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





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Thursday, June 30th, 2016

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Li, S., Li, S., Han, Y., Tong, C., Wang, B., Chen, Y. and Jiang, J. (2016). Regulation of Smoothened phosphorylation and high-level Hedgehog signaling activity by a plasma membrane associated kinase. PLoS Biol 14: e1002481. PubMed ID: 27280464
Summary:
Hedgehog (Hh) signaling controls embryonic development and adult tissue homeostasis through the G protein coupled receptor (GPCR)-family protein Smoothened (Smo). Upon stimulation, Smo accumulates on the cell surface in Drosophila or primary cilia in vertebrates, which is thought to be essential for its activation and function, but the underlying mechanisms remain poorly understood. This study shows that Hh stimulates the binding of Smo to a plasma membrane-associated kinase Gilgamesh (Gish)/CK1γ and that Gish fine-tunes Hh pathway activity by phosphorylating a Ser/Thr cluster (CL-II) in the juxtamembrane region of Smo carboxyl-terminal intracellular tail (C-tail). It was found that CL-II phosphorylation is promoted by protein kinase A (PKA)-mediated phosphorylation of Smo C-tail and depends on cell surface localization of both Gish and Smo. Consistent with CL-II being critical for high-threshold Hh target gene expression, its phosphorylation appears to require higher levels of Hh or longer exposure to the same level of Hh than PKA-site phosphorylation on Smo. Furthermore, vertebrate CK1γ localizes at the primary cilium to promote Smo phosphorylation and Sonic hedgehog (Shh) pathway activation. These data reveal a conserved mechanism whereby Hh induces a change in Smo subcellular localization to promote its association with and activation by a plasma membrane localized kinase, and provide new insight into how Hh morphogen progressively activates Smo. 

Harvey, B. M., Rana, N. A., Moss, H., Leonardi, J., Jafar-Nejad, H. and Haltiwanger, R. S. (2016). Mapping sites of O-glycosylation and fringe elongation on Drosophila Notch. J Biol Chem [Epub ahead of print]. PubMed ID: 27268051
Summary:
Glycosylation of the Notch receptor is essential for its activity and serves as an important modulator of signaling. Three major forms of O-glycosylation are predicted to occur at consensus sites within the epidermal growth factor-like repeats in the extracellular domain of the receptor: O-fucosylation, O-glucosylation and O-GlcNAcylation. Comprehensive mass spectral analyses of these three types of O-glycosylation was performed on Drosophila Notch produced in S2 cells, and peptides containing all twenty-two predicted O-fucose sites were identified, all eighteen predicted O-glucose sites, and all eighteen putative O-GlcNAc sites. Using semi-quantitative mass spectral methods, the occupancy and relative amount of glycans at each site were evaluated. The majority of the O-fucose sites were modified to high stoichiometries. Upon expression of the beta3-N-acetylglucosaminyltransferase Fringe with Notch, varying degrees of elongation were observed beyond O-fucose monosaccharide, indicating that Fringe preferentially modifies certain sites more than others. Rumi modified O-glucose sites to high stoichiometries, although elongation of the O-glucose was site specific. Although the current putative consensus sequence for O-GlcNAcylation predicts eighteen O-GlcNAc sites on Notch, apparent O-GlcNAc modification was observed at only five sites. In addition, mass spectral analysis was performed on endogenous Notch purified from Drosophila embryos, and the glycosylation states were similar to those found on Notch from S2 cells. These data provide foundational information for future studies investigating the mechanisms of how O-glycosylation regulates Notch activity.

Zhu, K., Shan, Z., Zhang, L. and Wen, W. (2016). Phospho-Pon binding-mediated fine-tuning of Plk1 activity. Structure [Epub ahead of print]. PubMed ID: 27238966
Summary:
In Drosophila neuroblasts (NBs), the asymmetrical localization and segregation of the cell-fate determinant Numb are regulated by its adaptor Partner of Numb (Pon) and the cell-cycle kinase Polo. Polo phosphorylates the Pon localization domain, thus leading to its basal distribution together with Numb, albeit through an unclear mechanism. This study finds that Cdk1 phosphorylates Pon at Thr63, thus creating a docking site for the Polo-box domain (PBD) of Polo-like kinase 1 (Plk1). The crystal structure of the Plk1 PBD/phospho-Pon complex reveals that two phospho-Pon bound PBDs associate to form a dimer of dimers. Evidence is provided that phospho-Pon binding-induced PBD dimerization relieves the autoinhibition of Plk1. Moreover, the priming Cdk1 phosphorylation of Pon was shown to be important for sequential Plk1 phosphorylation. These results not only provide structural insight into how phosphoprotein binding activates Plk1 but also suggest that binding to different phosphoproteins might mediate the fine-tuning of Plk1 activity.

Hao, Y., Frey, E., Yoon, C., Wong, H., Nestorovski, D., Holzman, L. B., Giger, R. J., DiAntonio, A. and Collins, C. (2016). An evolutionarily conserved mechanism for cAMP elicited axonal regeneration involves direct activation of the dual leucine zipper kinase DLK. Elife 5 [Epub ahead of print]. PubMed ID: 27268300
Summary:
A broadly known method to stimulate the growth potential of axons is to elevate intracellular levels of cAMP, however the cellular pathway(s) that mediate this are not known. This study identifies the Dual Leucine-zipper Kinase (DLK, Wallenda in Drosophila) as a critical target and effector of cAMP in injured axons. DLK/Wnd is thought to function as an injury 'sensor', as it becomes activated after axonal damage. These findings in both Drosophila and mammalian neurons indicate that the cAMP effector kinase PKA is a conserved and direct upstream activator of Wnd/DLK. PKA is required for the induction of Wnd signaling in injured axons, and DLK is essential for the regenerative effects of cAMP in mammalian DRG neurons. These findings link two important mediators of responses to axonal injury, DLK/Wnd and cAMP/PKA, into a unified and evolutionarily conserved molecular pathway for stimulating the regenerative potential of injured axons.

Wednesday, June 29th

Triphan, T., Nern, A., Roberts, S. F., Korff, W., Naiman, D. Q. and Strauss, R. (2016). A screen for constituents of motor control and decision making in Drosophila reveals visual distance-estimation neurons. Sci Rep 6: 27000. PubMed ID: 27255169
Summary:
Climbing over chasms larger than step size is vital to fruit flies, since foraging and mating are achieved while walking. Flies avoid futile climbing attempts by processing parallax-motion vision to estimate gap width. To identify neuronal substrates of climbing control, a large collection of fly lines with temporarily inactivated neuronal populations were screened in a novel high-throughput assay. The observed climbing phenotypes were classified; lines in each group are reported. Selected lines were further analysed by high-resolution video cinematography. One striking class of flies attempts to climb chasms of unsurmountable width; expression analysis led to C2 optic-lobe interneurons. C2 columnar feedback neurons project from the second visual neuropil, the medulla, to the most peripheral optic-lobe region, the lamina. Inactivation of C2 or the closely related C3 neurons with highly specific intersectional driver lines consistently reproduced hyperactive climbing whereas strong or weak artificial depolarization of C2/C3 neurons strongly or mildly decreased climbing frequency. Contrast-manipulation experiments support conclusion that C2/C3 neurons are part of the distance-evaluation system.
Guo, Y., Wang, Y., Zhang, W., Meltzer, S., Zanini, D., Yu, Y., Li, J., Cheng, T., Guo, Z., Wang, Q., Jacobs, J. S., Sharma, Y., Eberl, D. F., Gopfert, M. C., Jan, L. Y., Jan, Y. N. and Wang, Z. (2016). Transmembrane channel-like (tmc) gene regulates Drosophila larval locomotion. Proc Natl Acad Sci U S A [Epub ahead of print]. PubMed ID: 27298354
Summary:
Drosophila larval locomotion, which entails rhythmic body contractions, is controlled by sensory feedback from proprioceptors. The molecular mechanisms mediating this feedback are little understood. By using genetic knock-in and immunostaining, this study found that the Drosophila melanogaster transmembrane channel-like (tmc) gene is expressed in the larval class I and class II dendritic arborization (da) neurons and bipolar dendrite (bd) neurons, both of which are known to provide sensory feedback for larval locomotion. Larvae with knockdown or loss of tmc function displayed reduced crawling speeds, increased head cast frequencies, and enhanced backward locomotion. Expressing Drosophila TMC or mammalian TMC1 and/or TMC2 in the tmc-positive neurons rescued these mutant phenotypes. Bending of the larval body activated the tmc-positive neurons, and in tmc mutants this bending response was impaired. This implicates TMC's roles in Drosophila proprioception and the sensory control of larval locomotion. It also provides evidence for a functional conservation between Drosophila and mammalian TMCs.

Lin, H. H., Cao, D. S., Sethi, S., Zeng, Z., Chin, J. S., Chakraborty, T. S., Shepherd, A. K., Nguyen, C. A., Yew, J. Y., Su, C. Y. and Wang, J. W. (2016). Hormonal modulation of pheromone detection enhances male courtship success. Neuron 90: 1272-1285. PubMed ID: 27263969
Summary:
During the lifespans of most animals, reproductive maturity and mating activity are highly coordinated. In Drosophila melanogaster, for instance, male fertility increases with age, and older males are known to have a copulation advantage over young ones. The molecular and neural basis of this age-related disparity in mating behavior is unknown. This study shows that the Or47b odorant receptor is required for the copulation advantage of older males. Notably, the sensitivity of Or47b neurons to a stimulatory pheromone, palmitoleic acid, is low in young males but high in older ones, which accounts for older males' higher courtship intensity. Mechanistically, this age-related sensitization of Or47b neurons requires a reproductive hormone, juvenile hormone, as well as its binding protein Methoprene-tolerant in Or47b neurons. Together, this study identifies a direct neural substrate for juvenile hormone that permits coordination of courtship activity with reproductive maturity to maximize male reproductive fitness.

Zhang, S. X., Rogulja, D. and Crickmore, M. A. (2016). Dopaminergic circuitry underlying mating drive. Neuron [Epub ahead of print]. PubMed ID: 27292538
Summary:
This study developed a new system for studying how innate drives are tuned to reflect current physiological needs and capacities, and how they affect sensory-motor processing. The existence of male mating drive is demonstrated in Drosophila that is transiently and cumulatively reduced as reproductive capacity is depleted by copulations. Dopaminergic activity in the anterior of the superior medial protocerebrum (SMPa) is also transiently and cumulatively reduced in response to matings and serves as a functional neuronal correlate of mating drive. The dopamine signal is transmitted through the D1-like DopR2 receptor to P1 neurons, which also integrate sensory information relevant to the perception of females, and which project to courtship motor centers that initiate and maintain courtship behavior. Mating drive therefore converges with sensory information from the female at the point of transition to motor output, controlling the propensity of a sensory percept to trigger goal-directed behavior.

Tuesday, June 28th

Suzuki, T., Trush, O., Yasugi, T., Takayama, R. and Sato, M. (2016). Wnt signaling specifies anteroposterior progenitor zone identity in the Drosophila visual center. J Neurosci 36: 6503-6513. PubMed ID: 27307238
Summary:
During brain development, various types of neuronal populations are produced from different progenitor pools to produce neuronal diversity that is sufficient to establish functional neuronal circuits. However, the molecular mechanisms that specify the identity of each progenitor pool remain obscure. This study shows that Wnt signaling is essential for the specification of the identity of posterior progenitor pools in the Drosophila visual center. In the medulla, the largest component of the visual center, different types of neurons are produced from two progenitor pools: the outer proliferation center (OPC) and glial precursor cells (GPCs; also known as tips of the OPC). It was found that OPC-type neurons are produced from the GPCs at the expense of GPC-type neurons when Wnt signaling is suppressed in the GPCs. In contrast, GPC-type neurons are ectopically induced when Wnt signaling is ectopically activated in the OPC. These results suggest that Wnt signaling is necessary and sufficient for the specification of the progenitor pool identity. It was also found that Homothorax (Hth), which is temporally expressed in the OPC, is ectopically induced in the GPCs by suppression of Wnt signaling and that ectopic induction of Hth phenocopies the suppression of Wnt signaling in the GPCs. Thus, Wnt signaling is involved in regionalization of the fly visual center through the specification of the progenitor pool located posterior to the medulla by suppressing Hth expression.

Blumröder, R., Glunz, A., Dunkelberger, B.S., Serway, C.N., Berger, C., Mentzel, B., de Belle, J.S. and Raabe, T. (2016). Mcm3 replicative helicase mutation impairs neuroblast proliferation and memory in Drosophila. Genes Brain Behav [Epub ahead of print]. PubMed ID: 27283469
Summary:
This study performed the molecular and phenotypic characterization of a structural brain mutant called small mushroom bodies (smu), which was isolated in a screen for mutants with altered brain structure. Focusing on the mushroom body neuroblast lineages, it was shown that failure of neuroblasts to generate the normal number of mushroom body neurons (Kenyon cells) is the major cause of the smu phenotype. In particular, the premature loss of mushroom body neuroblasts causes a pronounced effect on the number of late-born Kenyon cells. Neuroblasts show no obvious defects in processes controlling asymmetric cell division, but generate less ganglion mother cells. Cloning of smu uncovers a single amino acid substitution in an evolutionary conserved protein interaction domain of the Minichromosome maintenance 3 (Mcm3) protein. Mcm3 is part of the multimeric Cdc45/Mcm/GINS (CMG) complex, which functions as a helicase during DNA replication. The study proposes that at least in the case of mushroom body neuroblasts, timely replication is not only required for continuous proliferation but also for their survival. The absence of Kenyon cells in smu reduces learning and early phases of conditioned olfactory memory. Corresponding to the absence of late-born Kenyon cells projecting to α'/β' and α/β lobes, smu is profoundly defective in later phases of persistent memory.

Akagi, K., Sarhan, M., Sultan, A. R., Nishida, H., Koie, A., Nakayama, T. and Ueda, H. (2016). A biological timer in the fat body comprised of Blimp-1, betaFTZ-F1 and Shade regulates pupation timing in Drosophila melanogaster. Development [Epub ahead of print]. PubMed ID: 27226323
Summary:
During the development of multicellular organisms, many events occur with precise timing. In Drosophila, pupation occurs about 12 hours after puparium formation, and its timing is believed to be determined by the release of a steroid hormone, ecdysone (E), from the prothoracic gland. This study demonstrates that the ecdysone-20-monooxygenase, Shade, determines the pupation timing by converting E to 20-hydroxyecdysone (20E) in the fat body, which is the organ that senses nutritional status. The timing of shade expression is determined by its transcriptional activator βFTZ-F1. The βFTZ-F1 gene is activated after a decline in the expression of its transcriptional repressor Blimp-1, which is temporally expressed around puparium formation in response to a high titer of 20E. The expression level and stability of Blimp-1 is critical for the precise timing of pupation. Thus, it is proposed that Blimp-1 molecules function as sands in an hourglass for this precise developmental timer system. Furthermore, the data suggest a biological advantage results from both the use of a transcriptional repressor for the time determination, and association of developmental timing with nutritional status of the organism.

Deb, B. K., Pathak, T. and Hasan, G. (2016). Store-independent modulation of Ca(2+) entry through Orai by Septin 7. Nat Commun 7 [Epub ahead of print]. PubMed ID: 27225060
Summary:
Orai channels are required for store-operated Ca(2+) entry (SOCE) in multiple cell types. Septins are a class of GTP-binding proteins that function as diffusion barriers in cells. This study shows that Septin 7 (Peanut) acts as a 'molecular brake' on activation of Orai channels in Drosophila neurons. Lowering Septin 7 levels results in dOrai-mediated Ca(2+) entry and higher cytosolic Ca(2+) in resting neurons. This Ca(2+) entry is independent of depletion of endoplasmic reticulum Ca(2+) stores and Ca(2+) release through the inositol-1,4,5-trisphosphate receptor. Importantly, store-independent Ca(2+) entry through Orai compensates for reduced SOCE in the Drosophila flight circuit. Moreover, overexpression of Septin 7 reduces both SOCE and flight duration, supporting its role as a negative regulator of Orai channel function in vivo. Septin 7 levels in neurons can, therefore, alter neural circuit function by modulating Orai function and Ca(2+) homeostasis.

Monday, June 27th

Behura, S. K., Sarro, J., Li, P., Mysore, K., Severson, D. W., Emrich, S. J. and Duman-Scheel, M. (2016). High-throughput cis-regulatory element discovery in the vector mosquito Aedes aegypti. BMC Genomics 17: 341. PubMed ID: 27161480
Summary:
Despite substantial progress in mosquito genomic and genetic research, few cis-regulatory elements (CREs), Formaldehyde-assisted isolation of regulatory elements paired with DNA sequencing, FAIRE-seq, is emerging as a powerful new high-throughput tool for global CRE discovery. FAIRE results in the preferential recovery of open chromatin DNA fragments that are not bound by nucleosomes. This investigation used FAIRE-seq to profile open chromatin and identify likely regulatory elements throughout the genome of the human disease vector mosquito Aedes aegypti. Genetic variation in the regulatory elements of dengue virus susceptible (Moyo-S) and refractory (Moyo-R) mosquito strains was assessed. Analysis of sequence data obtained through next generation sequencing of FAIRE DNA isolated from A. aegypti embryos revealed >121,000 FAIRE peaks (FPs), many of which clustered in the 1 kb 5' upstream flanking regions of genes known to be expressed at this stage. As expected, known transcription factor consensus binding sites were enriched in the FPs, and of these FoxA1, Hunchback, Gfi, Klf4, MYB/ph3 and Sox9 are most predominant. All of the elements tested in vivo were confirmed to drive gene expression in transgenic Drosophila reporter assays. Of the >13,000 single nucleotide polymorphisms (SNPs) recently identified in dengue virus-susceptible and refractory mosquito strains, 3365 were found to map to FPs. It is concluded that FAIRE-seq analysis of open chromatin in A. aegypti permitted genome-wide discovery of CREs. The results of this investigation indicate that FAIRE-seq is a powerful tool for identification of regulatory DNA in the genomes of non-model organisms, including human disease vector mosquitoes.

Fear, J.M., Leon-Novelo, L.G., Morse, A.M., Gerken, A.R., Van Lehman, K., Tower, J., Nuzhdin, S.V. and McIntyre, L.M. (2016). Buffering of genetic regulatory networks in Drosophila melanogaster. Genetics [Epub ahead of print]. PubMed ID: 27194752
Summary:
Regulatory variation in gene expression can be described by cis- and trans-genetic components. This study used RNA-seq data from a population panel of Drosophila melanogaster test crosses to compare allelic imbalance (AI) in female head tissue between mated and virgin flies, an environmental change known to affect transcription. Indeed, 3,048 exons (1,610 genes) are differentially expressed in this study. A Bayesian model for AI, with an intersection test, controls type I error. There are ~200 genes with AI exclusively in mated or virgin flies, indicating an environmental component of expression regulation. On average 34% of genes within a cross, and 54% of all genes show evidence for genetic regulation of transcription. Nearly all differentially regulated genes are affected in cis, with an average of 63% of expression variation explained by the cis-effects. Trans-effects explain 8% of the variance in AI on average and the interaction between cis and trans explains an average of 11% of the total variance in AI. In both environments cis- and trans-effects are compensatory in their overall effect, with a negative association between cis- and trans-effects 85% of the exons examined. The study hypothesizes that the gene expression level perturbed by cis-regulatory mutations is compensated through trans-regulatory mechanisms, e.g. trans and cis by trans factors buffering cis-mutations. In addition, when AI is detected in both environments, cis-mated, cis-virgin, and trans-mated-trans-virgin estimates are highly concordant with 99% of all exons positive correlated with a median correlation of 0.83 for cis and 0.95 for trans. The study concludes that the GRN are robust and that trans buffering explains robustness.

Loehlin, D. W. and Carroll, S. B. (2016). Expression of tandem gene duplicates is often greater than twofold. Proc Natl Acad Sci U S A [Epub ahead of print]. PubMed ID: 27162370
Summary:
Tandem gene duplication is an important mutational process in evolutionary adaptation and human disease. Hypothetically, two tandem gene copies should produce twice the output of a single gene, but this expectation has not been rigorously investigated. This study shows that tandem duplication often results in more than double the gene activity. A naturally occurring tandem duplication of the Alcohol dehydrogenase (Adh) gene exhibits 2.6-fold greater expression than the single-copy gene in transgenic Drosophila. This tandem duplication also exhibits greater activity than two copies of the gene in trans, demonstrating that it is the tandem arrangement and not copy number that is the cause of overactivity. It was also shown that tandem duplication of an unrelated synthetic reporter gene is overactive (2.3- to 5.1-fold) at all sites in the genome that were tested, suggesting that overactivity could be a general property of tandem gene duplicates. Overactivity occurs at the level of RNA transcription, and therefore tandem duplicate overactivity appears to be a previously unidentified form of position effect. The increment of surplus gene expression observed is comparable to many regulatory mutations fixed in nature and, if typical of other genomes, would shape the fate of tandem duplicates in evolution.

