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





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Saturday, April 30th, 2016

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Ott, S., Vishnivetskaya, A., Malmendal, A. and Crowther, D.C. (2016). Metabolic changes may precede proteostatic dysfunction in a Drosophila model of amyloid beta peptide toxicity. Neurobiol Aging 41: 39-52. PubMed ID: 27103517
Summary:
Amyloid beta (Aβ) peptide aggregation is linked to the initiation of Alzheimer's disease; accordingly, aggregation-prone isoforms of , expressed in the brain, shorten the lifespan of Drosophila melanogaster. However, the lethal effects of Aβ are not apparent until after day 15. This study used shibire(TS) flies that exhibit a temperature-sensitive paralysis phenotype as a reporter of proteostatic robustness. In this model, it was found that increasing age but not Aβ expression lowers the flies' permissive temperature, suggesting that Aβ does not exert its lethal effects by proteostatic disruption. Instead, it was observed that chemical challenges, in particular oxidative stressors, discriminate clearly between young (robust) and old (sensitive) flies. Using nuclear magnetic resonance spectroscopy in combination with multivariate analysis, the water-soluble metabolite profiles at various ages in flies expressing Aβ in their brains were compared. Two genotype-linked metabolomic signals were observed, the first reports the presence of any Aβ isoform and the second the effects of the lethal aggregation-prone Arctic Aβ. Lethality was found to be specifically associated with signs of oxidative respiration dysfunction and oxidative stress.

Siaw, J. T., Wan, H., Pfeifer, K., Rivera, V. M., Guan, J., Palmer, R. H. and Hallberg, B. (2016). Brigatinib, an anaplastic lymphoma kinase inhibitor, abrogates activity and growth in ALK-positive neuroblastoma cells in Drosophila and mice. Oncotarget [Epub ahead of print]. PubMed ID: 27049722
Summary:
Anaplastic lymphoma kinase (ALK) is a tyrosine kinase receptor which has been implicated in numerous solid and hematologic cancers. ALK mutations are reported in about 5-7% of neuroblastoma cases but the ALK-positive percentage increases significantly in the relapsed patient population. Crizotinib, the first clinically approved ALK inhibitor for the treatment of ALK-positive lung cancer, has had less dramatic responses in neuroblastoma. This study investigated the efficacy of a second-generation ALK inhibitor, brigatinib, in a neuroblastoma setting. Employing neuroblastoma cell lines, mouse xenograft and Drosophila melanogaster model systems expressing different constitutively active ALK variants, clear and efficient inhibition of ALK activity by brigatinib was shown. Similar abrogation of ALK activity was observed in vitro employing a set of different constitutively active ALK variants in biochemical assays. These results suggest that brigatinib is an effective inhibitor of ALK kinase activity in ALK addicted neuroblastoma that should be considered as a potential future therapeutic option for ALK-positive neuroblastoma patients alone or in combination with other treatments.

Chanu, S. I. and Sarkar, S. (2016). Targeted Downregulation of dMyc Suppresses Pathogenesis of Human Neuronal Tauopathies in Drosophila by Limiting Heterochromatin Relaxation and Tau Hyperphosphorylation. Mol Neurobiol. PubMed ID: 27000837
Summary:
Human tauopathies such as Alzheimer's Disease (AD), frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17), Pick's disease etc., are a group of neurodegenerative diseases which are characterized by abnormal hyperphosphorylation of tau that leads to formation of neurofibrillary tangles. Recapitulating several features of human neurodegenerative disorders, the Drosophila tauopathy model displays compromised lifespan, locomotor function impairment, and brain vacuolization in adult brain which is progressive and age dependent. This study demonstrates that tissue-specific downregulation of the Drosophila homolog of human c-myc proto-oncogene (dMyc) suppresses tau-mediated morphological and functional deficits by reducing abnormal tau hyperphosphorylation and restoring the heterochromatin loss. These studies show that the inherent chromatin remodeling ability of myc proto-oncogenes could be exploited to limit the pathogenesis of human neuronal tauopathies in the Drosophila disease model. Interestingly, recent reports on successful uses of some anti-cancer drugs against Alzheimer's and Parkinson's diseases in clinical trials and animal models strongly support these findings and proposed possibility.

Lehmann, S., Costa, A. C., Celardo, I., Loh, S. H. and Martins, L. M. (2016). Parp mutations protect against mitochondrial dysfunction and neurodegeneration in a PARKIN model of Parkinson's disease. Cell Death Dis 7: e2166. PubMed ID: 27031963
Summary:
The co-enzyme nicotinamide adenine dinucleotide (NAD+) is an essential co-factor for cellular energy generation in mitochondria as well as for DNA repair mechanisms in the cell nucleus involving NAD+-consuming poly (ADP-ribose) polymerases (PARPs). Mitochondrial function is compromised in animal models of Parkinson's disease (PD) associated with Parkin mutations. This study uncovered alterations in NAD+ salvage metabolism in Drosophila parkin mutants. This study found that dietary supplementation with the NAD+ precursor nicotinamide rescues mitochondrial function and is neuroprotective. Further, by mutating Parp in parkin mutants, it was shown that this increases levels of NAD+ and its salvage metabolites. This also rescues mitochondrial function and suppresses dopaminergic neurodegeneration. In is concluded that strategies to enhance NAD+ levels by administration of dietary precursors or the inhibition of NAD+-dependent enzymes, such as PARP, that compete with mitochondria for NAD+ could be used to delay neuronal death associated with mitochondrial dysfunction.

Zheng, Y., Mennella, V., Marks, S., Wildonger, J., Elnagdi, E., Agard, D. and Megraw, T. L. (2016). The Seckel syndrome and centrosomal protein Ninein localizes asymmetrically to stem cell centrosomes, but is not required for normal development, behavior, or DNA damage response in Drosophila. Mol Biol Cell [Epub ahead of print]. PubMed ID: 27053665
Summary:
Ninein (Nin) is a centrosomal protein whose gene is mutated in Seckel syndrome (SCKL, MIM 210600), an inherited recessive disease that results in primordial dwarfism, cognitive deficiencies, and increased sensitivity to genotoxic stress. Nin regulates neural stem cell self-renewal, interkinetic nuclear migration, and microtubule assembly in mammals. Nin is evolutionarily conserved, yet its role in cell division and development has not been investigated in a model organism. This study characterized the single Nin ortholog in Drosophila (Bsg25D; CG14025). Drosophila Nin localizes to the periphery of the centrosome, but not at centriolar structures as in mammals. However, Nin shares the property of its mammalian ortholog of promoting microtubule assembly. In neural and germline stem cells, Nin localizes asymmetrically to the younger (daughter) centrosome, yet it is not required for the asymmetric division of stem cells. In wing epithelia and muscle, Nin localizes to non-centrosomal microtubule-organizing centers. Surprisingly, loss of nin expression from a nin mutant does not significantly impact embryonic and brain development, fertility, or locomotor performance of mutant flies, nor their survival upon exposure to DNA damaging agents. While not essential, these data suggests that Nin plays a supportive role in centrosomal and extracentrosomal microtubule organization, and asymmetric stem cell division.

Ando, K., Maruko-Otake, A., Ohtake, Y., Hayashishita, M., Sekiya, M. and Iijima, K. M. (2016). Stabilization of microtubule-unbound Tau via Tau phosphorylation at Ser262/356 by Par-1/MARK contributes to augmentation of AD-related phosphorylation and Aβ42-induced Tau toxicity. PLoS Genet 12: e1005917. PubMed ID: 27023670
Summary:
To prevent the cascade of events leading to neurodegeneration in Alzheimer's disease (AD), it is essential to elucidate the mechanisms underlying the initial events of tau mismetabolism. In this study, using transgenic Drosophila co-expressing human tau and Aβ, tau phosphorylation at AD-related Ser262/356 stabilized microtubule-unbound tau was found in the early phase of tau mismetabolism, leading to neurodegeneration. Aβ increased the level of tau detached from microtubules, independent of the phosphorylation status at GSK3-targeted SP/TP sites. Such mislocalized tau proteins, especially the less phosphorylated species, were stabilized by phosphorylation at Ser262/356 via PAR-1/MARK. Levels of Ser262 phosphorylation were increased by Aβ42, and blocking this stabilization of tau suppressed Aβ42-mediated augmentation of tau toxicity and an increase in the levels of tau phosphorylation at the SP/TP site Thr231, suggesting that this process may be involved in AD pathogenesis. In contrast to PAR-1/MARK, blocking tau phosphorylation at SP/TP sites by knockdown of Sgg/GSK3 did not reduce tau levels, suppress tau mislocalization to the cytosol, or diminish Aβ-mediated augmentation of tau toxicity. These results suggest that stabilization of microtubule-unbound tau by phosphorylation at Ser262/356 via the PAR-1/MARK may act in the initial steps of tau mismetabolism in AD pathogenesis, and that such tau species may represent a potential therapeutic target for AD.

Friday, April 29th

Stroebele, E. and Erives, A. (2016). Integration of orthogonal signaling by the Notch and Dpp pathways in Drosophila. Genetics [Epub ahead of print]. PubMed ID: 26975664
Summary:
The transcription factor Suppressor of Hairless and its co-activator, the Notch intracellular domain, are polyglutamine (pQ)-rich factors that target enhancer elements and interact with other locally-bound pQ-rich factors. To understand the functional repertoire of such enhancers, conserved regulatory regions were identified with binding sites for the pQ-rich effectors of both Notch and BMP/Dpp signaling, and the pQ-deficient tissue selectors Apterous (Ap), Scalloped (Sd), and Vestigial (Vg). The densest such binding site cluster in the genome was found to be located in the BMP-inducible nab locus, a homolog of the vertebrate transcriptional co-factors NAB1/NAB2. This paper reports three major findings. First, this nab enhancer drives dorsal wing margin expression in regions of peak phosphorylated-Mad in wing imaginal discs. Second, Ap was shown to be developmentally required to license the nab dorsal wing margin enhancer (DWME) to read-out Notch and Dpp signaling in the dorsal compartment. Third, the nab DWME was found to be embedded in a complex of intronic enhancers, including a wing quadrant enhancer, a proximal wing disc enhancer, and a larval brain enhancer. This enhancer complex coordinates global nab expression via both tissue-specific activation and inter-enhancer silencing. It is suggested that DWME integration of BMP signaling maintains nab expression in proliferating margin descendants that have divided away from Notch-Delta boundary signaling. As such, uniform expression of genes like nab and vestigial in proliferating compartments would typically require both boundary and non-boundary lineage-specific enhancers.

Natsume-Kitatani, Y. and Mamitsuka, H. (2016). Classification of promoters based on the combination of core promoter elements exhibits different histone modification patterns. PLoS One 11: e0151917. PubMed ID: 27003446
Summary:
The associations between core promoter elements (CPEs) and histone modifications were systematically studied by integrating the Drosophila Core Promoter Database and time-series ChIP-seq data for histone modifications (H3K4me3, H3K27ac, and H3K27me3) during development in Drosophila via the modENCODE project. 96 core promoters were classified into four groups based on the presence or absence of the TATA box or DPE, calculated the histone modification ratio at the core promoter region, and transcribed region for each core promoter. Histone modifications found in TATA-less groups were static during development and the core promoters could be clearly divided into three types: 1) core promoters with continuous active marks (H3K4me3 and H3K27ac), 2) core promoters with a continuous inactive mark (H3K27me3) and occasional active marks, and 3) core promoters with occasional histone modifications. Linear regression analysis and non-linear regression by random forest showed that the TATA-containing groups included core promoters without histone modifications, for which the measured RNA expression values were not predictable accurately from the histone modification status. DPE-containing groups had a higher relative frequency of H3K27me3 in both the core promoter region and transcribed region. In summary, this analysis showed that there was a systematic link between the existence of the CPEs and the dynamics, frequency and influence on transcriptional activity of histone modifications (Natsume-Kitatani, 2016).

El-Sherif, E. and Levine, M. (2016). Shadow enhancers mediate dynamic shifts of gap gene expression in the Drosophila embryo. Curr Biol [Epub ahead of print]. PubMed ID: 27112292
Summary:
Drosophila patterning genes often contain pairs of primary and shadow enhancers that possess overlapping activities. It has been suggested that this regulatory "redundancy" helps ensure reliable activation of gene expression under stressful conditions such as increases in temperature. There is also evidence that shadow enhancers help produce sharp on/off boundaries of gene expression in response to small changes in the levels of regulatory factors, such as the maternal Bicoid gradient. This study uses live-imaging methods to visualize the temporal dynamics of the gap genes Kruppel and knirps, which are essential for the patterning of the thorax and abdomen, respectively. Previous analyses of fixed embryos suggested anterior shifts of the Kruppel and knirps expression patterns. Using computational visualization methods, the precise temporal dynamics of these shifts was revealed which leads to the suggestion that shadow enhancers are crucial for this process. The study also discusses potential mechanisms for enhancer dominance, whereby one enhancer represses the other to foster temporal dynamics.

Kachhap, S., Priyadarshini, P. and Singh, B. (2016). Insights into the Aristaless-Clawless-DNA ternary complex formation. J Biomol Struct Dyn: 1-40. PubMed ID: 27058822
Summary:
Aristaless (Al) and Clawless (Cll) homeodomains that are involved in leg development in Drosophila are known to bind cooperatively to 5'-(T/C)TAATTAA(T/A)(T/A)G-3' DNA sequence but the mechanism of their binding to DNA is unknown. Molecular dynamics (MD) studies have been carried out on binary, ternary and reconstructed protein-DNA complexes involving Al, Cll and DNA along with binding free energy analysis of these complexes. Analysis of MD trajectories of Cll-3A01 binary complex reveals that C-terminal end of helixIII of Cll unwinds in the absence of Al and remains so in reconstructed ternary complex, Cll-3A01-Al. In addition, this change in secondary structure of Cll does not allow it to form protein-protein interactions with Al in the ternary reconstructed complex. However, secondary structure of Cll and its interactions are maintained in other reconstructed ternary complex, Al-3A01-Cll where Cll binds to Al-3A01, binary complex to form ternary complex. These interactions as observed during MD simulations compare well with those observed in ternary crystal structure. Thus, this study highlights the role of secondary structure of helixIII of Cll and protein-protein interactions while proposing likely mechanism of recognition in ternary complex, Al-Cll-DNA.

Thursday, April 28th

Bae, H., Chen, S., Roche, J.P., Ai, M., Wu, C., Diantonio, A. and Graf, E.R. (2016). Rab3-GEF controls active zone development at the Drosophila neuromuscular junction. eNeuro 3(2). PubMed ID: 27022630
Summary:
Synaptic signaling involves the release of neurotransmitter from presynaptic active zones (AZs). Proteins that regulate vesicle exocytosis cluster at AZs, composing the cytomatrix at the active zone (CAZ). At the Drosophila neuromuscular junction (NMJ), the small GTPase Rab3 controls the distribution of CAZ proteins across release sites, thereby regulating the efficacy of individual AZs. This study identifies Rab3-GEF as a second protein that acts in conjunction with Rab3 to control AZ protein composition. At rab3-GEF mutant NMJs, Bruchpilot (Brp) and Ca(2+) channels are enriched at a subset of AZs, leaving the remaining sites devoid of key CAZ components in a manner that is indistinguishable from rab3 mutant NMJs. As the Drosophila homologue of mammalian DENN/MADD and Caenorhabditis elegans AEX-3, Rab3-GEF is a guanine nucleotide exchange factor (GEF) for Rab3 that stimulates GDP to GTP exchange. Mechanistic studies reveal that although Rab3 and Rab3-GEF act within the same mechanism to control AZ development, Rab3-GEF is involved in multiple roles. It was shown that Rab3-GEF is required for transport of Rab3. However, the synaptic phenotype in the rab3-GEF mutant cannot be fully explained by defective transport and loss of GEF activity. A transgenically expressed GTP-locked variant of Rab3 accumulates at the NMJ at wild-type levels and fully rescues the rab3 mutant but is unable to rescue the rab3-GEF mutant. These results suggest that although Rab3-GEF acts upstream of Rab3 to control Rab3 localization and likely GTP-binding, it also acts downstream to regulate CAZ development, potentially as a Rab3 effector at the synapse.

Pezier, A. P., Jezzini, S. H., Bacon, J. P. and Blagburn, J. M. (2016). Shaking B mediates synaptic coupling between auditory sensory neurons and the giant fiber of Drosophila melanogaster. PLoS One 11: e0152211. PubMed ID: 27043822
Summary:
The Johnston's Organ neurons (JONs) form chemical and electrical synapses onto the giant fiber neuron (GF), as part of the neuronal circuit that mediates the GF escape response in Drosophila. This study examined which of the 8 Drosophila innexins (invertebrate gap junction proteins) mediates the electrical connection at this synapse. The GF is known to express Shaking B (ShakB), specifically the ShakBN+16 isoform only, at its output synapses in the thorax. The shakB2 mutation disrupts these GF outputs and also abolishes JON-GF synaptic transmission. The amplitude of the compound action potential recorded in response to sound from the base of the antenna (sound-evoked potential, or SEP) was reduced by RNAi of the innexins Ogre, Inx3, Inx6 and, to a lesser extent Inx2, suggesting that they could be required in JONs for proper development, excitability, or synchronization of action potentials. The strength of the JON-GF connection itself was reduced to background levels only by RNAi of shakB, not of the other seven innexins. ShakB knockdown prevented Neurobiotin coupling between GF and JONs and removed the plaques of ShakB protein immunoreactivity that are present at the region of contact. Specific shakB RNAi lines that are predicted to target the ShakBL or ShakBN isoforms alone did not reduce the synaptic strength, implying that it is ShakBN+16 that is required in the presynaptic neurons. It was also suggested that gap junction proteins may have an instructive role in synaptic target choice.

Nguyen, M. U., Kwong, J., Chang, J., Gillet, V. G., Lee, R. M. and Johnson, K. G. (2016). The extracellular and cytoplasmic domains of Syndecan cooperate postsynaptically to promote synapse growth at the Drosophila neuromuscular junction. PLoS One 11: e0151621. PubMed ID: 26987116
Summary:
The heparan sulfate proteoglycan (HSPG) Syndecan (Sdc) is a crucial regulator of synapse development and growth in both vertebrates and invertebrates. In Drosophila, Sdc binds via its extracellular heparan sulfate (HS) sidechains to the receptor protein tyrosine phosphatase LAR to promote the morphological growth of the neuromuscular junction (NMJ). To date, however, little else is known about the molecular mechanisms by which Sdc functions to promote synapse growth. This study shows that all detectable Sdc found at the NMJ is provided by the muscle, strongly suggesting a post-synaptic role for Sdc. Both the cytoplasmic and extracellular domains of Sdc are required to promote synapse growth or to rescue Sdc loss of function. The results are reported of a yeast two-hybrid screen using the cytoplasmic domains of Sdc as bait, and several novel candidate binding partners were identified for the cytoplasmic domains of Sdc. Together, these studies provide new insight into the mechanism of Sdc function at the NMJ, and provide enticing future directions for further exploring how Sdc promotes synapse growth.

