What's hot today:
Current papers in developmental biology and gene function


Monday, February 29th, 2016

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Ghosh, S., Tibbit, C. and Liu, J. L. (2016). Effective knockdown of Drosophila long non-coding RNAs by CRISPR interference. Nucleic Acids Res [Epub ahead of print]. PubMed ID: 26850642
Long non-coding RNAs (lncRNAs) have emerged as regulators of gene expression across metazoa. Interestingly, some lncRNAs function independently of their transcripts - the transcription of the lncRNA locus itself affects target genes. However, current methods of loss-of-function analysis are insufficient to address the role of lncRNA transcription from the transcript which has impeded analysis of their function. Using the minimal CRISPR interference (CRISPRi) system, this study showed that coexpression of the catalytically inactive Cas9 (dCas9) and guide RNAs targeting the endogenous roX locus in the Drosophila cells results in a robust and specific knockdown of roX1 and roX2 RNAs, thus eliminating the need for recruiting chromatin modifying proteins for effective gene silencing. Additionally, it was found that the human and Drosophila codon optimized dCas9 genes are functional and show similar transcription repressive activity. Finally, it was demonstrated that the minimal CRISPRi system suppresses roX transcription efficiently in vivo resulting in loss-of-function phenotype, thus validating the method for the first time in a multicelluar organism. This analysis expands the genetic toolkit available for interrogating lncRNA function in situ and is adaptable for targeting multiple genes across model organisms.

Romero-Soriano, V. and Garcia Guerreiro, M. P. (2016). Expression of the retrotransposon Helena reveals a complex pattern of TE deregulation in Drosophila hybrids. PLoS One 11: e0147903. PubMed ID: 26812285
Their mobilizing capacity of transposable elements (TEs) confers on them a high mutagenic potential, which must be strongly regulated to guarantee genome stability. In the Drosophila germline, a small RNA-mediated silencing system, the piRNA (Piwi-interacting RNA) pathway, is the main responsible TE regulating mechanism. During interspecific hybridization, genomic stress caused by the shock of two different genomes can lead to higher transposition rates. This study has characterized one of the mobilized TEs, the retrotransposon Helena, and used quantitative expression to assess whether its high transposition rates in hybrids are preceded by increased expression. To give more insight into changes in TE regulation in hybrids, Helena-specific piRNA populations of hybrids and parental species were analyzed. Helena expression is not globally altered in somatic tissues, but male and female gonads have different patterns of deregulation. In testes, Helena is repressed in F1, increasing then its expression up to parental values. This is linked with a mislocation of Helena transcripts along with an increase of their specific piRNA levels. Ovaries have additive levels of Helena expression, but the ping-pong cycle efficiency seems to be reduced in F1 hybrids. This could be at the origin of new Helena insertions in hybrids, which would be transmitted to F1 hybrid female progeny.

Jiang, F., Lu, F., Li, P., Liu, W., Zhao, L., Wang, Q., Cao, X., Zhang, L. and Zhang, Y. Q. (2016). Drosophila homolog of FMRP maintains genome integrity by interacting with Piwi. J Genet Genomics 43: 11-24. PubMed ID: 26842990
Fragile X syndrome (FraX), the most common form of inherited mental retardation, is caused by the absence of the evolutionally conserved fragile X mental retardation protein (FMRP). While neuronal functions of FMRP have been intensively studied for the last two decades, its role in non-neuronal cells remains poorly understood. Piwi, a key component of the Piwi-interacting RNA (piRNA) pathway, plays an essential role in germline development. This study report that similar to piwi, dfmr1, the Drosophila homolog of human FMR1, is required for transposon suppression in the germlines. Genetic analyses showed that dfmr1 and piwi act synergistically in heterochromatic silencing, and in inhibiting the differentiation of primordial germline cells and transposon expression. Northern analyses showed that roo piRNA expression levels are reduced in dfmr1 mutant ovaries, suggesting a role of dfmr1 in piRNA biogenesis. Biochemical analysis demonstrated a physical interaction between dFMRP and Piwi via their N-termini. Taken together, it is proposed that dFMRP cooperates with Piwi in maintaining genome integrity by regulating heterochromatic silencing in somatic cells and suppressing transposon activity via the piRNA pathway in germlines.

Qian, J., Tu, R., Yuan, L. and Xie, W. (2016). Intronic miR-932 targets the coding region of its host gene, Drosophila neuroligin2. Exp Cell Res [Epub ahead of print]. PubMed ID: 26844630
Despite great progress for two decades in microRNAs (miRNAs), the direct regulation of host gene by intragenic (mostly intronic) miRNA is conceptually plausible but evidence-limited. This study reports that intronic miR-932 could target its host gene via binding with coding sequence (CDS) region rather than regular 3'UTR. The conserved miR-932 is embedded in the fourth intron of Drosophila neuroligin2 (dnlg2), which encodes a synaptic cell adhesion molecule, DNlg2. In silico analysis predicted two putative miR-932 target sites locate in the CDS region of dnlg2 instead of regular 3'-UTR miRNA binding sites. Employing luciferase reporter assay, miR-932 was further proved to regulates expression of its host gene dnlg2 via the binding CDS region of dnlg2. Consistently, miR-932 downregulated expression of dnlg2 in S2 cell, and the repression of dnlg2 by miR-932 at both protein and RNA level. Furthermore, CDS-located site1 is dominant for regulating expression of host dnlg2 by miR-932. In addition to providing thorough examination of one intronic miRNA targeting the CDS region of its host gene, this genome-wide analysis indicated that nearly half of fruitfly and human intronic miRNAs may target their own host gene at coding region. This study would be valuable in elucidating the regulation of intronic miRNA on host gene, and provide new information about the biological context of their genomic arrangements and functions.

Sunday, February 28th

Hartley, P. S., Motamedchaboki, K., Bodmer, R. and Ocorr, K. (2016). SPARC-dependent cardiomyopathy in Drosophila. Circ Cardiovasc Genet [Epub ahead of print]. PubMed ID: 26839388
The Drosophila heart is an important model for studying the genetics underpinning mammalian cardiac function. The system comprises contractile cardiomyocytes, adjacent to which are pairs of highly endocytic pericardial nephrocytes that modulate cardiac function by uncharacterized mechanisms. This work aimed to identify circulating cardiomodulatory factors of potential relevance to humans using the Drosophila nephrocyte-cardiomyocyte system. A Kruppel-Like Factor 15 (dKlf15) loss-of-function strategy was used to ablate nephrocytes and then heart function and the hemolymph proteome were analysed. Ablation of nephrocytes led to a severe cardiomyopathy characterized by a lengthening of diastolic interval. Rendering adult nephrocytes dysfunctional by disrupting their endocytic function or temporally-conditional knock-down of dKlf15 led to a similar cardiomyopathy. Proteomics revealed that nephrocytes regulate the circulating levels of many secreted proteins, the most notable of which was the evolutionarily conserved matricellular protein SPARC (Secreted Protein Acidic and Rich in Cysteine), a protein involved in mammalian cardiac function. Finally, reducing SPARC gene dosage ameliorated the cardiomyopathy that developed in the absence of nephrocytes. The data implicate SPARC in the non-cell autonomous control of cardiac function in Drosophila and suggest that modulation of SPARC gene expression may ameliorate cardiac dysfunction in humans.
Oyallon, J., Vanzo, N., Krzemien, J., Morin-Poulard, I., Vincent, A. and Crozatier, M. (2016). Two independent functions of Collier/Early B Cell Factor in the control of Drosophila blood cell homeostasis. PLoS One 11: e0148978. PubMed ID: 26866694
Blood cell production in the Drosophila hematopoietic organ, the lymph gland, is controlled by intrinsic factors and extrinsic signals. Initial analysis of Collier/Early B Cell Factor function in the lymph gland revealed the role of the Posterior Signaling Center (PSC) in mounting a dedicated cellular immune response to wasp parasitism. Further, premature blood cell differentiation when PSC specification or signaling was impaired, led to assigning the PSC a role equivalent to the vertebrate hematopoietic niche. Collier is expressed in a core population of lymph gland progenitors and cell autonomously maintains this population. The PSC contributes to lymph gland homeostasis by regulating blood cell differentiation, rather than by maintaining core progenitors. In addition to PSC signaling, switching off Collier expression in progenitors is required for efficient immune response to parasitism. These data show that two independent sites of Collier/Early B Cell Factor expression, hematopoietic progenitors and the PSC, achieve control of hematopoiesis.

Hu, J., Jiao, D., Xu, Q., Ying, X., Liu, W., Chi, Q., Ye, Y., Li, X. and Cheng, L. (2016). Identification of proteasome subunit beta type 2 associated with deltamethrin detoxification in Drosophila Kc cells by cDNA microarray analysis and bioassay analyses. Gene [Epub ahead of print]. PubMed ID: 26850132
Insecticide deltamethrin resistance has presented a difficult obstacle for pest control and the resistance development is complex and associated with many genes. To better understand the possible molecular mechanisms involved in DM stress, in this study, cDNA microarray analysis was employed. 448 differentially expressed genes with at least a 2-fold expression difference were identified in Drosophila cells after DM exposure. Moreover, some genes were confirmed with qPCR, which yielded results consistent with the microarray analysis. Three members of the ubiquitin-proteasome system were significantly elevated in DM-stressed cells, suggesting that the ubiquitin-proteasome pathway may play an important role in DM detoxification. The proteasome β2 subunit (Prosβ2) is a member of 20S proteasome subunit family, which forms the proteolytic core of 26S proteasome. Whether Prosβ2 participates in DM detoxification requires further study. RNAi and heterologous expression were conducted to investigate the contribution of Prosβ2 in DM detoxification. The results revealed Prosβ2 knockdown significantly reduce the level of DM detoxification in RNAi-treated cells after 48h. Overexpression of Prosβ2 increased cellular viability. These detoxification results represent the first evidence that Prosβ2 plays a role in the detoxification of DM, which may provide new idea and target for studying the molecular mechanisms of insect resistance.

Mercer, S. W., La Fontaine, S., Warr, C. G. and Burke, R. (2016). Reduced glutathione biosynthesis in Drosophila melanogaster causes neuronal defects linked to copper deficiency. J Neurochem [Epub ahead of print]. PubMed ID: 26851457
Glutathione (GSH) is a tripeptide often considered to be the master antioxidant in cells. GSH plays an integral role in cellular redox regulation and is also known to have a role in mammalian copper homeostasis. In vitro evidence suggests that GSH is involved in copper uptake, sequestration and efflux. This study was undertaken to further investigate the roles that GSH plays in neuronal copper homeostasis in vivo, using the model organism Drosophila melanogaster. RNA interference-mediated knockdown of the Glutamate-cysteine ligase catalytic subunit gene (Gclc) that encodes the rate-limiting enzyme in GSH biosynthesis, was utilised to genetically deplete GSH levels. When Gclc was knocked down in all neurons, this caused lethality, which was partially rescued by copper supplementation and was exacerbated by additional knockdown of the copper uptake transporter Ctr1A, or overexpression of the copper efflux transporter ATP7. Furthermore, when Gclc was knocked down in a subset of neuropeptide-producing cells, this resulted in adult progeny with unexpanded wings, a phenotype previously associated with copper dyshomeostasis. In these cells, Gclc suppression caused a decrease in axon branching, a phenotype further enhanced by ATP7 overexpression. Therefore it is concluded that GSH may play an important role in regulating neuronal copper levels and that reduction in GSH may lead to functional copper deficiency in neurons in vivo.

Rosas-Arellano, A., Vasquez-Procopio, J., Gambis, A., Blowes, L. M., Steller, H., Mollereau, B. and Missirlis, F. (2016). Ferritin Assembly in Enterocytes of Drosophila melanogaster. Int J Mol Sci 17 [Epub ahead of print]. PubMed ID: 26861293
Ferritins are protein nanocages that accumulate inside their cavity thousands of oxidized iron atoms bound to oxygen and phosphates. Both characteristic types of eukaryotic ferritin subunits are present in secreted ferritins from insects, but here dimers between Ferritin 1 Heavy Chain Homolog (Fer1HCH) and Ferritin 2 Light Chain Homolog (Fer2LCH) are further stabilized by disulfide-bridge in the 24-subunit complex. This study addressed ferritin assembly and iron loading in vivo using novel transgenic strains of Drosophila melanogaster. Concentration was placed on the intestine, where the ferritin induction process can be controlled experimentally by dietary iron manipulation. The expression pattern of Fer2LCH-Gal4 lines were shown to recapitulate iron-dependent endogenous expression of the ferritin subunits; and these lines were used to drive expression from UAS-mCherry-Fer2LCH transgenes. The Gal4-mediated induction of mCherry-Fer2LCH subunits was too slow to effectively introduce them into newly formed ferritin complexes. Endogenous Fer2LCH and Fer1HCH assembled and stored excess dietary iron, instead. In contrast, when flies were genetically manipulated to co-express Fer2LCH and mCherry-Fer2LCH simultaneously, both subunits were incorporated with Fer1HCH in iron-loaded ferritin complexes. This study provides fresh evidence that, in insects, ferritin assembly and iron loading in vivo are tightly regulated.

Kashio, S., Obata, F., Zhang, L., Katsuyama, T., Chihara, T. and Miura, M. (2016). Tissue nonautonomous effects of fat body methionine metabolism on imaginal disc repair in Drosophila. Proc Natl Acad Sci U S A [Epub ahead of print]. PubMed ID: 26831070
Regulatory mechanisms for tissue repair and regeneration within damaged tissue have been extensively studied. However, the systemic regulation of tissue repair remains poorly understood. To elucidate tissue nonautonomous control of repair process, it is essential to induce local damage, independent of genetic manipulations in uninjured parts of the body. This study developed a system in Drosophila for spatiotemporal tissue injury using a temperature-sensitive form of diphtheria toxin A domain driven by the Q system to study factors contributing to imaginal disc repair. Using this technique, it was demonstrated that methionine metabolism in the fat body, a counterpart of mammalian liver and adipose tissue, supports the repair processes of wing discs. Local injury to wing discs decreases methionine and S-adenosylmethionine, whereas it increases S-adenosylhomocysteine in the fat body. Fat body-specific genetic manipulation of methionine metabolism results in defective disc repair but does not affect normal wing development. The data indicate the contribution of tissue interactions to tissue repair in Drosophila, as local damage to wing discs influences fat body metabolism, and proper control of methionine metabolism in the fat body, in turn, affects wing regeneration.

Regan, J.C., Khericha, M., Dobson, A.J., Bolukbasi, E., Rattanavirotkul, N. and Partridge, L. (2016). Sex difference in pathology of the ageing gut mediates the greater response of female lifespan to dietary restriction. Elife [Epub ahead of print]. PubMed ID: 26878754
Women live on average longer than men, but have greater levels of late-life morbidity. This study uncovers a substantial sex difference in the pathology of the ageing gut in Drosophila. The intestinal epithelium of the ageing female undergoes major deterioration, driven by intestinal stem cell (ISC) division, while lower ISC activity in males associates with delay or absence of pathology, and better barrier function, even at old ages. Males succumb to intestinal challenges to which females are resistant, associated with fewer proliferating ISCs, suggesting a trade-off between highly active repair mechanisms and late-life pathology in females. Dietary restriction reduces gut pathology in ageing females, and extends female lifespan more than male. By genetic sex reversal of a specific gut region, female-like ageing pathologies were induced in males, associated with decreased lifespan, but also with a greater increase in longevity in response to dietary restriction.

Park, J. H., Chen, J., Jang, S., Ahn, T. J., Kang, K., Choi, M. S. and Kwon, J. Y. (2016). A subset of enteroendocrine cells is activated by amino acids in the Drosophila midgut. FEBS Lett [Epub ahead of print]. PubMed ID: 26801353
The intestine is involved in digestion and absorption, as well as the regulation of metabolism upon sensation of the internal intestinal environment. Enteroendocrine cells are thought to mediate these internal intestinal chemosensory functions. Using the CaLexA (calcium-dependent nuclear import of LexA) method, this study examined the enteroendocrine cell populations that are activated when flies are subjected to various dietary conditions such as starvation, sugar, high fat, protein or pathogen exposure. A specific subpopulation of enteroendocrine cells in the posterior midgut which express Diuretic hormone 31 and tachykinin are activated by the presence of proteins and amino acids.

Saturday, February 27th

Romero-Soriano, V., Burlet, N., Vela, D., Fontdevila, A., Vieira, C. and Garcia Guerreiro, M.P. (2016). Drosophila females undergo genome expansion after interspecific hybridization. Genome Biol Evol [Epub ahead of print]. PubMed ID: 26872773
Genome size (or C-value) can present a wide range of values among eukaryotes. This variation has been attributed to differences in the amplification and deletion of different non-coding repetitive sequences, particularly transposable elements (TEs). TEs can be activated under different stress conditions such as interspecific hybridization events, as described for several species of animals and plants. These massive transposition episodes can lead to considerable genome expansions that could ultimately be involved in hybrid speciation processes. This study describes the effects of hybridization and introgression on genome size of Drosophila hybrids. The genome size of two close Drosophila species, D. buzzatii and D. koepferae, their F1 offspring and the offspring from three generations of backcrossed hybrids, were measured; where mobilization of up to 28 different TEs was previously detected. It was found that hybrid females indeed present a genome expansion, especially in the first backcross, which could likely be explained by transposition events. Hybrid males, which exhibit more variable C-values among individuals of the same generation, do not present an increased genome size. Thus, the impact of hybridization on genome size can be detected through flow cytometry and is sex-dependent.

Lewis, S. H., Salmela, H. and Obbard, D. J. (2016). Duplication and diversification of Dipteran Argonaute genes, and the evolutionary divergence of Piwi and Aubergine. Genome Biol Evo [Epub ahead of print]. PubMed ID: 26868596
Genetic studies of Drosophila melanogaster have provided a paradigm for RNAi in arthropods, in which the miRNA and antiviral pathways are each mediated by a single Argonaute (Ago1 and Ago2) and germline suppression of transposable elements is mediated by a trio of Piwi-subfamily Argonaute proteins (Ago3, Aub and Piwi). Without a suitable evolutionary context, deviations from this can be interpreted as derived or idiosyncratic. This study analysed the evolution of Argonaute genes across the genomes and transcriptomes of 86 Dipteran species, showing that variation in copy number can occur rapidly, and that there is constant flux in some RNAi mechanisms. The lability of the RNAi pathways is illustrated by the divergence of Aub and Piwi (182-156 million years ago), independent origins of multiple Piwi-family genes in Aedes mosquitoes (less than 25mya), and the recent duplications of Ago2 and Ago3 in the tsetse fly Glossina morsitans. In each case the tissue-specificity of these genes has altered, suggesting functional divergence or innovation, and consistent with the action of dynamic selection pressures across the Argonaute gene family. There are large differences in evolutionary rates and gene turnover between pathways, and paralogues of Ago2, Ago3 and Piwi/Aub show contrasting rates of evolution after duplication. This suggests that Argonautes undergo frequent evolutionary expansions that facilitate functional divergence.

Sato, M. P., Makino, T. and Kawata, M. (2016). Natural selection in a population of Drosophila melanogaster explained by changes in gene expression caused by sequence variation in core promoter regions. BMC Evol Biol 16: 35. PubMed ID: 26860869
This study analyzed sequence variations in core promoter regions, which are critical regions for gene regulation in higher eukaryotes, in a natural population of Drosophila melanogaster; core promoter sequence variations associated with differences in gene expression levels subjected to natural selection were identified. Among the core promoter regions whose sequence variation could change transcription factor binding sites and explain differences in expression levels, three core promoter regions were detected as candidates associated with purifying selection or selective sweep and seven as candidates associated with balancing selection, excluding the possibility of linkage between these regions and core promoter regions. CHKov1, a reverse transcriptase that confers resistance to the sigma virus and related insecticides, was identified as core promoter regions that has been subject to selective sweep, although it could not be denied that selection for variation in core promoter regions was due to linked single nucleotide polymorphisms in the regulatory region outside core promoter regions. Nucleotide changes in core promoter regions of CHKov1 caused the loss of two basal transcription factor binding sites and acquisition of one transcription factor binding site, resulting in decreased gene expression levels. Of nine core promoter regions regions associated with balancing selection, brat, and CG9044 are associated with neuromuscular junction development, and Nmda1 are associated with learning, behavioral plasticity, and memory. Diversity of neural and behavioral traits may have been maintained by balancing selection. These results revealed the evolutionary process occurring by natural selection for differences in gene expression levels caused by sequence variation in core promoter regions in a natural population. The sequences of core promoter regions were diverse even within the population, possibly providing a source for natural selection.

Lynch, Z. R., Schlenke, T. A. and de Roode, J. C. (2016). Evolution of behavioral and cellular defenses against parasitoid wasps in the Drosophila melanogaster subgroup. J Evol Biol [Epub ahead of print]. PubMed ID: 26859227
It may be intuitive to predict that host immune systems will evolve to counter a broad range of potential challenges through simultaneous investment in multiple defenses. However, this would require diversion of resources from other traits, such as growth, survival, and fecundity. Therefore, ecological immunology theory predicts that hosts will specialize in only a subset of possible defenses. This hypothesis was tested through a comparative study of a cellular immune response and a putative behavioral defense used by eight fruit fly species against two parasitoid wasp species (one generalist and one specialist). Fly larvae can survive infection by melanotically encapsulating wasp eggs and female flies can potentially reduce infection rates in their offspring by laying fewer eggs when wasps are present. The strengths of both defenses varied significantly but were not negatively correlated across the chosen host species; thus, no evidence was found for a trade-off between behavioral and cellular immunity. Instead, cellular defenses were significantly weaker against the generalist wasp, whereas behavioral defenses were similar in strength against both wasps and positively correlated between wasps. The adaptive significance of wasp-induced oviposition reduction behavior was investigated by testing whether wasp-exposed parents produce offspring with stronger cellular defenses, but no support was found for this hypothesis. The sensory basis of this behavior was further investigated by testing mutants deficient in either vision or olfaction, both of which failed to reduce their oviposition rates in the presence of wasps, suggesting that both senses are necessary for detecting and responding to wasps.

