cytoplasmic phosphotyrosine signaling networks that operate during photoreceptor axon guidance and suggest specific points of interaction with Eya.

Clark, M. Q., McCumsey, S. J., Lopez-Darwin, S., Heckscher, E. S. and Doe, C. Q. (2016). Functional genetic screen to identify interneurons governing behaviorally distinct aspects of Drosophila larval motor programs. G3 (Bethesda) [Epub ahead of print]. PubMed ID: 27172197
Summary:
Drosophila larval crawling is an attractive system to study patterned motor output at the level of animal behavior. Larval crawling consists of waves of muscle contractions generating forward or reverse locomotion. In addition, larvae undergo additional behaviors including head casts, turning, and feeding. It is likely that some neurons are used in all these behaviors (e.g. motor neurons), but the identity (or even existence) of neurons dedicated to specific aspects of behavior is unclear. To identify neurons that regulate specific aspects of larval locomotion, a genetic screen was performed to identify neurons that, when activated, could elicit distinct motor programs. 165 Janelia CRM-Gal4 lines--chosen for sparse neuronal expression--were used to express the warmth-inducible neuronal activator TrpA1, and a screen was carried out for locomotor defects. The primary screen measured forward locomotion velocity, and 63 lines were identified that had locomotion velocities significantly slower than controls following TrpA1 activation (28 ° C). A secondary screen was performed on these lines, revealing multiple discrete behavioral phenotypes including slow forward locomotion, excessive reverse locomotion, excessive turning, excessive feeding, immobile, rigid paralysis, and delayed paralysis. While many of the Gal4 lines had motor, sensory, or muscle expression that may account for some or all of the phenotype, some lines showed specific expression in a sparse pattern of interneurons. These results show that distinct motor programs utilize distinct subsets of interneurons, and provide an entry point for characterizing interneurons governing different elements of the larval motor program.

Friday, May 27th

Trujillo, G. V., Nodal, D. H., Lovato, C. V., Hendren, J. D., Helander, L. A., Lovato, T. L., Bodmer, R. and Cripps, R. M. (2016). The canonical Wingless signaling pathway is required but not sufficient for inflow tract formation in the Drosophila melanogaster heart. Dev Biol [Epub ahead of print]. PubMed ID: 26983369
Summary:
The inflow tracts of the embryonic Drosophila cardiac tube, termed ostia, arise in its posterior three segments from cardiac cells that co-express the homeotic transcription factor Abdominal-A (abdA), the orphan nuclear receptor Seven-up (Svp), and the signaling molecule Wingless (Wg). To define the roles of these factors in inflow tract development, this study assessed their function in inflow tract formation. Using several criteria, it was demonstrated that abdA, svp, and wg are each critical for normal inflow tract formation. Wg acts in an autocrine manner to impact ostia fate, and it mediates this effect at least partially through the canonical Wg signaling pathway. By contrast, neither wg expression nor Wg signaling are sufficient for inflow tract formation when expressed in anterior Svp cells that do not normally form inflow tracts in the embryo. Instead, ectopic abd-A expression throughout the cardiac tube is required for the formation of ectopic inflow tracts, indicating that autocrine Wg signaling must be supplemented by additional Hox-dependent factors to effect inflow tract formation. Taken together, these studies define important cellular and molecular events that contribute to cardiac inflow tract development in Drosophila. Given the broad conservation of the cardiac regulatory network through evolution, these studies provide insight into mechanisms of cardiac development in higher animals.

Cui, J., Lai, Y. W., Sartain, C. V., Zuckerman, R. M. and Wolfner, M. F. (2016). The Drosophila prage gene, required for maternal transcript destabilization in embryos, encodes a predicted RNA exonuclease. G3 (Bethesda) [Epub ahead of print]. PubMed ID: 27172196
Summary:
Egg activation, the transition of mature oocytes into developing embryos, is critical for the initiation of embryogenesis. This process is characterized by resumption of meiosis, changes in the egg's coverings and by alterations in the transcriptome and proteome of the egg; all of these occur in the absence of new transcription. Activation of the egg is prompted by ionic changes in the cytoplasm (usually a rise in cytosolic calcium levels) that are triggered by fertilization in some animals and by mechanosensitive cues in others. The egg's transcriptome is dramatically altered during the process, including by the removal of many maternal mRNAs that are not needed for embryogenesis. However, the mechanisms and regulators of this selective RNA degradation are not yet fully known. Forward genetic approaches in Drosophila have identified maternal-effect genes whose mutations prevent the transcriptome changes. One of these genes, prage (prg) was identified by Tadros in a screen for mutants that fail to destabilize maternal transcripts. This study identified molecular nature of the prg gene through a combination of deficiency mapping, complementation analysis, and DNA sequencing of both extant prg mutant alleles. prg encodes a ubiquitously-expressed predicted exonuclease, consistent with its role in maternal mRNA destabilization during egg activation.

Kato, K., Dong, B., Wada, H., Tanaka-Matakatsu, M., Yagi, Y. and Hayashi, S. (2016). Microtubule-dependent balanced cell contraction and luminal-matrix modification accelerate epithelial tube fusion. Nat Commun 7: 11141. PubMed ID: 27067650
Summary:
Connection of tubules into larger networks is the key process for the development of circulatory systems. In Drosophila development, tip cells of the tracheal system lead the migration of each branch and connect tubules by adhering to each other and simultaneously changing into a torus-shape. This study shows that as adhesion sites form between fusion cells, myosin and microtubules form polarized bundles that connect the new adhesion site to the cells' microtubule-organizing centres, and that E-cadherin and retrograde recycling endosomes are preferentially deposited at the new adhesion site. It was demonstrated that microtubules help balancing tip cell contraction, which is driven by myosin, and is required for adhesion and tube fusion. Also, retrograde recycling and directed secretion of a specific matrix protein into the fusion-cell interface promote fusion. The study proposes that microtubule bundles connecting these cell-cell interfaces coordinate cell contractility and apical secretion to facilitate tube fusion. 

Liu, J., Xiao, Y., Zhang, T. and Ma, J. (2016). Time to move on: modeling transcription dynamics during an embryonic transition away from maternal control. Fly (Austin): [Epub ahead of print]. PubMed ID: 27172244
Summary:
A recent study investigated the regulation of hunchback (hb) transcription dynamics in Drosophila embryos. The results suggest that shutdown of hb transcription at early nuclear cycle (nc) 14 is an event associated with the global changes taking place during the mid-blastula transition (MBT). This study developed a simple model of hb transcription dynamics during this transition time. With kinetic parameters estimated from published experimental data, the model describes the dynamical processes of hb gene transcription and hb mRNA accumulation. With two steps, transcription onset upon exiting the previous mitosis followed by a sudden impact that blocks gene activation, the model recapitulates the observed dynamics of hb transcription during the nc14 interphase. The timing of gene inactivation is essential, as its alterations lead to changes in both hb transcription dynamics and hb mRNA levels. This model provides a clear dynamical picture of hb transcription regulation as one of the many, actively regulated events concurrently taking place during the MBT.

Thursday, May 26th

Harris, N., Braiser, D. J., Dickman, D. K., Fetter, R. D., Tong, A. and Davis, G. W. (2015). The innate immune receptor PGRP-LC controls presynaptic homeostatic plasticity. Neuron 88: 1157-1164. PubMed ID: 26687223
Summary:
It is now appreciated that the brain is immunologically active. Highly conserved innate immune signaling responds to pathogen invasion and injury and promotes structural refinement of neural circuitry. However, it remains generally unknown whether innate immune signaling has a function during the day-to-day regulation of neural function in the absence of pathogens and irrespective of cellular damage or developmental change. This study shows that an innate immune receptor, a member of the peptidoglycan pattern recognition receptor family (PGRP-LC), is required for the induction and sustained expression of homeostatic synaptic plasticity. This receptor functions presynaptically, controlling the homeostatic modulation of the readily releasable pool of synaptic vesicles following inhibition of postsynaptic glutamate receptor function. Thus, PGRP-LC is a candidate receptor for retrograde, trans-synaptic signaling, a novel activity for innate immune signaling and the first known function of a PGRP-type receptor in the nervous system of any organism.

Hussein, N. A., Delaney, T. L., Tounsel, B. L. and Liebl, F. L. (2016). The extracellular-regulated kinase effector Lk6 is required for Glutamate receptor localization at the Drosophila neuromuscular junction. J Exp Neurosci 10: 77-91. PubMed ID: 27199570
Summary:
The proper localization and synthesis of postsynaptic glutamate receptors are essential for synaptic plasticity. Synaptic translation initiation is thought to occur via the target of rapamycin (TOR) and mitogen-activated protein kinase signal-integrating kinase (Mnk) signaling pathways, which is downstream of extracellular-regulated kinase (ERK). This study used the model glutamatergic synapse, the Drosophila neuromuscular junction, to better understand the roles of the Mnk and TOR signaling pathways in synapse development. These synapses contain non-NMDA receptors that are most similar to AMPA receptors. The data show that Lk6, the Drosophila homolog of Mnk1 and Mnk2, is required in either presynaptic neurons or postsynaptic muscle for the proper localization of the GluRIIA glutamate receptor subunit. Lk6 may signal through eukaryotic initiation factor (eIF) 4E to regulate the synaptic levels of GluRIIA as either interfering with eIF4E binding to eIF4G or expression of a nonphosphorylatable isoform of eIF4E resulted in a significant reduction in GluRIIA at the synapse. It was also found that Lk6 and TOR may independently regulate synaptic levels of GluRIIA.

MacNamee, S. E., Liu, K. E., Gerhard, S., Tran, C. T., Fetter, R. D., Cardona, A., Tolbert, L. P. and Oland, L. A. (2016). Astrocytic glutamate transport regulates a Drosophila CNS synapse that lacks astrocyte ensheathment. J Comp Neurol [Epub ahead of print]. PubMed ID: 27073064
Summary:
Anatomical, molecular, and physiological interactions between astrocytes and neuronal synapses regulate information processing in the brain. The fruit fly Drosophila melanogaster has become a valuable experimental system for genetic manipulation of the nervous system and has enormous potential for elucidating mechanisms that mediate neuron-glia interactions. This study shows the first electrophysiological recordings from Drosophila astrocytes and characterizes their spatial and physiological relationship with particular synapses. Astrocyte intrinsic properties were found to be strongly analogous to those of vertebrate astrocytes, including a passive current-voltage relationship, low membrane resistance, high capacitance, and dye-coupling to local astrocytes. Responses to optogenetic stimulation of glutamatergic pre-motor neurons were correlated directly with anatomy using serial electron microscopy reconstructions of homologous identified neurons and surrounding astrocytic processes. Robust bidirectional communication was present: neuronal activation triggered astrocytic glutamate transport via Eaat1, and blocking Eaat1 extended glutamatergic interneuron-evoked inhibitory post-synaptic currents in motor neurons. The neuronal synapses were always located within a micron of an astrocytic process, but none were ensheathed by those processes. Thus, fly astrocytes can modulate fast synaptic transmission via neurotransmitter transport within these anatomical parameters.

Cai, W., Wei, Y., Jarnik, M., Reich, J. and Lilly, M. A. (2016). The GATOR2 component Wdr24 regulates TORC1 activity and lysosome function. PLoS Genet 12: e1006036. PubMed ID: 27166823
Summary:

TORC1 (see Drosophila Tor) is a master regulator of metabolism in eukaryotes that responds to multiple upstream signaling pathways. The GATOR complex is a newly defined upstream regulator of TORC1 that contains two sub-complexes, GATOR1, which inhibits TORC1 activity in response to amino acid starvation and GATOR2, which opposes the activity of GATOR1. The genome of Drosophila contains a single Sea2/Wdr24 homolog encoded by the gene CG7609 that shares 25% identity and 44% similarity to yeast Sea2 and 37% identity and 54% similarity to the human homolog WDR24. This study defines the in vivo role of the GATOR2 component Wdr24 in Drosophila. Wdr24 was shown to have both TORC1 dependent and independent functions in the regulation of cellular metabolism. Through the characterization of a null allele, it was shown that Wdr24 is a critical effector of the GATOR2 complex that promotes the robust activation of TORC1 and cellular growth in a broad array of Drosophila tissues. Additionally, epistasis analysis between wdr24 and genes that encode components of the GATOR1 complex revealed that Wdr24 has a second critical function, the TORC1 independent regulation of lysosome dynamics and autophagic flux. Notably, it was found that two additional members of the GATOR2 complex, Mio and Seh1, also have a TORC1 independent role in the regulation of lysosome function. Wdr24 was also shown to promote lysosome acidification and autophagic flux in mammalian cells. Taken together these data support the model that Wdr24 is a key effector of the GATOR2 complex, required for both TORC1 activation and the TORC1 independent regulation of lysosomes.

Wednesday, May 25th

Nguyen, D., Fayol, O., Buisine, N., Lecorre, P. and Uguen, P. (2016). Functional interaction between HEXIM and Hedgehog signaling during Drosophila wing development. PLoS One 11: e0155438. PubMed ID: 27176767
Summary:
Studying the dynamic of gene regulatory networks is essential in order to understand the specific signals and factors that govern cell proliferation and differentiation during development. This also has direct implication in human health and cancer biology. The general transcriptional elongation regulator P-TEFb regulates the transcriptional status of many developmental genes. Its biological activity is controlled by an inhibitory complex composed of HEXIM and the 7SK snRNA. This study examines the function of HEXIM during Drosophila development. It was found that HEXIM affects the Hedgehog signaling pathway. HEXIM knockdown flies display strong phenotypes and organ failures. In the wing imaginal disc, HEXIM knockdown initially induces ectopic expression of Hedgehog (Hh) and its transcriptional effector Cubitus interuptus (Ci). In turn, deregulated Hedgehog signaling provokes apoptosis, which is continuously compensated by apoptosis-induced cell proliferation. Thus, the HEXIM knockdown mutant phenotype does not result from the apoptotic ablation of imaginal disc but rather from the failure of dividing cells to commit to a proper developmental program due to Hedgehog signaling defects. Furthermore, ci was shown to be a genetic suppressor of hexim. Thus, HEXIM ensures the integrity of Hedgehog signaling in wing imaginal disc, by a yet unknown mechanism. 

Yang, E., Tacchelly-Benites, O., Wang, Z., Randall, M. P., Tian, A., Benchabane, H., Freemantle, S., Pikielny, C., Tolwinski, N. S., Lee, E. and Ahmed, Y. (2016). Wnt pathway activation by ADP-ribosylation. Nat Commun 7: 11430. PubMed ID: 27138857
Summary:
Wnt/beta-catenin signalling directs fundamental processes during metazoan development and can be aberrantly activated in cancer. Wnt stimulation induces the recruitment of the scaffold protein Axin from an inhibitory destruction complex to a stimulatory signalosome. This study analysed the early effects of Wnt on Axin and found that the ADP-ribose polymerase Tankyrase (Tnks)-known to target Axin for proteolysis-regulates Axin's rapid transition following Wnt stimulation. The pool of ADP-ribosylated Axin, which is degraded under basal conditions, increases immediately following Wnt stimulation in both Drosophila and human cells. ADP-ribosylation of Axin enhances its interaction with the Wnt co-receptor LRP6, an essential step in signalosome assembly. It is suggested that in addition to controlling Axin levels, Tnks-dependent ADP-ribosylation promotes the reprogramming of Axin following Wnt stimulation; and it is proposed that Tnks inhibition blocks Wnt signalling not only by increasing destruction complex activity, but also by impeding signalosome assembly.

Wang, Y. and DiMario, P. (2016). Loss of Drosophila nucleostemin 2 (NS2) blocks nucleolar release of the 60S subunit leading to ribosome stress. Chromosoma [Epub ahead of print]. PubMed ID: 27150106
Summary:
Four nucleostemin-like proteins (nucleostemin (NS) 1-4) have been identified in Drosophila. NS1 and NS2 are nucleolar proteins, while NS3 and NS4 are cytoplasmic proteins. Previous studies have shown that NS1 (homologous to human GNL3) enriches within the granular components (GCs) of Drosophila nucleoli and is required for efficient maturation or nucleolar release of the 60S subunit. This study shows that NS2 is homologous to the human nucleostemin-like protein, Ngp1 (GNL2), and that endogenous NS2 is expressed in both progenitor and terminally differentiated cell types. Exogenous GFP-NS2 enriched within nucleolar GCs versus endogenous fibrillarin that marked the dense fibrillar components (DFCs). Like NS1, depletion of NS2 in midgut cells blocked the release of the 60S subunit as detected by the accumulation of GFP-RpL11 within nucleoli, and this likely led to the general loss of 60S subunits as shown by immunoblot analyses of RpL23a and RpL34. At the ultrastructural level, nucleoli in midgut cells depleted of NS2 displayed enlarged GCs not only on the nucleolar periphery but interspersed within the DFCs. Depletion of NS2 caused ribosome stress: larval midgut cells displayed prominent autophagy marked by the appearance of autolysosomes containing mCherry-ATG8a and the appearance of rough endoplasmic reticulum (rER)-derived isolation membranes. Larval imaginal wing disc cells depleted of NS2 induced apoptosis as marked by anti-caspase 3 labeling; loss of these progenitor cells resulted in defective adult wings. It is concluded that nucleolar proteins NS1 and NS2 have similar but non-overlapping roles in the final maturation or nucleolar release of 60S ribosomal subunits.

Saadin, A. and Starz-Gaiano, M. (2016). Identification of novel regulators of the JAK/STAT signaling pathway that control border cell migration in the Drosophila ovary. G3 (Bethesda) [Epub ahead of print]. PubMed ID: 27175018
Summary:
The JAK/STAT signaling pathway is an essential regulator of cell migration both in mammals and fruit flies. Cell migration is required for normal embryonic development and immune response but can also lead to detrimental outcomes, such as tumor metastasis. A cluster of cells termed "border cells" in the Drosophila ovary provides an excellent example of a collective cell migration, in which two different cell types coordinate their movements. Border cells arise within the follicular epithelium and are required to invade the neighboring cells and migrate to the oocyte to contribute to a fertilizable egg. Multiple components of the STAT signaling pathway are required during border cell specification and migration; however, the functions and identities of other potential regulators of the pathway during these processes are not yet known. To find new components of the pathway that govern cell invasiveness, 48 predicted STAT modulators were knocked down using RNAi expression in follicle cells, and defective cell movement was assayed. Seven of these regulators were shown to be involved in either border cell specification or migration. Examination of the epistatic relationship between candidate genes and Stat92E reveals that the products of two genes, protein tyrosine phosphatase 61f (ptp61f) and brahma (brm), interact with Stat92E during both border cell specification and migration.