Zandany, N., Marciano, S., Magidovich, E., Frimerman, T., Yehezkel, R., Shem-Ad, T., Lewin, L., Abdu, U., Orr, I. and Yifrach, O. (2015). Alternative splicing modulates Kv channel clustering through a molecular ball and chain mechanism. Nat Commun 6: 6488. PubMed ID: 25813388
Summary:
Ion channel clustering at the post-synaptic density serves a fundamental role in action potential generation and transmission. This study shows that interaction between the Shaker Kv channel and the PSD-95 scaffold protein underlying channel clustering is modulated by the length of the intrinsically disordered C terminal channel tail. It was further shown that this tail functions as an entropic clock that times PSD-95 binding. A 'ball and chain' mechanism is proposed to explain Kv channel binding to scaffold proteins, analogous to the mechanism describing channel fast inactivation. The physiological relevance of this mechanism is demonstrated in that alternative splicing of the Shaker channel gene to produce variants of distinct tail lengths resulted in differential channel cell surface expression levels and clustering metrics that correlate with differences in affinity of the variants for PSD-95. It is suggested that modulating channel clustering by specific spatial-temporal spliced variant targeting serves a fundamental role in nervous system development and tuning.

Wednesday, April 27th

Halberg, K.A., Rainey, S.M., Veland, I.R., Neuert, H., Dornan, A.J., Klämbt, C., Davies, S.A. and Dow, J.A. (2016). The cell adhesion molecule Fasciclin2 regulates brush border length and organization in Drosophila renal tubules. Nat Commun 7: 11266. PubMed ID: 27072072
Summary:
Multicellular organisms rely on cell adhesion molecules to coordinate cell-cell interactions, and to provide navigational cues during tissue formation. In Drosophila, Fasciclin 2 (Fas2) has been intensively studied due to its role in nervous system development and maintenance; yet, Fas2 is most abundantly expressed in the adult renal (Malpighian) tubule rather than in neuronal tissues. The role Fas2 serves in this epithelium is unknown. This study shows that Fas2 is essential to brush border maintenance in renal tubules of Drosophila. Fas2 is dynamically expressed during tubule morphogenesis, localizing to the brush border whenever the tissue is transport competent. Genetic manipulations of Fas2 expression levels impact on both microvilli length and organization, which in turn dramatically affect stimulated rates of fluid secretion by the tissue. Consequently, the study demonstrates a radically different role for this well-known cell adhesion molecule, and proposes that Fas2-mediated intermicrovillar homophilic adhesion complexes help stabilize the brush border.

Chen, J., Kim, S. M. and Kwon, J. Y. (2016). A systematic analysis of Drosophila regulatory peptide expression in enteroendocrine cells. Mol Cells [Epub ahead of print]. PubMed ID: 27025390
Summary:
The digestive system is gaining interest as a major regulator of various functions including immune defense, nutrient accumulation, and regulation of feeding behavior. Intestinal stem cells constantly divide and differentiate into enterocytes that secrete digestive enzymes and absorb nutrients, or enteroendocrine cells that secrete regulatory peptides. This study systemically examined the expression of 45 regulatory peptide genes in the Drosophila midgut, and verified that at least 10 genes are expressed in the midgut enteroendocrine cells through RT-PCR, in situ hybridization, antisera, and 25 regulatory peptide-GAL transgenes. The Drosophila midgut is highly compartmentalized, and individual peptides in enteroendocrine cells were observed to express in specific regions of the midgut. It was also confirmed that some peptides expressed in the same region of the midgut are expressed in mutually exclusive enteroendocrine cells. These results indicate that the midgut enteroendocrine cells are functionally differentiated into different subgroups. Through this study, a basis has been established to study regulatory peptide functions in enteroendocrine cells as well as the complex organization of enteroendocrine cells in the Drosophila midgut.

Lee, J. E., Kim, Y., Kim, K. H., Lee do, Y. and Lee, Y. (2016). Contribution of Drosophila TRPA1 to metabolism. PLoS One 11: e0152935. PubMed ID: 27055172
Summary:
Transient receptor potential (TRP) cation channels are highly conserved in humans and insects. Some of these channels are expressed in internal organs and their functions remain incompletely understood. By direct knock-in of the GAL4 gene into the trpA1 locus in Drosophila, this study identified the expression of this gene in the subesophageal ganglion (SOGs) region. In addition, the neurites present in the dorsal posterior region as well as the Insulin-like peptide 2 (ILP2)-positive neurons send signals to the SOGs. The signal is sent to the crop, which is an enlarged organ of the esophagus and functions as a storage place for food in the digestive system. To systematically investigate the role of TRPA1 in metabolism, non-targeted metabolite profiling analysis together with gas-chromatography/time-of-flight mass spectrometry, were applied with an aim to identify a wide range of primary metabolites. Distinctive metabolomic phenotypes were effectively captured, and specific metabolic dysregulation triggered by TRPA1 mutation was identified based on reconstructed metabolic network analysis. Primarily, the network analysis pinpointed the simultaneous down-regulation of intermediates in the methionine salvation pathway, in contrast to the synchronized up-regulation of a range of free fatty acids. The gene dosage-dependent dynamics of metabolite levels among wild-type, hetero- and homozygous mutants, and their coordinated metabolic modulation under multiple gene settings across five different genotypes confirmed the direct linkages of TRPA1 to metabolism.

Wang, Y., da Cruz, T. C., Pulfemuller, A., Gregoire, S., Ferveur, J. F. and Moussian, B. (2016). Inhibition of fatty acid desaturases in Drosophila melanogaster larvae blocks feeding and developmental progression. Arch Insect Biochem Physiol [Epub ahead of print]. PubMed ID: 27037621
Summary:
Fatty acid desaturases are metabolic setscrews. To study their systemic impact on growth in Drosophila melanogaster, fatty acid desaturases were inhibited using the inhibitor CAY10566. As expected, the amount of desaturated lipids is reduced in larvae fed with CAY10566. These animals cease feeding soon after hatching, and their growth is strongly attenuated. A starvation program is not launched, but the expression of distinct metabolic genes is activated, possibly to mobilize storage material. Without attaining the normal size, inhibitor-fed larvae molt to the next stage indicating that the steroid hormone ecdysone triggers molting correctly. Nevertheless, after molting, expression of ecdysone-dependent regulators is not induced. While control larvae molt a second time, these larvae fail to do so and die after few days of straying. These effects are similar to those observed in experiments using larvae deficient for the fatty acid Desaturase1 gene. Based on these data, it is proposed that the ratio of saturated to unsaturated fatty acids adjusts a sensor system that directs feeding behavior. It is also hypothesized that loss of fatty acid desaturase activity leads to a block of the genetic program of development progression indirectly by switching on a metabolic compensation program.

Tuesday, April 25th

Petruccelli, E., Li, Q., Rao, Y. and Kitamoto, T. (2016). The unique dopamine/ecdysteroid receptor modulates ethanol-induced sedation in Drosophila. J Neurosci 36: 4647-4657. PubMed ID: 27098705
Summary:
Steroids profoundly influence behavioral responses to alcohol by activating canonical nuclear hormone receptors and exerting allosteric effects on ion channels. Accumulating evidence has demonstrated that steroids can also trigger biological effects by directly binding G-protein-coupled receptors (GPCRs), yet physiological roles of such unconventional steroid signaling in controlling alcohol-induced behaviors remain unclear. The dopamine/ecdysteroid receptor (DopEcR) is a GPCR that mediates nongenomic actions of ecdysteroids, the major steroid hormones in insects. This study reports that Drosophila DopEcR plays a critical role in ethanol-induced sedation. DopEcR mutants take longer than control flies to become sedated during exposure to ethanol, despite having normal ethanol absorption or metabolism. RNAi-mediated knockdown of DopEcR expression reveals that this receptor is necessary after eclosion, and is required in particular neuronal subsets, including cholinergic and peptidergic neurons, to mediate this behavior. Additionally, flies ubiquitously overexpressing DopEcR cDNA have a tendency to become sedated quickly upon ethanol exposure. These results indicate that neuronal subset-specific expression of DopEcR in adults is required for normal sedation upon exposure to ethanol. It was also found that DopEcR may promote ethanol sedation by suppressing epidermal growth factor receptor/extracellular signal-regulated kinase signaling. Last, genetic and pharmacological analyses suggest that in adult flies ecdysone may serve as an inverse agonist of DopEcR and suppress the sedation-promoting activity of DopEcR in the context of ethanol exposure. These findings provide the first evidence for the involvement of nongenomic G-protein-coupled steroid receptors in the response to alcohol, and shed new light on the potential roles of steroids in alcohol-use disorders.

Dau, A., Friederich, U., Dongre, S., Li, X., Bollepalli, M. K., Hardie, R. C. and Juusola, M. (2016). Evidence for dynamic network regulation of Drosophila photoreceptor function from mutants lacking the neurotransmitter histamine. Front Neural Circuits 10: 19. PubMed ID: 27047343
Summary:
Synaptic feedback from interneurons to photoreceptors can help to optimize visual information flow by balancing its allocation on retinal pathways under changing light conditions. But little is known about how this critical network operation is regulated dynamically. This study investigated this question by comparing signaling properties and performance of wild-type Drosophila R1-R6 photoreceptors to those of the HdcJK910 mutant, which lacks the neurotransmitter histamine and therefore cannot transmit information to interneurons. Recordings show that HdcJK910 photoreceptors sample similar amounts of information from naturalistic stimulation to wild-type photoreceptors, but this information is packaged in smaller responses, especially under bright illumination. Analyses reveal how these altered dynamics primarily resulted from network overload that affected HdcJK910 photoreceptors in two ways. First, the missing inhibitory histamine input to interneurons almost certainly depolarized them irrevocably, which in turn increased their excitatory feedback to HdcJK910 R1-R6s. This tonic excitation depolarized the photoreceptors to artificially high potentials, reducing their operational range. Second, rescuing histamine input to interneurons in HdcJK910 mutant also restored their normal phasic feedback modulation to R1-R6s, causing photoreceptor output to accentuate dynamic intensity differences at bright illumination, similar to the wild-type. These results provide mechanistic explanations of how synaptic feedback connections optimize information packaging in photoreceptor output and novel insight into the operation and design of dynamic network regulation of sensory neurons.

Cafaro, J. (2016). Multiple sites of adaptation lead to contrast encoding in the Drosophila olfactory system. Physiol Rep 4 [Epub ahead of print]. PubMed ID: 27053295
Summary:
Animals often encounter large increases in odor intensity that can persist for many seconds. These increases in the background odor are often accompanied by increases in the variance of the odor stimulus. Previous studies have shown that a persistent odor stimulus (odor background) results in a decrease in the response to brief odor pulses in the olfactory receptor neurons (ORNs). However, the contribution of adapting mechanisms beyond the ORNs is not clear. Thus, it is unclear how adaptive mechanisms are distributed within the olfactory circuit and what impact downstream adaptation may have on the encoding of odor stimuli. In this study, adaptation to the same odor stimulus is examined at multiple levels in the well studied and accessible Drosophila olfactory system. The responses of the ORNs are compared to the responses of the second order, projection neurons (PNs), directly connected to them. Adaptation in PN spike rate was found to be much greater than adaptation in the ORN spike rate. This greater adaptation allows PNs to encode odor contrast (ratio of pulse intensity to background intensity) with little ambiguity. Moreover, distinct neural mechanisms contribute to different aspects of adaptation; adaptation to the background odor is dominated by adaptation in spike generation in both ORNs and PNs, while adaptation to the odor pulse is dominated by changes within olfactory transduction and the glomerulus. These observations suggest that the olfactory system adapts at multiple sites to better match its response gain to stimulus statistics.

Williams, Z. M. (2016). Transgenerational influence of sensorimotor training on offspring behavior and its neural basis in Drosophila. Neurobiol Learn Mem 131: 166-175. PubMed ID: 27044678
Summary:
Whether specific learning experiences by parents influence the behavior of subsequent generations remains unclear. This study examines whether and what aspects of parental sensorimotor training prior to conception affect the behavior of subsequent generations and identifies the neural circuitries in Drosophila responsible for mediating these effects. Using genetic and anatomic techniques, this study found that both first- and second-generation offspring of parents who underwent prolonged olfactory training over many days displayed a weak but selective approach bias to the same trained odors. However, it was also found that the offspring did not differentiate between orders based on whether parental training was aversive or appetitive. Disruption of both olfactory-receptor and dorsal-paired-medial neuron input into the mushroom bodies abolished this change in offspring response, but disrupting synaptic output from α/β neurons of the mushroom body themselves had little effect on behavior even though they remained necessary for enacting newly trained conditioned responses. This study provides a circuit-based understanding of how specific sensory experiences in Drosophila may bias the behavior of subsequent generations, and identifies a transgenerational dissociation between the effects of conditioned and unconditioned sensory stimuli.

Miazzi, F., Hansson, B. S. and Wicher, D. (2016). Odor induced cAMP production in Drosophila melanogaster olfactory sensory neurons. J Exp Biol [Epub ahead of print]. PubMed ID: 27045092
Summary:
Insect odorant receptors are seven transmembrane domain proteins that form cation channels, whose functional properties such as the receptor sensitivity are subject of regulation by intracellular signaling cascades. This study used the cAMP fluorescent indicator Epac1-camps to investigate the presence of an odor-induced cAMP production in olfactory sensory neurons (OSNs) of Drosophila melanogaster. Stimulation of the receptor complex with an odor mixture or with the synthetic agonist VUAA1 was shown to induces a cAMP response. Moreover, it was shown that while the intracellular Ca2+ concentration influences the cAMP production, an OSN-specific receptor OrX is necessary to elicit cAMP responses in Ca2+-free conditions. These results provide direct evidence of a relationship between odorant receptor stimulation and cAMP production in olfactory sensory neurons in the fly antenna and show that this method can be used to further investigate the role that this second messenger plays in insect olfaction.

Naganos, S., Ueno, K., Horiuchi, J. and Saitoe, M. (2016). Learning defects in Drosophila growth restricted chico mutants are caused by attenuated adenylyl cyclase activity. Mol Brain 9: 37. PubMed ID: 27048332
Summary:
Reduced insulin/insulin-like growth factor signaling (IIS) is a major cause of symmetrical intrauterine growth retardation (IUGR), an impairment in cell proliferation during prenatal development that results in global growth defects and mental retardation. In Drosophila, chico encodes the only insulin receptor substrate. The physiological and molecular bases of learning defects caused by chico mutation are not clear. This study found that chico mutations impair memory-associated synaptic plasticity in the mushroom bodies (MBs), neural centers for olfactory learning. Mutations in chico reduce expression of the rutabaga-type adenylyl cyclase (rut), leading to decreased cAMP synthesis in the MBs. Expressing a rut + transgene in the MBs restores memory-associated plasticity and olfactory associative learning in chico mutants, without affecting growth. Thus chico mutations disrupt olfactory learning, at least in part, by reducing cAMP signaling in the MBs. These results suggest that some cognitive defects associated with reduced IIS may occur, independently of developmental defects, from acute reductions in cAMP signaling.

Monday, April 25th

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

Kwon, S. Y., Grisan, V., Jang, B., Herbert, J. and Badenhorst, P. (2016). Genome-wide mapping targets of the metazoan chromatin remodeling factor NURF reveals nucleosome remodeling at enhancers, core promoters and gene insulators. PLoS Genet 12: e1005969. PubMed ID: 27046080
Summary:
NURF is a conserved higher eukaryotic ISWI-containing chromatin remodeling complex that catalyzes ATP-dependent nucleosome sliding. By sliding nucleosomes, NURF is able to alter chromatin dynamics to control transcription and genome organization. Previous biochemical and genetic analysis of the specificity-subunit of Drosophila NURF (Nurf301/Enhancer of Bithorax (E(bx)) has defined NURF as a critical regulator of homeotic, heat-shock and steroid-responsive gene transcription. This study generated a comprehensive map of in vivo NURF activity, using MNase-sequencing to determine at base pair resolution NURF target nucleosomes, and ChIP-sequencing was used to define sites of NURF recruitment. The data show that, besides anticipated roles at enhancers, NURF interacts physically and functionally with the TRF2/DREF basal transcription factor to organize nucleosomes downstream of active promoters. Moreover, NURF remodeling and recruitment was detected at distal insulator sites, where NURF functionally interacts with and co-localizes with DREF and insulator proteins including CP190 to establish nucleosome-depleted domains. This insulator function of NURF is most apparent at subclasses of insulators that mark the boundaries of chromatin domains, where multiple insulator proteins co-associate. By visualizing the complete repertoire of in vivo NURF chromatin targets, these data provide new insights into how chromatin remodeling can control genome organization and regulatory interactions.

Lv, X., Han, Z., Chen, H., Yang, B., Yang, X., Xia, Y., Pan, C., Fu, L., Zhang, S., Han, H., Wu, M., Zhou, Z., Zhang, L., Li, L., Wei, G. and Zhao, Y. (2016). A positive role for polycomb in transcriptional regulation via H4K20me1. Cell Res. PubMed ID: 27002220
Summary:
The highly conserved polycomb group (PcG) proteins maintain heritable transcription repression of the genes essential for development from fly to mammals. However, sporadic reports imply a potential role of PcGs in positive regulation of gene transcription, although systematic investigation of such function and the underlying mechanism has rarely been reported. This study reports a Pc-mediated, H3K27me3-dependent positive transcriptional regulation of Senseless (Sens), a key transcription factor required for development. Mechanistic studies show that Pc regulates Sens expression by targeting H4K20me1 at the Sens locus. Further bioinformatic analysis at genome-wide level indicates that the existence of H4K20me1 acts as a selective mark for positive transcriptional regulation by Pc/H3K27me3. Both the intensities and specific patterns of Pc and H3K27me3 are important for the fates of target gene transcription. Moreover, binding of transcription factor Broad (Br), which physically interacts with Pc and positively regulates the transcription of Sens, is observed in Pc+H3K27me3+H4K20me1+ genes, but not in Pc+H3K27me3+H4K20me1- genes. Taken together, this study reveals that, coupling the transcription factor Br, Pc positively regulates transcription of Pc+H3K27me3+H4K20me1+ genes in developing Drosophila wing disc.

