What's hot today: Current papers in developmental biology and gene function Follow @interactivefly Tweet

Thursday, October 15th

Mishra, A.K., Sachan, N., Mutsuddi, M. and Mukherjee, A. (2015). Kinase active Misshapen regulates Notch signaling in Drosophila melanogaster. Exp Cell Res [Epub ahead of print]. PubMed ID: 26431585 Summary: Notch signaling pathway represents a principal cellular communication system that plays a pivotal role during development of metazoans. Drosophila misshapen (msn) encodes a protein kinase, which is related to the budding yeast Ste20p (sterile 20 protein) kinase. In a genetic screen, using candidate gene approach to identify novel kinases involved in Notch signaling, this study identified msn as a novel regulator of Notch signaling. Overexpression of kinase active form of Msn exhibits phenotypes similar to Notch loss-of-function condition and msn genetically interacts with components of Notch signaling pathway. Kinase active form of Msn associates with Notch receptor and regulates its signaling activity. It was further shown that kinase active Misshapen leads to accumulation of membrane-tethered form of Notch. Moreover, activated Msn also depletes Armadillo and DE-Cadherin from adherens junctions. Thus, this study provides a yet unknown mode of regulation of Notch signaling by Misshapen.

Ni, L., Zheng, Y., Hara, M., Pan, D. and Luo, X. (2015). Structural basis for Mob1-dependent activation of the core Mst-Lats kinase cascade in Hippo signaling. Genes Dev 29: 1416-1431. PubMed ID: 26108669 Summary: The Mst-Lats kinase cascade is central to the Hippo tumor-suppressive pathway that controls organ size and tissue homeostasis. The adaptor protein Mob1 promotes Lats activation by Mst, but the mechanism remains unknown. This study shows that human Mob1 binds to autophosphorylated docking motifs in active Mst2. This binding enables Mob1 phosphorylation by Mst2. Phosphorylated Mob1 undergoes conformational activation and binds to Lats1. We determine the crystal structures of phospho-Mst2-Mob1 and phospho-Mob1-Lats1 complexes, revealing the structural basis of both phosphorylation-dependent binding events. Further biochemical and functional analyses demonstrate that Mob1 mediates Lats1 activation through dynamic scaffolding and allosteric mechanisms. Thus, Mob1 acts as a phosphorylation-regulated coupler of kinase activation by virtue of its ability to engage multiple ligands. It is proposed that stepwise, phosphorylation-triggered docking interactions of nonkinase elements enhance the specificity and robustness of kinase signaling cascades.

Li, C., Kan, L., Chen, Y., Zheng, X., Li, W., Zhang, W., Cao, L., Lin, X., Ji, S., Huang, S., Zhang, G., Liu, X., Tao, Y., Wu, S. and Chen, D. (2015). Ci antagonizes Hippo signaling in the somatic cells of the ovary to drive germline stem cell differentiation. Cell Res [Epub ahead of print]. PubMed ID: 26403189 Summary: Many stem cell populations are tightly regulated by their local microenvironment (niche), which comprises distinct types of stromal cells. However, little is known about mechanisms by which niche subgroups coordinately determine the stem cell fate. This study identified that Yki, the key Hippo pathway component, is essential for escort cell (EC) function in promoting germline differentiation in Drosophila ovary. Hedgehog (Hh) signals emanating primarily from cap cells support the function of ECs, where Cubitus interruptus (Ci), the Hh signaling effector, acts to inhibit Hippo kinase cascade activity. Mechanistically, Ci competitively interacts with Hpo and impairs the Hpo-Wts signaling complex formation, thereby promoting Yki nuclear localization. The actions of Ci ensure effective Yki signaling to antagonize Sd/Tgi/Vg-mediated default repression in ECs. This study uncovers a mechanism explaining how subgroups of niche cells coordinate to determine the stem cell fate via Hh-Hippo signaling crosstalk, and enhances understanding of mechanistic regulations of the oncogenic Yki/YAP signaling.

Balmer, S., Dussert, A., Collu, G. M., Benitez, E., Iomini, C. and Mlodzik, M. (2015). Components of intraflagellar transport Complex A function independently of the cilium to regulate canonical Wnt signaling in Drosophila. Dev Cell 34: 705-718. PubMed ID: 26364750 Summary: The development of multicellular organisms requires the precisely coordinated regulation of an evolutionarily conserved group of signaling pathways. Temporal and spatial control of these signaling cascades is achieved through networks of regulatory proteins, segregation of pathway components in specific subcellular compartments, or both. In vertebrates, dysregulation of primary cilia function has been strongly linked to developmental signaling defects, yet it remains unclear whether cilia sequester pathway components to regulate their activation or cilia-associated proteins directly modulate developmental signaling events. To elucidate this question, an RNAi-based screen was conducted in Drosophila non-ciliated cells to test for cilium-independent loss-of-function phenotypes of ciliary proteins in developmental signaling pathways. The results show no effect on Hedgehog signaling. In contrast, the screen identified several cilia-associated proteins as functioning in canonical Wnt signaling. Further characterization of specific components of Intraflagellar Transport complex A uncovered a cilia-independent function in potentiating Wnt signals by promoting β-catenin/Armadillo activity.

Wednesday, October 14th

Karaiskos, S., Naqvi, A. S., Swanson, K. E. and Grigoriev, A. (2015). Age-driven modulation of tRNA-derived fragments in Drosophila and their potential targets. Biol Direct 10: 51. PubMed ID: 26374501 Summary: Development of sequencing technologies and supporting computation enable discovery of small RNA molecules that previously escaped detection or were ignored due to low count numbers. This study describes Drosophila melanogaster tRFs, which appear to have a number of structural and functional features similar to those of miRNAs but are less abundant. As is the case with miRNAs, (1) tRFs seem to have distinct isoforms preferentially originating from 5' or 3' end of a precursor molecule (in this case, tRNA), (2) ends of tRFs appear to contain short "seed" sequences matching conserved regions across 12 Drosophila genomes, preferentially in 3' UTRs but also in introns and exons; (3) tRFs display specific isoform loading into Ago1 Ago2 and thus likely function in RISC complexes; (4) levels of loading in Ago1 and Ago2 differ considerably; and (5) both tRF expression and loading appear to be age-dependent, indicating potential regulatory changes from young to adult organisms. Drosophila tRF reads mapped to both nuclear and mitochondrial tRNA genes for all 20 amino acids, while previous studies have usually reported fragments from only a few tRNAs. These tRFs show a number of similarities with miRNAs, including seed sequences. Based on complementarity with conserved Drosophila regions such seed sequences and their possible targets were identified with matches in the 3'UTR regions. Strikingly, the potential target genes of the most abundant tRFs show significant Gene Ontology enrichment in development and neuronal function. The latter suggests that involvement of tRFs in the RNA interfering pathway may play a role in brain activity or brain changes with age.

Coyne, A. N., Yamada, S. B., Siddegowda, B. B., Estes, P. S., Zaepfel, B. L., Johannesmeyer, J. S., Lockwood, D. B., Pham, L. T., Hart, M. P., Cassel, J. A., Freibaum, B., Boehringer, A. V., Taylor, J. P., Reitz, A. B., Gitler, A. D. and Zarnescu, D. C. (2015). Fragile X protein mitigates TDP-43 toxicity by remodeling RNA granules and restoring translation. Hum Mol Genet. PubMed ID: 26385636 Summary: RNA dysregulation is a newly recognized disease mechanism in amyotrophic lateral sclerosis (ALS). This study identified Drosophila fragile X mental retardation protein (dFMRP) as a robust genetic modifier of TDP-43-dependent toxicity in a Drosophila model of ALS. dFMRP overexpression (dFMRP OE) mitigates TDP-43 dependent locomotor defects and reduced lifespan in Drosophila. TDP-43 and FMRP form a complex in flies and human cells. In motor neurons, TDP-43 expression increases the association of dFMRP with stress granules and colocalizes with polyA binding protein in a variant-dependent manner. Furthermore, dFMRP dosage modulates TDP-43 solubility and molecular mobility with overexpression of dFMRP resulting in a significant reduction of TDP-43 in the aggregate fraction. Polysome fractionation experiments indicate that dFMRP OE also relieves the translation inhibition of futsch mRNA, a TDP-43 target mRNA, which regulates neuromuscular synapse architecture. Restoration of futsch translation by dFMRP OE mitigates Futsch-dependent morphological phenotypes at the neuromuscular junction including synaptic size and presence of satellite boutons. These data suggest a model whereby dFMRP is neuroprotective by remodeling TDP-43 containing RNA granules, reducing aggregation and restoring the translation of specific mRNAs in motor neurons.

Ramaswami, G., Deng, P., Zhang, R., Anna Carbone, M., Mackay, T. F. and Billy Li, J. (2015). Genetic mapping uncovers cis-regulatory landscape of RNA editing. Nat Commun 6: 8194. PubMed ID: 26373807 Summary: Adenosine-to-inosine (A-to-I) RNA editing, catalysed by ADAR enzymes, plays an important role in neurological functions. This study applied a quantitative trait loci (QTL) mapping approach to identify genetic variants associated with variability in RNA editing. With very accurate measurement of RNA editing levels at 789 sites in 131 Drosophila melanogaster strains, this study identified 545 editing QTLs (edQTLs) associated with differences in RNA editing. Many edQTLs can act through changes in the local secondary structure for edited dsRNAs. Furthermore, edQTLs located outside of the edited dsRNA duplex were found to be enriched in secondary structure, suggesting that distal dsRNA structure beyond the editing site duplex affects RNA editing efficiency. Thus work will facilitate the understanding of the cis-regulatory code of RNA editing.

Weng, R. and Cohen, S. M. (2015). Control of Drosophila type I and type II central brain neuroblast proliferation by bantam microRNA. Development [Epub ahead of print]. PubMed ID: 26395494 Summary: Post-transcriptional regulation of stem cell self-renewal by microRNAs is emerging as an important mechanism controlling tissue homeostasis. This report providse evidence that the bantam microRNA controls neuroblast number and proliferation in the Drosophila central brain. bantam also supports proliferation of the transit-amplifying intermediate neural progenitor cells in type II neuroblast lineages. The stem cell factors brat, prospero are identified as bantam targets acting on different aspects of these processes. Thus bantam appears to act in multiple regulatory steps in the maintenance and proliferation of neuroblasts and their progeny to regulate growth of the central brain.