Tuesday, May 24th

Chen, K., Koe, C. T., Xing, Z. B., Tian, X., Rossi, F., Wang, C., Tang, Q., Zong, W., Hong, W. J., Taneja, R., Yu, F., Gonzalez, C., Wu, C., Endow, S. and Wang, H. (2016). Arl2- and Msps-dependent microtubule growth governs asymmetric division. J Cell Biol 212: 661-676. PubMed ID: 26953351
Summary:
Asymmetric division of neural stem cells is a fundamental strategy to balance their self-renewal and differentiation. It is long thought that microtubules are not essential for cell polarity in asymmetrically dividing Drosophila melanogaster neuroblasts (NBs; neural stem cells). This study shows that Drosophila ADP ribosylation factor like-2 (Arl2) and Msps, a known microtubule-binding protein, control cell polarity and spindle orientation of NBs. Upon arl2 RNA intereference, Arl2-GDP expression, or arl2 deletions, microtubule abnormalities and asymmetric division defects were observed. Conversely, overactivation of Arl2 leads to microtubule overgrowth and depletion of NBs. Arl2 regulates microtubule growth and asymmetric division through localizing Msps to the centrosomes in NBs. Moreover, Arl2 regulates dynein function and in turn centrosomal localization of D-TACC and Msps. Arl2 physically associates with tubulin cofactors C, D, and E. Arl2 functions together with tubulin-binding cofactor D to control microtubule growth, Msps localization, and NB self-renewal. Therefore, Arl2- and Msps-dependent microtubule growth is a new paradigm regulating asymmetric division of neural stem cells.

Chatterjee, C., Benoit, M. P., DePaoli, V., Diaz-Valencia, J. D., Asenjo, A. B., Gerfen, G. J., Sharp, D. J. and Sosa, H. (2016). Distinct interaction modes of the Kinesin-13 motor domain with the microtubule. Biophys J 110: 1593-1604. PubMed ID: 27074684
Summary:
Kinesins-13s are members of the kinesin superfamily of motor proteins that depolymerize microtubules (MTs) and have no motile activity. Instead of generating unidirectional movement over the MT lattice, like most other kinesins, kinesins-13s undergo one-dimensional diffusion (ODD) and induce depolymerization at the MT ends. To understand the mechanism of ODD and the origin of the distinct kinesin-13 functionality, ensemble and single-molecule fluorescence polarization microscopy was used to analyze the behavior and conformation of Drosophila melanogaster kinesin-13 KLP10A protein constructs bound to the MT lattice. KLP10A was found to interact with the MT in two coexisting modes: one in which the motor domain binds with a specific orientation to the MT lattice and another where the motor domain is very mobile and able to undergo ODD. By comparing the orientation and dynamic behavior of mutated and deletion constructs it is concluded that 1) the Kinesin-13 class specific neck domain and loop-2 help orienting the motor domain relative to the MT. 2) During ODD the KLP10A motor-domain changes orientation rapidly (rocks or tumbles). 3) The motor domain alone is capable of undergoing ODD. 4) A second tubulin binding site in the KLP10A motor domain is not critical for ODD. 5) The neck domain is not the element preventing KLP10A from binding to the MT lattice like motile kinesins.

Aranjuez, G., Burtscher, A., Sawant, K., Majumder, P. and McDonald, J. A. (2016). Dynamic myosin activation promotes collective morphology and migration by locally balancing oppositional forces from surrounding tissue. Mol Biol Cell. PubMed ID: 27122602
Summary:
Migrating cells need to overcome physical constraints from the local microenvironment to navigate their way through tissues. Cells that move collectively have the additional challenge of negotiating complex environments in vivo while maintaining cohesion of the group as a whole. The mechanisms by which collectives maintain a migratory morphology while resisting physical constraints from the surrounding tissue are poorly understood. Drosophila border cells represent a genetic model of collective migration within a cell-dense tissue. Border cells move as a cohesive group of 6-10 cells, traversing a network of large germline-derived nurse cells within the ovary. This study shows that the border cell cluster is compact and round throughout their entire migration, a shape that is maintained despite the mechanical pressure imposed by the surrounding nurse cells. Non-muscle myosin II (Myo-II) activity at the cluster periphery becomes elevated in response to increased constriction by nurse cells. Furthermore, the distinctive border cell collective morphology requires highly dynamic and localized enrichment of Myo-II. Thus, activated Myo-II promotes cortical tension at the outer edge of the migrating border cell cluster to resist compressive forces from nurse cells. It is proposed that dynamic actomyosin tension at the periphery of collectives facilitates their movement through restrictive tissues.

Monteith, C. E., Brunner, M. E., Djagaeva, I., Bielecki, A. M., Deutsch, J. M. and Saxton, W. M. (2016). A mechanism for cytoplasmic streaming: Kinesin-driven alignment of microtubules and fast fluid flows. Biophys J 110: 2053-2065. PubMed ID: 27166813
Summary:
The transport of cytoplasmic components can be profoundly affected by hydrodynamics. Cytoplasmic streaming in Drosophila oocytes offers a striking example. Forces on fluid from kinesin-1 are initially directed by a disordered meshwork of microtubules, generating minor slow cytoplasmic flows. Subsequently, to mix incoming nurse cell cytoplasm with ooplasm, a subcortical layer of microtubules forms parallel arrays that support long-range, fast flows. To analyze the streaming mechanism, observations of microtubule and organelle motions were combined with detailed mathematical modeling. In the fast state, microtubules tethered to the cortex form a thin subcortical layer and undergo correlated sinusoidal bending. Organelles moving in flows along the arrays show velocities that are slow near the cortex and fast on the inward side of the subcortical microtubule layer. A quantitative coupled hydrodynamic model was developed for streaming. The fully detailed mathematical model and its simulations identify key variables that can shift the system between disordered (slow) and ordered (fast) states. This establishes a concrete mechanistic framework for the ooplasmic streaming process. The self-organizing fast phase is a result of viscous drag on kinesin-driven cargoes that mediates equal and opposite forces on cytoplasmic fluid and on microtubules whose minus ends are tethered to the cortex. Fluid moves toward plus ends and microtubules are forced backward toward their minus ends, resulting in buckling. Under certain conditions, the buckling microtubules self-organize into parallel bending arrays, guiding varying directions for fast plus-end directed fluid flows that facilitate mixing in a low Reynolds number regime.

Monday, May 23rd

Colomb, J. and Brembs, B. (2016). PKC in motorneurons underlies self-learning, a form of motor learning in Drosophila. PeerJ 4: e1971. PubMed ID: 27168980
Summary:
Tethering a fly for stationary flight allows for exquisite control of its sensory input, such as visual or olfactory stimuli or a punishing infrared laser beam. A torque meter measures the turning attempts of the tethered fly around its vertical body axis. By punishing, say, left turning attempts (in a homogeneous environment), one can train a fly to restrict its behaviour to right turning attempts. It was recently discovered that this form of operant conditioning (called operant self-learning), may constitute a form of motor learning in Drosophila. Previous work had shown that Protein Kinase C (PKC) and the transcription factor dFoxP were specifically involved in self-learning, but not in other forms of learning. These molecules are specifically involved in various forms of motor learning in other animals, such as compulsive biting in Aplysia, song-learning in birds, procedural learning in mice or language acquisition in humans. This study describes efforts to decipher which PKC gene is involved in self-learning in Drosophila. Evidence is provided that motorneurons may be one part of the neuronal network modified during self-learning experiments. The collected evidence is reminiscent of one of the simplest, clinically relevant forms of motor learning in humans, operant reflex conditioning, which also relies on motorneuron plasticity.

Shankar, S., Calvert, M. E. and Yew, J. Y. (2016). Measuring physiological responses of Drosophila sensory neurons to lipid Pheromones using live calcium imaging. J Vis Exp [Epub ahead of print]. PubMed ID: 27168110
Summary:
Unlike mammals, insects such as Drosophila have multiple taste organs. The chemosensory neurons on the legs, proboscis, wings and ovipositor of Drosophila express gustatory receptors, ion channels, and ionotropic receptors that are involved in the detection of volatile and non-volatile sensory cues. These neurons directly contact tastants such as food, noxious substances and pheromones and therefore influence many complex behaviors such as feeding, egg-laying and mating. Electrode recordings and calcium imaging have been widely used in insects to quantify the neuronal responses evoked by these tastants. However, electrophysiology requires specialized equipment and obtaining measurements from a single taste sensillum can be technically challenging depending on the cell-type, size, and position. In addition, single neuron resolution in Drosophila can be difficult to achieve since taste sensilla house more than one type of chemosensory neuron. The live calcium imaging method described in this study allows responses of single gustatory neurons in live flies to be measured. This method is especially suitable for imaging neuronal responses to lipid pheromones and other ligand types that have low solubility in water-based solvents.

Banerjee, S., Toral, M., Siefert, M., Conway, D., Dorr, M. and Fernandes, J. (2016). dHb9 expressing larval motor neurons persist through metamorphosis to innervate adult-specific muscle targets and function in Drosophila eclosion. Dev Neurobiol [Epub ahead of print]. PubMed ID: 27168166
Summary:
The Drosophila larval nervous system is radically restructured during metamorphosis to produce adult specific neural circuits and behaviors. Genesis of new neurons, death of larval neurons and remodeling of those neurons that persistent collectively act to shape the adult nervous system. This study examined the fate of a subset of larval motor neurons during this restructuring process. A dHb9 reporter (exex), in combination with the FLP/FRT system, was used to individually identify abdominal motor neurons in the larval to adult transition using a combination of relative cell body (CB) location, axonal position and muscle targets. Segment specific cell death of some dHb9 expressing motor neurons was found to occur throughout the metamorphosis period and to continue into the post-eclosion period. Many dHb9>GFP expressing neurons however persist in the two anterior abdominal hemisegments, A1 and A2, which have segment specific muscles required for eclosion while a smaller proportion also persist in A2-A5. Consistent with a functional requirement for these neurons, ablating them during the pupal period produces defects in adult eclosion. In adults, subsequent to the execution of eclosion behaviors, the NMJs of some of these neurons were found to be dismantled and their muscle targets degenerate. These studies demonstrate a critical continuity of some larval motor neurons into adults and reveal that multiple aspects of motor neuron remodeling and plasticity that are essential adult motor behaviors.
Shen, H. C., Wei, J. Y., Chu, S. Y., Chung, P. C., Hsu, T. C. and Yu, H. H. (2016). Morphogenetic studies of the Drosophila DA1 ventral olfactory projection neuron. PLoS One 11: e0155384. PubMed ID: 27163287
Summary:
In the Drosophila olfactory system, odorant information is sensed by olfactory sensory neurons and relayed from the primary olfactory center, the antennal lobe (AL), to higher olfactory centers via olfactory projection neurons (PNs). A major portion of the AL is constituted with dendrites of four groups of PNs, anterodorsal PNs (adPNs), lateral PNs (lPNs), lateroventral PNs (lvPNs) and ventral PNs (vPNs). Previous studies have been focused on the development and function of adPNs and lPNs, while the investigation on those of lvPNs and vPNs received less attention. This study examined the molecular and cellular mechanisms underlying the morphogenesis of a putative male-pheromone responding vPN, the DA1 vPN. Using an intersection strategy to remove background neurons labeled within a DA1 vPN-containing GAL4 line, morphological changes were depicted of the DA1 vPN that occurs at the pupal stage. A pilot screen was conducted using RNA interference knock-down approach to identify cell surface molecules, including Down syndrome cell adhesion molecule 1 and Semaphorin-1a, that might play essential roles for the DA1 vPN morphogenesis. Taken together, by revealing molecular and cellular basis of the DA1 vPN morphogenesis, this study should provide insights into future comprehension of how vPNs are assembled into the olfactory neural circuitry.

Sunday, May 22nd

Bratic, A., Clemente, P., Calvo-Garrido, J., Maffezzini, C., Felser, A., Wibom, R., Wedell, A., Freyer, C. and Wredenberg, A. (2016). Mitochondrial polyadenylation is a one-step process required for mRNA integrity and tRNA maturation. PLoS Genet 12: e1006028. PubMed ID: 27176048
Summary:
Polyadenylation has well characterised roles in RNA turnover and translation in a variety of biological systems. While polyadenylation on mitochondrial transcripts has been suggested to be a two-step process required to complete translational stop codons, its involvement in mitochondrial RNA turnover is less well understood. This study analyzed knockdown and knockout models of the mitochondrial poly(A) polymerase (MTPAP) in Drosophila melanogaster. It was demonstrated that polyadenylation of mitochondrial mRNAs is exclusively performed by MTPAP. Further, mitochondrial polyadenylation does not regulate mRNA stability but protects the 3' terminal integrity, and that despite a lack of functioning 3' ends, these trimmed transcripts are translated, suggesting that polyadenylation is not required for mitochondrial translation. Additionally, loss of MTPAP leads to reduced steady-state levels and disturbed maturation of tRNACys, indicating that polyadenylation in mitochondria might be important for the stability and maturation of specific tRNAs. 

Peter, D., Igreja, C., Weber, R., Wohlbold, L., Weiler, C., Ebertsch, L., Weichenrieder, O. and Izaurralde, E. (2015). Molecular architecture of 4E-BP translational inhibitors bound to eIF4E. Mol Cell 57: 1074-1087. PubMed ID: 25702871
Summary:
The eIF4E-binding proteins (4E-BPs) represent a diverse class of translation inhibitors that are often deregulated in cancer cells. 4E-BPs inhibit translation by competing with eIF4G for binding to eIF4E through an interface that consists of canonical and non-canonical eIF4E-binding motifs connected by a linker. The lack of high-resolution structures including the linkers, which contain phosphorylation sites, limits understanding of how phosphorylation inhibits complex formation. Furthermore, the binding mechanism of the non-canonical motifs is poorly understood. This study presents structures of human eIF4E bound to 4E-BP1 and fly eIF4E bound to Thor (4E-BP), eIF4E-Transporter (4E-T), and eIF4G. These structures reveal architectural elements that are unique to 4E-BPs and provide insight into the consequences of phosphorylation. Guided by these structures, a 4E-BP mimic was designed and crystallized that shows increased repressive activity. These studies pave the way for the rational design of 4E-BP mimics as therapeutic tools to decrease translation during oncogenic transformation.

Truscott, M., Islam, A. B. and Frolov, M. V. (2016). Novel regulation and functional interaction of polycistronic miRNAs. RNA 22: 129-138. PubMed ID: 26554028
Summary:
The importance of microRNAs in gene expression and disease is well recognized. However, what is less appreciated is that almost half of miRNA genes are organized in polycistronic clusters and are therefore coexpressed. The mir-11 approximately 998 cluster consists of two miRNAs, mir-11 and miR-998. This study describes a novel layer of regulation that links the processing and expression of miR-998 to the presence of the mir-11 gene. The presence of miR-11 in the pri-miRNA was shown to be required for processing by Drosha, and deletion of mir-11 prevents the expression of miR-998. Replacing mir-11 with an unrelated miRNA rescued miR-998 expression in vivo and in vitro, as did expressing miR-998 from a shorter, more canonical miRNA scaffold. The embedded regulation of miR-998 is functionally important because unchecked miR-998 expression in the absence of miR-11 resulted in pleiotropic developmental defects. This novel regulation of expression of miRNAs within a cluster is not limited to the mir-11 approximately 998 cluster and, thus, likely reflects the more general cis-regulation of expression of individual miRNAs. Collectively, these results uncover a novel layer of regulation within miRNA clusters that tempers the functions of the individual miRNAs. Unlinking their expression has the potential to change the expression of multiple miRNA targets and shift a biological response.

Chen, X. and Rosbash, M. (2016). mir-276a strengthens Drosophila circadian rhythms by regulating timeless expression. Proc Natl Acad Sci U S A [Epub ahead of print]. PubMed ID: 27162360
Summary:
Circadian rhythms in metazoan eukaryotes are controlled by an endogenous molecular clock. It functions in many locations, including subsets of brain neurons (clock neurons) within the central nervous system. Although the molecular clock relies on transcription/translation feedback loops, posttranscriptional regulation also plays an important role. This study shows that the abundant Drosophila melanogaster microRNA mir-276a regulates molecular and behavioral rhythms by inhibiting expression of the important clock gene timeless (tim). Misregulation of mir-276a in clock neurons alters tim expression and increases arrhythmicity under standard constant darkness (DD) conditions. mir-276a expression itself appears to be light-regulated because its levels oscillate under 24-h light-dark (LD) cycles but not in DD. mir-276a is regulated by the transcription activator Chorion factor 2 in flies and in tissue-culture cells. Evidence from flies mutated using the clustered, regularly interspaced, short palindromic repeats (CRISPR) tool shows that mir-276a inhibits tim expression: Deleting the mir-276a-binding site in the tim 3' UTR causes elevated levels of TIM and approximately 50% arrhythmicity. It is suggested that this pathway contributes to the more robust rhythms observed under light/dark LD conditions than under DD conditions.

Saturday, May 21st

Weir, P.T., Henze, M.J., Bleul, C., Baumann-Klausener, F., Labhart, T. and Dickinson, M.H. (2016). Anatomical reconstruction and functional imaging reveal an ordered array of skylight polarization detectors in Drosophila. J Neurosci 36: 5397-5404. PubMed ID: 27170135
Summary:
Drosophila photoreceptors R7 and R8 in the dorsal rim area (DRA) of the compound eye are specialized to detect the electric vector (e-vector) of linearly polarized light. These photoreceptors are arranged in stacked pairs with identical fields of view and spectral sensitivities, but mutually orthogonal microvillar orientations. This anatomical arrangement in larger flies suggests that the DRA constitutes a detector for skylight polarization, in which different e-vectors maximally excite different positions in the array. To test the hypothesis, responses to polarized light of varying e-vector angles in the terminals of R7/8 cells using genetically encoded calcium indicators were measured. Data confirm a progression of preferred e-vector angles from anterior to posterior in the DRA, and a strict orthogonality between the e-vector preferences of paired R7/8 cells. Decreased activity in photoreceptors was observed in response to flashes of light polarized orthogonally to their preferred e-vector angle, suggesting reciprocal inhibition between photoreceptors in the same medullar column, which may serve to increase polarization contrast. Together, these results indicate that the polarization-vision system relies on a spatial map of preferred e-vector angles at the earliest stage of sensory processing.