Ray, P., De, S., Mitra, A., Bezstarosti, K., Demmers, J. A., Pfeifer, K. and Kassis, J. A. (2016). Combgap contributes to recruitment of Polycomb group proteins in Drosophila. Proc Natl Acad Sci U S A [Epub ahead of print]. PubMed ID: 27001825
Summary:
Polycomb group (PcG) proteins are responsible for maintaining the silenced transcriptional state of many developmentally regulated genes. PcG proteins are organized into multiprotein complexes that are recruited to DNA via cis-acting elements known as "Polycomb response elements" (PREs). In Drosophila, PREs consist of binding sites for many different DNA-binding proteins, some known and others unknown. Identification of these DNA-binding proteins is crucial to understanding the mechanism of PcG recruitment to PREs. This study reports the identification of Combgap (Cg), a sequence-specific DNA-binding protein that is involved in recruitment of PcG proteins. Cg can bind directly to PREs via GTGT motifs and colocalizes with the PcG proteins Pleiohomeotic (Pho) and Polyhomeotic (Ph) at the majority of PREs in the genome. In addition, Cg colocalizes with Ph at a number of targets independent of Pho. Loss of Cg leads to decreased recruitment of Ph at only a subset of sites; some of these sites are binding sites for other Polycomb repressive complex 1 (PRC1) components, others are not. These data suggest that Cg can recruit Ph in the absence of PRC1 and illustrate the diversity and redundancy of PcG protein recruitment mechanisms.

Sunday, April 24th

Padash Barmchi, M., Samarasekera, G., Gilbert, M., Auld, V.J. and Zhang, B. (2016). Magi is associated with the Par complex and functions antagonistically with Bazooka to regulate the apical polarity complex. PLoS One 11: e0153259. PubMed ID: 27074039
Summary:
The mammalian MAGI proteins play important roles in the maintenance of adherens and tight junctions. The MAGI family of proteins contains modular domains such as WW and PDZ domains necessary for scaffolding of membrane receptors and intracellular signaling components. Loss of MAGI leads to reduced junction stability while overexpression of MAGI can lead to increased adhesion and stabilization of epithelial morphology. However, how Magi regulates junction assembly in epithelia is largely unknown. This study investigated the single Drosophila homologue of Magi to study the in vivo role of Magi in epithelial development. Magi is localized at the adherens junction and forms a complex with the polarity proteins, Par3/Bazooka and aPKC. A Magi null mutant was generated and found to be viable with no detectable morphological defects even though the Magi protein is highly conserved with vertebrate Magi homologues. However, overexpression of Magi results in the displacement of Baz/Par3 and aPKC and leads to an increase in the level of PIP3. Interestingly, it was found that Magi and Baz function in an antagonistic manner to regulate the localization of the apical polarity complex. Maintaining the balance between the level of Magi and Baz is an important determinant of the levels and localization of apical polarity complex.

Zhang, Y., Rai, M., Wang, C., Gonzalez, C. and Wang, H. (2016). Prefoldin and Pins synergistically regulate asymmetric division and suppress dedifferentiation. Sci Rep 6: 23735. PubMed ID: 27025979
Summary:
Prefoldin is a molecular chaperone complex that regulates tubulin function in mitosis. This study shows that Prefoldin depletion results in disruption of neuroblast polarity, leading to neuroblast overgrowth in Drosophila larval brains. Interestingly, co-depletion of Prefoldin and Partner of Inscuteable (Pins) leads to the formation of gigantic brains with severe neuroblast overgrowth, despite that Pins depletion alone results in smaller brains with partially disrupted neuroblast polarity. This study shows that Prefoldin acts synergistically with Pins to regulate asymmetric division of both neuroblasts and Intermediate Neural Progenitors (INPs). Surprisingly, co-depletion of Prefoldin and Pins also induces dedifferentiation of INPs back into neuroblasts, while depletion either Prefoldin or Pins alone is insufficient to do so. Furthermore, knocking down either α-tubulin or β-tubulin in pins- mutant background results in INP dedifferentiation back into neuroblasts, leading to the formation of ectopic neuroblasts. Overexpression of α-tubulin suppresses neuroblast overgrowth observed in prefoldin pins double mutant brains. These data elucidate an unexpected function of Prefoldin and Pins in synergistically suppressing dedifferentiation of INPs back into neural stem cells.

Lv, X., Pan, C., Zhang, Z., Xia, Y., Chen, H., Zhang, S., Guo, T., Han, H., Song, H., Zhang, L. and Zhao, Y. (2016). SUMO regulates somatic cyst stem cells maintenance and directly targets hedgehog pathway in adult Drosophila testis. Development [Epub ahead of print]. PubMed ID: 27013244
Summary:
SUMO (Small ubiquitin-related modifier) modification (SUMOylation) is a highly dynamic post-translational modification (PTM) playing important roles in tissue development and disease progression. However, its function in adult stem cell maintenance is largely unknown. This study reports the function of SUMOylation in somatic cyst stem cells (CySCs) self-renewal in adult Drosophila testis. The SUMO pathway cell-autonomously regulates CySCs maintenance. Reduction of SUMOylation promotes premature differentiation of CySCs and impedes the proliferation of CySCs, which finally reduce the number of CySCs. Consistently, CySC clones carrying mutation of the SUMO conjugating enzyme are rapidly lost. Furthermore, inhibition of SUMO pathway phenocopies the disruption of Hedgehog (Hh) pathway, and can block the promoted proliferation of CySCs by Hh activation. Importantly, SUMO pathway directly regulates the SUMOylation of Hh pathway transcriptional factor, Cubitus interruptus (Ci), which is required for promoting CySCs proliferation. Thus, it is concluded that SUMO directly targets Hh pathway and regulates CySCs maintenance in adult Drosophila testis.

Carvajal-Gonzalez, J. M., Balmer, S., Mendoza, M., Dussert, A., Collu, G., Roman, A. C., Weber, U., Ciruna, B. and Mlodzik, M. (2015). The clathrin adaptor AP-1 complex and Arf1 regulate planar cell polarity in vivo. Nat Commun 6: 6751. PubMed ID: 25849195
Summary:
A key step in generating a planar cell polarity (PCP) is the formation of restricted junctional domains containing Frizzled/Dishevelled/Diego (Fz/Dsh/Dgo) or Van Gogh/Prickle (Vang/Pk) complexes within the same cell, stabilized via Flamingo (Fmi) across cell membranes. Although models have been proposed for how these complexes acquire and maintain their polarized localization, the machinery involved in moving core PCP proteins around cells remains unknown. This study describes the AP-1 adaptor complex and Arf1 as major regulators of PCP protein trafficking in vivo. AP-1 and Arf1 disruption affects the accumulation of Fz/Fmi and Vang/Fmi complexes in the proximo-distal axis, producing severe PCP phenotypes. Using novel tools, a direct and specific Arf1 involvement was detected in Fz trafficking in vivo. Moreover, a conserved Arf1 PCP function was uncovered in vertebrates. These data support a model whereby the trafficking machinery plays an important part during PCP establishment, promoting formation of polarized PCP-core complexes in vivo.

Saturday, April 23rd

Camino, E. M., Butts, J. C., Ordway, A., Vellky, J. E., Rebeiz, M. and Williams, T. M. (2015). The evolutionary origination and diversification of a dimorphic gene regulatory network through parallel innovations in cis and trans. PLoS Genet 11: e1005136. PubMed ID: 25835988
Summary:
The origination and diversification of morphological characteristics represents a key problem in understanding the evolution of development. Morphological traits result from gene regulatory networks (GRNs) that form a web of transcription factors, which regulate multiple cis-regulatory element (CRE) sequences to control the coordinated expression of differentiation genes. The formation and modification of GRNs must ultimately be understood at the level of individual regulatory linkages (i.e., transcription factor binding sites within CREs) that constitute the network. This study investigated how elements within a network originated and diversified to generate a broad range of abdominal pigmentation phenotypes among Sophophora fruit flies. The data indicates that the coordinated expression of two melanin synthesis enzymes, Yellow and Tan, recently evolved through novel CRE activities that respond to the spatial patterning inputs of Hox proteins and the sex-specific input of Bric-a-brac transcription factors. Once established, it seems that these newly evolved activities were repeatedly modified by evolutionary changes in the network's trans-regulators to generate large-scale changes in pigment pattern. By elucidating how yellow and tan are connected to the web of abdominal trans-regulators, it was discovered that the yellow and tan abdominal CREs are composed of distinct regulatory inputs that exhibit contrasting responses to the same Hox proteins and Hox cofactors. These results provide an example in which CRE origination underlies a recently evolved novel trait, and highlights how coordinated expression patterns can evolve in parallel through the generation of unique regulatory linkages.

Aguilar-Hidalgo, D., Becerra-Alonso, D., Garcia-Morales, D. and Casares, F. (2016). Toward a study of gene regulatory constraints to morphological evolution of the Drosophila ocellar region. Dev Genes Evol [Epub ahead of print]. PubMed ID: 27038024
Summary:
The morphology and function of organs depend on coordinated changes in gene expression during development. These changes are controlled by transcription factors, signaling pathways, and their regulatory interactions, which are represented by gene regulatory networks (GRNs). Therefore, the structure of an organ GRN restricts the morphological and functional variations that the organ can experience-its potential morphospace. Therefore, two important questions arise when studying any GRN: what is the predicted available morphospace and what are the regulatory linkages that contribute the most to control morphological variation within this space. This paper explored these questions by analyzing a small "three-node" GRN model that captures the Hedgehog-driven regulatory interactions controlling a simple visual structure: the ocellar region of Drosophila. Analysis of the model predicts that random variation of model parameters results in a specific non-random distribution of morphological variants. Study of a limited sample of drosophilids and other dipterans finds a correspondence between the predicted phenotypic range and that found in nature. As an alternative to simulations, Bayesian networks methods were applied in order to identify the set of parameters with the largest contribution to morphological variation. The results predict the potential morphological space of the ocellar complex and identify likely candidate processes to be responsible for ocellar morphological evolution using Bayesian networks. The assumptions that the approach that was taken entails and their validity are discussed.

Collet, J.M., Fuentes, S., Hesketh, J., Hill, M.S., Innocenti, P., Morrow, E.H., Fowler, K. and Reuter, M. (2016). Rapid evolution of the intersexual genetic correlation for fitness in Drosophila melanogaster. Evolution 70: 781-795. PubMed ID: 27077679
Summary:
Sexual antagonism (SA) arises when male and female phenotypes are under opposing selection, yet genetically correlated. Until resolved, antagonism limits evolution toward optimal sex-specific phenotypes. Despite its importance for sex-specific adaptation and existing theory, the dynamics of SA resolution are not well understood empirically. This study presents data from Drosophila melanogaster, compatible with a resolution of SA. Two independent replicates of the "LHM" population, in which SA had previously been described, were compared. Both were maintained under identical, controlled conditions, and separated for around 200 generations. Although heritabilities of male and female fitness are similar, the intersexual genetic correlation differs significantly, being negative in one replicate (indicating SA) but close to zero in the other. Using population sequencing, it was shown that phenotypic differences are associated with population divergence in allele frequencies at nonrandom loci across the genome. Large frequency changes are more prevalent in the population without SA and are enriched at loci mapping to genes previously shown to have sexually antagonistic relationships between expression and fitness. These data suggest that rapid evolution toward SA resolution has occurred in one of the populations and open avenues toward studying the genetics of SA and its resolution. 

Sunaga, S., Akiyama, N., Miyagi, R. and Takahashi, A. (2016). Factors underlying natural variation in body pigmentation of Drosophila melanogaster. Genes Genet Syst. PubMed ID: 27021917
Summary:
Molecular mechanisms underlying standing genetic variation of an ecologically relevant trait such as pigmentation trait variation in a model insect, Drosophila melanogaster, are relevant to understanding of different kinds of intergenomic interactions. This study focused on the association between body pigmentation and stress resistance, and on genotype-by-environment interaction, both of which are likely to contribute to the persistence of phenotypic variation in a natural population. First, a significant association was detected between pigmentation traits in females and starvation resistance (darker strains were weaker) and a weak association between pigmentation and chill coma recovery time (darker strains showed shorter recovery time) among 20 inbred strains from the Drosophila melanogaster Genetic Reference Panel (DGRP), which originated from a natural population in North America. These associations revealed a complex relationship between body pigmentation and physiological traits that may give rise to balanced selective forces acting on the traits under fluctuating environmental conditions. Second, using four of the DGRP strains, a substantial degree of genotype (strain) x environment (rearing temperature) interaction was detected among expression levels of the genes encoding effector enzymes in the melanin biosynthesis pathway. These interactions can potentially reduce the efficiency of purifying selection on the pigmentation traits over a wide range of temperature conditions. Finally, possible mechanisms are discussed that contribute to the maintenance of the standing pigmentation variation in this species.

Ragsdale, A. P., Coffman, A. J., Hsieh, P., Struck, T. J. and Gutenkunst, R. N. (2016). Triallelic population genomics for inferring correlated fitness effects of same site nonsynonymous mutations. Genetics [Epub ahead of print]. PubMed ID: 27029732
Summary:
The distribution of mutational effects on fitness is central to evolutionary genetics. Typical univariate distributions, however, cannot model the effects of multiple mutations at the same site, so this study introduced a model in which mutations at the same site have correlated fitness effects. To infer the strength of that correlation, a diffusion approximation to the triallelic frequency spectrum was developed, that was applied to data from Drosophila melanogaster. A moderate positive correlation was found between the fitness effects of nonsynonymous mutations at the same codon, suggesting that both mutation identity and location are important for determining fitness effects in proteins. This approach was validated by comparing to biochemical mutational scanning experiments, finding strong quantitative agreement, even between different organisms. It was also found that the correlation of mutation fitness effects was not affected by protein solvent exposure or structural disorder. Together, these results suggest that the correlation of fitness effects at the same site is a previously overlooked yet fundamental property of protein evolution.
Sheehan, S. and Song, Y. S. (2016). Deep learning for population genetic inference. PLoS Comput Biol 12: e1004845. PubMed ID: 27018908
Summary:
Deep learning makes use of multilayer neural networks to learn a feature-based function from the input (e.g., hundreds of correlated summary statistics of data) to the output (e.g., population genetic parameters of interest). Deep learning was demonstrated to be effectively employed for population genetic inference and learning informative features of data. As a concrete application, this study focused on the challenging problem of jointly inferring natural selection and demography (in the form of a population size change history). The method is able to separate the global nature of demography from the local nature of selection, without sequential steps for these two factors. Studying demography and selection jointly is motivated by Drosophila, where pervasive selection confounds demographic analysis. The method was applied to 197 African Drosophila melanogaster genomes from Zambia to infer both their overall demography, and regions of their genome under selection. Many regions of the genome were found that have experienced hard sweeps, and fewer under selection on standing variation (soft sweep) or balancing selection. Interestingly, it was found that soft sweeps and balancing selection occur more frequently closer to the centromere of each chromosome. In addition, the demographic inference suggests that previously estimated bottlenecks for African Drosophila melanogaster are too extreme.

Friday, April 22nd

Nagel, K.I. and Wilson, R.I. (2016). Mechanisms underlying population response dynamics in inhibitory interneurons of the Drosophila antennal lobe. J Neurosci 36: 4325-4338. PubMed ID: 27076428
Summary:
Local inhibitory neurons control the timing of neural activity in many circuits. To understand how inhibition controls timing, it is important to understand the dynamics of activity in populations of local inhibitory interneurons, as well as the mechanisms that underlie these dynamics. This study describes the in vivo response dynamics of a large population of inhibitory local neurons (LNs) in the Drosophila melanogaster antennal lobe, the analog of the vertebrate olfactory bulb, and dissects the network and intrinsic mechanisms that give rise to these dynamics. Some LNs respond to odor onsets ("ON" cells) and others to offsets ("OFF" cells), whereas still others respond at both times. Moreover, different LNs signal odor concentration fluctuations on different timescales. Some respond rapidly, and can track rapid concentration fluctuations. Others respond slowly, and are best at tracking slow fluctuations. A continuous spectrum of preferred stimulation timescales was found among LNs, as well as a continuum of ON-OFF behavior. Using in vivo whole-cell recordings, it was shown that the timing of an LN's response (ON vs OFF) can be predicted from the interplay of excitatory and inhibitory synaptic currents that it receives. Meanwhile, the preferred timescale of an LN is related to its intrinsic properties. These results illustrate how a population of inhibitory interneurons can collectively encode bidirectional changes in stimulus intensity on multiple timescales, and how this can arise via an interaction between synaptic and intrinsic mechanisms.

Xiao, C. and Robertson, R. M. (2016). Timing of locomotor recovery from anoxia modulated by the white gene in Drosophila. Genetics [Epub ahead of print]. PubMed ID: 27029736
Summary:
Locomotor recovery from anoxia follows the restoration of disordered ion distributions and neuronal excitability. The time taken for locomotor recovery after 30 s anoxia (around 10 min) is longer than the time for the propagation of action potentials to be restored (less than 1 min) in Drosophila wild-type. This study reports that the white (w) gene modulates the timing of locomotor recovery. Wild-type flies displayed fast and consistent recovery of locomotion from anoxia, whereas mutants of w showed significantly delayed and more variable recovery. Genetic analysis including serial backcrossing revealed a strong association between the w locus and the timing of locomotor recovery, and haplo-insufficient function of w+ in promoting fast recovery. The locomotor recovery phenotype was independent of classic eye pigmentation, although both are associated with the w gene. Introducing mini-white (mw+) into w1118 was insufficient to promote fast and consistent locomotor recovery. However, flies carrying w+ duplicated to Y chromosome showed wild-type-like fast locomotor recovery. Furthermore, RNAi knockdown of w in neurons but not glia delayed locomotor recovery, and specifically, knockdown of w in subsets of serotonin neurons was sufficient to delay the locomotor recovery. These data reveal an additional role for w in modulating the timing of locomotor recovery from anoxia.

Erion, R., King, A.N., Wu, G., Hogenesch, J.B. and Sehgal, A. (2016). Neural clocks and Neuropeptide F/Y regulate circadian gene expression in a peripheral metabolic tissue. Elife [Epub ahead of print]. PubMed ID: 27077948
Summary:
Metabolic homeostasis requires coordination between circadian clocks in different tissues. Also, systemic signals appear to be required for some transcriptional rhythms in the mammalian liver and the Drosophila fat body. This study shows that free-running oscillations of the fat body clock require clock function in the PDF-positive cells of the fly brain. Interestingly, rhythmic expression of the cytochrome P450 transcripts, sex-specific enzyme 1 (sxe1) and Cyp6a21, which cycle in the fat body independently of the local clock, depends upon clocks in neurons expressing neuropeptide F (NPF). NPF signaling itself is required to drive cycling of sxe1 and Cyp6a21 in the fat body, and its mammalian ortholog, Npy, functions similarly to regulate cycling of cytochrome P450 genes in the mouse liver. These data highlight the importance of neuronal clocks for peripheral rhythms, particularly in a specific detoxification pathway, and identify a novel and conserved role for NPF/Npy in circadian rhythms.