Tuesday, October 13th

Lavrynenko, O., Rodenfels, J., Carvalho, M., Dye, N. A., Lafont, R., Eaton, S. and Shevchenko, A. (2015). The Ecdysteroidome of Drosophila: influence of diet and development. Development [Epub ahead of print]. PubMed ID: 26395481 Summary: Ecdysteroids are the hormones regulating development, physiology and fertility in arthropods, which synthesize them exclusively from dietary sterols. But how dietary sterol diversity influences the ecdysteroid profile, how animals ensure the production of desired hormones and whether there are functional differences between different ecdysteroids produced in vivo, remains unknown. This is because currently there is no analytical technology for unbiased, comprehensive and quantitative assessment of the full complement of endogenous ecdysteroids. This study developed a new LC-MS/MS method to screen the entire chemical space of ecdysteroid-related structures and to quantify known and newly discovered hormones and their catabolites. The ecdysteroidome was quantitated in Drosophila melanogaster. and how the ecdysteroid profile varies with diet and development was investigated. Drosophila can produce 4 different classes of ecdysteroids, which are obligatorily derived from 4 types of dietary sterol precursors. Drosophila produces makisterone A from plant sterols and epi-makisterone A from ergosterol, the major yeast sterol. However they prefer to selectively utilize scarce ergosterol precursors to make a novel hormone 24,28-dehydromakisterone A and trace cholesterol to synthesize 20-hydroxyecdysone. Interestingly, epi-makisterone A supports only larval development, while all other ecdysteroids allow full adult development. It is suggests that evolutionary pressure against producing epi-C24 ecdysteroids may explain selective utilization of ergosterol precursors and the puzzling preference for cholesterol.

Alex, A., et al. (2015). A circadian clock gene, cry, affects heart morphogenesis and function in Drosophila as revealed by optical coherence microscopy. PLoS One 10: e0137236. PubMed ID: 26348211 Summary: Circadian rhythms are endogenous, entrainable oscillations of physical, mental and behavioural processes in response to local environmental cues. The role that circadian clock genes play in heart development and function are poorly understood. The Drosophila cryptochrome (dCry) is a circadian clock gene that encodes a major component of the circadian clock negative feedback loop. Compared to the embryonic stage, the relative expression levels of dCry showed a significant increase (>100-fold) in Drosophila during the pupa and adult stages. This study performed analysis of functional and morphological changes in the Drosophila heart throughout its post-embryonic lifecycle. The Drosophila heart exhibited major morphological and functional alterations during its development. Notably, heart rate (HR) and cardiac activity period (CAP) of Drosophila showed significant variations during the pupa stage, when heart remodeling took place. From the M-mode (2D + time) OCM images, cardiac structural and functional parameters of Drosophila at different developmental stages were quantitatively determined. In order to study the functional role of dCry on Drosophila heart development, dCry was silenced by RNAi in the Drosophila heart and mesoderm, and quantitatively measured heart morphology and function in those flies throughout its development. Silencing of dCry resulted in slower HR, reduced CAP, smaller heart chamber size, pupal lethality and disrupted posterior segmentation that was related to increased expression of a posterior compartment protein, Wingless. Collectively, these studies provided novel evidence that the circadian clock gene, dCry, plays an essential role in heart morphogenesis and function.

Singh, S., Sanchez-Herrero, E. and Shashidhara, L. S. (2015). Critical role for Fat/Hippo and IIS/Akt pathways downstream of Ultrabithorax during haltere specification in Drosophila. Mech Dev [Epub ahead of print]. PubMed ID: 26299254 Summary: In Drosophila, differential development of wing and haltere, which differ in cell size, number and morphology, is dependent on the function of Hox gene Ultrabithorax (Ubx). This study reports studies on Ubx-mediated regulation of the Fat/Hippo and IIS/dAkt pathways, which control cell number and cell size during development. Over-expression of Yki or down regulation of negative components of the Fat/Hippo pathway, such as expanded, caused considerable increase in haltere size, mainly due to increase in cell number. These phenotypes were also associated with the activation of Akt pathways in developing haltere. Although activation of Akt alone did not affect the cell size or the organ size, dramatic increase was seen in haltere size when Akt was activated in the background where expanded is down regulated. This was associated with the increase in both cell size and cell number. The organ appeared flatter than wildtype haltere and the trichome morphology and spacing resembled that of wing suggesting homeotic transformations. Thus, these results suggest a link between cellular growth and pattern formation and the final differentiated state of the organ.

Wicker-Thomas, C., et al. (2015). Flexible origin of hydrocarbon/pheromone precursors in Drosophila melanogaster.J Lipid Res [Epub ahead of print]. PubMed ID: 26353752 Summary: In terrestrial insects, cuticular hydrocarbons (CHCs) provide protection from desiccation. Specific CHCs can also act as pheromones, which are important for successful mating. Oenocytes are abdominal cells thought to act as specialized units for CHC biogenesis that consists of long-chain fatty-acid (LCFA) synthesis, optional desaturation(s), elongation to very-long-chain fatty acids (VLCFAs) and removal of the carboxyl group. By investigating CHC biogenesis in Drosophila melanogaster, this study showed that VLCFA synthesis takes place only within the oenocytes. Conversely, several pathways, which may compensate for one another, can feed the oenocyte pool of LCFAs, suggesting that this step is a critical node for regulating CHC synthesis. Importantly, flies deficient in LCFA-synthesis sacrificed their triacylglycerol stores while maintaining some CHC production. Moreover, pheromone production was lower in adult flies that emerged from larvae that were fed excess dietary lipids and their mating success was lower. Further, pheromone production in the oenocytes was shown to depends on lipid metabolism in the fat tissue and that FATP, a bipartite acyl-CoA-synthase(ACS)/fatty-acid-transporter, likely acts through its ACS domain in the oenocyte pathway of CHC biogenesis. This study highlights the importance of environmental and physiological inputs in regulating LCFA synthesis to eventually control sexual communication in a polyphagous animal.

Monday, October 12th

Kruger, E., Mena, W., Lahr, E. C., Johnson, E. C. and Ewer, J. (2015). Genetic analysis of Eclosion hormone action during Drosophila larval ecdysis. Development [Epub ahead of print]. PubMed ID: 26395475 Summary: Insect growth is punctuated by molts, during which the animal produces a new exoskeleton. The molt culminates with ecdysis, an ordered sequence of behaviors that causes the old cuticle to be shed. This sequence is activated by Ecdysis Triggering Hormone (ETH), which acts on the CNS to activate neurons that produce neuropeptides implicated in ecdysis, including Eclosion hormone (EH), Crustacean Cardioactive Peptide (CCAP), and bursicon. Despite over 40 years of research on ecdysis, understanding of the precise roles of these neurohormones remains rudimentary. Of particular interest is EH, whose role beyond the well-accepted action of massively upregulating ETH release has remained elusive. This study reports on the isolation of an eh null mutant in Drosophila, and it's use to investigate the role of EH in larval ecdysis. Null mutant animals invariably died at around the time of ecdysis, revealing an essential role in its control. Unexpectedly, however, they failed to express the preparatory behavior of pre-ecdysis while directly expressing the motor program of ecdysis. In addition, although ETH release could not be detected in these animals, the lack of pre-ecdysis could not be rescued by injections of ETH, suggesting that EH is required within the CNS for ETH to trigger the normal ecdysial sequence. Using a genetically-encoded calcium probe it was shown that EH configures the response of the CNS to ETH. These findings show that EH plays an essential role in the Drosophila CNS in the control of ecdysis, in addition to its known role in the periphery of triggering ETH release.

Cavanaugh, D. J., Vigderman, A. S., Dean, T., Garbe, D. S. and Sehgal, A. (2015). The circadian clock gates sleep through time-of-day dependent modulation of sleep-promoting neurons. Sleep [Epub ahead of print]. PubMed ID: 26350473 Summary: Sleep is under the control of homeostatic and circadian processes, which interact to determine sleep timing and duration, but the mechanisms through which the circadian system modulates sleep are largely unknown. This study used adult-specific, temporally controlled neuronal activation and inhibition to identify an interaction between the circadian clock and a novel population of sleep-promoting neurons in Drosophila. In this study, transgenic flies expressed either dTRPA1, a neuronal activator, or Shibirets1, an inhibitor of synaptic release, in small subsets of neurons. Sleep, as determined by activity monitoring and video tracking, was assessed before and after temperature-induced activation or inhibition using these effector molecules. This study compared the effect of these manipulations in control flies and in mutant flies that lacked components of the molecular circadian clock. Adult-specific activation or inhibition of a population of neurons that projects to the sleep-promoting dorsal Fan-Shaped Body resulted in bidirectional control over sleep. Interestingly, the magnitude of the sleep changes were time-of-day dependent. Activation of sleep-promoting neurons was maximally effective during the middle of the day and night, and was relatively ineffective during the day-to-night and night-to-day transitions. These time-of-day specific effects were absent in flies that lacked functional circadian clocks. In conclusion, the circadian system functions to gate sleep through active inhibition at specific times of day. These data identify a mechanism through which the circadian system prevents premature sleep onset in the late evening, when homeostatic sleep drive is high.

Ahmad, M., Chaudhary, S.U., Afzal, A.J. and Tariq, M. (2015). Starvation-induced dietary behaviour in Drosophila melanogaster larvae and adults. Sci Rep 5: 14285. PubMed ID: 26399327 Summary: Drosophila melanogaster larvae are classified as herbivores and known to feed on non-carnivorous diet under normal conditions. However, when nutritionally challenged these larvae exhibit cannibalistic behaviour by consuming a diet composed of larger conspecifics. This study reports that cannibalism in Drosophila larvae is confined not only to scavenging on conspecifics that are larger in size, but also on their eggs. Moreover, such cannibalistic larvae develop as normally as those grown on standard cornmeal medium. When stressed, Drosophila melanogaster larvae can also consume a carnivorous diet derived from carcasses of organisms belonging to diverse taxonomic groups, including Musca domestica, Apis mellifera, and Lycosidae sp. While adults are ill-equipped to devour conspecific carcasses, they selectively oviposit on them and also consume damaged cadavers of conspecifics. Thus, these results suggest that nutritionally stressed Drosophila show distinct as well as unusual feeding behaviours that can be classified as detritivorous, cannibalistic and/or carnivorous.