Pettie, K. P., Dresch, J. M. and Drewell, R. A. (2016). Spatial distribution of predicted transcription factor binding sites in Drosophila ChIP peaks. Mech Dev [Epub ahead of print]. PubMed ID: 27264535
Summary:
In the development of the Drosophila embryo, gene expression is directed by the sequence-specific interactions of a large network of protein transcription factors (TFs) and DNA cis-regulatory binding sites. Once the identity of the typically 8-10bp binding sites for any given TF has been determined by one of several experimental procedures, the sequences can be represented in a position weight matrix (PWM) and used to predict the location of additional TF binding sites elsewhere in the genome. Often, alignments of large (>200bp) genomic fragments that have been experimentally determined to bind the TF of interest in Chromatin Immunoprecipitation (ChIP) studies are trimmed under the assumption that the majority of the binding sites are located near the center of all the aligned fragments. In this study, ChIP/chip datasets are analyzed using the corresponding PWMs for the well-studied TFs; Caudal, Hunchback, Knirps and Kruppel, to determine the distribution of predicted binding sites. All four TFs are critical regulators of gene expression along the anterio-posterior axis in early Drosophila development. For all four TFs, the ChIP peaks contain multiple binding sites that are broadly distributed across the genomic region represented by the peak, regardless of the prediction stringency criteria used. This result suggests that ChIP peak trimming may exclude functional binding sites from subsequent analyses.

Sunday, June 26th

Chakrabarti, S., Dudzic, J.P., Li, X., Collas, E.J., Boquete, J.P. and Lemaitre, B. (2016). Remote control of intestinal stem cell activity by haemocytes in Drosophila. PLoS Genet 12: e1006089. PubMed ID: 27194701
Summary:
Only one canonical JAK/STAT pathway exists in Drosophila. It is activated by three secreted proteins of the Unpaired family (Upd): Upd1, Upd2 and Upd3. Although many studies have established a link between JAK/STAT activation and tissue damage, the mode of activation and the precise function of this pathway in the Drosophila systemic immune response remain unclear. This study used mutations in upd2 and upd3 to investigate the role of the JAK/STAT pathway in the systemic immune response. It was shown that haemocytes express the three upd genes and that injury markedly induces the expression of upd3 by the JNK pathway in haemocytes, which in turn activates the JAK/STAT pathway in the fat body and the gut. Surprisingly, release of Upd3 from haemocytes upon injury can remotely stimulate stem cell proliferation and the expression of Drosomycin-like genes in the intestine. It was also found that a certain level of intestinal epithelium renewal is required for optimal survival to septic injury. While haemocyte-derived Upd promotes intestinal stem cell activation and survival upon septic injury, haemocytes are dispensable for epithelium renewal upon oral bacterial infection. Also, intestinal epithelium renewal is sensitive to insults from both the lumen and the haemocoel. The release of Upds by haemocytes coordinates the wound-healing program in multiple tissues, including the gut, an organ whose integrity is critical to fly survival. 

Dantoft, W., Lundin, D., Esfahani, S.S. and Engström, Y. (2016). The POU/Oct transcription factor Pdm1/nub is necessary for a beneficial gut microbiota and normal lifespan of Drosophila. J Innate Immun 8: 412-426. PubMed ID: 27231014
Summary:
Maintenance of a stable gut microbial community relies on a delicate balance between immune defense and immune tolerance. This study used Drosophila to study how the microbial gut flora is affected by changes in host genetic factors and immunity. Flies with a constitutively active gut immune system, due to a mutation in the POU transcriptional regulator Pdm1/nubbin (nub) gene, have higher loads of bacteria and a more diverse taxonomic composition than controls. In addition, the microbial composition shifts considerably during the short lifespan of the nub1 mutants. This shift is characterized by a loss of relatively few OTUs (operational taxonomic units) and a remarkable increase in a large number of Acetobacter spp. and Leuconostoc spp. Treating nub1 mutant flies with antibiotics prolongs their lifetime survival by more than 100%. Immune gene expression is also persistently high in the presence of antibiotics, indicating that the early death is not a direct consequence of an overactive immune defense but rather an indirect consequence of the microbial load and composition. Thus, changes in host genotype and an inability to regulate the normal growth and composition of the gut microbiota lead to a shift in the microbial community, dysbiosis and early death. 

Weavers, H., Evans, I. R., Martin, P. and Wood, W. (2016). Corpse engulfment generates a molecular memory that primes the macrophage inflammatory response. Cell [Epub ahead of print]. PubMed ID: 27212238
Summary:
Macrophages are multifunctional cells that perform diverse roles in health and disease. Emerging evidence has suggested that these innate immune cells might also be capable of developing immunological memory, a trait previously associated with the adaptive system alone. While recent studies have focused on the dramatic macrophage reprogramming that follows infection and protects against secondary microbial attack, can macrophages also develop memory in response to other cues? This study shows that apoptotic corpse engulfment by Drosophila macrophages is an essential primer for their inflammatory response to tissue damage and infection in vivo. Priming is triggered via calcium-induced JNK signaling, which leads to upregulation of the damage receptor Draper, thus providing a molecular memory that allows the cell to rapidly respond to subsequent injury or infection. This remarkable plasticity and capacity for memory places macrophages as key therapeutic targets for treatment of inflammatory disorders.

Karlikow, M., Goic, B., Mongelli, V., Salles, A., Schmitt, C., Bonne, I., Zurzolo, C. and Saleh, M. C. (2016). Drosophila cells use nanotube-like structures to transfer dsRNA and RNAi machinery between cells. Sci Rep 6: 27085. PubMed ID: 27255932
Summary:
Tunnelling nanotubes and cytonemes function as highways for the transport of organelles, cytosolic and membrane-bound molecules, and pathogens between cells. During viral infection in Drosophila, a systemic RNAi antiviral response is established presumably through the transport of a silencing signal from one cell to another via an unknown mechanism. Because of their role in cell-cell communication, this study investigated whether nanotube-like structures could be a mediator of the silencing signal. In the context of a viral infection, the presence of nanotube-like structures is described in different Drosophila cell types. These tubules, made of actin and tubulin, were associated with components of the RNAi machinery, including Argonaute 2, double-stranded RNA, and CG4572. Moreover, they were more abundant during viral, but not bacterial, infection. Super resolution structured illumination microscopy showed that Argonaute 2 and tubulin reside inside the tubules. It is proposed that nanotube-like structures are one of the mechanisms by which Argonaute 2, as part of the antiviral RNAi machinery, is transported between infected and non-infected cells to trigger systemic antiviral immunity in Drosophila.

Saturday, June 25th

Williams, M.J., Klockars, A., Eriksson, A., Voisin, S., Dnyansagar, R., Wiemerslage, L., Kasagiannis, A., Akram, M., Kheder, S., Ambrosi, V., Hallqvist, E., Fredriksson, R. and Schiöth, H.B. (2016). The Drosophila ETV5 homologue Ets96B: Molecular link between obesity and bipolar disorder. PLoS Genet 12: e1006104. PubMed ID: 27280443
Summary:
Several reports suggest obesity and bipolar disorder (BD) share some physiological and behavioural similarities. For instance, obese individuals are more impulsive and have heightened reward responsiveness, phenotypes associated with BD, while bipolar patients become obese at a higher rate and earlier age than people without BD; however, the molecular mechanisms of such an association remain obscure. Using whole transcriptome analysis, this study demonstrates that Drosophila Ets96B, homologue of obesity-linked gene ETV5, regulates cellular systems associated with obesity and BD. Consistent with a role in obesity and BD, loss of nervous system Ets96B during development increases triacylglyceride concentration, while inducing a heightened startle-response, as well as increasing hyperactivity and reducing sleep. Of notable interest, mouse Etv5 and Drosophila Ets96B are expressed in dopaminergic-rich regions, and loss of Ets96B specifically in dopaminergic neurons recapitulates the metabolic and behavioural phenotypes. Moreover, Ets96B inhibits dopaminergic-specific neuroprotective systems. Additionally, multiple SNPs in human ETV5 link to body mass index (BMI) and BD, providing further evidence for ETV5 as an important and novel molecular intermediate between obesity and BD. The Drosophila ETV5 homologue Ets96B regulates the expression of cellular systems with links to obesity and behaviour, including the expression of a conserved endoplasmic reticulum molecular chaperone complex known to be neuroprotective. Finally, a connection between the obesity-linked gene ETV5 and bipolar disorder emphasizes a functional relationship between obesity and BD at the molecular level.

Ma, J., Brennan, K. J., D'Aloia, M. R., Pascuzzi, P. E. and Weake, V. M. (2016). Transcriptome profiling identifies Multiplexin as a target of SAGA deubiquitinase activity in glia required for precise axon guidance during Drosophila visual development. G3 (Bethesda) [Epub ahead of print]. PubMed ID: 27261002
Summary:
The Spt-Ada-Gcn5 Acetyltransferase (SAGA) complex is a transcriptional coactivator with histone acetylase and deubiquitinase activities that plays an important role in visual development and function. In Drosophila melanogaster, four SAGA subunits are required for deubiquitination of monoubiquitinated histone H2B (ubH2B): Nonstop, Sgf11, E(y)2 and Ataxin 7. Mutations that disrupt SAGA deubiquitinase activity cause defects in neuronal connectivity in the developing Drosophila visual system. In addition, mutations in SAGA result in the human progressive visual disorder spinocerebellar ataxia type 7 (SCA7). Glial cells play a crucial role in both the neuronal connectivity defect in nonstop and sgf11 flies, and in the retinal degeneration in SCA7 patients. Thus, this study sought to identify the gene targets of SAGA deubiquitinase activity in glia in the Drosophila larval central nervous system. To do this, glia from wild-type, nonstop and sgf11 larval optic lobes were enriched using affinity-purification of KASH-EGFP tagged nuclei, and then examined each transcriptome using RNA-seq. The analysis showed that SAGA deubiquitinase activity is required for proper expression of 16% of actively transcribed genes in glia, especially genes involved in proteasome function, protein folding and axon guidance. It was further show, that the SAGA deubiquitinase-activated gene Multiplexin (Mp) is required in glia for proper photoreceptor axon targeting. Mutations in the human ortholog of Mp, COL18A1, have been identified in a family with a SCA7-like progressive visual disorder, suggesting that defects in the expression of this gene in SCA7 patients could play a role in the retinal degeneration that is unique to this ataxia.

Men, T. T., Thanh, D. N., Yamaguchi, M., Suzuki, T., Hattori, G., Arii, M., Huy, N. T. and Kamei, K. (2016). A Drosophila model for screening antiobesity agents. Biomed Res Int 2016: 6293163. PubMed ID: 27247940
Summary:
Although triacylglycerol, the major component for lipid storage, is essential for normal physiology, its excessive accumulation causes obesity in adipose tissue and is associated with organ dysfunction in nonadipose tissue. This study focused on the Drosophila model to develop therapeutics for preventing obesity. The brummer (bmm) gene in Drosophila is known to be homologous with human adipocyte triglyceride lipase, which is related to the regulation of lipid storage. A Drosophila model for monitoring bmm expression was developed by introducing the green fluorescent protein (GFP) gene as a downstream reporter of the bmm promoter. The third-instar larvae of Drosophila showed the GFP signal in all tissues observed and specifically in the salivary gland nucleus. To confirm the relationship between bmm expression and obesity, the effect of oral administration of glucose diets on bmm promoter activity was analyzed. The Drosophila flies given high-glucose diets showed higher lipid contents, indicating the obesity phenotype; this was suggested by a weaker intensity of the GFP signal as well as reduced bmm mRNA expression. These results demonstrated that the transgenic Drosophila model established in this study is useful for screening antiobesity agents. The effects of oral administration of histone deacetylase inhibitors and some vegetables on the bmm promoter activity is also reported.

Wang, T., Xu, W., Qin, M., Yang, Y., Bao, P., Shen, F., Zhang, Z. and Xu, J. (2016). Pathogenic mutations in the Valosin-containing protein/p97(VCP) N-domain inhibit the SUMOylation of VCP and lead to impaired stress response. J Biol Chem [Epub ahead of print]. PubMed ID: 27226613
Summary:
Valosin-containing protein/p97(VCP; see Drosophila TER94) is a hexameric ATPase vital to protein degradation during endoplasmic reticulum stress. It regulates diverse cellular functions including autophagy, chromatin remodeling and DNA repair. In addition, mutations in VCP cause inclusion body myopathy, Paget's disease of the bone, and frontotemporal dementia (IBMPFD), as well as amyotrophic lateral sclerosis (ALS). Nevertheless, how the VCP activities are regulated and how the pathogenic mutations affect the function of VCP during stress are not unclear. This study shows that the small ubiquitin-like modifier (SUMO)-ylation (see Drosophila SUMO) of VCP is a normal stress response inhibited by the disease-causing mutations in the N-domain. Under oxidative and Endoplasmic-reticulum(ER) stress conditions, the SUMOylation of VCP facilitates the distribution of VCP to stress granules and nucleus, and promotes the VCP hexamer assembly. In contrast, pathogenic mutations in the VCP N-domain lead to reduced SUMOylation and weakened VCP hexamer formation upon stress. Defective SUMOylation of VCP also causes altered co-factor binding and attenuated ER-associated protein degradation. Furthermore, SUMO-defective VCP fails to protect against stress-induced toxicity in Drosophila. Therefore, these results have revealed SUMOylation as a molecular signaling switch to regulate the distribution and functions of VCP during stress response, and suggest that deficiency in VCP SUMOylation caused by pathogenic mutations will render cells vulnerable to stress insults.

Friday, June 24th

Ables, E.T., Hwang, G.H., Finger, D.S., Hinnant, T.D. and Drummond-Barbosa, D. (2016). A genetic mosaic screen reveals ecdysone-responsive genes regulating Drosophila oogenesis. G3 (Bethesda) [Epub ahead of print]. PubMed ID: 27226164
Summary:
Multiple aspects of Drosophila oogenesis, including germline stem cell activity, germ cell differentiation, and follicle survival are regulated by the steroid hormone ecdysone. While the transcriptional targets of ecdysone signaling have been studied extensively during development, targets in the ovary remain largely unknown. Early studies of salivary gland polytene chromosomes led to the model that ecdysone stimulates a hierarchical transcriptional cascade, wherein a core group of ecdysone-sensitive transcription factors induce tissue-specific responses by activating secondary branches of transcriptional targets. More recently, genome-wide approaches have identified hundreds of putative ecdysone-responsive targets. Determining whether these putative targets represent bona fide targets in vivo, however, requires that they be tested via traditional mutant analysis in a cell-type specific fashion. To investigate the molecular mechanisms whereby ecdysone signaling regulates oogenesis, this study used genetic mosaic analysis to screen putative ecdysone-responsive genes for novel roles in the control of the earliest steps of oogenesis. A cohort of genes required for stem cell maintenance, stem and progenitor cell proliferation, and follicle encapsulation, growth, and survival were identified. These genes encode transcription factors, chromatin modulators, and factors required for RNA transport, stability, and ribosome biogenesis, suggesting that ecdysone might control a wide range of molecular processes during oogenesis. Results suggest that although ecdysone target genes are known to have cell type-specific roles, many ecdysone response genes that control larval or pupal cell types at developmental transitions are reiteratively used in the adult ovary. These results provide novel insight into the molecular mechanisms by which ecdysone signaling controls oogenesis, laying new ground for future studies.

Perry, J.C., Joag, R., Hosken, D.J., Wedell, N., Radwan, J. and Wigby, S. (2016). Experimental evolution under hyper-promiscuity in Drosophila melanogaster. BMC Evol Biol 16: 131. PubMed ID: 27311887
Summary:
The number of partners that individuals mate with over their lifetime is a defining feature of mating systems, and variation in mate number is thought to be a major driver of sexual evolution. Although previous research has investigated the evolutionary consequences of reductions in the number of mates, little is known about the costs and benefits of increased numbers of mates. This study uses genetic manipulation of mating frequency in Drosophila melanogaster to create a novel, highly promiscuous mating system. D. melanogaster populations in which flies are deficient for the sex peptide receptor (SPR) gene were generated resulting in SPR- females that mate more frequently - and were allowed them to evolve for 55 generations. At several time-points during this experimental evolution, the behavioural, morphological and transcriptional reproductive phenotypes expected to evolve in response to increased population mating frequencies were assayed. It was found that males from the high mating frequency SPR- populations evolve decreased ability to inhibit the receptivity of their mates and decrease copulation duration, in line with predictions of decreased per-mating investment with increased sperm competition. Unexpectedly, SPR- population males also evolve weakly increased sex peptide (SP) gene expression. Males from SPR- populations initially (i.e., before experimental evolution) exhibit more frequent courtship and faster time until mating relative to controls, but over evolutionary time these differences diminish or reverse. In response to experimentally increased mating frequency, SPR- males evolve behavioural responses consistent with decreased male post-copulatory investment at each mating and decrease overall pre-copulatory performance. The trend towards increased SP gene expression might plausibly relate to functional differences in the two domains of the SP protein. These data highlight the utility of genetic manipulations of animal social and sexual environments coupled with experimental evolution.

Ma, H. and O'Farrell, P.H. (2016). Selfish drive can trump function when animal mitochondrial genomes compete. Nat Genet [Epub ahead of print]. PubMed ID: 27270106
Summary:
Mitochondrial genomes compete for transmission from mother to progeny. This study explored this competition by introducing a second genome into Drosophila melanogaster to follow transmission. Competitions between closely related genomes favor those functional in electron transport, resulting in a host-beneficial purifying selection. In contrast, matchups between distantly related genomes often favor those with negligible, negative or lethal consequences, indicating selfish selection. Exhibiting powerful selfish selection, a genome carrying a detrimental mutation displaces a complementing genome, leading to population death after several generations. In a different pairing, opposing selfish and purifying selection counterbalances to give stable transmission of two genomes. Sequencing of recombinant mitochondrial genomes shows that the noncoding region, containing origins of replication, governs selfish transmission. Uniparental inheritance prevents encounters between distantly related genomes. Nonetheless, in each maternal lineage, constant competition among sibling genomes selects for super-replicators. The study suggests that this relentless competition drives positive selection, promoting change in the sequences influencing transmission.

Ameku, T. and Niwa, R. (2016). Mating-induced increase in germline stem cells via the neuroendocrine system in female Drosophila. PLoS Genet 12: e1006123. PubMed ID: 27310920
Summary:
Mating and gametogenesis are two essential components of animal reproduction. Gametogenesis must be modulated by the need for gametes, yet little is known of how mating, a process that utilizes gametes, may modulate the process of gametogenesis. This study reports that mating stimulates female germline stem cell (GSC) proliferation in Drosophila melanogaster. Mating-induced increase in GSC number is not simply owing to the indirect effect of emission of stored eggs, but rather is stimulated by a male-derived Sex Peptide (SP) and its receptor SPR, the components of a canonical neuronal pathway that induces a post-mating behavioral switch in females. It was shown that ecdysteroid, the major insect steroid hormone, regulates mating-induced GSC proliferation independently of insulin signaling. Ovarian ecdysteroid level increases after mating and transmits its signal directly through the ecdysone receptor expressed in the ovarian niche to increase the number of GSCs. Impairment of ovarian ecdysteroid biosynthesis disrupts mating-induced increase in GSCs as well as egg production. Importantly, feeding of ecdysteroid rescues the decrease in GSC number caused by impairment of neuronal SP signaling. This study illustrates how female GSC activity is coordinately regulated by the neuroendocrine system to sustain reproductive success in response to mating.

Thursday, June 23rd

Deng, Q., Guo, T., Zhou, X., Xi, Y., Yang, X. and Ge, W. (2016). Crosstalk between mitochondrial fusion and the Hippo pathway in controlling cell proliferation during Drosophila development. Genetics [Epub ahead of print]. PubMed ID: 27317679
Summary:
Cell proliferation and tissue growth depend on the coordinated regulation of multiple signaling molecules and pathways during animal development. Previous studies have linked mitochondrial function and the Hippo signaling pathway in growth control. However, the underlying molecular mechanisms are not fully understood. This study identifies a Drosophila mitochondrial inner membrane protein ChChd3 as a novel regulator for tissue growth during larval development. Loss of ChChd3 leads to tissue undergrowth and cell proliferation defects. ChChd3 is required for mitochondrial fusion and removal of ChChd3 increases mitochondrial fragmentation. ChChd3 is another mitochondrial target of the Hippo pathway, although it is only partially required for Hippo pathway mediated overgrowth. Interestingly, lacking of ChChd3 leads to inactivation of Hippo activity under normal development, which is also dependent on the transcriptional co-activator Yorkie (Yki). Furthermore, loss of ChChd3 induces oxidative stress and activates the JNK pathway. In addition, depletion of other mitochondrial fusion components, Opa1 or Marf, inactivates the Hippo pathway as well. Taken together, the study proposes that there is a crosstalk between mitochondrial fusion and the Hippo pathway which is essential in controlling cell proliferation and tissue homeostasis in Drosophila.