Suzuki, T., Hasegawa, E., Nakai, Y., Kaido, M., Takayama, R. and Sato, M. (2016). Formation of neuronal circuits by interactions between neuronal populations derived from different origins in the Drosophila visual center. Cell Rep [Epub ahead of print]. PubMed ID: 27068458
Summary:
A wide variety of neurons, including populations derived from different origins, are precisely arranged and correctly connected with their partner to establish a functional neural circuit during brain development. The molecular mechanisms that orchestrate the production and arrangement of these neurons have been obscure. This study demonstrates that cell-cell interactions play an important role in establishing the arrangement of neurons of different origins in the Drosophila visual center. Specific types of neurons born outside the medulla primordium migrate tangentially into the developing medulla cortex. During their tangential migration, these neurons express the repellent ligand Slit, and the two layers that the neurons intercalate between express the receptors Robo2 and Robo3. Genetic analysis suggests that Slit-Robo signaling may control the positioning of the layer cells or their processes to form a path for migration. These results suggest that conserved axon guidance signaling is involved in the interactions between neurons of different origins during brain development.

Becker, H., Renner, S., Technau, G.M. and Berger, C. (2016). Cell-autonomous and non-cell-autonomous function of Hox genes specify segmental neuroblast identity in the gnathal region of the embryonic CNS in Drosophila. PLoS Genet 12: e1005961. PubMed ID: 27015425
Summary:
In thoracic and abdominal segments of Drosophila, the expression pattern of Bithorax-Complex Hox genes is known to specify the segmental identity of neuroblasts (NB) prior to their delamination from the neuroectoderm. This study identified and characterized a set of serially homologous NB-lineages in the gnathal segments and used one of them (NB6-4 lineage) as a model to investigate the mechanism conferring segment-specific identities to gnathal NBs. It was shown that NB6-4 is primarily determined by the cell-autonomous function of the Hox gene Deformed (Dfd). Interestingly, however, it also requires a non-cell-autonomous function of labial and Antennapedia that are expressed in adjacent anterior or posterior compartments. The secreted molecule Amalgam (Ama) was identified as a downstream target of the Antennapedia-Complex Hox genes labial, Dfd, Sex combs reduced and Antennapedia. In conjunction with its receptor Neurotactin (Nrt) and the effector kinase Abelson tyrosine kinase (Abl), Ama is necessary in parallel to the cell-autonomous Dfd pathway for the correct specification of the maxillary identity of NB6-4. Both pathways repress CyclinE (CycE) and loss of function of either of these pathways leads to a partial transformation (40%), whereas simultaneous mutation of both pathways leads to a complete transformation (100%) of NB6-4 segmental identity. Finally, the study provides genetic evidences, that the Ama-Nrt-Abl-pathway regulates CycE expression by altering the function of the Hippo effector Yorkie in embryonic NBs. The disclosure of a non-cell-autonomous influence of Hox genes on neural stem cells provides new insight into the process of segmental patterning in the developing CNS. 

Xiao, X., Zhang, R., Pang, X., Liang, G., Wang, P. and Cheng, G. (2015). A neuron-specific antiviral mechanism prevents lethal flaviviral infection of mosquitoes. PLoS Pathog 11: e1004848. PubMed ID: 25915054
Summary:
Mosquitoes are natural vectors for many etiologic agents of human viral diseases. Mosquito-borne flaviviruses can persistently infect the mosquito central nervous system without causing dramatic pathology or influencing the mosquito behavior and lifespan. The mechanism by which the mosquito nervous system resists flaviviral infection is still largely unknown. This study reports that an Aedes aegypti homologue of the neural factor Hikaru genki (AaHig) efficiently restricts flavivirus infection of the central nervous system. AaHig was predominantly expressed in the mosquito nervous system and localized to the plasma membrane of neural cells. Functional blockade of AaHig enhanced Dengue virus (DENV) and Japanese encephalitis virus (JEV), but not Sindbis virus (SINV), replication in mosquito heads and consequently caused neural apoptosis and a dramatic reduction in the mosquito lifespan. Consistently, delivery of recombinant AaHig to mosquitoes reduced viral infection. Furthermore, the membrane-localized AaHig directly interfaced with a highly conserved motif in the surface envelope proteins of DENV and JEV, and consequently interrupted endocytic viral entry into mosquito cells. Loss of either plasma membrane targeting or virion-binding ability rendered AaHig nonfunctional. Interestingly, Culex pipien pallens Hig also demonstrated a prominent anti-flavivirus activity, suggesting a functionally conserved function for Hig. These results demonstrate that an evolutionarily conserved antiviral mechanism prevents lethal flaviviral infection of the central nervous system in mosquitoes, and thus may facilitate flaviviral transmission in nature.

Thursday, April 21st

Vakaloglou, K. M., Chrysanthis, G. and Zervas, C. G. (2016). IPP complex reinforces adhesion by relaying tension-dependent signals to inhibit integrin turnover. Cell Rep 14: 2668-2682. PubMed ID: 26972014
Summary:
Cytoskeleton-mediated forces regulate the assembly and function of integrin adhesions; however, the underlying mechanisms remain unclear. The tripartite IPP complex, comprising ILK, Parvin, and PINCH, mediates the integrin-actin link at Drosophila embryo muscle attachment sites (MASs). This study demonstrate a developmentally earlier function for the IPP complex: to reinforce integrin-extracellular matrix (ECM) adhesion in response to tension. In IPP-complex mutants, the integrin-ECM linkage at MASs breaks in response to intense muscle contractility. Mechanistically, the IPP complex is required to relay force-elicited signals that decelerate integrin turnover at the plasma membrane so that the integrin immobile fraction is adequate to withstand tension. Epistasis analysis shows that alleviation of muscle contractility, downregulation of endocytosis, and enhanced integrin binding to the ECM are sufficient to restore integrin-ECM adhesion and maintain integrin-adhesome organization in IPP-complex mutants. These findings reveal a role for the IPP complex as an essential mechanosensitive regulatory switch of integrin turnover in vivo.

Castillo-Quan, J.I., Li, L., Kinghorn, K.J., Ivanov, D.K., Tain, L.S., Slack, C., Kerr, F., Nespital, T., Thornton, J., Hardy, J., Bjedov, I. and Partridge, L. (2016). Lithium promotes longevity through GSK3/NRF2-dependent hormesis. Cell Rep [Epub ahead of print]. PubMed ID: 27068460
Summary:
The quest to extend healthspan via pharmacological means is becoming increasingly urgent, both from a health and economic perspective. This study shows that lithium, a drug approved for human use, promotes longevity and healthspan. Lithium was shown to extend lifespan in female and male Drosophila, when administered throughout adulthood or only later in life. The life-extending mechanism involves the inhibition of glycogen synthase kinase-3 (GSK-3) and activation of the transcription factor nuclear factor erythroid 2-related factor (NRF-2). Combining genetic loss of the NRF-2 repressor Kelch-like ECH-associated protein 1 (Keap1) with lithium treatment revealed that high levels of NRF-2 activation confer stress resistance, while low levels additionally promote longevity. The discovery of GSK-3 as a therapeutic target for aging will likely lead to more effective treatments that can modulate mammalian aging and further improve health in later life.

Krishnan, H. R., Li, X., Ghezzi, A. and Atkinson, N. S. (2016). A DNA element in the slo gene modulates ethanol tolerance. Alcohol 51: 37-42. PubMed ID: 26992698
Summary:
In Drosophila, the slo gene encodes BK-type Ca(2+)-activated K(+) channels and is involved in producing rapid functional tolerance to sedation with ethanol. Drosophila are ideal for the study of functional ethanol tolerance because the adult does not acquire metabolic ethanol tolerance. It has been shown that mutations in slo block the capacity to acquire tolerance, that sedation with ethanol vapor induces slo gene expression in the nervous system, and that transgenic induction of slo can phenocopy tolerance. This study used ethanol-induced histone acetylation to map a DNA regulatory element in the slo transcriptional control region. The chromatin immunoprecipitation assay was used to map histone acetylation changes following ethanol sedation to identify an ethanol-responsive DNA element. Ethanol sedation induced an increase in histone acetylation over a 60 n DNA element called 6b, which is situated between the two ethanol-responsive neural promoters of the slo gene. Removal of the 6b element from the endogenous slo gene affected the production of functional ethanol tolerance as assayed in an ethanol-vapor recovery from sedation assay. Removal of element 6b extended the period of functional ethanol tolerance from approximately 10 days to more than 21 days after a single ethanol-vapor sedation. This study demonstrates that mapping the position of ethanol-induced histone acetylation is an effective way to identify DNA regulatory elements that help to mediate the response of a gene to ethanol.

Gleixner, E., Ripp, F., Gorr, T. A., Schuh, R., Wolf, C., Burmester, T. and Hankeln, T. (2016). Knockdown of Drosophila hemoglobin suggests a role in O homeostasis. Insect Biochem Mol Biol 72: 20-30. PubMed ID: 27001071
Summary:
Almost all insects are equipped with a tracheal system, which appears to be sufficient for O2 supply even in phases of high metabolic activity. Therefore, with the exception of a few species dwelling in hypoxic habitats, specialized respiratory proteins had been considered unnecessary in insects. The recent discovery and apparently universal presence of intracellular hemoglobins in insects has remained functionally unexplained. The fruitfly Drosophila melanogaster harbors three different globin genes (referred to as glob1-3). Glob1 is the most highly expressed globin and essentially occurs in the tracheal system and the fat body. To better understand the functions of insect globins, the levels of glob1 were modulated in Drosophila larvae and adults by RNAi-mediated knockdown and transgenic over-expression. No effects on the development were observed in flies with manipulated glob1 levels. However, the knockdown of glob1 led to a significantly reduced survival rate of adult flies under hypoxia (5% and 1.5% O2). Surprisingly, the glob1 knockdown flies also displayed increased resistance towards the reactive oxygen species-forming agent paraquat, which may be explained by a restricted availability of O2 resulting in decreased formation of harmful O2-. In summary, these results suggest an important functional role of glob1 in O2 homeostasis, possibly by enhancing O2 supply.

Wednesday, April 20th

Qi, S. and Calvi, B.R. (2016). Different cell cycle modifications repress apoptosis at different steps independent of developmental signaling in Drosophila. Mol Biol Cell [Epub ahead of print]. PubMed ID: 27075174
Summary:
Apoptotic cell death is important for the normal development of a variety of organisms. Apoptosis is also a response to DNA damage and an important barrier to oncogenesis. The apoptotic response to DNA damage is dampened in specific cell types during development. Developmental signaling pathways can repress apoptosis, and reduced cell proliferation also correlates with a lower apoptotic response. However, because developmental signaling regulates both cell proliferation and apoptosis, the relative contribution of cell division to the apoptotic response has been hard to discern in vivo. This study used Drosophila oogenesis as an in vivo model system to determine the extent to which cell proliferation influences the apoptotic response to DNA damage. It was found that different types of cell cycle modifications are sufficient to repress the apoptotic response to ionizing radiation independent of developmental signaling. The step(s) at which the apoptosis pathway is repressed depends on the type of cell cycle modification; either upstream or downstream of expression of the p53-regulated proapoptotic genes. These findings have important implications for understanding the coordination of cell proliferation with the apoptotic response in development and disease, including cancer and the tissue specific responses to radiation therapy.

Etchegaray, J. I., Elguero, E. J., Tran, J. A., Sinatra, V., Feany, M. B. and McCall, K. (2016). Defective phagocytic corpse processing results in neurodegeneration and can be rescued by TORC1 activation. J Neurosci 36: 3170-3183. PubMed ID: 26985028
Summary:
The removal of apoptotic cell corpses is important for maintaining homeostasis. Previously, defects in apoptotic cell clearance have been linked to neurodegeneration. However, the mechanisms underlying this are still poorly understood. This study reports that the absence of the phagocytic receptor Draper in glia leads to a pronounced accumulation of apoptotic neurons in the brain of Drosophila melanogaster. These dead cells persist in the brain throughout the lifespan of the organism and are associated with age-dependent neurodegeneration. The data indicate that corpses persist because of defective phagosome maturation, rather than recognition defects. TORC1 activation, or inhibition of Atg1, in glia is sufficient to rescue corpse accumulation as well as neurodegeneration. These results suggest that phagocytosis of apoptotic neurons by glia during development is essential for brain homeostasis in adult flies. Furthermore, it suggests that TORC1 regulates Draper-mediated phagosome maturation. Previously, defects in dead cell clearance were linked to neurodegeneration, but the exact mechanisms are not well understood. This study reports that the absence of an engulfment receptor leads to a pronounced accumulation of dead neurons in the brain of the fruit fly Drosophila melanogaster. These dead cells persist in the brain throughout the lifespan of the organism and are associated with age-dependent neurodegeneration. The data indicate that corpses persist because of defective degradation of cells rather than recognition of dead cells.

Aram, L., Braun, T., Braverman, C., Kaplan, Y., Ravid, L., Levin-Zaidman, S. and Arama, E. (2016). A Krebs cycle component limits caspase activation rate through mitochondrial surface restriction of CRL activation. Dev Cell 37: 15-33. PubMed ID: 27052834
Summary:
How cells avoid excessive caspase activity and unwanted cell death during apoptotic caspase-mediated removal of large cellular structures is poorly understood. This study investigated caspase-mediated extrusion of spermatid cytoplasmic contents in Drosophila during spermatid individualization. It was shown that a Krebs cycle component, the ATP-specific form of the succinyl-CoA synthetase β subunit (A-Sβ), binds to and activates the Cullin-3-based ubiquitin ligase (CRL3) complex required for caspase activation in spermatids. In vitro and in vivo evidence suggests that this interaction occurs on the mitochondrial surface, thereby limiting the source of CRL3 complex activation to the vicinity of this organelle and reducing the potential rate of caspase activation by at least 60%. Domain swapping between A-Sβ and the GTP-specific SCSβ (G-Sβ), which functions redundantly in the Krebs cycle, show that the metabolic and structural roles of A-Sβ in spermatids can be uncoupled, highlighting a moonlighting function of this Krebs cycle component in CRL activation. 

Ding, A. X., Sun, G., Argaw, Y. G., Wong, J. O., Easwaran, S. and Montell, D. J. (2016). CasExpress reveals widespread and diverse patterns of cell survival of caspase-3 activation during development. Elife 5. PubMed ID: 27058168
Summary:
Caspase-3 carries out the executioner phase of apoptosis, however under special circumstances, cells can survive its activity. To document systematically where and when cells survive caspase-3 activation in vivo, a system, CasExpress, was designed that drives fluorescent protein expression, transiently or permanently, in cells that survive caspase-3 activation in Drosophila. Widespread survival was discovered of caspase-3 activity. Distinct spatial and temporal patterns emerged in different tissues. Some cells activated caspase-3 during their normal development in every cell and in every animal without evidence of apoptosis. In other tissues, such as the brain, expression was sporadic both temporally and spatially and overlapped with periods of apoptosis. In adults, reporter expression was evident in a large fraction of cells in most tissues of every animal; however the precise patterns varied. Inhibition of caspase activity in wing discs reduced wing size demonstrating functional significance. The implications of these patterns are discussed.

Tuesday, April 19th

Trannoy, S., Penn, J., Lucey, K., Popovic, D. and Kravitz, E.A. (2016). Short and long-lasting behavioral consequences of agonistic encounters between male Drosophila melanogaster. Proc Natl Acad Sci U S A [Epub ahead of print]. PubMed ID: 27071097
Summary:
In many animal species, learning and memory have been found to play important roles in regulating intra- and interspecific behavioral interactions in varying environments. In such contexts, aggression is commonly used to obtain desired resources. Previous defeats or victories during aggressive interactions have been shown to influence the outcome of later contests, revealing loser and winner effects. This study analyzed whether short- and/or long-term behavioral consequences accompany victories and defeats in dyadic pairings between male Drosophila melanogaster and how long those effects remain. The results demonstrate that single fights induce important behavioral changes in both combatants and result in the formation of short-term loser and winner effects. These decay over several hours, with the duration depending on the level of familiarity of the opponents. Repeated defeats induce a long-lasting loser effect that is dependent on de novo protein synthesis, whereas repeated victories have no long-term behavioral consequences. This suggests that separate mechanisms govern the formation of loser and winner effects. The study aims to lay a foundation for future investigations exploring the molecular mechanisms and circuitry underlying the nervous system changes induced by winning and losing bouts during agonistic encounters.

Dissel, S., Seugnet, L., Thimgan, M. S., Silverman, N., Angadi, V., Thacher, P. V., Burnham, M. M. and Shaw, P. J. (2015). Differential activation of immune factors in neurons and glia contribute to individual differences in resilience/vulnerability to sleep disruption. Brain Behav Immun 47: 75-85. PubMed ID: 25451614
Summary:
Individuals frequently find themselves confronted with a variety of challenges that threaten their wellbeing. While some individuals face these challenges efficiently and thrive (resilient) others are unable to cope and may suffer persistent consequences (vulnerable). Resilience/vulnerability to sleep disruption may contribute to the vulnerability of individuals exposed to challenging conditions. With that in mind this study exploited individual differences in a fly's ability to form short-term memory (STM) following 3 different types of sleep disruption to identify the underlying genes. The analysis showed that in each category of flies examined, there are individuals that form STM in the face of sleep loss (resilient) while other individuals show dramatic declines in cognitive behavior (vulnerable). Molecular genetic studies revealed that Antimicrobial Peptides, factors important for innate immunity, were candidates for conferring resilience/vulnerability to sleep deprivation. Specifically, Metchnikowin (Mtk), drosocin (dro) and Attacin (Att) transcript levels seemed to be differentially increased by sleep deprivation in glia (Mtk), neurons (dro) or primarily in the head fat body (Att). Follow-up genetic studies confirmed that expressing Mtk in glia but not neurons, and expressing dro in neurons but not glia, disrupted memory while modulating sleep in opposite directions. These data indicate that various factors within glia or neurons can contribute to individual differences in resilience/vulnerability to sleep deprivation.