Berck, M.E., Khandelwal, A., Claus, L., Hernandez-Nunez, L., Si, G., Tabone, C.J., Li, F., Truman, J.W., Fetter, R.D., Louis, M., Samuel, A.D. and Cardona, A. (2016). The wiring diagram of a glomerular olfactory system. Elife [Epub ahead of print]. PubMed ID: 27177418
Summary:
The sense of smell enables animals to react to long-distance cues according to learned and innate valences. Using electron microscopy, this study mapped the complete wiring diagram of the Drosophila larval antennal lobe, an olfactory neuropil similar to the vertebrate olfactory bulb. A canonical circuit with uniglomerular projection neurons (uPNs) relaying gain-controlled ORN activity to the mushroom body and the lateral horn was found. A second, parallel circuit with multiglomerular projection neurons (mPNs) and hierarchically connected local neurons (LNs) selectively integrates multiple ORN signals already at the first synapse. LN-LN synaptic connections putatively implement a bistable gain control mechanism that either computes odor saliency through panglomerular inhibition, or allows some glomeruli to respond to faint aversive odors in the presence of strong appetitive odors. This complete wiring diagram will support experimental and theoretical studies towards bridging the gap between circuits and behavior.

Klose, M., Duvall, L. B., Li, W., Liang, X., Ren, C., Steinbach, J. H. and Taghert, P. H. (2016). Functional PDF signaling in the Drosophila circadian neural circuit is gated by Ral A-dependent modulation. Neuron [Epub ahead of print]. PubMed ID: 27161526
Summary:
The neuropeptide PDF promotes the normal sequencing of circadian behavioral rhythms in Drosophila, but its signaling mechanisms are not well understood. This study reports daily rhythmicity in responsiveness to PDF in critical pacemakers called small LNvs. There is a daily change in potency, as great as 10-fold higher, around dawn. The rhythm persists in constant darkness and does not require endogenous ligand (PDF) signaling or rhythmic receptor gene transcription. Furthermore, rhythmic responsiveness reflects the properties of the pacemaker cell type, not the receptor. Dopamine responsiveness also cycles, in phase with that of PDF, in the same pacemakers, but does not cycle in large LNv. The activity of RalA GTPase in s-LNv regulates PDF responsiveness and behavioral locomotor rhythms. Additionally, cell-autonomous PDF signaling reversed the circadian behavioral effects of lowered RalA activity. Thus, RalA activity confers high PDF responsiveness, providing a daily gate around the dawn hours to promote functional PDF signaling.
Teseo, S., Veerus, L. and Mery, F. (2016). Fighting experience affects fruit fly behavior in a mating context. Naturwissenschaften 103: 38. PubMed ID: 27108453
Summary:
In animals, correlations exist among behaviors within individuals, but it is unclear whether experience in a specific functional context can affect behavior across different contexts. This study used Drosophila to investigate the effects of conflict-induced behavioral modifications on male mating behavior. In Drosophila, males fight for territories and experience a strong winner-loser effect, meaning that winners become more likely to win subsequent fights compared to losers, who continue to lose. In this protocol, males were tested for courtship intensity before and after fighting against other males. Male motivation to copulate before fights cannot predict the fight outcomes, but, afterwards, losers mate less than before and less than winner and control males. Contrarily, winners show no differences between pre- and post-fight courtship intensity, and do not differ from control males. This suggests that the physiological modifications resulting from fight outcomes indirectly affect male reproductive behavior.

Friday, May 20th

Li, X., Xie, Y. and Zhu, S. (2016). Notch maintains Drosophila type II neuroblasts by suppressing the expression of the Fez transcription factor Earmuff. Development [Epub ahead of print]. PubMed ID: 27151950
Summary:
Notch signaling is critical for maintaining neural stem cell (NSC) self-renewal and heterogeneity, however the underlying mechanism is not well understood. In Drosophila, loss of Notch prematurely terminates the self-renewal of larval type II neuroblasts (NBs, the Drosophila NSCs) and transforms type II NBs into type I NBs. This study demonstrates that Notch maintains type II NBs by suppressing the activation of earmuff (erm) by Pointed P1 (PntP1). It was shown that loss of Notch or components of its canonical pathway leads to PntP1-dependent ectopic Erm expression in type II NBs. Knockdown of Erm significantly rescues the loss of Notch phenotypes and misexpression of Erm phenocopies the loss of Notch. Ectopically expressed Erm promotes the transformation of type II NBs into type I NBs by inhibiting PntP1's function and expression in type II NBs. These data not only elucidate a critical mechanism of Notch-mediated maintenance of type II NB self-renewal and identity, but also reveals a novel function of Erm.

Crocker, A., Guan, X.J., Murphy, C.T. and Murthy, M. (2016). Cell-type-specific transcriptome analysis in the Drosophila mushroom body reveals memory-related changes in gene expression. Cell Rep [Epub ahead of print]. PubMed ID: 27160913
Summary:
Learning and memory formation in Drosophila rely on a network of neurons in the mushroom bodies (MBs). Whereas numerous studies have delineated roles for individual cell types within this network in aspects of learning or memory, whether or not these cells can also be distinguished by the genes they express remains unresolved. In addition, the changes in gene expression that accompany long-term memory formation within the MBs have not yet been studied by neuron type. This study addresses both issues by performing RNA sequencing on single cell types (harvested via patch pipets) within the MB. It was found that the expression of genes that encode cell surface receptors is sufficient to identify cell types and that a subset of these genes, required for sensory transduction in peripheral sensory neurons, is not only expressed within individual neurons of the MB in the central brain, but is also critical for memory formation.

Chen, Z., Del Valle Rodriguez, A., Li, X., Erclik, T., Fernandes, V.M. and Desplan, C. (2016). A unique class of neural progenitors in the Drosophila optic lobe generates both migrating neurons and glia. Cell Rep [Epub ahead of print]. PubMed ID: 27151460
Summary:
How neuronal and glial fates are specified from neural precursor cells is an important question for developmental neurobiologists. This study addresses this question in the Drosophila optic lobe, composed of the lamina, medulla, and lobula complex. It was shown that two gliogenic regions posterior to the prospective lamina also produce lamina wide-field (Lawf) neurons, which share common progenitors with lamina glia. These progenitors express neither canonical neuroblast nor lamina precursor cell markers. They bifurcate into two sub-lineages in response to Notch signaling, generating lamina glia or Lawf neurons, respectively. The newly born glia and Lawfs then migrate tangentially over substantial distances to reach their target tissue. Thus, Lawf neurogenesis, which includes a common origin with glia, as well as neuronal migration, resembles several aspects of vertebrate neurogenesis.

Cameron, S., Chen, Y. and Rao, Y. (2016). Borderless regulates glial extension and axon ensheathment. Dev Biol [Epub ahead of print]. PubMed ID: 27131624
Summary:
Ensheathment of axons by glial processes is essential for normal brain function. While considerable progress has been made to define molecular and cellular mechanisms underlying the maintenance of axon ensheathment, less is known about molecular details of early events for the wrapping of axons by glial processes in the developing nervous system. This study investigated the role of the transmembrane protein Borderless (Bdl) in the developing Drosophila visual system. Bdl belongs to the immunoglobulin (Ig) superfamily, and its in vivo function is unknown. This study shows that Bdl is expressed in wrapping glia (WG) in the developing eye disc. Cell-type-specific transgene rescue and knockdown indicate that Bdl is specifically required in WG for the extension of glial processes along photoreceptor axons in the optic lobe, and axon ensheathment. These results identify Bdl as a novel glia-specific cell-surface recognition molecule in regulating glial extension and axon ensheathment.

Thursday, May 19th

Gao, H., Baldeosingh, R., Wu, X. and Fossett, N. (2016). The Friend of GATA transcriptional co-regulator, U-Shaped, is a downstream antagonist of dorsal-driven prohemocyte differentiation in Drosophila. PLoS One 11: e0155372. PubMed ID: 27163255
Summary:
Recent studies suggest that mammalian hematopoietic stem and progenitor cells (HSPCs) respond directly to infection and inflammatory signaling. These signaling pathways also regulate HSPCs during steady-state conditions (absence of infection), and dysregulation may lead to cancer or age-related loss of progenitor repopulation capacity. Toll-like receptors (TLRs) are a major class of pathogen recognition receptors, and are expressed on the surface of immune effector cells and HSPCs. TLR/NF-κB activation promotes HSPCs differentiation; however, the mechanisms by which this signaling pathway alters the intrinsic transcriptional landscape are not well understood. Although Drosophila prohemocytes are the functional equivalent of mammalian HSPCs, a prohemocyte-specific function for Toll signaling has not been reported. Using Drosophila transgenics, this study identified prohemocyte-specific roles for Toll pathway members, Dorsal and Cactus. It was shown that Dorsal is required to limit the size of the progenitor pool. Additionally, activation of Toll signaling in prohemocytes drives differentiation in a manner that is analogous to TLR/NF-κB-driven HSPC differentiation. This was accomplished by showing that over-expression of Dorsal, or knockdown of Cactus, promotes differentiation. The study also investigated whether Dorsal and Cactus control prohemocyte differentiation by regulating a key intrinsic prohemocyte factor, U-shaped (Ush), which is known to promote multipotency and block differentiation. It was found that Dorsal represses Ush expression levels to promote differentiation, whereas Cactus maintains Ush levels to block differentiation. Additionally, another Toll antagonist, Lesswright, also maintains the level of Ush to block differentiation and promote proliferative quiescence. Collectively, these results identify a novel role for Ush as a downstream target of Toll signaling. 

Ishimaru, Y., Tomonari, S., Matsuoka, Y., Watanabe, T., Miyawaki, K., Bando, T., Tomioka, K., Ohuchi, H., Noji, S. and Mito, T. (2016). TGF-beta signaling in insects regulates metamorphosis via juvenile hormone biosynthesis. Proc Natl Acad Sci U S A [Epub ahead of print]. PubMed ID: 27140602
Summary:
Although butterflies undergo a dramatic morphological transformation from larva to adult via a pupal stage (holometamorphosis), crickets undergo a metamorphosis from nymph to adult without formation of a pupa (hemimetamorphosis). Despite these differences, both processes are regulated by common mechanisms that involve 20-hydroxyecdysone (20E) and juvenile hormone (JH). JH regulates many aspects of insect physiology, such as development, reproduction, diapause, and metamorphosis. Consequently, strict regulation of JH levels is crucial throughout an insect's life cycle. However, it remains unclear how JH synthesis is regulated. This study reports that in the corpora allata of the cricket, Gryllus bimaculatus, Myoglianin (Gb'Myo), a homolog of Drosophila Myoglianin/vertebrate GDF8/11, is involved in the down-regulation of JH production by suppressing the expression of a gene encoding JH acid O-methyltransferase, Gb'jhamt. In contrast, JH production is up-regulated by Decapentaplegic (Gb'Dpp) and Glass-bottom boat/60A (Gb'Gbb) signaling that occurs as part of the transcriptional activation of Gb'jhamt. Gb'Myo defines the nature of each developmental transition by regulating JH titer and the interactions between JH and 20E. When Gb'myo expression is suppressed, the activation of Gb'jhamt expression and secretion of 20E induce molting, thereby leading to the next instar before the last nymphal instar. Conversely, high Gb'myo expression induces metamorphosis during the last nymphal instar through the cessation of JH synthesis. Gb'myo also regulates final insect size. Because Myo/GDF8/11 and Dpp/bone morphogenetic protein (BMP)2/4-Gbb/BMP5–8 are conserved in both invertebrates and vertebrates, the present findings provide common regulatory mechanisms for endocrine control of animal development.

Liang, X., Mahato, S., Hemmerich, C. and Zelhof, A. C. (2016). Two temporal functions of Glass: Ommatidium patterning and photoreceptor differentiation. Dev Biol [Epub ahead of print]. PubMed ID: 27105580
Summary:
The downstream mechanisms that maintain identity and regulate differentiation of retinal cells remain poorly understood. This study report that the transcription factor Glass has a dual role in establishing a functional Drosophila eye. Persistent defects in ommatidium patterning combined with cell death correlate with the overall disruption of eye morphology in glass mutants. In addition, Glass exhibits a separable role in regulating photoreceptor differentiation. In particular, the apparent loss of glass mutant photoreceptors is not only due to cell death but also a failure of the surviving photoreceptors to complete differentiation. Moreover, the late reintroduction of Glass in these developmentally stalled photoreceptors is capable of restoring differentiation in the absence of correct ommatidium patterning. Mechanistically, Glass is necessary for the expression of many genes implicated in differentiation, i.e. rhabdomere morphogenesis, phototransduction, and synaptogenesis. Specifically, Glass was shown to directly regulate the expression of Pph13, which encodes a transcription factor necessary for opsin expression and rhabdomere morphogenesis. Finally, Glass choreographing of photoreceptor differentiation is conserved between Drosophila and Tribolium, two holometabolous insects. Altogether, this work identifies a fundamental regulatory mechanism to generate the full complement of cells required for a functional rhabdomeric visual system and provides a critical framework to investigate the basis of differentiation and maintenance of photoreceptor identity.

Zhu, H., Owen, M. R. and Mao, Y. (2016). The spatiotemporal order of signaling events unveils the logic of development signaling. Bioinformatics [Epub ahead of print]. PubMed ID: 27153573
Summary:
Animals from worms and insects to birds and mammals show distinct body plans; however, the embryonic development of diverse body plans with tissues and organs within is controlled by a surprisingly few signaling pathways. It is well recognized that combinatorial use of and dynamic interactions among signaling pathways follow specific logic to control complex and accurate developmental signaling and patterning, but it remains elusive what such logic is, or even, what it looks like. This study developed a computational model for Drosophila eye development with innovated methods to reveal how interactions among multiple pathways control the dynamically generated hexagonal array of R8 cells. Two novel findings were obtained. First, the coupling between the long-range inductive signals produced by the proneural Hedgehog signaling and the short-range restrictive signals produced by the antineural Notch and EGFR signaling is essential for generating accurately spaced R8s. Second, the spatiotemporal orders of key signaling events reveal a robust pattern of lateral inhibition conducted by Atonal-coordinated Notch and EGFR signaling to collectively determine R8 patterning. This pattern, stipulating the orders of signaling and comparable to the protocols of communication, may help decipher the well-appreciated but poorly defined logic of developmental signaling.

Wednesday, May 18th

Enjin, A., Zaharieva, E.E., Frank, D.D., Mansourian, S., Suh, G.S., Gallio, M. and Stensmyr, M.C. (2016). Humidity sensing in Drosophila. Curr Biol [Epub ahead of print]. PubMed ID: 27161501
Summary:
Environmental humidity influences the fitness and geographic distribution of all animals. Insects in particular use humidity cues to navigate the environment, and previous work suggests the existence of specific sensory mechanisms to detect favorable humidity ranges. Yet, the molecular and cellular basis of humidity sensing (hygrosensation) remains poorly understood. This study describes genes and neurons necessary for hygrosensation in the vinegar fly Drosophila melanogaster. It was found that members of the Drosophila genus display species-specific humidity preferences related to conditions in their native habitats. Using a simple behavioral assay, it was found that the ionotropic receptors IR40a, IR93a, and IR25a are all required for humidity preference in D. melanogaster. Yet, whereas IR40a is selectively required for hygrosensory responses, IR93a and IR25a mediate both humidity and temperature preference. Consistent with this, the expression of IR93a and IR25a includes thermosensory neurons of the arista. In contrast, IR40a is excluded from the arista but is expressed (and required) in specialized neurons innervating pore-less sensilla of the sacculus, a unique invagination of the third antennal segment. Indeed, calcium imaging showed that IR40a neurons directly respond to changes in humidity, and IR40a knockdown or IR93a mutation reduces their responses to stimuli. Taken together, these results suggest that the preference for a specific humidity range depends on specialized sacculus neurons, and that the processing of environmental humidity can happen largely in parallel to that of temperature.

Post, S. and Tatar, M. (2016). Nutritional geometric profiles of insulin/IGF expression in Drosophila melanogaster. PLoS One 11: e0155628. PubMed ID: 27171400
Summary:
Insulin/IGF signaling (IIS) in Drosophila melanogaster is propagated by eight Drosophila insulin-like peptides (dilps) and is regulated by nutrition. To understand how dietary protein and sugar affect dilp expression, this study followed the analytical concepts of the Nutritional Geometric Framework, feeding Drosophila adults media comprised of seven protein-to-carbohydrate ratios at four caloric concentrations. Transcript levels of all dilps and three IIS-regulated genes were measured. Each dilp presents a unique pattern upon a bivariate plot of sugar and protein. Dilp2 expression is greatest upon diets with low protein-to-carbohydrate ratio regardless of total caloric value. Dilp5 is highly expressed at approximately a 1:2 protein-to-carbohydrate ratio and its level increases with diet caloric content. Regression analysis revealed that protein-to-carbohydrate ratio and the interaction between this ratio and caloric content significantly affects dilp expression. The IIS-regulated transcripts 4eBP and InR show strikingly different responses to diet composition: 4eBP is minimally expressed except when elevated at low caloric diets. InR expression increases with protein level, independent of caloric content. Values of published life history traits measured on similar diets reveal correlations between egg production and the expression of dilp8 4eBP, while low protein-to-carbohydrate ratio diets associated with long lifespan correlated with elevated dilp2. Analyzing how nutient composition associates with dilp expression and IIS reveals that nutritional status is modulated by different combinations of insulin-like peptides, and these features variously correlate to IIS-regulated life history traits. 

Raad, H., Ferveur, J.F., Ledger, N., Capovilla, M. and Robichon, A. (2016). Functional gustatory role of chemoreceptors in Drosophila wings. Cell Rep [Epub ahead of print]. PubMed ID: 27160896
Summary:
Neuroanatomical evidence argues for the presence of taste sensilla in Drosophila wings; however, the taste physiology of insect wings remains hypothetical, and a comprehensive link to mechanical functions, such as flight, wing flapping, and grooming, is lacking. This study shows that the sensilla of the Drosophila anterior wing margin respond to both sweet and bitter molecules through an increase in cytosolic Ca2+ levels. Conversely, genetically modified flies presenting a wing-specific reduction in chemosensory cells show severe defects in both wing taste signaling and the exploratory guidance associated with chemodetection. In Drosophila, the chemodetection machinery includes mechanical grooming, which facilitates the contact between tastants and wing chemoreceptors, and the vibrations of flapping wings that nebulize volatile molecules as carboxylic acids. Together, these data demonstrate that the Drosophila wing chemosensory sensilla are a functional taste organ and that they may have a role in the exploration of ecological niches.