Bergstralh, D.T., Lovegrove, H.E., Kujawiak, I., Dawney, N.S., Zhu, J., Cooper, S., Zhang, R. and St Johnston, D. (2016). Pins is not required for spindle orientation in the Drosophila wing disc. Development [Epub ahead of print]. PubMed ID: 27287805
Summary:
In animal cells, mitotic spindles are oriented by the dynein/dynactin motor complex, which exerts a pulling force on astral microtubules. Dynein/dynactin localization depends on Mud/NUMA, which is typically recruited to the cortex by Pins/LGN. In Drosophila neuroblasts, the Inscuteable/Baz/Par-6/aPKC complex recruits Pins apically to induce vertical spindle orientation, whereas in epithelial cells, Dlg recruits Pins laterally to orient the spindle horizontally. This study investigated division orientation in the Drosophila imaginal wing disc epithelium. Live imaging reveals that spindle angles vary widely during prometaphase and metaphase, and therefore do not reliably predict division orientation. Next, the mutants that have been reported to disrupt division orientation in this tissue were re-examined. Loss of Mud/NUMA misorients divisions, but Inscuteable expression and aPKC, dlg and pins mutants have no effect. Furthermore, Mud localizes to the apical-lateral cortex of the wing epithelium independently of both Pins and cell cycle stage. Thus, Pins is not required in the wing disc because there are parallel mechanisms for Mud localization and hence spindle orientation, making it a more robust system than other epithelia.

Liu, Y., Liao, S., Veenstra, J. A. and Nassel, D. R. (2016). Drosophila insulin-like peptide 1 (DILP1) is transiently expressed during non-feeding stages and reproductive dormancy. Sci Rep 6: 26620. PubMed ID: 27197757
Summary:
The insulin/insulin-like growth factor signaling pathway is evolutionarily conserved in animals, and is part of nutrient-sensing mechanisms that control growth, metabolism, reproduction, stress responses, and lifespan. In Drosophila, eight insulin-like peptides (DILP1-8) are known, six of which have been investigated in some detail, whereas expression and functions of DILP1 and DILP4 remain enigmatic. This study demonstrates that dilp1/DILP1 is transiently expressed in brain insulin producing cells (IPCs) from early pupa until a few days of adult life. However, in adult female flies where diapause is triggered by low temperature and short days, within a time window 0-10h post-eclosion, the dilp1/DILP1 expression remains high for at least 9 weeks. The dilp1 mRNA level is increased in dilp2, 3, 5 and dilp6 mutant flies, indicating feedback regulation. Furthermore, the DILP1 expression in IPCs is regulated by short neuropeptide F, juvenile hormone and presence of larval adipocytes. Male dilp1 mutant flies display increased lifespan and reduced starvation resistance, whereas in female dilp1 mutants oviposition is reduced. Thus, DILP1 is expressed in non-feeding stages and in diapausing flies, is under feedback regulation and appears to play sex-specific functional roles.

Wang, D., Li, L., Lu, J., Liu, S. and Shen, J. (2016). Complementary expression of optomotor-blind and the Iroquois complex promotes fold formation to separate wing notum and hinge territories. Dev Biol. PubMed ID: 27212024
Summary:
Animal morphogenesis requires folds or clefts to separate populations of cells which are often associated with different cell affinities. In the Drosophila wing imaginal disc, the regional expression of the Iroquois complex (Iro-C) in the notum leads to the formation of the hinge/notum (H/N) fold that separates the wing hinge and notum territories. Although Decapentaplegic (Dpp) signaling has been revealed as essential for the hinge/notum subdivision through the restriction of Iro-C toward the notum region, the mechanism by which the H/N border develops into a fold is unknown. This study reports that a Dpp target gene, optomotor-blind (omb), mediates the role of Dpp signaling in Iro-C inhibition. omb is complementarily expressed on the dorsal hinge side, abutting the Iro-C domain along the H/N border. Ectopic omb expression inhibits Iro-C in the notum territory, independent of known Iro-C regulators Msh and Stat92E. Uniform manipulation of either omb or Iro-C genes spanning the presumptive H/N border significantly suppresses H/N fold formation via inhibition of the apical microtubule enrichment. Ectopically sharp border or discontinuity in level of Iro-C or Omb is enough to generate ectopic fold formation. These results reveal that omb and Iro-C not only are complementarily expressed but also cooperate to promote H/N fold formation. These data help to understand how Dpp signaling is interpreted region-specifically during tissue subdivision.

Wednesday, June 22

Kenmoku, H., Ishikawa, H., Ote, M., Kuraishi, T. and Kurata, S. (2016). A subset of neurons controls the permeability of the peritrophic matrix and midgut structure in Drosophila adults. J Exp Biol. PubMed ID: 27229474
Summary:
The metazoan gut performs multiple physiologic functions, including digestion and absorption of nutrients, and also serves as a physical and chemical barrier against ingested pathogens and abrasive particles. Maintenance of these functions and structures is partly controlled by the nervous system, yet the precise roles and mechanisms of the neural control of gut integrity remain to be clarified in Drosophila. This study screened for GAL4 enhancer-trap strains and labeled specific subsets of neurons. The strong inward rectifier potassium channel Kir2.1 was used to inhibit their neuronal activity. An NP3253 line was identified that is susceptible to oral infection by Gram-negative bacteria. The subset of neurons driven by the NP3253 line includes some of the enteric neurons innervating the anterior midgut, and these flies have a disorganized proventricular structure with high permeability of the peritrophic matrix and epithelial barrier. The findings of the present study indicate that neural control is crucial for maintaining the barrier function of the gut, and provide a route for genetic dissection of the complex brain-gut axis in the model organism Drosophila adults.

Kim, D. H., Han, M. R., Lee, G., Lee, S. S., Kim, Y. J. and Adams, M. E. (2015). Rescheduling behavioral subunits of a fixed action pattern by genetic manipulation of peptidergic signaling. PLoS Genet 11: e1005513. PubMed ID: 26401953
Summary:
The ecdysis behavioral sequence in insects is a classic fixed action pattern (FAP) initiated by hormonal signaling. Ecdysis triggering hormones (ETHs) release the FAP through direct actions on the CNS. This study presents evidence implicating two groups of central ETH receptor (ETHR) neurons in scheduling the first two steps of the FAP: kinin (aka drosokinin, leucokinin) neurons regulate pre-ecdysis behavior and CAMB neurons (CCAP, AstCC, MIP, and Bursicon) initiate the switch to ecdysis behavior. Ablation of kinin neurons or altering levels of ETH receptor (ETHR) expression in these neurons modifies timing and intensity of pre-ecdysis behavior. Cell ablation or ETHR knockdown in CAMB neurons delays the switch to ecdysis, whereas overexpression of ETHR or expression of pertussis toxin in these neurons accelerates timing of the switch. Calcium dynamics in kinin neurons are temporally aligned with pre-ecdysis behavior, whereas activity of CAMB neurons coincides with the switch from pre-ecdysis to ecdysis behavior. Activation of CCAP or CAMB neurons through temperature-sensitive TRPM8 gating is sufficient to trigger ecdysis behavior. These findings demonstrate that kinin and CAMB neurons are direct targets of ETH and play critical roles in scheduling successive behavioral steps in the ecdysis FAP (Kim, 2015).

Cervantes-Sandoval, I., Chakraborty, M., MacMullen, C. and Davis, R.L. (2016). Scribble scaffolds a signalosome for active forgetting. Neuron [Epub ahead of print]. PubMed ID: 27263975
Summary:
Forgetting, one part of the brain's memory management system, provides balance to the encoding and consolidation of new information by removing unused or unwanted memories or by suppressing their expression. Recent studies have identified the small G protein, Rac1, as a key player in the Drosophila mushroom bodies neurons (MBn) for active forgetting. It has also been shown that a few dopaminergic neurons (DAn) that innervate the MBn mediate forgetting. This study shows that Scribble, a scaffolding protein known primarily for its role as a cell polarity determinant, orchestrates the intracellular signaling for normal forgetting. Knocking down scribble expression in either MBn or DAn impairs normal memory loss. Scribble interacts physically and genetically with Rac1, Pak3, and Cofilin within MBn, nucleating a forgetting signalosome that is downstream of dopaminergic inputs that regulate forgetting. These results bind disparate molecular players in active forgetting into a single signaling pathway: Dopamine→ Dopamine Receptor→ Scribble→ Rac→ Cofilin.

Liu, S., Liu, Q., Tabuchi, M. and Wu, M. N. (2016). Sleep drive is encoded by neural plastic changes in a dedicated circuit. Cell 165: 1347-1360. PubMed ID: 27212237
Summary:
Prolonged wakefulness leads to an increased pressure for sleep, but how this homeostatic drive is generated and subsequently persists is unclear. From a neural circuit screen in Drosophila, this study identified a subset of ellipsoid body (EB) neurons whose activation generates sleep drive. Patch-clamp analysis indicates these EB neurons are highly sensitive to sleep loss, switching from spiking to burst-firing modes. Functional imaging and translational profiling experiments reveal that elevated sleep need triggers reversible increases in cytosolic Ca(2+) levels, NMDA receptor expression, and structural markers of synaptic strength, suggesting these EB neurons undergo 'sleep-need'-dependent plasticity. Strikingly, the synaptic plasticity of these EB neurons is both necessary and sufficient for generating sleep drive, indicating that sleep pressure is encoded by plastic changes within this circuit. These studies define an integrator circuit for sleep homeostasis and provide a mechanism explaining the generation and persistence of sleep drive.

Tuesday, June 21st

Lee, H. G., Kahn, T. G., Simcox, A., Schwartz, Y. B. and Pirrotta, V. (2015). Genome-wide activities of Polycomb complexes control pervasive transcription. Genome Res 25: 1170-1181. PubMed ID: 25986499
Summary:
Polycomb group (PcG) complexes PRC1 and PRC2 are well known for silencing specific developmental genes. PRC2 is a methyltransferase targeting histone H3K27 and producing H3K27me3, essential for stable silencing. Less well known but quantitatively much more important is the genome-wide role of PRC2 that dimethylates approximately 70% of total H3K27. H3K27me2 occurs in inverse proportion to transcriptional activity in most non-PcG target genes and intergenic regions and is governed by opposing roaming activities of PRC2 and complexes containing the H3K27 demethylase UTX. Surprisingly, loss of H3K27me2 results in global transcriptional derepression proportionally greatest in silent or weakly transcribed intergenic and genic regions and accompanied by an increase of H3K27ac and H3K4me1. H3K27me2 therefore sets a threshold that prevents random, unscheduled transcription all over the genome and even limits the activity of highly transcribed genes. PRC1-type complexes also have global roles. Unexpectedly, a pervasive distribution of histone H2A ubiquitylated at lysine 118 (H2AK118ub) was found outside of canonical PcG target regions, dependent on the RING/Sce subunit of PRC1-type complexes. It was shown, however, that H2AK118ub does not mediate the global PRC2 activity or the global repression and is predominantly produced by a new complex involving L(3)73Ah, a homolog of mammalian PCGF3.

Mourad, R. and Cuvier, O. (2016). Computational identification of genomic features that influence 3D chromatin domain formation. PLoS Comput Biol 12: e1004908. PubMed ID: 27203237
Summary:
Recent advances in long-range Hi-C contact mapping have revealed the importance of the 3D structure of chromosomes in gene expression. A current challenge is to identify the key molecular drivers of this 3D structure. Several genomic features, such as architectural proteins and functional elements, were shown to be enriched at topological domain borders using classical enrichment tests. This study proposes multiple logistic regression to identify those genomic features that positively or negatively influence domain border establishment or maintenance. The model is flexible, and can account for statistical interactions among multiple genomic features. Using both simulated and real data, the model was shown to outperform enrichment test and non-parametric models, such as random forests, for the identification of genomic features that influence domain borders. Using Drosophila Hi-C data at a very high resolution of 1 kb, the model suggests that, among architectural proteins, BEAF-32 and CP190 are the main positive drivers of 3D domain borders. In humans, this model identifies well-known architectural proteins CTCF and cohesin, as well as ZNF143 and Polycomb group proteins as positive drivers of domain borders. The model also reveals the existence of several negative drivers that counteract the presence of domain borders including P300, RXRA, BCL11A and ELK1 (Mourad, 2016).

Wani, A. H., Boettiger, A. N., Schorderet, P., Ergun, A., Munger, C., Sadreyev, R. I., Zhuang, X., Kingston, R. E. and Francis, N. J. (2016). Chromatin topology is coupled to Polycomb group protein subnuclear organization. Nat Commun 7: 10291. PubMed ID: 26759081
Summary:
The genomes of metazoa are organized at multiple scales. Many proteins that regulate genome architecture, including Polycomb group (PcG) proteins, form subnuclear structures. Deciphering mechanistic links between protein organization and chromatin architecture requires precise description and mechanistic perturbations of both. Using super-resolution microscopy, this study shows that PcG proteins are organized into hundreds of nanoscale protein clusters. PcG clusters were manipulated by disrupting the polymerization activity of the sterile alpha motif (SAM) of the PcG protein Polyhomeotic (Ph) or by increasing Ph levels. Ph with mutant SAM disrupts clustering of endogenous PcG complexes and chromatin interactions while elevating Ph level increases cluster number and chromatin interactions. These effects can be captured by molecular simulations based on a previously described chromatin polymer model. Both perturbations also alter gene expression. Organization of PcG proteins into small, abundant clusters on chromatin through Ph SAM polymerization activity may shape genome architecture through chromatin interactions.

Chatterjee, N., Tian, M., Spirohn, K., Boutros, M. and Bohmann, D. (2016). Keap1-independent Regulation of Nrf2 activity by protein acetylation and a BET bromodomain protein. PLoS Genet 12: e1006072. PubMed ID: 27233051
Summary:
Mammalian BET proteins comprise a family of bromodomain-containing epigenetic regulators with complex functions in chromatin organization and gene regulation. This study identified the sole member of the BET protein family in Drosophila, Fs(1)h, as an inhibitor of the stress responsive transcription factor CncC, the fly ortholog of Nrf2. Fs(1)h physically interacts with CncC in a manner that requires the function of its bromodomains and the acetylation of CncC. Treatment of cultured Drosophila cells or adult flies with fs(1)h RNAi or with the BET protein inhibitor JQ1 de-represses CncC transcriptional activity and engages protective gene expression programs. The mechanism by which Fs(1)h inhibits CncC function is distinct from the canonical mechanism that stimulates Nrf2 function by abrogating Keap1-dependent proteasomal degradation. Consistent with the independent modes of CncC regulation by Keap1 and Fs(1)h, combinations of drugs that can specifically target these pathways cause a strong synergistic and specific activation of protective CncC- dependent gene expression and boosts oxidative stress resistance. This synergism might be exploitable for the design of combinatorial therapies to target diseases associated with oxidative stress or inflammation.

Monday, June 20th

Adlesic, M., Frei, C. and Frew, I. J. (2016). Cdk4 functions in multiple cell types to control Drosophila intestinal stem cell proliferation and differentiation. Biol Open [Epub ahead of print]. PubMed ID: 26879465
Summary:
The proliferation of intestinal stem cells (ISCs) and differentiation of enteroblasts to form mature enteroendocrine cells and enterocytes in the Drosophila intestinal epithelium must be tightly regulated to maintain homeostasis. This study shows that genetic modulation of CyclinD/Cdk4 activity or mTOR-dependent signalling cell-autonomously regulates enterocyte growth, which influences ISC proliferation and enteroblast differentiation. Increased enterocyte growth results in higher numbers of ISCs and defective enterocyte growth reduces ISC abundance and proliferation in the midgut. Adult midguts deficient for Cdk4 show severe disruption of intestinal homeostasis characterised by decreased ISC self-renewal, enteroblast differentiation defects and low enteroendocrine cell and enterocyte numbers. The ISC/enteroblast phenotypes result from a combination of cell autonomous and non-autonomous requirements for Cdk4 function. One non-autonomous consequence of Cdk4-dependent deficient enterocyte growth is high expression of Delta in ISCs and Delta retention in enteroblasts. It is postulated that aberrant activation of the Delta-Notch pathway is a possible partial cause of lost ISC stemness. These results support the idea that enterocytes contribute to a putative stem cell niche that maintains intestinal homeostasis in the Drosophila anterior midgut.

Kotov, A. A., Olenkina, O. M., Kibanov, M. V. and Olenina, L. V. (2016). RNA helicase Belle (DDX3) is essential for male germline stem cell maintenance and division in Drosophila. Biochim Biophys Acta [Epub ahead of print]. PubMed ID: 26876306
Summary:
The present study showed that RNA helicase Belle (DDX3) was required intrinsically for mitotic progression and survival of germline stem cells (GSCs) and spermatogonial cells in the Drosophila melanogaster testes. Deficiency of Belle in the male germline resulted in a strong germ cell loss phenotype. Early germ cells are lost through cell death, whereas somatic hub and cyst cell populations are maintained. The observed phenotype is related to that of the human Sertoli Cell-Only Syndrome caused by the loss of DBY (DDX3) expression in the human testes and results in a complete lack of germ cells with preservation of somatic Sertoli cells. This study found the hallmarks of mitotic G2 delay in early germ cells of the larval testes of bel mutants. Both mitotic cyclins, A and B, are markedly reduced in the gonads of bel mutants. Transcription levels of cycB and cycA decrease significantly in the testes of hypomorph bel mutants. Overexpression of Cyclin B in the germline partially rescues germ cell survival, mitotic progression and fertility in the bel-RNAi knockdown testes. Taken together, these results suggest that a role of Belle in GSC maintenance and regulation of early germ cell divisions is associated with the expression control of mitotic cyclins.

Lee, J. Y., Chen, J. Y., Shaw, J. L. and Chang, K. T. (2016). Maintenance of stem cell niche integrity by a novel activator of integrin signaling. PLoS Genet 12: e1006043. PubMed ID: 27191715
Summary:
Stem cells depend critically on the surrounding microenvironment, or niche, for their maintenance and self-renewal. While much is known about how the niche regulates stem cell self-renewal and differentiation, mechanisms for how the niche is maintained over time are not well understood. At the apical tip of the Drosophila testes, germline stem cells (GSCs) and somatic stem cells share a common niche formed by hub cells. This study demonstrates that a novel protein named Shriveled (Shv; CG4164) is necessary for the maintenance of hub/niche integrity. Depletion of Shv protein results in age-dependent deterioration of the hub structure and loss of GSCs, whereas upregulation of Shv preserves the niche during aging. Shv is a secreted protein that modulates DE-cadherin levels through extracellular activation of integrin signaling (see Myospheroid). This work identifies Shv as a novel activator of integrin signaling and suggests a new integration model in which crosstalk between integrin and DE-cadherin in niche cells promote their own preservation by maintaining the niche architecture.
Chen, J., Xu, N., Huang, H., Cai, T. and Xi, R. (2016). A feedback amplification loop between stem cells and their progeny promotes tissue regeneration and tumorigenesis. Elife 5 [Epub ahead of print]. PubMed ID: 27187149
Summary:
Homeostatic renewal of many adult tissues requires balanced self-renewal and differentiation of local stem cells, but the underlying mechanisms are poorly understood. This study identified a novel feedback mechanism in controlling intestinal regeneration and tumorigenesis in Drosophila. Sox21a, a group B Sox protein, is preferentially expressed in the committed progenitor named enteroblast (EB) to promote enterocyte differentiation. In Sox21a mutants, EBs do not divide, but cannot differentiate properly and have increased expression of mitogens, which then act as paracrine signals to promote intestinal stem cell (ISC) proliferation. This leads to a feedback amplification loop for rapid production of differentiation-defective EBs and tumorigenesis. Notably, in normal intestine following damage, Sox21a is temporally downregulated in EBs to allow the activation of the ISC-EB amplification loop for epithelial repair. It is proposed that executing a feedback amplification loop between stem cells and their progeny could be a common mechanism underlying tissue regeneration and tumorigenesis.

Sunday, June 19th

Snee, M. J., Wilson, W. C., Zhu, Y., Chen, S. Y., Wilson, B. A., Kseib, C., O'Neal, J., Mahajan, N., Tomasson, M. H., Arur, S. and Skeath, J. B. (2016). Collaborative control of cell cycle progression by the RNA exonuclease Dis3 and Ras is conserved across species. Genetics 203: 749-762. PubMed ID: 27029730
Summary:
Dis3 encodes a conserved RNase that degrades or processes all RNA species via an N-terminal PilT N terminus (PIN) domain and C-terminal RNB domain that harbor, respectively, endonuclease activity and 3'-5' exonuclease activity. In Schizosaccharomyces pombe, dis3 mutations cause chromosome missegregation and failure in mitosis, suggesting dis3 promotes cell division. In humans, apparently hypomorphic dis3 mutations are found recurrently in multiple myeloma, suggesting dis3 opposes cell division. Except for the observation that RNAi-mediated depletion of dis3 function drives larval arrest and reduces tissue growth in Drosophila, the role of dis3 has not been rigorously explored in higher eukaryotic systems. Using the Drosophila system and newly generated dis3 null alleles, this study found that absence of dis3 activity inhibits cell division. A conserved CDK1 phosphorylation site was found that when phosphorylated inhibits Dis3's exonuclease, but not endonuclease, activity. Leveraging this information, Dis3's exonuclease function was shown to be required for mitotic cell division: in its absence, cells are delayed in mitosis and exhibit aneuploidy and overcondensed chromosomes. In contrast, modest reduction dis3 function was found enhances cell proliferation in the presence of elevated Ras activity, apparently by accelerating cells through G2/M even though each insult by itself delays G2/M. Additionally, dis3 and ras were found to genetically interact in worms and that dis3 can enhance cell proliferation under growth stimulatory conditions in murine B cells. Thus, reduction, but not absence, of dis3 activity can enhance cell proliferation in higher organisms.