Stern, U., He, R. and Yang, C. H. (2015). Analyzing animal behavior via classifying each video frame using convolutional neural networks. Sci Rep 5: 14351. PubMed ID: 26394695 Summary: High-throughput analysis of animal behavior requires software to analyze videos. Such software analyzes each frame individually, detecting animals' body parts. But the image analysis rarely attempts to recognize "behavioral states"-e.g., actions or facial expressions-directly from the image instead of using the detected body parts. This study shows that convolutional neural networks (CNNs)-a machine learning approach that recently became the leading technique for object recognition, human pose estimation, and human action recognition-were able to recognize directly from images whether Drosophila were "on" (standing or walking) or "off" (not in physical contact with) egg-laying substrates for each frame of the videos. Nultiple nets and image transformations were to optimize accuracy for the classification task, achieving a surprisingly low error rate of just 0.072%. Classifying one of the 8 h videos took less than 3 h using a fast GPU. The approach enabled uncovering a novel egg-laying-induced behavior modification in Drosophila. Furthermore, it should be readily applicable to other behavior analysis tasks.

Sunday, October 11th

Carvalho, A.B., Vicoso, B., Russo, C.A., Swenor, B. and Clark, A.G. (2015). Birth of a new gene on the Y chromosome of Drosophila melanogaster. Proc Natl Acad Sci U S A 112(40):12450-5. PubMed ID: 26385968 Summary: Contrary to the pattern seen in mammalian sex chromosomes, where most Y-linked genes have X-linked homologs, the Drosophila X and Y chromosomes appear to be unrelated. Most of the Y-linked genes have autosomal paralogs, so autosome-to-Y transposition must be the main source of Drosophila Y-linked genes. This study shows how these genes were acquired. It was found that a previously unidentified gene (flagrante delicto Y, FDY) originated from a recent duplication of the autosomal gene vig2 to the Y chromosome of Drosophila melanogaster. Four contiguous genes were duplicated along with vig2, but they became pseudogenes through the accumulation of deletions and transposable element insertions, whereas FDY remained functional, acquired testis-specific expression, and now accounts for ∼20% of the vig2-like mRNA in testis. FDY is absent in the closest relatives of D. melanogaster, and DNA sequence divergence indicates that the duplication to the Y chromosome occurred ∼2 million years ago. Thus, FDY provides a snapshot of the early stages of the establishment of a Y-linked gene and demonstrates how the Drosophila Y has been accumulating autosomal genes.

Kao, J. Y., Lymer, S., Hwang, S. H., Sung, A. and Nuzhdin, S. V. (2015). Postmating reproductive barriers contribute to the incipient sexual isolation of the United States and Caribbean Drosophila melanogaster. Ecol Evol 5: 3171-3182. PubMed ID: 26357543 Summary: The nascent stages of speciation start with the emergence of sexual isolation. Understanding the influence of reproductive barriers in this evolutionary process is an ongoing effort. This paper presents a study of Drosophila melanogaster admixed populations from the southeast United States and the Caribbean islands known to be a secondary contact zone of European- and African-derived populations undergoing incipient sexual isolation. The existence of premating reproductive barriers has been previously established, but these types of barriers are not the only source shaping sexual isolation. To assess the influence of postmating barriers, this study investigated putative postmating barriers of female remating and egg-laying behavior, as well as hatchability of eggs laid and female longevity after mating. In the central region of the putative hybrid zone of American and Caribbean populations, lower hatchability of eggs laid was observed accompanied by increased resistance to harm after mating to less-related males. These results illustrate that postmating reproductive barriers act alongside premating barriers and genetic admixture such as hybrid incompatibilities and influence early phases of sexual isolation.

Hollis, B., Houle, D. and Kawecki, T. J. (2015). Evolution of reduced postcopulatory molecular interactions in Drosophila populations lacking sperm competition. J Evol Biol [Epub ahead of print]. PubMed ID: 26395588 Summary: In many species with internal fertilization, molecules transferred in the male ejaculate trigger and interact with physiological changes in females. It is controversial to what extent these interactions between the sexes act synergistically to mediate the female switch to a reproductive state or instead reflect sexual antagonism evolved as a byproduct of sexual selection on males. To address this question, this study eliminated sexual selection by enforcing monogamy in populations of Drosophila melanogaster for 65 generations and then measured the expression of male seminal fluid protein genes and genes involved in the female response to mating. In the absence of sperm competition, male and female reproductive interests are perfectly aligned and any antagonism should be reduced by natural selection. Consistent with this idea, males from monogamous populations showed reduced expression of seminal fluid protein genes, 16% less on average than in polygamous males. After mating, females with an evolutionary history of monogamy exhibited lower relative expression of genes that were upregulated in response to mating and higher expression of genes that were downregulated. Surprisingly, these genes showed a similar pattern even before mating, suggesting that monogamous females evolved to be less poised for mating and the accompanying receipt of male seminal fluid proteins. This reduced investment by both monogamous males and females in molecules involved in postcopulatory interactions points to a pervasive role of sexual conflict in shaping these interactions.

Huang, Y., Stinchcombe, J. R. and Agrawal, A. F. (2015). Quantitative genetic variance in experimental fly populations evolving with or without environmental heterogeneity. Evolution 69(10):2735-46. PubMed ID: 26362112 Summary: Heterogeneous environments are typically expected to maintain more genetic variation in fitness within populations than homogeneous environments. However, the accuracy of this claim depends on the form of heterogeneity as well as the genetic basis of fitness traits and how similar the assay environment is to the environment of past selection. This study measured quantitative genetic (QG) variance for three traits important for fitness using replicated experimental populations of Drosophila melanogaster evolving under four selective regimes: constant salt-enriched medium (Salt), constant cadmium-enriched medium (Cad), and two heterogeneous regimes that vary either temporally (Temp) or spatially (Spatial). As theory predicts, Spatial populations tended to harbor more genetic variation than Temp populations or those maintained in a constant environment that is the same as the assay environment. Contrary to expectation, Salt populations tend to have more genetic variation than Cad populations in both assay environments. The patterns for QG variances across regimes in relation to previously reported data on genome-wide sequence diversity. For some traits, the QG patterns are similar to the diversity patterns of ecological selected SNPs, whereas the QG patterns for some other traits resembled that of neutral SNPs.

Saturday, October 10th

Carnes, M. U., et al. 2015. The genomic basis of postponed senescence in Drosophila melanogaster. PLoS One 10: e0138569. PubMed ID: 26378456 Summary: Natural populations harbor considerable genetic variation for lifespan. While evolutionary theory provides general explanations for the existence of this variation, knowledge of the genes harboring naturally occurring polymorphisms affecting lifespan is limited. This study assessed the genetic divergence between five Drosophila melanogaster lines selected for postponed senescence for over 170 generations (O lines) and five lines from the same base population maintained at a two week generation interval for over 850 generations (B lines). On average, O lines live 70% longer than B lines, are more productive at all ages, and have delayed senescence for other traits than reproduction. Population sequencing of pools of individuals was performed from all B and O lines, and 6,394 genetically divergent variants were identified in or near 1,928 genes at a false discovery rate of 0.068. A 2.6 Mb region at the tip of the X chromosome contained many variants fixed for alternative alleles in the two populations, suggestive of a hard selective sweep. Genome wide gene expression of O and B lines at one and five weeks of age was also analyzed using RNA sequencing, and genes were identified with significant effects on gene expression with age, population and the age by population interaction, separately for each sex. Transcripts were identified that exhibited the transcriptional signature of postponed senescence, and the gene expression and genetic divergence data were integrated to identify 98 (175) top candidate genes in females (males) affecting postponed senescence and increased lifespan. While several of these genes have been previously associated with Drosophila lifespan, most are novel and constitute a rich resource for future functional validation.

Dubos, A., et al. (2015). Conditional depletion of intellectual disability and Parkinsonism candidate gene ATP6AP2 in fly and mouse induces cognitive impairment and neurodegeneration. Hum Mol Genet [Epub ahead of print]. PubMed ID: 26376863 Summary: ATP6AP2, an essential accessory component of the vacuolar H+ ATPase (V-ATPase), has been associated with intellectual disability (ID) and Parkinsonism. ATP6AP2 has been implicated in several signalling pathways; however, little is known regarding its role in the nervous system. To decipher its function in behaviour and cognition, conditional knockdowns of ATP6AP2 were generated and characterized in the nervous system of Drosophila and mouse models. In Drosophila, ATP6AP2 knockdown induced defective phototaxis and vacuolated photoreceptor neurons and pigment cells when depleted in eyes and altered short- and long-term memory when depleted in the mushroom body. In mouse, conditional Atp6ap2 deletion in glutamatergic neurons caused increased spontaneous locomotor activity and altered fear memory. Both Drosophila ATP6AP2 knockdown and deletion mice presented with presynaptic transmission defects, and with an abnormal number and morphology of synapses. In addition, deletion mice showed autophagy defects that led to axonal and neuronal degeneration in the cortex and hippocampus. Surprisingly, axon myelination was affected in the mutant mice, and axonal transport alterations were observed in Drosophila. In accordance with the identified phenotypes across species, genome-wide transcriptome profiling of deletion mouse hippocampi revealed dysregulation of genes involved in myelination, action potential, membrane-bound vesicles and motor behaviour. In summary, ATP6AP2 disruption in mouse and fly leads to cognitive impairment and neurodegeneration, mimicking aspects of the neuropathology associated with ATP6AP2 mutations in humans. These results identify ATP6AP2 as an essential gene for the nervous system.

Khanna, M. R. and Fortini, M. E. (2015). Transcriptomic analysis of Drosophila mushroom body neurons lacking Amyloid-beta precursor-like protein activity. J Alzheimers Dis 46: 913-928. PubMed ID: 26402626 Summary: The amyloid-&beta: protein precursor (AbetaPP; see Drosophila Appl) is subjected to sequential intramembrane proteolysis by α-, &beta:-, and γ-secretases, producing secreted amyloid-&beta: (A&beta:) peptides and a cytoplasmically released A&beta:PP Intracellular Domain (AICD). AICD complexes with transcription factors in the nucleus, suggesting that this AβPP fragment serves as an active signaling effector that regulates downstream genes, although its nuclear targets are poorly defined. To further understand this potential signaling mechanism mediated by AβPP, a transcriptomic identification of the Drosophila genome that is regulated by the fly AβPP orthologue was performed in fly mushroom body neurons, which control learning- and memory-based behaviors. Significant changes were found in expression of 245 genes, representing approximately 1.6% of the Drosophila genome, with the changes ranging from +6 fold to -40 fold. The largest class of responsive targets corresponds to non-protein coding genes and includes microRNAs that have been previously implicated in Alzheimer's disease pathophysiology. Several genes were identified in the Drosophila microarray analyses that have also emerged as putative AβPP targets in similar mammalian transcriptomic studies. These results also indicate a role for AβPP in cellular pathways involving the regulation of Drosophila Casein Kinase II, mitochondrial oxidative phosphorylation, RNA processing, and innate immunity. These findings provide insights into the intracellular events that are regulated by AβPP activity in healthy neurons and that might become dysregulated as a result of abnormal AβPP proteolysis in AD.