Slade, J. D. and Staveley, B. E. (2016).. Extended longevity and survivorship during amino-acid starvation in a Drosophila Sir2 mutant heterozygote. Genome [Epub ahead of print] PubMed ID: 27074822
Summary:
The regulation of energy homeostasis is pivotal to survive periods of inadequate nutrition. The sirtuin deacetylase Sir2 is well conserved from single-celled yeast to mammals, and it controls a number of downstream targets that are active during periods of extreme stress. Overexpression of Sir2 has been established to enhance survival of a number of model organisms undergoing calorie restriction, during which insulin receptor signalling (IRS) is reduced, a condition that itself can enhance survivorship during starvation. Increased Sir2 expression and reduced IRS result in an increase in the activity of the transcription factor foxo, an advantageous activation during stress but lethal when overly active. This study found that a lowered gene dosage of Sir2, in mutant heterozygotes, can extend normal longevity and greatly augment survivorship during amino-acid starvation in Drosophila. Additionally, these mutants, in either heterozygous or homozygous form, do not appear to have any disadvantageous effects upon development or cell growth of the organism unlike IRS mutants. These results may advance the understanding of the biological response to starvation and allow for the development of a model organism to mimic the ability of individuals to tolerate nutrient deprivation.

Tuesday, May 17

Li, Y., Armstrong, R. L., Duronio, R. J. and MacAlpine, D. M. (2016). Methylation of histone H4 lysine 20 by PR-Set7 ensures the integrity of late replicating sequence domains in Drosophila. Nucleic Acids Res [Epub ahead of print]. PubMed ID: 27131378
Summary:
The methylation state of lysine 20 on histone H4 (H4K20) has been linked to chromatin compaction, transcription, DNA repair and DNA replication. Monomethylation of H4K20 (H4K20me1) is mediated by the cell cycle-regulated histone methyltransferase PR-Set7. PR-Set7 depletion in mammalian cells results in defective S phase progression and the accumulation of DNA damage, which has been partially attributed to defects in origin selection and activation. However, these studies were limited to only a handful of mammalian origins, and it remains unclear how PR-Set7 and H4K20 methylation impact the replication program on a genomic scale. This study employed genetic, cytological, and genomic approaches to better understand the role of PR-Set7 and H4K20 methylation in regulating DNA replication and genome stability in Drosophila cells. Deregulation of H4K20 methylation had no impact on origin activation throughout the genome. Instead, depletion of PR-Set7 and loss of H4K20me1 results in the accumulation of DNA damage and an ATR-dependent cell cycle arrest. Coincident with the ATR-dependent cell cycle arrest, increased DNA damage was found that is specifically limited to late replicating regions of the Drosophila genome, suggesting that PR-Set7-mediated monomethylation of H4K20 is critical for maintaining the genomic integrity of late replicating domains.

Messina, G., Atterrato, M. T., Fanti, L., Giordano, E. and Dimitri, P. (2016). Expression of human Cfdp1 gene in Drosophila reveals new insights into the function of the evolutionarily conserved BCNT protein family. Sci Rep 6: 25511. PubMed ID: 27151176
Summary:
The Bucentaur (BCNT) protein family is widely distributed in eukaryotes and is characterized by a highly conserved C-terminal domain. This family was identified two decades ago in ruminants, but its role(s) remained largely unknown. Investigating cellular functions and mechanism of action of BCNT proteins is challenging, because they have been implicated in human craniofacial development. Recently, it was found that YETI, the D. melanogaster BCNT, is a chromatin factor that participates to H2A.V deposition. This study reports the effects of in vivo expression of CFDP1, the human BCNT protein, in Drosophila melanogaster. CFDP1, similarly to YETI, binds to chromatin and its expression results in a wide range of abnormalities highly reminiscent of those observed in Yeti null mutants. This indicates that CFDP1 expressed in flies behaves in a dominant negative fashion disrupting the YETI function. Moreover, GST pull-down provides evidence indicating that 1) both YETI and CFDP1 undergo homodimerization and 2) YETI and CFDP1 physically interact each other by forming inactive heterodimers that would trigger the observed dominant-negative effect. Overall, these findings highlight unanticipated evidences suggesting that homodimerization mediated by the BCNT domain is integral to the chromatin functions of BCNT proteins.

Ozawa, N., Furuhashi, H., Masuko, K., Numao, E., Makino, T., Yano, T. and Kurata, S. (2016). Organ identity specification factor WGE localizes to the histone locus body and regulates histone expression to ensure genomic stability in Drosophila. Genes Cells 21: 442-456. PubMed ID: 27145109
Summary:
Over-expression of Winged-Eye (WGE) in the Drosophila eye imaginal disc induces an eye-to-wing transformation. Endogenous WGE is required for organ development, and wge-deficient mutants exhibit growth arrest at the larval stage, suggesting that WGE is critical for normal growth. The function of WGE, however, remains unclear. This study analyzed the subcellular localization of WGE to gain insight into its endogenous function. Immunostaining showed that WGE localized to specific nuclear foci called the histone locus body (HLB), an evolutionarily conserved nuclear body required for S phase-specific histone mRNA production. Histone mRNA levels and protein levels in cytosolic fractions were aberrantly up-regulated in wge mutant larva, suggesting a role for WGE in regulating histone gene expression. Genetic analyses showed that wge suppresses position-effect variegation, and that WGE and a HLB component Mute appears to be synergistically involved in heterochromatin formation. Further supporting a role in chromatin regulation, wge-deficient mutants showed derepression of retrotransposons and increased γH2Av signals, a DNA damage marker. These findings suggest that WGE is a component of HLB in Drosophila with a role in heterochromatin formation and transposon silencing. It is proposed that WGE at HLB contributes to genomic stability and development by regulating heterochromatin structure via histone gene regulation.
Frey, F., Sheahan, T., Finkl, K., Stoehr, G., Mann, M., Benda, C. and Muller, J. (2016). Molecular basis of PRC1 targeting to Polycomb response elements by PhoRC. Genes Dev 30: 1116-1127. PubMed ID: 27151979
Summary:
Polycomb group (PcG) protein complexes repress transcription by modifying target gene chromatin. In Drosophila, this repression requires association of PcG protein complexes with cis-regulatory Polycomb response elements (PREs), but the interactions permitting formation of these assemblies are poorly understood. This study shows that the Sfmbt subunit of the DNA-binding Pho-repressive complex (PhoRC) and the Scm subunit of the canonical Polycomb-repressive complex 1 (PRC1) directly bind each other through their SAM domains. The 1.9 A crystal structure of the Scm-SAM:Sfmbt-SAM complex reveals the recognition mechanism and shows that Sfmbt-SAM lacks the polymerization capacity of the SAM domains of Scm and its PRC1 partner subunit, Ph. Functional analyses in Drosophila demonstrate that Sfmbt-SAM and Scm-SAM are essential for repression and that PhoRC DNA binding is critical to initiate PRC1 association with PREs. Together, this suggests that PRE-tethered Sfmbt-SAM nucleates PRC1 recruitment and that Scm-SAM/Ph-SAM-mediated polymerization then results in the formation of PRC1-compacted chromatin.

Monday, May 16th

Sayal, R., Dresch, J.M., Pushel, I., Taylor, B.R. and Arnosti, D.N. (2016). Quantitative perturbation-based analysis of gene expression predicts enhancer activity in early Drosophila embryo. Elife 5. PubMed ID: 27152947
Summary:
Enhancers constitute one of the major components of regulatory machinery of metazoans. Although several genome-wide studies have focused on finding and locating enhancers in the genomes, the fundamental principles governing their internal architecture and cis-regulatory grammar remain elusive. This study describes an extensive, quantitative perturbation analysis targeting the dorsal-ventral patterning gene regulatory network (GRN) controlled by Drosophila NF-κB homolog Dorsal. To understand transcription factor interactions on enhancers, an ensemble of mathematical models were employed to test effects of cooperativity, repression, and factor potency. Models trained on the dataset correctly predict activity of evolutionarily divergent regulatory regions, providing insights into spatial relationships between repressor and activator binding sites. Importantly, the collective predictions of sets of models are effective at novel enhancer identification and characterization. The study demonstrates how experimental dataset and modeling can be effectively combined to provide quantitative insights into cis-regulatory information on a genome-wide scale. 

Jia, D., Bryant, J., Jevitt, A., Calvin, G. and Deng, W. M. (2016). The ecdysone and Notch pathways synergistically regulate Cut at the dorsal-ventral boundary in Drosophila wing discs. J Genet Genomics [Epub ahead of print]. PubMed ID: 27117286
Summary:
Metazoan development requires coordination of signaling pathways to regulate patterns of gene expression. In Drosophila, the wing imaginal disc provides an excellent model for the study of how signaling pathways interact to regulate pattern formation. The determination of the dorsal-ventral (DV) boundary of the wing disc depends on the Notch pathway, which is activated along the DV boundary and induces the expression of the homeobox transcription factor, Cut. This study shows that Broad (Br), a zinc-finger transcription factor, is also involved in regulating Cut expression in the DV boundary region. However, Br expression is not regulated by Notch signaling in wing discs, ecdysone signaling is the upstream signal that induces Br for Cut upregulation. Also, it was found that the ecdysone-Br cascade upregulates cut-lacZ expression, a reporter containing a 2.7 kb cut enhancer region, implying that ecdysone signaling, similar to Notch, regulates cut at the transcriptional level. Collectively, these findings reveal that the Notch and ecdysone signaling pathways synergistically regulate Cut expression for proper DV boundary formation in the wing disc. Additionally, br was shown to promote Delta, a Notch ligand, near the DV boundary to suppress aberrant high Notch activity, indicating further interaction between the two pathways for DV patterning of the wing disc.

Samee, M. A., Lim, B., Samper, N., Lu, H., Rushlow, C. A., Jimenez, G., Shvartsman, S. Y. and Sinha, S. (2015). A systematic ensemble approach to thermodynamic modeling of gene expression from sequence data. Cell Syst 1: 396-407. PubMed ID: 27136354
Summary:
To understand the relationship between an enhancer DNA sequence and quantitative gene expression, thermodynamics-driven mathematical models of transcription are often employed. These 'sequence-to-expression' models can describe an incomplete or even incorrect set of regulatory relationships if the parameter space is not searched systematically. This study focused on an enhancer of the Drosophila gene ind and demonstrate how a systematic search of parameter space can reveal a more comprehensive picture of a gene's regulatory mechanisms, resolve outstanding ambiguities, and suggest testable hypotheses. An approach is described that generates an ensemble of ind models; all of these models are technically acceptable solutions to the sequence-to-expression problem in light of wild-type data, and some represent mechanistically distinct hypotheses about the regulation of ind. This ensemble can be restricted to biologically plausible models using requirements gleaned from in vivo perturbation experiments. Biologically plausible models make unique predictions about how specific ind enhancer sequences affect ind expression; these predictions were validated in vivo through site mutagenesis in transgenic Drosophila embryos.

Spirov, A. V., Myasnikova, E. M. and Holloway, D. M. (2016). Sequential construction of a model for modular gene expression control, applied to spatial patterning of the Drosophila gene hunchback. J Bioinform Comput Biol 14: 1641005. PubMed ID: 27122317
Summary:
Gene network simulations are increasingly used to quantify mutual gene regulation in biological tissues. These are generally based on linear interactions between single-entity regulatory and target genes. Biological genes, by contrast, commonly have multiple, partially independent, cis-regulatory modules (CRMs) for regulator binding, and can produce variant transcription and translation products. This study presents a modeling framework to address some of the gene regulatory dynamics implied by this biological complexity. Spatial patterning of the hunchback (hb) gene in Drosophila development involves control by three CRMs producing two distinct mRNA transcripts. This example was used to develop a differential equations model for transcription which takes into account the cis-regulatory architecture of the gene. Potential regulatory interactions are screened by a genetic algorithms (GAs) approach and compared to biological expression data.

Sunday, May 15th

Hussain, A., Ucpunar, H. K., Zhang, M., Loschek, L. F. and Grunwald Kadow, I. C. (2016). Neuropeptides modulate female chemosensory processing upon mating in Drosophila. PLoS Biol 14: e1002455. PubMed ID: 27145127
Summary:
A female's reproductive state influences her perception of odors and tastes along with her changed behavioral state and physiological needs. The mechanism that modulates chemosensory processing, however, remains largely elusive. Using Drosophila, this study has identified a behavioral, neuronal, and genetic mechanism that adapts the senses of smell and taste, the major modalities for food quality perception, to the physiological needs of a gravid female. Pungent smelling polyamines, such as putrescine and spermidine, are essential for cell proliferation, reproduction, and embryonic development in all animals. A polyamine-rich diet increases reproductive success in many species, including flies. Using a combination of behavioral analysis and in vivo physiology, this study shows that polyamine attraction is modulated in gravid females through a G-protein coupled receptor, the sex peptide receptor (SPR), and its neuropeptide ligands, MIPs (myoinhibitory peptides), which act directly in the polyamine-detecting olfactory and taste neurons. This modulation is triggered by an increase of SPR expression in chemosensory neurons, which is sufficient to convert virgin to mated female olfactory choice behavior. Together, these data show that neuropeptide-mediated modulation of peripheral chemosensory neurons increases a gravid female's preference for important nutrients, thereby ensuring optimal conditions for her growing progeny.

Hussain, A., Zhang, M., Ucpunar, H. K., Svensson, T., Quillery, E., Gompel, N., Ignell, R. and Grunwald Kadow, I. C. (2016). Ionotropic chemosensory receptors mediate the taste and smell of polyamines. PLoS Biol 14: e1002454. PubMed ID: 27145030
Summary:
The ability to find and consume nutrient-rich diets for successful reproduction and survival is fundamental to animal life. Among the nutrients important for all animals are polyamines, a class of pungent smelling compounds required in numerous cellular and organismic processes. Polyamine deficiency or excess has detrimental effects on health, cognitive function, reproduction, and lifespan. This study shows that a diet high in polyamine is beneficial and increases reproductive success of flies and unravels the sensory mechanisms that attract Drosophila to polyamine-rich food and egg-laying substrates. Using a combination of behavioral genetics and in vivo calcium imaging, Drosophila was shown to use multisensory detection to find and evaluate polyamines present in overripe and fermenting fruit, their favored feeding and egg-laying substrate. In the olfactory system, two coexpressed ionotropic receptors (IRs), IR76b and IR41a, mediate the long-range attraction to the odor. In the gustatory system, multimodal taste sensation by IR76b receptor and GR66a bitter receptor neurons is used to evaluate quality and valence of the polyamine providing a mechanism for the fly's high attraction to polyamine-rich and sweet decaying fruit. Given their universal and highly conserved biological roles, it is proposed that the ability to evaluate food for polyamine content may impact health and reproductive success also of other animals including humans.

Ko, K. I., Root, C. M., Lindsay, S. A., Zaninovich, O. A., Shepherd, A. K., Wasserman, S. A., Kim, S. M. and Wang, J. W. (2015). Starvation promotes concerted modulation of appetitive olfactory behavior via parallel neuromodulatory circuits. Elife 4. PubMed ID: 26208339
Summary:
The internal state of an organism influences its perception of attractive or aversive stimuli and thus promotes adaptive behaviors that increase its likelihood of survival. The mechanisms underlying these perceptual shifts are critical to understanding of how neural circuits support animal cognition and behavior. Starved flies exhibit enhanced sensitivity to attractive odors and reduced sensitivity to aversive odors. This study shows that a functional remodeling of the olfactory map is mediated by two parallel neuromodulatory systems that act in opposing directions on olfactory attraction and aversion at the level of the first synapse. Short neuropeptide F sensitizes an antennal lobe glomerulus wired for attraction, while tachykinin (DTK) suppresses activity of a glomerulus wired for aversion. Thus this study shows parallel neuromodulatory systems functionally reconfigure early olfactory processing to optimize detection of nutrients at the risk of ignoring potentially toxic food resources.

Navawongse, R., Choudhury, D., Raczkowska, M., Stewart, J. C., Lim, T., Rahman, M., Toh, A. G., Wang, Z. and Claridge-Chang, A. (2016). Drosophila learn efficient paths to a food source. Neurobiol Learn Mem 131: 176-181. PubMed ID: 27063671
Summary:
Elucidating the genetic, and neuronal bases for learned behavior is a central problem in neuroscience. Methods to study adaptive food-seeking behavior in Drosophila have lagged decades behind rodent feeding analysis, largely due to the challenges presented by their small scale. There is currently no method to dynamically control flies' access to food. In rodents, protocols that use dynamic food delivery are a central element of experimental paradigms that date back to the influential work of Skinner. This method is still commonly used in the analysis of learning, memory, addiction, feeding, and many other subjects in experimental psychology. The difficulty of microscale food delivery means this is not a technique used in fly behavior. In this paper describe a microfluidic chip integrated with machine vision and automation to dynamically control defined liquid food presentations and sensory stimuli. Strikingly, repeated presentations of food at a fixed location produced improvements in path efficiency during food approach. This shows that improved path choice is a learned behavior. Active control of food availability using this microfluidic system is a valuable addition to the methods currently available for the analysis of learned feeding behavior in flies.