Friday, February 26th

Mukherjee, S., Tucker-Burden, C., Zhang, C., Moberg, K., Read, R., Hadjipanayis, C. and Brat, D.J. (2016). Drosophila Brat and human ortholog TRIM3 maintain stem cell equilibrium and suppress brain tumorigenesis by attenuating Notch nuclear transport. Cancer Res [Epub ahead of print]. PubMed ID: 26893479
Cancer stem cells exert enormous influence on neoplastic behavior, in part by governing asymmetric cell division and the balance between self-renewal and multipotent differentiation. Mutation of a single gene in Drosophila, Brain Tumor (Brat), leads to disrupted asymmetric cell division resulting in dramatic neoplastic proliferation of neuroblasts and massive larval brain overgrowth. To uncover mechanisms relevant to deregulated cell division in human glioma stem cells, this study developed a novel adult Drosophila brain tumor model using brat-RNAi driven by the neuroblast specific promoter inscuteable. Suppressing Brat in this population leads to accumulation of actively proliferating neuroblasts and a lethal brain tumor phenotype. brat-RNAi causes upregulation of Notch signaling, a node critical for self-renewal, by increasing protein expression and enhancing nuclear transport of NICD. In human glioblastoma, it was demonstrated that the human ortholog of Drosophila Brat, TRIM3, similarly suppresses NOTCH1 signaling and markedly attenuates the stem cell component. TRIM3 was also found to suppress nuclear transport of active NOTCH1 (NICD) in glioblastoma, and these effects are mediated by direct binding of TRIM3 to the Importin complex. Together, these results support a novel role for Brat/TRIM3 in maintaining stem cell equilibrium and suppressing tumor growth by regulating NICD nuclear transport.

Cate, S., Gajendra, S., Alsbury, S., Raabe, T., Tear, G. and Mitchell, K.J. (2016). Mushroom body defect is required in parallel to Netrin for midline axon guidance in Drosophila. Development [Epub ahead of print]. PubMed ID: 26893348
The outgrowth of many neurons within the central nervous system is initially directed towards or away from the cells lying at the midline. Recent genetic evidence suggests that a simple model of differential sensitivity to the conserved Netrin attractants and Slit repellents is not sufficient to explain the guidance of all axons at the midline. In the Drosophila embryonic ventral nerve cord, many axons still cross the midline in the absence of the Netrin genes or their receptor frazzled. This study shows that mutation of mushroom body defect (mud) dramatically enhances the phenotype of Netrin or frazzled mutants, resulting in many more axons failing to cross the midline, though mutations in mud alone have little effect. This suggests that mud, which encodes a microtubule-binding coiled-coil protein homologous to NuMA and Lin-5, is an essential component of a Netrin-independent pathway that acts in parallel to promote midline crossing. This novel role in axon guidance is independent of Mud's previously described role in neural precursor development. These studies identify a parallel pathway controlling midline guidance in Drosophila and highlight a novel role for Mud potentially acting downstream of Frizzled to aid axon guidance.

Meltzer, S., Yadav, S., Lee, J., Soba, P., Younger, S. H., Jin, P., Zhang, W., Parrish, J., Jan, L. Y. and Jan, Y. N. (2016). Epidermis-derived Semaphorin promotes dendrite self-avoidance by regulating dendrite-substrate adhesion in Drosophila sensory neurons. Neuron 89: 741-755. PubMed ID: 26853303
Precise patterning of dendritic arbors is critical for the wiring and function of neural circuits. Dendrite-extracellular matrix (ECM) adhesion ensures that the dendrites of Drosophila dendritic arborization (da) sensory neurons are properly restricted in a 2D space, and thereby facilitates contact-mediated dendritic self-avoidance and tiling. However, the mechanisms regulating dendrite-ECM adhesion in vivo are poorly understood. This study shows that mutations in the semaphorin ligand sema-2b lead to a dramatic increase in self-crossing of dendrites due to defects in dendrite-ECM adhesion, resulting in a failure to confine dendrites to a 2D plane. Furthermore, Sema-2b is secreted from the epidermis and signals through the Plexin B receptor in neighboring neurons. Importantly, it was found that Sema-2b/PlexB genetically and physically interacts with TORC2 complex, Tricornered (Trc) kinase, and integrins. These results reveal a novel role for semaphorins in dendrite patterning and illustrate how epidermal-derived cues regulate neural circuit assembly.

Ziegler, A. B., et al. (2016). The amino acid transporter JhI-21 coevolves with glutamate receptors, impacts NMJ physiology, and influences locomotor activity in Drosophila larvae. Sci Rep 6: 19692. PubMed ID: 26805723
Changes in synaptic physiology underlie neuronal network plasticity and behavioral phenomena, which are adjusted during development. The Drosophila larval glutamatergic neuromuscular junction (NMJ) represents a powerful synaptic model to investigate factors impacting these processes. Amino acids such as glutamate have been shown to regulate Drosophila NMJ physiology by modulating the clustering of postsynaptic glutamate receptors and thereby regulating the strength of signal transmission from the motor neuron to the muscle cell. This study used Evolutionary Rate Covariation (ERC), a recently developed bioinformatic tool, to identify amino acid transporters impacting glutmatergic signal transmission. This screen identified ten proteins co-evolving with NMJ glutamate receptors. One candidate transporter, the SLC7 (Solute Carrier) transporter family member JhI-21 (Juvenile hormone Inducible-21), which is expressed in Drosophila larval motor neurons, was selected for further study. JhI-21 was shown to suppress postsynaptic muscle glutamate receptor abundance, and JhI-21 expression in motor neurons regulates larval crawling behavior in a developmental stage-specific manner.

Serbe, E., Meier, M., Leonhardt, A. and Borst, A. (2016). Comprehensive characterization of the major presynaptic elements to the Drosophila OFF motion detector. Neuron 89: 829-841. PubMed ID: 26853306
Estimating motion is a fundamental task for the visual system of sighted animals. In the Drosophila optic lobe, direction-selective T4 and T5 cells respond to moving brightness increments (ON) and decrements (OFF), respectively. Current algorithmic models of the circuit are based on the interaction of two differentially filtered signals. However, electron microscopy studies have shown that T5 cells receive their major input from four classes of neurons: Tm1, Tm2, Tm4, and Tm9. Using two-photon calcium imaging, this study demonstrates that T5 is the first direction-selective stage within the OFF pathway. The four cells provide an array of spatiotemporal filters to T5. Silencing their synaptic output in various combinations, it was found that all input elements are involved in OFF motion detection to varying degrees. This comprehensive survey challenges the simplified view of how neural systems compute the direction of motion and suggests that an intricate interplay of many signals results in direction selectivity.

Loncle, N., Agromayor, M., Martin-Serrano, J. and Williams, D. W. (2015). An ESCRT module is required for neuron pruning. Sci Rep 5: 8461. PubMed ID: 25676218
Neural circuits are refined by both functional and structural changes. Structural remodeling by large-scale pruning occurs where relatively long neuronal branches are cut away from their parent neuron and removed by local degeneration. Until now, the molecular mechanisms executing such branch severing events have remained poorly understood. This study reveal a role for the Endosomal Sorting Complex Required for Transport (ESCRT) machinery during neuronal remodeling. The data show that a specific ESCRT pruning module, including members of the ESCRT-I and ESCRT-III complexes, but not ESCRT-0 or ESCRT-II, are required for the neurite scission event during pruning. Furthermore it was shown that this ESCRT module requires a direct, in vivo, interaction between Shrub/CHMP4B and the accessory protein Myopic/HD-PTP.

Thursday, February 25th

Long, H., Yoshikawa, S. and Thomas, J. B. (2016). Equivalent activities of repulsive axon guidance receptors. J Neurosci 36: 1140-1150. PubMed ID: 26818503
Receptors on the growth cone at the leading edge of elongating axons play critical guidance roles by recognizing cues via their extracellular domains and transducing signals via their intracellular domains, resulting in changes in direction of growth. An important concept to have emerged in the axon guidance field is the importance of repulsion as a major guidance mechanism. Given the number and variety of different repulsive receptors, it is generally thought that there are likely to be qualitative differences in the signals they transduce. However, the nature of these possible differences is unknown. By creating chimeras using the extracellular and intracellular domains of three different Drosophila repulsive receptors, Unc5, Roundabout (Robo), and Derailed (Drl) and expressing them in defined cells within the embryonic nervous system, the responses elicited by their intracellular domains were examined systematically. Surprisingly, no qualitative differences were found in growth cone response or axon growth, suggesting that, despite their highly diverged sequences, each intracellular domain elicits repulsion via a common pathway. In terms of the signaling pathway(s) used by the repulsive receptors, mutations in the guanine nucleotide exchange factor Trio strongly enhance the repulsive activity of all three intracellular domains, suggesting that repulsion by Unc5, Robo, and Drl, and perhaps repulsion in general, involves Trio activity.

Richards, G. S. and Rentzsch, F. (2015). Regulation of Nematostella neural progenitors by SoxB, Notch and bHLH genes. Development 142: 3332-3342. PubMed ID: 26443634
Notch signalling, SoxB (Drosophila SoxNeuro and Dichaete) and Group A bHLH 'proneural' genes are conserved regulators of the neurogenic program in many bilaterians. However, the ancestry of their functions and interactions is not well understood. This study addresses this question in the sea anemone Nematostella vectensis, a representative of the Cnidaria, the sister clade to the Bilateria. The SoxB orthologue NvSoxB2 is expressed in neural progenitor cells (NPCs) in Nematostella and promotes the development of both neurons and nematocytes. Inhibition of Notch signalling increases the numbers of both neurons and nematocytes, as well as increasing the number of NvSoxB2-expressing cells. This suggests that Notch restricts neurogenesis by limiting the generation of NPCs. Then NvAth-like (Atonal/Neurogenin family) was characterized as a positive regulator of neurogenesis that is co-expressed with NvSoxB2 in a subset of dividing NPCs, while it was found that NvAshA (Achaete-scute family) and NvSoxBsup>2 are co-expressed in non-dividing cells only. Reciprocal knockdown experiments reveal a mutual requirement for NvSoxBsup>2 and NvAth-like in neural differentiation; however, the primary expression of each gene is independent of the other. Together, these data demonstrate that Notch signalling and NvSoxBsup>2 regulate Nematostella neural progenitors via parallel yet interacting mechanisms; with different aspects of these interactions being shared with Drosophila and/or vertebrate neurogenesis.

Quan, X. J., Yuan, L., Tiberi, L., Claeys, A., De Geest, N., Yan, J., van der Kant, R., Xie, W. R., Klisch, T. J., Shymkowitz, J., Rousseau, F., Bollen, M., Beullens, M., Zoghbi, H. Y., Vanderhaeghen, P. and Hassan, B. A. (2016). Post-translational control of the temporal dynamics of transcription factor activity regulates neurogenesis. Cell 164: 460-475. PubMed ID: 26824657
Neurogenesis is initiated by the transient expression of the highly conserved proneural proteins, bHLH transcriptional regulators. This study discovered a conserved post-translational switch governing the duration of proneural protein activity that is required for proper neuronal development. Phosphorylation of a single Serine at the same position in Scute and Atonal proneural proteins governs the transition from active to inactive forms by regulating DNA binding. The equivalent Neurogenin2 Threonine also regulates DNA binding and proneural activity in the developing mammalian neocortex. Using genome editing in Drosophila, this study showed that Atonal outlives its mRNA but is inactivated by phosphorylation. Inhibiting the phosphorylation of the conserved proneural Serine causes quantitative changes in expression dynamics and target gene expression resulting in neuronal number and fate defects. Strikingly, even a subtle change from Serine to Threonine appears to shift the duration of Atonal activity in vivo, resulting in neuronal fate defects.

Halachmi, N., Nachman, A. and Salzberg, A. (2016). A newly identified type of attachment cell is critical for normal patterning of chordotonal neurons. Dev Biol [Epub ahead of print]. PubMed ID: 26794680
This work describes unknown aspects of chordotonal organ (ChO) morphogenesis revealed in post-embryonic stages through the use of new fluorescently labeled markers. Towards the end of embryogenesis a hitherto unnoticed phase of cell migration commences in which the cap cells of the ventral ChOs elongate and migrate towards their prospective attachment sites. This migration and consequent cell attachment generates a continuous zigzag line of proprioceptors, stretching from the ventral midline to a dorsolateral position in each abdominal segment. The observation that the cap cell of the ventral-most ChO attaches to a large tendon cell near the midline provides the first evidence for a direct physical connection between the contractile and proprioceptive systems in Drosophila. This analysis has also provided an answer to a longstanding enigma that is what anchors the neurons of the ligamentless ventral ChOs on their axonal side. A new type of ChO attachment cell was identified that binds to the scolopale cells of these organs, thus behaving like a ligament cell, but on the other hand exhibits all the typical features of a ChO attachment cell and is critical for the correct anchoring of these organs.

Wednesday, February 24th

Nall, A.H., Shakhmantsir, I., Cichewicz, K., Birman, S., Hirsh, J. and Sehgal, A. (2016). Caffeine promotes wakefulness via dopamine signaling in Drosophila. Sci Rep 6: 20938. PubMed ID: 26868675
Caffeine is the most widely-consumed psychoactive drug in the world, but the understanding of how caffeine affects brains is relatively incomplete. Most studies focus on effects of caffeine on adenosine receptors, but there is evidence for other, more complex mechanisms. In the fruit fly Drosophila melanogaster, which shows a robust diurnal pattern of sleep/wake activity, caffeine reduces nighttime sleep behavior independently of the one known adenosine receptor. This study shows that dopamine is required for the wake-promoting effect of caffeine in the fly, and that caffeine likely acts presynaptically to increase dopamine signaling. A cluster of neurons, the paired anterior medial (PAM) cluster of dopaminergic neurons, were identified as the ones relevant for the caffeine response. PAM neurons show increased activity following caffeine administration, and promote wake when activated. Also, inhibition of these neurons abrogates sleep suppression by caffeine. While previous studies have focused on adenosine-receptor mediated mechanisms for caffeine action, this study identifies a role for dopaminergic neurons in the arousal-promoting effect of caffeine.

Germain, M., Blanchet, S., Loyau, A. and É, D. (2016). Mate-choice copying in Drosophila melanogaster: Impact of demonstration conditions and male-male competition. Behav Processes [Epub ahead of print]. PubMed ID: 26851455
Individuals of many species, including invertebrates, have been shown to use social information in mate choice, notably by extracting information from the mating performance of opposite sex conspecifics, a process called 'mate-choice copying' (MCC). Four experiments with Drosophila melanogaster were performed to investigate two aspects of MCC methodology: whether (1) providing positive and negative social information simultaneously or sequentially during the demonstration phase of the protocol, and (2) male-male competition during the mate-choice test, affect MCC. The simultaneous provision of positive and negative information during demonstrations were found to be hampered female MCC performance, compared to the sequential provision of information. This can be interpreted in two alternative, yet not exclusive, ways: (1) attentional mechanisms may restrict the focus of the brain to one source of information at a time, and/or (2) the shorter duration of demonstrations in the simultaneous protocol may have not permitted full social learning use and may explain the non-detection of MCC in that protocol. Moreover, no significant effect was detected of male-male competition on female choice. This study thus provides further evidence for MCC in D. melanogaster and expands on the necessary methodology for detailed studies.

Das, A., Holmes, T. C. and Sheeba, V. (2016). dTRPA1 in Non-circadian Neurons Modulates Temperature-Dependent Rhythmic Activity in Drosophila melanogaster. J Biol Rhythms [Epub ahead of print]. PubMed ID: 26868037
In fruit flies Drosophila melanogaster, environmental cycles of light and temperature are known to influence behavioral rhythms through dedicated sensory receptors. But the thermosensory pathways and molecular receptors by which thermal cycles modulate locomotor activity rhythms remain unclear. This study reports that neurons expressing warmth-activated ion channel Drosophila Transient Receptor Potential-A1 (dTRPA1) modulate distinct aspects of the rhythmic activity/rest rhythm in a light-dependent manner. Under light/dark (LD) cycles paired with constantly warm ambient conditions, flies deficient in dTRPA1 expression are unable to phase morning and evening activity bouts appropriately. Correspondingly, it was shown that electrical activity of a few neurons targeted by the dTRPA1SH-GAL4 driver modulates temperature-dependent phasing of activity/rest rhythm under LD cycles. The expression of dTRPA1 also affects behavior responses to temperature cycles combined with constant dark (DD) or light (LL) conditions. The mid-day 'siesta' exhibited by flies under temperature cycles in DD is dependent on dTRPA1 expression in a small number of neurons that include thermosensory anterior cell neurons. Although a small subset of circadian pacemaker neurons may express dTRPA1, it was shown that CRY-negative dTRPA1SH-GAL4 driven neurons are critical for the suppression of mid-thermophase activity, thus enabling flies to exhibit siesta. In contrast to temperature cycles in DD, under LL, dTRPA1 is not required for exhibiting siesta but is important for phasing of evening peak. These studies show that activity/rest rhythms are modulated in a temperature-dependent manner via signals from dTRPA1SH-GAL4 driven neurons. Taken together, these results emphasize the differential influence of thermoreceptors on rhythmic behavior in fruit flies in coordination with light inputs.

Fournier-Level, A., Neumann-Mondlak, A., Good, R. T., Green, L. M., Schmidt, J. M. and Robin, C. (2016). Behavioral response to combined insecticide and temperature stress in natural populations of Drosophila melanogaster. J Evol Biol. PubMed ID: 26864706
Insecticide resistance evolves extremely rapidly, providing an illuminating model for the study of adaptation. With climate change reshaping species distribution, pest and disease vector control needs rethinking to include the effects of environmental variation and insect stress physiology. This study assessed how both long term adaptation of populations to temperature and immediate temperature variation affects the genetic architecture of DDT insecticide response in Drosophila melanogaster. Mortality assays and behavioral assays based on continuous activity monitoring were used to assess the interaction between DDT and temperature on three field-derived populations from climate extremes (Raleigh for warm temperate, Tasmania for cold oceanic and Queensland for hot tropical). The Raleigh population showed the highest mortality to DDT whereas the Queensland population, epicentre for derived alleles of the resistance gene Cyp6g1, showed the lowest. Interaction between insecticide and temperature strongly affected mortality, particularly for the Tasmanian population. Activity profiles analyzed using self-organizing maps show the insecticide promoted an early response while elevated temperature promoted a later response. These distinctive early or later activity phases revealed similar responses to temperature and DDT dose alone but with more or less genetic variance depending on the population. This change in genetic variance among populations suggests that selection particularly depleted genetic variance for DDT response in the Queensland population. Finally, despite similar (co)variation between traits in benign conditions, the genetic responses across population differed under stressful conditions. This showed how stress-responsive genetic variation only reveals itself in specific conditions and thereby escapes potential trade-offs in benign environments.

Teseo, S., Veerus, L., Moreno, C. and Mery, F. (2016). Sexual harassment induces a temporary fitness cost but does not constrain the acquisition of environmental information in fruit flies. Biol Lett 12 [Epub ahead of print]. PubMed ID: 26763219
Across animals, sexual harassment induces fitness costs for females and males. However, little is known about the cognitive costs involved, i.e. whether it constrains learning processes, which could ultimately affect an individual's fitness. This study evaluated the acquisition of environmental information in groups of fruit flies challenged with various levels of male sexual harassment. Although high sexual harassment induces a temporary fitness cost for females, all fly groups of both sexes exhibit similar levels of learning. This suggests that, in fruit flies, the fitness benefits of acquiring environmental information are not affected by the fitness costs of sexual harassment, and that selection may favour cognition even in unfavourable social contexts. This study provides novel insights into the relationship between sexual conflicts and cognition and the evolution of female counterstrategies against male sexual harassment.

Coen, P., Xie, M., Clemens, J. and Murthy, M. (2016). Sensorimotor transformations underlying variability in song intensity during Drosophila courtship. Neuron 89: 629-644. PubMed ID: 26844835
Diverse animal species, from insects to humans, utilize acoustic signals for communication. Studies of the neural basis for song or speech production have focused almost exclusively on the generation of spectral and temporal patterns, but animals can also adjust acoustic signal intensity when communicating. For example, humans naturally regulate the loudness of speech in accord with a visual estimate of receiver distance. The underlying mechanisms for this ability remain uncharacterized in any system. This study shows that Drosophila males modulate courtship song amplitude with female distance, and each stage was examined of the sensorimotor transformation underlying this behavior, from the detection of particular visual stimulus features and the timescales of sensory processing to the modulation of neural and muscle activity that generates song. The results demonstrate an unanticipated level of control in insect acoustic communication and uncover novel computations and mechanisms underlying the regulation of acoustic signal intensity.

Tuesday, February 23

Suijkerbuijk, S. J., Kolahgar, G., Kucinski, I. and Piddini, E. (2016). Cell competition drives the growth of intestinal adenomas in Drosophila. Curr Biol [Epub ahead of print]. PubMed ID: 26853366
Tumor-host interactions play an increasingly recognized role in modulating tumor growth. Thus, understanding the nature and impact of this complex bidirectional communication is key to identifying successful anti-cancer strategies. It has been proposed that tumor cells compete with and kill neighboring host tissue to clear space that they can expand into; however, this has not been demonstrated experimentally. This study used the adult fly intestine to investigate the existence and characterize the role of competitive tumor-host interactions. APC-/--driven intestinal adenomas were shown to compete with and kill surrounding cells, causing host tissue attrition. Importantly, this study demonstrates that preventing cell competition, by expressing apoptosis inhibitors, restores host tissue growth and contains adenoma expansion, indicating that cell competition is essential for tumor growth. It was further shown that JNK signaling is activated inside the tumor and in nearby tissue and is required for both tumor growth and cell competition. Lastly, it was found that APC-/- cells display higher Yorkie (YAP) activity than host cells and that this promotes tumor growth, in part via cell competition. Crucially, it was found that relative, rather than absolute, Hippo activity determines adenoma growth. Overall, these data indicate that the intrinsic over-proliferative capacity of APC-/- cells is not uncontrolled and can be constrained by host tissues if cell competition is inhibited, suggesting novel possible therapeutic approaches.