Cutler, T., Sarkar, A., Moran, M., Steffensmeier, A., Puli, O. R., Mancini, G., Tare, M., Gogia, N. and Singh, A. (2015). Drosophila eye model to study neuroprotective role of CREB binding protein (CBP) in Alzheimer's disease. PLoS One 10: e0137691. PubMed ID: 26367392 Summary: This study utilized Gal4/UAS system to develop a transgenic fruit fly model for Aβ42 (see Drosophila Appl) mediated neurodegeneration. Targeted misexpression of human Aβ42 in the differentiating photoreceptor neurons of the developing eye of transgenic fly triggers neurodegeneration. This progressive neurodegenerative phenotype resembles Alzheimer's like neuropathology. A histone acetylase, CREB Binding Protein (CBP), was identified as a genetic modifier of Aβ42 mediated neurodegeneration. Targeted misexpression of CBP along with Aβ42 in the differentiating retina can significantly rescue neurodegeneration. Gain-of-function of CBP rescues Aβ42 mediated neurodegeneration by blocking cell death. Misexpression of Aβ42 affects the targeting of axons from retina to the brain but misexpression of full length CBP along with Aβ42 can restore this defect. The CBP protein has multiple domains and is known to interact with many different proteins. This structure function analysis using truncated constructs lacking one or more domains of CBP protein, in transgenic flies revealed that Bromo, HAT and polyglutamine (BHQ) domains together are required for the neuroprotective function of CBP. This BHQ domain of CBP has not been attributed to promote survival in any other neurodegenerative disorders. This study has identified CBP as a genetic modifier of Aβ42 mediated neurodegeneration. Furthermore, this study had identified BHQ domain of CBP is being responsible for its neuroprotective function. These studies may have significant bearing on understanding of genetic basis of AD.

Friday, October 9th

Kulshammer, E., Mundorf, J., Kilinc, M., Frommolt, P., Wagle, P. and Uhlirova, M. (2015). Interplay among Drosophila transcription factors Ets21c, Fos and Ftz-F1 drives JNK-mediated tumor malignancy. Dis Model Mech 8: 1279-1293. PubMed ID: 26398940 Summary: This study defines TF network that triggers an abnormal gene expression program promoting malignancy of clonal tumors, generated in Drosophila imaginal disc epithelium by gain of oncogenic Ras (RasV12) and loss of the tumor suppressor Scribble (scrib1). Malignant transformation of the rasV12scrib1 tumors requires TFs of distinct families, namely the bZIP protein Fos, the ETS-domain factor Ets21c and the nuclear receptor Ftz-F1, all acting downstream of Jun-N-terminal kinase (JNK). Depleting any of the three TFs improves viability of tumor-bearing larvae, and this positive effect can be enhanced further by their combined removal. Although both Fos and Ftz-F1 synergistically contribute to rasV12scrib1 tumor invasiveness, only Fos is required for JNK-induced differentiation defects and Matrix metalloprotease (MMP1) upregulation. In contrast, the Fos-dimerizing partner Jun is dispensable for JNK to exert its effects in rasV12scrib1 tumors. Interestingly, Ets21c and Ftz-F1 are transcriptionally induced in these tumors in a JNK- and Fos-dependent manner, thereby demonstrating a hierarchy within the tripartite TF network, with Fos acting as the most upstream JNK effector. Of the three TFs, only Ets21c can efficiently substitute for loss of polarity and cooperate with Ras(V12) in inducing malignant clones that, like rasV12scrib1 tumors, invade other tissues and overexpress MMP1 and the Drosophila insulin-like peptide 8 (Dilp8). While rasV12ets21c tumors require JNK for invasiveness, the JNK activity is dispensable for their growth. In conclusion, this study delineates both unique and overlapping functions of distinct TFs that cooperatively promote aberrant expression of target genes, leading to malignant tumor phenotypes.

Housden, B. E., Valvezan, A. J., Kelley, C., Sopko, R., Hu, Y., Roesel, C., Lin, S., Buckner, M., Tao, R., Yilmazel, B., Mohr, S. E., Manning, B. D. and Perrimon, N. (2015). Identification of potential drug targets for tuberous sclerosis complex by synthetic screens combining CRISPR-based knockouts with RNAi. Sci Signal 8: rs9. PubMed ID: 26350902 Summary: The tuberous sclerosis complex (TSC) family of tumor suppressors, TSC1 and TSC2, function together in an evolutionarily conserved protein complex that is a point of convergence for major cell signaling pathways that regulate mTOR complex 1 (mTORC1). Mutation or aberrant inhibition of the TSC complex is common in various human tumor syndromes and cancers. The discovery of novel therapeutic strategies to selectively target cells with functional loss of this complex is therefore of clinical relevance to patients with nonmalignant TSC and those with sporadic cancers. This study developed a CRISPR-based method to generate homogeneous mutant Drosophila cell lines. By combining TSC1 or TSC2 mutant cell lines with RNAi screens against all kinases and phosphatases, synthetic interactions with TSC1 and TSC2 were identified. Individual knockdown of three candidate genes (mRNA-cap, Pitslre, and CycT; orthologs of RNGTT, CDK11, and CCNT1 in humans) reduced the population growth rate of Drosophila cells lacking either TSC1 or TSC2 but not that of wild-type cells. Moreover, individual knockdown of these three genes had similar growth-inhibiting effects in mammalian TSC2-deficient cell lines, including human tumor-derived cells, illustrating the power of this cross-species screening strategy to identify potential drug targets.

Talbert, M. E., Barnett, B., Hoff, R., Amella, M., Kuczynski, K., Lavington, E., Koury, S., Brud, E. and Eanes, W. F. (2015). Genetic perturbation of key central metabolic genes extends lifespan in Drosophila and affects response to dietary restriction. Proc Biol Sci 282. PubMed ID: 26378219 Summary: There is a connection between nutrient inputs, energy-sensing pathways, lifespan variation and aging. Despite the role of metabolic enzymes in energy homeostasis and their metabolites as nutrient signals, little is known about how their gene expression impacts lifespan. This report uses P-element mutagenesis in Drosophila to study the effect on lifespan of reductions in expression of seven central metabolic enzymes, and contrast the effects on normal diet and dietary restriction. The major observation is that for five of seven genes, the reduction of gene expression extends lifespan on one or both diets. Two genes are involved in redox balance, and it was observed that lower activity genotypes significantly extend lifespan. The hexokinases also show extension of lifespan with reduced gene activity. Since both affect the ATP/ADP ratio, this connects with the role of AMP-activated protein kinase as an energy sensor in regulating lifespan and mediating caloric restriction. These genes possess significant expression variation in natural populations, and the experimental genotypes in this study span this level of natural activity variation. These studies link the readout of energy state with the perturbation of the genes of central metabolism and demonstrate their effect on lifespan.

Kopp, Z. A., et al. (2015). Heart-specific Rpd3 downregulation enhances cardiac function and longevity. Aging (Albany NY) 7: 648-663. PubMed ID: 26399365 Summary: Downregulation of Rpd3, a homologue of mammalian Histone Deacetylase 1 (HDAC1), extends lifespan in Drosophila melanogaster. Once revealed that long-lived fruit flies exhibit limited cardiac decline, whether Rpd3 downregulation would improve stress resistance and/or lifespan when targeted in the heart was investigated. Contested against three different stressors (oxidation, starvation and heat), heart-specific Rpd3 downregulation significantly enhanced stress resistance in flies. However, these higher levels of resistance were not observed when Rpd3 downregulation was targeted in other tissues or when other long-lived flies were tested in the heart-specific manner. Interestingly, the expressions of anti-aging genes such as Sod2, foxo and Thor, were systemically increased as a consequence of heart-specific Rpd3 downregulation. Showing higher resistance to oxidative stress, the heart-specific Rpd3 downregulation concurrently exhibited improved cardiac functions, demonstrating an increased heart rate, decreased heart failure and accelerated heart recovery. Conversely, Rpd3 upregulation in cardiac tissue reduced systemic resistance against heat stress with decreased heart function, also specifying phosphorylated Rpd3 levels as a significant modulator. Continual downregulation of Rpd3 throughout aging increased lifespan, implicating that Rpd3 deacetylase in the heart plays a significant role in cardiac function and longevity to systemically modulate the fly's response to the environment.

Thursday, October 8th

Deligiannaki, M., Casper, A. L., Jung, C. and Gaul, U. (2015). Pasiflora proteins are novel core components of the septate junction. Development 142: 3046-3057. PubMed ID: 26329602 Summary: Epithelial sheets play essential roles as selective barriers insulating the body from the environment and establishing distinct chemical compartments within it. In invertebrate epithelia, septate junctions (SJs) consist of large multi-protein complexes that localize at the apicolateral membrane and mediate barrier function. This study reports the identification of two novel SJ components, Pasiflora1 (CG7713) and Pasiflora2 (CG8121), through a genome-wide glial RNAi screen in Drosophila. Pasiflora mutants show permeable blood-brain and tracheal barriers, overelongated tracheal tubes and mislocalization of SJ proteins. Consistent with the observed phenotypes, the genes are co-expressed in embryonic epithelia and glia and are required cell-autonomously to exert their function. Pasiflora1 and Pasiflora2 belong to a previously uncharacterized family of tetraspan membrane proteins conserved across the protostome-deuterostome divide. Both proteins localize at SJs and their apicolateral membrane accumulation depends on other complex components. In fluorescence recovery after photobleaching experiments, pasiflora proteins were found to be core SJ components as they are required for complex formation and exhibit restricted mobility within the membrane of wild-type epithelial cells, but rapid diffusion in cells with disrupted SJs. Taken together, these results show that Pasiflora1 and Pasiflora2 are novel integral components of the SJ and implicate a new family of tetraspan proteins in the function of these ancient and crucial cell junctions.