Saturday, May 14th

Tsai, H. Z., Lin, R. K. and Hsieh, T. S. (2016). Drosophila mitochondrial topoisomerase III alpha affects the aging process via maintenance of mitochondrial function and genome integrity. J Biomed Sci 23: 38. PubMed ID: 27067525
Summary:
Mitochondria play important roles in providing metabolic energy and key metabolites for synthesis of cellular building blocks. Mitochondria have additional functions in other cellular processes, including programmed cell death and aging. A previous study revealed Drosophila mitochondrial topoisomerase III α (Top3α) contributes to the maintenance of the mitochondrial genome and male germ-line stem cells. However, the involvement of mitochondrial Top3α in the mitochondrion-mediated aging process remains unclear. In this study, the M1L flies, in which Top3α protein lacks the mitochondrial import sequence and is thus present in cell nuclei but not in mitochondria, were used as a model system to examine the role of mitochondrial Top3α in the aging of fruit flies. M1L flies were shown to exhibit mitochondrial defects which affect the aging process. First, it was observed that M1L flies have a shorter life span, which was correlated with a significant reduction in the mitochondrial DNA copy number, the mitochondrial membrane potential, and ATP content compared with those of both wild-type and transgene-rescued flies of the same age. Second, a mobility assay and electron microscopic analysis was performed to demonstrate that the locomotion defect and mitophagy of M1L flies were enhanced with age, as compared with the controls. Finally, it was shown that the correlation between the mtDNA deletion level and aging in M1L flies resembles what was reported in mammalian systems. The results demonstrate that mitochondrial Top3α ablation results in mitochondrial genome instability and its dysfunction, thereby accelerating the aging process.

Xu, W., et al. (2016). Amyloid precursor protein-mediated endocytic pathway disruption induces axonal dysfunction and neurodegeneration. J Clin Invest [Epub ahead of print]. PubMed ID: 27064279
Summary:
The endosome/lysosome pathway is disrupted early in the course of both Alzheimer's disease (AD) and Down syndrome (DS); however, it is not clear how dysfunction in this pathway influences the development of these diseases. This study explored the cellular and molecular mechanisms by which endosomal dysfunction contributes to the pathogenesis of AD and DS. It was determined that full-length amyloid precursor protein (APP; see Drosophila Appl) and its β-C-terminal fragment (β-CTF) act though increased activation of Rab5 to cause enlargement of early endosomes and to disrupt retrograde axonal trafficking of nerve growth factor (NGF) signals. The functional impacts of APP and its various products were investigated in PC12 cells, cultured rat basal forebrain cholinergic neurons (BFCNs), and BFCNs from a mouse model of DS. The full-length wild-type APP (APPWT) and β-CTF both induced endosomal enlargement and disrupted NGF signaling and axonal trafficking. β-CTF alone induced atrophy of BFCNs that was rescued by the dominant-negative Rab5 mutant, Rab5S34N. Moreover, expression of a dominant-negative Rab5 construct markedly reduced APP-induced axonal blockage in Drosophila. Therefore, increased APP and/or β-CTF impact the endocytic pathway to disrupt NGF trafficking and signaling, resulting in trophic deficits in BFCNs. These data strongly support the emerging concept that dysregulation of Rab5 activity contributes importantly to early pathogenesis of AD and DS.

Achal, M., et al. (2016). A restrictive cardiomyopathy mutation in an invariant proline at the myosin head/rod junction enhances head flexibility and function, yielding muscle defects in Drosophila. J Mol Biol [Epub ahead of print]. PubMed ID: 27107639
Summary:
An 'invariant proline' separates the myosin S1 head from its S2 tail and is proposed to be critical for orienting S1 during its interaction with actin, a process that leads to muscle contraction. Mutation of the invariant proline to leucine (P838L) caused dominant restrictive cardiomyopathy in a pediatric patient. This study used Drosophila to model this mutation. P838L mutant myosin isolated from indirect flight muscles of transgenic Drosophila showed elevated ATPase and actin sliding velocity in vitro. Further, the mutant heads exhibited increased rotational flexibility and there was an increase in the average angle between the two heads. Indirect flight muscle myofibril assembly was minimally affected in mutant homozygotes and isolated fibers displayed normal mechanical properties. However, myofibrils degraded during aging, correlating with reduced flight abilities. In contrast, hearts from homozygotes and heterozygotes showed normal morphology, myofibrillar arrays and contractile parameters. Overall, the studies suggest that increased rotational flexibility of myosin S1 enhances myosin ATPase and actin sliding. Further, instability of P838L myofibrils leads to decreased function during aging of Drosophila skeletal muscle, but not cardiac muscle, despite the strong evolutionary conservation of the P838 residue.

Barekat, A., et al. (2016). Using Drosophila as an integrated model to study mild repetitive traumatic brain injury. Sci Rep 6: 25252. PubMed ID: 27143646
Summary:
Traumatic brain injury (TBI) is a major cause of morbidity and mortality worldwide. In addition, there has been a growing appreciation that even repetitive, milder forms of TBI (mTBI) can have long-term deleterious consequences to neural tissues. Hampering understanding of genetic and environmental factors that influence the cellular and molecular responses to injury has been the limited availability of effective genetic model systems that could be used to identify the key genes and pathways that modulate both the acute and long-term responses to TBI. This study reports the development of a severe and mild-repetitive TBI model using Drosophila. Using this system, key features that are typically found in mammalian TBI models were also identified in flies, including the activation of inflammatory and autophagy responses, increased Tau phosphorylation and neuronal defects that impair sleep-related behaviors. This novel injury paradigm demonstrates the utility of Drosophila as an effective tool to validate genetic and environmental factors that influence the whole animal response to trauma and to identify prospective therapies needed for the treatment of TBI.

Friday, May 13th

Tseng, C. Y., Kao, S. H. and Hsu, H. J. (2016). Snail controls proliferation of Drosophila ovarian epithelial follicle stem cells, independently of E-cadherin. Dev Biol [Epub ahead of print]. PubMed ID: 27141871
Summary:
Epithelial-mesenchymal transition (EMT), which is primarily mediated by Snail via the suppression of E-cadherin, is able to generate cells with stem cell properties. However, the role of Snail in epithelial stem cells remains unclear. This study reports that Snail directly controls proliferation of follicle stem cells (FSCs) in Drosophila females. Disruption of Snail expression in FSCs compromises their proliferation, but not their maintenance. Conversely, FSCs with excessive Snail expression display increased proliferation and lifespan, which is accompanied by a moderate decrease in the expression of E-cadherin (required for adhesion of FSCs to their niche) at the junction between their adjacent cells, indicating a conserved role of Snail in E-cadherin inhibition, which promote epithelial cell proliferation. Interestingly, a decrease in E-cadherin in snail-knock down FSCs does not restore the decreased proliferation of snail-knock down FSCs, suggesting that adhesion strength of FSCs to their niche is dispensable for Snail-mediated FSC division. These results demonstrate that Snail controls epithelial stem cell division independently of its known role in the EMT, which contributes to induction of cancer stem cells.

Upadhyay, M., Martino Cortez, Y., Wong-Deyrup, S., Tavares, L., Schowalter, S., Flora, P., Hill, C., Nasrallah, M. A., Chittur, S. and Rangan, P. (2016). Transposon dysregulation modulates dWnt4 signaling to control germline stem cell differentiation in Drosophila. PLoS Genet 12: e1005918. PubMed ID: 27019121
Summary:
Germline stem cell (GSC) self-renewal and differentiation are required for the sustained production of gametes. GSC differentiation in Drosophila oogenesis requires expression of the histone methyltransferase dSETDB1/Eggless by the somatic niche, however its function in this process is unknown. This study shows that dSETDB1 is required for the expression of a Wnt ligand, Wnt4, in the somatic niche. Wnt4 signaling acts on the somatic niche cells to facilitate their encapsulation of the GSC daughter, which serves as a differentiation cue. dSETDB1 is known to repress transposable elements (TEs) to maintain genome integrity. Unexpectedly, this study found that independent upregulation of TEs also downregulated Wnt4, leading to GSC differentiation defects. This suggests that Wnt4 expression is sensitive to the presence of TEs. Together these results reveal a chromatin-transposon-Wnt signaling axis that regulates stem cell fate.

Elgart, M., Stern, S., Salton, O., Gnainsky, Y., Heifetz, Y. and Soen, Y. (2016). Impact of gut microbiota on the fly's germ line. Nat Commun 7: 11280. PubMed ID: 27080728
Summary:
Unlike vertically transmitted endosymbionts, which have broad effects on their host's germ line, the extracellular gut microbiota is transmitted horizontally and is not known to influence the germ line. This study provides evidence supporting the influence of these gut bacteria on the germ line of Drosophila melanogaster. Removal of the gut bacteria represses oogenesis, expedites maternal-to-zygotic-transition in the offspring and unmasks hidden phenotypic variation in mutants. It was further shown that the main impact on oogenesis is linked to the lack of gut Acetobacter species, and the Drosophila Aldehyde dehydrogenase (Aldh) gene was identified as an apparent mediator of repressed oogenesis in Acetobacter-depleted flies. The finding of interactions between the gut microbiota and the germ line has implications for reproduction, developmental robustness and adaptation. 

Sanghavi, P., Liu, G., Veeranan-Karmegam, R., Navarro, C. and Gonsalvez, G. B. (2016). Multiple roles for Egalitarian in polarization of the Drosophila egg chamber. Genetics [Epub ahead of print]. PubMed ID: 27017624
Summary:
RNA-binding protein Egalitarian (Egl) is required for specification and maintenance of oocyte fate. Mutants in egl either completely fail to specify an oocyte, or if specified, the oocyte eventually reverts back to nurse cell fate. Due to this very early role for Egl in egg chamber maturation, it is unclear whether later stages of egg chamber development also require Egl function. In this study, Egl was depleted at specific stages of egg chamber development. In early stage egg chambers, Egl was shown to have an additional role in organization of oocyte microtubules. In the absence of Egl function, oocyte microtubules completely fail to reorganize. As such, the localization of microtubule motors and their cargo is disrupted. In addition, Egl also appears to function in regulating the translation of critical polarity determining mRNAs. Finally, in mid stage egg chambers, Egl does not appear to be required for microtubule organization, but rather for the correct spatial localization of oskar, bicoid and gurken mRNAs.

Thursday, May 12th

Chen, D.Y., Lipari, K.R., Dehghan, Y., Streichan, S.J. and Bilder, D. (2016). Symmetry breaking in an edgeless epithelium by Fat2-regulated microtubule polarity. Cell Rep [Epub ahead of print]. PubMed ID: 27134170
Summary:
Planar cell polarity (PCP) information is a critical determinant of organ morphogenesis. While PCP in bounded epithelial sheets is increasingly well understood, how PCP is organized in tubular and acinar tissues is not known. Drosophila egg chambers (follicles) are an acinus-like "edgeless epithelium" and exhibit a continuous, circumferential PCP that does not depend on pathways active in bounded epithelia; this follicle PCP directs formation of an ellipsoid rather than a spherical egg. This study uses an imaging algorithm to "unroll" the entire 3D tissue surface and comprehensively analyze PCP onset. This approach traces chiral symmetry breaking to plus-end polarity of microtubules in the germarium, well before follicles form and rotate. PCP germarial microtubules provide chiral information that predicts the direction of whole-tissue rotation as soon as independent follicles form. Concordant microtubule polarity, but not microtubule alignment, requires the atypical cadherin Fat2, which acts at an early stage to translate plus-end bias into coordinated actin-mediated collective cell migration. Because microtubules are not required for PCP or migration after follicle rotation initiates, while dynamic actin and extracellular matrix are, polarized microtubules lie at the beginning of a handoff mechanism that passes early chiral PCP of the cytoskeleton to a supracellular planar polarized extracellular matrix and elongates the organ.

Han, Y., Shi, Q. and Jiang, J. (2015). Multisite interaction with Sufu regulates Ci/Gli activity through distinct mechanisms in Hh signal transduction. Proc Natl Acad Sci U S A 112: 6383-6388. PubMed ID: 25941387
Summary:
The tumor suppressor protein Suppressor of fused (Sufu) plays a conserved role in the Hedgehog (Hh) signaling pathway by inhibiting Cubitus interruptus (Ci)/Glioma-associated oncogene homolog (Gli) transcription factors, but the molecular mechanism by which Sufu inhibits Ci/Gli activity remains poorly understood. This study shows that Sufu can bind Ci/Gli through a C-terminal Sufu-interacting site (SIC) in addition to a previously identified N-terminal site (SIN), and that both SIC and SIN are required for optimal inhibition of Ci/Gli by Sufu. Sufu can sequester Ci/Gli in the cytoplasm through binding to SIN while inhibiting Ci/Gli activity in the nucleus depending on SIC. It was also found that binding of Sufu to SIC and the middle region of Ci can impede recruitment of the transcriptional coactivator CBP by masking its binding site in the C-terminal region of Ci. Indeed, moving the CBP-binding site to an 'exposed' location can render Ci resistant to Sufu-mediated inhibition in the nucleus. Hence, this study identifies a previously unidentified and conserved Sufu-binding motif in the C-terminal region of Ci/Gli and provides mechanistic insight into how Sufu inhibits Ci/Gli activity in the nucleus.

Le, T.P., Vuong, L.T., Kim, A.R., Hsu, Y.C. and Choi, K.W. (2016). 14-3-3 proteins regulate Tctp-Rheb interaction for organ growth in Drosophila. Nat Commun 7: 11501. PubMed ID: 27151460
Summary:
14-3-3 family proteins regulate multiple signalling pathways. Understanding biological functions of 14-3-3 proteins has been limited by the functional redundancy of conserved isotypes. This study provides evidence that 14-3-3 proteins regulate two interacting components of Tor signalling in Drosophila, translationally controlled tumour protein (Tctp) and Rheb GTPase. Single knockdown of 14-3-3ɛ or 14-3-3ζ isoform does not show obvious defects in organ development but causes synergistic genetic interaction with Tctp and Rheb to impair tissue growth. 14-3-3 proteins physically interact with Tctp and Rheb. Knockdown of both 14-3-3 isoforms abolishes the binding between Tctp and Rheb, disrupting organ development. Depletion of 14-3-3s also reduces the level of phosphorylated S6 kinase, phosphorylated Thor/4E-BP and cyclin E (CycE). Growth defects from knockdown of 14-3-3 and Tctp are suppressed by CycE overexpression. This study suggests a novel mechanism of Tor regulation mediated by 14-3-3 interaction with Tctp and Rheb.

Liu, X., Greer, C. and Secombe, J. (2014). KDM5 interacts with Foxo to modulate cellular levels of oxidative stress. PLoS Genet 10: e1004676. PubMed ID: 25329053
Summary:
Increased cellular levels of oxidative stress are implicated in a large number of human diseases. This study describes the transcription co-factor KDM5 (also known as Lid) as a new critical regulator of cellular redox state. Moreover, this occurs through a novel KDM5 activity whereby it alters the ability of the transcription factor Foxo to bind to DNA. Microarray analyses of kdm5 mutants revealed a striking enrichment for genes required to regulate cellular levels of oxidative stress. Consistent with this, loss of kdm5 results in increased sensitivity to treatment with oxidizers, elevated levels of oxidized proteins, and increased mutation load. KDM5 activates oxidative stress resistance genes by interacting with Foxo to facilitate its recruitment to KDM5-Foxo co-regulated genes. Significantly, this occurs independently of KDM5's well-characterized demethylase activity. Instead, KDM5 interacts with the lysine deacetylase HDAC4 to promote Foxo deacetylation, which affects Foxo DNA binding.

Wednesday, May 11th

Saberi, M. and Seyed-Allaei, H. (2016). Odorant receptors of Drosophila are sensitive to the molecular volume of odorants. Sci Rep 6: 25103. PubMed ID: 27112241
Summary:
Which properties of a molecule define its odor? This is a basic yet unanswered question regarding the olfactory system. The olfactory system of Drosophila has a repertoire of approximately 60 odorant receptors. Molecules bind to odorant receptors with different affinities and activate them with different efficacies, thus providing a combinatorial code that identifies odorants. This study hypothesized that the binding affinity of an odorant-receptor pair is affected by their relative sizes. The maximum affinity can be attained when the molecular volume of an odorant matches the volume of the binding pocket. The affinity drops to zero when the sizes are too different, thus obscuring the effects of other molecular properties. A mathematical formulation of this hypothesis was developed and verified using Drosophila data. The volume and structural flexibility of the binding site of each odorant receptor were also predicted; these features significantly differ between odorant receptors. The differences in the volumes and structural flexibilities of different odorant receptor binding sites may explain the difference in the scents of similar molecules with different sizes.

Vogt, K., Aso, Y., Hige, T., Knapek, S., Ichinose, T., Friedrich, A. B., Turner, G. C., Rubin, G. M. and Tanimoto, H. (2016). Direct neural pathways convey distinct visual information to mushroom bodies. Elife 5. PubMed ID: 27083044. Journal and Pubmed
Summary:
Previous studies have identified that visual and olfactory associative memories of Drosophila share the mushroom body (MB) circuit. Despite well-characterized odor representations in the Drosophila MB, the MB circuit for visual information is totally unknown. This study shows that a small subset of MB Kenyon cells (KCs) selectively responds to visual but not olfactory stimulation. The dendrites of these atypical KCs form a ventral accessory calyx (vAC), distinct from the main calyx that receives olfactory input. Two types of visual projection neurons (VPNs) directly connecting the optic lobes and the vAC were identified. Strikingly, these VPNs are differentially required for visual memories of color and brightness. The segregation of visual and olfactory domains in the MB allows independent processing of distinct sensory memories and may be a conserved form of sensory representations among insects.

Gai, Y., Liu, Z., Cervantes-Sandoval, I. and Davis, R.L. (2016). DrosophilaSLC22A transporter is a memory suppressor gene that influences cholinergic neurotransmission to the mushroom bodies. Neuron 90: 581-595. PubMed ID: 27146270
Summary:
The mechanisms that constrain memory formation are of special interest because they provide insights into the brain's memory management systems and potential avenues for correcting cognitive disorders. RNAi knockdown in the Drosophila mushroom body neurons (MBn) of a newly discovered memory suppressor gene, Solute Carrier DmSLC22A, a member of the organic cation transporter family, enhances olfactory memory expression, while overexpression inhibits it. The protein localizes to the dendrites of the MBn, surrounding the presynaptic terminals of cholinergic afferent fibers from projection neurons (Pn). Cell-based expression assays show that this plasma membrane protein transports cholinergic compounds with the highest affinity among several in vitro substrates. Feeding flies choline or inhibiting acetylcholinesterase in Pn enhances memory, an effect blocked by overexpression of the transporter in the MBn. The data argue that DmSLC22A is a memory suppressor protein that limits memory formation by helping to terminate cholinergic neurotransmission at the Pn:MBn synapse.