Bielmeier, C., Alt, S., Weichselberger, V., La Fortezza, M., Harz, H., Julicher, F., Salbreux, G. and Classen, A. K. (2016). Interface contractility between differently fated cells drives cell elimination and cyst formation. Curr Biol [Epub ahead of print]. PubMed ID: 26853359
Although cellular tumor-suppression mechanisms are widely studied, little is known about mechanisms that act at the level of tissues to suppress the occurrence of aberrant cells in epithelia. This study found that ectopic expression of transcription factors that specify cell fates causes abnormal epithelial cysts in Drosophila imaginal discs. Cysts do not form cell autonomously but result from the juxtaposition of two cell populations with divergent fates. Juxtaposition of wild-type and aberrantly specified cells induces enrichment of actomyosin at their entire shared interface, both at adherens junctions as well as along basolateral interfaces. Experimental validation of 3D vertex model simulations demonstrates that enhanced interface contractility is sufficient to explain many morphogenetic behaviors, which depend on cell cluster size. These range from cyst formation by intermediate-sized clusters to segregation of large cell populations by formation of smooth boundaries or apical constriction in small groups of cells. In addition, single cells experiencing lateral interface contractility were found to be eliminated from tissues by apoptosis. Cysts, which disrupt epithelial continuity, form when elimination of single, aberrantly specified cells fails and cells proliferate to intermediate cell cluster sizes. Thus, increased interface contractility functions as error correction mechanism eliminating single aberrant cells from tissues, but failure leads to the formation of large, potentially disease-promoting cysts.

Liu, B., Zheng, Y., Yin, F., Yu, J., Silverman, N. and Pan, D. (2016). Toll receptor-mediated Hippo signaling controls innate immunity in Drosophila. Cell 164: 406-419. PubMed ID: 26824654
The Hippo signaling pathway functions through Yorkie to control tissue growth and homeostasis. How this pathway regulates non-developmental processes remains largely unexplored. This study reports an essential role for Hippo signaling in innate immunity whereby Yorkie directly regulates the transcription of the Drosophila IκB homolog, Cactus, in Toll receptor-mediated antimicrobial response. Loss of Hippo pathway tumor suppressors or activation of Yorkie in fat bodies, the Drosophila immune organ, leads to elevated cactus mRNA levels, decreased expression of antimicrobial peptides, and vulnerability to infection by Gram-positive bacteria. Furthermore, Gram-positive bacteria acutely activate Hippo-Yorkie signaling in fat bodies via the Toll-Myd88-Pelle cascade through Pelle-mediated phosphorylation and degradation of the Cka subunit of the Hippo-inhibitory STRIPAK PP2A complex. These results elucidate a Toll-mediated Hippo signaling pathway in antimicrobial response, highlight the importance of regulating IκB/Cactus transcription in innate immunity, and identify Gram-positive bacteria as extracellular stimuli of Hippo signaling under physiological settings. 

Herteleer, L., Zwarts, L., Hens, K., Forero, D., Del-Favero, J. and Callaerts, P. (2016). Mood stabilizing drugs regulate transcription of immune, neuronal and metabolic pathway genes in Drosophila. Psychopharmacology (Berl) [Epub ahead of print]. PubMed ID: 26852229
Lithium and valproate (VPA) are drugs used in the management of bipolar disorder. Even though they reportedly act on various pathways, the transcriptional targets relevant for disease mechanism and therapeutic effect remain unclear. This study used Drosophila culture cells and adult flies to analyze the transcriptional effects of lithium and VPA and define mechanistic pathways. Transcriptional profiles were determined for Drosophila S2-cells and adult fly heads following lithium or VPA treatment. Treatment of cultured cells and adult flies with lithium and VPA induces transcriptional responses in genes with similar ontology, with as most prominent immune response, neuronal development, neuronal function, and metabolism. The following is concluded (1) Transcriptional effects of lithium and VPA in Drosophila S2 cells and heads show significant overlap. (2) The overlap between transcriptional alterations in peripheral versus neuronal cells at the single gene level is negligible, but at the gene ontology and pathway level considerable overlap can be found. (3) Lithium and VPA act on evolutionarily conserved pathways in Drosophila and mammalian models.

Monday, February 22nd

Mavor, L. M., Miao, H., Zuo, Z., Holly, R. M., Xie, Y., Loerke, D. and Blankenship, J. T. (2016). Rab8 directs furrow ingression and membrane addition during epithelial formation in Drosophila melanogaster. Development [Epub ahead of print]. PubMed ID: 26839362
One of the most fundamental changes in cell morphology is the ingression of a plasma membrane furrow. The Drosophila embryo undergoes several cycles of rapid furrow ingression during early development that culminates in the formation of an epithelial sheet. Previous studies have demonstrated the requirement for intracellular trafficking pathways in furrow ingression; however, the pathways that link compartmental behaviors with cortical furrow ingression events have remained unclear. This study shows that Rab8 has striking dynamic behaviors in vivo. As furrows ingress, cytoplasmic Rab8 puncta are depleted and Rab8 accumulates at the plasma membrane in a location that coincides with known regions of directed membrane addition. CRISPR/Cas9 technology was used to N-terminally tag Rab8, which is then used to address both endogenous localization and function. Endogenous Rab8 displays partial coincidence with Rab11 and the Golgi, and this colocalization is enriched during the fast phase of cellularization. When Rab8 function is disrupted, furrow formation in the early embryo is completely abolished. Rab8 behaviors require the function of the exocyst complex subunit Sec5 as well as the recycling endosome Rab11. Active, GTP-locked Rab8 is primarily associated with dynamic membrane compartments and the plasma membrane, while GDP-locked Rab8 forms large cytoplasmic aggregates. These studies suggest a model in which active Rab8 populations direct furrow ingression by guiding the targeted delivery of cytoplasmic membrane stores to the cell surface through exocyst tethering complex interactions.

Pires, C. V., Freitas, F. C., Cristino, A. S., Dearden, P. K. and Simoes, Z. L. (2016). Transcriptome analysis of honeybee (Apis mellifera) haploid and diploid embryos reveals early zygotic transcription during cleavage. PLoS One 11: e0146447. PubMed ID: 26751956
In honeybees, the haplodiploid sex determination system promotes a unique embryogenesis process wherein females develop from fertilized eggs and males develop from unfertilized eggs. However, the developmental strategies of honeybees during early embryogenesis are virtually unknown. Similar to most animals, the honeybee oocytes are supplied with proteins and regulatory elements that support early embryogenesis. As the embryo develops, the zygotic genome is activated and zygotic products gradually replace the preloaded maternal material. The analysis of small RNA and mRNA libraries of mature oocytes and embryos originated from fertilized and unfertilized eggs has allowed exploration of the gene expression dynamics in the first steps of development and during the maternal-to-zygotic transition (MZT). A short sequence motif identified as TAGteam motif was identified and was hypothesized to play a similar role in honeybees as in fruit flies, which includes the timing of early zygotic expression (MZT), a function sustained by the presence of the zelda ortholog, which is the main regulator of genome activation. Predicted microRNA (miRNA)-target interactions indicated that there were specific regulators of haploid and diploid embryonic development and an overlap of maternal and zygotic gene expression during the early steps of embryogenesis. Although a number of functions are highly conserved during the early steps of honeybee embryogenesis, the results showed that zygotic genome activation occurs earlier in honeybees than in Drosophila based on the presence of three primary miRNAs (pri-miRNAs) (ame-mir-375, ame-mir-34 and ame-mir-263b) during the cleavage stage in haploid and diploid embryonic development.

Asadzadeh, J., Neligan, N., Kramer, S.G. and Labrador, J.P. (2016). Tinman regulates NetrinB in the cardioblasts of the Drosophila dorsal vessel. PLoS One 11: e0148526. PubMed ID: 26840059
Morphogenesis of the Drosophila dorsal vessel (DV) shares similarities with that of the vertebrate heart. Precursors line up at both sides of the embryo, migrate towards the midline and fuse to form a tubular structure. Guidance receptors and their ligands have been implicated in this process in vertebrates and invertebrates, as have been a series of evolutionarily conserved cardiogenic transcriptional regulators including Tinman, the Drosophila homolog of the transcription factor Nkx-2.5. NetrinB (NetB), a repulsive ligand for the Unc-5 receptor is required to preserve the dorsal vessel hollow. It localizes to the luminal space of the dorsal vessel but its source and its regulation is unknown. Using genetics together with in situ hybridization with single cell resolution, this study shows how tin is required for NetrinB expression in cardioblasts during DV tubulogenesis and is sufficient to promote NetB transcription ectopically. The study further identifies a dorsal vessel-specific NetB enhancer and shows that it is also regulated by tin in a similar fashion to NetB.

Guglielmi, G., Barry, J. D., Huber, W. and De Renzis, S. (2015). An optogenetic method to modulate cell contractility during tissue morphogenesis. Dev Cell. PubMed ID: 26777292
Morphogenesis of multicellular organisms is driven by localized cell shape changes. How, and to what extent, changes in behavior in single cells or groups of cells influence neighboring cells and large-scale tissue remodeling remains an open question. Indeed, understanding of multicellular dynamics is limited by the lack of methods allowing the modulation of cell behavior with high spatiotemporal precision. This study developed an optogenetic approach to achieve local modulation of cell contractility and used it to control morphogenetic movements during Drosophila embryogenesis. Local inhibition of apical constriction was shown to be sufficient to cause a global arrest of mesoderm invagination. By varying the spatial pattern of inhibition during invagination, it was further demonstrated that coordinated contractile behavior responds to local tissue geometrical constraints. Together, these results show the efficacy of this optogenetic approach to dissect the interplay between cell-cell interaction, force transmission, and tissue geometry during complex morphogenetic processes.

Sunday, February 21st

Hudry, B., Khadayate, S. and Miguel-Aliaga, I. (2016). The sexual identity of adult intestinal stem cells controls organ size and plasticity. Nature 530: 344-348. PubMed ID: 26887495
Sex differences in physiology and disease susceptibility are commonly attributed to developmental and/or hormonal factors, but there is increasing realization that cell-intrinsic mechanisms play important and persistent roles. This study uses the Drosophila melanogaster intestine to investigate the nature and importance of cellular sex in an adult somatic organ in vivo. It was found that the adult intestinal epithelium is a cellular mosaic of different sex differentiation pathways, and displays extensive sex differences in expression of genes with roles in growth and metabolism. Cell-specific reversals of the sexual identity of adult intestinal stem cells uncovers the key role this identity has in controlling organ size, reproductive plasticity and response to genetically induced tumours. Unlike previous examples of sexually dimorphic somatic stem cell activity, the sex differences in intestinal stem cell behaviour arise from intrinsic mechanisms that control cell cycle duration and involve a new doublesex- and fruitless-independent branch of the sex differentiation pathway downstream of transformer. Together, these findings indicate that the plasticity of an adult somatic organ is reversibly controlled by its sexual identity, imparted by a new mechanism that may be active in more tissues than previously recognized. 

Sharp, K.A. and Axelrod, J.D. (2016). Prickle isoforms control the direction of tissue polarity by microtubule independent and dependent mechanisms. Biol Open [Epub ahead of print]. PubMed ID: 26863941
Planar cell polarity signaling directs the polarization of cells within the plane of many epithelia. While these tissues exhibit asymmetric localization of a set of core module proteins, in Drosophila, more than one mechanism links the direction of core module polarization to the tissue axes. One signaling system establishes a polarity bias in the parallel, apical microtubules upon which vesicles containing core proteins traffic. Swapping expression of the differentially expressed Prickle isoforms, Prickle and Spiny-legs, reverses the direction of core module polarization. Studies in the proximal wing and the anterior abdomen indicated that this results from their differential control of microtubule polarity. Prickle and Spiny-legs also control the direction of polarization in the distal wing (D-wing) and the posterior abdomen (P-abd). It was found that this occurs without affecting microtubule polarity in these tissues. The direction of polarity in the D-wing is therefore likely determined by a novel mechanism independent of microtubule polarity. In the P-abd, Prickle and Spiny-legs interpret at least two directional cues through a microtubule-polarity-independent mechanism.

Clemente-Ruiz, M., Murillo-Maldonado, J.M., Benhra, N., Barrio, L., Pérez, L., Quiroga, G., Nebreda, A.R. and Milán, M. (2016). Gene dosage imbalance contributes to chromosomal instability-induced tumorigenesis. Dev Cell 36: 290-302. PubMed ID: 26859353
Chromosomal instability (CIN) is thought to be a source of mutability in cancer. However, CIN often results in aneuploidy, which compromises cell fitness. This study used the dosage compensation mechanism (DCM) of Drosophila to demonstrate that chromosome-wide gene dosage imbalance contributes to the deleterious effects of CIN-induced aneuploidy and its pro-tumorigenic action. Resetting of the DCM counterbalances the damaging effects caused by CIN-induced changes in X chromosome number. Importantly, interfering with the DCM suffices to mimic the cellular effects of aneuploidy in terms of reactive oxygen species (ROS) production, JNK-dependent cell death, and tumorigenesis upon apoptosis inhibition. A role of ROS was found in JNK activation and a variety of cellular and tissue-wide mechanisms that buffer the deleterious effects of CIN, including DNA-damage repair, activation of the p38 pathway, and cytokine induction were found to promote compensatory proliferation. These data reveal the existence of robust compensatory mechanisms that counteract CIN-induced cell death and tumorigenesis.

Breitkopf, S. B., Yang, X., et al. (2016). A cross-species study of PI3K protein-protein interactions reveals the direct interaction of P85 and SHP2. Sci Rep 6: 20471. PubMed ID: 26839216
A fly-human cross-species comparison of the phosphoinositide-3-kinase (PI3K) interactome was conducted in a Drosophila S2R+ cell line and several NSCLC and human multiple myeloma cell lines to identify conserved interacting proteins to PI3K, a critical signaling regulator of the AKT pathway. These data revealed an unexpected direct binding of Corkscrew, the Drosophila ortholog of the non-receptor protein tyrosine phosphatase type II (SHP2) to the Pi3k21B (p60) regulatory subunit of PI3K (p50/p85 human ortholog) but no association with Pi3k92e, the human ortholog of the p110 catalytic subunit. The p85-SHP2 association was validated in human cell lines, and formed a ternary regulatory complex with GRB2-associated-binding protein 2 (human GAB2 but not Drosophila Dos). Validation experiments with knockdown of GAB2 and Far-Western blots proved the direct interaction of SHP2 with p85, independent of adaptor proteins and transfected FLAG-p85 provided evidence that SHP2 binding on p85 occurred on the SH2 domains. A disruption of the SHP2-p85 complex took place after insulin/IGF1 stimulation or imatinib treatment, suggesting that the direct SHP2-p85 interaction was both independent of AKT activation and positively regulates the ERK signaling pathway.

Saturday, February 20th

Doll, C. A. and Broadie, K. (2016). Neuron class-specific requirements for Fragile X Mental Retardation Protein in critical period development of calcium signaling in learning and memory circuitry. Neurobiol Dis 89: 76-87. PubMed ID: 26851502
Fragile X Mental Retardation Protein (FMRP), the gene product lost in Fragile X syndrome (FXS), acts as an activity sensor during critical period development, both as an RNA-binding translation regulator and channel-binding excitability regulator. This study employed a Drosophila FXS disease model to assay calcium signaling dynamics with a targeted transgenic GCaMP reporter during critical period development of the mushroom body (MB) learning/memory circuit. FMRP was found to regulate depolarization-induced calcium signaling in a neuron-specific manner within this circuit, suppressing activity-dependent calcium transients in excitatory cholinergic MB input projection neurons and enhancing calcium signals in inhibitory GABAergic MB output neurons. Both changes are restricted to the developmental critical period and rectified at maturity. Importantly, conditional genetic (dfmr1) rescue of null mutants during the critical period corrects calcium signaling defects in both neuron classes, indicating a temporally restricted FMRP requirement. Likewise, conditional dfmr1 knockdown (RNAi) during the critical period replicates constitutive null mutant defects in both neuron classes, confirming cell-autonomous requirements for FMRP in developmental regulation of calcium signaling dynamics. Optogenetic stimulation during the critical period enhances depolarization-induced calcium signaling in both neuron classes, but this developmental change is eliminated in dfmr1 null mutants, indicating the activity-dependent regulation requires FMRP. These results show FMRP shapes neuron class-specific calcium signaling in excitatory vs. inhibitory neurons in developing learning/memory circuitry, and that FMRP mediates activity-dependent regulation of calcium signaling specifically during the early-use critical period.

Frenkel-Pinter, M., Tal, S., Scherzer-Attali, R., Abu-Hussien, M., Alyagor, I., Eisenbaum, T., Gazit, E. and Segal, D. (2016). Naphthoquinone-tryptophan hybrid inhibits aggregation of the Tau-derived peptide PHF6 and reduces neurotoxicity. J Alzheimers Dis [Epub ahead of print]. PubMed ID: 26836184
Tauopathies, such as Alzheimer's disease (AD), are a group of disorders characterized neuropathologically by intracellular toxic accumulations of abnormal protein aggregates formed by misfolding of the microtubule-associated protein tau. Since protein self-assembly appears to be an initial key step in the pathology of this group of diseases, intervening in this process can be both a prophylactic measure and a means for modifying the course of the disease for therapeutic purposes. Aromatic small molecules can be effective inhibitors of aggregation of various protein assemblies, by binding to the aromatic core in aggregation-prone motifs and preventing their self-assembly. Specifically, series of small aromatic naphthoquinone-tryptophan hybrid molecules were designed as candidate aggregation inhibitors of β-sheet based assembly, and their efficacy was demonstrated toward inhibiting aggregation of the amyloid-β peptide, another culprit of AD, as well as of various other aggregative proteins involved in other protein misfolding diseases. This study tested whether a leading naphthoquinone-tryptophan hybrid molecule, namely NQTrp, can be repurposed as an inhibitor of the aggregation of the tau protein in vitro and in vivo. The molecule was shown to inhibit the in vitro assembly of PHF6, the aggregation-prone fragment of tau protein, reduces hyperphosphorylated tau deposits and ameliorates tauopathy-related behavioral defect in an established transgenic Drosophila model expressing human tau. It is suggested that NQTrp, or optimized versions of it, could act as novel disease modifying drugs for AD and other tauopathies.

Levine, B. D. and Cagan, R. L. (2016). Drosophila lung cancer models identify Trametinib plus Statin as candidate therapeutic. Cell Rep [Epub ahead of print]. PubMed ID: 26832408
A Drosophila lung cancer model was developed by targeting Ras1G12V-alone or in combination with PTEN knockdown-to the Drosophila tracheal system. This led to overproliferation of tracheal tissue, formation of tumor-like growths, and animal lethality. Screening a library of FDA-approved drugs identified several that improved overall animal survival. Two hits were explored: the MEK inhibitor trametinib and the HMG-CoA reductase inhibitor fluvastatin. Oral administration of these drugs inhibited Ras and PI3K pathway activity, respectively; in addition, fluvastatin inhibited protein prenylation downstream of HMG-CoA reductase to promote survival. Combining drugs led to synergistic suppression of tumor formation and rescue lethality; similar synergy was observed in human A549 lung adenocarcinoma cells. Notably, fluvastatin acted both within transformed cells and also to reduce whole-body trametinib toxicity in flies. This work supports and provides further context for exploring the potential of combining statins with MAPK inhibitors such as trametinib to improve overall therapeutic index.

Li, H., Qi, Y. and Jasper, H. (2016). Preventing age-related decline of gut compartmentalization limits microbiota dysbiosis and extends lifespan. Cell Host Microbe 19: 240-253. PubMed ID: 26867182
Compartmentalization of the gastrointestinal (GI) tract of metazoans is critical for health. GI compartments contain specific microbiota, and microbiota dysbiosis is associated with intestinal dysfunction. Dysbiosis develops in aging intestines, yet how this relates to changes in GI compartmentalization remains unclear. The Drosophila GI tract is an accessible model to address this question. This study shows that the stomach-like copper cell region (CCR) in the middle midgut controls distribution and composition of the microbiota. It was found that chronic activation of JAK/Stat signaling in the aging gut induces a metaplasia of the gastric epithelium, CCR decline, and subsequent commensal dysbiosis and epithelial dysplasia along the GI tract. Accordingly, inhibition of JAK/Stat signaling in the CCR specifically prevents age-related metaplasia, commensal dysbiosis and functional decline in old guts, and extends lifespan. These results establish a mechanism by which age-related chronic inflammation causes the decline of intestinal compartmentalization and microbiota dysbiosis, limiting lifespan. 

Sen, A. and Cox, R. T. (2016). Clueless is a conserved ribonucleoprotein that binds the ribosome at the mitochondrial outer membrane. Biol Open [Epub ahead of print]. PubMed ID: 26834020
Mitochondrial function is tied to the nucleus, in that hundreds of proteins encoded by nuclear genes must be imported into mitochondria. While post-translational import is fairly well understood, emerging evidence supports that mitochondrial site-specific import, or co-translational import, also occurs. However, the mechanism and the extent to which it is used are not fully understood. Previous studies have shown that Clueless (Clu), a conserved multi-domain protein, associates with mitochondrial outer membrane proteins, including Translocase of outer membrane 20, and genetically and physically interacts with the PINK1-Parkin pathway. The human ortholog of Clu, Cluh, was shown to bind nuclear-encoded mitochondrially destined mRNAs. This study identified the conserved tetratricopeptide domain of Clu as predominantly responsible for binding mRNA. In addition, Clu was shown to interact with the ribosome at the mitochondrial outer membrane. Taken together, these data support a model whereby Clu binds to and mitochondrially targets mRNAs to facilitate mRNA localization to the outer mitochondrial membrane, potentially for site-specific or co-translational import. This role may link the presence of efficient mitochondrial protein import to mitochondrial quality control through the PINK1-Parkin pathway.