Ordan, E. and Volk, T. (2015). A non-signaling role of Robo2 in tendons is essential for Slit processing and muscle patterning. Development 142(20):3512-8. PubMed ID: 26400093 Summary: Coordinated locomotion of an organism relies on the development of proper musculoskeletal connections. In Drosophila, the Slit-Robo signaling pathway guides muscles to tendons. This study shows that the Slit receptor Roundabout 2 (Robo2) plays a non-cell-autonomous role in directing muscles to their corresponding tendons. Robo2 is expressed by tendons, and its non signaling activity in these cells promotes Slit cleavage producing a cleaved Slit-N-terminal guiding signal, which provides short-range signaling into muscles. Consistently, robo2 mutant embryos exhibited a muscle phenotype similar to that of slit, which could not be rescued by a muscle-specific Robo2 expression but rather by an ectodermally derived Robo2. Alternatively this muscle phenotype could be induced by tendon-specific robo2RNAi. Membrane immobilization of Slit, or its N-terminal cleaved form on tendons bypasses the functional requirement for Robo2 in tendons, verifying that the major role of Robo2 is to promote the association of Slit with the tendon cell membrane. Cleaved Slit (Slit-N) tends to oligomerize whereas full-length uncleavable Slit does not. It is therefore proposed that Slit-N oligomers produced at the tendon membrane by Robo2 signal to the approaching muscle by combined Robo;Robo3 activity. These findings establish a Robo2-mediated mechanism, independent of signaling essential to limiting Slit distribution, which might be relevant to the regulation of Slit-mediated short-range signaling in additional systems.

Fear, J. M., Arbeitman, M. N., Salomon, M. P., Dalton, J. E., Tower, J., Nuzhdin, S. V. and McIntyre, L. M. (2015). The Wright stuff: Reimagining path analysis reveals novel components of the sex determination hierarchy in Drosophila melanogaster. BMC Syst Biol 9: 53. PubMed ID: 26335107 Summary: This study used a structural equation modeling approach, leveraging natural genetic variation from two studies on Drosophila female head tissues to expand understanding of the sex hierarchy gene regulatory network (GRN). The GRN was expanded adding novel links among genes, including a link from fruitless (fru) to Sex-lethal (Sxl). This link is further supported by the presence of fru binding sites in the Sxl locus. 754 candidate genes were added to the pathway, including the splicing factors male-specific lethal 2 and Rm62 as downstream targets of Sxl. Independent studies of doublesex and transformer mutants support evidence for a link between the sex hierarchy and metabolism, via Insulin-like receptor. The genes added in one population were enriched for genes with sex-biased splicing and components of the spliceosome. Using natural alleles this approach not only identifies novel relationships, but using supervised approaches can order genes into a regulatory hierarchy.

Dong, Q., Brenneman, B., Fields, C. and Srivastava, A. (2015). A Cathepsin-L is required for invasive behavior during air sac primordium development in Drosophila melanogaster. FEBS Lett 589(20 Pt B):3090-7. PubMed ID: 26341534 Summary: The Drosophila Air Sac Primordium (ASP) has emerged as an important structure where cellular, genetic and molecular events responsible for invasive behavior and branching morphogenesis can be studied. This report presents data which demonstrate that a Cathepsin-L encoded by the gene Cysteine proteinase-1 (CP1) in Drosophila is necessary for invasive behavior during ASP development. CP1 is expressed in ASP and knockdown of CP1 results in suppression of migratory and invasive behavior observed during ASP development. It was further shown that CP1 possibly regulates invasive behavior by promoting degradation of Basement Membrane. These data provide clues to the possible role of Cathepsin L in human lung development and tumor invasion, especially, given the similarities between human lung and Drosophila ASP development.

Wednesday, October 7th

Zanet, J., Benrabah, E., Li, T., Pelissier-Monier, A., Chanut-Delalande, H., Ronsin, B., Bellen, H. J., Payre, F. and Plaza, S. (2015). Pri sORF peptides induce selective proteasome-mediated protein processing. Science 349: 1356-1358. PubMed ID: 26383956 Summary: A wide variety of RNAs encode small open-reading-frame (smORF/sORF) peptides, but their functions are largely unknown. This study shows that Drosophila polished-rice (pri) sORF peptides trigger proteasome-mediated protein processing, converting the Shavenbaby (Svb) transcription repressor into a shorter activator. A genome-wide RNA interference screen identifies an E2-E3 ubiquitin-conjugating complex, UbcD6-Ubr3, which targets Svb to the proteasome in a pri-dependent manner. Upon interaction with Ubr3, Pri peptides promote the binding of Ubr3 to Svb. Ubr3 can then ubiquitinate the Svb N terminus, which is degraded by the proteasome. The C-terminal domains protect Svb from complete degradation and ensure appropriate processing. These data show that Pri peptides control selectivity of Ubr3 binding, which suggests that the family of sORF peptides may contain an extended repertoire of protein regulators.

Zheng, Y., Wang, W., Liu, B., Deng, H., Uster, E. and Pan, D. (2015). Identification of Happyhour/MAP4K as alternative Hpo/Mst-like kinases in the Hippo kinase cascade. Dev Cell 34(6):642-55. PubMed ID: 26364751 Summary: In Drosophila and mammals, the canonical Hippo kinase cascade is mediated by Hpo/Mst acting through the intermediary kinase Wts/Lats to phosphorylate the transcriptional coactivator Yki/YAP/TAZ. However, the underlying mechanisms linking Yki/YAP/TAZ activity to the actin cytoskeleton are poorly understood. Using Drosophila imaginal discs as an in vivo model, this study shows that Wts, but not Hpo, is genetically indispensable for cytoskeleton-mediated subcellular localization of Yki. Through a systematic screen, the Ste-20 kinase Happyhour (Hppy) and its mammalian counterpart MAP4K1/2/3/5 were identified as an alternative kinase that phosphorylates the hydrophobic motif of Wts/Lats in a similar manner as Hpo/Mst. Consistent with their redundant function as activating kinases of Wts/Lats, combined loss of Hpo/Mst and Hppy/MAP4K abolishes cytoskeleton-mediated regulation of Yki/YAP subcellular localization, as well as YAP cytoplasmic translocation induced by contact inhibition.

Lebreton, G. and Casanova, J. (2015). Ligand-binding and constitutive FGF receptors in single Drosophila tracheal cells. Implications for the role of FGF in collective migration. Dev Dyn [Epub ahead of print]. PubMed ID: 26342211 Summary: The migration of individual cells relies on their capacity to evaluate differences across their bodies and to move either towards or against a chemoattractant or a chemorepellent signal respectively. However, the direction of collective migration is believed to depend on the internal organisation of the cell cluster while the role of the external signal is limited to single out some cells in the cluster, confering them with motility properties. This study analysed the role of Fibroblast Growth Factor (FGF) signalling in collective migration in the Drosophila trachea. While ligand-binding FGF receptor (FGFR) activity in a single cell can drive migration of a tracheal cluster, this study shows that activity from a constitutively activated FGFR cannot - an observation that contrasts with previously analysed cases. These results indicate that individual cells in the tracheal cluster can 'read' differences in the distribution of FGFR activity and lead migration of the cluster accordingly. Thus, FGF can act as a chemoattractant rather than as a motogen in collective cell migration. This finding has many implications in both development and pathology.

Kim, K., Yoon, J., Yim, J. and Kim, H. J. (2015). Deneddylase 1 regulates Deneddylase activity of the Cop9 signalosome in Drosophila melanogaster. Insect Sci [Epub ahead of print]. PubMed ID: 26332639 Summary: NEDD8 conjugation of Cullin has an important role in ubiquitin-mediated protein degradation. The COP9 signalosome, of which CSN5 is the major catalytic subunit, is a major Cullin deneddylase. Another deneddylase, Deneddylase 1, has also been shown to process the Nedd8 precursor. In Drosophila, the DEN1 mutants do not have increased levels of Cullin neddylation, but instead show a significant decrease in neddylated Cullin. This characteristic decrease in neddylated Cullins in the DEN1null background can be rescued by UAS-dDEN1WT overexpression but not by overexpression of mature NEDD8, indicating that this phenotype is distinct from the NEDD8-processing function of DEN1. This study examined the role of DEN1-CSN interaction in regulating Cullin neddylation. Overexpression of DEN1 in a CSN5hypo background slightly reduced unneddylated Cullin levels. The CSN5, DEN1 double mutation partially rescues the premature lethality associated with the CSN5 single mutation. These results suggest that DEN1 regulates Cullin neddylation by suppressing CSN deneddylase activity.

Tuesday, October 6th

Chen, S., Gendelman, H. K., Roche, J. P., Alsharif, P. and Graf, E. R. (2015). Mutational analysis of Rab3 function for controlling active zone protein composition at the Drosophila neuromuscular junction. PLoS One 10: e0136938. PubMed ID: 26317909 Summary: At synapses, the release of neurotransmitter is regulated by molecular machinery that aggregates at specialized presynaptic release sites termed active zones. The complement of active zone proteins at each site is a determinant of release efficacy and can be remodeled to alter synapse function. The small GTPase Rab3 plays a novel role that controls the distribution of active zone proteins to individual release sites at the Drosophila neuromuscular junction. Rab3 has been extensively studied for its role in the synaptic vesicle cycle; however, the mechanism by which Rab3 controls active zone development remains unknown. To explore this mechanism, a mutational analysis was conducted to determine the molecular and structural requirements of Rab3 function at Drosophila synapses. GTP-binding was found to be required for Rab3 to traffick to synapses and distribute active zone components across release sites. Conversely, the hydrolytic activity of Rab3 is unnecessary for this function. Through a structure-function analysis specific residues were identified within the effector-binding switch regions that are required for Rab3 function, and it was determined that membrane attachment is essential. These findings suggest that Rab3 controls the distribution of active zone components via a vesicle docking mechanism that is consistent with standard Rab protein function.