Mabuchi, I., Shimada, N., Sato, S., Ienaga, K., Inami, S. and Sakai, T. (2016). Mushroom body signaling is required for locomotor activity rhythms in Drosophila. Neurosci Res [Epub ahead of print]. PubMed ID: 27106579
Summary:
In the fruitfly Drosophila melanogaster, circadian rhythms of locomotor activity under constant darkness are controlled by pacemaker neurons. To understand how behavioral rhythmicity is generated by the nervous system, it is essential to identify the output circuits from the pacemaker neurons. The importance of mushroom bodies (MBs) in generating behavioral rhythmicity remains controversial because contradicting results have been reported as follows: (1) locomotor activity in MB-ablated flies is substantially rhythmic, but (2) activation of restricted neuronal populations including MB neurons induces arrhythmic locomotor activity. This study reports that neurotransmission in MBs is required for behavioral rhythmicity. For adult-specific disruption of neurotransmission in MBs, the GAL80/GAL4/UAS ternary gene expression system was used in combination with the temperature-sensitive dynamin mutation shibirets1. Blocking of neurotransmission in GAL4-positive neurons including MB neurons induced arrhythmic locomotor activity, whereas this arrhythmicity was rescued by the MB-specific expression of GAL80. These results indicate that MB signaling plays a key role in locomotor activity rhythms in Drosophila.

Tuesday, May 10

Chen, H., Zheng, X., Xiao, D. and Zheng, Y. (2016). Age-associated de-repression of retrotransposons in the Drosophila fat body, its potential cause and consequence. Aging Cell [Epub ahead of print]. PubMed ID: 27072046
Summary:
Eukaryotic genomes contain transposable elements (TE) that can move into new locations upon activation. Since uncontrolled transposition of TEs, including the retrotransposons and DNA transposons, can lead to DNA breaks and genomic instability, multiple mechanisms, including heterochromatin-mediated repression, have evolved to repress TE activation. Studies in model organisms have shown that TEs become activated upon aging as a result of age-associated deregulation of heterochromatin. Considering that different organisms or cell types may undergo distinct heterochromatin changes upon aging, it is important to identify pathways that lead to TE activation in specific tissues and cell types. Through deep sequencing of isolated RNAs, this study report an increased expression of many retrotransposons in the old Drosophila fat body, an organ equivalent to the mammalian liver and adipose tissue. This de-repression correlates with an increased number of DNA damage foci and decreased level of Drosophila lamin-B in the old fat body cells. Depletion of the Drosophila lamin-B in the young or larval fat body results in a reduction of heterochromatin and a corresponding increase in retrotransposon expression and DNA damage. Further manipulations of lamin-B and retrotransposon expression suggest a role of the nuclear lamina in maintaining the genome integrity of the Drosophila fat body by repressing retrotransposons.

Zolotarev, N., Fedotova, A., Kyrchanova, O., Bonchuk, A., Penin, A.A., Lando, A.S., Eliseeva, I.A., Kulakovskiy, I.V., Maksimenko, O. and Georgiev, P. (2016). Architectural proteins Pita, Zw5,and ZIPIC contain homodimerization domain and support specific long-range interactions in Drosophila. Nucleic Acids Res [Epub ahead of print]. PubMed ID: 27137890
Summary:
According to recent models, as yet poorly studied architectural proteins appear to be required for local regulation of enhancer-promoter interactions, as well as for global chromosome organization. Transcription factors ZIPIC, Pita and Zw5 belong to the class of chromatin insulator proteins and preferentially bind to promoters near the TSS and extensively colocalize with cohesin and condensin complexes. ZIPIC, Pita and Zw5 are structurally similar in containing the N-terminal zinc finger-associated domain (ZAD) and different numbers of C2H2-type zinc fingers at the C-terminus. This study shows that the ZAD domains of ZIPIC, Pita and Zw5 form homodimers. In Drosophila transgenic lines, these proteins are able to support long-distance interaction between GAL4 activator and the reporter gene promoter. However, no functional interaction between binding sites for different proteins was found, suggesting that such interactions are highly specific. ZIPIC facilitates long-distance stimulation of the reporter gene by GAL4 activator in yeast model system. Many of the genomic binding sites of ZIPIC, Pita and Zw5 are located at the boundaries of topologically associated domains (TADs). Thus, ZAD-containing zinc-finger proteins can be attributed to the class of architectural proteins.

Melnikova, L., Shapovalov, I., Kostyuchenko, M., Georgiev, P. and Golovnin, A. (2016). EAST affects the activity of Su(Hw) insulators by two different mechanisms in Drosophila melanogaster. Chromosoma [Epub ahead of print]. PubMed ID: 27136940
Summary:
Recent data suggest that insulators organize chromatin architecture in the nucleus. The best characterized Drosophila insulator, found in the gypsy retrotransposon, contains 12 binding sites for the Su(Hw) protein. Enhancer blocking, along with Su(Hw), requires BTB/POZ domain proteins, Mod(mdg4)-67.2 and CP190. Inactivation of Mod(mdg4)-67.2 leads to a direct repression of the yellow gene promoter by the gypsy insulator. This study shows that such repression is regulated by the level of the EAST protein, which is an essential component of the interchromatin compartment. Deletion of the EAST C-terminal domain suppresses Su(Hw)-mediated repression. Partial inactivation of EAST by mutations in the east gene suppresses the enhancer-blocking activity of the gypsy insulator. The binding of insulator proteins to chromatin is highly sensitive to the level of EAST expression. These results suggest that EAST, one of the main components of the interchromatin compartment, can regulate the activity of chromatin insulators.

Zhang, W., et al. (2016). . The nucleosome remodeling and deacetylase complex NuRD is built from preformed catalytically active sub-modules. J Mol Biol [Epub ahead of print]. PubMed ID: 27117189
Summary:
The Nucleosome Remodeling Deacetylase (NuRD) complex is a highly conserved regulator of chromatin structure and transcription. Structural studies have shed light on this and other chromatin modifying machines, but much less is known about how they assemble and whether stable and functional sub-modules exist that retain enzymatic activity. Purification of the endogenous Drosophila NuRD complex shows that it consists of a stable core of subunits, while others, in particular the chromatin remodeller CHD4, associate transiently. To dissect the assembly and activity of NuRD, all possible combinations of different components were systematically produced using the MultiBac system, and their activity and biophysical properties were determined. Single molecule imaging of CHD4 was carried out in live mouse ES cells, in the presence and absence of one of core components (MBD3), to show how the core deacetylase and chromatin-remodeling sub-modules associate in-vivo. These experiments suggest a pathway for the assembly of NuRD via preformed and active sub-modules. These retain enzymatic activity and are present in both the nucleus and the cytosol, an outcome with important implications for understanding NuRD function.

Monday, May 9th

Matsumoto, K., Ayukawa, T., Ishio, A., Sasamura, T., Yamakawa, .T and Matsuno, K. (2016). Dual roles of O-glucose glycans redundant with monosaccharide O-fucose on Notch in Notch trafficking. J Biol Chem [Epub ahead of print]. PubMed ID: 27129198
Summary:
The extracellular domain of Notch contains multiple EGF-like repeats. At least five different glycans are found in distinct sites within these EGF-like repeats. The potential functional interactions between these glycans are just beginning to be understood. Monosaccharide O-fucose and O-glucose trisaccharide (O-glucose-xylose-xylose) are added to many of the Notch EGF-like repeats. In Drosophila, Shams adds a xylose specifically to the monosaccharide O-glucose. Loss of the terminal dixylose of O-glucose-linked saccharides has little effect on Notch signaling. Analyses of double mutants of shams and other genes required for glycan modifications reveals that both the monosaccharide O-glucose and the terminal dixylose of O-glucose-linked saccharides function redundantly with the monosaccharide O-fucose in Notch activation and trafficking. The terminal dixylose of O-glucose-linked saccharides and the monosaccharide O-glucose are required in distinct Notch-trafficking processes: Notch transport from the apical plasma membrane to adherens junctions, and Notch export from the endoplasmic reticulum, respectively. Therefore, the monosaccharide O-glucose and terminal dixylose of O-glucose-linked saccharides have distinct activities in Notch trafficking, although a loss of these activities is compensated for by the presence of monosaccharide O-fucose. Given that various glycans attached to a protein motif may have redundant functions, these results suggest that these potential redundancies may lead to a serious underestimation of glycan functions.

Gomez-Lamarca, M. J., Snowdon, L. A., Seib, E., Klein, T. and Bray, S. J. (2015). Rme-8 depletion perturbs Notch recycling and predisposes to pathogenic signaling. J Cell Biol 210: 303-318. PubMed ID: 26169355
Summary:
Notch signaling is a major regulator of cell fate, proliferation, and differentiation. Like other signaling pathways, its activity is strongly influenced by intracellular trafficking. Besides contributing to signal activation and down-regulation, differential fluxes between trafficking routes can cause aberrant Notch pathway activation. Investigating the function of the retromer-associated DNAJ protein Rme-8 in vivo, this study demonstrated a critical role in regulating Notch receptor recycling. In the absence of Rme-8, Notch accumulated in enlarged tubulated Rab4-positive endosomes, and as a consequence, signaling was compromised. Strikingly, when the retromer component Vps26 was depleted at the same time, Notch no longer accumulated and instead was ectopically activated. Likewise, depletion of ESCRT-0 components Hrs or Stam in combination with Rme-8 also led to high levels of ectopic Notch activity. Together, these results highlight the importance of Rme-8 in coordinating normal endocytic recycling route and reveal that its absence predisposes toward conditions in which pathological Notch signaling can occur.

Aerne, B. L., Gailite, I., Sims, D. and Tapon, N. (2015). Hippo stabilises its adaptor Salvador by antagonising the HECT ubiquitin ligase Herc4. PLoS One 10: e0131113. PubMed ID: 26125558
Summary:
Signalling through the Hippo (Hpo) pathway involves a kinase cascade, which leads to the phosphorylation and inactivation of the pro-growth transcriptional co-activator Yorkie (Yki). Despite the identification of a large number of pathway members and modulators, understanding of the molecular events that lead to activation of Hpo and the downstream kinase Warts (Wts) remain incomplete. Recently, targeted degradation of several Hpo pathway components has been demonstrated as a means of regulating pathway activity. In particular, the stability of scaffold protein Salvador (Sav), which is believed to promote Hpo/Wts association, is crucially dependent on its binding partner Hpo. In a cell-based RNAi screen for ubiquitin regulators involved in Sav stability, this study identified the HECT domain protein Herc4 (HECT and RLD domain containing E3 ligase) as a Sav E3 ligase. Herc4 expression promotes Sav ubiquitylation and degradation, while Herc4 depletion stabilises Sav. Interestingly, Hpo reduces Sav/Herc4 interaction in a kinase-dependent manner. This suggests the existence of a positive feedback loop, where Hpo stabilises its own positive regulator by antagonising Herc4-mediated degradation of Sav.

Cho, B., Pierre-Louis, G., Sagner, A., Eaton, S. and Axelrod, J. D. (2015). Clustering and negative feedback by endocytosis in planar cell polarity signaling is modulated by ubiquitinylation of Prickle. PLoS Genet 11: e1005259. PubMed ID: 25996914
Summary:
The core components of the planar cell polarity (PCP) signaling system, including both transmembrane and peripheral membrane associated proteins, form asymmetric complexes that bridge apical intercellular junctions. While these can assemble in either orientation, coordinated cell polarization requires the enrichment of complexes of a given orientation at specific junctions. This might occur by both positive and negative feedback between oppositely oriented complexes, and requires the peripheral membrane associated PCP components. However, the molecular mechanisms underlying feedback are not understood. This study found that the E3 ubiquitin ligase complex Cullin1(Cul1)/SkpA/Supernumerary limbs(Slimb) regulates the stability of one of the peripheral membrane components, Prickle (Pk). Excess Pk disrupts PCP feedback and prevents asymmetry. Pk was found to participate in negative feedback by mediating internalization of PCP complexes containing the transmembrane components Van Gogh (Vang) and Flamingo (Fmi), and that internalization is activated by oppositely oriented complexes within clusters. Pk also participates in positive feedback through an unknown mechanism promoting clustering. these results therefore identify a molecular mechanism underlying generation of asymmetry in PCP signaling.

Sunday, May 8th

Qi, Y., Huang, J., Li, M. Q., Wu, Y. S., Xia, R. Y. and Ye, G. Y. (2016). Serotonin modulates insect hemocyte phagocytosis via two different serotonin receptors. Elife 5 [Epub ahead of print]. PubMed ID: 26974346
Summary:
Serotonin (5-HT) modulates both neural and immune responses in vertebrates, but its role in insect immunity remains uncertain. This study reports that hemocytes in the caterpillar, Pieris rapae are able to synthesize 5-HT following activation by lipopolysaccharide. The inhibition of a serotonin-generating enzyme with either pharmacological blockade or RNAi knock-down impaired hemocyte phagocytosis. Biochemical and functional experiments showed that naive hemocytes primarily express 5-HT1B and 5-HT2B receptors. The blockade of 5-HT1B significantly reduced phagocytic ability, however the blockade of 5-HT2B increased hemocyte phagocytosis. The 5-HT1B-null Drosophila melanogaster mutants showed higher mortality than controls when infected with bacteria, due to their decreased phagocytotic ability. Flies expressing 5-HT1B or 5-HT2B RNAi in hemocytes also showed similar sensitivity to infection. Combined, these data demonstrate that 5-HT mediates hemocyte phagocytosis through 5-HT1B and 5-HT2B receptors and serotonergic signaling performs critical modulatory functions in immune systems of animals separated by 500 million years of evolution.

Wong, Z. S., Brownlie, J. C. and Johnson, K. N. (2016). Impact of ERK activation on fly survival and Wolbachia-mediated protection during virus infection. J Gen Virol [Epub ahead of print]. PubMed ID: 26977591
Summary:
Elevated levels of reactive oxygen species (ROS) provide protection against virus-induced mortality in Drosophila. In addition to contributing to oxidative stress, ROS are known to activate a number of signaling pathways including the extracellular signal-regulated kinases (ERK) signaling cascade. It was recently shown that ERK signaling is important for resistance against viral replication and invasion in cultured Drosophila cells and the gut epithelium of adult flies. Here, using a Drosophila loss-of-function ERK (rolled) mutant it was demonstrated that ERK is important for fly survival during virus infection. ERK mutant flies subjected to Drosophila C virus (DCV) oral and systemic infection were more susceptible to virus-induced mortality as compared to wild type flies. It was demonstrated experimentally that ERK activation is important for fly survival during oral and systemic virus infection. Given that elevated ROS correlates with Wolbachia-mediated antiviral protection, the involvement of ERK in antiviral protection was also investigated in flies infected by Wolbachia. The results indicate that ERK activation is increased in the presence of Wolbachia but this does not appear to influence Wolbachia-mediated antiviral protection, at least during systemic infection.

Rainey, S. M., et al. (2016). Wolbachia blocks viral genome replication early in infection without a transcriptional response by the endosymbiont or host small RNA pathways. PLoS Pathog 12: e1005536. PubMed ID: 27089431
Summary:
The intracellular endosymbiotic bacterium Wolbachia can protect insects against viral infection. To investigate the mechanisms underlying this antiviral protection, this study developed a new model system combining Wolbachia-infected Drosophila melanogaster cell culture with the model mosquito-borne Semliki Forest virus (SFV; Togaviridae, Alphavirus). Wolbachia provides strong antiviral protection rapidly after infection, suggesting that an early stage post-infection is being blocked. Wolbachia does appear to have major effects on events distinct from entry, assembly or exit as it inhibits the replication of an SFV replicon transfected into the cells. Furthermore, it causes a far greater reduction in the expression of proteins from the 3 open reading frame than the 5 non-structural protein open reading frame, indicating that it is blocking the replication of viral RNA. Further to this separation of the replicase proteins and viral RNA in transreplication assays shows that uncoupling of viral RNA and replicase proteins does not overcome Wolbachia's antiviral activity. This further suggests that replicative processes are disrupted, such as translation or replication, by Wolbachia infection. This may occur by Wolbachia mounting an active antiviral response, but the virus did not cause any transcriptional response by the bacterium, suggesting that this is not the case. Host microRNAs (miRNAs) have been implicated in protection, but again it was found that host cell miRNA expression was unaffected by the bacterium and neither do the findings suggest any involvement of the antiviral siRNA pathway. It is concluded that Wolbachia may directly interfere with early events in virus replication such as translation of incoming viral RNA or RNA transcription, and this likely involves an intrinsic (as opposed to an induced) mechanism.

Lamiable, O., Arnold, J., da Silva de Faria, I. J., Proveti Olmo, R., Bergami, F., Meignin, C., Hoffmann, J. A., Marques, J. T. and Imler, J. L. (2016). Analysis of the contribution of hemocytes and autophagy to Drosophila antiviral immunity. J Virol [Epub ahead of print]. PubMed ID: 27009948
Summary:
Antiviral immunity in Drosophila involves the broadly active intrinsic mechanism of RNA interference (RNAi) and virus-specific inducible responses. Using a panel of six viruses, this study investigated the role of hemocytes and autophagy in the control of viral infections. Injection of latex beads to saturate phagocytosis, or genetic depletion of hemocytes, resulted in decreased survival and increased viral titers following infection with cricket paralysis virus (CrPV), Flock House Virus (FHV) and vesicular stomatitis virus (VSV), but had no impact on Drosophila C virus (DCV), Sindbis virus (SINV) and invertebrate iridescent virus 6 (IIV6). In the case of CrPV and FHV, apoptosis was induced in infected cells, which were phagocytosed by hemocytes. In contrast, VSV did not trigger any significant apoptosis but the autophagy gene Atg7 was required for full virus resistance, suggesting that hemocytes use autophagy to recognize the virus. However, this recognition does not depend on the Toll-7 receptor. Autophagy had no impact on DCV, CrPV, SINV or IIV6, and was required for replication of the sixth virus, FHV. Even in the case of VSV the increase in titers were modest in Atg7 mutant flies suggesting that autophagy does not play a major role in antiviral immunity in Drosophila Altogether, these results indicate that, while autophagy plays a minor role, phagocytosis contributes to virus-specific immune responses in insects.