Flegel, K., Grushko, O., Bolin, K., Griggs, E. and Buttitta, L. (2016). The role of the histone modifying and exchange complex NuA4 in cell cycle progression in Drosophila melanogaster. Genetics [Epub ahead of print]. PubMed ID: 27184390
Summary:
Robust and synchronous repression of E2F-dependent gene expression is critical to the proper timing of cell cycle exit when cells transition to a post-mitotic state. Previously histone Modifying and Exchange Complex NuA4 was suggested to act as a barrier to proliferation in Drosophila, by repressing E2F-dependent gene expression. This study shows that NuA4 activity is required for proper cell cycle exit and the repression of cell cycle genes during the transition to a post-mitotic state in vivo However, the delay of cell cycle exit caused by compromising NuA4 is not due to additional proliferation or effects on E2F activity. Instead NuA4 inhibition results in slowed cell cycle progression through late S and G2 phases due to aberrant activation of an intrinsic p53-independent DNA damage response. A reduction in NuA4 function ultimately produces a paradoxical cell cycle gene expression program, where certain cell cycle genes become de-repressed in cells that are delayed during the G2 phase of the final cell cycle. Bypassing the G2 delay when NuA4 is inhibited leads to abnormal mitoses and results in severe tissue defects. NuA4 physically and genetically interacts with components of the E2F complex termed DREAM/MMB (Rbf, E2F and Myb/Multi-vulva class B), and modulates a DREAM/MMB-dependent ectopic neuron phenotype in the posterior wing margin. However, this effect is also likely due to the cell cycle delay, as simply reducing Cdk1 is sufficient to generate a similar phenotype. This work reveals that the major requirement for NuA4 in the cell cycle in vivo is to suppress an endogenous DNA damage response, which is required to coordinate proper S and G2 cell cycle progression with differentiation and cell cycle gene expression.

Bretscher, H.S. and Fox, D.T. (2016). Proliferation of double-strand break-resistant polyploid cells requires Drosophila FANCD2. Dev Cell 37: 444-457. PubMed ID: 27270041
Summary:
Conserved DNA-damage responses (DDRs) sense genome damage and prevent mitosis of broken chromosomes. How cells lacking DDRs cope with broken chromosomes during mitosis is poorly understood. DDRs are frequently inactivated in cells with extra genomes (polyploidy), suggesting that study of polyploidy can reveal how cells with impaired DDRs/genome damage continue dividing. This study shows that continued division and normal organ development occurs in polyploid, DDR-impaired Drosophila papillar cells. As papillar cells become polyploid, they naturally accumulate broken acentric chromosomes but do not apoptose/arrest the cell cycle. To survive mitosis with acentric chromosomes, papillar cells require Fanconi anemia proteins FANCD2 and FANCI, as well as Blm helicase, but not canonical DDR signaling. FANCD2 acts independently of previous S phases to promote alignment and segregation of acentric DNA produced by double-strand breaks, thus avoiding micronuclei and organ malformation. Because polyploidy and impaired DDRs can promote cancer, these findings provide insight into disease-relevant DNA-damage tolerance mechanisms.

Huang, F., Saraf, A., Florens, L., Kusch, T., Swanson, S. K., Szerszen, L. T., Li, G., Dutta, A., Washburn, M. P., Abmayr, S. M. and Workman, J. L. (2016). The Enok acetyltransferase complex interacts with Elg1 and negatively regulates PCNA unloading to promote the G1/S transition. Genes Dev 30: 1198-1210. PubMed ID: 27198229
Summary:
KAT6 histone acetyltransferases (HATs) are highly conserved in eukaryotes and are involved in cell cycle regulation. However, information regarding their roles in regulating cell cycle progression is limited. This study reports the identification of subunits of the Drosophila Enok complex and demonstrates that all subunits are important for its HAT activity. A novel interaction is reported between the Enok complex and the Elg1 proliferating cell nuclear antigen (PCNA)-unloader complex. Depletion of Enok in S2 cells resulted in a G1/S cell cycle block, and this block can be partially relieved by depleting Elg1. Furthermore, depletion of Enok reduced the chromatin-bound levels of PCNA in both S2 cells and early embryos, suggesting that the Enok complex may interact with the Elg1 complex and down-regulate its PCNA-unloading function to promote the G1/S transition. Supporting this hypothesis, depletion of Enok also partially rescued the endoreplication defects in Elg1-depleted nurse cells. Taken together, this study provides novel insights into the roles of KAT6 HATs in cell cycle regulation through modulating PCNA levels on chromatin.

Saturday, June 18th

De Lella Ezcurra, A. L., Bertolin, A. P., Kim, K., Katz, M. J., Gandara, L., Misra, T., Luschnig, S., Perrimon, N., Melani, M. and Wappner, P. (2016). miR-190 enhances HIF-dependent responses to hypoxia in Drosophila by inhibiting the prolyl-4-hydroxylase Fatiga. PLoS Genet 12: e1006073. PubMed ID: 27223464
Summary:
Cellular and systemic responses to low oxygen levels are principally mediated by Hypoxia Inducible Factors (HIFs), a family of evolutionary conserved heterodimeric transcription factors, whose alpha- and beta-subunits belong to the bHLH-PAS family. In normoxia, HIFalpha is hydroxylated by specific prolyl-4-hydroxylases, targeting it for proteasomal degradation, while in hypoxia the activity of these hydroxylases decreases due to low oxygen availability, leading to HIFalpha accumulation and expression of HIF target genes. To identify microRNAs required for maximal HIF activity, an overexpression screen was conducted in Drosophila melanogaster, evaluating the induction of a HIF transcriptional reporter. miR-190 overexpression was found to enhanced HIF-dependent biological responses, including terminal sprouting of the tracheal system, while in miR-190 loss of function embryos the hypoxic response was impaired. In hypoxic conditions, miR-190 expression was upregulated and required for induction of HIF target genes by directly inhibiting the HIF prolyl-4-hydroxylase Fatiga. Thus, miR-190 is a novel regulator of the hypoxia response that represses the oxygen sensor Fatiga, leading to HIFalpha stabilization and enhancement of hypoxic responses.

Nyberg, K. G. and Machado, C. A. (2016). Comparative expression dynamics of intergenic long noncoding RNAs (lncRNAs) in the genus Drosophila. Genome Biol Evol [Epub ahead of print]. PubMed ID: 27189981
Summary:
This study identified and characterized long noncoding RNAs (lncRNAs) in D. pseudoobscura. Using RNA-Seq and computational filtering of protein-coding potential, 1,589 intergenic lncRNA loci were identified in D. pseudoobscura. Multiple sex-specific developmental stages were surveyed and, like in D. melanogaster, increasingly prolific lncRNA expression was found through male development and an overrepresentation of lncRNAs was found in the testes. Other trends seen in D. melanogaster, like reduced pupal expression, were not observed. Nonrandom distributions of female-biased and non-testis-specific male-biased lncRNAs between the X chromosome and autosomes are consistent with selection-based models of gene trafficking to optimize genomic location of sex-biased genes. The numerous testis-specific lncRNAs, however, are randomly distributed between the X and autosomes, and the hypothesis that many of these are likely to be spurious transcripts cannot be rejected. Finally, using annotated lncRNAs in both species, 134 putative lncRNA homologs were found between D. pseudoobscura and D. melanogaster, and many were found to have conserved developmental expression dynamics, making them ideal candidates for future functional analyses.

Ito, H., Sato, K., Kondo, S., Ueda, R. and Yamamoto, D. (2016). Fruitless represses robo1 transcription to shape male-specific neural morphology and behavior in Drosophila. Curr Biol [Epub ahead of print]. PubMed ID: 27265393
Summary:
The Drosophila fruitless (fru) gene is regarded as a master regulator of the formation of male courtship circuitry, yet little is known about its molecular basis of action. This study shows that roundabout 1 (robo1) knockdown in females promotes formation of the male-specific neurite in sexually dimorphic mAL interneurons and that overexpression of the male-specific BM diminishes the expression of Robo1 in the fly brain. Electrophoretic mobility shift and reporter assays identify the 42-bp segment encompassing the palindrome sequence T T C G C T G C G C C G T G A A in the 5' UTR of robo1 exon1 as the FruBM-responsive element. It was also found that ~10-bp deletions in the palindrome sequence induce a loss of the male-specific neurite and disrupt male courtship patterns. These data paves the way for a thorough understanding of the mechanism whereby Fru proteins orchestrate transcription for the formation of courtship circuitry.

Lim, M. Y., Ng, A. W., Chou, Y., Lim, T. P., Simcox, A., Tucker-Kellogg, G. and Okamura, K. (2016). The Drosophila Dicer-1 partner Loquacious enhances miRNA processing from hairpins with unstable structures at the dicing site. Cell Rep 15: 1795-1808. PubMed ID: 27184838
Summary:
In Drosophila, Dicer-1 binds Loquacious-PB (Loqs-PB) as its major co-factor. Previous analyses indicated that loqs mutants only partially impede miRNA processing, but the activity of minor isoforms or maternally deposited Loqs was not eliminated in these studies. This was addressed by generating a cell line from loqs-null embryos and it was found that only approximately 40% of miRNAs showed clear Loqs dependence. Genome-wide comparison of the hairpin structure and Loqs dependence suggested that Loqs substrates are influenced by base-pairing status at the dicing site. Artificial alteration of base-pairing stability at this position in model miRNA hairpins resulted in predicted changes in Loqs dependence, providing evidence for this hypothesis. Finally, evolutionarily young miRNA genes tended to be Loqs dependent. It is proposed that Loqs may have roles in assisting the de novo emergence of miRNA genes by facilitating dicing of suboptimal hairpin substrates.

Friday, June 17th

Zhuang, L., Sun, Y., Hu, M., Wu, C., La, X., Chen, X., Feng, Y., Wang, X., Hu, Y. and Xue, L. (2016). Or47b plays a role in Drosophila males' preference for younger mates. Open Biol 6. PubMed ID: 27278650
Summary:
Reproductive behaviour is important for animals to keep their species existing on Earth. A key question is how to generate more and healthier progenies by choosing optimal mates. In Drosophila melanogaster, males use multiple sensory cues, including vision, olfaction and gustation, to achieve reproductive success. These sensory inputs are important, yet not all these different modalities are simultaneously required for courtship behaviour to occur. Moreover, the roles of these sensory inputs for male courtship choice remain largely unknown. This study demonstrates that males court younger females with greater preference and that olfactory inputs are indispensable for this male courtship choice. Specifically, the olfactory receptor Or47b is required for males to discriminate younger female mates from older ones. In combination with previous studies indicating that gustatory perception is necessary for this preference behaviour, these data demonstrates the requirement of both olfaction and gustation in Drosophila males' courtship preference, thus providing new insights into the role of sensory cues in reproductive behaviour and success.

Morimoto, J. and Wigby, S. (2016). Differential effects of male nutrient balance on pre- and post-copulatory traits, and consequences for female reproduction in Drosophila melanogaster. Sci Rep 6: 27673. PubMed ID: 27270223
Summary:
Male fitness depends on the expression of costly traits involved in obtaining mates (pre-copulatory) and fertilization (post-copulatory). However, very little is known about the nutrient requirements for these traits and whether males compromise their diet to maximize one trait at the expense of another. This study used Nutritional Geometry to investigate macronutrient requirements for pre- and post-copulatory traits in Drosophila, when males were the first or second to mate with females. No significant effects of male diet on sperm competitiveness were found. However, although males self-regulate their macronutrient intake at a protein-to-carbohydrate ratio ("P:C ratio") of 1:1.5, this ratio does not coincide with their optima for several key reproductive traits: both the short-term (~24 hr) rate of offspring production after a female's first mating, as well as the total offspring number sired when males were second to mate are maximized at a P:C ratio of 1:9, whereas male attractiveness (latency to mate), are maximised at a P:C ratio of 1:1. These results suggest a compromised optimum diet, and no single diet that simultaneously maximizes all male reproductive traits. The protein intake of first males also negatively affected female offspring production following remating, suggesting a long-term intersexual effect of male nutrition. 

Eck, S., Helfrich-Förster, C. and Rieger, D. (2016). The timed depolarization of morning and evening oscillators phase shifts the circadian clock of Drosophila. J Biol Rhythms [Epub ahead of print]. PubMed ID: 27269519
Summary:
Phase response curves (PRCs) for light or temperature stimuli have been shown to be most valuable in understanding how circadian clocks are entrained to daily environmental cycles. Nowadays, PRC experiments in which clock neurons are manipulated in a temporally restricted manner by thermogenetic or optogenetic tools are also useful to comprehend clock network properties. In this study, specific clock neurons of Drosophila melanogaster were temporally depolarized by activating temperature-sensitive dTrpA1 channels to unravel their role in phase shifting the flies' activity rhythm. The depolarization of all clock neurons causes a PRC resembling the flies' light PRC, with strong phase delays in the first half of the subjective night and modest phase advances in its second half. However, the activation of the flies' pigment-dispersing factor (PDF)-positive morning (M) neurons (s-LNvs) only induces phase advances, and these reach into the subjective day, where the light PRC has its dead zone. This indicates that the M neurons are very potent in accelerating the clock, which is in line with previous observations. In contrast, the evening (E) neurons together with the PDF-positive l-LNvs appear to mediate phase delays. Most interestingly, the molecular clock (Period protein cycling) of the depolarized clock neurons is shifted in parallel to the behavior, and this shift is already visible within the first cycle after the temperature pulse. The cAMP response element binding protein B (CREB) was identified as a putative link between membrane depolarization and the molecular clock.

Gomez-Marin, A., Oron, E., Gakamsky, A., Valente, D. Benjamini, Y. and Golani, I. (2016). Generative rules of Drosophila locomotor behavior as a candidate homology across phyla. Sci Rep 6: 27555. PubMed ID: 27271799
Summary:
The discovery of shared behavioral processes across phyla is a significant step in the establishment of a comparative study of behavior. This study used immobility as an origin and reference for the measurement of fly locomotor behavior; speed, walking direction and trunk orientation as the degrees of freedom shaping this behavior; and cocaine as the parameter inducing progressive transitions in and out of immobility. Using these, the generative rules that shape Drosophila locomotor behavior, bringing about a gradual buildup of kinematic degrees of freedom during the transition from immobility to normal behavior, and the opposite narrowing down into immobility, were characterized. Transitions into immobility unfold via sequential enhancement and then elimination of translation, curvature and finally rotation. Transitions out of immobility unfold by progressive addition of these degrees of freedom in the opposite order. The same generative rules have been found in vertebrate locomotor behavior in several contexts (pharmacological manipulations, ontogeny, social interactions) involving transitions in-and-out of immobility. Recent claims for deep homology between arthropod central complex and vertebrate basal ganglia provide an opportunity to examine whether the rules reported in this study also share common descent. This approach prompts the discovery of behavioral homologies, contributing to the elusive problem of behavioral evolution. 

Thursday, June 16th

Aggarwal, P., Gera, J., Mandal, L. and Mandal, S. (2016). The morphogen Decapentaplegic employs a two-tier mechanism to activate target retinal determining genes during ectopic eye formation in Drosophila. Sci Rep 6: 27270. PubMed ID: 27270790
Summary:
Understanding the role of morphogen in activating its target genes, otherwise epigenetically repressed, during change in cell fate specification is a very fascinating yet relatively unexplored domain. The in vivo loss-of-function genetic analyses in this study reveal that specifically during ectopic eye formation, the morphogen Decapentaplegic (Dpp), in conjunction with the canonical signaling responsible for transcriptional activation of retinal determining (RD) genes, triggers another signaling cascade. Involving dTak1 and JNK, this pathway down-regulates the expression of polycomb group of genes to do away with their repressive role on RD genes. Upon genetic inactivation of members of this newly identified pathway, the canonical Dpp signaling fails to trigger RD gene expression beyond a threshold, critical for ectopic photoreceptor differentiation. Moreover, the drop in ectopic RD gene expression and subsequent reduction in ectopic photoreceptor differentiation resulting from inactivation of dTak1 can be rescued by down-regulating the expression of polycomb group of genes. These results unravel an otherwise unknown role of morphogen in coordinating simultaneous transcriptional activation and de-repression of target genes implicating its importance in cellular plasticity. 

Murmu, M. S. and Martin, J. R. (2016). Interaction between cAMP and intracellular Ca-signaling pathways during odor-perception and adaptation in Drosophila. Biochim Biophys Acta 1863: 2156-2174. PubMed ID: 27212269
Summary:
Binding of an odorant to olfactory receptors triggers cascades of second messenger systems in olfactory receptor neurons (ORNs). The transduction mechanism at ORNs is mediated by cAMP and/or inositol,1,4,5-triphosphate (InsP3)-signaling pathways in an odorant-dependent manner. This study used interfering-RNAi to disrupt the level of cAMP alone or in combination with the InsP3-signaling pathway cellular targets, InsP3 receptor (InsP3R) or ryanodine receptor (RyR) in ORNs, and quantify at ORN axon terminals in the antennal lobe, the odor-induced Ca2+-response. In-vivo functional bioluminescence Ca2+-imaging indicates that a single 5s application of an odor increased Ca2+-transients at ORN axon terminals. However, compared to wild-type controls, the magnitude and duration of ORN Ca2+-response was significantly diminished in cAMP-defective flies. In a behavioral assay, perception of odorants was defective in flies with a disrupted cAMP level suggesting that the ability of flies to correctly detect an odor depends on cAMP. Simultaneous disruption of cAMP level and InsP3R or RyR further diminished the magnitude and duration of ORN response to odorants and affected the flies' ability to detect an odor. In conclusion, this study provides functional evidence that cAMP and InsP3-signaling pathways act in synergy to mediate odor processing within the ORN axon terminals, which is encoded in the magnitude and duration of ORN response.

Li, T., Fan, J., Blanco-Sanchez, B., Giagtzoglou, N., Lin, G., Yamamoto, S., Jaiswal, M., Chen, K., Zhang, J., Wei, W., Lewis, M. T., Groves, A. K., Westerfield, M., Jia, J. and Bellen, H. J. (2016). Ubr3, a novel modulator of Hh signaling affects the degradation of Costal-2 and Kif7 through poly-ubiquitination. PLoS Genet 12: e1006054. PubMed ID: 27195754
Summary:
Hedgehog (Hh) signaling regulates multiple aspects of metazoan development and tissue homeostasis, and is constitutively active in numerous cancers. This study identified Ubr3, an E3 ubiquitin ligase, as a novel, positive regulator of Hh signaling in Drosophila and vertebrates. Hh signaling regulates the Ubr3-mediated poly-ubiquitination and degradation of Cos2, a central component of Hh signaling. In developing Drosophila eye discs, loss of ubr3 leads to a delayed differentiation of photoreceptors and a reduction in Hh signaling. In zebrafish, loss of Ubr3 causes a decrease in Shh signaling in the developing eyes, somites, and sensory neurons. However, not all tissues that require Hh signaling are affected in zebrafish. Mouse UBR3 poly-ubiquitinates Kif7, the mammalian homologue of Cos2. Finally, loss of UBR3 up-regulates Kif7 protein levels and decreases Hh signaling in cultured cells. In summary, this work identifies Ubr3 as a novel, evolutionarily conserved modulator of Hh signaling that boosts Hh in some tissues.
Norman, M., Vuilleumier, R., Springhorn, A., Gawlik, J. and Pyrowolakis, G. (2016). Pentagone internalises glypicans to fine-tune multiple signalling pathways. Elife [Epub ahead of print]. PubMed ID: 27269283
Summary:
Tight regulation of signalling activity is crucial for proper tissue patterning and growth. This study investigates the function of Pentagone (Pent), a secreted protein that acts in a regulatory feedback during establishment and maintenance of BMP/Dpp morphogen signalling during Drosophila wing development. It was shown that Pent internalises the Dpp co-receptors, the glypicans Dally and Dally-like protein (Dlp), and the study proposes that this internalisation is important in the establishment of a long range Dpp gradient. Pent-induced endocytosis and degradation of glypicans requires dynamin- and Rab5, but not clathrin or active BMP signalling. Thus, Pent modifies the ability of cells to trap and transduce BMP by fine-tuning the levels of the BMP reception system at the plasma membrane. In addition, and in accordance with the role of glypicans in multiple signalling pathways, a requirement of Pent was found to be required for Wg signalling. These data propose a novel mechanism by which morphogen signalling is regulated.

Wednesday, June 15th

Newell, N.R., New, F.N., Dalton, J.E., McIntyre, L.M. and Arbeitman, M.N. (2016). Neurons that underlie Drosophila melanogaster reproductive behaviors: detection of a large male-bias in gene expression in fruitless-expressing neurons. G3 (Bethesda) [Epub ahead of print]. PubMed ID: 27247289
Summary:
Male and female reproductive behaviors in Drosophila melanogaster are vastly different, but neurons that express sex-specifically spliced fruitless transcripts (fru P1) underlie these behaviors in both sexes. How this set of neurons can generate such different behaviors between the two sexes is an unresolved question. A particular challenge is that fru P1-expressing neurons comprise only 2-5% of the adult nervous system, and so studies of adult head tissue or whole brain may not reveal crucial differences. Translating Ribosome Affinity Purification (TRAP) identifies the actively translated pool of mRNAs from fru P1-expressing neurons allowing a sensitive, cell-type-specific assay. It was also found that TRAP mRNAs from fru P1-expressing neurons exhibit four times more male-biased than female-biased genes. This suggests a potential mechanism to generate dimorphism in behavior. The male-biased genes may direct male behaviors by establishing cell fate in a similar context of gene expression observed in females. These results suggest a possible global mechanism for how distinct behaviors can arise from a shared set of neurons.