Dumenil, C., Woud, D., Pinto, F., Alkema, J. T., Jansen, I., Van Der Geest, A. M., Roessingh, S. and Billeter, J. C. (2016). Pheromonal Cues Deposited by Mated Females Convey Social Information about Egg-Laying Sites in Drosophila Melanogaster. J Chem Ecol [Epub ahead of print]. PubMed ID: 26994611
Summary:
Individuals can make choices based on information learned from others, a phenomenon called social learning. How observers differentiate between which individual they should or should not learn from is, however, poorly understood. This study showed that Drosophila melanogaster females can influence the choice of egg-laying site of other females through pheromonal marking. Mated females mark territories of high quality food by ejecting surplus male sperm containing the aggregation pheromone cis-11-vaccenyl acetate (cVA) and, in addition, deposit several sex- and species-specific cuticular hydrocarbon (CHC) pheromones. These pheromonal cues affect the choices of other females, which respond by preferentially laying eggs on the marked food. This system benefits both senders and responders, as communal egg laying increases offspring survival. Virgin females, however, do not elicit a change in the egg-laying decision of mated females, even when food has been supplemented with ejected sperm from mated females, thus indicating the necessity for additional cues. Genetic ablation of either a female's CHC pheromones or those of their mate results in loss of ability of mated females to attract other females. We conclude that mated females use a pheromonal marking system, comprising cVA acquired from male ejaculate with sex- and species-specific CHCs produced by both mates, to indicate egg-laying sites. This system ensures information reliability because mated, but not virgin, females have both the ability to generate the pheromone blend that attracts other flies to those sites and a direct interest in egg-laying site quality.

Mohammad, F., Aryal, S., Ho, J., Stewart, J. C., Norman, N. A., Tan, T. L., Eisaka, A. and Claridge-Chang, A. (2016). Ancient anxiety pathways influence Drosophila defense behaviors. Curr Biol 26: 981-986. PubMed ID: 27020741
Summary:
Anxiety helps us anticipate and assess potential danger in ambiguous situations; however, the anxiety disorders are the most prevalent class of psychiatric illness. Emotional states are shared between humans and other animals, as observed by behavioral manifestations, physiological responses, and gene conservation. Anxiety research makes wide use of three rodent behavioral assays-elevated plus maze, open field, and light/dark box-that present a choice between sheltered and exposed regions. Exposure avoidance in anxiety-related defense behaviors was confirmed to be a correlate of rodent anxiety by treatment with known anxiety-altering agents and is now used to characterize anxiety systems. Modeling anxiety with a small neurogenetic animal would further aid the elucidation of its neuronal and molecular bases. Drosophila neurogenetics research has elucidated the mechanisms of fundamental behaviors and implicated genes that are often orthologous across species. In an enclosed arena, flies stay close to the walls during spontaneous locomotion, a behavior proposed to be related to anxiety. This study tested this hypothesis with manipulations of the GABA receptor, serotonin signaling, and stress. The effects of these interventions were strikingly concordant with rodent anxiety, verifying that these behaviors report on an anxiety-like state. Application of this method was able to identify several new fly anxiety genes. The presence of conserved neurogenetic pathways in the insect brain identifies Drosophila as an attractive genetic model for the study of anxiety and anxiety-related disorders, complementing existing rodent systems.

Monday, April 18th

Agrawal, P. and Hardin, P. E. (2016). The Drosophila receptor protein tyrosine phosphatase LAR is required for development of circadian pacemaker neuron processes that support rhythmic activity in constant darkness but not during light/dark cycles. J Neurosci 36: 3860-3870. PubMed ID: 27030770
Summary:
Little is known about phosphatases that control clock protein dephosphorylation in Drosophila. This study screened RNAi knockdowns of Drosophila phosphatases for altered activity rhythms. One phosphatase that was identified, the receptor protein tyrosine phosphatase leukocyte-antigen-related (LAR), abolished activity rhythms in constant darkness (DD) without disrupting the timekeeping mechanism in brain pacemaker neurons. However, expression of the neuropeptide pigment-dispersing factor (PDF), which mediates pacemaker neuron synchrony and output, is eliminated in the dorsal projections from small ventral lateral (sLNv) pacemaker neurons when Lar expression is knocked down during development, but not in adults. Loss of Lar function eliminates sLNv dorsal projections, but PDF expression persists in sLNv and large ventral lateral neuron cell bodies and their remaining projections. In contrast to the defects in lights-on and lights-off anticipatory activity seen in flies that lack PDF, LarRNAi knockdown flies anticipate the lights-on and lights-off transition normally. These results demonstrate that Lar is required for sLNv dorsal projection development and suggest that PDF expression in LNv cell bodies and their remaining projections mediate anticipation of the lights-on and lights-off transitions during a light/dark cycle.
Yapici, N., Cohn, R., Schusterreiter, C., Ruta, V. and Vosshall, L.B. (2016). A taste circuit that regulates ingestion by integrating food and hunger signals. Cell [Epub ahead of print]. PubMed ID: 27040496
Summary:
Ingestion is a highly regulated behavior that integrates taste and hunger cues to balance food intake with metabolic needs. To study the dynamics of ingestion in the vinegar fly Drosophila melanogaster, this study developed Expresso, an automated feeding assay that measures individual meal-bouts with high temporal resolution at nanoliter scale. Flies show discrete, temporally precise ingestion that is regulated by hunger state and sucrose concentration. 12 cholinergic local interneurons (IN1, for "ingestion neurons") were found to be necessary for this behavior. Sucrose ingestion causes a rapid and persistent increase in IN1 interneuron activity in fasted flies that decreases proportionally in response to subsequent feeding bouts. Sucrose responses of IN1 interneurons in fed flies are significantly smaller and lack persistent activity. The study proposes that IN1 neurons monitor ingestion by connecting sugar-sensitive taste neurons in the pharynx to neural circuits that control the drive to ingest. Similar mechanisms for monitoring and regulating ingestion may exist in vertebrates.

Isakov, A., Buchanan, S. M., Sullivan, B., Ramachandran, A., Chapman, J. K., Lu, E. S., Mahadevan, L. and de Bivort, B. (2016). Recovery of locomotion after injury in Drosophila depends on proprioception. J Exp Biol. PubMed ID: 26994176
Summary:
Locomotion is necessary for survival in most animal species. However, injuries to the appendages mediating locomotion are common. This study assessed the recovery of walking in Drosophila melanogaster following leg amputation. Whereas flies pre-amputation explore open arenas in a symmetric fashion, foreleg amputation induces a strong turning bias away from the side of the amputation. However, unbiased walking behavior was found to return over time in wild type flies, while recovery is significantly impaired in proprioceptive mutants. To identify the biomechanical basis of this locomotor impairment and recovery, individual leg motion (gait) were examined at a fine scale. A minimal mathematical model that links neurodynamics to body mechanics during walking shows that redistributing leg forces between the right and left side enables the observed recovery. Altogether, this study suggests that proprioceptive input from the intact limbs plays a critical role in the behavioral plasticity associated with locomotor recovery after injury.

D'Rozario, M., Zhang, T., Waddell, E.A., Zhang, Y., Sahin, C., Sharoni, M., Hu, T., Nayal, M., Kutty, K., Liebl, F., Hu, W. and Marenda, D.R. (2016). Type I bHLH proteins Daughterless and Tcf4 restrict neurite branching and synapse formation by repressing Neurexin in postmitotic neurons. Cell Rep [Epub ahead of print]. PubMed ID: 27050508
Summary:
Proneural proteins of the class I/II basic-helix-loop-helix (bHLH) family are highly conserved transcription factors. Class I bHLH proteins are expressed in a broad number of tissues during development, whereas class II bHLH protein expression is more tissue restricted. The understanding of the function of class I/II bHLH transcription factors in both invertebrate and vertebrate neurobiology is largely focused on their function as regulators of neurogenesis. This study shows that the class I bHLH proteins Daughterless and Tcf4 are expressed in postmitotic neurons in Drosophila melanogaster and mice, respectively, where they function to restrict neurite branching and synapse formation. Data indicate that Daughterless performs this function in part by restricting the expression of the cell adhesion molecule Neurexin. This suggests a role for these proteins outside of their established roles in neurogenesis.

Sunday, April 17th

Palu, R.A. and Thummel, C.S. (2016). Sir2 acts through Hepatocyte Nuclear Factor 4 to maintain insulin signaling and metabolic homeostasis in Drosophila. PLoS Genet 12: e1005978. PubMed ID: 27058248
Summary:
SIRT1 is a member of the sirtuin family of NAD+-dependent deacetylases, which couple cellular metabolism to systemic physiology. This study shows that loss of the Drosophila SIRT1 homolog sir2 leads to the age-progressive onset of hyperglycemia, obesity, glucose intolerance, and insulin resistance. Tissue-specific functional studies show that Sir2 is both necessary and sufficient in the fat body to maintain glucose homeostasis and peripheral insulin sensitivity. This study reveals a major overlap with genes regulated by the nuclear receptor Hepatocyte Nuclear Factor 4 (HNF4). Drosophila HNF4 mutants display diabetic phenotypes similar to those of sir2 mutants, and protein levels for dHNF4 are reduced in sir2 mutant animals. Sir2 exerts these effects by deacetylating and stabilizing dHNF4 through protein interactions. Increasing dHNF4 expression in sir2 mutants is sufficient to rescue their insulin signaling defects, defining this nuclear receptor as an important downstream effector of Sir2 signaling. This study provides a genetic model for functional studies of phenotypes related to type 2 diabetes and establishes HNF4 as a critical downstream target by which Sir2 maintains metabolic health. 

Tsokanos, F. F., Albert, M. A., Demetriades, C., Spirohn, K., Boutros, M. and Teleman, A. A. (2016). eIF4A inactivates TORC1 in response to amino acid starvation. EMBO J [Epub ahead of print]. PubMed ID: 26988032
Summary:
Amino acids regulate TOR complex 1 (TORC1) via two counteracting mechanisms, one activating and one inactivating. The presence of amino acids causes TORC1 recruitment to lysosomes where TORC1 is activated by binding Rheb. How the absence of amino acids inactivates TORC1 is less well understood. Amino acid starvation recruits the TSC1/TSC2 complex to the vicinity of TORC1 to inhibit Rheb; however, the upstream mechanisms regulating TSC2 are not known. This study identified the the eIF4A-containing eIF4F translation initiation complex (composed of three subunits: eIF4E, eIF4A and eIF4G) as an upstream regulator of TSC2 in response to amino acid withdrawal in Drosophila. TORC1 and translation preinitiation complexes bind each other. Cells lacking eIF4F components retain elevated TORC1 activity upon amino acid removal. This effect is specific for eIF4F and not a general consequence of blocked translation. This study identifies specific components of the translation machinery as important mediators of TORC1 inactivation upon amino acid removal.

Willsey, H. R., Zheng, X., Carlos Pastor-Pareja, J., Willsey, A. J., Beachy, P. A. and Xu, T. (2016). Localized JNK signaling regulates organ size during development. Elife 5 [Epub ahead of print]. PubMed ID: 26974344
Summary:
A fundamental question of biology is what determines organ size. Despite demonstrations that factors within organs determine their sizes, intrinsic size control mechanisms remain elusive. This study shows that Drosophila wing size is regulated by JNK signaling during development. JNK is active in a stripe along the center of developing wings, and modulating JNK signaling within this stripe changes organ size. This JNK stripe influences proliferation in a non-canonical, Jun-independent manner by inhibiting the Hippo pathway. Localized JNK activity is established by Hedgehog signaling, where Ci elevates dTRAF1 expression. As the dTRAF1 homolog, TRAF4, is amplified in numerous cancers, these findings provide a new mechanism for how the Hedgehog pathway could contribute to tumorigenesis, and, more importantly, provides a new strategy for cancer therapies. Finally, modulation of JNK signaling centers in developing antennae and legs changes their sizes, suggesting a more generalizable role for JNK signaling in developmental organ size control.

Chang, Y. J., Zhou, L., Binari, R., Manoukian, A., Mak, T., McNeill, H. and Stambolic, V. (2016). The Rho guanine nucleotide exchange factor DRhoGEF2 is a genetic modifier of the PI3K pathway in Drosophila. PLoS One 11: e0152259. PubMed ID: 27015411
Summary:
The insulin/IGF-1 signaling pathway mediates various physiological processes associated with human health. Components of this pathway are highly conserved throughout eukaryotic evolution. In Drosophila, the PTEN ortholog and its mammalian counterpart downregulate insulin/IGF signaling by antagonizing the PI3-kinase function. From a dominant loss-of-function genetic screen, this study discovered that mutations of a Dbl-family member, the guanine nucleotide exchange factor DRhoGEF2 (DRhoGEF22(l)04291), suppressed the PTEN-overexpression eye phenotype. dAkt/dPKB phosphorylation, a measure of PI3K signaling pathway activation, increased in the eye discs from the heterozygous DRhoGEF2 wandering third instar larvae. Overexpression of DRhoGEF2, and it's functional mammalian ortholog PDZ-RhoGEF (ArhGEF11), at various stages of eye development, resulted in both dPKB/Akt-dependent and -independent phenotypes, reflecting the complexity in the crosstalk between PI3K and Rho signaling in Drosophila.

Saturday, April 16th

Yassin, A., Debat, V., Bastide, H., Gidaszewski, N., David, J.R. and Pool, J.E. (2016). Recurrent specialization on a toxic fruit in an island Drosophila population. Proc Natl Acad Sci U S A [Epub ahead of print]. PubMed ID: 27044093
Summary:
Recurrent specialization on similar host plants offers a unique opportunity to unravel the evolutionary and genetic mechanisms underlying dietary shifts. Recent studies have focused on ecological races belonging to the same species, but it is hard in many cases to untangle the role of adaptive introgression versus distinct mutations in facilitating recurrent evolution. This study discovered on the island of Mayotte a population of the generalist fly Drosophila yakuba that is strictly associated with noni (Morinda citrifolia). This case strongly resembles Drosophila sechellia, a genetically isolated insular relative of D. yakuba whose intensely studied specialization on toxic noni fruits has always been considered a unique event in insect evolution. Experiments revealed that unlike mainland D. yakuba strains, Mayotte flies show strong olfactory attraction and significant toxin tolerance to noni. Island females strongly discriminate against mainland males, suggesting that dietary adaptation has been accompanied by partial reproductive isolation. Population genomic analysis indicated a recent colonization (~29 kya), at a time when year-round noni fruits may have presented a predictable resource on the small island, with ongoing migration after colonization. This relatively recent time scale allowed the search for putatively adaptive loci based on genetic variation. Strong signals of genetic differentiation were found for several detoxification genes, including a major toxin tolerance locus in D. sechellia. These results suggest that recurrent evolution on a toxic resource can involve similar historical events and common genetic bases, and they establish an important genetic system for the study of early stages of ecological specialization and speciation.

Kang, L., Aggarwal, D. D., Rashkovetsky, E., Korol, A. B. and Michalak, P. (2016). Rapid genomic changes in Drosophila melanogaster adapting to desiccation stress in an experimental evolution system. BMC Genomics 17: 233. PubMed ID: 26979755
Summary:
Experimental evolution studies, coupled with whole genome resequencing and advances in bioinformatics, have become a powerful tool for exploring how populations respond to selection at the genome-wide level, complementary to genome-wide association studies (GWASs) and linkage mapping experiments as strategies to connect genotype and phenotype. This experiment analyzed genomes of Drosophila melanogaster from lines evolving under long-term directional selection for increased desiccation resistance in comparison with control (no-selection) lines. Aadaptive responses to desiccation stress were shown to have exerted extensive footprints on the genomes, manifested through a high degree of fixation of alleles in surrounding neighborhoods of eroded heterozygosity. These patterns were highly convergent across replicates, consistent with signatures of 'soft' selective sweeps, where multiple alleles present as standing genetic variation become beneficial and sweep through the replicate populations at the same time. Albeit much less frequent, line-unique sweep regions with zero or near-zero heterozygosity were also observed, consistent with classic, or 'hard', sweeps, where novel rather than pre-existing adaptive mutations may have been driven to fixation. Genes responsible for cuticle and protein deubiquitination seemed to be central to these selective sweeps. High divergence within coding sequences between selected and control lines was also reflected by significant results of the McDonald-Kreitman and Ka/Ks tests, showing that as many as 347 genes may have been under positive selection. It is concluded that desiccation stress, a common challenge to many organisms inhabiting dry environments, proves to be a very potent selecting factor having a big impact on genome diversity.

Dobler, R. and Reinhardt, K. (2016). Heritability, evolvability, phenotypic plasticity and temporal variation in sperm-competition success of Drosophila melanogaster. J Evol Biol [Epub ahead of print]. PubMed ID: 26990919
Summary:
Sperm-competition success (SCS) is seen as centrally important for evolutionary change: superior fathers sire superior sons and thereby inherit the traits that make them superior. Additional hypotheses, that phenotypic plasticity in SCS and sperm ageing explain variation in paternity, are less considered. Even though various alleles have individually been shown to be correlated with variation in SCS, few studies have addressed the heritability, or evolvability, of overall SCS. Those studies that have, found low or no heritability and have not examined evolvability. They have further not excluded phenotypic plasticity, and temporal effects on SCS, despite their known dramatic effects on sperm function. In Drosophila melanogaster, this study found that both standard components of sperm competition, sperm defence and sperm offence, showed non-significant or insignificant heritability across several offspring cohorts. Instead, the analysis revealed, for the first time, the existence of phenotypic plasticity in SCS across an extreme environment (5% CO2), and an influence of sperm ageing. Evolvability of SCS was substantial for sperm defence but virtually absent for sperm offence. These results suggest that the paradigm of explaining evolution by sperm competition is more complex and will benefit from further experimental work on the heritability or evolvability of SCS, measuring phenotypic plasticity, and separating the effects of sperm competition and sperm ageing.

Seong, K. M., Sun, W., Clark, J. M. and Pittendrigh, B. R. (2016). Splice form variant and amino acid changes in MDR49 confers DDT resistance in transgenic Drosophila. Sci Rep 6: 23355. PubMed ID: 27003579
Summary:
The ATP-binding cassette (ABC) transporters represent a superfamily of proteins that have important physiological roles in both prokaryotes and eukaryotes. In insects, ABC transporters have previously been implicated in insecticide resistance. The 91-R strain of Drosophila melanogaster has been intensely selected with DDT over six decades. A recent selective sweeps analysis of 91-R implicated the potential role of MDR49, an ABC transporter, in DDT resistance, however, to date the details of how MDR49 may play a role in resistance have not been elucidated. This study investigated the impact of structural changes and an alternative splicing event in MDR49 on DDT-resistance in 91-R, as compared to the DDT susceptible strain 91-C. Three amino acid differences in MDR49 were observed when 91-R was compared with 91-C, and only one isoform (MDR49B) was implicated in DDT resistance. A transgenic Drosophila strain containing the 91-R-MDR49B isoform had a significantly higher LD50 value as compared to the 91-C-MDR49B isoform at the early time points (6 h to 12 h) during DDT exposure. These data support the hypothesis that the MDR49B isoform, with three amino acid mutations, plays a role in the early aspects of DDT resistance in 91-R.