Saturday, May 7th

Wang, Q., Taliaferro, J.M., Klibaite, U., Hilgers, V., Shaevitz, J.W. and Rio, D.C. (2016). The PSI-U1 snRNP interaction regulates male mating behavior in Drosophila. Proc Natl Acad Sci U S A [Epub ahead of print]. PubMed ID: 27114556
Summary:
Fruitless alternative pre-mRNA splicing (AS) isoforms have been shown to influence male courtship behavior, but the underlying mechanisms are unknown. Using genome-wide approaches and quantitative behavioral assays, this study shows that the P-element somatic inhibitor (PSI) and its interaction with the U1 small nuclear ribonucleoprotein complex (snRNP) control male courtship behavior. PSI mutants lacking the U1 snRNP-interacting domain (PSIΔAB mutant) exhibit extended but futile mating attempts. The PSIΔAB mutant results in significant changes in the AS patterns of ∼1,200 genes in the Drosophila brain, many of which have been implicated in the regulation of male courtship behavior. PSI directly regulates the AS of at least one-third of these transcripts, suggesting that PSI-U1 snRNP interactions coordinate the behavioral network underlying courtship behavior. Importantly, one of these direct targets is fruitless, the master regulator of courtship. Thus, PSI imposes a specific mode of regulatory control within the neuronal circuit controlling courtship, even though it is broadly expressed in the fly nervous system. This study reinforces the importance of AS in the control of gene activity in neurons and integrated neuronal circuits, and provides a surprising link between a pleiotropic pre-mRNA splicing pathway and the precise control of successful male mating behavior.

Kopytova, D., Popova, V., Kurshakova, M., Shidlovskii, Y., Nabirochkina, E., Brechalov, A., Georgiev, G. and Georgieva, S. (2016). ORC interacts with THSC/TREX-2 and its subunits promote Nxf1 association with mRNP and mRNA export in Drosophila. Nucleic Acids Res [Epub ahead of print]. PubMed ID: 27016737
Summary:
The origin recognition complex (ORC) of eukaryotes associates with the replication origins and initiates the pre-replication complex assembly. In the literature, there are several reports of interaction of ORC with different RNAs. This study demonstrates for the first time a direct interaction of ORC with the THSC/TREX-2 mRNA nuclear export complex. The THSC/TREX-2 was purified from the Drosophila embryonic extract and found to bind with a fraction of the ORC. This interaction occurred via several subunits and was essential for Drosophila viability. Also, ORC was associated with mRNP, which was facilitated by TREX-2. ORC subunits interacted with the Nxf1 receptor mediating the bulk mRNA export. The knockdown of Orc5 led to a drop in the Nxf1 association with mRNP, while Orc3 knockdown increased the level of mRNP-bound Nxf1. The knockdown of Orc5, Orc3 and several other ORC subunits led to an accumulation of mRNA in the nucleus, suggesting that ORC participates in the regulation of the mRNP export.

Macdonald, P. M., Kanke, M. and Kenny, A. (2016). Community effects in regulation of translation. Elife 5 [Epub ahead of print]. PubMed ID: 27104756
Summary:
Certain forms of translational regulation, and translation itself, rely on long-range interactions between proteins bound to the different ends of mRNAs. A widespread assumption is that such interactions occur only in cis, between the two ends of a single transcript. However, certain translational regulatory defects of the Drosophila oskar (osk) mRNA can be rescued in trans. It is proposed that inter-transcript interactions, promoted by assembly of the mRNAs in particles, allow regulatory elements to act in trans. This study confirms predictions of that model and shows that disruption of Polypyrimidine tract binding protein (PTB) dependent particle assembly inhibits rescue in trans. Communication between transcripts is not limited to different osk mRNAs, as regulation imposed by cis-acting elements embedded in the osk mRNA spreads to gurken mRNA. It is concluded that community effects exist in translational regulation.

McMahon, A. C., Rahman, R., Jin, H., Shen, J. L., Fieldsend, A., Luo, W. and Rosbash, M. (2016). TRIBE: Hijacking an RNA-editing enzyme to identify cell-specific targets of RNA-binding proteins. Cell 165: 742-753. PubMed ID: 27040499
Summary:
RNA transcripts are bound and regulated by RNA-binding proteins (RBPs). Current methods for identifying in vivo targets of an RBP are imperfect and not amenable to examining small numbers of cells. TRIBE (targets of RNA-binding proteins identified by editing) technique that couples an RBP to the catalytic domain of the Drosophila RNA-editing enzyme ADAR and expresses the fusion protein in vivo, was developed to address these issues. RBP targets are marked with novel RNA editing events and identified by sequencing RNA. TRIBE was used to identify the targets of three RBPs (Hrp48, dFMR1, and NonA). TRIBE compares favorably to other methods, including CLIP, and this study has identified RBP targets from as little as 150 specific fly neurons. TRIBE can be performed without an antibody and in small numbers of specific cells.

Friday, May 6th

Yamaki, T., Yasuda, G. K. and Wakimoto, B. T. (2016). The Deadbeat paternal effect of uncapped sperm telomeres on cell cycle progression and chromosome behavior in Drosophila melanogaster. Genetics [Epub ahead of print]. PubMed ID: 27029731
Summary:
Telomere-capping complexes (TCCs) protect the ends of linear chromosomes from illegitimate repair and end-to-end fusions and are required for genome stability. The identity and assembly of TCC components have been extensively studied, but whether TCCs require active maintenance in non-dividing cells remains an open question. This study shows that Drosophila melanogaster requires Deadbeat (Ddbt), a sperm nuclear basic protein (SNBP) that is recruited to the telomere by the TCC and is required for TCC maintenance during genome-wide chromatin remodeling that transforms spermatids to mature sperm. Ddbt-deficient males produce sperm lacking TCCs. Their offspring delay the initiation of anaphase as early as cycle 1 but progress through the first two cycles. Persistence of uncapped paternal chromosomes induces arrest at or around cycle 3. This early arrest can be rescued by selective elimination of paternal chromosomes and production of gynogenetic haploid or haploid mosaics. Progression past cycle 3 can also occur if embryos have reduced levels of the maternally provided checkpoint kinase Chk2. The findings provide insights into how telomere integrity affects the regulation of the earliest embryonic cell cycles. They also suggest that other SNBPs, including those in humans, may have analogous roles and manifest as paternal effects on embryo quality.

Tao, L., Fasulo, B., Warecki, B. and Sullivan, W. (2016). Tum/RacGAP functions as a switch activating the Pav/kinesin-6 motor. Nat Commun 7: 11182. PubMed ID: 27091402

Summary:
Centralspindlin is essential for central spindle and cleavage furrow formation. Drosophila centralspindlin consists of a kinesin-6 motor (Pav/kinesin-6) and a GTPase-activating protein (Tum/RacGAP). Centralspindlin localization to the central spindle is mediated by Pav/kinesin-6. While Tum/RacGAP has well-documented scaffolding functions, whether it influences Pav/kinesin-6 function is less well-explored. This study demonstrates that both Pav/kinesin-6 and the centralspindlin complex (co-expressed Pav/Tum) have strong microtubule bundling activity. Centralspindlin also has robust plus-end-directed motility. In contrast, Pav/kinesin-6 alone cannot move microtubules. However, the addition of Tum/RacGAP or a 65 amino acid Tum/RacGAP fragment to Pav/kinesin-6 restores microtubule motility. Further, ATPase assays reveal that microtubule-stimulated ATPase activity of centralspindlin is seven times higher than that of Pav/kinesin-6. These findings are supported by in vivo studies demonstrating that in Tum/RacGAP-depleted S2 Drosophila cells, Pav/kinesin-6 exhibits severely reduced localization to the central spindle and an abnormal concentration at the centrosomes.

Ye, A. A., Deretic, J., Hoel, C. M., Hinman, A. W., Cimini, D., Welburn, J. P. and Maresca, T. J. (2015). Aurora A kinase contributes to a pole-based error correction pathway. Curr Biol 25: 1842-1851. PubMed ID: 26166783
Summary:
Chromosome biorientation, where sister kinetochores attach to microtubules (MTs) from opposing spindle poles, is the configuration that best ensures equal partitioning of the genome during cell division. Erroneous kinetochore-MT attachments are commonplace but are often corrected prior to anaphase. Error correction, thought to be mediated primarily by the centromere-enriched Aurora B kinase (ABK), typically occurs near spindle poles; however, the relevance of this locale is unclear. Furthermore, polar ejection forces (PEFs), highest near poles, can stabilize improper attachments by pushing mal-oriented chromosome arms away from spindle poles. Hence, there is a conundrum: erroneous kinetochore-MT attachments are weakened where PEFs are most likely to strengthen them. This study reports that Aurora A kinase (AAK) opposes the stabilizing effect of PEFs. AAK activity contributes to phosphorylation of kinetochore substrates near poles and its inhibition results in chromosome misalignment and an increased incidence of erroneous kinetochore-MT attachments. Furthermore, AAK directly phosphorylates a site in the N-terminal tail of Ndc80/Hec1 that has been implicated in reducing the affinity of the Ndc80 complex for MTs when phosphorylated. It is proposed that an AAK activity gradient contributes to correcting mal-oriented kinetochore-MT attachments in the vicinity of spindle poles.

Eisman, R. C., Phelps, M. A. and Kaufman, T. C. (2016). The End of a Monolith: Deconstructing the Cnn-Polo interaction. Fly (Austin): [Epub ahead of print]. PubMed ID: 27096551
Summary:
In Drosophila melanogaster a functional pericentriolar matrix (PCM) at mitotic centrosomes requires Centrosomin-Long Form (Cnn-LF) proteins. Moreover, tissue culture cells have shown that the centrosomal localization of both Cnn-LF and Polo kinase are co-dependent, suggesting a direct interaction. A recent study found Cnn potentially binds to and is phosphorylated by Polo kinase at two residues encoded by Exon1A, the initiating exon of a subset of Cnn isoforms. These interactions are required for the centrosomal localization of Cnn-LF in syncytial embryos and a mutation of either phosphorylation site is sufficient to block localization of both mutant and wild-type Cnn when they are co-expressed. Immunoprecipitation experiments show that Cnn-LF interacts directly with mitotically activated Polo kinase and requires the two phosphorylation sites in Exon1A. These IP experiments also show that Cnn-LF proteins form multimers. Depending on the stoichiometry between functional and mutant peptides, heteromultimers exhibit dominant negative or positive trans-complementation (rescue) effects on mitosis. Additionally, following the completion of meiosis, Cnn-Short Form (Cnn-SF) proteins are required for polar body formation in embryos, a process previously shown to require Polo kinase. These findings, when combined with previous work, clearly demonstrate the complexity of cnn and show that a view of cnn as encoding a single peptide is too simplistic.

Thursday, May 5th

Chaubal, A., Todi, S.V. and Pile, L.A. (2016). Inter-isoform-dependent regulation of the Drosophila master transcriptional regulator SIN3. J Biol Chem [Epub ahead of print]. PubMed ID: 27129248
Summary:
SIN3 is a transcriptional corepressor that acts as a scaffold for a histone deacetylase (HDAC) complex. The SIN3 complex regulates various biological processes, including organ development, cell proliferation and energy metabolism. Little is known, however, about the regulation of SIN3 itself. There are two major isoforms of Drosophila SIN3, 187 and 220, which are differentially expressed. Intrigued by the developmentally timed exchange of SIN3 isoforms, this study examined whether SIN3 187 controls the fate of the 220 counterpart. It was shown that in developing tissue there is interplay between SIN3 isoforms: when SIN3 187 protein levels increase, SIN3 220 protein decreases concomitantly. SIN3 187 has a dual effect on SIN3 220. Expression of 187 leads to reduced 220 transcript, while also increasing the turnover of SIN3 220 protein by the proteasome. These data support the presence of a novel, inter-isoform-dependent mechanism that regulates the amount of SIN3 protein, and potentially the level of specific SIN3 complexes, during distinct developmental stages.

Coulthard, A. B., Taylor-Kamall, R. W., Hallson, G., Axentiev, A., Sinclair, D. A., Honda, B. M. and Hilliker, A. J. (2016). Meiotic recombination is suppressed near the histone-defined border of euchromatin and heterochromatin on chromosome 2L of Drosophila melanogaster. Genome 59: 289-294. PubMed ID: 27031007
Summary:
In Drosophila melanogaster, the borders between pericentric heterochromatin and euchromatin on the major chromosome arms have been defined in various ways, including chromatin-specific histone modifications, the binding patterns of heterochromatin-enriched chromosomal proteins, and various cytogenetic techniques. Elucidation of the genetic properties that independently define the different chromatin states associated with heterochromatin and euchromatin should help refine the boundary. Since meiotic recombination is present in euchromatin, but absent in heterochromatin, it constitutes a key genetic property that can be observed transitioning between chromatin states. Using P element insertion lines marked with a su(Hw) insulated mini-white gene, meiotic recombination was found to transition in a region consistent with the H3K9me2 transition observed in ovaries.

Ramachandran, S. and Henikoff, S. (2016). Transcriptional regulators compete with nucleosomes post-replication. Cell 165: 580-592. PubMed ID: 27062929
Summary:
Every nucleosome across the genome must be disrupted and reformed when the replication fork passes, but how chromatin organization is re-established following replication is unknown. To address this problem, Mapping In vivo Nascent Chromatin with EdU and sequencing (MINCE-seq) was developed to characterize the genome-wide location of nucleosomes and other chromatin proteins behind replication forks at high temporal and spatial resolution. The characteristic chromatin landscape at Drosophila promoters and enhancers is lost upon replication. The most conspicuous changes are at promoters that have high levels of RNA polymerase II (RNAPII) stalling and DNA accessibility and show specific enrichment for the BRM remodeler. Enhancer chromatin is also disrupted during replication, suggesting a role for transcription factor (TF) competition in nucleosome re-establishment. Thus, the characteristic nucleosome landscape emerges from a uniformly packaged genome by the action of TFs, RNAPII, and remodelers minutes after replication fork passage.

Li, H. B., Ohno, K., Gui, H. and Pirrotta, V. (2013). Insulators target active genes to transcription factories and polycomb-repressed genes to polycomb bodies. PLoS Genet 9: e1003436. PubMed ID: 23637616
Summary:
Polycomb bodies are foci of Polycomb proteins in which different Polycomb target genes are thought to co-localize in the nucleus, looping out from their chromosomal context. WInsulators, not Polycomb response elements (PREs), have been shown to mediate associations among Polycomb Group (PcG) targets to form Polycomb bodies. This study used live imaging and 3C interactions to show that transgenes containing PREs and endogenous PcG-regulated genes are targeted by insulator proteins to different nuclear structures depending on their state of activity. When two genes are repressed, they co-localize in Polycomb bodies. When both are active, they are targeted to transcription factories in a fashion dependent on Trithorax and enhancer specificity as well as the insulator protein CTCF. In the absence of CTCF, assembly of Polycomb bodies is essentially reduced to those representing genomic clusters of Polycomb target genes. The critical role of Trithorax suggests that stable association with a specialized transcription factory underlies the cellular memory of the active state.

Wednesday, May 4th

Jaiswal, M., Haelterman, N. A., Sandoval, H., Xiong, B., Donti, T., Kalsotra, A., Yamamoto, S., Cooper, T. A., Graham, B. H. and Bellen, H. J. (2015). Impaired mitochondrial energy production causes light-induced photoreceptor degeneration independent of oxidative stress. PLoS Biol 13: e1002197. PubMed ID: 26176594
Summary:
In an unbiased forward genetic screen designed to isolate mutations that cause photoreceptor degeneration, mutations were identified in a nuclear-encoded mitochondrial gene, ppr, a homolog of human LRPPRC. ppr was found to be required for protection against light-induced degeneration. Its function is essential to maintain membrane depolarization of the photoreceptors upon repetitive light exposure, and an impaired phototransduction cascade in ppr mutants results in excessive Rhodopsin1 endocytosis. Moreover, loss of ppr results in a reduction in mitochondrial RNAs, reduced electron transport chain activity, and reduced ATP levels. Oxidative stress, however, is not induced. It is proposed that the reduced ATP level in ppr mutants underlies the phototransduction defect, leading to increased Rhodopsin1 endocytosis during light exposure, causing photoreceptor degeneration independent of oxidative stress. This hypothesis is bolstered by characterization of two other genes isolated in the screen, pyruvate dehydrogenase and citrate synthase. Their loss also causes a light-induced degeneration, excessive Rhodopsin1 endocytosis and reduced ATP without concurrent oxidative stress, unlike many other mutations in mitochondrial genes that are associated with elevated oxidative stress and light-independent photoreceptor demise.

Ruan, W., Srinivasan, A., Lin, S., Kara, K. I. and Barker, P. A. (2016). Eiger-induced cell death relies on Rac1-dependent endocytosis. Cell Death Dis 7: e2181. PubMed ID: 27054336
Summary:
Signaling via tumor necrosis factor receptor (TNFR) superfamily members regulates cellular life and death decisions. A subset of mammalian TNFR proteins, most notably the p75 neurotrophin receptor (p75NTR), induces cell death through a pathway that requires activation of c-Jun N-terminal kinases (JNKs). However the receptor-proximal signaling events that mediate this remain unclear. Drosophila express a single tumor necrosis factor (TNF) ligand termed Eiger (Egr) that activates JNK-dependent cell death. This model was exploited to identify phylogenetically conserved signaling events that allow Egr to induce JNK activation and cell death in vivo. This study reports that Rac1, a small GTPase, is specifically required in Egr-mediated cell death. rac1 loss of function blocks Egr-induced cell death, whereas Rac1 overexpression enhances Egr-induced killing. Vav was identified as a GEF for Rac1 in this pathway, and dLRRK functions were identified as a negative regulator of Rac1 that normally acts to constrain Egr-induced death. Thus dLRRK loss of function increases Egr-induced cell death in the fly. Rac1-dependent entry of Egr into early endosomes was shown to be a crucial prerequisite for JNK activation and for cell death and show that this entry requires the activity of Rab21 and Rab7. These findings reveal novel regulatory mechanisms that allow Rac1 to contribute to Egr-induced JNK activation and cell death.