Zhang, Q., Tsoi, H., Peng, S., Li, P. P., Lau, K. F., Rudnicki, D. D., Ngo, J. C. and Chan, H. Y. (2016). A peptidylic inhibitor-based therapeutic approach that simultaneously suppresses RNA- and protein-mediated toxicities in polyglutamine diseases. Dis Model Mech [Epub ahead of print]. PubMed ID: 26839389
Polyglutamine (polyQ) diseases represent a group of progressive neurodegenerative disorders that are caused by abnormal expansion of CAG triplet nucleotides in disease genes. Recent evidence indicates that not only mutant polyQ protein, but also their corresponding mutant RNAs contribute to the pathogenesis of polyQ diseases. This study describes the identification of a 13-amino acid peptide, P3, which binds directly and preferentially to long CAG RNA within the pathogenic range. When administered to cell and Drosophila disease models, as well as to patient-derived fibroblasts, P3 inhibited expanded CAG RNA-induced nucleolar stress and suppressed neurotoxicity. The combined therapeutic effect of P3 and polyQ-binding peptide 1 (QBP1), a well-characterized polyQ protein toxicity inhibitor, on neurodegeneration was further examined. When P3 and QBP1 were co-administered to disease models, both RNA and protein toxicities were effectively mitigated, resulting in a notable improvement of neurotoxicity suppression compared with the P3 and QBP1 single treatment controls. These findings indicate that targeting toxic RNAs and/or simultaneous targeting of toxic RNAs and their corresponding proteins may open up a new therapeutic strategy for treating polyQ degeneration.

Friday, February 19th

Liao, J., Seggio, J. A. and Ahmad, S. T. (2016). Mutations in the circadian gene period alter behavioral and biochemical responses to ethanol in Drosophila. Behav Brain Res 302: 213-219. PubMed ID: 26802726
Clock genes, such as period, which maintain an organism's circadian rhythm, can have profound effects on metabolic activity, including ethanol metabolism. In turn, ethanol exposure has been shown in Drosophila and mammals to cause disruptions of the circadian rhythm. Previous studies from our labs have shown that larval ethanol exposure disrupted the free-running period and period expression of Drosophila. In addition, a recent study has shown that arrhythmic flies show no tolerance to ethanol exposure. As such, Drosophila period mutants, which have either a shorter than wild-type free-running period (perS) or a longer one (perL), may also exhibit altered responses to ethanol due to their intrinsic circadian differences. This study tested the initial sensitivity and tolerance of ethanol exposure on Canton-S, perS, and perL, and then measured their Alcohol Dehydrogenase (ADH) and body ethanol levels. perL flies had slower sedation rate, longer recovery from ethanol sedation, and generated higher tolerance for sedation upon repeated ethanol exposure compared to Canton-S wild-type flies. Furthermore, perL flies had lower ADH activity and had a slower ethanol clearance compared to wild-type flies. The findings of this study suggest that period mutations influence ethanol induced behavior and ethanol metabolism in Drosophila and that flies with longer circadian periods are more sensitive to ethanol exposure.

Bhat, S. and Jones, W. D. (2016). An accelerated miRNA-based screen implicates Atf-3 in Drosophila odorant receptor expression. Sci Rep 6: 20109. PubMed ID: 26848073
The Drosophila olfactory system is highly stereotyped in form and function; olfactory sensory neurons (OSNs) expressing a specific odorant receptor (OR) always appear in the same antennal location and the axons of OSNs expressing the same OR converge on the same antennal lobe glomeruli. Although some transcription factors have been implicated in a combinatorial code specifying OR expression and OSN identity, it is clear other players remain unidentified. In hopes of mitigating the challenges of genome-wide screening, this study examined the feasibility of a two-tiered approach comprising a primary "pooling" screen for miRNAs whose tissue-specific over-expression causes a phenotype of interest followed by a focused secondary screen using gene-specific RNAi. Since miRNAs down-regulate their targets, miRNA over-expression phenotypes should be attributable to target loss-of-function. It is the sequence-dependence of miRNA-target pairing that suggests candidates for the secondary screen. Since miRNAs are short, however, miRNA misexpression will likely uncover non-biological miRNA-target relationships. Rather than focusing on miRNA function itself where these non-biological relationships could be misleading, it is proposed using miRNAs as tools to focus a more traditional RNAi-based screen. This study describes such a screen that uncovers a role for Atf3 in the expression of the odorant receptor Or47b.

Koenig, S., Wolf, R. and Heisenberg, M. (2016). Vision in flies: Measuring the attention span. PLoS One 11: e0148208. PubMed ID: 26848852
A visual stimulus at a particular location of the visual field may elicit a behavior while at the same time equally salient stimuli in other parts do not. This property of visual systems is known as selective visual attention (SVA). The animal is said to have a focus of attention (FoA) which it has shifted to a particular location. Visual attention normally involves an attention span at the location to which the FoA has been shifted. Here the attention span is measured in Drosophila. The fly is tethered and hence has its eyes fixed in space. It can shift its FoA internally. This shift is revealed using two simultaneous test stimuli with characteristic responses at their particular locations. In tethered flight a wild type fly keeps its FoA at a certain location for up to 4s. Flies with a mutation in the radish gene, that has been suggested to be involved in attention-like mechanisms, display a reduced attention span of only 1s.

Tadros, W., Xu, S., Akin, O., Yi, C. H., Shin, G. J., Millard, S. S. and Zipursky, S. L. (2016). Dscam proteins direct dendritic targeting through adhesion. Neuron 89: 480-493. PubMed ID: 26844831
Cell recognition molecules are key regulators of neural circuit assembly. The Dscam family of recognition molecules in Drosophila has been shown to regulate interactions between neurons through homophilic repulsion. This is exemplified by Dscam1 and Dscam2, which together repel dendrites of lamina neurons, L1 and L2, in the visual system. By contrast, this study shows that Dscam2 directs dendritic targeting of another lamina neuron, L4, through homophilic adhesion. Through live imaging and genetic mosaics to dissect interactions between specific cells, Dscam2 was shown to be required in L4 and its target cells for correct dendritic targeting. In a genetic screen, Dscam4 was identified as another regulator of L4 targeting which acts with Dscam2 in the same pathway to regulate this process. This ensures tiling of the lamina neuropil through heterotypic interactions. Thus, different combinations of Dscam proteins act through distinct mechanisms in closely related neurons to pattern neural circuits.

Ou, J., Gao, Z., Song, L. and Ho, M. S. (2016). Analysis of glial distribution in Drosophila adult brains. Neurosci Bull [Epub ahead of print]. PubMed ID: 26810782
Neurons and glia are the two major cell types in the nervous system and work closely with each other to program neuronal interplay. Traditionally, neurons are thought to be the major cells that actively regulate processes like synapse formation, plasticity, and behavioral output. Glia, on the other hand, serve a more supporting role. To date, accumulating evidence has suggested that glia are active participants in virtually every aspect of neuronal function. Despite this, fundamental features of how glia interact with neurons, and their spatial relationships, remain elusive. This study describes the glial cell population in Drosophila adult brains. Glial cells extend and tightly associate their processes with major structures such as the mushroom body (MB), ellipsoid body (EB), and antennal lobe (AL) in the brain. Glial cells are distributed in a more concentrated manner in the MB. Furthermore, subsets of glia exhibit distinctive association patterns around different neuronal structures. Whereas processes extended by astrocyte-like glia and ensheathing glia wrap around the MB and infiltrate into the EB and AL, cortex glia stay where cell bodies of neurons are and remain outside of the synaptic regions structured by EB or AL.

Hsu, C. T. and Bhandawat, V. (2016). Organization of descending neurons in Drosophila melanogaster. Sci Rep 6: 20259. PubMed ID: 26837716
Neural processing in the brain controls behavior through descending neurons (DNs) - neurons which carry signals from the brain to the spinal cord (or thoracic ganglia in insects). Because DNs arise from multiple circuits in the brain, the numerical simplicity and availability of genetic tools make Drosophila a tractable model for understanding descending motor control. As a first step towards a comprehensive study of descending motor control, this study estimates the number and distribution of DNs in the Drosophila brain. DNs were labelled by backfilling them with dextran dye applied to the neck connective and it was estimated that there are ~1100 DNs distributed in 6 clusters in Drosophila. To assess the distribution of DNs by neurotransmitters, labeled DNs in flies were labeled in which neurons expressing the major neurotransmitters were also labeled. DNs belonging to every neurotransmitter class were tested: acetylcholine, GABA, glutamate, serotonin, dopamine and octopamine. Both the major excitatory neurotransmitter (acetylcholine) and the major inhibitory neurotransmitter (GABA) are employed equally; this stands in contrast to vertebrate DNs which are predominantly excitatory. By comparing the distribution of DNs in Drosophila to those reported previously in other insects, it is concluded that the organization of DNs in insects is highly conserved.

Thursday, February 18th

Slabbaert, J.R., Kuenen, S., Swerts, J., Maes, I., Uytterhoeven, V., Kasprowicz, J., Fernandes, A.C., Blust, R. and Verstreken, P. (2016). Shawn, the Drosophila homolog of SLC25A39/40, is a mitochondrial carrier that promotes neuronal survival. J Neurosci 36: 1914-1929. PubMed ID: 26865615
Mitochondria play an important role in the regulation of neurotransmission, and mitochondrial impairment is a key event in neurodegeneration. Cells rely on mitochondrial carrier proteins of the SLC25 family to shuttle ions, cofactors, and metabolites necessary for enzymatic reactions. Mutations in these carriers often result in rare but severe pathologies in the brain, and some of the genes, including SLC25A39 and SLC25A40, reside in susceptibility loci of severe forms of epilepsy. However, the role of most of these carriers has not been investigated in neurons in vivo. This study identified shawn, the Drosophila homolog of SLC25A39 and SLC25A40, in a genetic screen to identify genes involved in neuronal function. Shawn localizes to mitochondria, and missense mutations result in an accumulation of reactive oxygen species, mitochondrial dysfunction, and neurodegeneration. Shawn regulates metal homeostasis, and shawn mutants exhibit increased levels of manganese, calcium, and mitochondrial free iron. Mitochondrial mutants often cannot maintain synaptic transmission under demanding conditions, but shawn mutants do, and they also do not display endocytic defects. In contrast, shawn mutants harbor a significant increase in neurotransmitter release. These data provide the first functional annotation of these essential mitochondrial carriers in the nervous system, and suggest that metal imbalances and mitochondrial dysfunction may contribute to defects in synaptic transmission and neuronal survival.

Zhang, Y., Lamba, P., Guo, P. and Emery, P. (2016). miR-124 regulates the phase of Drosophila circadian locomotor behavior. J Neurosci 36: 2007-2013. PubMed ID: 26865623
Animals use circadian rhythms to anticipate daily environmental changes. Circadian clocks have a profound effect on behavior. In Drosophila, for example, brain pacemaker neurons dictate that flies are mostly active at dawn and dusk. miRNAs are small, regulatory RNAs (≈22 nt) that play important roles in posttranscriptional regulation. This study identifies miR-124 as an important regulator of Drosophila circadian locomotor rhythms. Under constant darkness, flies lacking miR-124 (miR-124(KO)) have a dramatically advanced circadian behavior phase. However, whereas a phase defect is usually caused by a change in the period of the circadian pacemaker, this is not the case in miR-124(KO) flies. Moreover, the phase of the circadian pacemaker in the clock neurons that control rhythmic locomotion is not altered either. Therefore, miR-124 modulates the output of circadian clock neurons rather than controlling their molecular pacemaker. Circadian phase is also advanced under temperature cycles, but a light/dark cycle partially corrects the defects in miR-124(KO) flies. Indeed, miR-124(KO) shows a normal evening phase under the latter conditions, but morning behavioral activity is suppressed. In summary, miR-124 controls diurnal activity and determines the phase of circadian locomotor behavior without affecting circadian pacemaker function. It thus provides a potent entry point to elucidate the mechanisms by which the phase of circadian behavior is determined.

Cao, L. H., Jing, B. Y., Yang, D., Zeng, X., Shen, Y., Tu, Y. and Luo, D. G. (2016). Distinct signaling of Drosophila chemoreceptors in olfactory sensory neurons. Proc Natl Acad Sci U S A. PubMed ID: 26831094
In Drosophila, olfactory sensory neurons (OSNs) rely primarily on two types of chemoreceptors, odorant receptors (Ors) and ionotropic receptors (Irs), to convert odor stimuli into neural activity. The cellular signaling of these receptors in their native OSNs remains unclear because of the difficulty of obtaining intracellular recordings from Drosophila OSNs. This study developed an antennal preparation that enabled the first recordings from targeted Drosophila OSNs through a patch-clamp technique. Brief odor pulses triggered graded inward receptor currents with distinct response kinetics and current-voltage relationships between Or- and Ir-driven responses. When stimulated with long-step odors, the receptor current of Ir-expressing OSNs did not adapt. In contrast, Or-expressing OSNs showed a strong Ca2+-dependent adaptation. The adaptation-induced changes in odor sensitivity obeyed the Weber-Fechner relation; however, surprisingly, the incremental sensitivity was reduced at low odor backgrounds but increased at high odor backgrounds. This model for odor adaptation revealed two opposing effects of adaptation, desensitization and prevention of saturation, in dynamically adjusting odor sensitivity and extending the sensory operating range.
Zhang, K. X., Tan, L., Pellegrini, M., Zipursky, S. L. and McEwen, J. M. (2016). Rapid changes in the translatome during the conversion of growth cones to synaptic terminals. Cell Rep 14: 1258-1271. PubMed ID: 26832407
A common step in the formation of neural circuits is the conversion of growth cones to presynaptic terminals. Characterizing patterns of global gene expression during this process is problematic due to the cellular diversity of the brain and the complex temporal dynamics of development. This study takes advantage of the synchronous conversion of Drosophila photoreceptor growth cones into presynaptic terminals to explore global changes in gene expression during presynaptic differentiation. Using a tandemly tagged ribosome trap (T-TRAP) and RNA sequencing (RNA-seq) at multiple developmental times, dramatic changes were observed in coding and non-coding RNAs with presynaptic differentiation. Marked changes in the mRNA encoding transmembrane and secreted proteins occurred preferentially. The 3' UTRs of transcripts encoding synaptic proteins were preferentially lengthened, and these extended UTRs were preferentially enriched for sites recognized by RNA binding proteins. These data provide a rich resource for uncovering the regulatory logic underlying presynaptic differentiation.

Boyle, S. M., McInally, S., Tharadra, S. and Ray, A. (2016). Short-term memory trace mediated by termination kinetics of olfactory receptor. Sci Rep 6: 19863. PubMed ID: 26830661
Odorants activate receptors in the peripheral olfactory neurons, which sends information to higher brain centers where behavioral valence is determined. Movement and airflow continuously change what odor plumes an animal encounters and little is known about the effect one plume has on the detection of another. Using the simple Drosophila melanogaster larval model to study this relationship, an unexpected phenomenon was identified: response to an attractant can be selectively blocked by previous exposure to some odorants that activates the same receptor. At a mechanistic level, it was found that exposure to this type of odorant causes prolonged tonic responses from a receptor (Or42b), which can block subsequent detection of a strong activator of that same receptor. Naturally occurring odorants were identify dwith prolonged tonic responses for other odorant receptors (Ors) as well, suggesting that termination-kinetics is a factor for olfactory coding mechanisms. This mechanism has implications for odor-coding in any system and for designing applications to modify odor-driven behaviors.
van Giesen, L., Hernandez-Nunez, L., Delasoie-Baranek, S., Colombo, M., Renaud, P., Bruggmann, R., Benton, R., Samuel, A.D. and Sprecher, S.G. (2016). Multimodal stimulus coding by a gustatory sensory neuron in Drosophila larvae. Nat Commun 7: 10687. PubMed ID: 26864722
Accurate perception of taste information is crucial for animal survival. In adult Drosophila, gustatory receptor neurons (GRNs) perceive chemical stimuli of one specific gustatory modality associated with a stereotyped behavioural response, such as aversion or attraction. This study shows that GRNs of Drosophila larvae employ a surprisingly different mode of gustatory information coding. Using a novel method for calcium imaging in the larval gustatory system, a multimodal GRN was identified that responds to chemicals of different taste modalities with opposing valence, such as sweet sucrose and bitter denatonium, reliant on different sensory receptors. This multimodal neuron is essential for bitter compound avoidance, and its artificial activation is sufficient to mediate aversion. However, the neuron is also essential for the integration of taste blends. These findings support a model for taste coding in larvae, in which distinct receptor proteins mediate different responses within the same, multimodal GRN. 

Wednesday, February 17th

Tie, F., Banerjee, R., Fu, C., Stratton, C.A., Fang, M. and Harte, P.J. (2016). Polycomb inhibits histone acetylation by CBP by binding directly to its catalytic domain. Proc Natl Acad Sci U S A [Epub ahead of print]. PubMed ID: 26802126
Drosophila Polycomb (PC), a subunit of Polycomb repressive complex 1 (PRC1), is well known for its role in maintaining repression of the homeotic genes and many others and for its binding to trimethylated histone H3 on Lys 27 (H3K27me3) via its chromodomain. This study identifies a novel activity of PC: inhibition of the histone acetylation activity of CREB-binding protein (CBP). It was shown that PC and its mammalian CBX orthologs interact directly with the histone acetyltransferase (HAT) domain of CBP, binding to the previously identified autoregulatory loop, whose autoacetylation greatly enhances HAT activity. A conserved PC motif adjacent to the chromodomain required for CBP binding was identified and it was shown that PC binding inhibits acetylation of histone H3. CBP autoacetylation impairs PC binding in vitro, and PC is preferentially associated with unacetylated CBP in vivo. PC knockdown elevates the acetylated H3K27 (H3K27ac) level globally and at promoter regions of some genes that are bound by both PC and CBP. Conversely, PC overexpression decreases the H3K27ac level in vivo and also suppresses CBP-dependent Polycomb phenotypes caused by overexpression of Trithorax, an antagonist of Polycomb silencing. It was found that PC physically associates with the initiating form of RNA polymerase II (Pol II) and many promoters co-occupied by PC and CBP are associated with paused Pol II, suggesting that PC may play a role in Pol II pausing. These results suggest that PC/PRC1 inhibition of CBP HAT activity plays a role in regulating transcription of both repressed and active PC-regulated genes.

Beh, C. Y., El-Sharnouby, S., Chatzipli, A., Russell, S., Choo, S. W. and White, R. (2016). Roles of cofactors and chromatin accessibility in Hox protein target specificity. Epigenetics Chromatin 9: 1. PubMed ID: 26753000
The regulation of specific target genes by transcription factors is central to understanding of gene network control in developmental and physiological processes, yet how target specificity is achieved is still poorly understood. This is well illustrated by the Hox family of transcription factors as their limited in vitro DNA-binding specificity contrasts with their clear in vivo functional specificity. This study generated genome-wide binding profiles for three Hox proteins, Ubx, Abd-A and Abd-B, following transient expression in Drosophila Kc167 cells, revealing clear target specificity and a striking influence of chromatin accessibility. In the absence of the TALE class homeodomain cofactors Exd and Hth, Ubx and Abd-A bind at a very similar set of target sites in accessible chromatin, whereas Abd-B binds at an additional specific set of targets. Provision of Hox cofactors Exd and Hth considerably modifies the Ubx genome-wide binding profile enabling Ubx to bind at an additional novel set of targets. Both the Abd-B specific targets and the cofactor-dependent Ubx targets are in chromatin that is relatively DNase1 inaccessible prior to the expression of Hox proteins/Hox cofactors. It is concluded that there is a strong role for chromatin accessibility in Hox protein binding, and the results suggest that Hox protein competition with nucleosomes has a major role in Hox protein target specificity in vivo.

Basu, A., Tomar, A., Dasari, V., Mishra, R.K. and Khosla, S. (2016). DNMT3L enables accumulation and inheritance of epimutations in transgenic Drosophila. Sci Rep 6: 19572. PubMed ID: 26795243
DNMT3L is an important epigenetic regulator in mammals, integrating DNA methylation and histone modification based epigenetic circuits. This study shows DNMT3L to be a part of the machinery that enables inheritance of epigenetic modifications from one generation to the next. Ectopic expression of DNMT3L in Drosophila, which lacks DNMT3L and its normal interacting partners DNMT3A and DNMT3B, lead to nuclear reprogramming that is gradual and progressive, resulting in melanotic tumors that are observed only when these flies are maintained for five generations. This global gene expression misregulation is accompanied by aberrations in the levels of H3K4me3 and H3K36me3, globally as well as at specific gene promoters. The levels of these epigenetic aberrations (epimutations) also increase progressively across successive generations. The accumulation and inheritance of epimutations across multiple generations recapitulates the important role of DNMT3L in intergenerational epigenetic inheritance in mammals.

Gajan, A., Barnes, V. L., Liu, M., Saha, N. and Pile, L. A. (2016). The histone demethylase dKDM5/LID interacts with the SIN3 histone deacetylase complex and shares functional similarities with SIN3. Epigenetics Chromatin 9: 4. PubMed ID: 26848313
Two histone-modifying enzymes, RPD3, a deacetylase, and dKDM5/LID, a demethylase, are present in a single complex, coordinated through the SIN3 scaffold protein. This study analyzed the developmental and transcriptional activities of dKDM5/LID in relation to SIN3. Knockdown of either Sin3A or lid resulted in decreased cell proliferation in S2 cells and wing imaginal discs. Conditional knockdown of either Sin3A or lid resulted in flies that displayed wing developmental defects. Interestingly, overexpression of dKDM5/LID rescued the wing developmental defect due to reduced levels of SIN3 in female flies, indicating a major role for dKDM5/LID in cooperation with SIN3 during development. Together, these observed phenotypes strongly suggest that dKDM5/LID as part of the SIN3 complex can impact previously uncharacterized transcriptional networks. Transcriptome analysis revealed that a significant affect was observed on genes required to mount an effective stress response. Together, the data provide a solid framework for analyzing the gene regulatory pathways through which SIN3 and dKDM5/LID control diverse biological processes in the organism.