Ullrich, A., Bohme, M. A., Schoneberg, J., Depner, H., Sigrist, S. J. and Noe, F. (2015). Dynamical organization of Syntaxin-1A at the presynaptic active zone. PLoS Comput Biol 11: e1004407. PubMed ID: 26367029 Summary: Synaptic vesicle fusion is mediated by SNARE proteins forming in between synaptic vesicle (v-SNARE) and plasma membrane (t-SNARE), one of which is Syntaxin-1A. Although exocytosis mainly occurs at active zones, Syntaxin-1A appears to cover the entire neuronal membrane. By using STED super-resolution light microscopy and image analysis of Drosophila neuro-muscular junctions, this study shows that Syntaxin-1A clusters are more abundant and have an increased size at active zones. A computational particle-based model of syntaxin cluster formation and dynamics is developed. The model is parametrized to reproduce Syntaxin cluster-size distributions found by STED analysis, and successfully reproduces existing FRAP results. The model shows that the neuronal membrane is adjusted in a way to strike a balance between having most syntaxins stored in large clusters, while still keeping a mobile fraction of syntaxins free or in small clusters that can efficiently search the membrane or be traded between clusters. This balance is subtle and can be shifted toward almost no clustering and almost complete clustering by modifying the syntaxin interaction energy on the order of only 1 kBT. This capability appears to be exploited at active zones. The larger active-zone syntaxin clusters are more stable and provide regions of high docking and fusion capability, whereas the smaller clusters outside may serve as flexible reserve pool or sites of spontaneous ectopic release.

Beck, K., Ehmann, N., Andlauer, T. F., Ljaschenko, D., Strecker, K., Fischer, M., Kittel, R. J. and Raabe, T. (2015). Loss of the Coffin-Lowry syndrome associated gene RSK2 alters ERK activity, synaptic function and axonal transport in Drosophila motoneurons. Dis Model Mech 8(11):1389-400. PubMed ID: 26398944 Summary: Plastic changes in synaptic properties are considered as fundamental for adaptive behaviors. Extracellular-signal-regulated kinase (ERK)-mediated signaling (see Drosophila Rolled) has been implicated in regulation of synaptic plasticity. Ribosomal S6 kinase 2 (RSK2) acts as a regulator and downstream effector of ERK. In the brain, RSK2 is predominantly expressed in regions required for learning and memory. Loss-of-function mutations in human RSK2 cause Coffin-Lowry Syndrome, which is characterized by severe mental retardation and low IQ scores in male patients. Knockout of RSK2 in mice or the RSK ortholog in Drosophila (see S6K) result in a variety of learning and memory defects. However, overall brain structure in these animals is not affected, leaving open the question of the pathophysiological consequences. Using the fly neuromuscular system as a model for excitatory glutamatergic synapses, this study shows that removal of RSK function causes distinct defects in motoneurons and at the neuromuscular junction. Based on histochemical and electrophysiological analyses it is concluded that RSK is required for normal synaptic morphology and function. Furthermore, loss of RSK function interferes with ERK signaling at different levels. Elevated ERK activity was evident in the somata of motoneurons, whereas decreased ERK activity was observed in axons and the presynapse. In addition, a novel function of RSK in anterograde axonal transport was uncovered. These results emphasize the importance of fine tuning ERK activity in neuronal processes underlying higher brain functions. In this context, RSK acts as a modulator of ERK signaling.

Ziegler, A. B., Menage, C., Gregoire, S., Garcia, T., Ferveur, J. F., Bretillon, L. and Grosjean, Y. (2015). Lack of dietary polyunsaturated fatty acids causes synapse dysfunction in the Drosophila visual system. PLoS One 10: e0135353. PubMed ID: 26308084 Summary: Polyunsaturated fatty acids (PUFAs) are essential nutrients for animals and necessary for the normal functioning of the nervous system. A lack of PUFAs can result from the consumption of a deficient diet or genetic factors, which impact PUFA uptake and metabolism. Both can cause synaptic dysfunction, which is associated with numerous disorders. However, there is a knowledge gap linking these neuronal dysfunctions and their underlying molecular mechanisms. Because of its genetic manipulability and its easy, fast, and cheap breeding, Drosophila melanogaster has emerged as an excellent model organism for genetic screens, helping to identify the genetic bases of such events. As a first step towards the understanding of PUFA implications in Drosophila synaptic physiology a breeding medium containing only very low amounts of PUFAs was designed. The fly's visual system, a well-established model for studying signal transmission and neurological disorders, was used to measure the effects of a PUFA deficiency on synaptic function. Using both visual performance and eye electrophysiology, it was found that PUFA deficiency strongly affected synaptic transmission in the fly's visual system. These defects were rescued by diets containing omega-3 or omega-6 PUFAs alone or in combination. In summary, manipulating PUFA contents in the fly's diet was powerful to investigate the role of these nutrients on the fly's visual synaptic function. This study aims at showing how the first visual synapse of Drosophila can serve as a simple model to study the effects of PUFAs on synapse function. A similar approach could be further used to screen for genetic factors underlying the molecular mechanisms of synaptic dysfunctions associated with altered PUFA levels.

Monday, October 5th

Clemens, J., Girardin, C. C., Coen, P., Guan, X. J., Dickson, B. J. and Murthy, M. (2015). Connecting neural codes with behavior in the auditory system of Drosophila. Neuron 87: 1332-1343. PubMed ID: 26365767 Summary: Brains are optimized for processing ethologically relevant sensory signals. However, few studies have characterized the neural coding mechanisms that underlie the transformation from natural sensory information to behavior. This study focused on acoustic communication in Drosophila melanogaster and used computational modeling to link natural courtship song, neuronal codes, and female behavioral responses to song. Melanogaster females are sensitive to long timescale song structure (on the order of tens of seconds). From intracellular recordings, models were generated that recapitulate neural responses to acoustic stimuli. These neural codes were linked with female behavior by generating model neural responses to natural courtship song. Using a simple decoder, female behavioral responses were predicted to the same song stimuli with high accuracy. This modeling approach reveals how long timescale song features are represented by the Drosophila brain and how neural representations can be decoded to generate behavioral selectivity for acoustic communication signals.

Rabinovich, D., Mayseless, O. and Schuldiner, O. (2015). Long term ex vivo culturing of Drosophila brain as a method to live image pupal brains: insights into the cellular mechanisms of neuronal remodeling. Front Cell Neurosci 9: 327. PubMed ID: 26379498 Summary: Research on the stereotypic remodeling of Drosophila mushroom body (MB) γ neurons has contributed to knowledge of the molecular mechanisms of remodeling but knowledge of the cellular mechanisms remain poorly understood. A major hurdle in understanding various dynamic processes that occur during metamorphosis is the lack of time-lapse resolution. The pupal case and opaque fat bodies that enwrap the central nervous system (CNS) make live-imaging of the central brain in-vivo impossible. This study describes an ex vivo long-term brain culture system that supports the development and neuronal remodeling of pupal brains. By optimizing culture conditions and dissection protocols, development was observed in culture at kinetics similar to what occurs in vivo. Using this new method, the first time-lapse sequence of MB gamma neurons undergoing remodeling was observed in up to a single cell resolution. Axon pruning was found to be initiated by blebbing, followed by one-two nicks that seem to initiate a more widely spread axon fragmentation. The long-term ex vivo brain culture system could be used to study dynamic aspects of neurodevelopment of any Drosophila neuron.

Smith-Trunova, S., Prithviraj, R., Spurrier, J., Kuzina, I., Gu, Q. and Giniger, E. (2015). Cdk5 regulates developmental remodeling of mushroom body neurons in Drosophila. Dev Dyn [Epub ahead of print]. PubMed ID: 26394609 Summary: During metamorphosis, axons and dendrites of the mushroom body (MB) in the Drosophila central brain are remodeled extensively to support the transition from larval to adult behaviors. This study shows that the neuronal cyclin-dependent kinase, Cdk5, regulates the timing and rate of mushroom body remodeling: reduced Cdk5 activity causes a delay in pruning of MB neurites, while hyperactivation accelerates it. It was shown that Cdk5 cooperates with the ubiquitin-proteasome system in this process. Finally, Cdk5 modulates the first overt step in neurite disassembly, dissolution of the neuronal tubulin cytoskeleton, and it also acts at additional steps of MB pruning. These data show that Cdk5 regulates the onset and extent of remodeling of the Drosophila MB. Given the wide phylogenetic conservation of Cdk5, the study suggests that it is likely to play a role in developmental remodeling in other systems, as well. Moreover, it can be speculated that the well-established role of Cdk5 in neurodegeneration may involve some of the same cellular mechanisms that it employs during developmental remodeling.

Valmalette, J. C., Raad, H., Qiu, N., Ohara, S., Capovilla, M. and Robichon, A. (2015). Nano-architecture of gustatory chemosensory bristles and trachea in Drosophila wings. Sci Rep 5: 14198. PubMed ID: 26381332 Summary: In the Drosophila wing anterior margin, the dendrites of gustatory neurons occupy the interior of thin and long bristles that present tiny pores at their extremities. The functions of this gustatory activity remain elusive and controversial. This study investigated the architecture of the wing chemosensory bristles and wing trachea using Raman spectroscopy and fluorescence microscopy. It was hypothesized that the wing gustatory hair, an open-ended capillary tube, and the wing trachea constitute biological systems similar to nano-porous materials. Evidence is presented that argues in favour of the existence of a layer or a bubble of air beneath the pore inside the gustatory hair. These hollow hairs and wing tracheal tubes fulfill conditions for which the physics of fluids applied to open-ended capillaries and porous materials are relevant. The wing gustatory hair and tracheal architectures were shown to be capable of trapping volatile molecules from the environment, which might increase the efficiency of their spatial detection by way of wing vibrations or during flight.

Sunday, October 4th

Newton, F. G., Harris, R. E., Sutcliffe, C. and Ashe, H. L. (2015). Coordinate post-transcriptional repression of Dpp-dependent transcription factors attenuates signal range during development. Development 142(19):3362-73. PubMed ID: 26293305 Summary: Precise control of the range of signalling molecule action is critical for correct cell fate patterning during development. For example, Drosophila ovarian germline stem cells (GSCs) are maintained by exquisitely short-range BMP signalling from the niche. In the absence of BMP signalling, one GSC daughter differentiates into a cystoblast (CB) and this fate is stabilised by Brain Tumour (Brat) and Pumilio (Pum)-mediated post-transcriptional repression of mRNAs, including that encoding the Dpp transducer, Mad. However, the identity of other repressed mRNAs and the mechanism of post-transcriptional repression are currently unknown. This study identified the Medea and schnurri mRNAs, which encode transcriptional regulators required for activation and/or repression of Dpp target genes, as additional Pum-Brat targets suggesting that tripartite repression of the transducers is deployed to desensitise the CB to Dpp. In addition, this study shows that repression by Pum-Brat requires recruitment of the CCR4 and Pop2 deadenylases, with knockdown of deadenylases in vivo giving rise to ectopic GSCs. Consistent with this, Pum-Brat repression leads to poly(A) tail shortening and mRNA degradation in tissue culture cells and a reduced number of Mad and shn transcripts in the CB relative to the GSC based on single molecule mRNA quantitation. Finally, the generality of the mechanism was shown by demonstrating that Brat also attenuates pMad and Dpp signalling range in the early embryo. Together these data serve as a platform for understanding how post-transcriptional repression restricts interpretation of BMPs and other cell signals in order to allow robust cell fate patterning during development.