Huang, Z., Ren, S., Jiang, Y. and Wang, T. (2016). PINK1 and Parkin cooperatively protect neurons against constitutively active TRP channel-induced retinal degeneration in Drosophila. Cell Death Dis 7: e2179. PubMed ID: 27054334
Summary:
Calcium has an important role in regulating numerous cellular activities. However, extremely high levels of intracellular calcium can lead to neurotoxicity, a process commonly associated with degenerative diseases. Despite the clear role of calcium cytotoxicity in mediating neuronal cell death in this context, the pathological mechanisms remain controversial. This study used a well-established Drosophila model of retinal degeneration, which involves the constitutively active TRPP365 channels, to study calcium-induced neurotoxicity. Disruption of mitochondrial function was found to be associated with the degenerative process. Further, increasing autophagy flux prevented cell death in TrpP365PINK1/Parkin pathway. In addition, the retinal degeneration process was also suppressed by the coexpression of PINK1 and Parkin. These results provide genetic evidence that mitochondrial dysfunction has a key role in the pathology of cellular calcium neurotoxicity. In addition, the results demonstrated that maintaining mitochondrial homeostasis via PINK1/Parkin-dependent mitochondrial quality control can potentially alleviate cell death in a wide range of neurodegenerative diseases.

Lee, T. V., Kamber Kaya, H. E., Simin, R., Baehrecke, E. H. and Bergmann, A. (2016). The initiator caspase Dronc is subject of enhanced autophagy upon proteasome impairment in Drosophila. Cell Death Differ [Epub ahead of print]. PubMed ID: 27104928
Summary:
A major function of ubiquitylation is to deliver target proteins to the proteasome for degradation. In the apoptotic pathway in Drosophila, the inhibitor of apoptosis protein 1 (Diap1) regulates the activity of the initiator caspase Dronc (death regulator Nedd2-like caspase; caspase-9 ortholog) by ubiquitylation, supposedly targeting Dronc for degradation by the proteasome. Using a genetic approach, this study showed that Dronc protein fails to accumulate in epithelial cells with impaired proteasome function suggesting that it is not degraded by the proteasome, contrary to the expectation. Similarly, decreased autophagy, an alternative catabolic pathway, does not result in increased Dronc protein levels. However, combined impairment of the proteasome and autophagy triggers accumulation of Dronc protein levels suggesting that autophagy compensates for the loss of the proteasome with respect to Dronc turnover. Consistently, it was shown that loss of the proteasome enhances endogenous autophagy in epithelial cells. It is proposed that enhanced autophagy degrades Dronc if proteasome function is impaired.

Tuesday, May 3rd

Croy, H. E., et al. (2016). The PARP enzyme Tankyrase antagonizes activity of the β-catenin destruction complex through ADP-ribosylation of Axin and APC2. J Biol Chem [Epub ahead of print]. PubMed ID: 27068743
Summary:
Most colon cancer cases are initiated by truncating mutations in APC. APC is a critical negative regulator of the Wnt signaling pathway that participates in a multi-protein destruction complex to target the key effector protein βcatenin for proteolysis. Poly ADP-ribose Polymerase (PARP) enzyme Tankyrase (TNKS) has been shown antagonizes destruction complex activity by promoting degradation of the scaffold protein Axin. A yeast two-hybrid (Y2H) screen uncovered TNKS as a putative binding partner of Drosophila APC2, suggesting that TNKS may play multiple roles in destruction complex regulation. TNKS was found to bind a C-terminal RPQPSG motif in Drosophila APC2, and that this motif is conserved in human APC2, but not human APC1. In addition, APC2 can recruit TNKS into the βcatenin destruction complex, placing the APC2/TNKS interaction at the correct intracellular location to regulate βcatenin proteolysis. TNKS directly PARylates both Drosophila Axin and APC2, but that PARylation does not globally regulate APC2 protein levels as it does for Axin. Moreover, TNKS inhibition in colon cancer cells decreases βcatenin signaling, which cannot be explained solely through Axin stabilization. Instead, these findings suggest that TNKS regulates destruction complex activity at the level of both Axin and APC2, providing further mechanistic insight into TNKS inhibition as a potential Wnt pathway cancer therapy.

Satoh, T., Nakamura, Y. and Satoh, A.K. (2016). Rab6 functions in polarized transport in Drosophila photoreceptors. Fly (Austin) [Epub ahead of print]. PubMed ID: 27116570
Summary:
Selective membrane transport pathways are essential for cells in situ to construct and maintain a polarized structure comprising multiple plasma membrane domains, which is essential for their specific cellular functions. Genetic screening in Drosophila photoreceptors harboring multiple plasma membrane domains enables the identification of genes involved in polarized transport pathways. This study performed genome-wide high-throughput screening and identified a Rab6-null mutant with a rare phenotype characterized by a loss of 2 apical transport pathways with an intact basolateral transport. Although the functions of Rab6 in the Golgi apparatus are well known, its function in polarized transport is unexpected. The mutant phenotype and localization of Rab6 strongly indicate that Rab6 regulates transport between the trans-Golgi network (TGN) and recycling endosomes (REs): basolateral cargos are segregated at the TGN before Rab6 functions, but cargos going to multiple apical domains are sorted at REs. Both the medial-Golgi resident protein MPPE and the TGN marker GalT::CFP exhibit diffused co-localized distributions in Rab6-deficient cells, suggesting they are trapped in the retrograde transport vesicles returning to trans-Golgi cisternae. Hence, the study proposes that Rab6 regulates the fusion of retrograde transport vesicles containing medial, trans-Golgi resident proteins to the Golgi cisternae, which causes Golgi maturation to REs.

Deshpande, G., Manry, D., Jourjine, N., Mogila, V., Mozes, H., Bialistoky, T., Gerlitz, O. and Schedl, P. (2016). Functioning of an ABC transporter, Mdr49, in Hh signaling and germ cell migration. Development [Epub ahead of print]. PubMed ID: 27122170
Summary:
Coalescence of the embryonic gonad in Drosophila melanogaster requires directed migration of the primordial germ cells (PGCs) towards the somatic gonadal precursor cells (SGPs). It has been recently proposed that an ATP-Binding Cassette (ABC) transporter, Mdr49, functions in the embryonic mesoderm to facilitate the transmission of the PGC attractant from the SGPs; however, the precise molecular identity of the mdr49 dependent guidance signal remains elusive. Employing the 'loss' and 'gain' of function strategies, this study shows that mdr49 is a component of the Hedgehog pathway and it potentiates the signaling activity. This function is direct as, in mdr49 mutant embryos, Hh ligand is inappropriately sequestered in the hh expressing cells. Data also suggest that role of Mdr49 is to provide cholesterol for the correct processing of the Hh precursor protein. Supporting this conclusion, PGC migration defects in mdr49 embryos are substantially ameliorated by a cholesterol-rich diet.

Agrawal, N., Delanoue, R., Mauri, A., Basco, D., Pasco, M., Thorens, B. and Leopold, P. (2016). The Drosophila TNF Eiger is an adipokine that acts on insulin-producing cells to mediate nutrient response. Cell Metab 23: 675-684. PubMed ID: 27076079
Summary:
Adaptation of organisms to ever-changing nutritional environments relies on sensor tissues and systemic signals. Identification of these signals would help understand the physiological crosstalk between organs contributing to growth and metabolic homeostasis. This study shows that Eiger, the Drosophila TNF-alpha, is a metabolic hormone that mediates nutrient response by remotely acting on insulin-producing cells (IPCs). In the condition of nutrient shortage, a metalloprotease of the TNF-alpha converting enzyme (TACE) family is active in fat body (adipose-like) cells, allowing the cleavage and release of adipose Eiger in the hemolymph. In the brain IPCs, Eiger activates its receptor Grindelwald, leading to JNK-dependent inhibition of insulin production. Therefore, this study has identified a humoral connexion between the fat body and the brain insulin-producing cells relying on TNF-alpha that mediates adaptive response to nutrient deprivation.

Monday, May 2

Bivik, C., MacDonald, R. B., Gunnar, E., Mazouni, K., Schweisguth, F. and Thor, S. (2016) . Control of neural daughter cell proliferation by multi-level Notch/Su(H)/E(spl)-HLH signaling. PLoS Genet 12: e1005984. PubMed ID: 27070787
Summary:
The Notch pathway controls proliferation during development and in adulthood, and is frequently affected in many disorders. However, the genetic sensitivity and multi-layered transcriptional properties of the Notch pathway has made its molecular decoding challenging. This study addresses the complexity of Notch signaling with respect to proliferation, using the developing Drosophila CNS as model. A Notch/Su(H)/E(spl)-HLH cascade was found to specifically controls daughter, but not progenitor proliferation. Additionally, it was found that different E(spl)-HLH genes are required in different neuroblast lineages. The Notch/Su(H)/E(spl)-HLH cascade alters daughter proliferation by regulating four key cell cycle factors: Cyclin E, String/Cdc25, E2f and Dacapo (mammalian p21CIP1/p27KIP1/p57Kip2). ChIP and DamID analysis of Su(H) and E(spl)-HLH indicates direct transcriptional regulation of the cell cycle genes, and of the Notch pathway itself. These results point to a multi-level signaling model and may help shed light on the dichotomous proliferative role of Notch signaling in many other systems.

Corty, M.M., Tam, J. and Grueber, W.B. (2016). Dendritic diversification through transcription factor-mediated suppression of alternative morphologies. Development 143: 1351-1362. PubMed ID: 27095495
Summary:
Neurons display a striking degree of functional and morphological diversity, and the developmental mechanisms that underlie diversification are of significant interest for understanding neural circuit assembly and function. This study finds that the morphology of Drosophila sensory neurons is diversified through a series of suppressive transcriptional interactions involving the POU domain transcription factors Pdm1 (Nubbin) and Pdm2, the homeodomain transcription factor Cut, and the transcriptional regulators Scalloped and Vestigial. Pdm1 and Pdm2 are expressed in a subset of proprioceptive sensory neurons and function to inhibit dendrite growth and branching. A subset of touch receptors show a capacity to express Pdm1/2, but Cut represses this expression and promotes more complex dendritic arbors. Levels of Cut expression are diversified in distinct sensory neurons by selective expression of Scalloped and Vestigial. Different levels of Cut impact dendritic complexity and, consistent with this, it was found that Scalloped and Vestigial suppress terminal dendritic branching. This transcriptional hierarchy therefore acts to suppress alternative morphologies to diversify three distinct types of somatosensory neurons. 

Peng, Q., Wang, Y., Li, M., Yuan, D., Xu, M., Li, C., Gong, Z., Jiao, R. and Liu, L. (2016). cGMP-dependent protein kinase encoded by foraging regulates motor axon guidance in Drosophila by suppressing Lola function. J Neurosci 36: 4635-4646. PubMed ID: 27098704
Summary:
Correct pathfinding and target recognition of a developing axon are exquisitely regulated processes that require multiple guidance factors. Among these factors, the second messengers, cAMP and cGMP, are known to be involved in establishing the guidance cues for axon growth through different intracellular signaling pathways. However, whether and how cGMP-dependent protein kinase (PKG) regulates axon guidance remains poorly understood. This study shows that the motor axons of intersegmental nerve b (ISNb) in the Drosophila embryo display targeting defects during axon development in the absence of foraging (for), a gene encoding PKG. In vivo tag expression reveals PKG to be present in the ventral nerve code at late embryonic stages, supporting its function in embryonic axon guidance. Mechanistic studies show that the transcription factor longitudinal lacking (lola) genetically interacts with for. PKG physically associates with the LolaT isoform via the C-terminal zinc-finger-containing domain. Overexpression of PKG leads to the cytoplasmic retention of LolaT in S2 cells, suggesting a role for PKG in mediating the nucleocytoplasmic trafficking of Lola. Together, these findings reveal a novel function of PKG in regulating the establishment of neuronal connectivity by sequestering Lola in the cytoplasm.

Urbach, R., Jussen, D. and Technau, G.M. (2016). Gene expression profiles uncover individual identities of gnathal neuroblasts and serial homologies in the embryonic CNS of Drosophila. Development 143: 1290-1301. PubMed ID: 27095493
Summary:
This study constructed comprehensive neuroblast maps for the three gnathal head segments. Based on the spatiotemporal pattern of neuroblast formation and the expression profiles of 46 marker genes (41 transcription factors), each neuroblast can be uniquely identified. Compared with the thoracic ground state, neuroblast numbers are progressively reduced in labial, maxillary and mandibular segments due to smaller sizes of neuroectodermal anlagen and, partially, to suppression of neuroblast formation and induction of programmed cell death by the Hox gene Deformed. Neuroblast patterns are further influenced by segmental modifications in dorsoventral and proneural gene expression. With the previously published neuroblast maps and those presented here for the gnathal region, all neuroectodermal neuroblasts building the CNS of the fly (ventral nerve cord and brain, except optic lobes) are now individually identified (in total 2×567 neuroblasts). This allows, for the first time, a comparison of the characteristics of segmental populations of stem cells and to screen for serially homologous neuroblasts throughout the CNS. It was found that approximately half of the deutocerebral and all of the tritocerebral (posterior brain) and gnathal neuroblasts, but none of the protocerebral (anterior brain) neuroblasts, display serial homology to neuroblasts in thoracic/abdominal neuromeres. Modifications in the molecular signature of serially homologous neuroblasts are likely to determine the segment-specific characteristics of their lineages.

Sunday, May 1st

Rosin, L. and Mellone, B.G. (2016). Co-evolving CENP-A and CAL1 domains mediate centromeric CENP-A deposition across Drosophila species. Dev Cell 37: 136-147. PubMed ID: 27093083
Summary:
Centromeres mediate the conserved process of chromosome segregation, yet centromeric DNA and the centromeric histone, CENP-A, are rapidly evolving. The rapid evolution of Drosophila CENP-A loop 1 (L1) is thought to modulate the DNA-binding preferences of CENP-A to counteract centromere drive, the preferential transmission of chromosomes with expanded centromeric satellites. Consistent with this model, CENP-A from Drosophila bipectinata (bip) cannot localize to Drosophila melanogaster (mel) centromeres. It was shown that this result is due to the inability of the mel CENP-A chaperone, CAL1, to deposit bip CENP-A into chromatin. Co-expression of bip CENP-A and bip CAL1 in mel cells restores centromeric localization, and similar findings apply to other Drosophila species. Two co-evolving regions, CENP-A L1 and the CAL1 N terminus, were identified as critical for lineage-specific CENP-A incorporation. Collectively, these data show that the rapid evolution of L1 modulates CAL1-mediated CENP-A assembly, suggesting an alternative mechanism for the suppression of centromere drive.

Webb, A. E., Kundaje, A. and Brunet, A. (2016). Characterization of the direct targets of FOXO transcription factors throughout evolution. Aging Cell [Epub ahead of print]. PubMed ID: 27061590
Summary:
FOXO transcription factors (FOXOs) are central regulators of lifespan across species, yet they also have cell-specific functions, including adult stem cell homeostasis and immune function. Whether FOXO targets are specific to cell types and species or conserved across cell types and throughout evolution remains uncharacterized. This study consisted of a analysis of direct FOXO targets across tissues and organisms, using data from mammals as well as C. elegans and Drosophila. FOXOs were shown to bind cell type-specific targets, which have functions related to that particular cell. Interestingly, FOXOs also share targets across different tissues in mammals, and the function and even the identity of these shared mammalian targets are conserved in invertebrates. Evolutionarily conserved targets show enrichment for growth factor signaling, metabolism, stress resistance, and proteostasis, suggesting an ancestral, conserved role in the regulation of these processes. Candidate cofactors at conserved FOXO targets were identified that change in expression with age, including CREB and ETS family factors. This analysis provides insight into the evolution of the FOXO network and highlights downstream genes and cofactors that may be important for FOXO's conserved function in adult homeostasis and longevity.

Kim, J. H., Kim, S. K., Lee, J. H., Kim, Y. J., Goddard, W. A. and Kim, Y. C. (2016). Homology modeling and molecular docking studies of Drosophila and Aedes sex peptide receptors. J Mol Graph Model 66: 115-122. PubMed ID: 27060892
Summary:
The Drosophila melanogaster Sex peptide receptor (DrmSPR), a G protein-coupled receptor (GPCR), is known as the specific receptor for sex peptide (SP). It is responsible for the reproductive behavior in the Drosophila model system; in particular, it is involved in the post-mating responses such as the increase in egg-laying ability and decrease in receptivity in females. A previous studydiscovered a small molecule agonist of DrmSPR which could not, however, activate Aedes aegypti SPR (AedesSPR). To investigate the binding mechanism of the small molecule agonist of DrmSPR, the ensemble structures of low-lying packing structures of DrmSPR and AedesSPR were assembled using the GEnSeMBLE (GPCR Ensemble of Structures in Membrane BiLayer Environment) method. The generated homology models exhibited the typical pattern of inter-helical interactions of the class A GPCRs. The docking experiments of the small molecule agonist suggest that Tyr5.35 and Phe2.67 residues may be involved in a hydrophobic interaction and that Ser3.25 forms a hydrogen bond with the agonist. Additionally, the docking results were found to be consistent with the experimental data of the reference compounds with variable agonistic activities. Moreover, a potential distinction of the putative binding sites in two GPCR models of DrmSPR and AedesSPR, which was determined in this study, can explain the selective action of the agonist for DrmSPR but not for AedesSPR.

Kriesner, P., Conner, W. R., Weeks, A. R., Turelli, M. and Hoffmann, A. A. (2016). Persistence of a Wolbachia infection frequency cline in Drosophila melanogaster and the possible role of reproductive dormancy. Evolution [Epub ahead of print]. PubMed ID: 27076356
Summary:
Field populations of arthropods are often polymorphic for Wolbachia but the factors maintaining intermediate Wolbachia frequencies are generally not understood. In Drosophila melanogaster, Wolbachia frequencies are highly variable across the globe. This study documented the persistence of a Wolbachia infection frequency cline in D. melanogaster populations from eastern Australia across at least 20 years, with frequencies generally high in the tropics but lower in cool temperate regions. The results are interpreted using a model of frequency dynamics incorporating cytoplasmic incompatibility, imperfect maternal transmission and Wolbachia effects on fitness. Clinal variation is less pronounced in eastern North America which may reflect annual recolonization at higher latitudes. Limited samples from Africa from latitudes matching the tropical and subtropical samples from Australia and North America show comparably high infection frequencies, but some equatorial samples show lower frequencies. Adult dormancy across cold periods may contribute to the Australian Wolbachia cline. Infected flies exposed to cold conditions for an extended period had reduced fecundity and viability, an effect not evident in unexposed controls. These fitness costs may contribute to the relatively low Wolbachia frequencies in Australian temperate areas; whereas different processes, including cytoplasmic incompatibility induced by young males, may contribute to higher frequencies in tropical locations.

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