Tuesday, February 16th

Wang, P., Larouche, M., Normandin, K., Kachaner, D., Mehsen, H., Emery, G. and Archambault, V. (2016). Spatial regulation of Greatwall by Cdk1 and PP2A-Tws in the cell cycle. Cell Cycle: [Epub ahead of print] PubMed ID: 26761639
Entry into mitosis requires the phosphorylation of multiple substrates by cyclin B-Cdk1, while exit from mitosis requires their dephosphorylation, which depends largely on the phosphatase PP2A in complex with its B55 regulatory subunit (Tws in Drosophila). At mitotic entry, cyclin B-Cdk1 activates the Greatwall kinase, which phosphorylates Endosulfine proteins, thereby activating their ability to inhibit PP2A-B55 competitively. The inhibition of PP2A-B55 at mitotic entry facilitates the accumulation of phosphorylated Cdk1 substrates. The coordination of these enzymes involves major changes in their localization. In interphase, Gwl is nuclear while PP2A-B55 is cytoplasmic. Gwl suddenly relocalizes from the nucleus to the cytoplasm in prophase, before nuclear envelope breakdown, and this controlled localization of Gwl is required for its function. Phosphorylation of Gwl by cyclin B-Cdk1 at multiple sites is required for its nuclear exclusion, but the precise mechanisms remained unclear. In addition, how Gwl returns to its nuclear localization was not explored. This study shows that cyclin B-Cdk1 directly inactivates a Nuclear Localization Signal in the central region of Gwl. This phosphorylation facilitates the cytoplasmic retention of Gwl, which is exported to the cytoplasm in a Crm1-dependent manner. In addition, this study shows that PP2A-Tws promotes the return of Gwl to its nuclear localization during cytokinesis. These results indicate that the cyclic changes in Gwl localization at mitotic entry and exit are directly regulated by the antagonistic cyclin B-Cdk1 and PP2A-Tws enzymes.

Bradley-Gill, M.R., Kim, M., Feingold, D., Yergeau, C., Houde, J. and Moon, N.S. (2016). Alternate transcripts of the Drosophila "activator" E2F are necessary for maintenance of cell cycle exit during development Dev Biol [Epub ahead of print]. PubMed ID: 26859702
The E2F family of transcription factors are evolutionarily conserved regulators of the cell cycle that can be divided into two groups based on their ability to either activate or repress transcription. In Drosophila, there is only one "activator" E2F, dE2F1, which provides all of the pro-proliferative activity of E2F during development. Interestingly, the de2f1 gene can be transcribed from multiple promoters resulting in six alternate transcripts. This study investigated the biological significance of the alternate transcriptional start sites. The de2f1 promoter region shows tissue and cell-type specific enhancer activities at the larval stage. While a genomic deletion of this region, de2f1ΔRA, decreases the overall expression level of dE2F1, flies develop normally with no obvious proliferation defects. However, a detailed analysis of the de2f1ΔRA mutant eye imaginal discs revealed that dE2F1 is needed for proper cell cycle exit. dE2F1 expression during G1 arrest prior to the differentiation process of the developing eye is important for maintaining cell cycle arrest at a later stage of the eye development. Overall, this study suggests that specific alternate transcripts of "activator" E2F, dE2F1, may have a dual function on cell cycle progression and cannot simply be viewed as a pro-proliferative transcription factor.

Cipressa, F., Morciano, P., Bosso, G., Mannini, L., Galati, A., Daniela Raffa, G., Cacchione, S., Musio, A. and Cenci, G. (2016). A role for Separase in telomere protection. Nat Commun 7: 10405. PubMed ID: 26778495
Drosophila telomeres are elongated by transposition of specialized retroelements rather than telomerase activity and are assembled independently of the sequence. Fly telomeres are protected by the terminin complex that localizes and functions exclusively at telomeres and by non-terminin proteins that do not serve telomere-specific functions. This study shows that mutations in the Drosophila Separase encoding gene Sse lead not only to endoreduplication but also telomeric fusions (TFs), suggesting a role for Sse in telomere capping. Separase binds terminin proteins and HP1, and it is enriched at telomeres. Furthermore, loss of Sse is shown to strongly reduces HP1 levels, and HP1 overexpression in Sse mutants suppresses TFs, suggesting that TFs are caused by a HP1 diminution. Finally, this study finds that siRNA-induced depletion of ESPL1, the Sse human orthologue, causes telomere dysfunction and HP1 level reduction in primary fibroblasts, highlighting a conserved role of Separase in telomere protection.

Ramdas Nair, A., Singh, P., Salvador Garcia, D., Rodriguez-Crespo, D., Egger, B. and Cabernard, C. (2016). The microcephaly-associated protein Wdr62/CG7337 is required to maintain centrosome asymmetry in Drosophila neuroblasts. Cell Rep [Epub ahead of print]. PubMed ID: 26804909
Centrosome asymmetry has been implicated in stem cell fate maintenance in both flies and vertebrates, but the underlying molecular mechanisms are incompletely understood. This study reports that loss of CG7337, the fly ortholog of WDR62, compromises interphase centrosome asymmetry in fly neural stem cells (neuroblasts). Wdr62 maintains an active interphase microtubule-organizing center (MTOC) by stabilizing microtubules (MTs), which are necessary for sustained recruitment of Polo/Plk1 to the pericentriolar matrix (PCM) and downregulation of Pericentrin-like protein (Plp). The loss of an active MTOC in wdr62 mutants compromises centrosome positioning, spindle orientation, and biased centrosome segregation. wdr62 mutant flies also have an approximately 40% reduction in brain size as a result of cell-cycle delays. It is proposed that CG7337/Wdr62, a microtubule-associated protein, is required for the maintenance of interphase microtubules, thereby regulating centrosomal Polo and Plp levels. Independent of this function, Wdr62 is also required for the timely mitotic entry of neural stem cells.

Monday, February 15th

Harris, R.E., Setiawan, L., Saul, J. and Hariharan, I.K. (2016). Localized epigenetic silencing of a damage-activated WNT enhancer limits regeneration in mature Drosophila imaginal discs. Elife [Epub ahead of print]. PubMed ID: 26840050
Many organisms lose the capacity to regenerate damaged tissues as they mature. Damaged Drosophila imaginal discs regenerate efficiently early in the third larval instar (L3) but progressively lose this ability. This correlates with reduced damage-responsive expression of multiple genes, including the WNT genes wingless (wg) and Wnt6. This study demonstrates that damage-responsive expression of both genes requires a bipartite enhancer whose activity declines during L3. Within this enhancer, a damage-responsive module stays active throughout L3, while an adjacent silencing element nucleates increasing levels of epigenetic silencing restricted to this enhancer. Cas9-mediated deletion of the silencing element alleviates WNT repression, but is, in itself, insufficient to promote regeneration. However, directing Myc expression to the blastema overcomes repression of multiple genes, including wg, and restores cellular responses necessary for regeneration. Localized epigenetic silencing of damage-responsive enhancers can therefore restrict regenerative capacity in maturing organisms without compromising gene functions regulated by developmental signals.

Crocker, J, Ilsley, G.R. and Stern, D.L. (2016). Quantitatively predictable control of Drosophila transcriptional enhancers in vivo with engineered transcription factors. Nat Genet [Epub ahead of print]. PubMed ID: 26854918
Genes are regulated by transcription factors that bind to regions of genomic DNA called enhancers. Considerable effort is focused on identifying transcription factor binding sites, with the goal of predicting gene expression from DNA sequence. Despite this effort, general, predictive models of enhancer function are currently lacking. This study combine quantitative models of enhancer function with manipulations using engineered transcription factors to examine the extent to which enhancer function can be controlled in a quantitatively predictable manner. These models, which incorporate few free parameters, can accurately predict the contributions of ectopic transcription factor inputs. The effect of individual transcription factors can be considered as independent submodules of activity that are combined in a linear manner to produce a sigmoidal output. Individual submodules can also encode more complex inputs. For example, a submodule is represented by the saturating cooperativity displayed by Dorsal and Twist, whose combined output has an upper limit. The models allow the predictable 'tuning' of enhancers, providing a framework for the quantitative control of enhancers with engineered transcription factors.

Hoermann, A., Cicin-Sain, D. and Jaeger, J. (2016). A quantitative validated model reveals two phases of transcriptional regulation for the gap gene giant in Drosophila. Dev Biol [Epub ahead of print]. PubMed ID: 26806702
Understanding eukaryotic transcriptional regulation and its role in development and pattern formation is one of the big challenges in biology today. Most attempts at tackling this problem either focus on the molecular details of transcription factor binding, or aim at genome-wide prediction of expression patterns from sequence through bioinformatics and mathematical modelling. This study bridges the gap between these two complementary approaches by providing an integrative model of cis-regulatory elements governing the expression of the gap gene giant (gt) in the blastoderm embryo. A reverse-engineering method, where mathematical models are fit to quantitative spatio-temporal reporter gene expression data, was used to infer the regulatory mechanisms underlying gt expression in its anterior and posterior domains. These models are validated through prediction of gene expression in mutant backgrounds. A detailed analysis of the data and models reveals that gt is regulated by domain-specific CREs at early stages, while a late element drives expression in both the anterior and the posterior domains. Initial gt expression depends exclusively on inputs from maternal factors. Later, gap gene cross-repression and gt auto-activation become increasingly important. Auto-regulation creates a positive feedback, which mediates the transition from early to late stages of regulation. The existence and role of gt auto-activation was confirmed through targeted mutagenesis of Gt transcription factor binding sites. In summary, this analysis provides a comprehensive picture of spatio-temporal gene regulation by different interacting enhancer elements for an important developmental regulator.

Sato, M.P., Makino, T. and Kawata, M. (2016). Natural selection in a population of Drosophila melanogaster explained by changes in gene expression caused by sequence variation in core promoter regions. BMC Evol Biol 16: 35. PubMed ID: 26860869
This study analyzed sequence variations in core promoter regions in a natural population of Drosophila melanogaster, and identified core promoter sequence variations associated with differences in gene expression levels subjected to natural selection. Among the core promoter regions whose sequence variation could change transcription factor binding sites and explain differences in expression levels, three core promoter regions were detected as candidates associated with purifying selection or selective sweep and seven as candidates associated with balancing selection, excluding the possibility of linkage between these regions and core promoter regions. CHKov1, which confers resistance to the sigma virus and related insecticides, was identified as core promoter regions that has been subject to selective sweep, although it could not be denied that selection for variation in core promoter regions was due to linked single nucleotide polymorphisms in the regulatory region outside core promoter regions. Nucleotide changes in core promoter regions of CHKov1 cause the loss of two basal transcription factor binding sites and acquisition of one transcription factor binding site, resulting in decreased gene expression levels. Of nine core promoter regions regions associated with balancing selection, brat, and CG9044 are associated with neuromuscular junction development, and Nmda1 are associated with learning, behavioral plasticity, and memory. Diversity of neural and behavioral traits may have been maintained by balancing selection. These results reveal the evolutionary process occurring by natural selection for differences in gene expression levels caused by sequence variation in core promoter regions in a natural population. The sequences of core promoter regions are diverse even within the population, possibly providing a source for natural selection.

Sunday, February 14th

Rose, G., Krzywinska, E., Kim, J., Revuelta, L., Ferretti, L. and Krzywinski, J. (2016). Dosage compensation in the African malaria mosquito Anopheles gambiae. Genome Biol Evol [Epub ahead of print]. PubMed ID: 26782933
Dosage compensation is the fundamental process, by which gene expression from the male monosomic X chromosome and from the diploid set of autosomes is equalized. Various molecular mechanisms have evolved in different organisms to achieve this task. In Drosophila, genes on the male X chromosome are upregulated to the levels of expression from the two X chromosomes in females. To test whether a similar mechanism is operating in immature stages of Anopheles mosquitoes, global gene expression was analyzed in the A. gambiae fourth instar larvae and pupae using high-coverage RNA-seq data. In pupae of both sexes, the median expression ratios of X-linked to autosomal genes (X:A) were close to 1.0, and within the ranges of expression ratios between the autosomal pairs, consistent with complete compensation. Gene-by-gene comparisons of expression in males and females revealed mild female bias, likely attributable to a deficit of male-biased X-linked genes. In larvae, male to female ratios of the X chromosome expression levels were more female biased than in pupae, suggesting that compensation may not be complete. No compensation mechanism appears to operate in male germline of early pupae. Confirmation of the existence of dosage compensation in Anopheles gambiae lays the foundation for research into the components of dosage compensation machinery in this important vector species.

Nikhil, K. L., Abhilash, L. and Sharma, V. K. (2016). Molecular correlates of circadian clocks in fruit fly Drosophila melanogaster populations exhibiting early and late emergence chronotypes. J Biol Rhythms [Epub ahead of print]. PubMed ID: 26833082
This study used a laboratory selection approach to raise populations of Drosophila melanogaster that emerge in the morning (early) or in the evening (late), and over 14 years of continued selection, clear divergence of their circadian phenotypes is reported. The molecular correlates of early and late emergence chronotypes were also assessed, and significant divergence is reported in transcriptional regulation, including the mean phase, amplitude and levels of period (per), timeless (tim), clock (clk) and vrille (vri) messenger RNA (mRNA) expression. Corroborating some of the previously reported light-sensitivity and oscillator network coupling differences between the early and the late populations, differences are also reported in mRNA expression of the circadian photoreceptor cryptochrome (cry) and in the mean phase, amplitude and levels of the neuropeptide pigment-dispersing factor (PDF). These results provide the first-ever direct evidence for divergent evolution of molecular circadian clocks in response to selection imposed on an overt rhythmic behavior and highlight early and late populations as potential models for chronotype studies by providing a preliminary groundwork for further exploration of molecular-genetic correlates underlying circadian clock-chronotype association.

Yukilevich, R., Harvey, T., Nguyen, S., Kehlbeck, J. and Park, A. (2016). The search for causal traits of speciation: Divergent female mate preferences target male courtship song, not pheromones, in Drosophila athabasca species complex. Evolution [Epub ahead of print]. PubMed ID: 26831347
Understanding speciation requires the identification of traits that cause reproductive isolation. This remains a major challenge since it is difficult to determine which of the many divergent traits actually caused speciation. To overcome this difficulty, the sexual cue traits and behaviors associated with rapid speciation were studied between EA and WN sympatric behavioral races of Drosophila athabasca that diverged only 16,000-20,000 years ago. First, it was found that sexual isolation was essentially complete and driven primarily by divergent female mating preferences. To determine the target of female mate choice, it was found that, unlike cuticular hydrocarbons (CHCs), male courtship song is highly divergent between EA and WN in both allopatry and sympatry and is not affected by latitudinal variation. Pheromone rub-off experiments were used to show no effect of CHCs on divergent female mate choice. In contrast, both male song differences and male mating success in hybrids exhibited a large X-effect, and playback song experiments confirmed that male courtship song is indeed the target of sexual isolation. These results show that a single secondary sexual trait is a major driver of speciation and suggest that the number of traits involved in speciation might be overestimated when older taxa are studied.

Schrider, D. R., Hahn, M. W. and Begun, D. J. (2016). Parallel evolution of copy-number variation across continents in Drosophila melanogaster. Mol Biol Evol [Epub ahead of print]. PubMed ID: 26809315
Genetic differentiation across populations that is maintained in the presence of gene flow is a hallmark of spatially varying selection. In Drosophila melanogaster, the latitudinal clines across the eastern coasts of Australia and North America appear to be examples of this type of selection, with recent studies showing that a substantial portion of the D. melanogaster genome exhibits allele frequency differentiation with respect to latitude on both continents. As of yet there has been no genome-wide examination of differentiated copy-number variants (CNVs) in these geographic regions, despite their potential importance for phenotypic variation in Drosophila and other taxa. This study presents an analysis is presented of geographic variation in CNVs in D. melanogaster. The first genomic analysis of geographic variation for copy-number variation in the sister species, D. simulans, in order to investigate patterns of parallel evolution in these close relatives. In D. melanogaster hundreds of CNVs were found, many of which show parallel patterns of geographic variation on both continents, lending support to the idea that they are influenced by spatially varying selection. These findings support the idea that polymorphic CNVs contribute to local adaptation in D. melanogaster. In contrast, very few CNVs were found in D. simulans that are geographically differentiated in parallel on both continents, consistent with earlier work suggesting that clinal patterns are weaker in this species.

Yassin, A., Bastide, H., Chung, H., Veuille, M., David, J. R. and Pool, J. E. (2016). Ancient balancing selection at tan underlies female colour dimorphism in Drosophila erecta. Nat Commun 7: 10400. PubMed ID: 26778363
Dimorphic traits are ubiquitous in nature, but the evolutionary factors leading to dimorphism are largely unclear. This study investigate a potential case of sexual mimicry in Drosophila erecta, in which females show contrasting resemblance to males. The genetic basis of this sex-limited colour dimorphism was mapped to a region containing the gene tan. A striking signal of ancient balancing selection was found at the 'male-specific enhancer' of tan, with exceptionally high sequence divergence between light and dark alleles, suggesting that this dimorphism has been adaptively maintained for millions of years. Using transgenic reporter assays, it was confirmed that these enhancer alleles encode expression differences that are predicted to generate this pigmentation dimorphism. These results are compatible with the theoretical prediction that divergent phenotypes maintained by selection can evolve simple genetic architectures.

Lima, T. G. (2014). Higher levels of sex chromosome heteromorphism are associated with markedly stronger reproductive isolation. Nat Commun 5: 4743. PubMed ID: 25144162
The two 'rules of speciation', Haldane's rule and the large X-effect, describe the genetic basis of postzygotic isolation, and have led to the realization that sex chromosomes play an important role in this process. However, a range of sex determination mechanisms exists in nature, not always involving sex chromosomes. Based on these 'rules of speciation', this study tested the hypothesis that the presence of sex chromosomes will contribute to a faster evolution of intrinsic postzygotic isolation. Taxa that do not have sex chromosomes were shown to evolve lower levels of postzygotic isolation than taxa with sex chromosomes, at a similar amount of genetic divergence. Taxa with young homomorphic sex chromosomes show an intermediate pattern compared to taxa with heteromorphic sex chromosomes and taxa without sex chromosomes. These results are consistent with predictions from the two 'rules of speciation', and emphasize the importance of sex chromosomes for the evolution of intrinsic postzygotic isolation.

Saturday, February 13th

Bouge, A. L. and Parmentier, M. L. (2016). Tau excess impairs mitosis and kinesin-5 function, leading to aneuploidy and cell death. Dis Model Mech [Epub ahead of print]. PubMed ID: 26822478
In neurodegenerative diseases like Alzheimer's disease (AD), cell cycle defects and associated aneuploidy have been described. However, the importance of these defects in the physiopathology of AD and the underlying mechanistic processes are largely unknown in particular with respect to the microtubule-binding protein Tau, which is found in excess in the brain and cerebrospinal fluid of patients. Although it has long been known that Tau is phosphorylated during mitosis to generate a lower affinity for microtubules, there has been no indication that an excess of this protein could affect mitosis. The effect of an excess of human Tau (hTau) protein on cell mitosis was studied in vivo. Using the Drosophila developing wing disc epithelium as a model, this study shows that an excess of hTau induces a mitotic arrest, with the presence of monopolar spindles. This mitotic defect leads to aneuploidy and apoptotic cell death. The mechanism of action of hTau was studied and it was found that the MT-binding domain of hTau is responsible for these defects. hTau effects occur via the inhibition of the function of the kinesin Klp61F, the Drosophila homologue of kinesin-5 (also called Eg5 or KIF11). This deleterious effect of hTau is also found in other Drosophila cell types (neuroblasts) and tissues (the developing eye disc) as well as in human Hela cells.By demonstrating that microtubule-bound Tau inhibits the Eg5/KIF11 kinesin and cell mitosis, this work provides a new framework to consider the role of Tau in neurodegenerative diseases.

Hervas, R., Li, L., Majumdar, A., Fernandez-Ramirez Mdel, C., Unruh, J. R., Slaughter, B. D., Galera-Prat, A., Santana, E., Suzuki, M., Nagai, Y., Bruix, M., Casas-Tinto, S., Menendez, M., Laurents, D. V., Si, K. and Carrion-Vazquez, M. (2016). Molecular basis of Orb2 amyloidogenesis and blockade of memory consolidation. PLoS Biol 14: e1002361. PubMed ID: 26812143
Amyloids are ordered protein aggregates that are typically associated with neurodegenerative diseases and cognitive impairment. By contrast, the amyloid-like state of the neuronal RNA binding protein Orb2 in Drosophila was recently implicated in memory consolidation, but it remains unclear what features of this functional amyloid-like protein give rise to such diametrically opposed behaviour. Using an array of biophysical, cell biological and behavioural assays this study has characterized the structural features of Orb2 from the monomer to the amyloid state. Surprisingly, it was found that Orb2 shares many structural traits with pathological amyloids, including the intermediate toxic oligomeric species, which can be sequestered in vivo in hetero-oligomers by pathological amyloids. However, unlike pathological amyloids, Orb2 rapidly forms amyloids and its toxic intermediates are extremely transient, indicating that kinetic parameters differentiate this functional amyloid from pathological amyloids. It was also observed that a well-known anti-amyloidogenic peptide interferes with long-term memory in Drosophila. These results provide structural insights into how the amyloid-like state of the Orb2 protein can stabilize memory and be nontoxic. They also provide insight into how amyloid-based diseases may affect memory processes.

Slade, J. D. and Staveley, B. E. (2015). Enhanced survival of Drosophila Akt1 hypomorphs during amino-acid starvation requires foxo. Genome: 1-7. PubMed ID: 26783834
Disordered eating includes any pattern of irregular eating that may lead to either extreme weight loss or obesity. The conserved insulin receptor signalling pathway acts to regulate energy balance and nutrient intake, and its central component Akt1 and endpoint effector foxo are pivotal for survival during nutritional stress. Recently generated Akt1 hypomorphic mutant lines exhibit a moderate decrease in lifespan when aged upon standard media, yet show a considerable increase in survival upon amino-acid starvation media. While the loss of foxo function significantly reduces the survival response to amino-acid starvation, a combination of these Akt1 hypomorphs and a null foxo mutation reveal a synergystic and severe reduction in lifespan upon standard media, and an epistatic relationship when undergoing amino-acid starvation. Evaluation of survivorship upon amino-acid starvation media of these double mutants indicate a phenotype similar to the original foxo mutant demonstrating the role of foxo in this Akt1 phenotype. These results indicate that the subtle manipulation of foxo through Akt1 can enhance survival during adverse nutrient conditions to model the ability of individuals to tolerate nutrient deprivation. Ultimately, a Drosophila model of disordered eating could generate new avenues to develop potential therapies for related human conditions.