Marco, A. (2015). Selection against maternal microRNA target sites in maternal transcripts. G3 (Bethesda) 5(10):2199-207. PubMed ID: 26306531 Summary: In animals, before the zygotic genome is expressed, the egg already contains gene products deposited by the mother. These maternal products are crucial during the initial steps of development. In Drosophila melanogaster a large number of maternal products are found in the oocyte, some of which are indispensable. Many of these products are RNA molecules, such as gene transcripts and ribosomal RNAs. Recently, microRNAs - small RNA gene regulators - have been detected early during development and are important in these initial steps. The presence of some microRNAs in unfertilized eggs has been reported, but whether they have a functional impact in the egg or early embryo has not being explored. This study extracted and sequenced small RNAs from Drosophila unfertilized eggs. The unfertilized egg is rich in small RNAs and contains multiple microRNA products. Maternal microRNAs are often encoded within the intron of maternal genes, suggesting that many maternal microRNAs are the product of transcriptional hitch-hiking. Comparative genomics analyses suggest that maternal transcripts tend to avoid target sites for maternal microRNAs. A microRNA target mutation model was developed to study the functional impact of polymorphisms at microRNA target sites. The analysis of Drosophila populations suggests that there is selection against maternal microRNA target sites in maternal transcripts. A potential role of the maternal microRNA mir-9c in maternal-to-zygotic transition is also discussed. In conclusion, maternal microRNAs in Drosophila have a functional impact in maternal protein-coding transcripts.

Wang, W., Han, B. W., Tipping, C., Ge, D. T., Zhang, Z., Weng, Z. and Zamore, P. D. (2015). Slicing and binding by Ago3 or Aub trigger Piwi-bound piRNA production by distinct mechanisms. Mol Cell 59: 819-830. PubMed ID: 26340424 Summary: In Drosophila ovarian germ cells, PIWI-interacting RNAs (piRNAs) direct Aubergine and Argonaute3 to cleave transposon transcripts and instruct Piwi to repress transposon transcription, thereby safeguarding the germline genome. This study reports that RNA cleavage by Argonaute3 initiates production of most Piwi-bound piRNAs. The cardinal function of Argonaute3, whose piRNA guides predominantly correspond to sense transposon sequences, is to produce antisense piRNAs that direct transcriptional silencing by Piwi, rather than to make piRNAs that guide post-transcriptional silencing by Aubergine. It was also found that the Tudor domain protein Qin prevents Aubergine's cleavage products from becoming Piwi-bound piRNAs, ensuring that antisense piRNAs guide Piwi. Although Argonaute3 slicing is required to efficiently trigger phased piRNA production, an alternative, slicing-independent pathway suffices to generate Piwi-bound piRNAs that repress transcription of a subset of transposon families. This alternative pathway may help flies silence newly acquired transposons for which they lack extensively complementary piRNAs.

Bertin, B., Renaud, Y., Aradhya, R., Jagla, K. and Junion, G. (2015). TRAP-rc, translating ribosome affinity purification from rare cell populations of Drosophila embryos. J Vis Exp [Epub ahead of print]. PubMed ID: 26381166 Summary: Measuring levels of mRNAs in the process of translation in individual cells provides information on the proteins involved in cellular functions at a given point in time. The protocol dubbed Translating Ribosome Affinity Purification (TRAP) is able to capture this mRNA translation process in a cell-type-specific manner. Based on the affinity purification of polysomes carrying a tagged ribosomal subunit, TRAP can be applied to translatome analyses in individual cells, making it possible to compare cell types during the course of developmental processes or to track disease development progress and the impact of potential therapies at molecular level. This study reports an optimized version of the TRAP protocol, called TRAP-rc (rare cells), dedicated to identifying engaged-in-translation RNAs from rare cell populations. TRAP-rc was validated using the Gal4/UAS targeting system in a restricted population of muscle cells in Drosophila embryos. This novel protocol allows the recovery of cell-type-specific RNA in sufficient quantities for global gene expression analytics such as microarrays or RNA-seq. The robustness of the protocol and the large collections of Gal4 drivers make TRAP-rc a highly versatile approach with potential applications in cell-specific genome-wide studies.

Saturday, October 3rd

Heidari, R., Monnier, V., Martin, E. and Tricoire, H. (2015). Methylene blue partially rescues heart defects in a Drosophila model of Huntington's disease. J Huntingtons Dis 4: 173-186. PubMed ID: 26397898 Summary: Huntington's disease (HD) is a Polyglutamine disease caused by the presence of CAG repeats in the first exon of Huntingtin (Htt), a large protein with multiple functions. This study reports the construction of inducible Drosophila HD heart models, expressing two Nter fragments of the protein encompassing either exon 1 or the first 171 amino acids and the characterization of heart phenotypes in vivo. Both mHtt fragments were shown to be able to impair fly cardiac function with different characteristics. Additionally, expression of mHtt, which was limited to adulthood only, leads to mild heart impairment, as opposed to a strong and age-dependent phenotype observed when mHtt expression was driven during both developmental and adult stages. Also, treatment with methylene blue (MB), a protective compound in mitochondria-related diseases, partially protects the fly's heart against mHtt-induced toxicity, but does not rescue neuronal or glial phenotypes in other fly models of HD. This may be linked to its low penetration through the fly's blood-brain barrier. These data suggest that improvement of mitochondrial function by MB, or related compounds, could be an efficient therapeutic strategy to prevent cardiac failure in HD patients.

Babcock, D. T. and Ganetzky, B. (2015). Transcellular spreading of huntingtin aggregates in the Drosophila brain. Proc Natl Acad Sci U S A. 112(39):E5427-33. PubMed ID: 26351672 Summary: A key feature of many neurodegenerative diseases is the accumulation and subsequent aggregation of misfolded proteins. Recent studies have highlighted the transcellular propagation of protein aggregates in several major neurodegenerative diseases, although the precise mechanisms underlying this spreading and how it relates to disease pathology remain unclear. This study used a polyglutamine-expanded form of human huntingtin (Htt; see Drosophila huntingtin) with a fluorescent tag to monitor the spreading of aggregates in the Drosophila brain in a model of Huntington's disease. Upon expression of this construct in a defined subset of neurons, it was demonstrated that protein aggregates accumulate at synaptic terminals and progressively spread throughout the brain. These aggregates are internalized and accumulate within other neurons. Htt aggregates cause non-cell-autonomous pathology, including loss of vulnerable neurons that can be prevented by inhibiting endocytosis in these neurons. Finally it was shown that the release of aggregates requires N-ethylmalemide-sensitive fusion protein 1, demonstrating that active release and uptake of Htt aggregates are important elements of spreading and disease progression.

Clark, R. I., Salazar, A., Yamada, R., Fitz-Gibbon, S., Morselli, M., Alcaraz, J., Rana, A., Rera, M., Pellegrini, M., Ja, W. W. and Walker, D. W. (2015). Distinct shifts in microbiota composition during Drosophila aging impair intestinal function and drive mortality. Cell Rep 12: 1656-1667. PubMed ID: 26321641 Summary: Alterations in the composition of the intestinal microbiota have been correlated with aging and measures of frailty in the elderly. However, the relationships between microbial dynamics, age-related changes in intestinal physiology, and organismal health remain poorly understood. This study shows that dysbiosis of the intestinal microbiota, characterized by an expansion of the Gammaproteobacteria, is tightly linked to age-onset intestinal barrier dysfunction in Drosophila. Indeed, alterations in the microbiota precede and predict the onset of intestinal barrier dysfunction in aged flies. Changes in microbial composition occurring prior to intestinal barrier dysfunction contribute to changes in excretory function and immune gene activation in the aging intestine. In addition, a distinct shift in microbiota composition was shown to follow intestinal barrier dysfunction, leading to systemic immune activation and organismal death. These results indicate that alterations in microbiota dynamics could contribute to and also predict varying rates of health decline during aging in mammals.

Obata, F. and Miura, M. (2015). Enhancing S-adenosyl-methionine catabolism extends Drosophila lifespan. Nat Commun 6: 8332. PubMed ID: 26383889 Summary: Methionine restriction extends the lifespan of various model organisms. Limiting S-adenosyl-methionine (SAM) synthesis, the first metabolic reaction of dietary methionine, extends longevity in Caenorhabditis elegans but accelerates pathology in mammals. This study shows that, as an alternative to inhibiting SAM synthesis, enhancement of SAM catabolism by Glycine N-methyltransferase (Gnmt) extends the lifespan in Drosophila. Gnmt strongly buffers systemic SAM levels by producing sarcosine in either high-methionine or low-sams conditions. During ageing, systemic SAM levels in flies are increased. Gnmt is transcriptionally induced in a dFoxO-dependent manner; however, this is insufficient to suppress SAM elevation completely in old flies. Overexpression of gnmt suppresses this age-dependent SAM increase and extends longevity. Pro-longevity regimens, such as dietary restriction or reduced insulin signalling, attenuate the age-dependent SAM increase, and rely at least partially on Gnmt function to exert their lifespan-extending effect in Drosophila. This study suggests that regulation of SAM levels by Gnmt is a key component of lifespan extension.

Friday, October 2nd

Breuer, M. and Ohkura, H. (2015). A negative loop within the nuclear pore complex controls global chromatin organization. Genes Dev 29: 1789-1794. PubMed ID: 26341556 Summary: The nuclear pore complex (NPC) tethers chromatin to create an environment for gene regulation, but little is known about how this activity is regulated to avoid excessive tethering of the genome. Tethering specific genomic loci to the NPC appears to contribute to transcriptional activation. Also, the NPC has been further implicated in creating a repressive environment or retaining genes at the periphery after repression, possibly contributing to epigenetic transcriptional memory. This paper proposes a negative regulatory loop within the NPC controlling the chromatin attachment state, in which Nup155 and Nup93 recruit Nup62 to suppress chromatin tethering by Nup155. Depletion of Nup62 severely disrupts chromatin distribution in the nuclei of female germlines and somatic cells, which can be reversed by codepleting Nup155. See a model for the chromatin attachment state controlled by an internal regulatory circuit in the NPC. Thus, this universal regulatory system within the NPC is crucial to control large-scale chromatin organization in the nucleus.