Friday, April 15th

Chen, Z., Zhu, J. Y., Fu, Y., Richman, A. and Han, Z. (2016). Wnt4 is required for ostia development in the Drosophila heart. Dev Biol [Epub ahead of print]. PubMed ID: 26994311
Summary:
The Drosophila ostia are valve-like structures in the heart with functional similarity to vertebrate cardiac valves. The Wnt/β-catenin signaling pathway is critical for valve development in zebrafish and mouse, but the key ligand(s) for valve induction remains unclear. This study observed high levels of Wnt4 gene expression in Drosophila ostia progenitor cells, immediately prior to morphological differentiation of these cells associated with ostia formation. This differentiation was blocked in Wnt4 mutants and in flies expressing canonical Wnt signaling pathway inhibitors but not inhibitors of the planar cell polarity pathway. High levels of Wnt4 dependent activation of a canonical Wnt signaling reporter was observed specifically in ostia progenitor cells. In vertebrate valve formation Wnt signaling is active in cells undergoing early endothelial-mesenchymal transition (EMT) and the Wnt9 homolog of Drosophila Wnt4 is expressed in valve progenitors. In demonstrating an essential role for Wnt4 in ostia development this study has identified similarities between molecular and cellular events associated with early EMT during vertebrate valve development and the differentiation and partial delamination of ostia progenitor cells in the process of ostia formation.

Rong, Y. S., Golic, M. M. and Golic, K. G. (2016). The pugilistDominant mutation of Drosophila melanogaster: A simple-sequence repeat disorder reveals localized transport in the eye. PLoS One 11: e0151377. PubMed ID: 26999432
Summary:
The pugilist-Dominant mutation results from fusion of a portion of the gene encoding the tri-functional Methylene Tetrahydrofolate Dehydrogenase to ~1 kb of a heterochromatic satellite repeat. Expression of this fusion gene results in an unusual ring pattern of pigmentation around the eye. By using FLP-mediated DNA mobilization to place different pugD transgenes at pre-selected sites, it was found that variation in repeat length makes a strong contribution to variability of the pug phenotype. This variation is manifest primarily as differences in the thickness of the pigmented ring. Similar phenotypic variation can also be achieved by changing gene copy number. The pugD pattern is not controlled by wingless, which is normally expressed in a similar ring pattern. Finally, it was found that physical injury to a pugD eye can lead to pigment deposition in parts of the eye that would not have been pigmented in the absence of injury. These results are consistent with a model in which a metabolite vital for pigment formation is imported from the periphery of the eye, and pugD limits the extent of its transport towards the center of the eye, thus revealing the existence of a hitherto unknown mechanism of localized transport in the eye.

Xia, B. and de Belle, S. (2016). Transgenerational programming of longevity and reproduction by post-eclosion dietary manipulation in Drosophila. Aging (Albany NY) [Epub ahead of print]. PubMed ID: 27025190
Summary:
Accumulating evidence suggests that early-life diet may program one's health status by causing permanent alternations in specific organs, tissues, or metabolic or homeostatic pathways, and such programming effects may propagate across generations through heritable epigenetic modifications. However, it remains uninvestigated whether postnatal dietary changes may program longevity across generations. To address this question of important biological and public health implications, newly-born flies (F0) were collected and subjected to various post-eclosion dietary manipulations (PDMs) with different protein-carbohydrate (i.e., LP, IP or HP for low-, intermediate- or high-protein) contents or a control diet (CD). Longevity and fecundity analyses were performed with these treated F0 flies and their F1, F2 and F3 offspring, while maintained on CD at all times. The LP and HP PDMs were found to shorten longevity, while the IP PDM extends longevity significantly up to the F3 generation. Furthermore, the LP reduces while the IP PDM increases lifetime fecundity across the F0-F2 generations. These observations establish the first animal model for studying transgenerational inheritance of nutritional programming of longevity, making it possible to investigate the underlying epigenetic mechanisms and identify gene targets for drug discovery in future studies.

Kuleesha, Y., Puah, W. C. and Wasser, M. (2016). A model of muscle atrophy based on live microscopy of muscle remodelling in Drosophila metamorphosis. R Soc Open Sci 3: 150517. PubMed ID: 26998322
Summary:
Genes controlling muscle size and survival play important roles in muscle wasting diseases. In Drosophila melanogaster metamorphosis, larval abdominal muscles undergo two developmental fates. While a doomed population is eliminated by cell death, another persistent group is remodelled and survives into adulthood. To identify and characterize genes involved in the development of remodelled muscles, a workflow was developed consisting of in vivo imaging, targeted gene perturbation and quantitative image analysis. Inhibition of TOR signalling and activation of autophagy promote developmental muscle atrophy in early, while TOR and yorkie activation are required for muscle growth in late pupation. Changes were discovered in the localization of myonuclei during remodelling that involve anti-polar migration leading to central clustering followed by polar migration resulting in localization along the midline. The Cathepsin L orthologue Cp1 was demonstrated to be required for myonuclear clustering in mid, while autophagy contributes to central positioning of nuclei in late metamorphosis. In conclusion, studying muscle remodelling in metamorphosis can provide new insights into the cell biology of muscle wasting.

Benmimoun, B., Haenlin, M. and Waltzer, L. (2016). Blood cell progenitor maintenance: Collier barks out of the niche. Fly (Austin): [Epub ahead of print]. PubMed ID: 26925971
Summary:
Drosophila lymph gland, a larval hematopoietic organ, has emerged as a popular model to study regulatory mechanisms controlling blood cell progenitor fate. In this organ, the Posterior Signaling Centre (PSC), a small group of cells expressing the EBF transcription factor Collier, has been proposed to act as a niche required for progenitor maintenance. Accordingly, several reports showed that PSC size/activity modulation impacts on blood cell differentiation. Yet recent results challenge this model. Indeed, this study found that PSC ablation does not affect hematopoietic progenitor maintenance. This unexpected result led to a reinvestigation of the role of the PSC and collier in hematopoiesis. Consistent with previous findings, the PSC appears required for the production of a specialized blood cell type in response to parasitization. Moreover, the results indicate that the massive blood cell differentiation observed in collier mutant larvae is not due to the lack of PSC but to its expression within the hematopoietic progenitors. A paradigm shift is proposed whereby larval blood cell progenitor maintenance is largely independent of the PSC but requires the cell-autonomous function of collier.

Koyama, T. and Mirth, C. K. (2016). Growth-blocking peptides as nutrition-sensitive signals for insulin secretion and body size regulation. PLoS Biol 14: e1002392. PubMed ID: 26928023
Summary:
In Drosophila, the fat body, functionally equivalent to the mammalian liver and adipocytes, plays a central role in regulating systemic growth in response to nutrition. The fat body senses intracellular amino acids through Target of Rapamycin (TOR) signaling, and produces an unidentified humoral factor(s) to regulate insulin-like peptide (ILP) synthesis and/or secretion in the insulin-producing cells. This study found that two peptides, Growth-Blocking Peptide (GBP1) and CG11395 (GBP2), are produced in the fat body in response to amino acids and TOR signaling. Reducing the expression of GBP1 and GBP2 (GBPs) specifically in the fat body results in smaller body size due to reduced growth rate. In addition, GBPs were found to stimulate ILP secretion from the insulin-producing cells, either directly or indirectly, thereby increasing insulin and insulin-like growth factor signaling activity throughout the body. These findings fill an important gap in understanding of how the fat body transmits nutritional information to the insulin producing cells to control body size.

Thursday, April 14th

Baldwin, K.R., Godena, V.K., Hewitt, V.L. and Whitworth, A.J. (2016). Axonal transport defects are a common phenotype in Drosophila models of ALS. Hum Mol Genet [Epub ahead of print]. PubMed ID: 27056981
Summary:
Amyotrophic lateral sclerosis (ALS) is characterized by the degeneration of motor neurons resulting in a catastrophic loss of motor function. Current therapies are severely limited owing to a poor mechanistic understanding of the pathobiology. Mutations in a large number of genes have now been linked to ALS, including SOD1, TARDBP (TDP-43), FUS and C9orf72. Functional analyses of these genes and their pathogenic mutations have provided great insights into the underlying disease mechanisms. Defective axonal transport is hypothesized to be a key factor in the selective vulnerability of motor nerves due to their extraordinary length and evidence that ALS occurs as a distal axonopathy. Axonal transport is seen as an early pathogenic event that precedes cell loss and clinical symptoms and so represents an upstream mechanism for therapeutic targeting. Studies have begun to describe the impact of a few pathogenic mutations on axonal transport but a broad survey across a range of models and cargos is warranted. This study assessed the axonal transport of different cargos in multiple Drosophila models of ALS. It was found that axonal transport defects are common across all models tested, although they often show a differential effect between mitochondria and vesicle cargos. Motor deficits are also common across the models and generally worsen with age, though surprisingly there isn't a clear correlation between the severity of axonal transport defects and motor ability. These results further support defects in axonal transport as a common factor in models of ALS that may contribute to the pathogenic process.

Furukubo-Tokunaga, K., et al. (2016). DISC1 causes associative memory and neurodevelopmental defects in fruit flies. Mol Psychiatry. PubMed ID: 26976042
Summary:
Originally found in a Scottish family with diverse mental disorders, the DISC1 protein has been characterized as an intracellular scaffold protein that associates with diverse binding partners in neural development. To explore its functions in a genetically tractable system, the human DISC1 was expressed in fruit flies. Overexpression of DISC1 impairs associative memory. Experiments with deletion/mutation constructs have revealed the importance of amino-terminal domain (46-290) for memory suppression whereas carboxyl domain (598-854) and the amino-terminal residues (1-45) including the nuclear localization signal (NLS1) are dispensable. DISC1 overexpression also causes suppression of axonal and dendritic branching of mushroom body neurons, which mediate a variety of cognitive functions in the fly brain. Analyses with deletion/mutation constructs reveal that protein domains 598-854 and 349-402 are both required for the suppression of axonal branching, while amino-terminal domains including NLS1 are dispensable. In contrast, NLS1 was required for the suppression of dendritic branching, suggesting a mechanism involving gene expression. Moreover, domain 403-596 is also required for the suppression of dendritic branching. Overexpression of DISC1 suppresses glutamatergic synaptogenesis in developing neuromuscular junctions. Deletion/mutation experiments have revealed the importance of protein domains 403-596 and 349-402 for synaptic suppression, while amino-terminal domains including NLS1 are dispensable. Finally, DISC1 functionally interacts with the fly homolog of Dysbindin (DTNBP1) via direct protein-protein interaction in developing synapses.

Williams, A.A., White, R., Siniard, A., Corneveaux, J., Huentelman, M. and Duch, C. (2016). MECP2 impairs neuronal structure by regulating KIBRA. Neurobiol Dis [Epub ahead of print]. PubMed ID: 27015692
Summary:
MECP2 is a chromatin-associated protein that binds methylated CpGs and can both activate and repress transcription. Using a Drosophila model of MECP2 gain-of-function, this study identified memory associated Kibra as a target of MECP2 in regulating dendritic growth. It was found that expression of human MECP2 increases kibra expression in Drosophila, and targeted RNAi knockdown of kibra in identified neurons fully rescues dendritic defects as induced by MECP2 gain-of-function. Validation in mouse confirmed that Kibra is similarly regulated by Mecp2 in a mammalian system. It was found that Mecp2 gain-of-function in cultured mouse cortical neurons causes dendritic impairments and increases Kibra levels. Accordingly, Mecp2 loss-of-function in vivo leads to decreased Kibra levels in hippocampus, cortex, and cerebellum. Together, these results functionally link two neuronal genes of high interest in human health and disease and highlight the translational utility of the Drosophila model for understanding MECP2 function.

Dambroise, E., Monnier, L., Ruisheng, L., Aguilaniu, H., Joly, J. S., Tricoire, H. and Rera, M. (2016). Two phases of aging separated by the Smurf transition as a public path to death. Sci Rep 6: 23523. PubMed ID: 27002861
Summary:
Aging's most obvious characteristic is the time dependent increase of an individual's probability to die. This lifelong process is accompanied by a large number of molecular and physiological changes. Although numerous genes involved in aging have been identified in the past decades its leading factors have yet to be determined. To identify the very processes driving aging, an assay has been developed to identify physiologically old individuals in a synchronized population of Drosophila melanogaster. Those individuals show an age-dependent increase of intestinal permeability followed by a high risk of death. In Drosophila, the Smurf phenotype is a dramatic increase of intestinal permeability. This study shows that this physiological marker of aging is conserved in 3 invertebrate species Drosophila mojavensis, Drosophila virilis, Caenorhabditis elegans as well as in 1 vertebrate species Danio rerio. These findings suggest that intestinal barrier dysfunction may be an important event in the aging process conserved across a broad range of species, thus raising the possibility that it may also be the case in Homo sapiens.

Wednesday, April 13

Dhahbi, J.M., Atamna, H., Li, R., Yamakawa, A., Guerrero, N., Lam, H.T., Mote, P. and Spindler, S.R. (2016). MicroRNAs circulate in the hemolymph of Drosophila and accumulate relative to tissue microRNAs in an age-dependent manner. Genomics Insights 9: 29-39. PubMed ID: 27042094
Summary:
In mammals, extracellular miRNAs circulate in biofluids as stable entities that are secreted by normal and diseased tissues, and can enter cells and regulate gene expression. Drosophila melanogaster is a proven system for the study of human diseases. They have an open circulatory system in which hemolymph (HL) circulates in direct contact with all internal organs, in a manner analogous to vertebrate blood plasma. Using deep sequencing, this study shows that Drosophila HL contains RNase-resistant circulating miRNAs (HL-miRNAs). Limited subsets of body tissue miRNAs (BT-miRNAs) accumulate in HL, suggesting that they may be specifically released from cells or particularly stable in HL. Alternatively, they might arise from specific cells, such as hemocytes, that are in intimate contact with HL. Young and old flies accumulate unique populations of HL-miRNAs, suggesting that their accumulation is responsive to the physiological status of the fly. These HL-miRNAs in flies may function similar to the miRNAs circulating in mammalian biofluids. The discovery of these HL-miRNAs will provide a new venue for health and disease-related research in Drosophila.

Harrington, A. W. and Steiniger, M. (2016). Bioinformatic analyses of sense and antisense expression from terminal inverted repeat transposons in Drosophila somatic cells. Fly (Austin): [Epub ahead of print]. PubMed ID: 26986720
Summary:
Generally, transposons move via one of two mechanisms; retrotransposons utilize an RNA intermediate, therefore copying themselves and amplifying throughout the genome, while terminal inverted repeat transposons (TIR Tns) excise DNA sequences from the genome and integrate into a new location. Recently work indicates that retrotransposons in Drosophila tissue culture cells are actively transcribed in the antisense direction. The data support a model in which convergent transcription of retrotransposons from intra element transcription start sites results in complementary RNAs that hybridize to form substrates for Dicer-2, the endogenous small interfering (esi)RNA generating enzyme. This previous analysis has now been extended to TIR Tns. In contrast to retrotransposons, the data show that antisense TIR Tn RNAs result from transcription of intronic TIR Tns oriented antisense to their host genes. Also, disproportionately less esiRNAs are generated from TIR transcripts than from retrotransposons and transcription of very few individual TIR Tns could be confirmed. Collectively, these data support a model in which TIR Tns are regulated at the level of Transposase production while retrotransposons are regulated with esiRNA post-transcriptional mechanisms in Drosophila somatic cells.

Chen, B., Zhang, Y., Zhang, X., Jia, S., Chen, S. and Kang, L. (2016). Genome-wide identification and developmental expression profiling of long noncoding RNAs during Drosophila metamorphosis. Sci Rep 6: 23330. PubMed ID: 26996731
Summary:
An increasing number of long noncoding RNAs (lncRNAs) have been discovered with the recent advances in RNA-sequencing technologies. lncRNAs play key roles across diverse biological processes, and are involved in developmental regulation. However, knowledge about how the genome-wide expression of lncRNAs is developmentally regulated is still limited. This study performed a whole-genome identification of lncRNAs followed by a global expression profiling of these lncRNAs during development in Drosophila melanogaster. Bioinformatic prediction of lncRNAs were combined with stringent filtering of protein-coding transcripts and experimental validation to define a high-confidence set of Drosophila lncRNAs. 1,077 lncRNAs were identified in the given transcriptomes that contain 43,967 transcripts; among these, 646 lncRNAs are novel. In vivo expression profiling of these lncRNAs in 27 developmental processes revealed that the expression of lncRNAs is highly temporally restricted relative to that of protein-coding genes. Remarkably, 21% and 42% lncRNAs were significantly upregulated at late embryonic and larval stage, the critical time for developmental transition. The results highlight the developmental specificity of lncRNA expression, and reflect the regulatory significance of a large subclass of lncRNAs for the onset of metamorphosis. The systematic annotation and expression analysis of lncRNAs during Drosophila development form the foundation for future functional exploration.

Chen, M. J., et al. (2016). Integrating RNA-seq and ChIP-seq data to characterize long non-coding RNAs in Drosophila melanogaster. BMC Genomics 17: 220. PubMed ID: 26969372
Summary:
This study developed a computational approach to identify new long noncoding RNAs (lncRNAs) from two tissue-specific RNA-seq datasets using the poly(A)-enriched and the ribo-zero method, respectively. In these results, 462 novel lncRNA transcripts were identified, that were combined with 4137 previously published lncRNA transcripts into a curated dataset. 61 RNA-seq and 32 ChIP-seq datasets were used to improve the annotation of the curated lncRNAs with regards to transcriptional direction, exon regions, classification, expression in the brain, possession of a poly(A) tail, and presence of conventional chromatin signatures. Furthermore, 30 time-course RNA-seq datasets and 32 ChIP-seq datasets were used to investigate whether the lncRNAs reported by RNA-seq have active transcription signatures. The results showed that more than half of the reported lncRNAs did not have chromatin signatures related to active transcription. To clarify this issue, RT-qPCR experiments were conducted and it was found that ~95.24 % of the selected lncRNAs were truly transcribed, regardless of whether they were associated with active chromatin signatures or not. This study has discovered a large number of novel lncRNAs, which suggests that many remain to be identified in D. melanogaster. For the lncRNAs that are known, this study improved their characterization by integrating a large number of sequencing datasets (93 sets in total) from multiple sources (lncRNAs, RNA-seq and ChIP-seq). The RT-qPCR experiments demonstrated that RNA-seq is a reliable platform to discover lncRNAs. This set of curated lncRNAs with improved annotations can serve as an important resource for investigating the function of lncRNAs in D. melanogaster.