Streit, A.K., Fan, Y.N., Masullo, L. and Baines, R.A. (2016). Calcium imaging of neuronal activity in Drosophila can identify anticonvulsive compounds. PLoS One 11: e0148461. PubMed ID: 26863447
This study uses neuronal expression of GCaMP, a potent calcium reporter, to image neuronal activity. Expression in motoneurons in the isolated CNS of third instar larvae shows waves of calcium-activity that pass between segments of the ventral nerve cord. Time between calcium peaks, in the same neurons, between adjacent segments usually shows a temporal separation of greater than 200 ms. Exposure to proconvulsants (picrotoxin or 4-aminopyridine) reduces separation to below 200 ms showing increased synchrony of activity across adjacent segments. Increased synchrony, characteristic of epilepsy, is similarly observed in genetic seizure mutants: bangsenseless1 and paralyticK1270T . Exposure of bss1 to clinically-used antiepileptic drugs (phenytoin or gabapentin) significantly reduces synchrony. The measure of synchronicity was used to evaluate the effectiveness of known and novel anticonvulsive compounds (antipain, isethionate, etopiside rapamycin and dipyramidole) to reduce seizure-like CNS activity. It was shown that such compounds also reduce the Drosophila voltage-gated persistent Na+ current (INaP) in an identified motoneuron (aCC). These combined assays provide a rapid and reliable method to screen unknown compounds for potential to function as anticonvulsants.

Friday, February 12th

Kemppainen, E., George, J., Garipler, G., Tuomela, T., Kiviranta, E., Soga, T., Dunn, C.D. and Jacobs, H.T. (2016). Mitochondrial dysfunction plus high-sugar diet provokes a metabolic crisis that inhibits growth. PLoS One 11: e0145836. PubMed ID: 26812173
The Drosophila mutant tko25t, a nuclear mis-sense mutation in the gene for mitoribosomal protein Technical knockout, exhibits a deficiency of mitochondrial protein synthesis, leading to a global insufficiency of respiration and oxidative phosphorylation. This entrains an organismal phenotype of developmental delay and sensitivity to seizures induced by mechanical stress. This study found that the mutant phenotype is exacerbated in a dose-dependent fashion by high dietary sugar levels. tko25t larvae were found to exhibit severe metabolic abnormalities that were further accentuated by high-sugar diet. These include elevated pyruvate and lactate, decreased ATP and NADPH. Dietary pyruvate or lactate supplementation phenocopies the effects of high sugar. Based on tissue-specific rescue, the crucial tissue in which this metabolic crisis initiates is the gut. It is accompanied by down-regulation of the apparatus of cytosolic protein synthesis and secretion at both the RNA and post-translational levels, including a novel regulation of S6 kinase at the protein level. 

Musselman, L. P., Fink, J. L. and Baranski, T. J. (2016). CoA protects against the deleterious effects of caloric overload in Drosophila. J Lipid Res [Epub ahead of print]. PubMed ID: 26805007
A Drosophila model of type 2 diabetes was developed in which high sugar (HS) feeding leads to insulin resistance. In this model, adipose triglyceride storage is protective against fatty acid toxicity and diabetes. Initial biochemical and gene expression studies suggested that deficiency in acetyl-CoA might underlie reduced triglyceride synthesis in animals during chronic HS feeding. Focusing on the Drosophila fat body, which is specialized for triglyceride storage and lipolysis, a series of experiments was undertaken to test the hypothesis that CoA could protect against the deleterious effects of caloric overload. Quantitative metabolomics revealed a reduction in substrate availability for CoA synthesis in the face of an HS diet. Further reducing CoA synthetic capacity by expressing fat body-specific RNAi targeting pantothenate kinase (fumble) or phosphopantothenoylcysteine decarboxylase (PPCS) exacerbated HS-diet-induced accumulation of free fatty acids. Dietary supplementation with pantothenic acid (vitamin B5, a precursor of CoA) ameliorated HS-diet-induced free fatty acid accumulation and hyperglycemia while increasing triglyceride synthesis. Taken together, these data support a model where free CoA is required to support fatty acid esterification and to protect against the toxicity of HS diets.

Kristensen, T. N., Kjeldal, H., Schou, M. F. and Nielsen, J. L. (2016). Proteomic data reveals a physiological basis for costs and benefits associated with thermal acclimation. J Exp Biol [Epub ahead of print]. PubMed ID: 26823104
Physiological adaptation through acclimation is one way to cope with temperature changes. Biochemical studies on acclimation responses in ectotherms have so far mainly investigated consequences of short-term acclimation at the adult stage and focussed on adaptive responses. This study assessed the consequences of developmental and adult rearing at low (12 ° C), benign (25 ° C) and high (31 ° C) temperatures in Drosophila. Cold and heat tolerance were assessed and detailed proteomic profiles were obtained of flies from the three temperatures. The proteomic profiles provided a holistic understanding of the underlying biology associated with both adaptive and non-adaptive temperature responses. Results show strong benefits and costs across tolerances: rearing at low temperature increased adult cold tolerance and decreased adult heat tolerance and vice versa with development at high temperatures. In the proteomic analysis a large number of proteins were identified and quantified compared to previous studies on ectotherms (1440 proteins across all replicates and rearing regimes), enabling extension of the proteomic approach using enrichment analyses. This gave both detailed information on individual proteins as well as pathways affected by rearing temperature, pinpointing mechanisms likely responsible for the strong costs and benefits of rearing temperature on functional phenotypes. Several well-known heat shock proteins as well as proteins not previously associated with thermal stress were among the differentially expressed proteins. Upregulation of proteasome proteins was found to be an important adaptive process at high stressful rearing temperatures, and occurs at the expense of downregulation of basal metabolic functions.

Browne, A. and O'Donnell, M. J. (2016). Segment-specific Ca transport by isolated Malpighian tubules of Drosophila melanogaster: A comparison of larval and adult stages. J Insect Physiol 87: 1-11. PubMed ID: 26802560
Haemolymph calcium homeostasis in insects is achieved through the regulation of calcium excretion by Malpighian tubules in two ways: (1) sequestration of calcium within biomineralized granules and (2) secretion of calcium in soluble form within the primary urine. Using the scanning ion-selective electrode technique (SIET), basolateral Ca2+ transport was measured at the distal, transitional, main and proximal tubular segments of anterior tubules isolated from both 3rd instar larvae and adults of Drosophila. Basolateral Ca2+ transport exceeded transepithelial secretion by 800-fold and 11-fold in anterior tubules of larvae and adults, respectively. The magnitude of Ca2+ fluxes across the distal tubule of larvae and adults were larger than fluxes across the downstream segments by 10 and 40 times, respectively, indicating a dominant role for the distal segment in whole animal Ca2+ regulation. Basolateral Ca2+ transport across distal tubules of Drosophila varied throughout the life cycle; Ca2+ was released by distal tubules of larvae, taken up by distal tubules of young adults and was released once again by tubules of adults 168h post-eclosion. In adults and larvae, SIET measurements revealed sites of both Ca2+ uptake and Ca2+ release across the basolateral surface of the distal segment of the same tubule, indicating that Ca2+ transport is bidirectional. Ca2+ uptake across the distal segment of tubules of young adults and Ca2+ release across the distal segment of tubules of older adults was also suggestive of reversible Ca2+ storage. These results suggest that the distal tubules of Drosophila are dynamic calcium stores which allow efficient haemolymph calcium regulation through active Ca2+ sequestration during periods of high dietary calcium intake and passive Ca2+ release during periods of calcium deficiency.

Thursday, February 11th

Weiner, A. T., Lanz, M. C., Goetschius, D. J., Hancock, W. O. and Rolls, M. M. (2016). Kinesin-2 and Apc function at dendrite branch points to resolve microtubule collisions. Cytoskeleton (Hoboken) 73: 35-44. PubMed ID: 26785384
In Drosophila neurons, kinesin-2, EB1 and Apc are required to maintain minus-end-out dendrite microtubule polarity, and it has been proposed they steer microtubules at branch points. Motor-mediated steering of microtubule plus ends could be accomplished in two ways: 1) by linking a growing microtubule tip to the side of an adjacent microtubule as it navigates the branch point (bundling), or 2) by directing a growing microtubule after a collision with a stable microtubule (collision resolution). Using live imaging to distinguish between these two mechanisms, this study found that reduction of kinesin-2 did not alter the number of microtubules that grew along the edge of the branch points where stable microtubules are found. However, reduction of kinesin-2 or Apc did affect the number of microtubules that slowed down or depolymerized as they encountered the side of the branch opposite to the entry point. These results are consistent with kinesin-2 functioning with Apc to resolve collisions. However, they do not pinpoint stable microtubules as the collision partner as stable microtubules are typically very close to the membrane. To determine whether growing microtubules were steered along stable ones after a collision, the behavior was analyzed of growing microtubules at dendrite crossroads where stable microtubules run through the middle of the branch point. In control neurons, microtubules turned in the middle of the crossroads. However, when kinesin-2 was reduced some microtubules grew straight through the branch point and failed to turn. It is proposed that kinesin-2 functions to steer growing microtubules along stable ones following collisions.

Dollar, G., Gombos, R., Barnett, A. A., Sanchez Hernandez, D., Maung, S. M., Mihaly, J. and Jenny, A. (2016). Unique and overlapping functions of formins Frl and DAAM during ommatidial rotation and neuronal development in Drosophila. Genetics [Epub ahead of print]. PubMed ID: 26801180
The non-canonical Frizzled/Planar cell polarity (PCP) pathway regulates establishment of polarity within the plane of an epithelium to generate diversity of cell fates, asymmetric, but highly aligned structures, or to orchestrate the directional migration of cells during convergent extension during vertebrate gastrulation. In Drosophila, PCP signaling is essential to orient actin wing hairs and to align ommatidia in the eye, in part by coordinating the movement of groups of photoreceptor cells during ommatidial rotation. Importantly, the coordination of PCP signaling with changes in the cytoskeleton is essential for proper epithelial polarity. Formins polymerize linear actin filaments and are key regulators of the actin cytoskeleton. This study shows that the Diaphanous related formin Frl, the single fly member of the FMNL (Formin related in Leukocytes/ Formin-like) formin subfamily affects ommatidial rotation in the Drosophila eye and is controlled by the Rho family GTPase Cdc42. Interestingly, it was also found that frl mutants exhibit an axon growth phenotype in the mushroom body, a center for olfactory learning in the Drosophila brain, which is also affected in a subset of PCP genes. Significantly, Frl cooperates with Cdc42 and another formin, DAAM, during mushroom body formation. This study thus suggests that different formins can cooperate or act independently in distinct tissues, likely integrating various signaling inputs with the regulation of the cytoskeleton. It furthermore highlights the importance and complexity of formin dependent cytoskeletal regulation in multiple organs and developmental contexts.

Izumi, Y., Motoishi, M., Furuse, K. and Furuse, M. (2016). A tetraspanin regulates septate junction formation in Drosophila midgut. J Cell Sci [Epub ahead of print]. PubMed ID: 26848177
Septate junctions (SJs) are membrane specializations that restrict the free diffusion of solutes via the paracellular pathway in invertebrate epithelia. In arthropods, two morphologically different types of SJs are observed: pleated SJs (pSJs) and smooth SJs (sSJs), which are present in ectodermally- and endodermally-derived epithelia, respectively. Recent identification of sSJ-specific proteins, Mesh and Ssk, in Drosophila indicates that the molecular compositions of sSJs and pSJs differ. A deficiency screen based on immunolocalization of Mesh, identified a tetraspanin family protein, Tsp2A, as a novel protein involved in sSJ formation in Drosophila. Tsp2A specifically localizes at sSJs in the midgut and Malpighian tubules. Compromised Tsp2A expression caused by RNAi or the CRISPR/Cas9 system is associated with defects in the ultrastructure of sSJs, changes localization of other sSJ proteins, and impairs barrier function of the midgut. In most Tsp2A-mutant cells, Mesh fails to localize to sSJs and is distributed through the cytoplasm. Tsp2A forms a complex with Mesh and Ssk and these proteins are mutually interdependent for their localization. These observations suggest that Tsp2A cooperates with Mesh and Ssk to organize sSJs.

Jolly, A. L., Luan, C. H., Dusel, B. E., Dunne, S. F., Winding, M., Dixit, V. J., Robins, C., Saluk, J. L., Logan, D. J., Carpenter, A. E., Sharma, M., Dean, D., Cohen, A. R. and Gelfand, V. I. (2016). A genome-wide RNAi screen for microtubule bundle formation and lysosome motility regulation in Drosophila S2 Cells. Cell Rep 14: 611-620. PubMed ID: 26774481
Long-distance intracellular transport of organelles, mRNA, and proteins ("cargo") occurs along the microtubule cytoskeleton by the action of kinesin and dynein motor proteins, but the vast network of factors involved in regulating intracellular cargo transport are still unknown. This study capitalized on the Drosophila melanogaster S2 model cell system to monitor lysosome transport along microtubule bundles, which require enzymatically active kinesin-1 motor protein for their formation. This study used an automated tracking program and a naive Bayesian classifier for the multivariate motility data to analyze 15,683 gene phenotypes and find 98 proteins involved in regulating lysosome motility along microtubules and 48 involved in the formation of microtubule filled processes in S2 cells. Innate immunity genes, ion channels, and signaling proteins were identified having a role in lysosome motility regulation; an unexpected relationship was found between the dynein motor, Rab7a, and lysosome motility regulation.

Wednesday, February 10th

Bosveld, F., Guirao, B., Wang, Z., Riviere, M., Bonnet, I., Graner, F. and Bellaiche, Y. (2016). Modulation of junction tension by tumor-suppressors and proto-oncogenes regulates cell-cell contacts. Development [Epub ahead of print]. PubMed ID: 26811379
Tumor-suppressor and proto-oncogenes play critical roles in tissue proliferation. Furthermore, deregulation of their functions is deleterious to tissue architecture and can result in the sorting of somatic rounded clones minimizing their contact with surrounding wild-type (wt) cells. Defects in somatic clones shape correlate with defects in proliferation, cell affinity, cell-cell adhesion, oriented cell division and cortical elasticity. Combining genetics, live-imaging, laser ablation and computer simulations, whether distinct or similar mechanisms can account for the common role of tumor-suppressor and proto-oncogenes in cell-cell contact regulation was analyzed. In Drosophila epithelia, Fat (Ft) and Dachsous (Ds) tumor-suppressors regulate cell proliferation, tissue morphogenesis, planar cell polarity and junction tension. By analyzing the time evolution of ft mutant cells and clones, this study shows that ft clones reduce their cell-cell contact with surrounding wt tissue in the absence of concomitant cell divisions and over-proliferation. This contact reduction depends on opposite changes of junction tensions in the clone bulk and its boundary with neighboring wt tissue. More generally, either clone bulk or boundary junction tensions is modulated by the activation of Yorkie, Myc and Ras yielding similar contact reductions with wt cells. Together these data highlight mechanical roles for proto-oncogene and tumor-suppressor pathways in cell-cell interactions.

Bielmeier, C., Alt, S., Weichselberger, V., La Fortezza, M., Harz, H., Jülicher, F., Salbreux, G. and Classen, A.K. (2016). Interface contractility between differently fated cells drives cell elimination and cyst formation. Curr Biol [Epub ahead of print]. PubMed ID: 26853359
This study finds that ectopic expression of transcription factors that specify cell fates causes abnormal epithelial cysts in Drosophila imaginal discs. Cysts do not form cell autonomously but result from the juxtaposition of two cell populations with divergent fates. Juxtaposition of wild-type and aberrantly specified cells induces enrichment of actomyosin at their entire shared interface, both at adherens junctions as well as along basolateral interfaces. Experimental validation of 3D vertex model simulations demonstrates that enhanced interface contractility is sufficient to explain many morphogenetic behaviors, which depend on cell cluster size. These range from cyst formation by intermediate-sized clusters to segregation of large cell populations by formation of smooth boundaries or apical constriction in small groups of cells. In addition, single cells experiencing lateral interface contractility are eliminated from tissues by apoptosis. Cysts, which disrupt epithelial continuity, form when elimination of single, aberrantly specified cells fails and cells proliferate to intermediate cell cluster sizes. Thus, increased interface contractility functions as error correction mechanism eliminating single aberrant cells from tissues, but failure leads to the formation of large, potentially disease-promoting cysts. These results provide a novel perspective on morphogenetic mechanisms, which arise from cell-fate heterogeneities within tissues and maintain or disrupt epithelial homeostasis.

Eichenlaub, T., Cohen, S.M. and Herranz, H. (2016). Cell competition drives the formation of metastatic tumors in a Drosophila model of epithelial tumor formation. Curr Biol [Epub ahead of print]. PubMed ID: 26853367
Cell competition is a homeostatic process in which proliferating cells compete for survival. Elimination of otherwise normal healthy cells through competition is important during development and has recently been shown to contribute to maintaining tissue health during organismal aging. The mechanisms that allow for ongoing cell competition during adult life could, in principle, contribute to tumorigenesis. However, direct evidence supporting this hypothesis has been lacking. This study provides evidence that cell competition drives tumor formation in a Drosophila model of epithelial cancer. Cells expressing EGFR together with the conserved microRNA miR-8 acquire the properties of supercompetitors. Neoplastic transformation and metastasis depend on the ability of these cells to induce apoptosis and engulf nearby cells. miR-8 expression causes genome instability by downregulating expression of the Septin family protein Peanut. Cytokinesis failure due to downregulation of Peanut is required for tumorigenesis. The study provides evidence that the cellular mechanisms that drive cell competition during normal tissue growth can be co-opted to drive tumor formation and metastasis. Analogous mechanisms for cytokinesis failure may lead to polyploid intermediates in tumorigenesis in mammalian cancer models.

Ma, M., Zhao, H., Zhao, H., Binari, R., Perrimon, N. and Li, Z. (2016). Wildtype adult stem cells, unlike tumor cells, are resistant to cellular damages in Drosophila. Dev Biol [Epub ahead of print]. PubMed ID: 26845534
Adult stem cells or residential progenitor cells are critical to maintain the structure and function of adult tissues (homeostasis) throughout the lifetime of an individual. Mis-regulation of stem cell proliferation and differentiation often leads to diseases including cancer, however, how wildtype adult stem cells and cancer cells respond to cellular damages remains unclear. This study found that in the adult Drosophila midgut, intestinal stem cells (ISCs), unlike tumor intestinal cells, are resistant to various cellular damages. Tumor intestinal cells, unlike wildtype ISCs, are easily eliminated by apoptosis. Further, their proliferation is inhibited upon autophagy induction, and autophagy-mediated tumor inhibition is independent of caspase-dependent apoptosis. Interestingly, inhibition of tumorigenesis by autophagy is likely through the sequestration and degradation of mitochondria, as compromising mitochondria activity in these tumor models mimics the induction of autophagy and increasing the production of mitochondria alleviates the tumor-suppression capacity of autophagy. Together, these data demonstrate that wildtype adult stem cells and tumor cells show dramatic differences in sensitivity to cellular damages, thus providing potential therapeutic implications targeting tumorigenesis.

Tuesday, February 9th

Ma, Q., de Cuevas, M. and Matunis, E.L. (2016). Chinmo is sufficient to induce male fate in somatic cells of the adult Drosophila ovary. Development [Epub ahead of print]. PubMed ID: 26811385
Sexual identity is continuously maintained in specific differentiated cell types long after sex determination occurs during development. In the adult Drosophila testis, the putative transcription factor Chronologically inappropriate morphogenesis (Chinmo) acts with the canonical male sex determinant DoublesexM (DsxM) to maintain the male identity of somatic cyst stem cells and their progeny. This study reports that ectopic expression of chinmo is sufficient to induce a male identity in adult ovarian somatic cells, but it acts through a DsxM-independent mechanism. In contrast, the feminization of the testis somatic stem cell lineage caused by loss of chinmo is enhanced by loss of the canonical female sex determinant DsxF, indicating that chinmo acts together with the canonical sex determination pathway to maintain the male identity of testis somatic cells. Consistent with this finding, ectopic expression of female sex determinants in the adult testis disrupts tissue morphology. The miRNA let-7 downregulates chinmo in many contexts, and ectopic expression of let-7 in the adult testis is sufficient to recapitulate the chinmo loss of function phenotype, but no apparent phenotypes were found upon removal of let-7 in the adult ovary or testis. The finding that chinmo is necessary and sufficient to promote a male identity in adult gonadal somatic cells suggests that the sexual identity of somatic cells can be reprogrammed in the adult Drosophila ovary as well as in the testis.

Ku, H. Y., Gangaraju, V. K., Qi, H., Liu, N. and Lin, H. (2016). Tudor-SN interacts with Piwi antagonistically in regulating spermatogenesis but synergistically in silencing transposons in Drosophila. PLoS Genet 12: e1005813. PubMed ID: 26808625
Piwi interacts withTudor-SN (Tudor staphylococcal nuclease, TSN) antagonistically in regulating spermatogenesis but synergistically in silencing transposons. However, it is not required for piRNA biogenesis. This study shows that TSN colocalizes with Piwi in primordial germ cells (PGCs) and embryonic somatic cells. In adult ovaries and testes, TSN is ubiquitously expressed and enriched in the cytoplasm of both germline and somatic cells. The tsn mutants display a higher mitotic index of spermatogonia, accumulation of spermatocytes, defects in meiotic cytokinesis, a decreased number of spermatids, and eventually reduced male fertility. Germline-specific TSN-expression analysis demonstrates that this function is germline-dependent. Different from other known Piwi interters, TSN represses Piwi expression at both protein and mRNA levels. Furthermore, reducing piwi expression in the germline rescues tsn mutant phenotype in a dosage-dependent manner, demonstrating that Piwi and TSN interact antagonistically in germ cells to regulate spermatogenesis. However, the tsn deficiency has little, if any, impact on piRNA biogenesis but displays a synergistic effect with piwi mutants in transposon de-silencing. These results reveal the biological function of TSN and its contrasting modes of interaction with Piwi in spermatogenesis, transposon silencing, and piRNA biogenesis.