Li, M., Ma, Z., Liu, J. K., Roy, S., Patel, S. K., Lane, D. C. and Cai, H. N. (2015). An organizational hub of developmentally regulated chromatin loops in the Drosophila Antennapedia complex. Mol Cell Biol 35(23):4018-29. PubMed ID: 26391952 Summary: The complex expression pattern of the Drosophila homeotic gene Sex combs reduced (Scr) is directed by an unusually long regulatory sequence harboring diverse cis elements and an intervening neighbor gene fushi tarazu (ftz). This study reports the presence of a multitude of Chromatin boundary elements (CBEs) in the Scr regulatory region. Selective and dynamic pairing among these CBEs mediates developmentally regulated chromatin loops. In particular, the SF1 boundary plays a central role in organizing two subsets of chromatin loops: one subset encloses ftz, limiting its access by the surrounding Scr enhancers and compartmentalizing distinct histone modifications; and the other subset subdivides the Scr regulatory sequences into independent enhancer access domains. Tandem pairing of SF1 and SF2, two strong CBEs that flank the ftz domain, providing a mechanism for the endogenous Scr enhancer to circumvent the ftz domain. This study demonstrates how an endogenous CBE network, centrally orchestrated by SF1, could remodel the genomic environment to facilitate gene regulation during development.

Singh, A.K. and Lakhotia, S.C. (2015). The hnRNP A1 homolog Hrb87F/Hrp36 is important for telomere maintenance in Drosophila melanogaster. Chromosoma [Epub ahead of print]. PubMed ID: 26373285 Summary: Unlike the telomerase-dependent mammalian telomeres, HeT-A, TART, and TAHRE (HTT) retroposon arrays regulate Drosophila telomere length. Cap prevents telomeric associations (TAs) and telomeric fusions (TFs). Results from this study suggest important roles of Hrb87F in telomeric HTT array and cap maintenance in Drosophila. All chromosome arms, except 2L, in Df(3R)Hrb87F homozygotes (Hrb87F-null) display significantly elongated telomeres with amplified HTT arrays and high TAs, all of which resolve without damage. Presence of FLAG-tagged Hrb87F (FLAG-Hrb87F) on cap and subtelomeric regions following hsFLAG-Hrb87F transgene expression in Df(3R)Hrb87F homozygotes suppresses TAs without affecting telomere length. A normal X-chromosome telomere expands within five generations in Hrb87F-null background and displays high TAs, but not when hsFLAG-Hrb87F is co-expressed. Tel 1 /Gaiano line or HP1 loss-of-function mutant-derived expanded telomeres carry Hrb87F on cap and HTT arrays while Hrb87F-null telomeres have HP1 and HOAP on caps and expanded HTT arrays. ISWI, seen only on cap on normal telomeres, is abundant on Hrb87F-null expanded HTT arrays. Together, these suggest complex interactions between members of the proteome of telomeres so that absence of any key member leads to telomere expansion and/or enhanced TAs/TFs. HTT expansion in Hrb87F-null condition is not developmental but a germline event presumably because absence of Hrb87F in germline may deregulate HTT retroposition/replication leading to telomere elongation.

Shimaji, K., Konishi, T., Tanaka, S., Yoshida, H., Kato, Y., Ohkawa, Y., Sato, T., Suyama, M., Kimura, H. and Yamaguchi, M. (2015). Genomewide identification of target genes of histone methyltransferase dG9a during Drosophila embryogenesis. Genes Cells 20(11):902-14. PubMed ID: 26334932 Summary: Post-translational modification of the histone plays important roles in epigenetic regulation of various biological processes. Among the identified histone methyltransferases (HMTases), G9a is a histone H3 Lys 9 (H3K9)-specific example active in euchromatic regions. Drosophila G9a (dG9a) has been reported to feature H3K9 dimethylation activity in vivo. This study shows that the time required for hatching of a homozygous dG9a null mutant and heteroallelic combination of dG9a null mutants is delayed, suggesting that dG9a is at least partially responsible for progression of embryogenesis. Immunocytochemical analyses of the wild-type and the dG9a null mutant flies indicated that dG9a localizes in cytoplasm up to nuclear division cycle 7 where it is likely responsible for di-methylation of nucleosome-free H3K9. From cycles 8-11, dG9a moves into the nucleus and is responsible for di-methylating H3K9 in nucleosomes. RNA-sequence analysis utilizing early wild-type and dG9a mutant embryos showed that dG9a down-regulates expression of genes responsible for embryogenesis. RNA fluorescent in situ hybridization analysis further showed temporal and spatial expression patterns of these mRNAs did not significantly change in the dG9a mutant. These results indicate that dG9a controls transcription levels of some zygotic genes without changing temporal and spatial expression patterns of the transcripts of these genes.

Thursday, October 1st

Isabella, A. J. and Horne-Badovinac, S. (2015). Dynamic regulation of basement membrane protein levels promotes egg chamber elongation in Drosophila. Dev Biol [Epub ahead of print]. PubMed ID: 26348027 Summary: Basement membranes (BMs) are sheet-like extracellular matrices that provide essential support to epithelial tissues. Recent evidence suggests that regulated changes in BM architecture can direct tissue morphogenesis. The Drosophila egg chamber transforms from a spherical to an ellipsoidal shape as it matures. This elongation coincides with a stage-specific increase in Type IV Collagen (Col IV) levels in the BM surrounding the egg chamber. This study identified the Collagen-binding protein SPARC as a negative regulator of egg chamber elongation and shows that SPARC down-regulation is necessary for the increase in Col IV levels to occur. SPARC was found to interact with Col IV prior to secretion and it is proposed that, through this interaction, SPARC blocks the incorporation of newly synthesized Col IV into the BM. A decrease was observed in Perlecan levels during elongation, and Perlecan was shown to be a negative regulator of this process. These data provide mechanistic insight into SPARC's conserved role in matrix dynamics and demonstrate that regulated changes in BM composition influence organ morphogenesis.

Ng, W.C., Chin, J.S., Tan, K.J. and Yew, J.Y. (2015). The fatty acid elongase Bond is essential for Drosophila sex pheromone synthesis and male fertility. Nat Commun 6: 8263. PubMed ID: 26369287 Summary: Insects use a spectacular variety of chemical signals to guide their social behaviours. How such chemical diversity arises is a long-standing problem in evolutionary biology. This study describes the contribution of the fatty acid elongase Bond to both pheromone diversity and male fertility in Drosophila. Genetic manipulation and mass spectrometry analysis reveal that the loss of bond eliminates the male sex pheromone (3R,11Z,19Z)-3-acetoxy-11,19-octacosadien-1-ol (CH503). Unexpectedly, silencing bond expression severely suppresses male fertility and the fertility of conspecific rivals. These deficits are rescued on ectopic expression of bond in the male reproductive system. A comparative analysis across six Drosophila species shows that the gain of a novel transcription initiation site is correlated with bond expression in the ejaculatory bulb, a primary site of male pheromone production. Taken together, these results indicate that modification of cis-regulatory elements and subsequent changes in gene expression pattern is one mechanism by which pheromone diversity arises

Reubens, M.C., Biller, M.D., Bedsole, S.E., Hopkins, L.T., Ables, E.T. and Christensen, T.W. (2015). Mcm10 is required for oogenesis and early embryogenesis in Drosophila. Mech Dev [Epub ahead of print]. PubMed ID: 26369283 Summary: Efficient replication of the genome and the establishment of endogenous chromatin states are processes that are essential to eukaryotic life. It is well documented that Mcm10 is intimately linked to both of these important biological processes; therefore, it is not surprising that Mcm10 is commonly misregulated in many human cancers. Most of the research regarding the biological roles of Mcm10 has been performed in single-cell or cell-free in-vitro systems. Though these systems are informative, they are unable to provide information on the cell-specific function of Mcm10 in the context of the tissue and organ systems that comprise multicellular eukaryotes. This study sought to identify the potential biological functions of Mcm10 in the context of a complex multicellular organism by analysis in Drosophila using three novel hypomorphic alleles. Observation of embryonic nuclear morphology and quantification of embryo hatch rates reveal that maternal loading of Mcm10 is required for embryonic nuclear stability and suggest a role for Mcm10 post zygotic transition. Contrary to the essential nature of Mcm10 depicted in the literature, it does not appear to be required for adult viability in Drosophila if embryonic requirements are met. Although not required for adult somatic viability, analysis of fecundity and ovarian morphology in mutant females suggest that Mcm10 plays a role in maintenance of the female germline. Taken together, these results demonstrate critical roles for Mcm10 during early embryogenesis, and mark the first data linking Mcm10 to female specific reproduction in multicellular eukaryotes.

Liu, G., Sanghavi, P., Bollinger, K. E., Perry, L., Marshall, B., Roon, P., Tanaka, T., Nakamura, A. and Gonsalvez, G. B. (2015). Efficient endocytic uptake and maturation in Drosophila oocytes requires Dynamitin/p50. Genetics 201(2):631-49. PubMed ID: 26265702 Summary: Dynactin is a multi-subunit complex that functions as a regulator of the Dynein motor. A central component of this complex is Dynamitin/p50 (Dmn). Dmn is required for endosome motility in mammalian cell lines. However, the extent to which Dmn participates in the sorting of cargo via the endosomal system is unknown. This study examined the endocytic role of Dmn using the Drosophila melanogaster oocyte as a model. Yolk proteins are internalized into the oocyte via clathrin-mediated endocytosis, trafficked through the endocytic pathway, and stored in condensed yolk granules. Oocytes that were depleted of Dmn contained fewer yolk granules than controls. In addition, these oocytes accumulated numerous endocytic intermediate structures. Particularly prominent were enlarged endosomes that were relatively devoid of yolk proteins. Ultrastructural and genetic analyses indicate that the endocytic intermediates are produced downstream of Rab5. Similar phenotypes were observed upon depleting Dynein heavy chain (Dhc) or Lis1. Dhc is the motor subunit of the Dynein complex and Lis1 is a regulator of Dynein activity. It is therefore proposed that Dmn performs its function in endocytosis via the Dynein motor. Consistent with a role for Dynein in endocytosis, the motor co-localized with the endocytic machinery at the oocyte cortex in an endocytosis-dependent manner. These results suggest a model whereby endocytic activity recruits Dynein to the oocyte cortex. The motor along with its regulators, Dynactin and Lis1, functions to ensure efficient endocytic uptake and maturation.

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