Tuesday, April 12th

Giauque, C.C. and Bickel, S.E. (2016). Heterochromatin-associated proteins HP1a and Piwi collaborate to maintain the association of achiasmate homologs in Drosophila oocytes. Genetics [Epub ahead of print]. PubMed ID: 26984058
Summary:
Accurate segregation of homologous chromosomes during meiosis depends on their ability to remain physically connected throughout prophase I. For homologs that achieve a crossover, sister chromatid cohesion distal to the chiasma keeps them attached until anaphase I. However, in Drosophila melanogaster wild-type oocytes, the 4th chromosomes never recombine and X chromosomes fail to cross over in 6-10% of oocytes. Proper segregation of these achiasmate homologs relies on their pericentric heterochromatin-mediated association, but the mechanism(s) underlying this attachment remains poorly understood. Using an inducible RNAi strategy combined with FISH to monitor centromere proximal association of the achiasmate FM7a/X homolog pair, this study analyzed whether specific heterochromatin-associated proteins are required for the association and proper segregation of achiasmate homologs in Drosophila oocytes. Upon knocking down HP1a, H3K9 methytransferases or the HP1a binding partner Piwi during mid-prophase, significant disruption of pericentric heterochromatin-mediated association of FM7a/X homologs was observed. Furthermore, for both HP1a and Piwi knockdown oocytes, transgenic co-expression of the corresponding wild-type protein is able to rescue RNAi-induced defects. Piwi is stably bound to numerous sites along the meiotic chromosomes, including centromere proximal regions. In addition, reduction of HP1a or Piwi during meiotic prophase induces a significant increase in FM7a/X segregation errors. The study presents a speculative model outlining how HP1a and Piwi could collaborate to keep achiasmate chromosomes associated in a homology dependent manner.

Fabbretti, F., Iannetti, I., Guglielmi, L., Perconti, S., Evangelistella, C., Proietti De Santis, L., Bongiorni, S. and Prantera, G. (2016). Confocal analysis of nuclear lamina behavior during male meiosis and spermatogenesis in Drosophila melanogaster. PLoS One 11: e0151231. PubMed ID: 26963718
Summary:
Lamin family proteins are structural components of a filamentous framework, the nuclear lamina (NL), underlying the inner membrane of nuclear envelope. The NL not only plays a role in nucleus mechanical support and nuclear shaping, but is also involved in many cellular processes including DNA replication, gene expression and chromatin positioning. Spermatogenesis is a very complex differentiation process in which each stage is characterized by nuclear architecture dramatic changes, from the early mitotic stage to the sperm differentiation final stage. Nevertheless, very few data are present in the literature on the NL behavior during this process. This study shows the first and complete description of NL behavior during meiosis and spermatogenesis in Drosophila melanogaster. By confocal imaging, the NL modifications wee characterized from mitotic stages, through meiotic divisions to sperm differentiation with an anti-laminDm0 antibody against the major component of the Drosophila NL. It was observed that continuous changes in the NL structure occurred in parallel with chromatin reorganization throughout the whole process and that meiotic divisions occurred in a closed context. Finally, NL was examined in solofuso meiotic mutant, where chromatin segregation is severely affected, and a strict correlation was found between the presence of chromatin and that of NL.

Elnfati, A. H., Iles, D. and Miller, D. (2016). Nucleosomal chromatin in the mature sperm of Drosophila melanogaster. Genom Data 7: 175-177. PubMed ID: 26981400
Summary:
During spermiogenesis in mammals and many other vertebrate classes, histone-containing nucleosomes are replaced by protamine toroids, which can repackage chromatin at a 10 to 20-fold higher density than in a typical somatic nucleus. However, recent evidence suggests that sperm of many species, including human and mouse retain a small compartment of nucleosomal chromatin, particularly near genes important for embryogenesis. As in mammals, spermiogenesis in the fruit fly, Drosophila melanogaster has also been shown to undergo a programmed substitution of nucleosomes with protamine-like proteins. Using chromatin immunoprecipitation (ChIP) and whole-genome tiling array hybridization (ChIP-chip), supported by immunocytochemical evidence, this stuy shows that in a manner analogous to nucleosomal chromatin retention in mammalian spermatozoa, distinct domains packaged by the canonical histones H2A, H2B, H3 and H4 are present in the fly sperm nucleus. Evidence was also found for the retention of nucleosomes with specific histone H3 trimethylation marks characteristic of chromatin repression (H3K9me3, H3K27me3) and active transcription (H3K36me3).

Helleu, Q., Gerard, P. R., Dubruille, R., Ogereau, D., Prud'homme, B., Loppin, B. and Montchamp-Moreau, C. (2016). Rapid evolution of a Y-chromosome heterochromatin protein underlies sex chromosome meiotic drive. Proc Natl Acad Sci U S A [Epub ahead of print]. PubMed ID: 26979956
Summary:
Sex chromosome meiotic drive, the non-Mendelian transmission of sex chromosomes, is the expression of an intragenomic conflict that can have extreme evolutionary consequences. However, the molecular bases of such conflicts remain poorly understood. This study shows that a young and rapidly evolving X-linked heterochromatin protein 1 (HP1) gene, HP1D2, plays a key role in the classical Paris sex-ratio (SR) meiotic drive occurring in Drosophila simulans. Driver HP1D2 alleles prevent the segregation of the Y chromatids during meiosis II, causing female-biased sex ratio in progeny. HP1D2 accumulates on the heterochromatic Y chromosome in male germ cells, strongly suggesting that it controls the segregation of sister chromatids through heterochromatin modification. This study shows that Paris SR drive is a consequence of dysfunctional HP1D2 alleles that fail to prepare the Y chromosome for meiosis, thus providing evidence that the rapid evolution of genes controlling the heterochromatin structure can be a significant source of intragenomic conflicts.

Monday, April 11th

Liu, Y., Petrovic, A., Rombaut, P., Mosalaganti, S., Keller, J., Raunser, S., Herzog, F. and Musacchio, A. (2016). Insights from the reconstitution of the divergent outer kinetochore of Drosophila melanogaster. Open Biol 6. PubMed ID: 26911624
Summary:
Accurate chromosome segregation during mitosis and meiosis is crucial for cellular and organismal viability. Kinetochores connect chromosomes with spindle microtubules and are essential for chromosome segregation. These large protein scaffolds emerge from the centromere, a specialized region of the chromosome enriched with the histone H3 variant CENP-A. In most eukaryotes, the kinetochore core consists of the centromere-proximal constitutive centromere-associated network (CCAN), which binds CENP-A and contains 16 subunits, and of the centromere-distal Knl1 complex, Mis12 complex, Ndc80 complex (KMN) network, which binds microtubules and contains 10 subunits. In the fruitfly, Drosophila melanogaster, the kinetochore underwent remarkable simplifications. All CCAN subunits, with the exception of centromeric protein C (CENP-C), and two KMN subunits, Dsn1 and Zwint, cannot be identified in this organism. In addition, two paralogues of the KMN subunit Nnf1 (Nnf1a and Nnf1b) are present. Finally, the Spc105R subunit, homologous to human Knl1/CASC5, underwent considerable sequence changes in comparison with other organisms. This study combined biochemical reconstitution with biophysical and structural methods to investigate how these changes reflect on the organization of the Drosophila KMN network. The Nnf1a and Nnf1b paralogues were demonstrated to be subunits of distinct complexes, both of which interact directly with Spc105R and with CENP-C, for the latter of which a binding site was identified on the Mis12 subunit. Our studies shed light on the structural and functional organization of a highly divergent kinetochore particle.

Ayeni, J. O., Audibert, A., Fichelson, P., Srayko, M., Gho, M. and Campbell, S. D. (2016). G2-phase arrest prevents bristle progenitor self-renewal and synchronizes cell divisions with cell fate differentiation. Development [Epub ahead of print]. PubMed ID: 26893341
Summary:
Developmentally regulated cell cycle arrest is a fundamental feature of neurogenesis, whose significance is poorly understood. During Drosophila sensory organ (SO) development, primary progenitor (pI) cells arrest in G2-phase for precisely defined periods. Upon re-entering the cell cycle in response to developmental signals, these G2-arrested precursor cells divide and generate specialized neuronal and non-neuronal cells. To study how G2-phase arrest affects SO lineage specification, pI-cells were forced to divide prematurely. This produced SO with normal neuronal lineages but supernumerary non-neuronal cell types. The reason was that prematurely dividing pI-cells generated a secondary pI-cell that produced a complete SO and an external precursor cell that underwent amplification divisions producing supernumerary non-neural cells. This means that pI-cells are capable to undergo self-renewal before transit to a terminal mode of division. Regulation of G2-phase arrest therefore serves a dual role in SO development: preventing progenitor self-renewal and synchronizing cell division with developmental signals. Cell cycle arrest in G2-phase therefore temporally coordinates the precursor cells proliferation potential with terminal cell fate determination to ensure formation of organs with a normal set of sensory cells.

Richter, M. M., Poznanski, J., Zdziarska, A., Czarnocki-Cieciura, M., Lipinszki, Z., Dadlez, M., Glover, D. M. and Przewloka, M. R. (2016). Network of protein interactions within the Drosophila inner kinetochore. Open Biol 6. PubMed ID: 26911623
Summary:
The kinetochore provides a physical connection between microtubules and the centromeric regions of chromosomes that is critical for their equitable segregation. The trimeric Mis12 sub-complex of the Drosophila kinetochore binds to the mitotic centromere using CENP-C as a platform. However, knowledge of the precise connections between Mis12 complex components and CENP-C has remained elusive despite the fundamental importance of this part of the cell division machinery. This study employed hydrogen-deuterium exchange coupled with mass spectrometry to reveal that Mis12 and Nnf1 (Nnf1a and Nnf1b) form a dimer maintained by interacting coiled-coil (CC) domains within the carboxy-terminal parts of both proteins. Adjacent to these interacting CCs is a carboxy-terminal domain that also interacts with Nsl1. The amino-terminal parts of Mis12 and Nnf1 form a CENP-C-binding surface, which docks the complex and thus the entire kinetochore to mitotic centromeres. Mutational analysis confirms these precise interactions are critical for both structure and function of the complex. Thus, it is concluded the organization of the Mis12-Nnf1 dimer confers upon the Mis12 complex a bipolar, elongated structure that is critical for kinetochore function.
Rai, M., Katti, P. and Nongthomba, U. (2016). Spatio-temporal coordination of cell cycle exit, fusion and differentiation of adult muscle precursors by Drosophila Erect wing (Ewg). Mech Dev [Epub ahead of print]. PubMed ID: 27039019
Summary:
The mechanisms of cell cycle exit by myoblasts during skeletal muscle development are poorly understood. Cell cycle arrest is known to be a prerequisite for myoblast fusion and subsequent differentiation. Despite tremendous knowledge on myoblast fusion and differentiation, tissue-specific factors that spatio-temporally regulate the cell cycle exit are not well known. This study shows that the transcriptional factor/co-activator "Erect wing" (Ewg) synchronises myoblast cell cycle exit with that of the fusion process. Ewg-null myoblasts show delayed temporal development of dorsal longitudinal muscles (DLMs), a group of indirect flight muscles (IFMs), which culminates to abnormal and asymmetric muscle pattern. A role for Ewg in cell cycle exit at G1/S stage is also shown. Reducing Cyclin E dose in Ewg-null mutant rescues the lack of IFMs and flight ability. Thus, Ewg repression of Cyclin E expression is required for the arrest of myoblast proliferation and initiation of myoblast fusion and terminal differentiation.

Sunday, April 10th

Wang, Z., Tacchelly-Benites, O., Yang, E., Thorne, C. A., Nojima, H., Lee, E. and Ahmed, Y. (2016). Wnt/Wingless pathway activation is promoted by a critical threshold of Axin maintained by the tumor suppressor APC and the ADP-ribose polymerase Tankyrase. Genetics [Epub ahead of print]. PubMed ID: 26975665
Summary:
Wnt/β-catenin signal transduction directs metazoan development and is deregulated in numerous human congenital disorders and cancers. In the absence of Wnt stimulation, a multi-protein "destruction complex", assembled by the scaffold protein Axin, targets the key transcriptional activator β-catenin for proteolysis. Axin is maintained at very low levels that limit destruction complex activity, a property that is currently being exploited in the development of novel therapeutics for Wnt-driven cancers. This study used an in vivo approach in Drosophila to determine how tightly basal Axin levels must be controlled for Wnt/Wingless pathway activation, and how Axin stability is regulated. For nearly all Wingless-driven developmental processes, a three- to four-fold increase in Axin was found to be insufficient to inhibit signaling, setting a lower-limit for the threshold level of Axin in the majority of in vivo contexts. Further, both the tumor suppressor Adenomatous polyposis coli (APC) and the ADP-ribose polymerase Tankyrase (Tnks) were found to have evolutionarily conserved roles in maintaining basal Axin levels below this in vivo threshold, and separable domains were defined in Axin that are important for APC- or Tnks-dependent destabilization. Together, these findings reveal that both APC and Tnks maintain basal Axin levels below a critical in vivo threshold to promote robust pathway activation following Wnt stimulation.

Ko, C., Kim, Y.G., Le, T.P. and Choi, K.W. (2016). Twinstar/cofilin is required for regulation of epithelial integrity and tissue growth in Drosophila. Oncogene [Epub ahead of print]. PubMed ID: 27041568
Summary:
Regulation of actin assembly and depolymerization is important for the organization of epithelia. Recent studies have shown that the actin-capping proteins are required to prevent cell extrusion and inappropriate activation of Yorkie (Yki) activity in Drosophila, implicating the importance of actin regulation for epithelial integrity and Yki-dependent tissue growth. However, the role of Twinstar (Tsr), the Drosophila homolog for cofilin/actin depolymerization factor, in epithelial integrity and Hippo signaling is unknown. This study demonstrates that reduction of Tsr by RNA interference (RNAi) or mutant clones in wing disc induces not only F-actin accumulation but also ectopic expression of Wingless (Wg) and Yki target gene expanded. Knockdown of Yki in Tsr-depleted cells reduces the level of ectopic Wg expression. Reduced Tsr also leads to downregulation of cell junction proteins and extrusion of affected cells from the basal part of the epithelium. Rho is upregulated in Tsr-depleted tissue, supporting the Tsr function in the inhibition of cell extrusion from the epithelium. Tsr is also required for blocking cell death and JNK signaling. Ectopic JNK activation induces caspase activation but does not cause cell extrusion. Taken together, these data suggest that Tsr is required for cell survival and tissue growth by regulating JNK and Yki signaling while maintaining the epithelial integrity by controlling cell junctions. The study provides an insight into potential roles of ADF/cofilin in invasive cell migration and tumor suppression in higher animals.

Wiemerslage, L., Gohel, P.A., Maestri, G., Hilmarsson, T.G., Mickael, M., Fredriksson, R., Williams, M.J. and Schioth, H.B. (2016). The Drosophila ortholog of TMEM18 regulates insulin and glucagon-like signaling. J Endocrinol [Epub ahead of print]. PubMed ID: 27029472
Summary:
Transmembrane protein 18 (TMEM18) is an ill-described, obesity-related gene, but few studies have explored its molecular function. This study found SNP data suggesting TMEM18 may be involved in the regulation/physiology of metabolic syndrome based on associations with insulin, HOMAb, triglycerides, and blood sugar. An ortholog, Drosophila Tmem18, was found in the Drosophila genome, was knocked down specifically in insulin-producing cells, and was tested for effects on metabolic function. Data suggest that TMEM18 affects substrate levels through insulin and glucagon signaling, and its downregulation induces a metabolic state resembling type-II diabetes. This work is the first to experimentally describe the metabolic consequences of TMEM18 knockdown, and further supports its association with obesity.

Fischer, P., Preiss, A. and Nagel, A. C. (2016). A triangular connection between Cyclin G, PP2A and Akt1 in the regulation of growth and metabolism in Drosophila. Fly (Austin): [Epub ahead of print]. PubMed ID: 26980713
Summary:
Cyclin G (CycG) has been identified an important modulator of InR/TOR signaling activity in Drosophila. cycG mutant flies are underweight and show a disturbed fat metabolism resembling TOR mutants. InR/TOR signaling activity is disturbed in cycG mutants at the level of Akt1, the central kinase linking InR and TORC1. Akt1 is negatively regulated by protein phosphatase PP2A. Notably the binding of the PP2A B'-regulatory subunit Widerborst (Wdb) to Akt1 is differentially regulated in cycG mutants. Since the metabolic defects of cycG mutant animals are abrogated by a concomitant loss of Wdb, CycG presumably cumbers Akt1 activity at the PP2A nexus. This study shows that Well rounded (Wrd), another B' subunit of PP2A in Drosophila, binds CycG similar to Wdb, and that its loss ameliorates some but not all of the metabolic defects of cycG mutants. A model is proposed whereby the binding of CycG to a particular B'-regulatory subunit influences the tissue specific activity of PP2A, required for the fine tuning of the InR/TOR signaling cascade in Drosophila.

Saturday, April 9th

Levine, M. T., Vander Wende, H. M., Hsieh, E., Baker, E. P. and Malik, H. S. (2016). Recurrent gene duplication diversifies genome defense repertoire in Drosophila. Mol Biol Evol [Epub ahead of print]. PubMed ID: 26979388
Summary:
Transposable elements (TEs) comprise large fractions of many eukaryotic genomes and imperil host genome integrity. The host genome combats these challenges by encoding proteins that silence TE activity. Both the introduction of new TEs via horizontal transfer and TE sequence evolution requires constant innovation of host-encoded TE silencing machinery to keep pace with TEs. One form of host innovation is the adaptation of existing, single-copy host genes. Indeed, host suppressors of TE replication often harbor signatures of positive selection. Such signatures are especially evident in genes encoding the piwi-interacting-RNA pathway of gene silencing, for example, the female germline-restricted TE silencer, HP1D/Rhino. Host genomes can also innovate via gene duplication and divergence. However, the importance of gene family expansions, contractions, and gene turnover to host genome defense has been largely unexplored. This study functionally characterize Oxpecker, a young, tandem duplicate gene of HP1D/rhino. Oxpecker was shown to support female fertility in Drosophila melanogaster and silences several TE families that are incompletely silenced by HP1D/Rhino in the female germline. It was further shown that, like Oxpecker, at least ten additional, structurally diverse, HP1D/rhino-derived daughter and “granddaughter” genes emerged during a short 15-million year period of Drosophila evolution. These young paralogs are transcribed primarily in germline tissues, where the genetic conflict between host genomes and TEs plays out. These findings suggest that gene family expansion is an underappreciated yet potent evolutionary mechanism of genome defense diversification.