Sieber, M. H., Thomsen, M. B. and Spradling, A. C. (2016). Electron transport chain remodeling by GSK3 during oogenesis connects nutrient state to reproduction. Cell 164: 420-432. PubMed ID: 26824655
Reproduction is heavily influenced by nutrition and metabolic state. Many common reproductive disorders in humans are associated with diabetes and metabolic syndrome. This study characterized the metabolic mechanisms that support oogenesis and found that mitochondria in mature Drosophila oocytes enter a low-activity state of respiratory quiescence by remodeling the electron transport chain (ETC). This shift in mitochondrial function leads to extensive glycogen accumulation late in oogenesis and is required for the developmental competence of the oocyte. Decreased insulin signaling initiates ETC remodeling and mitochondrial respiratory quiescence through glycogen synthase kinase 3 (GSK3). Intriguingly, similar ETC remodeling and glycogen uptake was observed in maturing Xenopus oocytes, suggesting that these processes are evolutionarily conserved aspects of oocyte development. These studies reveal an important link between metabolism and oocyte maturation.

Pearson, J. R., Zurita, F., Tomas-Gallardo, L., Diaz-Torres, A., Diaz de la Loza Mdel, C., Franze, K., Martin-Bermudo, M. D. and Gonzalez-Reyes, A. (2016). ECM-Regulator timp is required for stem cell niche organization and cyst production in the Drosophila ovary. PLoS Genet 12: e1005763. PubMed ID: 26808525
The extracellular matrix (ECM) is a pivotal component adult tissues and of many tissue-specific stem cell niches. It provides structural support and regulates niche signaling during tissue maintenance and regeneration. In many tissues, ECM remodeling depends on the regulation of MMP (matrix metalloproteinase) activity by inhibitory TIMP (tissue inhibitors of metalloproteinases) proteins. This study reports that the only Drosophila timp gene is required for maintaining the normal organization and function of the germline stem cell niche in adult females. timp mutant ovaries show reduced levels of both Drosophila Collagen IV α chains. In addition, tissue stiffness and the cellular organization of the ovarian niche are affected in timp mutants. Finally, loss of timp impairs the ability of the germline stem cell niche to generate new cysts. These results demonstrating a crucial role for timp in tissue organization and gamete production thus provide a link between the regulation of ECM metabolism and tissue homeostasis.

Monday, February 8th

Okumura, T., Takeda, K., Kuchiki, M., Akaishi, M., Taniguchi, K. and Takashi, A. Y. (2015). GATAe regulates intestinal stem cell maintenance and differentiation in Drosophila adult midgut. Dev Biol [Epub ahead of print]. PubMed ID: 26719127
Adult intestinal tissues, exposed to the external environment, play important roles including barrier and nutrient-absorption functions. These functions are ensured by adequately controlled rapid-cell metabolism. GATA transcription factors play essential roles in the development and maintenance of adult intestinal tissues both in vertebrates and invertebrates. This study investigated the roles of GATAe, the Drosophila intestinal GATA factor, in adult midgut homeostasis with its first-generated knock-out mutant as well as cell type-specific RNAi and overexpression experiments. These results indicate that GATAe is essential for proliferation and maintenance of intestinal stem cells (ISCs). Also, GATAe is involved in the differentiation of enterocyte (EC) and enteroendocrine (ee) cells in both Notch (N)-dependent and -independent manner. The results also indicate that GATAe has pivotal roles in maintaining normal epithelial homeostasis of the Drosophila adult midgut through interaction of N signaling. Since recent reports showed that mammalian GATA-6 regulates normal and cancer stem cells in the adult intestinal tract, these data also provide information on the evolutionally conserved roles of GATA factors in stem-cell regulation.

Tian, A., Benchabane, H., Wang, Z. and Ahmed, Y. (2016). Regulation of stem cell proliferation and cell fate specification by Wingless/Wnt signaling gradients enriched at adult intestinal compartment boundaries. PLoS Genet 12: e1005822. PubMed ID: 26845150
Intestinal stem cell (ISC) self-renewal and proliferation are directed by Wnt/β-catenin signaling in mammals, whereas aberrant Wnt pathway activation in ISCs triggers the development of human colorectal carcinoma. This study utilized the Drosophila midgut, a powerful model for ISC regulation, to elucidate the mechanisms by which Wingless (Wg)/Wnt regulates intestinal homeostasis and development. It was shown that the Wg signaling pathway, activation of which peaks at each of the major compartment boundaries of the adult intestine, has essential functions. Wg pathway activation in the intestinal epithelium is required not only to specify cell fate near compartment boundaries during development, but also to control ISC proliferation within compartments during homeostasis. Further, in contrast with the previous focus on Wg pathway activation within ISCs, it was demonstrated that the primary mechanism by which Wg signaling regulates ISC proliferation during homeostasis is non-autonomous. Activation of the Wg pathway in absorptive enterocytes is required to suppress JAK-STAT signaling in neighboring ISCs, and thereby their proliferation. The study concludes that Wg signaling gradients have essential roles during homeostasis and development of the adult intestine, non-autonomously controlling stem cell proliferation inside compartments, and autonomously specifying cell fate near compartment boundaries.

Ding, R., Weynans, K., Bossing, T., Barros, C.S. and Berger, C. (2016). The Hippo signalling pathway maintains quiescence in Drosophila neural stem cells. Nat Commun 7: 10510. PubMed ID: 26821647
Stem cells control their mitotic activity to decide whether to proliferate or to stay in quiescence. Drosophila neural stem cells (NSCs) are quiescent at early larval stages, when they are reactivated in response to metabolic changes. This study reports that cell-contact inhibition of growth through the canonical Hippo signalling pathway maintains NSC quiescence. Loss of the core kinases hippo or warts leads to premature nuclear localization of the transcriptional co-activator Yorkie and initiation of growth and proliferation in NSCs. Yorkie is necessary and sufficient for NSC reactivation, growth and proliferation. The Hippo pathway activity is modulated via inter-cellular transmembrane proteins Crumbs and Echinoid that are both expressed in a nutrient-dependent way in niche glial cells and NSCs. Loss of crumbs or echinoid in the niche only is sufficient to reactivate NSCs. Finally, the Hippo pathway activity discriminates quiescent from non-quiescent NSCs in the Drosophila nervous system.

Baechler, B. L., McKnight, C., Pruchnicki, P. C., Biro, N. A. and Reed, B. H. (2015). Hindsight/RREB-1 functions in both the specification and differentiation of stem cells in the adult midgut of Drosophila. Biol Open [Epub ahead of print]. PubMed ID: 26658272
The adult Drosophila midgut is established during the larval/pupal transition from undifferentiated cells known as adult midgut precursors (AMPs). Four fundamental cell types are found in the adult midgut epithelium: undifferentiated intestinal stem cells (ISCs) and their committed daughter cells, enteroblasts (EBs), plus enterocytes (ECs) and enteroendocrine cells (EEs). Using the Drosophila posterior midgut as a model, the function of the transcription factor Hindsight (Hnt)/RREB-1 was studied and its relationship to the Notch and Egfr signaling pathways. hnt wash shown to be required for EC differentiation in the context of ISC-to-EC differentiation, but not in the context of AMP-to-EC differentiation. In addition, hnt is required for the establishment of viable or functional ISCs. Overall, these studies introduce hnt as a key factor in the regulation of both the developing and the mature adult midgut. It is suggested that the nature of these contextual differences can be explained through the interaction of hnt with multiple signaling pathways.

Sunday, February 7th

Petley-Ragan, L.M., Ardiel, E.L., Rankin, C.H. and Auld, V.J. (2016). Accumulation of laminin monomers in Drosophila glia leads to glial endoplasmic reticulum stress and disrupted larval locomotion. J Neurosci 36: 1151-1164. PubMed ID: 26818504
The nervous system is surrounded by an extracellular matrix composed of large glycoproteins, including perlecan, collagens, and laminins. Glial cells in many organisms secrete laminin, a large heterotrimeric protein consisting of an α, β, and γ subunit. Prior studies have found that loss of laminin subunits from vertebrate Schwann cells causes loss of myelination and neuropathies, results attributed to loss of laminin-receptor signaling. This study demonstrates that loss of the laminin γ subunit (LanB2) in the peripheral glia of Drosophila melanogaster results in the disruption of glial morphology due to disruption of laminin secretion. Specifically, knockdown of LanB2 in peripheral glia results in accumulation of the β subunit (LanB1), leading to distended endoplasmic reticulum (ER), ER stress, and glial swelling. The physiological consequences of disruption of laminin secretion in glia included decreased larval locomotion and ultimately lethality. Loss of the γ subunit from wrapping glia resulted in a disruption in the glial ensheathment of axons but surprisingly did not affect animal locomotion. It was found that Tango1, a protein thought to exclusively mediate collagen secretion, is also important for laminin secretion in glia via a collagen-independent mechanism. However loss of secretion of the laminin trimer does not disrupt animal locomotion. Rather, it is the loss of one subunit that leads to deleterious consequences through the accumulation of the remaining subunits.

Kashio, S., Obata, F., Zhang, L., Katsuyama, T., Chihara, T. and Miura, M. (2016). Tissue nonautonomous effects of fat body methionine metabolism on imaginal disc repair in Drosophila. Proc Natl Acad Sci U S A [Epub ahead of print]. PubMed ID: 26831070
Regulatory mechanisms for tissue repair and regeneration within damaged tissue have been extensively studied. However, the systemic regulation of tissue repair remains poorly understood. To elucidate tissue nonautonomous control of repair process, it is essential to induce local damage, independent of genetic manipulations in uninjured parts of the body. This study developed a system in Drosophila for spatiotemporal tissue injury using a temperature-sensitive form of diphtheria toxin A domain driven by the Q system to study factors contributing to imaginal disc repair. Using this technique, it was demonstrated that methionine metabolism in the fat body, a counterpart of mammalian liver and adipose tissue, supports the repair processes of wing discs. Local injury to wing discs decreases methionine and S-adenosylmethionine, whereas it increases S-adenosylhomocysteine in the fat body. Fat body-specific genetic manipulation of methionine metabolism results in defective disc repair but does not affect normal wing development. These data indicate the contribution of tissue interactions to tissue repair in Drosophila, as local damage to wing discs influences fat body metabolism, and proper control of methionine metabolism in the fat body, in turn, affects wing regeneration.

Yasin, H. W., van Rensburg, S. H., Feiler, C. E. and Johnson, R. I. (2016). The adaptor protein Cindr regulates JNK activity to maintain epithelial sheet integrity. Dev Biol [Epub ahead of print]. PubMed ID: 26772997
Epithelia are essential barrier tissues that must be appropriately maintained for their correct function. To achieve this a plethora of protein interactions regulate epithelial cell number, structure and adhesion, and differentiation. This study shows that Cindr (the Drosophila Cin85 and Cd2ap ortholog) is required to maintain epithelial integrity. Reducing Cindr triggered cell delamination and movement. Most delaminating cells died. These behaviors were consistent with JNK activation previously associated with loss of epithelial integrity in response to ectopic oncogene activity. This study has confirmed a novel interaction between Cindr and Drosophila JNK (dJNK), which when perturbed caused inappropriate JNK signaling. Genetically reducing JNK signaling activity suppressed the effects of reducing Cindr. Furthermore, ectopic JNK signaling phenocopied loss of Cindr and was partially rescued by concomitant cindr over-expression. Thus, correct Cindr-dJNK stoichiometry is essential to maintain epithelial integrity and disturbing this balance may contribute to the pathogenesis of disease states, including cancer.

Safi, F., Shteiman-Kotler, A., Zhong, Y., Iliadi, K. G., Boulianne, G. L. and Rotin, D. (2016). Drosophila Nedd4-long reduces Amphiphysin levels in muscles and leads to impaired T-tubule formation. Mol Biol Cell [Epub ahead of print]. PubMed ID: 26823013
Drosophila Nedd4 (dNedd4) is a HECT ubiquitin ligase with two main splice isoforms: dNedd4 short (dNedd4S) and long (dNedd4Lo). DNedd4Lo has a unique N-terminus containing a Pro-rich region. While dNedd4S promotes neuromuscular synaptogenesis, dNedd4Lo inhibits it and impairs larval locomotion. To delineate the cause of the impaired locomotion, binding partners to the N-terminal unique region of dNedd4Lo were sought in larval lysates using mass-spectrometry and Amphiphysin (dAmph) was identified. dAmph is a postsynaptic protein containing SH3-BAR domains, which regulates muscle transverse tubule (T-tubule) formation in flies. The interaction was validated by coimmunoprecipitation, and direct binding between dAmph-SH3 domain and dNedd4Lo-N-terminus was demonstrated. Accordingly, dNedd4Lo was colocalized with dAmph postsynaptically and at muscle T-tubules. Moreover, expression of dNedd4Lo in muscle during embryonic development led to disappearance of dAmph and to impaired T-tubule formation, phenocopying amph null mutants. This effect was not seen in muscles expressing dNedd4S or a catalytically-inactive dNedd4Lo(C->A). It is proposed that dNedd4Lo destabilizes dAmph in muscles, leading to impaired T-tubule formation and muscle function.

Saturday, February 6th

Coen, P., Xie, M., Clemens, J. and Murthy, M. (2016). Sensorimotor transformations underlying variability in song intensity during Drosophila courtship. Neuron 89: 629-644. PubMed ID: 26844835
Diverse animal species, from insects to humans, utilize acoustic signals for communication. Studies of the neural basis for song or speech production have focused almost exclusively on the generation of spectral and temporal patterns, but animals can also adjust acoustic signal intensity when communicating. For example, humans naturally regulate the loudness of speech in accord with a visual estimate of receiver distance. The underlying mechanisms for this ability remain uncharacterized in any system. This study shows that Drosophila males modulate courtship song amplitude with female distance. The study investigates each stage of the sensorimotor transformation underlying this behavior, from the detection of particular visual stimulus features and the timescales of sensory processing to the modulation of neural and muscle activity that generates song. The results demonstrate an unanticipated level of control in insect acoustic communication and uncover novel computations and mechanisms underlying the regulation of acoustic signal intensity.

Gorter, J. A., Jagadeesh, S., Gahr, C., Boonekamp, J. J., Levine, J. D. and Billeter, J. C. (2016). The nutritional and hedonic value of food modulate sexual receptivity in Drosophila melanogaster females. Sci Rep 6: 19441. PubMed ID: 26777264
Food and sex often go hand in hand because of the nutritional cost of reproduction. For Drosophila melanogaster females, this relationship is especially intimate because their offspring develop on food. Since yeast and sugars are important nutritional pillars for Drosophila, availability of these foods should inform female reproductive behaviours. Yet mechanisms coupling food and sex are poorly understood. This study shows that yeast increases female sexual receptivity through interaction between its protein content and its odorous fermentation product acetic acid, sensed by the Ionotropic odorant receptor neuron Ir75a. A similar interaction between nutritional and hedonic value applies to sugars where taste and caloric value only increase sexual receptivity when combined. Integration of nutritional and sensory values would ensure that there are sufficient internal nutrients for egg production as well as sufficient environmental nutrients for offspring survival. These findings provide mechanisms through which females may maximize reproductive output in changing environments.

Lihoreau, M., Clarke, I. M., Buhl, J., Sumpter, D. J. and Simpson, S. J. (2016). Collective selection of food patches in Drosophila. J Exp Biol [Epub ahead of print]. PubMed ID: 26747899
The fruit fly Drosophila melanogaster has emerged as a model organism for research on social interactions. While recent studies describe how individuals interact on foods for nutrition and reproduction, the complex dynamics by which groups initially develop and disperse have received little attention. This study investigated the dynamics of collective foraging decisions by Drosophila and their variation with group size and composition. Groups of adults and larvae facing a choice between two identical, nutritionally balanced, food patches distributed themselves asymmetrically, thereby exploiting one patch more than the other. The speed of the collective decisions increased with group size, as a result of flies joining foods faster. However, smaller groups exhibited more pronounced distribution asymmetries than larger ones. Using computer simulations, these non-linear phenomena were shown to emerge from social attraction towards occupied food patches, whose effects add up or compete depending on group size. The results open new opportunities for exploring complex dynamics of nutrient selection in simple and genetically tractable groups.

Sunouchi, K., Koganezawa, M. and Yamamoto, D. (2016). Requirement of the tec family tyrosine kinase Btk29a for courtship memory in Drosophila males. Arch Insect Biochem Physiol [Epub ahead of print]. PubMed ID: 26782301
A male Drosophila that is not successful in courtship will reduce his courtship efforts in the next encounter with a female. This courtship suppression persists for more than 1 h in wild-type males. The Btk29AficP mutant males null for the Btk29A type 2 isoform, a fly homolog of the nonreceptor tyrosine kinase Btk, show no courtship suppression, while Btk29A hypomorphic males exhibit a rapid decline in courtship suppression, leading to its complete loss within 30 min. The males of a revertant stock or Btk29AficP males that are also mutant for parkas, a gene encoding the presumptive negative regulator of Btk29A, exhibit normal courtship suppression. Since another behavioral assay has shown that Btk29AficP mutants are sensitization-defective, it is hypothesized that the mutant flies are unable to maintain the neural excitation state acquired by experience, resulting in the rapid loss of courtship suppression.

Friday, February 5th

Li, Q., Barish, S., Okuwa, S., Maciejewski, A., Brandt, A. T., Reinhold, D., Jones, C. D. and Volkan, P. C. (2016). A functionally conserved gene regulatory network module governing olfactory neuron diversity. PLoS Genet 12: e1005780. PubMed ID: 26765103
Sensory neuron diversity is required for organisms to decipher complex environmental cues. In Drosophila, the olfactory environment is detected by 50 different olfactory receptor neuron (ORN) classes that are clustered in combinations within distinct sensilla subtypes. Each sensilla subtype houses stereotypically clustered 1-4 ORN identities that arise through asymmetric divisions from a single multipotent sensory organ precursor (SOP). How each class of SOPs acquires a unique differentiation potential that accounts for ORN diversity is unknown. Previously, it was reported that a critical component of SOP diversification program, Rotund (Rn), increases ORN diversity by generating novel developmental trajectories from existing precursors within each independent sensilla type lineages. This study shows that Rn, along with BarH1/H2 (Bar), Bric-a-brac/ (Bab), Apterous (Ap) and Dachshund (Dac), constitutes a transcription factor (TF) network that patterns the developing olfactory tissue. This network was previously shown to pattern the segmentation of the leg, which suggests that this network is functionally conserved. In antennal imaginal discs, precursors with diverse ORN differentiation potentials are selected from concentric rings defined by unique combinations of these TFs along the proximodistal axis of the developing antennal disc. The combinatorial code that demarcates each precursor field is set up by cross-regulatory interactions among different factors within the network. Modifications of this network lead to predictable changes in the diversity of sensilla subtypes and ORN pools. In light of these data, a molecular map is proposed that defines each unique SOP fate. These results highlight the importance of the early prepatterning gene regulatory network as a modulator of SOP and terminally differentiated ORN diversity. Finally, this model illustrates how conserved developmental strategies are used to generate neuronal diversity.

Mishra, A. K., Bargmann, B. O., Tsachaki, M., Fritsch, C. and Sprecher, S. G. (2016). Functional genomics identifies regulators of the phototransduction machinery in the Drosophila larval eye and adult ocelli. Dev Biol [Epub ahead of print]. PubMed ID: 26769100
Sensory perception of light is mediated by specialized Photoreceptor neurons (PRs) in the eye. During development all PRs are genetically determined to express a specific Rhodopsin (Rh) gene and genes mediating a functional phototransduction pathway. While the genetic and molecular mechanisms of PR development is well described in the adult compound eye, it remains unclear how the expression of Rhodopsins and the phototransduction cascade is regulated in other visual organs in Drosophila, such as the larval eye and adult ocelli. Using transcriptome analysis of larval PR-subtypes and ocellar PRs this study identified and studied new regulators required during PR differentiation or necessary for the expression of specific signaling molecules of the functional phototransduction pathway. The transcription factor Kruppel (Kr) is enriched in the larval eye and controls PR differentiation by promoting Rh5 and Rh6 expression. Camta, Lola, Dve and Hazy were also identified as key genes acting during ocellar PR differentiation. These transcriptional regulators control gene expression of the phototransduction cascade in both larval eye and adult ocelli. The results show that PR cell type-specific transcriptome profiling is a powerful tool to identify key transcriptional regulators involved during several aspects of PR development and differentiation. The findings greatly contribute to the understanding of how combinatorial action of key transcriptional regulators control PR development and the regulation of a functional phototransduction pathway in both larval eye and adult ocelli.

Matsuo, E., Seki, H., Asai, T., Morimoto, T., Miyakawa, H., Ito, K. and Kamikouchi, A. (2016). The organization of projection neurons and local neurons of the primary auditory center in the fruit fly Drosophila melanogaster. J Comp Neurol [Epub ahead of print]. PubMed ID: 26762251
Acoustic communication between insects serves as an excellent model system for analyzing the neuronal mechanisms underlying auditory information processing. To understand the central auditory pathways a large-scale analysis was performed of the interneurons associated with the primary Drosophila auditory center. By screening expression driver strains and performing single-cell labeling of these strains, 44 types of interneurons were identified innervating the primary auditory center - 5 types were local interneurons whereas the other 39 types were projection interneurons connecting the primary auditory center with other brain regions. The projection neurons comprised three frequency-selective pathways and two frequency-embracive pathways. Mapping of their connection targets revealed that five neuropils in the brain - the wedge, anterior ventrolateral protocerebrum, posterior ventrolateral protocerebrum (PVLP), saddle (SAD), and gnathal ganglia (GNG) - were intensively connected with the primary auditory center. In addition, several other neuropils, including visual and olfactory centers in the brain, were directly connected to the primary auditory center. The distribution patterns of the spines and boutons of the identified neurons suggest that auditory information is sent mainly from the primary auditory center to the PVLP, WED, SAD, GNG, and the thoracico-abdominal ganglia. Based on these findings, this study has established the first comprehensive map of secondary auditory interneurons, which indicates the downstream information flow to parallel ascending pathways, multimodal pathways, and descending pathways.