Dweck, H. K., Ebrahim, S. A., Khallaf, M. A., Koenig, C., Farhan, A., Stieber, R., Weissflog, J., Svatos, A., Grosse-Wilde, E., Knaden, M. and Hansson, B. S. (2016). Olfactory channels associated with the maxillary palp mediate short- and long-range attraction. Elife 5. PubMed ID: 27213519
Summary:
The vinegar fly Drosophila melanogaster is equipped with two peripheral olfactory organs, antenna and maxillary palp. The antenna is involved in finding food, oviposition sites and mates. However, the functional significance of the maxillary palp remains unknown. This study screened the olfactory sensory neurons of the maxillary palp (MP-OSNs) using a large number of natural odor extracts to identify novel ligands for each MP-OSN type. Each type was found to be the sole or the primary detector for a specific compound, and detects these compounds with high sensitivity. Next the contribution of MP-OSNs to behaviors evoked by their key ligands was dissected and MP-OSNs were found to mediate short- and long-range attraction. Furthermore, the organization, detection and olfactory receptor (Or) genes of MP-OSNs are conserved in the agricultural pest D. suzukii. The novel short and long-range attractants could potentially be used in integrated pest management (IPM) programs of this pest species.

Roberts, L., Leise, T. L., Welsh, D. K. and Holmes, T. C. (2016). Functional contributions of strong and weak cellular oscillators to synchrony and light-shifted phase dynamics. J Biol Rhythms [Epub ahead of print]. PubMed ID: 27221103
Summary:
Light is the primary signal that calibrates circadian neural circuits and thus coordinates daily physiological and behavioral rhythms with solar entrainment cues. Drosophila and mammalian circadian circuits consist of diverse populations of cellular oscillators that exhibit a wide range of dynamic light responses, periods, phases, and degrees of synchrony. How heterogeneous circadian circuits can generate robust physiological rhythms while remaining flexible enough to respond to synchronizing stimuli has long remained enigmatic. Cryptochrome is a short-wavelength photoreceptor that is endogenously expressed in approximately half of Drosophila circadian neurons. This study applied analysis of real-time bioluminescence experimental data to show detailed dynamic ensemble representations of whole circadian circuit light entrainment at single neuron resolution. Organotypic whole-brain explants were either maintained in constant darkness (DD) for 6 days or exposed to a phase-advancing light pulse on the second day. Stronger circadian oscillators were found to support robust overall circuit rhythmicity in DD, whereas weaker oscillators can be pushed toward transient desynchrony and damped amplitude to facilitate a new state of phase-shifted network synchrony. Additionally, mathematical modeling was used to examine how a network composed of distinct oscillator types can give rise to complex dynamic signatures in DD conditions and in response to simulated light pulses. Simulations suggest that complementary coupling mechanisms and a combination of strong and weak oscillators may enable a robust yet flexible circadian network that promotes both synchrony and entrainment. A more complete understanding of how the properties of oscillators and their signaling mechanisms facilitate their distinct roles in light entrainment may allow direction and augmentation of the circadian system to speed recovery from jet lag, shift work, and seasonal affective disorder.

Rajpurohit, S. and Schmidt, P. S. (2016). Measuring thermal behavior in smaller insects: a case study in Drosophila melanogaster demonstrates effects of sex, geographic origin, and rearing temperature on adult behavior. Fly (Austin): [Epub ahead of print] PubMed ID: 27230726
Summary:
Measuring thermal behavior in smaller insects is particularly challenging. This study describes a new horizontal thermal gradient apparatus designed to study adult thermal behavior in small insects and applied it using Drosophila as a model and case study. Specifically, this apparatus and associated methodology were used to examine the effects of sex, geographic origin, and developmental rearing temperature on temperature preferences exhibited by adults in a controlled laboratory environment. The thermal gradient established by the apparatus was stable over diurnal and calendar time. Furthermore, the distribution of adult flies across thermal habitats within the apparatus remained stable following the period of acclimation, as evidenced by the high degree of repeatability across both biological and technical replicates. The data demonstrate significant and predictable variation in temperature preference for all three assayed variables. Behaviorally, females were more sensitive than males to higher temperatures. Flies originating from high latitude, temperate populations exhibited a greater preference for cooler temperatures; conversely, flies originating from low latitude, tropical habitats demonstrated a relative preference for higher temperatures. Similarly, larval rearing temperature was positively associated with adult thermal behavior: low culture temperatures increased the relative adult preference for cooler temperatures, and this response was distinct between the sexes and for flies from the temperate and subtropical geographic regions. Together, these results demonstrate that the temperature chamber apparatus elicits robust, predictable, and quantifiable thermal preference behavior that could readily be applied to other taxa to examine the role of temperature-mediated behavior in a variety of contexts.

Tuesday, June 14th

Pimenta-Marques, A., Bento, I., Lopes, C.A., Duarte, P., Jana, S.C. and Bettencourt-Dias, M. (2016). A mechanism for the elimination of the female gamete centrosome in Drosophila melanogaster. Science [Epub ahead of print]. PubMed ID: 27229142
Summary:
An important feature of fertilization is the asymmetric inheritance of centrioles. In most species it is the sperm that contributes the initial centriole, which builds the first centrosome that is essential for early development. However, given that centrioles are thought to be exceptionally stable structures, the mechanism behind centriole disappearance in the female germline remains elusive and paradoxical. Using fruit flies, this study elucidated a program for centriole maintenance. This program is led by Polo kinase and the pericentriolar matrix (PCM). The PCM is down-regulated in the female germline during oogenesis, which results in centriole loss. Perturbing this program prevents centriole loss, leads to abnormal meiotic and mitotic divisions, and thus to female sterility. This mechanism challenges the view that centrioles are intrinsically stable structures and reveals general functions for Polo kinase and the PCM in centriole maintenance. The study propose that regulation of this maintenance program is essential for successful sexual reproduction, and defines centriole life span in different tissues in homeostasis and disease, shaping the cytoskeleton.

Cummings, C. F., et al. (2016). Extracellular chloride signals collagen IV network assembly during basement membrane formation. J Cell Biol 213: 479-494. PubMed ID: 27216258
Summary:
Basement membranes are defining features of the cellular microenvironment; however, little is known regarding their assembly outside cells. This study reports that extracellular Cl(-) ions signal the assembly of collagen IV networks outside cells by triggering a conformational switch within collagen IV noncollagenous 1 (NC1) domains. Depletion of Cl(-) in cell culture perturbed collagen IV networks, disrupted matrix architecture, and repositioned basement membrane proteins. Phylogenetic evidence indicates this conformational switch is a fundamental mechanism of collagen IV network assembly throughout Metazoa. Using recombinant triple helical protomers, this study proves that NC1 domains direct both protomer and network assembly and shows in Drosophila that NC1 architecture is critical for incorporation into basement membranes. These discoveries provide an atomic-level understanding of the dynamic interactions between extracellular Cl(-) and collagen IV assembly outside cells, a critical step in the assembly and organization of basement membranes that enable tissue architecture and function. Moreover, this provides a mechanistic framework for understanding the molecular pathobiology of NC1 domains.

Tetley, R. J., Blanchard, G. B., Fletcher, A. G., Adams, R. J. and Sanson, B. (2016). Unipolar distributions of junctional Myosin II identify cell stripe boundaries that drive cell intercalation throughout axis extension. Elife 5 [Epub ahead of print]. PubMed ID: 27183005
Summary:
Convergence and extension movements elongate tissues during development. Drosophila germ-band extension (GBE) is one example, which requires active cell rearrangements driven by Myosin II planar polarisation. A combinatorial code of Toll receptors downstream of pair-rule genes contributes to this polarization via local cell-cell interactions. Novel computational methods have been developed to analyse the spatiotemporal dynamics of Myosin II. Initial Myosin II bipolar cell polarization gives way to unipolar enrichment at parasegmental boundaries and two further boundaries within each parasegment, concomitant with a doubling of cell number as the tissue elongates. These boundaries are the primary sites of cell intercalation, behaving as mechanical barriers and providing a mechanism for how cells remain ordered during GBE. Enrichment at parasegment boundaries during GBE is independent of Wingless signaling, suggesting pair-rule gene control. An updated cell-cell interaction model is proposed for Myosin II polarization that was tested in a vertex-based simulation.

Khanal, I., Elbediwy, A., Diaz de la Loza, M.D., Fletcher, G.C. and Thompson, B.J. (2016). Shot and Patronin polarise microtubules to direct membrane traffic and biogenesis of microvilli in epithelia. J Cell Sci [Epub ahead of print]. PubMed ID: 27231092
Summary:
In epithelial tissues, polarisation of microtubules and actin microvilli occurs along the apical-basal axis of each cell, yet how these cytoskeletal polarisation events are coordinated remains unclear. This study examines the hierarchy of events during cytoskeletal polarisation in Drosophila and human epithelia. Core apical-basal polarity determinants polarise the Spectrin cytoskeleton to recruit the microtubule-binding proteins Patronin (CAMSAP1/2/3 in humans) and Shortstop (Shot; MACF1/BPAG1 in humans) to the apical membrane domain. Patronin and Shot then act to polarise microtubules along the apical-basal axis to enable apical transport of Rab11 endosomes by the Nuf-Dynein microtubule motor complex. Finally, Rab11 endosomes are transferred to the MyoV actin motor to deliver the key microvillar determinant Cadherin99C to the apical membrane to organise the biogenesis of actin microvilli.

Monday, June 13th

Harris, K.P., Zhang, Y.V., Piccioli, Z.D., Perrimon, N. and Littleton, J.T. (2016). The postsynaptic t-SNARE Syntaxin 4 controls traffic of Neuroligin 1 and Synaptotagmin 4 to regulate retrograde signaling. Elife 5. PubMed ID: 27223326
Summary:
Postsynaptic cells can induce synaptic plasticity through the release of activity-dependent retrograde signals. A Ca(2+)-dependent retrograde signaling pathway mediated by postsynaptic Synaptotagmin 4 (Syt4) has been previously described in this context. To identify proteins involved in postsynaptic exocytosis, this study conducted a screen for candidates that disrupt trafficking of a pHluorin-tagged Syt4 at Drosophila neuromuscular junctions (NMJs). The study further characterized one candidate, the postsynaptic t-SNARE Syntaxin 4 (Syx4). Analysis of Syx4 mutants reveals that Syx4 mediates retrograde signaling, modulating the membrane levels of Syt4 and the transsynaptic adhesion protein Neuroligin 1 (Nlg1). Syx4-dependent trafficking regulates synaptic development, including controlling synaptic bouton number and the ability to bud new varicosities in response to acute neuronal stimulation. Genetic interaction experiments demonstrate Syx4, Syt4, and Nlg1 regulate synaptic growth and plasticity through both shared and parallel signaling pathways. These findings suggest a conserved postsynaptic SNARE machinery controls multiple aspects of retrograde signaling and cargo trafficking within the postsynaptic compartment.

Li, W. et al. (2016). Angelman syndrome protein Ube3a regulates synaptic growth and endocytosis by inhibiting BMP signaling in Drosophila. PLoS Genet 12: e1006062. PubMed ID: 27232889
Summary:
Altered expression of the E3 ubiquitin ligase UBE3A, which is involved in protein degradation through the proteasome-mediated pathway, is associated with neurodevelopmental and behavioral defects observed in Angelman syndrome (AS) and autism. However, little is known about the neuronal function of UBE3A and the pathogenesis of UBE3A-associated disorders. This study generated multiple mutations of ube3a, the Drosophila ortholog of UBE3A. A significantly increased number of total boutons and satellite boutons in conjunction with compromised endocytosis were found in the neuromuscular junctions (NMJs) of ube3a mutants compared to the wild type. Genetic and biochemical analysis showed upregulation of bone morphogenetic protein (BMP) signaling in the nervous system of ube3a mutants. An immunochemical study revealed a specific increase in the protein level of Thickveins (Tkv), a type I BMP receptor, but not other BMP receptors Wishful thinking (Wit) and Saxophone (Sax), in ube3a mutants. Ube3a is associated with and specifically ubiquitinated lysine 227 within the cytoplasmic tail of Tkv, and promotes its proteasomal degradation in Schneider 2 cells. Negative regulation of Tkv by Ube3a is conserved in mammalian cells. These results reveal a critical role for Ube3a in regulating NMJ synapse development by repressing BMP signaling. This study sheds new light onto the neuronal functions of UBE3A and provides novel perspectives for understanding the pathogenesis of UBE3A-associated disorders.

Harris, K.P., Akbergenova, Y., Cho, R.W., Baas-Thomas, M.S. and Littleton, J.T. (2016). Shank modulates postsynaptic wnt signaling to regulate synaptic development. J Neurosci.  36: 5820-5832. PubMed ID: 27225771
Summary:
Prosap/Shank scaffolding proteins regulate the formation, organization, and plasticity of excitatory synapses. Mutations in SHANK family genes are implicated in autism spectrum disorder and other neuropsychiatric conditions. However, the molecular mechanisms underlying Shank function are not fully understood, and no study to date has examined the consequences of complete loss of all Shank proteins in vivo. This study characterized the single Drosophila Prosap/Shank family homolog. Shank is enriched at the postsynaptic membrane of glutamatergic neuromuscular junctions and controls multiple parameters of synapse biology in a dose-dependent manner. Both loss and overexpression of Shank result in defects in synaptic bouton number and maturation. It was found that Shank regulates a noncanonical Wnt signaling pathway in the postsynaptic cell by modulating the internalization of the Wnt receptor Fz2. This study identifies Shank as a key component of synaptic Wnt signaling, defining a novel mechanism for how Shank contributes to synapse maturation during neuronal development.

Imai, Y., et al., (2015) The Parkinson's disease-associated protein linase LRRK2 modulates Notch signaling through the endosomal pathway. PLoS Genet 11: e1005503. PubMed ID: 26355680
Summary:
Leucine-rich repeat kinase 2 (LRRK2) is a key molecule in the pathogenesis of familial and idiopathic Parkinson's disease (PD). This study identified two novel LRRK2-associated proteins, a HECT-type ubiquitin ligase, HERC2, and an adaptor-like protein with six repeated Neuralized domains, NEURL4. LRRK2 binds to NEURL4 and HERC2 via the LRRK2 Ras of complex proteins (ROC) domain and NEURL4, respectively. HERC2 and NEURL4 link LRRK2 to the cellular vesicle transport pathway and Notch signaling, through which the LRRK2 complex promotes the recycling of the Notch ligand Delta-like 1 (Dll1)/Delta (Dl) through the modulation of endosomal trafficking. This process negatively regulates Notch signaling through cis-inhibition by stabilizing Dll1/Dl, which accelerates neural stem cell differentiation and modulates the function and survival of differentiated dopaminergic neurons. These effects are strengthened by the R1441G ROC domain-mutant of LRRK2. These findings suggest that the alteration of Notch signaling in mature neurons is a component of PD etiology linked to LRRK2.

Sunday, June 12th

Nozawa, M., Fujimi, M., Iwamoto, C., Onizuka, K., Fukuda, N., Ikeo, K. and Gojobori, T. (2016). Evolutionary transitions of microRNA-target pairs. Genome Biol Evol [Epub ahead of print]. PubMed ID: 27189995
Summary:
How newly-generated microRNA (miRNA) genes are integrated into gene regulatory networks during evolution is fundamental in understanding the molecular and evolutionary bases of robustness and plasticity in gene regulation. A recent model proposed that after the birth of a miRNA, the miRNA is generally integrated into the network by decreasing the number of target genes during evolution. However, this decreasing model remains to be carefully examined by considering in vivo conditions. This study compared the number of target genes among miRNAs with different ages, combining experiments with bioinformatics predictions. First, a focused was placed on three Drosophila miRNAs with different ages. As a result, an older miRNA was found to have a greater number of target genes than a younger miRNA, suggesting the increasing number of targets for each miRNA during evolution (increasing model). To further confirm these results, all target genes were predicted for all miRNAs in D. melanogaster, considering co-expression of miRNAs and mRNAs in vivo. The results obtained also do not support the decreasing model but are reasonably consistent with the increasing model of miRNA-target pairs. Furthermore, the large-scale analyses of currently available experimental data of miRNA-target pairs also showed a weak but the same trend in humans. These results indicate that the current decreasing model of miRNA-target pairs should be reconsidered and the increasing model may be more appropriate to explain the evolutionary transitions of miRNA-target pairs in many organisms.

Rius, N., Guillen, Y., Delprat, A., Kapusta, A., Feschotte, C. and Ruiz, A. (2016). Exploration of the Drosophila buzzatii transposable element content suggests underestimation of repeats in Drosophila genomes. BMC Genomics 17: 344. PubMed ID: 27164953
Summary:
This study compares the TE content of three genomes: D. buzzatii st-1, j-19, and D. mojavensis. A new D. buzzatii genome (j-19) was sequenced that complements the D. buzzatii reference genome (st-1) already published, and their TE contents were compared with that of D. mojavensis. An underestimation of TE sequences was found in Drosophila genus NGS-genomes when compared to Sanger-genomes. To be able to compare genomes sequenced with different technologies, a coverage-based method was developed and applied to the D. buzzatii st-1 and j-19 genome. Between 10.85 and 11.16 % of the D. buzzatii st-1 genome is made up of TEs, between 7 and 7.5 % of D. buzzatii j-19 genome, while TEs represent 15.35 % of the D. mojavensis genome. Helitrons, rolling-circle transposable elements which are hypothesized to transpose by a rolling circle replication mechanism via a single-stranded DNA intermediate, are the most abundant order in the three genomes. It is concluded that TEs in D. buzzatii are less abundant than in D. mojavensis, as expected according to the genome size and TE content positive correlation. However, TEs alone do not explain the genome size difference. TEs accumulate in the dot chromosomes and proximal regions of D. buzzatii and D. mojavensis chromosomes. A significantly higher TE density is reported in D. buzzatii and D. mojavensis X chromosomes, which is not expected under the current models. This easy-to-use correction method allowed identification of recently active families in D. buzzatii st-1 belonging to the LTR-retrotransposon superfamily Gypsy.

Kang, L., Settlage, R., McMahon, W., Michalak, K., Tae, H., Garner, H. R., Stacy, E., Price, D. K. and Michalak, P. (2016). Genomic signatures of speciation in sympatric and allopatric Hawaiian picture-winged Drosophila. Genome Biol Evol [Epub ahead of print]. PubMed ID: 27189993
Summary:
The Hawaiian archipelago provides a natural arena for understanding adaptive radiation and speciation. The Hawaiian Drosophila are one of the most diverse endemic groups in Hawai'i with up to 1000 species. This study sequenced and analyzed entire genomes of recently diverged species of Hawaiian picture-winged Drosophila, Drosophila silvestris and D. heteroneura from Hawai'i Island, in comparison with D. planitibia, their sister species from Maui, a neighboring island where a common ancestor of all three had likely occurred. Genome-wide SNP patterns suggest the more recent origin of D. silvestris and D. heteroneura, as well as a pervasive influence of positive selection on divergence of the three species, with the signatures of positive selection more prominent in sympatry than allopatry. Positively selected genes were significantly enriched for functional terms related to sensory detection and mating, suggesting that sexual selection played an important role in speciation of these species. In particular, sequence variation in Olfactory receptor and Gustatory receptor genes seems to play a major role in adaptive radiation in Hawaiian pictured-winged Drosophila (Kang, 2016).

Cardoso-Moreira, M., Arguello, J. R., Gottipati, S., Harshman, L. G., Grenier, J. K. and Clark, A. G. (2016). Evidence for the fixation of gene duplications by positive selection in Drosophila. Genome Res 26: 787-798. PubMed ID: 27197209
Summary:
Gene duplications play a key role in the emergence of novel traits and in adaptation. But despite their centrality to evolutionary processes, it is still largely unknown how new gene duplicates are initially fixed within populations and later maintained in genomes. Long-standing debates on the evolution of gene duplications could be settled by determining the relative importance of genetic drift vs. positive selection in the fixation of new gene duplicates. Using the Drosophila Global Diversity Lines (GDL), genome-wide SNP polymorphism data was combined with a novel set of copy number variant calls and gene expression profiles to characterize the polymorphic phase of new genes. Approximately half of the roughly 500 new complete gene duplications were found segregating in the GDL lead to significant increases in the expression levels of the duplicated genes and that these duplications are more likely to be found at lower frequencies, suggesting a negative impact on fitness. However, six of the nine gene duplications that are fixed or close to fixation in at least one of the five populations in this study show signs of being under positive selection, and these duplications are likely beneficial because of dosage effects, with a possible role for additional mutations in two duplications. This work suggests that in Drosophila, theoretical models that posit that gene duplications are immediately beneficial and fixed by positive selection are most relevant to explain the long-term evolution of gene duplications in this species.

Saturday, June 11th

Li, J., et al. (2016). An obligatory role for neurotensin in high-fat-diet-induced obesity. Nature 533: 411-415. PubMed ID: 27193687
Summary:
Obesity and its associated comorbidities (for example, diabetes mellitus and hepatic steatosis) contribute to approximately 2.5 million deaths annually and are among the most prevalent and challenging conditions confronting the medical profession. Neurotensin (NT; also known as NTS), a 13-amino-acid peptide predominantly localized in specialized enteroendocrine cells of the small intestine and released by fat ingestion, facilitates fatty acid translocation in rat intestine, and stimulates the growth of various cancers. The effects of NT are mediated through three known NT receptors (NTR1, 2 and 3; also known as NTSR1, 2, and NTSR3, respectively). Increased fasting plasma levels of pro-NT (a stable NT precursor fragment produced in equimolar amounts relative to NT) are associated with increased risk of diabetes, cardiovascular disease and mortality; however, a role for NT as a causative factor in these diseases is unknown. This study shows that NT-deficient mice demonstrate significantly reduced intestinal fat absorption and are protected from obesity, hepatic steatosis and insulin resistance associated with high fat consumption. It was further demonstrated that NT attenuates the activation of AMP-activated protein kinase (AMPK) and stimulates fatty acid absorption in mice and in cultured intestinal cells, and that this occurs through a mechanism involving NTR1 and NTR3 (also known as sortilin). Consistent with the findings in mice, expression of NT in Drosophila midgut enteroendocrine cells results in increased lipid accumulation in the midgut, fat body, and oenocytes (specialized hepatocyte-like cells) and decreased AMPK activation. Remarkably, in humans, it was shown that both obese and insulin-resistant subjects have elevated plasma concentrations of pro-NT, and in longitudinal studies among non-obese subjects, high levels of pro-NT denote a doubling of the risk of developing obesity later in life. These findings directly link NT with increased fat absorption and obesity and suggest that NT may provide a prognostic marker of future obesity and a potential target for prevention and treatment.

M'Angale, P. G. and Staveley, B. E. (2016). The Bcl-2 homologue Buffy rescues alpha-synuclein-induced Parkinson disease-like phenotypes in Drosophila. BMC Neurosci 17: 24. PubMed ID: 27192974
Summary:
Only two Bcl-2 family genes have been found in Drosophila melanogaster including the pro-cell survival, human Bok-related orthologue, Buffy. The directed expression of alpha-synuclein, a gene contributing to inherited forms of Parkinson disease (PD), in the dopaminergic neurons (DA) of flies provides a robust model of PD complete with the loss of neurons and accompanying motor defects. This study altered the expression of Buffy in the dopamine producing neurons and in the developing neuron-rich eye, with and without the expression of alpha-synuclein. To alter the expression of Buffy in the dopaminergic neurons of Drosophila. The directed expression of Buffy in the dopamine producing neurons, via aDdc-Gal4 transgene, resulted in flies with increased climbing ability and enhanced survival, while the inhibition of Buffy in the dopaminergic neurons reduced climbing ability over time prematurely, similar to the phenotype observed in the alpha-synuclein-induced Drosophila model of PD. Subsequently, the expression of Buffy was altered in the alpha-synuclein-induced Drosophila model of PD. Analysis revealed that Buffy acted to rescue the associated loss of locomotor ability observed in the alpha-synuclein-induced model of PD, while Buffy RNA interference resulted in an enhanced alpha-synuclein-induced loss of climbing ability. In complementary experiments the overexpression of Buffy in the developing eye suppressed the mild rough eye phenotype that results from Gal4 expression and from alpha-synuclein expression. When Buffy is inhibited the roughened eye phenotype is enhanced. It is concluded that the inhibition of Buffy in DA neurons produces a novel model of PD in Drosophila. The directed expression of Buffy in DA neurons provides protection and counteracts the alpha-synuclein-induced Parkinson disease-like phenotypes. Taken all together this demonstrates a role for Buffy, a Bcl-2 pro-cell survival gene, in neuroprotection.

Luu, L.M., Nguyen, L., Peng, S., Lee, J., Lee, H.Y., Wong, C.H., Hergenrother, P.J., Chan, H.Y. and Zimmerman, S.C. (2016). A potent inhibitor of protein sequestration by expanded triplet (CUG) repeats that shows phenotypic improvements in a Drosophila model of myotonic dystrophy. ChemMedChem [Epub ahead of print]. PubMed ID: 27245480
Summary:
Myotonic dystrophy is the most common form of adult-onset muscular dystrophy, originating in a CTG repeat expansion in the DMPK gene. The expanded CUG transcript sequesters MBNL1, a key regulator of alternative splicing, leading to the misregulation of numerous pre-mRNAs. This study reports an RNA-targeted agent as a possible lead compound for the treatment of myotonic dystrophy type 1 (DM1) that reveals both the promise and challenges for this type of small-molecule approach. The agent is a potent inhibitor of the MBNL1-rCUG complex with an inhibition constant (Ki ) of 25±8 nm, and is also relatively nontoxic to HeLa cells, able to dissolve nuclear foci, and correct the insulin receptor splicing defect in DM1 model cells. Moreover, treatment with this compound improves two separate disease phenotypes in a Drosophila model of DM1: adult external eye degeneration and larval crawling defect. However, the compound has a relatively low maximum tolerated dose in mice, and its cell uptake may be limited, providing insight into directions for future development.

Fowler, P. C. and O'Sullivan, N. C. (2016). ER-shaping proteins are required for ER and mitochondrial network organisation in motor neurons. Hum Mol Genet [Epub ahead of print]. PubMed ID: 27170313
Summary:
Hereditary spastic paraplegias (HSPs) are a group of neurodegenerative disorders characterised by degeneration of the longest motor neurons in the corticospinal tract, leading to muscle weakness and spasticity of the lower limbs. Pathogenic variants in genes encoding proteins that shape the endoplasmic-reticulum (ER) network are a leading cause of HSP, however, the mechanisms by which loss of ER-shaping proteins underpin degeneration of selective neurons in HSP remain poorly understood. To begin to address this, a novel in vivo model of HSP in Drosophila melanogaster was generated by targeted knockdown of the ER-shaping protein Arl6IP1. Variants in the human homolog of this gene have recently been linked to HSP subtype SPG61. Arl6IP1 RNAi flies display progressive locomotor deficits without a marked reduction in lifespan, recapitulating key features of HSP in human patients. Loss of Arl6IP1 leads to fragmentation of the smooth ER and disrupted mitochondrial network organisation within the distal ends of long motor neurons. Furthermore, genetically increasing mitochondrial fission, by overexpression of Dynamin related protein 1 (Drp1), restores mitochondrial network organisation and rescues locomotor deficits in two independent Drosophila models of HSP. Taken together, these results propose a role for ER-shaping proteins in mitochondrial network organisation in vivo and suggest that impaired mitochondrial organisation may be a common mechanism underpinning some forms of HSP.

Friday, June 10th

Men, T.T., Thanh, D.N., Yamaguchi, M., Suzuki, T., Hattori, G., Arii, M., Huy, N.T. and Kamei, K. (2016). A Drosophila model for screening antiobesity agents. Biomed Res Int 2016: 6293163. PubMed ID: 27247940
Summary:
Although triacylglycerol, the major component for lipid storage, is essential for normal physiology, its excessive accumulation causes obesity in adipose tissue and is associated with organ dysfunction in nonadipose tissue. This study focused on the Drosophila model to develop therapeutics for preventing obesity. The brummer (bmm) gene in Drosophila melanogaster is known to be homologous with human adipocyte triglyceride lipase, which is related to the regulation of lipid storage. A Drosophila model was established for monitoring bmm expression by introducing the green fluorescent protein (GFP) gene as a downstream reporter of the bmm promoter. The third-instar larvae of these Drosophila show the GFP signal in all tissues observed and specifically in the salivary gland nucleus. To confirm the relationship between bmm expression and obesity, the effect of oral administration of glucose diets on bmm promoter activity was analyzed. Drosophila flies given high-glucose diets show higher lipid contents, indicating the obesity phenotype; this was suggested by a weaker intensity of the GFP signal as well as reduced bmm mRNA expression. These results demonstrate that the transgenic Drosophila model established in this study is useful for screening antiobesity agents. The study also reports the effects of oral administration of histone deacetylase inhibitors and some vegetables on the bmm promoter activity.

Reis, M., Silva, A. C., Vieira, C. P. and Vieira, J. (2016). The Drosophila melanogaster Muc68E Mucin gene influences adult size, starvation tolerance, and cold recovery. G3 (Bethesda) [Epub ahead of print]. PubMed ID: 27172221
Summary:
Mucins have been implicated in many different biological processes such as protection from mechanical damage, microorganisms and toxic molecules, as well as providing a luminal scaffold during development. This study shows that the Drosophila Muc68E gene is 40-60 million years old, and is present in Drosophila species of the subgenus Sophophora only. The central repeat region of this gene is fast evolving and shows evidence for repeated expansions/contractions. This and/or frequent gene conversion events lead to the homogenization of its repeats. The repeat region can occur multiple times within a single conserved repeat block and thus may have functional significance. Muc68E is a non-essential gene under laboratory conditions, but Muc68E mutant flies are smaller and lighter than controls at birth. However, at four days of age, Muc68E mutants are heavier, recover faster from chill-coma and are more resistant to starvation than control flies, although they have the same percentage of lipids as controls. Mutant flies have enlarged abdominal size one day after chill-coma recovery, which is associated with higher lipid content. These results suggest that Muc68E has a role in metabolism modulation, food absorption and/or feeding patterns in larvae and adults, and under normal and stress conditions. Such biological function is novel for mucin genes.

Overend, G., Luo, Y., Henderson, L., Douglas, A.E., Davies, S.A. and Dow, J.A. (2016). Molecular mechanism and functional significance of acid generation in the Drosophila midgut. Sci Rep 6: 27242. PubMed ID: 27250760
Summary:
The gut of Drosophila melanogaster includes a proximal acidic region (~pH 2), however the genome lacks the H+/K+ ATPase characteristic of the mammalian gastric parietal cell, and the molecular mechanisms of acid generation are poorly understood. This study shows that maintenance of the low pH of the acidic region is dependent on H+ V-ATPase, together with carbonic anhydrase and five further transporters or channels that mediate K+, Cl- and HCO3- transport. Abrogation of the low pH does not influence larval survival under standard laboratory conditions, but is deleterious for insects subjected to high Na+ or K+ load. Insects with elevated pH in the acidic region display increased susceptibility to Pseudomonas pathogens and increased abundance of key members of the gut microbiota (Acetobacter and Lactobacillus), suggesting that the acidic region has bacteriostatic or bacteriocidal activity. Conversely, the pH of the acidic region is significantly reduced in germ-free Drosophila, indicative of a role of the gut bacteria in shaping the pH conditions of the gut. These results demonstrate that the acidic gut region protects the insect and gut microbiome from pathological disruption, and shed light on the mechanisms by which low pH can be maintained in the absence of H+, K+ ATPase. 

Scopelliti, A., Bauer, C., Cordero, J. B. and Vidal, M. (2016). Bursicon-α subunit modulates dLGR2 activity in the adult Drosophila melanogaster midgut independently to Bursicon-β. Cell Cycle: 1-7. PubMed ID: 27191973
Summary:
Bursicon is the main regulator of post molting and post eclosion processes during arthropod development. The active Bursicon hormone is a heterodimer of Burs-α and Burs-β. However, adult the midgut expresses Burs-α to regulate the intestinal stem cell niche. This study examined the potential expression and function of its heterodimeric partner, Burs-β in the adult midgut. Unexpectedly, evidence suggests that Burs-β is not significantly expressed in the adult midgut. burs-β mutants display the characteristic developmental defects but show wild type-like adult midgut, thus uncoupling the developmental and adult phenotypes seen in burs-α mutants. Gain of function data and ex vivo experiments using a cAMP biosensor, demonstrated that Burs-α is sufficient to drive stem cell quiescence and to activate Rickets/dLGR2 in the adult midgut. The evidence suggests that the post developmental transactivation of dLGR2 in the adult midgut is mediated by Burs-α and that the β subunit of Bursicon is dispensable for these activities.

Thursday, June 9th

Morimoto, J., Pizzari, T. and Wigby, S. (2016). Developmental environment effects on sexual selection in male and female Drosophila melanogaster. PLoS One 11: e0154468. PubMed ID: 27167120
Summary:
The developmental environment can potentially alter the adult social environment and influence traits targeted by sexual selection such as body size. This study manipulated larval density in male and female Drosophila resulting in distinct adult size phenotypes-high (low) densities for small (large) adults-and measured sexual selection in experimental groups consisting of adult males and females from high, low, or a mixture of low and high larval densities. Overall, large adult females (those reared at low larval density) had more matings, more mates and produced more offspring than small females (those reared at high larval density). The number of offspring produced by females was positively associated with their number of mates (i.e. there was a positive female Bateman gradient) in social groups where female size was experimentally varied, likely due to the covariance between female productivity and mating rate. For males, evidence was found that the larval environment affected the relative importance of sexual selection via mate number (Bateman gradients), mate productivity, paternity share, and their covariances. Mate number and mate productivity were significantly reduced for small males in social environments where males were of mixed sizes, versus social environments where all males were small, suggesting that social heterogeneity altered selection on this subset of males. Males are commonly assumed to benefit from mating with large females, but in contrast to expectations it was found that in groups where both the male and female size varied, males did not gain more offspring per mating with large females. Collectively, these results indicate sex-specific effects of the developmental environment on the operation of sexual selection, via both the phenotype of individuals, and the phenotype of their competitors and mates.

Rezaei, A., Krishna, M. S. and Santhosh, H. T. (2015). Male age affects female mate preference, quantity of accessory gland proteins, and sperm traits and female fitness in D. melanogaster. Zoolog Sci 32: 16-24. PubMed ID: 25660692
Summary:
For species in which mating is resource-independent and offspring do not receive parental care, theoretical models of age-based female mate preference predict that females should prefer to mate with older males as they have demonstrated ability to survive. Thus, females should obtain a fitness benefit from mating with older males. However, male aging is often associated with reductions in quantity of sperm. The adaptive significance of age-based mate choice is therefore unclear. Various hypotheses have made conflicting predictions concerning this issue, because published studies have not investigated the effect of age on accessory gland proteins and sperm traits. D. melanogaster exhibits resource-independent mating, and offspring do not receive parental care, making this an appropriate model for studying age-based mate choice. The present study found that D. melanogaster females of all ages preferred to mate with the younger of two competing males. Young males performed significantly greater courtship attempts and females showed least rejection for the same than middle-aged and old males. Young males had small accessory glands that contained very few main cells that were larger than average. Nevertheless, compared with middle-aged or old males, the young males transferred greater quantities of accessory gland proteins and sperm to mated females. As a result, females that mated with young male produced more eggs and progeny than those that mated with older males. Furthermore, mating with young male reduced female's lifespan. These studies indicate that quantity of accessory gland proteins and sperm traits decreased with male age and females obtain direct fitness benefit from mating with preferred young males.

Wu, C. L., Fu, T. F., Chiang, M. H., Chang, Y. W., Her, J. L. and Wu, T. (2016).. Magnetoreception regulates male courtship activity in Drosophila. PLoS One 11: e0155942. PubMed ID: 27195955
Summary:
The possible neurological and biophysical effects of magnetic fields on animals is an area of active study. This study reports that courtship activity of male Drosophila increases in a magnetic field and that this effect is regulated by the blue light-dependent photoreceptor Cryptochrome (CRY). Naive male flies exhibited significantly increased courtship activities when they were exposed to a >/= 20-Gauss static magnetic field, compared with their behavior in the natural environment (0 Gauss). CRY-deficient flies, cryb and crym, did not show an increased courtship index in a magnetic field. RNAi-mediated knockdown of cry in cry-GAL4-positive neurons disrupted the increased male courtship activity in a magnetic field. Genetically expressing cry under the control of cry-GAL4 in the CRY-deficient flies restored the increase in male courtship index that occurred in a magnetic field. Interestingly, artificially activating cry-GAL4-expressing neurons, which include large ventral lateral neurons and small ventral lateral neurons, via expression of thermosensitive cation channel dTrpA1, also increased the male courtship index. This enhancement was abolished by the addition of the cry-GAL80 transgene. These results highlight the phenomenon of increased male courtship activity caused by a magnetic field through CRY-dependent magnetic sensation in CRY expression neurons in Drosophila.

Ojelade, S. A., Acevedo, S. F., Kalahasti, G., Rodan, A. R. and Rothenfluh, A. (2015). RhoGAP18B isoforms act on distinct Rho-Family GTPases and regulate behavioral responses to alcohol via cofilin. PLoS One 10: e0137465. PubMed ID: 26366560
Summary:
Responses to the effects of ethanol are highly conserved across organisms, with reduced responses to the sedating effects of ethanol being predictive of increased risk for human alcohol dependence. Regulators of actin dynamics, such as the Rho-family GTPases Rac1, Rho1, and Cdc42, alter Drosophila's sensitivity to ethanol-induced sedation. The GTPase activating protein RhoGAP18B also affects sensitivity to ethanol. To better understand how different RhoGAP18B isoforms affect ethanol sedation, they were examined for their effects on cell shape, GTP-loading of Rho-family GTPase, activation of the actin-severing cofilin, and actin filamentation. The results suggest that the RhoGAP18B-PA isoform acts on Cdc42, while PC and PD act via Rac1 and Rho1 to activate cofilin. In vivo, a loss-of-function mutation in the cofilin-encoding gene twinstar leads to reduced ethanol-sensitivity and acts in concert with RhoGAP18B. Different RhoGAP18B isoforms, therefore, act on distinct subsets of Rho-family GTPases to modulate cofilin activity, actin dynamics, and ethanol-induced behaviors.

Koganezawa, M., Kimura, K. I. and Yamamoto, D. (2016). The neural circuitry that functions as a switch for courtship versus aggression in Drosophila males. Curr Biol [Epub ahead of print]. PubMed ID: 27185554
Summary:
Courtship and aggression are induced in a mutually exclusive manner in male Drosophila melanogaster, which quickly chooses one of these behavioral repertoires to run depending on whether the encountered conspecific is a female or male, yet the neural mechanism underlying this decision making remains obscure. By targeted excitation and synaptic blockage in a subset of brain neurons, this study demonstrates that the fruitless (fru)-negative subfraction (approximately 20 cells) of a doublesex-positive neural cluster, pC1, acts as the aggression-triggering center whereas the fru-positive subfraction (approximately 20 cells) of pC1 acts as the courtship-triggering center, and that the mutually exclusive activation of these two centers is attained by a double-layered inhibitory switch composed of two fru single-positive clusters, LC1 and mAL. This is the first report to unravel the cellular identity of the neural switch that governs the alternative activation of aggression and courtship in the animal kingdom.

Bae, J. E., Bang, S., Min, S., Lee, S. H., Kwon, S. H., Lee, Y., Lee, Y. H., Chung, J. and Chae, K. S. (2016). Positive geotactic behaviors induced by geomagnetic field in Drosophila. Mol Brain 9: 55. PubMed ID: 27192976
Summary:
Appropriate vertical movement is critical for the survival of flying animals. Although negative geotaxis (moving away from Earth) driven by gravity has been extensively studied, much less is understood concerning a static regulatory mechanism for inducing positive geotaxis (moving toward Earth). Using Drosophila melanogaster as a model organism, this study showed that geomagnetic field (GMF) induces positive geotaxis and antagonizes negative gravitaxis. Remarkably, GMF acts as a sensory cue for an appetite-driven associative learning behavior through the GMF-induced positive geotaxis. This GMF-induced positive geotaxis requires the three geotaxis genes, such as cry, the cation channel pyx and pdf, and the corresponding neurons residing in Johnston's organ of the fly's antennae. These findings provide a novel concept with the neurogenetic basis on the regulation of vertical movement by GMF in the flying animals.

Wednesday, June 8th

Engel, G. L., Marella, S., Kaun, K. R., Wu, J., Adhikari, P., Kong, E. C. and Wolf, F. W. (2016). Sir2/Sirt1 links acute inebriation to presynaptic changes and the development of alcohol tolerance, preference, and reward. J Neurosci 36: 5241-5251. PubMed ID: 27170122
Summary:
Acute ethanol inebriation causes neuroadaptive changes in behavior that favor increased intake. Ethanol-induced alterations in gene expression, through epigenetic and other means, are likely to change cellular and neural circuit function. Ethanol markedly changes histone acetylation, and the sirtuin Sir2/SIRT1 that deacetylates histones and transcription factors is essential for the rewarding effects of long-term drug use. This study found that Sir2 in the mushroom bodies of the fruit fly Drosophila promotes short-term ethanol-induced behavioral plasticity by allowing changes in the expression of presynaptic molecules. Acute inebriation strongly reduces Sir2 levels and increases histone H3 acetylation in the brain. Flies lacking Sir2 globally, in the adult nervous system, or specifically in the mushroom body α/β-lobes show reduced ethanol sensitivity and tolerance. Sir2-dependent ethanol reward is also localized to the mushroom bodies, and Sir2 mutants prefer ethanol even without a priming ethanol pre-exposure. Transcriptomic analysis reveals that specific presynaptic molecules, including the synaptic vesicle pool regulator Synapsin, depend on Sir2 to be regulated by ethanol. Synapsin is required for ethanol sensitivity and tolerance. It is proposed that the regulation of Sir2/SIRT1 by acute inebriation forms part of a transcriptional program in mushroom body neurons to alter presynaptic properties and neural responses to favor the development of ethanol tolerance, preference, and reward.