Budelli, G., Sun, Q., Ferreira, J., Butler, A., Santi, C. M. and Salkoff, L. (2016). SLO2 channels are inhibited by all divalent cations that activate SLO1 K+ channels. J Biol Chem [Epub ahead of print]. PubMed ID: 26823461
Two members of the family of high conductance K+ Slowpoke channels SLO1 and SLO2 are both activated by intracellular cations. However, SLO1 is activated by Ca2+ and other divalent cations, while SLO2 (Slack or SLO2.2 from rat) is activated by Na+. Curiously though, this study found that SLO2.2 is inhibited by all divalent cations that activate SLO1, with Zn2+ being the most effective inhibitor with an IC50 of ~8 micromolar in contrast to Mg2+, the least effective, with an IC50 of ~ 1.5 mM. These results suggest that divalent cations are not SLO2 pore blockers, but rather inhibit channel activity by an allosteric modification of channel gating. By site-directed mutagenesis this study showed that a histidine residue (H347) down-stream of S6 reduces inhibition by divalent cations. An analogous His residue present in some CNG channels is an inhibitory cation binding site. To investigate whether inhibition by divalent cations is conserved in an invertebrate SLO2 channel the SLO2 channel was cloned from Drosophila (dSLO2) and its properties were compared to those of rat SLO2.2. Like rat SLO2.2, dSLO2 was also activated by Na+ and inhibited by divalent cations. Inhibition of SLO2 channels in mammals and Drosophila by divalent cations that have second messenger functions may reflect the physiological regulation of these channels by one or more of these ions.

Thursday, February 4th

Harnisch, C., Cuzic-Feltens, S., Dohm, J.C., Götze, M., Himmelbauer, H. and Wahle, E. (2016). Oligoadenylation of 3' decay intermediates promotes cytoplasmic mRNA degradation in Drosophila cells. RNA [Epub ahead of print]. PubMed ID: 26786835
Post-transcriptional 3' end addition of nucleotides is important in a variety of RNA decay pathways. This study examined the 3' end addition of nucleotides during the decay of the Hsp70 mRNA and a corresponding reporter RNA in Drosophila S2 cells by conventional sequencing of cDNAs obtained after mRNA circularization and by deep sequencing of dedicated libraries enriched for 3' decay intermediates along the length of the mRNA. Approximately 5%-10% of 3' decay intermediates carry nonencoded oligo(A) tails with a mean length of 2-3 nucleotides. RNAi experiments showed that the oligoadenylated RNA fragments are intermediates of exosomal decay and the noncanonical poly(A) polymerase Trf4-1 is mainly responsible for A addition. A hot spot of A addition corresponds to an intermediate of 3' decay that accumulates upon inhibition of decapping, and knockdown of Trf4-1 increases the abundance of this intermediate, suggesting that oligoadenylation facilitates 3' decay. Oligoadenylated 3' decay intermediates were found in the cytoplasmic fraction in association with ribosomes, and fluorescence microscopy revealed a cytoplasmic localization of Trf4-1. Thus, oligoadenylation enhances exosomal mRNA degradation in the cytoplasm.

Çiçek, I.Ö., Karaca, S., Brankatschk, M., Eaton, S., Urlaub, H. and Shcherbata, H.R. (2016). Hedgehog signaling strength is orchestrated by the mir-310 cluster of microRNAs in response to diet. Genetics [Epub ahead of print]. PubMed ID: 26801178
This study proposes a new workflow for miRNA function analysis, using which it was found that the evolutionarily young miRNA family, the mir-310s, are important regulators of Drosophila metabolic status. mir-310s-deficient animals have an abnormal diet-dependent expression profile for numerous diet-sensitive components, accumulate fats, and show various physiological defects. It was found that the mir-310s simultaneously repress the production of several regulatory factors (Rab23, DHR96 and Ttk) of the evolutionarily conserved Hedgehog (Hh) pathway to sharpen dietary response. As the mir-310s expression is highly dynamic and nutrition-sensitive, this signal relay model helps to explain the molecular mechanism governing quick and robust Hh signaling responses to nutritional changes. Additionally, a new component of the Hh signaling pathway in Drosophila, Rab23, was discovered which cell autonomously regulates Hh ligand trafficking in the germline stem cell niche. How organisms adjust to dietary fluctuations to sustain healthy homeostasis is an intriguing research topic. These data are the first report showing that miRNAs can act as executives that transduce nutritional signals to an essential signaling pathway. This suggests miRNAs as plausible therapeutic agents that can be used in combination with low calorie and cholesterol diets to manage quick and precise tissue-specific responses to nutritional changes.

Quinn, J. J., Zhang, Q. C., Georgiev, P., Ilik, I. A., Akhtar, A. and Chang, H. Y. (2016). Rapid evolutionary turnover underlies conserved lncRNA-genome interactions. Genes Dev 30: 191-207. PubMed ID: 26773003
This study adapted an integrative strategy that identifies lncRNA orthologs in different species despite limited sequence similarity, that is applicable to mammalian and insect lncRNAs. Analysis of the roX lncRNAs, which are essential for dosage compensation of the single X chromosome in Drosophila males, revealed 47 new roX orthologs in diverse Drosophilid species across approximately 40 million years of evolution. Genetic rescue by roX orthologs and engineered synthetic lncRNAs showed that altering the number of focal, repetitive RNA structures determines roX ortholog function. Genomic occupancy maps of roX RNAs in four species revealed conserved targeting of X chromosome neighborhoods but rapid turnover of individual binding sites. Many new roX-binding sites evolved from DNA encoding a pre-existing RNA splicing signal, effectively linking dosage compensation to transcribed genes. Thus, dynamic change in lncRNAs and their genomic targets underlies conserved and essential lncRNA-genome interactions.

Delatte, B., et al. (2016).. RNA biochemistry. Transcriptome-wide distribution and function of RNA hydroxymethylcytosine. Science 351: 282-285. PubMed ID: 26816380
Hydroxymethylcytosine, well described in DNA, occurs also in RNA. This study shows that hydroxymethylcytosine preferentially marks polyadenylated RNAs and is deposited by Tet in Drosophila. The transcriptome-wide hydroxymethylation landscape was mapped, revealing hydroxymethylcytosine in the transcripts of many genes, notably in coding sequences, and consensus sites were identified for hydroxymethylation. RNA hydroxymethylation can favor mRNA translation. Tet and hydroxymethylated RNA are found to be most abundant in the Drosophila brain, and Tet-deficient fruitflies suffer impaired brain development, accompanied by decreased RNA hydroxymethylation. This study highlights the distribution, localization, and function of cytosine hydroxymethylation and identifies central roles for this modification in Drosophila.

Wednesday, February 3rd

Chougule, A.B., Hastert, M.C. and Thomas, J.H. (2016). Drak is required for actomyosin organization during Drosophila cellularization. G3 (Bethesda) [Epub ahead of print]. PubMed ID: 26818071
The generation of force by actomyosin contraction is critical for a variety of cellular and developmental processes. Nonmuscle myosin II is the motor that drives actomyosin contraction, and its activity is largely regulated by phosphorylation of myosin regulatory light chain. During the formation of the Drosophila cellular blastoderm, actomyosin contraction drives constriction of microfilament rings, modified cytokinesis rings. This study found that Drak is necessary for most of the phosphorylation of myosin regulatory light chain during cellularization. It was shown that Drak is required for organization of myosin II within the microfilament rings. Proper actomyosin contraction of the microfilament rings during cellularization also requires Drak activity. Constitutive activation of myosin regulatory light chain bypasses the requirement for Drak, suggesting that actomyosin organization and contraction are mediated through Drak's regulation of myosin activity. Drak also is involved in the maintenance of furrow canal structure and lateral plasma membrane integrity during cellularization. Together, these observations suggest that Drak is the primary regulator of actomyosin dynamics during cellularization.

Brinkmann, K., Winterhoff, M., Onel, S. F., Schultz, J., Faix, J. and Bogdan, S. (2015). WHAMY is a novel actin polymerase promoting myoblast fusion, macrophage cell motility and sensory organ development. J Cell Sci. PubMed ID: 26675239
Wiskott-Aldrich syndrome proteins (WASP) are nucleation promoting factors (NPF) that differentially control the Arp2/3 complex. In Drosophila, three different family members, SCAR/WAVE, WASP and WASH, have been analyzed so far. This study characterizes WHAMY, the fourth Drosophila WASP family member. whamy originated from a wasp gene duplication and underwent a sub-neofunctionalization. Unlike WASP, WHAMY specifically interacts with activated Rac1 through its two CRIB domains that are sufficient for targeting WHAMY to lamellipodial and filopodial tips. Biochemical analyses showed that WHAMY promotes exceptionally fast actin filament elongation, while it does not activate the Arp2/3 complex. Loss- and gain-of function studies revealed an important function of WHAMY in membrane protrusions and cell migration in macrophages. Genetic data further imply synergistic functions between WHAMY and WASP during morphogenesis. Double mutants are late-embryonic lethal and show severe defects in myoblast fusion. Trans-heterozygous mutant animals show strongly increased defects in sensory cell fate specification. Thus, WHAMY is a novel actin polymerase with an initial partitioning of ancestral WASP functions in development and subsequent acquisition of a new function in cell motility during evolution.

Weng, M. and Wieschaus, E. (2016). Myosin-dependent remodeling of adherens junctions protects junctions from Snail-dependent disassembly. J Cell Biol [Epub ahead of print]. PubMed ID: 26754645
Although Snail is essential for disassembly of adherens junctions during epithelial-mesenchymal transitions (EMTs), loss of adherens junctions in Drosophila melanogaster gastrula is delayed until mesoderm is internalized, despite the early expression of Snail in that primordium. By combining live imaging and quantitative image analysis, the behavior of E-cadherin-rich junction clusters were tracked, demonstrating that in the early stages of gastrulation most subapical clusters in mesoderm not only persist, but move apically and enhance in density and total intensity. All three phenomena depend on myosin II and are temporally correlated with the pulses of actomyosin accumulation that drive initial cell shape changes during gastrulation. When contractile myosin is absent, the normal Snail expression in mesoderm, or ectopic Snail expression in ectoderm, is sufficient to drive early disassembly of junctions. In both cases, junctional disassembly can be blocked by simultaneous induction of myosin contractility. These findings provide in vivo evidence for mechanosensitivity of cell-cell junctions and imply that myosin-mediated tension can prevent Snail-driven EMT.

Kerridge, S., Munjal, A., Philippe, J. M., Jha, A., de Las Bayonas, A. G., Saurin, A. J. and Lecuit, T. (2016). Modular activation of Rho1 by GPCR signalling imparts polarized myosin II activation during morphogenesis. Nat Cell Biol [Epub ahead of print]. PubMed ID: 26780298
Polarized cell shape changes during tissue morphogenesis arise by controlling the subcellular distribution of myosin II. For instance, during Drosophila gastrulation, apical constriction and cell intercalation are mediated by medial-apical myosin II pulses that power deformations, and polarized accumulation of myosin II that stabilizes these deformations. It remains unclear how tissue-specific factors control different patterns of myosin II activation and the ratchet-like myosin II dynamics. This study reports the function of a common pathway comprising the heterotrimeric G proteins Galpha12/13, Gβ13F and Gγ1 in activating and polarizing myosin II during Drosophila gastrulation. Galpha12/13 and the Gbeta13F/gamma1 complex constitute distinct signalling modules, which regulate myosin II dynamics medial-apically and/or junctionally in a tissue-dependent manner. A ubiquitously expressed GPCR called Smog (CG31660) was identified as being required for cell intercalation and apical constriction. Smog functions with other GPCRs to quantitatively control G proteins, resulting in stepwise activation of myosin II and irreversible cell shape changes. It is proposed that GPCR and G proteins constitute a general pathway for controlling actomyosin contractility in epithelia and that the activity of this pathway is polarized by tissue-specific regulators.

Tuesday, February 2nd

Tan, W., Schauder, C., Naryshkina, T., Minakhina, S. and Steward, R. (2016). Zfrp8 forms a complex with fragile-X mental retardation protein and regulates its localization and function. Dev Biol. PubMed ID: 26772998
Fragile-X syndrome is the most commonly inherited cause of autism and mental disabilities. The Fmr1 (Fragile-X Mental Retardation 1) gene is essential in humans and Drosophila for the maintenance of neural stem cells, and Fmr1 loss results in neurological and reproductive developmental defects in humans and flies. FMRP (Fragile-X Mental Retardation Protein) is a nucleo-cytoplasmic shuttling protein, involved in mRNA silencing and translational repression. Both Zfrp8 and Fmr1 have essential functions in the Drosophila ovary. This study identifies FMRP, Nufip (Nuclear Fragile-X Mental Retardation Protein-interacting Protein) and Tral (Trailer Hitch) as components of a Zfrp8 protein complex. Zfrp8 is required in the nucleus, and controls localization of FMRP in the cytoplasm. In addition, Zfrp8 genetically interacts with Fmr1 and tral in an antagonistic manner. Zfrp8 and FMRP both control heterochromatin packaging, also in opposite ways. It is proposed that Zfrp8 functions as a chaperone, controlling protein complexes involved in RNA processing in the nucleus.

Xu, Z., Chikka, M. R., Xia, H. and Ready, D. F. (2016). Ire1 supports normal ER differentiation in developing Drosophila photoreceptors. J Cell Sci [Epub ahead of print]. PubMed ID: 26787744
The endoplasmic reticulum (ER) serves virtually all aspects of cell physiology and, by pathways incompletely understood, is dynamically remodeled to meet changing cell needs. Inositol-requiring enzyme 1 (Ire1), a conserved core of the Unfolded Protein Response (UPR), participates in ER remodeling and is particularly required during the differentiation of cells devoted to intense secretory activity, "professional" secretory cells. This study characterize Ire1's role in ER differentiation in developing Drosophila compound eye photoreceptors (R cells). As part of normal development, R cells take a turn as professional secretory cells with a massive secretory effort that builds the photosensitive membrane organelle, the rhabdomere. Rough ER sheets proliferate as rhabdomere biogenesis culminates and Ire1 is required for normal ER differentiation. Ire1 is active early in R cell development and is required in anticipation of peak biosynthesis. Without Ire1, rough ER sheets are strongly reduced and the extensive cortical ER network at the rhabdomere base, the subrhabdomere cisterna (SRC), fails. Instead, ER proliferates in persistent, ribosome-poor tubular tangles. A phase of Ire1 activity early in R cell development thus shapes dynamic ER.

Sanchez, G. M., Alkhori, L., Hatano, E., Schultz, S. W., Kuzhandaivel, A., Jafari, S., Granseth, B. and Alenius, M. (2016). Hedgehog signaling regulates the ciliary transport of odorant receptors in Drosophila. Cell Rep 14: 464-470. PubMed ID: 26774485
Hedgehog (Hh) signaling is a key regulatory pathway during development and also has a functional role in mature neurons. This study shows that Hh signaling regulates the odor response in adult Drosophila olfactory sensory neurons (OSNs). This is achieved by regulating odorant receptor (OR) transport to and within the primary cilium in OSN neurons. Regulation relies on ciliary localization of the Hh signal transducer Smoothened (Smo). This study further demonstrates that the Hh- and Smo-dependent regulation of the kinesin-like protein Cos2 acts in parallel to the intraflagellar transport system (IFT) to localize ORs within the cilium compartment. These findings expand knowledge of Hh signaling to encompass chemosensory modulation and receptor trafficking.

Deng, H., Wang, W., Yu, J., Zheng, Y., Qing, Y. and Pan, D. (2015). Spectrin regulates Hippo signaling by modulating cortical actomyosin activity. Elife 4: e06567. PubMed ID: 25826608
The Hippo pathway controls tissue growth through a core kinase cascade that impinges on the transcription of growth-regulatory genes. Understanding how this pathway is regulated in development remains a major challenge. Recent studies suggested that Hippo signaling can be modulated by cytoskeletal tension through a Rok-myosin II pathway. How cytoskeletal tension is regulated or its relationship to the other known upstream regulators of the Hippo pathway remains poorly defined. This study identifies the spectrins, α-spec, β-spec, or βH-spec contractile proteins at the cytoskeleton-membrane interface, as an upstream regulator of the Hippo signaling pathway. In contrast to canonical upstream regulators such as Crumbs, Kibra, Expanded, and Merlin, spectrin regulates Hippo signaling in a distinct way by modulating cortical actomyosin activity through non-muscle myosin II. These results uncover an essential mediator of Hippo signaling by cytoskeleton tension, providing a new entry point to dissecting how mechanical signals regulate Hippo signaling in living tissues.

Monday, February 1st

Sulkowski, M.J., Han, T.H., Ott, C., Wang, Q., Verheyen, E.M., Lippincott-Schwartz, J. and Serpe, M. (2016). A novel, noncanonical BMP pathway modulates synapse maturation at the Drosophila neuromuscular junction. PLoS Genet 12: e1005810. PubMed ID: 26815659
At the Drosophila NMJ, BMP signaling is critical for synapse growth and homeostasis. Signaling by the BMP7 homolog, Gbb, in motor neurons triggers a canonical pathway-which modulates transcription of BMP target genes, and a noncanonical pathway-which connects local BMP/BMP receptor complexes with the cytoskeleton. This study describes a novel noncanonical BMP pathway characterized by the accumulation of the pathway effector, the phosphorylated Smad (pMad), at synaptic sites. Using genetic epistasis, histology, super resolution microscopy, and electrophysiology approaches, it was demonstrated that this novel pathway is genetically distinguishable from all other known BMP signaling cascades. This novel pathway does not require Gbb, but depends on presynaptic BMP receptors and specific postsynaptic glutamate receptor subtypes, the type-A receptors. Synaptic pMad is coordinated to BMP's role in the transcriptional control of target genes by shared pathway components, but it has no role in the regulation of NMJ growth. Instead, selective disruption of presynaptic pMad accumulation reduces the postsynaptic levels of type-A receptors, revealing a positive feedback loop which appears to function to stabilize active type-A receptors at synaptic sites. Thus, BMP pathway may monitor synapse activity then function to adjust synapse growth and maturation during development.

Nakayama, M., Suzuki, E., Tsunoda, S. and Hama, C. (2016). The matrix proteins Hasp and Hig exhibit segregated distribution within synaptic clefts and play distinct roles in synaptogenesis. J Neurosci 36: 590-606. PubMed ID: 26758847
The synaptic cleft is the space through which neurotransmitters convey neural information between two synaptic terminals. This space is presumably filled with extracellular matrix molecules involved in synaptic function or differentiation. However, little is known about the identities of the matrix components, and it remains unclear how these molecules organize the matrix in synaptic clefts. This study identified Hasp, a Drosophila secretory protein containing CCP and WAP domains. Molecular genetic analysis revealed that Hasp diffuses extracellularly and is predominantly captured at synaptic clefts of cholinergic synapses. Furthermore, Hasp regulates levels of DLG and the nAChR subunits Dα6 and Dα7 at postsynaptic terminals. Hasp is required for trapping of another matrix protein, Hig, which is also secreted and diffused in the brain, at synaptic clefts of cholinergic synapses; however, Hig is dispensable for localization of Hasp at synaptic clefts. In addition, in the brains of triple mutants for the nAChR subunits Dα5, Dα6, and Dα7, the level of Hig, but not Hasp, was markedly reduced in synaptic regions, indicating that these nAChR subunits are required to anchor Hig to synaptic clefts. High-resolution microscopy revealed that Hasp and Hig exhibit segregated distribution within individual synaptic clefts, reflecting their differing roles in synaptogenesis. These data provide insight into how Hasp and Hig construct the synaptic cleft matrix and regulate the differentiation of cholinergic synapses, and also illuminate a previously unidentified architecture within synaptic clefts.

Rybak, J., Talarico, G., Ruiz, S., Arnold, C., Cantera, R. and Hansson, B. S. (2016). Synaptic circuitry of identified neurons in the antennal lobe of Drosophila melanogaster. J Comp Neurol. PubMed ID: 26780543
In Drosophila melanogaster olfactory sensory neurons (OSNs) establish synapses with projection neurons (PNs) and local interneurons within antennal lobe (AL) glomeruli. To fill this gap serial sections of three glomeruli were studied using electron microscopy. The data proves that each of the three major types of AL neurons is both pre- and postsynaptic to the other two types as previously indicated by functional studies. PN dendrites carry a large proportion of output synapses, with approximately one output per every three input synapses. Detailed reconstructions of PN dendrites showed that these synapses are distributed unevenly, with input and output sites partially segregated along a proximal-distal gradient and the thinnest branches carrying solely input synapses. Moreover, the data indicate synapse clustering, as evidence was found of dendritic tiling of PN dendrites. PN output synapses exhibited T-shaped presynaptic densities, mostly arranged as tetrads. In contrast, output synapses from putative OSNs showed elongated presynaptic densities in which the T-bar platform was supported by several pedestals and contacted as many as 20 postsynaptic profiles. Synaptic contacts were also discovered between the putative OSNs. These results are discussed with regard to current models of olfactory glomerular microcircuits across species.

Robinson, J.E., Paluch, J., Dickman, D.K. and Joiner, W.J. (2016). ADAR-mediated RNA editing suppresses sleep by acting as a brake on glutamatergic synaptic plasticity. Nat Commun 7: 10512. PubMed ID: 26813350
It has been postulated that synaptic potentiation during waking is offset by a homoeostatic reduction in net synaptic strength during sleep. However, molecular mechanisms to support such a process are lacking. This study demonstrates that deficiencies in the RNA-editing gene Adar increase sleep due to synaptic dysfunction in glutamatergic neurons in Drosophila. Specifically, the vesicular glutamate transporter is upregulated, leading to over-activation of NMDA receptors, and the reserve pool of glutamatergic synaptic vesicles is selectively expanded in Adar mutants. Collectively these changes lead to sustained neurotransmitter release under conditions that would otherwise result in synaptic depression. The study proposes that a shift in the balance from synaptic depression towards synaptic potentiation in sleep-promoting neurons underlies the increased sleep pressure of Adar-deficient animals. These findings provide a plausible molecular mechanism linking sleep and synaptic plasticity. 

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