Chen, L.P., Wang, P., Sun, Y.J. and Wu, Y.J. (2016). Direct interaction of avermectin with epidermal growth factor receptor mediates the penetration resistance in Drosophila larvae. Open Biol 6. PubMed ID: 27249340
Summary:
With the widespread use of avermectins (AVMs) for managing parasitic and agricultural pests, the resistance of worms and insects to AVMs has emerged as a serious threat to human health and agriculture worldwide. The reduced penetration of AVMs is one of the main reasons for the development of the resistance to the chemicals. However, the detailed molecular mechanisms remain elusive. This study used the larvae of Drosophila melanogaster as a model system to explore the molecular mechanisms underlying the development of penetration resistance to AVMs. It was shown that the chitin layer is thickened and the efflux transporter P-glycoprotein (P-gp) is overexpressed in the AVM-resistant larvae epidermis. The activation of the transcription factor Relish by the over-activated epidermal growth factor receptor (EGFR)/AKT/ERK pathway was found to induce the overexpression of the chitin synthases DmeCHS1/2 and P-gp in the resistant larvae. Interestingly, AVM was found to directly interact with EGFR and lead to the activation of the EGFR/AKT/ERK pathway, which activates the transcription factor Relish and induces the overexpression of DmeCHS1/2 and P-gp. These findings provide new insights into the molecular mechanisms underlying the development of penetration resistance to drugs. 

Calleja, M., Morata, G. and Casanova, J. (2016). The tumorigenic properties of Drosophila epithelial cells mutant for lethal giant larvae. Dev Dyn [Epub ahead of print]. PubMed ID: 27239786
Summary:
Mutations in Drosophila tumour suppressor genes (TSGs) lead to the formation of invasive tumours in the brain and imaginal discs. This study analyzed the tumorigenic properties of imaginal discs mutant for the TSG gene lethal giant larvae (lgl). lgl mutant cells display the characteristic features of mammalian tumour cells: they can proliferate indefinitely, induce additional tracheogenesis (an insect counterpart of vasculogenesis) and invade neighbouring tissues. Lgl mutant tissues exhibit high apoptotic levels, which lead to the activation of the Jun-N-Terminal Kinase (JNK) pathway. The study proposes that JNK is a key factor in the acquisition of these tumorigenic properties; it promotes cell proliferation and induces high levels of Mmp1 and confers tumour cells capacity to invade wildtype tissue. Noteworthy, lgl RNAi-mediated down regulation does not produce similar transformations in the CNS, thereby indicating a fundamental difference between the cells of developing imaginal discs and those of differentiated organs. The study discusses these results in the light of the "single big-hit origin" of some human paediatric or developmental cancers.

Chlamydas, S., et al. (2016). Functional interplay between MSL1 and CDK7 controls RNA polymerase II Ser5 phosphorylation. Nat Struct Mol Biol [Epub ahead of print]. PubMed ID: 27183194
Summary:
Proper gene expression requires coordinated interplay among transcriptional coactivators, transcription factors and the general transcription machinery. This study reports that MSL1, a central component of the dosage compensation complex in Drosophila melanogaster and Drosophila virilis, displays evolutionarily conserved sex-independent binding to promoters. Genetic and biochemical analyses reveal a functional interaction of MSL1 with CDK7, a subunit of the Cdk-activating kinase (CAK) complex of the general transcription factor TFIIH. Importantly, MSL1 depletion leads to decreased phosphorylation of Ser5 of RNA polymerase II. In addition, it was demonstrated that MSL1 is a phosphoprotein, and transgenic flies expressing MSL1 phosphomutants show mislocalization of the histone acetyltransferase MOF and histone H4 K16 acetylation, thus ultimately causing male lethality due to a failure of dosage compensation. It is proposed that, by virtue of its interaction with components of the general transcription machinery, MSL1 exists in different phosphorylation states, thereby modulating transcription in flies.

Tuesday, June 7th

Jukam, D., Viets, K., Anderson, C., Zhou, C., DeFord, P., Yan, J., Cao, J. and Johnston, R.J. (2016). The BEAF-32 insulator protein is required for Hippo pathway activity in the terminal differentiation of neuronal subtypes. Development [Epub ahead of print]. PubMed ID: 27226322
Summary:
The Hippo pathway is critical for not only normal growth and apoptosis but also cell fate specification during development. What controls Hippo pathway activity during cell fate specification is incompletely understood. This study identified the BEAF-32 insulator protein as a regulator of Hippo pathway activity in Drosophila photoreceptor differentiation. Though morphologically uniform, the fly eye is composed of two subtypes of R8 photoreceptor neurons defined by expression of light-detecting Rhodopsin proteins. In one R8 subtype, active Hippo signaling induces Rhodopsin6 (Rh6) and represses Rhodopsin5 (Rh5) whereas in the alternate subtype, inactive Hippo signaling induces Rh5 and represses Rh6. The activity state of the Hippo pathway in R8 is determined by the expression of warts, a core pathway kinase, which interacts with the growth regulator melted in a double negative feedback loop. It was shown that the BEAF-32 insulator is required for expression of warts and repression of melted. Furthermore, BEAF-32 plays a second role downstream of Warts to induce Rh6 and prevent Rh5 fate. BEAF-32 is dispensable for Warts feedback, indicating that BEAF-32 differentially regulates warts and Rhodopsins. Loss of BEAF-32 does not noticeably impair the functions of the Hippo pathway in eye growth regulation. In summary, the study identifies a context-specific regulator of Hippo pathway activity in post-mitotic neuronal fate, and reveals a developmentally specific role for a broadly expressed insulator protein.

Regna, K., Kurshan, P. T., Harwood, B. N., Jenkins, A. M., Lai, C. Q., Muskavitch, M. A., Kopin, A. S. and Draper, I. (2016). A critical role for the Drosophila dopamine D1-like receptor Dop1R2 at the onset of metamorphosis. BMC Dev Biol 16: 15. PubMed ID: 27184815
Summary:
Insect metamorphosis relies on temporal and spatial cues that are precisely controlled. Previous studies in Drosophila have shown that untimely activation of genes that are essential to metamorphosis results in growth defects, developmental delay and death. Multiple factors exist that safeguard these genes against dysregulated expression. The list of identified negative regulators that play such a role in Drosophila development continues to expand. By using RNAi transgene-induced gene silencing coupled to spatio/temporal assessment, this study has unraveled an important role for the Drosophila dopamine 1-like receptor, Dop1R2, in development. Dop1R2 knockdown leads to pre-adult lethality. In adults that escape death, abnormal wing expansion and/or melanization defects occur. Furthermore salivary gland expression of this GPCR during the late larval/prepupal stage is essential for the flies to survive through adulthood. In addition to RNAi-induced effects, treatment of larvae with the high affinity D1-like receptor antagonist flupenthixol, also results in developmental arrest, and in morphological defects comparable to those seen in Dop1R2 RNAi flies. To examine the basis for pupal lethality in Dop1R2 RNAi flies, transcriptome analysis was carried out. These studies revealed up-regulation of genes that respond to ecdysone, regulate morphogenesis and/or modulate defense/immunity. Taken together these findings suggest a role for Dop1R2 in the repression of genes that coordinate metamorphosis. Premature release of this inhibition is not tolerated by the developing fly.

Sobala, L.F. and Adler, P.N. (2016). The gene expression program for the formation of wing cuticle in Drosophila. PLoS Genet 12: e1006100. PubMed ID: 27232182
Summary:
The cuticular exoskeleton of insects and other arthropods is a remarkably versatile material with a complex multilayer structure. This study isolated cuticle synthesizing cells in relatively pure form by dissecting pupal wings and used RNAseq to identify genes expressed during the formation of the adult wing cuticle. Dramatic changes in gene expression during cuticle deposition were observed, and combined with transmission electron microscopy, candidate genes for the deposition of the different cuticular layers were identified. Among genes of interest that dramatically change their expression during the cuticle deposition program are ones that encode cuticle proteins, ZP domain proteins, cuticle modifying proteins and transcription factors, as well as genes of unknown function. A striking finding is that mutations in a number of genes that are expressed almost exclusively during the deposition of the envelope (the thin outermost layer that is deposited first) result in gross defects in the procuticle (the thick chitinous layer that is deposited last). An attractive hypothesis to explain this is that the deposition of the different cuticle layers is not independent with the envelope instructing the formation of later layers. Alternatively, some of the genes expressed during the deposition of the envelope could form a platform that is essential for the deposition of all cuticle layers. 

Sanchez-Higueras, C. and Hombria, J. C. (2016). Precise long-range migration results from short-range stepwise migration during ring gland organogenesis. Dev Biol. [Epub ahead of print] PubMed ID: 27063193
Summary:
Many organs are specified far from the location they occupy when functional, having to migrate long distances through the heterogeneous and dynamic environment of the early embryo. The formation of the main Drosophila endocrine organ, the ring gland, was studied as a new model to investigate in vivo the genetic regulation of collective cell migration. The ring gland results from the fusion of three independent gland primordia that migrate from the head towards the anterior aorta as the embryo is experiencing major morphogenetic movements. To complete their long-range migration, the glands extend filopodia moving sequentially towards a nearby intermediate target and from there to more distal ones. Thus, the apparent long-range migration is composed of several short-range migratory steps that facilitate reaching the final destination. The target tissues react to the gland's proximity by sending filopodia towards it. This finding of a succession of independent migration stages is consistent with the stepwise evolution of ring gland assembly and fits with the observed gland locations found in extant crustaceans, basal insects and flies.

Monday, June 6th

Paranjape, N. P. and Calvi, B. R. (2016). The histone variant H3.3 is enriched at Drosophila amplicon origins but does not mark them for activation. G3 (Bethesda) [Epub ahead of print]. PubMed ID: 27172191
Summary:
Eukaryotic DNA replication begins from multiple origins. The origin recognition complex (ORC) binds origin DNA and scaffolds assembly of a pre-Replicative Complex (pre-RC), which is subsequently activated to initiate DNA replication. In multicellular eukaryotes, origins do not share a strict DNA consensus sequence and their activity changes in concert with chromatin status during development, but mechanisms are ill-defined. Previous genome-wide analyses in Drosophila and other organisms have revealed a correlation between ORC binding sites and the histone variant H3.3. This correlation suggests that H3.3 may designate origin sites, but this idea has remained untested. To address this question, this study examined the enrichment and function of H3.3 at the origins responsible for developmental gene amplification in the somatic follicle cells of the Drosophila ovary. H3.3 was found to be abundant at these amplicon origins. H3.3 levels remained high when replication initiation was blocked, indicating that H3.3 is abundant at the origins before activation of the pre-RC. H3.3 was also enriched at the origins during early oogenesis, raising the possibility that H3.3 bookmarks sites for later amplification. However, flies null mutant for both of the H3.3 genes in Drosophila did not have overt defects in developmental gene amplification or genomic replication, suggesting that H3.3 is not essential for the assembly or activation of the pre-RC at origins. Instead, the results imply that the correlation between H3.3 and ORC sites reflects other chromatin attributes that are important for origin function.

Stegeman, R., Spreacker, P. J., Swanson, S. K., Stephenson, R., Florens, L., Washburn, M. P. and Weake, V. M. (2016). The spliceosomal protein SF3B5 is a novel component of Drosophila SAGA that functions in gene expression independent of splicing. J Mol Biol [Epub ahead of print]. PubMed ID: 27185460
Summary:
The interaction between splicing factors and the transcriptional machinery provides an intriguing link between the coupled processes of transcription and splicing. This study shows that the two components of the SF3B complex, SF3B3 and SF3B5, that form part of the U2 small nuclear ribonucleoprotein particle (snRNP) are also subunits of the Spt-Ada-Gcn5 acetyltransferase (SAGA) transcriptional coactivator complex in Drosophila melanogaster. Whereas SF3B3 had previously been identified as a human SAGA subunit, SF3B5 had not been identified as a component of SAGA in any species. This study shows that SF3B3 and SF3B5 bind to SAGA independent of RNA and interact with multiple SAGA subunits including Sgf29 and Spt7 in a yeast two-hybrid assay. Through analysis of sf3b5 mutant flies, this study shows that SF3B5 is necessary for proper development and cell viability but not for histone acetylation. Although SF3B5 does not appear to function in SAGA's histone-modifying activities, SF3B5 is still required for expression of a subset of SAGA-regulated genes independent of splicing. Thus, these data support an independent function of SF3B5 in SAGA's transcription coactivator activity that is separate from its role in splicing.

Schwartz, S., Truglio, M., Scott, M.J. and Fitzsimons, H.L. (2016). Long-term memory in Drosophila is influenced by the histone deacetylase HDAC4 interacting with the SUMO-conjugating enzyme Ubc9. Genetics [Epub ahead of print]. PubMed ID: 27182943
Summary:
HDAC4 is a potent memory repressor with overexpression of wild-type or a nuclear-restricted mutant resulting in memory deficits. Interestingly, reduction of HDAC4 also impairs memory via an as yet unknown mechanism. Although histone deacetylase family members are important mediators of epigenetic mechanisms in neurons, HDAC4 is predominantly cytoplasmic in the brain and there is increasing evidence for interactions with non-histone proteins, suggesting HDAC4 has roles beyond transcriptional regulation. To that end, this study performed a genetic interaction screen in Drosophila and identified twenty-six genes that interact with HDAC4, including Ubc9, the sole SUMO E2-conjugating enzyme. RNAi-induced reduction of Ubc9 in the adult brain impairs long-term memory in the courtship suppression assay, a Drosophila model of associative memory. It was also demonstrated that HDAC4 and Ubc9 interact genetically during memory formation, opening new avenues for investigating the mechanisms through which HDAC4 regulates memory formation and other neurological processes.

Onorati, M. C., Arancio, W., Cavalieri, V., Ingrassia, A. M., Pavesi, G. and Corona, D. F. (2015). Trans-reactivation: A new epigenetic phenomenon underlying transcriptional reactivation of silenced genes. PLoS Genet 11: e1005444. PubMed ID: 26292210
Summary:
In order to study the role played by cellular RNA pools produced by homologous genomic loci in defining the transcriptional state of a silenced gene, this study tested the effect of non-functional alleles of the white gene in the presence of a functional copy of white, silenced by heterochromatin. Non-functional alleles of white, which were unable to produce a coding transcript, could reactivate in trans the expression of a wild type copy of the same gene silenced by heterochromatin. This new epigenetic phenomenon of transcriptional trans-reactivation is heritable, relies on the presence of homologous RNA's and is affected by mutations in genes involved in post-transcriptional gene silencing. These data suggest a general new unexpected level of gene expression control mediated by homologous RNA molecules in the context of heterochromatic genes. It is concluded that homologous non-coding RNA can reactivate the expression of genes silenced by heterochromatin.

Sunday, July 5th

McCormack, S., Yadav, S., Shokal, U., Kenney, E., Cooper, D. and Eleftherianos, I. (2016). The insulin receptor substrate Chico regulates antibacterial immune function in Drosophila. Immun Ageing 13: 15. PubMed ID: 27134635
Summary:
Molecular and genetic studies in model organisms have recently revealed a dynamic interplay between immunity and ageing mechanisms. In Drosophila, inhibition of the insulin signaling pathway prolongs lifespan, and mutations in the insulin receptor substrate Chico extend the survival of mutant flies against certain bacterial pathogens. This study investigated the immune function of chico mutant adult flies against the virulent insect pathogen Photorhabdus luminescens as well as to non-pathogenic E. coli. chico loss-of-function mutant flies were equally able to survive infection by P. luminescens or E. coli compared to their background controls, but they contain fewer numbers of bacterial cells at most time-points after the infection. Analysis of immune signaling activation in flies infected with either bacteria shows reduced transcript levels of antimicrobial peptide genes in the chico mutants than in controls. Evaluation of immune function in infected flies reveals increased phenoloxidase activity and melanization response to P. luminescens and E. coli together with reduced phagocytosis of bacteria in the chico mutants. Changes in the antibacterial immune function in the chico mutants is not due to altered metabolic activity. These results indicate a novel role for chico in the regulation of the antibacterial immune function in D. melanogaster.

Sorvina, A., Shandala, T. and Brooks, D. A. (2016). Drosophila Pkaap regulates Rab4/Rab11-dependent traffic and Rab11 exocytosis of innate immune cargo. Biol Open [Epub ahead of print]. PubMed ID: 27190105
Summary:
The secretion of immune-mediators is a critical step in the host innate immune response to pathogen invasion, and Rab GTPases have an important role in the regulation of this process. Rab4/Rab11 recycling endosomes are involved in the sorting of immune-mediators into specialist Rab11 vesicles that can traffic this cargo to the plasma membrane; however, how this sequential delivery process is regulated has yet to be fully defined. This study reports that Drosophila Pkaap, an orthologue of the human dual-specific A-kinase-anchoring protein 2 or D-AKAP2 (also called AKAP10), appeared to have a nucleotide-dependent localisation to Rab4 and Rab11 endosomes. RNAi silencing of pkaap altered Rab4/Rab11 recycling endosome morphology, suggesting that Pkaap functions in cargo sorting and delivery in the secretory pathway. The depletion of pkaap also had a direct effect on Rab11 vesicle exocytosis and the secretion of the antimicrobial peptide Drosomycin at the plasma membrane. It is proposed that Pkaap has a dual role in antimicrobial peptide traffic and exocytosis, making it an essential component for the secretion of inflammatory mediators and the defence of the host against pathogens.

Ekstrom, J. O. and Hultmark, D. (2016). A novel strategy for live detection of viral infection in Drosophila melanogaster. Sci Rep 6: 26250. PubMed ID: 27189868
Summary:
A transgenic reporter has been created for virus infection, and it to has been used study Nora virus infection in Drosophila melanogaster. The transgenic construct, Munin, expresses the yeast transcription factor Gal4, tethered to a transmembrane anchor via a linker that can be cleaved by a viral protease. In infected cells, liberated Gal4 will then transcribe any gene that is linked to a promoter with a UAS motif, the target for Gal4 transcription. For instance, infected cells will glow red in the offspring of a cross between the Munin stock and flies with a UAS-RFP(nls) transgene (expressing a red fluorescent protein). In such flies, after natural infection via the faecal-oral route, 5-15% of the midgut cells are infected, but there is little if any infection elsewhere. By contrast, infection can be detected in many other tissues after injection of virus into the body cavity. The same principle could be applied for other viruses and it could also be used to express or suppress any gene of interest in infected cells.

Morin-Poulard, I., Sharma, A., Louradour, I., Vanzo, N., Vincent, A. and Crozatier, M. (2016). Vascular control of the Drosophila haematopoietic microenvironment by Slit/Robo signalling. Nat Commun 7: 11634. PubMed ID: 27193394
Summary:
Self-renewal and differentiation of mammalian haematopoietic stem cells (HSCs) are controlled by a specialized microenvironment called 'the niche'. In the bone marrow, HSCs receive signals from both the endosteal and vascular niches. The posterior signalling centre (PSC) of the larval Drosophila haematopoietic organ, the lymph gland, regulates blood cell differentiation under normal conditions and also plays a key role in controlling haematopoiesis under immune challenge. This study reports that the Drosophila vascular system also contributes to the lymph gland homoeostasis. Vascular cells produce Slit that activates Robo receptors in the PSC. Robo activation controls proliferation and clustering of PSC cells by regulating Myc, and small GTPase and DE-cadherin activity, respectively. These findings reveal that signals from the vascular system contribute to regulating the rate of blood cell differentiation via the regulation of PSC morphology.

Saturday, June 4

Maor, G., Cabasso, O., Krivoruk, O., Rodriguez, J., Steller, H., Segal, D. and Horowitz, M. (2016). The contribution of mutant GBA to the development of parkinson disease in Drosophila. Hum Mol Genet [Epub ahead of print]. PubMed ID: 27162249
Summary:
Gaucher disease (GD) results from mutations in the acid beta-glucocerebrosidase (GCase) encoding gene, GBA, which leads to accumulation of glucosylceramides. GD patients and carriers of GD mutations have a significantly higher propensity to develop Parkinson disease (PD) in comparison to the non-GD population. This study used Drosophila to show that development of PD in carriers of GD mutations results from the presence of mutant GBA alleles. Drosophila has two GBA orthologs (CG31148 and CG31414), each of which has a minos insertion, which creates C-terminal deletion in the encoded GCase. Flies double heterozygous for the endogenous mutant GBA orthologs presented Unfolded Protein Response (UPR) and developed parkinsonian signs, manifested by death of dopaminergic cells, defective locomotion and a shorter life span. Transgenic flies carrying the mutant human N370S, L444P and the 84GG variants were established. UPR activation and development of parkinsonian signs could be recapitulated in flies expressing these three mutant variants.UPR and parkinsonian signs could be partially rescued by growing the double heterozygous flies, or flies expressing the N370S or the L444P human mutant GCase variants, in the presence of the pharmacological chaperone ambroxol, which binds and removes mutant GCase from the ER. However flies expressing the 84GG mutant, that does not express mature GCase, did not exhibit rescue by ambroxol. These results strongly suggest that the presence of a mutant GBA allele in dopaminergic cells leads to ER stress and to their death, and contributes to development of Parkinson disease.

Merzetti, E. M. and Staveley, B. E. (2016). Altered expression of CG5961, a putative Drosophila melanogaster homologue of FBXO9, provides a new model of Parkinson disease. Genet Mol Res 15. PubMed ID: 27173356
Summary:
F-box proteins act as the protein recognition component of the Skp-Cul-F-box class of ubiquitin ligases. Two members of a gene sub-family encoding these proteins, FBXO7 and FBXO32, have been implicated in the onset and progression of degenerative disease. FBXO7 is responsible for rare genetic forms of Parkinson disease, while FBXO32 has been implicated in muscle wasting. The third gene in this family, FBXO9, is related to growth signaling, but the role of this gene in degenerative disease pathways has not been thoroughly investigated. Characterizing the putative Drosophila melanogaster homologue of this gene, CG5961, enables modeling and analysis of the consequence of targeted alteration of gene function and the effects on the overall health of the organism. Comparison of the protein domains of Homo sapiens FBXO9 and the putative D. melanogaster homologue CG5961 revealed a high degree of conservation between the protein domains. Directed expression of CG5961 (via CG5961EP) and inhibition of CG5961 (through a stable RNAi transgene) in the developing D. melanogaster eye caused abnormalities in adult structures (ommatidia and inter-ommatidial bristles). Directed expression of either CG5961 or CG5961-RNAi in the dopaminergic neurons led to a reduced lifespan compared to that in lacZ controls. Protein structures of CG5961 and FBXO9 are highly similar, and the effects of altered expression of CG5961 in neuron-rich tissues was studied. The results suggest that CG5961 activity is necessary for the proper formation of neuronal tissue and that targeted alteration of gene expression in dopaminergic neurons leads to a reduced lifespan.

Esmaeeli-Nieh, S., et al. (2016). BOD1 is required for cognitive function in humans and Drosophila. PLoS Genet 12: e1006022. PubMed ID: 27166630
Summary:
This study reports a stop-mutation in the BOD1 (Biorientation Defective 1) gene, which co-segregates with intellectual disability in a large consanguineous family. The BOD1 protein is required for proper chromosome segregation, regulating phosphorylation of PLK1 (see Drosophila Polo) substrates by modulating Protein Phosphatase 2A (PP2A; see Drosophila Twins) activity during mitosis. Fibroblast cell lines derived from homozygous BOD1 mutation carriers show aberrant localisation of the cell cycle kinase PLK1 and its phosphatase PP2A at mitotic kinetochores. The relatively normal cell cycle progression observed in cultured cells is in line with the absence of gross structural brain abnormalities in the affected individuals. Moreover, normal adult brain tissues BOD1 expression is maintained at considerable levels, in contrast to PLK1 expression, and evidence is provided for synaptic localization of Bod1 in murine neurons. These observations suggest that BOD1 plays a cell cycle-independent role in the nervous system. To address this possibility, two Drosophila models were established, where neuron-specific knockdown of BOD1 caused pronounced learning deficits and significant abnormalities in synapse morphology. Together these results reveal novel postmitotic functions of BOD1 as well as pathogenic mechanisms that strongly support a causative role of BOD1 deficiency in the aetiology of intellectual disability. Moreover, by demonstrating its requirement for cognitive function in humans and Drosophila evidence is provided for a conserved role of BOD1 in the development and maintenance of cognitive features.

Mushtaq, Z., Choudhury, S. D., Gangwar, S. K., Orso, G. and Kumar, V. (2016). Human Senataxin modulates structural plasticity of the neuromuscular junction in Drosophila through a neuronally conserved TGFbeta signalling pathway. Neurodegener Dis 16: 324-336. PubMed ID: 27197982
Summary:
Mutations in the human Senataxin (hSETX) gene have been shown to cause two forms of neurodegenerative disorders - a dominant form called amyotrophic lateral sclerosis type 4 (ALS4) and a recessive form called ataxia with oculomotor apraxia type 2 (AOA2). SETX is a putative DNA/RNA helicase involved in RNA metabolism. Although several dominant mutations linked with ALS4 have been identified in SETX, their contribution towards ALS4 pathophysiology is still elusive. In order to model ALS4 in Drosophila and to elucidate the morphological, physiological and signalling consequences, the wild-type and pathological forms of hSETX were overexpressed in Drosophila. The pan-neuronal expression of wild-type or mutant forms of hSETX induced morphological plasticity at neuromuscular junction (NMJ) synapses. Surprisingly, it was found that while the NMJ synapses were increased in number, the neuronal function was normal. Analysis of signalling pathways revealed that hSETX modulates the Highwire (Hiw; a conserved neuronal E3 ubiquitin ligase)-dependent bone morphogenetic protein/TGFbeta pathway. Thus, this study could pave the way for a better understanding of ALS4 progression by SETX through the regulation of neuronal E3 ubiquitin pathways.

Friday, June 3rd

Lüpold, S., Manier, M.K., Puniamoorthy, N., Schoff, C., Starmer, W.T., Luepold, S.H., Belote, J.M. and Pitnick, S. (2016). How sexual selection can drive the evolution of costly sperm ornamentation. Nature 533: 535-538. PubMed ID: 27225128
Summary:
Post-copulatory sexual selection (PSS), fuelled by female promiscuity, is credited with the rapid evolution of sperm quality traits across diverse taxa. Yet, the understanding of the adaptive significance of sperm ornaments and the cryptic female preferences driving their evolution is extremely limited. This study reviews the evolutionary allometry of exaggerated sexual traits (for example, antlers, horns, tail feathers, mandibles and dewlaps), shows that the giant sperm of some Drosophila species are possibly the most extreme ornaments in all of nature and demonstrates how their existence challenges theories explaining the intensity of sexual selection, mating-system evolution and the fundamental nature of sex differences. By combining quantitative genetic analyses of interacting sex-specific traits in D. melanogaster with comparative analyses of the condition dependence of male and female reproductive potential across species with varying ornament size, a complex dynamics was found that may underlie sperm-length evolution. Data suggest that producing few gigantic sperm evolved by (1) Fisherian runaway selection mediated by genetic correlations between sperm length, the female preference for long sperm and female mating frequency, and (2) longer sperm increasing the indirect benefits to females. Also, that the developmental integration of sperm quality and quantity renders post-copulatory sexual selection on ejaculates unlikely to treat male-male competition and female choice as discrete processes. 

Hemmer, L. W. and Blumenstiel, J. P. (2016). Holding it together: rapid evolution and positive selection in the synaptonemal complex of Drosophila. BMC Evol Biol 16: 91. PubMed ID: 27150275
Summary:
The synaptonemal complex (SC) is a highly conserved meiotic structure that functions to pair homologs and facilitate meiotic recombination in most eukaryotes. Five Drosophila SC proteins have been identified and localized within the complex: C(3)G, C(2)M, CONA, ORD, and the newly identified Corolla. The SC is required for meiotic recombination in Drosophila and absence of these proteins leads to reduced crossing over and chromosomal nondisjunction. The proteins display little apparent sequence conservation outside the genus. To identify factors that explain this lack of apparent conservation, a molecular evolutionary analysis of these genes was performed across the Drosophila genus. For the five SC components, gene sequence similarity declines rapidly with increasing phylogenetic distance and only ORD and C(2)M are identifiable outside of the Drosophila genus. SC gene sequences have a higher dN/dS (omega) rate ratio than the genome wide average and this can in part be explained by the action of positive selection in almost every SC component. Omega estimates for the five SC components are in accordance with their physical position within the SC. Components interacting with chromatin evolve slowest and components comprising the central elements evolve the most rapidly. Thus, the Drosophila SC is proposed to be evolving rapidly due to two combined effects: 1) a high rate of evolution can be partly explained by low purifying selection on protein components whose function is to simply hold chromosomes together, 2) positive selection in the SC is driven by its sex-specificity combined with its role in facilitating both recombination and centromere clustering in the face of recurrent bouts of drive in female meiosis.

Zatsepina, O. G., Przhiboro, A. A., Yushenova, I. A., Shilova, V., Zelentsova, E. S., Shostak, N. G., Evgen'ev, M. B. and Garbuz, D. G. (2016). A Drosophila heat shock response represents an exception rather than a rule amongst Diptera species. Insect Mol Biol [Epub ahead of print]. PubMed ID: 27089053
Summary:
Heat shock protein 70 (Hsp70) is the major player that underlies adaptive response to hyperthermia in all organisms studied to date. This study investigated patterns of Hsp70 expression in larvae of dipteran species collected from natural populations of species belonging to four families from different evolutionary lineages of the order Diptera: Stratiomyidae (soldier flies), Tabanidae (Horse-flies), Chironomidae (nonbiting midges) and Ceratopogonidae (biting midges). All investigated species showed a Hsp70 expression pattern that was different from the pattern in Drosophila. In contrast to Drosophila, all of the species in the families studied were characterized by high constitutive levels of Hsp70, which was more stable than that in Drosophila. When Stratiomyidae Hsp70 proteins were expressed in Drosophila cells, they became as short-lived as the endogenous Hsp70. Interestingly, three species of Ceratopogonidae and a cold-water species of Chironomidae exhibited high constitutive levels of Hsp70 mRNA and high basal levels of Hsp70. Furthermore, two species of Tabanidae were characterized by significant constitutive levels of Hsp70 and highly stable Hsp70 mRNA. In most cases, heat-resistant species were characterized by a higher basal level of Hsp70 than more thermosensitive species. These data suggest that different trends were realized during the evolution of the molecular mechanisms underlying the regulation of the responses of Hsp70 genes to temperature fluctuations in the studied families.

Catalan, A., Glaser-Schmitt, A., Argyridou, E., Duchen, P. and Parsch, J. (2016). An indel polymorphism in the MtnA 3' untranslated region is associated with gene expression variation and local adaptation in Drosophila melanogaster. PLoS Genet 12: e1005987. PubMed ID: 27120580
Summary:
Insertions and deletions (indels) are a major source of genetic variation within species and may result in functional changes to coding or regulatory sequences. This study reports that an indel polymorphism in the 3' untranslated region (UTR) of the metallothionein gene MtnA is associated with gene expression variation in natural populations of Drosophila melanogaster. A derived allele of MtnA with a 49-bp deletion in the 3' UTR segregates at high frequency in populations outside of sub-Saharan Africa. The frequency of the deletion increases with latitude across multiple continents and approaches 100% in northern Europe. Flies with the deletion have more than 4-fold higher MtnA expression than flies with the ancestral sequence. Using reporter gene constructs in transgenic flies, this study showed that the 3' UTR deletion significantly contributes to the observed expression difference. Population genetic analyses uncovered signatures of a selective sweep in the MtnA region within populations from northern Europe. It was also found that the 3' UTR deletion is associated with increased oxidative stress tolerance. These results suggest that the 3' UTR deletion has been a target of selection for its ability to confer increased levels of MtnA expression in northern European populations, likely due to a local adaptive advantage of increased oxidative stress tolerance.

Thursday, June 2nd

He, B., Martin, A. and Wieschaus, E. (2016). Flow-dependent myosin recruitment during Drosophila cellularization requires zygotic dunk activity. Development [Epub ahead of print]. PubMed ID: 27226317
Summary:
Actomyosin contractility underlies force generation in morphogenesis ranging from cytokinesis to epithelial extension or invagination. In Drosophila, the cleavage of the syncytial blastoderm is initiated by an actomyosin network at the base of membrane furrows that invaginate from the surface of the embryo. It remains unclear how this network forms and how it affects tissue mechanics. This study shows that during Drosophila cleavage, myosin recruitment to the cleavage furrows proceeds in temporally distinct phases of tension-driven cortical flow and direct recruitment, regulated by different zygotic genes. The study identified the gene dunk and showed that it is transiently transcribed when cellularization starts and functions to maintain cortical myosin during the flow phase. The subsequent direct myosin recruitment, however, is Dunk-independent but requires Slam. The Slam-dependent direct recruitment of myosin is sufficient to drive cleavage in the dunk mutant, and the subsequent development of the mutant is normal. In the dunk mutant, cortical myosin loss triggers misdirected flow and disrupts the hexagonal packing of the ingressing furrows. Computer simulation coupled with laser ablation suggests that Dunk-dependent maintenance of cortical myosin enables mechanical tension build-up, thereby providing a mechanism to guide myosin flow and define the hexagonal symmetry of the furrows.

Figard, L., Wang, M., Zheng, L., Golding, I. and Sokac, A. M. (2016). Membrane supply and demand regulates F-Actin in a cell surface reservoir. Dev Cell 37: 267-278. PubMed ID: 27165556
Summary:
Cells store membrane in surface reservoirs of pits and protrusions. These membrane reservoirs facilitate cell shape change and buffer mechanical stress, but how reservoir dynamics are regulated is not known. During cellularization, the first cytokinesis in Drosophila embryos, a reservoir of microvilli unfolds to fuel cleavage furrow ingression. This study found that regulated exocytosis adds membrane to the reservoir before and during unfolding. Dynamic F-actin deforms exocytosed membrane into microvilli. Single microvilli extend and retract in ~20 s, while the overall reservoir is depleted in sync with furrow ingression over 60-70 min. Using pharmacological and genetic perturbations, this study shows that exocytosis promotes microvillar F-actin assembly, while furrow ingression controls microvillar F-actin disassembly. Thus, reservoir F-actin and, consequently, reservoir dynamics are regulated by membrane supply from exocytosis and membrane demand from furrow ingression.

Jodoin, J. N., Coravos, J. S., Chanet, S., Vasquez, C. G., Tworoger, M., Kingston, E. R., Perkins, L. A., Perrimon, N. and Martin, A. C. (2015). Stable force balance between epithelial cells arises from F-Actin turnover. Dev Cell 35: 685-697. PubMed ID: 26688336
Summary:
The propagation of force in epithelial tissues requires that the contractile cytoskeletal machinery be stably connected between cells through E-cadherin-containing adherens junctions. In many epithelial tissues, the cells' contractile network is positioned at a distance from the junction. However, the mechanism or mechanisms that connect the contractile networks to the adherens junctions, and thus mechanically connect neighboring cells, are poorly understood. This study identified the role for F-actin turnover in regulating the contractile cytoskeletal network's attachment to adherens junctions. Perturbing F-actin turnover via gene depletion or acute drug treatments that slow F-actin turnover destabilized the attachment between the contractile actomyosin network and adherens junctions. This work identifies a critical role for F-actin turnover in connecting actomyosin to intercellular junctions, defining a dynamic process required for the stability of force balance across intercellular contacts in tissues.

Tran, D. T., Masedunskas, A., Weigert, R. and Ten Hagen, K. G. (2015). Arp2/3-mediated F-actin formation controls regulated exocytosis in vivo. Nat Commun 6: 10098. PubMed ID: 26639106
Summary:
The actin cytoskeleton plays crucial roles in many cellular processes, including regulated secretion. However, the mechanisms controlling F-actin dynamics in this process are largely unknown. Through 3D time-lapse imaging in a secreting organ, this study shows that F-actin is actively disassembled along the apical plasma membrane at the site of secretory vesicle fusion and re-assembled directionally on vesicle membranes. Moreover, fusion pore formation and PIP2 redistribution was shown to precedes actin and myosin recruitment to secretory vesicle membranes. Finally, essential roles were shown for the branched actin nucleators Arp2/3- and WASp in the process of secretory cargo expulsion and integration of vesicular membranes with the apical plasma membrane. These results highlight previously unknown roles for branched actin in exocytosis and provide a genetically tractable system to image the temporal and spatial dynamics of polarized secretion in vivo.

Wednesday, June 1st

Quénerch'du, E., Anand, A. and Kai, T. (2016). The piRNA pathway is developmentally regulated during spermatogenesis in Drosophila. RNA [Epub ahead of print]. PubMed ID: 27208314
Summary:
PIWI-interacting RNAs (piRNAs) are predominantly produced in animal gonads to suppress transposons during germline development. Understanding about the piRNA biogenesis and function is predominantly from studies of the Drosophila female germline. piRNA pathway function in the male germline, however, remains poorly understood. To study overall and stage-specific features of piRNAs during spermatogenesis, this study analyzed small RNAs extracted from entire wild-type testes and stage-specific arrest mutant testes enriched with spermatogonia or primary spermatocytes. It was shown that most active piRNA clusters in the female germline do not majorly contribute to piRNAs in testes, and abundance patterns of piRNAs mapping to different transposon families also differ between male and female germlines. piRNA production is regulated in a stage-specific manner during spermatogenesis. The piRNAs in spermatogonia-enriched testes are predominantly transposon-mapping piRNAs, and almost half of those exhibit a ping-pong signature. In contrast, the primary spermatocyte-enriched testes have a dramatically high amount of piRNAs targeting repeats like suppressor of stellate and AT-chX The transposon-mapping piRNAs in the primary spermatocyte stages lacking Argonaute3 expression also show a ping-pong signature, albeit to a lesser extent. Consistently, argonaute3 mutant testes also retain ping-pong signature-bearing piRNAs, suggesting that a noncanonical ping-pong cycle might act during spermatogenesis. The study found stage-specific regulation of piRNA biogenesis during spermatogenesis: An active ping-pong cycle produces abundant transposon-mapping piRNAs in spermatogonia, while in primary spermatocytes, piRNAs act to suppress the repeats and transposons.

Sen, A., Karasik, A., Shanmuganathan, A., Mirkovic, E., Koutmos, M. and Cox, R.T. (2016). Loss of the mitochondrial protein-only ribonuclease P complex causes aberrant tRNA processing and lethality in Drosophila. Nucleic Acids Res [Epub ahead of print]. PubMed ID: 27131785
Summary:
Proteins encoded by mitochondrial DNA are translated using mitochondrially encoded tRNAs and rRNAs. As with nuclear encoded tRNAs, mitochondrial tRNAs must be processed to become fully functional. The mitochondrial form of ribonuclease P (mt:RNase P) is responsible for 5'-end maturation and is comprised of three proteins; mitochondrial RNase P protein (MRPP) 1 and 2 together with proteinaceous RNase P (PRORP). However, its mechanism and impact on development is not yet known. Using homology searches, this study identified the three proteins composing Drosophila mt:RNase P: Mulder (PRORP), Scully (MRPP2) and Roswell (MRPP1). It was shown that each protein is essential and localizes with mitochondria. Furthermore, reducing levels of each causes mitochondrial deficits, which appear to be due at least in part to defective mitochondrial tRNA processing. Overexpressing two members of the complex, Mulder and Roswell, is also lethal, and in the case of Mulder, causes abnormal mitochondrial morphology. These data are the first evidence that defective mt:RNase P causes mitochondrial dysfunction, lethality and aberrant mitochondrial tRNA processing in vivo, underscoring its physiological importance. This in vivo mt:RNase P model will advance understanding of how loss of mitochondrial tRNA processing causes tissue failure, an important aspect of human mitochondrial disease.

Homolka, D., Pandey, R. R., Goriaux, C., Brasset, E., Vaury, C., Sachidanandam, R., Fauvarque, M. O. and Pillai, R. S. (2015). PIWI slicing and RNA elements in precursors instruct directional primary piRNA biogenesis. Cell Rep 12: 418-428. PubMed ID: 26166577
Summary:
PIWI proteins and PIWI-interacting RNAs (piRNAs) mediate repression of transposons in the animal gonads. Primary processing converts long single-stranded RNAs into approximately 30-nt piRNAs, but their entry into the biogenesis pathway is unknown. This study demonstrates that an RNA element at the 5' end of a piRNA cluster-which has been termed piRNA trigger sequence (PTS)-can induce primary processing of any downstream sequence. It is proposes that such signals are triggers for the generation of the original pool of piRNAs. It was also demonstrated that endonucleolytic cleavage of a transcript by a cytosolic PIWI results in its entry into primary processing, which triggers the generation of non-overlapping, contiguous primary piRNAs in the 3' direction from the target transcript. These piRNAs are loaded into a nuclear PIWI, thereby linking cytoplasmic post-transcriptional silencing to nuclear transcriptional repression.

Lepennetier, G. and Catania, F. (2016). mRNA-associated processes and their influence on exon-intron structure in Drosophila melanogaster. G3 (Bethesda) [Epub ahead of print]. PubMed ID: 27172210
Summary:
This study examined the roles that capping, splicing, cleavage/polyadenylation, and telescripting (i.e., the protection of nascent transcripts from premature cleavage/polyadenylation by the splicing factor U1) might play in shaping exon-intron architecture in protein-coding genes. The findings suggest that the distance between subsequent internal 5' splice sites (5'ss) in Drosophila genes is constrained such that telescripting effects are maximized, in theory, and thus nascent transcripts are less vulnerable to premature termination. Exceptionally weak 5'ss and constraints on intron-exon size at the gene 5' end also indicate that capping might enhance the recruitment of U1 and, in turn, promote telescripting at this location. Finally, a positive correlation between last exon length and last 5'ss strength suggests that optimal donor splice sites in proximity of the pre-mRNA tail may inhibit the processing of downstream polyadenylation signals more than weak donor splice sites do. These findings support the possibility, hitherto scantly explored, that mRNA-associated processes impose significant constraints on the evolution of the eukaryotic gene structure.

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