Hunter, C.M., Huang, W., Mackay, T.F. and Singh, N.D. (2016). The genetic architecture of natural variation in recombination rate in Drosophila melanogaster. PLoS Genet 12: e1005951. PubMed ID: 27035832
Summary:
Meiotic recombination ensures proper chromosome segregation in many sexually reproducing organisms. Despite this crucial function, rates of recombination are highly variable within and between taxa, and the genetic basis of this variation remains poorly understood. This study exploits natural variation in the inbred, sequenced lines of the Drosophila melanogaster Genetic Reference Panel (DGRP) to map genetic variants affecting recombination rate. A two-step crossing scheme and visible markers were used to measure rates of recombination in a 33 cM interval on the X chromosome and in a 20.4 cM interval on chromosome 3R for 205 DGRP lines. Though it could not be excluded that some biases exist due to viability effects associated with the visible markers used in this study, ~2-fold variation was found in recombination rate among lines. Interestingly, it was further found that recombination rates are uncorrelated between the two chromosomal intervals. A genome-wide association study was performed to identify genetic variants associated with recombination rate in each of the two intervals surveyed. The list of candidate variants and genes associated with recombination rate variation was refined and twenty genes were selected for functional assessment. The study presents strong evidence that five genes are likely to contribute to natural variation in recombination rate in D. melanogaster; these genes lie outside the canonical meiotic recombination pathway. A weak effect of Wolbachia infection was also found on recombination rate and the interchromosomal effect was confirmed. These results highlight the magnitude of population variation in recombination rate present in D. melanogaster and implicate new genetic factors mediating natural variation in this quantitative trait.

Sharp, N.P. and Agrawal, A.F. (2016). Low genetic quality alters key dimensions of the mutational spectrum. PLoS Biol 14: e1002419. PubMed ID: 27015430
Summary:
Mutations affect individual health, population persistence, adaptation, diversification, and genome evolution. There is evidence that the mutation rate varies among genotypes, but the causes of this variation are poorly understood. This study links differences in genetic quality, the number of deleterious alleles already present in the genome, with variation in spontaneous mutation in a Drosophila mutation accumulation experiment. Chromosomes maintained in low-quality genetic backgrounds were found to experience a higher rate of indel mutation and a lower rate of gene conversion in a manner consistent with condition-based differences in the mechanisms used to repair DNA double strand breaks. These aspects of the mutational spectrum are also associated with body mass, suggesting that the effect of genetic quality on DNA repair is mediated by overall condition, and providing a mechanistic explanation for the differences in mutational fitness decline among these genotypes. The rate and spectrum of substitutions is unaffected by genetic quality, but variation was found in the probability of substitutions and indels with respect to several aspects of local sequence context, particularly GC content, with implications for models of molecular evolution and genome scans for signs of selection. The finding that the chances of mutation depend on genetic context and overall condition has important implications for how sequences evolve, the risk of extinction, and human health.

Taylor, M.L., Price, T.A., Skeats, A. and Wedell, N. (2016). Temperature can shape a cline in polyandry, but only genetic variation can sustain it over time. Behav Ecol 27: 462-469. PubMed ID: 27004012
Summary:
Multiple mating by females (polyandry) is a widespread behavior occurring in diverse taxa, species, and populations. Polyandry can also vary widely within species, and individual populations, so that both monandrous and polyandrous females occur together. Genetic differences can explain some of this intraspecific variation in polyandry, but environmental factors are also likely to play a role. One environmental factor that influences many fundamental biological processes is temperature. Higher temperatures have been shown to directly increase remating in laboratory studies of insects. In the longer term, high temperature could also help to drive the evolution of larger-scale patterns of behavior by changing the context-dependent balance of costs and benefits of polyandry across environments. This study examined the relative influence of rearing and mating temperatures on female remating in populations of Drosophila pseudoobscura that show a latitudinal cline in polyandry in nature, using a range of ecologically relevant temperatures. Females of all genotypes were found to remate more at cooler temperatures, which fits with the observation of higher average frequencies of polyandry at higher latitudes in this species. However, the impact of temperature is outweighed by the strong genetic control of remating in females in this species. It is likely that genetic factors provide the primary explanation for the latitudinal cline in polyandry in this species.

Friday, April 8th

Hur, J.K., Luo, Y., Moon, S., Ninova, M., Marinov, G.K., Chung, Y.D. and Aravin, A.A. (2016). Splicing-independent loading of TREX on nascent RNA is required for efficient expression of dual-strand piRNA clusters in Drosophila. Genes Dev 30: 840-855. PubMed ID: 27036967
Summary:
The conserved THO/TREX (transcription/export) complex is critical for pre-mRNA processing and mRNA nuclear export. In metazoa, TREX is loaded on nascent RNA transcribed by RNA polymerase II in a splicing-dependent fashion; however, how TREX functions is poorly understood. This study shows that Thoc5 and other TREX components are essential for the biogenesis of piRNA, a distinct class of small noncoding RNAs that control expression of transposable elements (TEs) in the Drosophila germline. Mutations in TREX lead to defects in piRNA biogenesis, resulting in derepression of multiple TE families, gametogenesis defects, and sterility. TREX components are enriched on piRNA precursors transcribed from dual-strand piRNA clusters and colocalize in distinct nuclear foci that overlap with sites of piRNA transcription. The localization of TREX in nuclear foci and its loading on piRNA precursor transcripts depend on Cutoff, a protein associated with chromatin of piRNA clusters. Finally, it was shown that TREX is required for accumulation of nascent piRNA precursors. These data reveal a novel splicing-independent mechanism for TREX loading on nascent RNA and its importance in piRNA biogenesis. 

Bosch, J.A., Sumabat, T.M. and Hariharan, I.K. (2016). Persistence of RNAi-mediated knockdown in Drosophila complicates mosaic analysis yet enables highly sensitive lineage tracing. Genetics [Epub ahead of print]. PubMed ID: 26984059
Summary:
RNA interference (RNAi) has emerged as a powerful way of reducing gene function in Drosophila melanogaster tissues. By expressing synthetic short hairpin RNAs (shRNAs) using the Gal4/UAS system, knockdown is efficiently achieved in specific tissues or in clones of marked cells. This study shows that knockdown by shRNAs is so potent and persistent that even transient exposure of cells to shRNAs can reduce gene function in their descendants. When using the FLP-out Gal4 method, in some instances, unmarked "shadow RNAi" clones adjacent to Gal4-expressing clones were observed, which may have resulted from brief Gal4 expression following recombination but prior to cell division. Similarly, Gal4 driver lines with dynamic expression patterns can generate shadow RNAi cells after their activity has ceased in those cells. Importantly, these effects can lead to erroneous conclusions regarding the cell autonomy of knockdown phenotypes. This study also investigates the basis of this phenomenon and suggests experimental designs for eliminating ambiguities in interpretation. The persistence of shRNA-mediated knockdown was exploited to design a sensitive lineage-tracing method, i-TRACE, which is capable of detecting even low levels of past reporter expression. Using i-TRACE, transient infidelities in the expression of some cell-identity markers near compartment boundaries in the wing imaginal disc were demonstrated.

Carreira-Rosario, A., Bhargava, V., Hillebrand, J., Kollipara, R. K., Ramaswami, M. and Buszczak, M. (2016). Repression of Pumilio protein expression by Rbfox1 promotes germ cell differentiation. Dev Cell 36: 562-571. PubMed ID: 26954550
Summary:
RNA-binding Fox (Rbfox) proteins have well-established roles in regulating alternative splicing, but specific Rbfox isoforms lack nuclear localization signals and accumulate in the cytoplasm. The potential splicing-independent functions of these proteins remain unknown. This study demonstrates that cytoplasmic Drosophila Rbfox1 regulates germ cell development and represses the translation of mRNAs containing (U)GCAUG elements within their 3'UTRs. During germline cyst differentiation, Rbfox1 targets pumilio mRNA for destabilization and translational silencing, thereby promoting germ cell development. Mis-expression of pumilio results in the formation of germline tumors, which contain cysts that break down and dedifferentiate back to single, mitotically active cells. Together, these results reveal that cytoplasmic Rbfox family members regulate the translation of specific target mRNAs. In the Drosophila ovary, this activity provides a genetic barrier that prevents germ cells from reverting back to an earlier developmental state. The finding that Rbfox proteins regulate mRNA translation has implications for Rbfox-related diseases.

Raisch, T., Bhandari, D., Sabath, K., Helms, S., Valkov, E., Weichenrieder, O. and Izaurralde, E. (2016). Distinct modes of recruitment of the CCR4-NOT complex by Drosophila and vertebrate Nanos. EMBO J. PubMed ID: 26968986
Summary:
Nanos proteins repress the expression of target mRNAs by recruiting effector complexes through non-conserved N-terminal regions. In vertebrates, Nanos proteins interact with the NOT1 subunit of the CCR4-NOT effector complex through a NOT1 interacting motif (NIM), which is absent in Nanos orthologs from several invertebrate species. Therefore, it has remained unclear whether the Nanos repressive mechanism is conserved and whether it also involves direct interactions with the CCR4-NOT deadenylase complex (see Drosophila Twin) in invertebrates. This study identified an effector domain (NED) that is necessary for the Drosophila melanogaster (Dm) Nanos to repress mRNA targets. The NED recruits the CCR4-NOT complex through multiple and redundant binding sites, including a central region that interacts with the NOT module, which comprises the C-terminal domains of NOT1-3. The crystal structure of the NED central region bound to the NOT module reveals an unanticipated bipartite binding interface that contacts NOT1 and NOT3 and is distinct from the NIM of vertebrate Nanos. Thus, despite the absence of sequence conservation, the N-terminal regions of Nanos proteins recruit CCR4-NOT to assemble analogous repressive complexes.

Thursday, April 7th

Garaulet, D.L., Sun, K., Li, W., Wen, J., Panzarino, A.M., O'Neil, J.L., Hiesinger, P.R., Young, M.W. and Lai, E.C. (2016). miR-124 regulates diverse aspects of rhythmic behavior in Drosophila. J Neurosci 36: 3414-3421. PubMed ID: 27013671
Summary:
Circadian clocks enable organisms to anticipate and adapt to fluctuating environmental conditions. Despite substantial knowledge of central clock machineries, there is less understanding of how the central clock's behavioral outputs are regulated. This study identifies Drosophila miR-124 as a critical regulator of diurnal activity. During normal light/dark cycles, mir-124 mutants exhibit profoundly abnormal locomotor activity profiles, including loss of anticipatory capacities at morning and evening transitions. Moreover, mir-124 mutants exhibit striking behavioral alterations in constant darkness (DD), including a temporal advance in peak activity. Nevertheless, anatomical and functional tests demonstrate a normal circadian pacemaker in mir-124 mutants, indicating this miRNA regulates clock output. Among the extensive miR-124 target network, heterozygosity for targets in the BMP pathway substantially correct the evening activity phase shift in DD. Thus, excess BMP signaling drives specific circadian behavioral output defects in mir-124 knock-outs.

Lacin, H. and Truman, J. W. (2016). Lineage mapping identifies molecular and architectural similarities between the larval and adult Drosophila central nervous system. Elife 5 [Epub ahead of print]. PubMed ID: 26975248
Summary:
Neurogenesis in Drosophila occurs in two phases, embryonic and post-embryonic, in which the same set of neuroblasts give rise to the distinct larval and adult nervous systems, respectively. This study identified the embryonic neuroblast origin of the adult neuronal lineages in the ventral nervous system via lineage-specific GAL4 lines and molecular markers. This lineage mapping revealed that neurons born late in the embryonic phase show axonal morphology and transcription factor profiles that are similar to the neurons born post-embryonically from the same neuroblast. Moreover, three thorax-specific neuroblasts not previously characterized were identified, and it was shown that HOX genes confine them to the thoracic segments. Two of these, NB2-3 and NB3-4, generate leg motor neurons. The other neuroblast is novel and appears to have arisen recently during insect evolution. These findings provide a comprehensive view of neurogenesis and show how proliferation of individual neuroblasts is dictated by temporal and spatial cues.
Schneider-Mizell, C. M., Gerhard, S., Longair, M., Kazimiers, T., Li, F., Zwart, M. F., Champion, A., Midgley, F. M., Fetter, R. D., Saalfeld, S. and Cardona, A. (2016). Quantitative neuroanatomy for connectomics in Drosophila. Elife 5. PubMed ID: 26990779
Summary:
Neuronal circuit mapping using electron microscopy demands laborious proofreading or reconciliation of multiple independent reconstructions. This study describes new methods to apply quantitative arbor and network context to iteratively proofread and reconstruct circuits and create anatomically enriched wiring diagrams. The morphological underpinnings of connectivity were measured in new and existing reconstructions of Drosophila sensorimotor (larva) and visual (adult) systems. Synaptic inputs were preferentially located on numerous small, microtubule-free 'twigs' which branch off a single microtubule-containing 'backbone'. Omission of individual twigs accounted for 96% of errors. However, the synapses of highly connected neurons were distributed across multiple twigs. Thus, the robustness of a strong connection to detailed twig anatomy was associated with robustness to reconstruction error. By comparing iterative reconstruction to the consensus of multiple reconstructions, it was shown that this method overcomes the need for redundant effort through the discovery and application of relationships between cellular neuroanatomy and synaptic connectivity.

Kulkarni, A., Ertekin, D., Lee, C. H. and Hummel, T. (2016). Birth order dependent growth cone segregation determines synaptic layer identity in the visual system. Elife 5. PubMed ID: 26987017
Summary:
The precise recognition of appropriate synaptic partner neurons is a critical step during neural circuit assembly. However, little is known about the developmental context in which recognition specificity is important to establish synaptic contacts. This study shows that in the Drosophila visual system, sequential segregation of photoreceptor afferents, reflecting their birth order, lead to differential positioning of their growth cones in the early target region. By combining loss- and gain-of-function analyses it was demonstrated that relative differences in the expression of the transcription factor Sequoia regulate R cell growth cone segregation. This initial growth cone positioning is consolidated via cell-adhesion molecule Capricious in R8 axons. Further, the initial growth cone positioning was shown to determine synaptic layer selection through proximity-based axon-target interactions. Taken together, this study demonstrates that birth order dependent pre-patterning of afferent growth cones is an essential pre-requisite for the identification of synaptic partner neurons during visual map formation in Drosophila.

Kidd, S. and Lieber, T. (2016). Mechanism of Notch pathway activation and its role in the regulation of olfactory plasticity in Drosophila melanogaster. PLoS One 11: e0151279. PubMed ID: 26986723
Summary:
The neural plasticity of sensory systems is being increasingly recognized as playing a role in learning and memory. Notch, part of an evolutionarily conserved intercellular signaling pathway, is required in adult Drosophila melanogaster olfactory receptor neurons (ORNs) for the structural and functional plasticity of olfactory glomeruli that is induced by chronic odor exposure. This paper addresses how long-term exposure to odor activates Notch and how Notch in conjunction with chronic odor mediates olfactory plasticity. Upon chronic odor exposure a non-canonical Notch pathway mediates an increase in the volume of glomeruli by a mechanism that is autonomous to ORNs. In addition to activating a pathway that is autonomous to ORNs, chronic odor exposure also activates the Notch ligand Delta in second order projection neurons (PNs), but this does not appear to require acetylcholine receptor activation in PNs. Delta on PNs then feeds back to activate canonical Notch signaling in ORNs, which restricts the extent of the odor induced increase in glomerular volume. Surprisingly, even though the pathway that mediates the increase in glomerular volume is autonomous to ORNs, nonproductive transsynaptic Delta/Notch interactions that do not activate the canonical pathway can block the increase in volume. In conjunction with chronic odor, the canonical Notch pathway also enhances cholinergic activation of PNs. Evidence is presented suggesting that this is due to increased acetylcholine release from ORNs. In regulating physiological plasticity, Notch functions solely by the canonical pathway, suggesting that there is no direct connection between morphological and physiological plasticity.

Majeed, Z. R., Abdeljaber, E., Soveland, R., Cornwell, K., Bankemper, A., Koch, F. and Cooper, R. L. (2016). Modulatory action by the serotonergic system: behavior and neurophysiology in Drosophila melanogaster. Neural Plast 2016: 7291438. PubMed ID: 26989517
Summary:
Serotonin modulates various physiological processes and behaviors. This study investigates the role of 5-HT in locomotion and feeding behaviors as well as in modulation of sensory-motor circuits. The 5-HT biosynthesis was dysregulated by feeding Drosophila larvae 5-HT, a 5-HT precursor, or an inhibitor of tryptophan hydroxylase during early stages of development. The effects of feeding fluoxetine, a selective serotonin reuptake inhibitor, during early second instars were also examined. 5-HT receptor subtypes were manipulated using RNA interference mediated knockdown and 5-HT receptor insertional mutations. Moreover, synaptic transmission at 5-HT neurons was blocked or enhanced in both larvae and adult flies. The results demonstrate that disruption of components within the 5-HT system significantly impairs locomotion and feeding behaviors in larvae. Acute activation of 5-HT neurons disrupts normal locomotion activity in adult flies. To determine which 5-HT receptor subtype modulates the evoked sensory-motor activity, pharmacological agents were used. In addition, the activity of 5-HT neurons was enhanced by expressing and activating TrpA1 channels or channelrhodopsin-2 while recording the evoked excitatory postsynaptic potentials (EPSPs) in muscle fibers. 5-HT2 receptor activation mediates a modulatory role in a sensory-motor circuit, and the activation of 5-HT neurons can suppress the neural circuit activity, while fluoxetine can significantly decrease the sensory-motor activity.

Wednesday, April 6th

Carvajal-Gonzalez, J.M., Roman, A.C. and Mlodzik, M. (2016). Positioning of centrioles is a conserved readout of Frizzled planar cell polarity signalling. Nat Commun 7: 11135. PubMed ID: 27021213
Summary:
Planar cell polarity (PCP) signalling is a well-conserved developmental pathway regulating cellular orientation during development. An evolutionarily conserved pathway readout is not established and, moreover, it is thought that PCP mediated cellular responses are tissue-specific. A key PCP function in vertebrates is to regulate coordinated centriole/cilia positioning, a function that has not been associated with PCP in Drosophila. This study reports instructive input of Frizzled-PCP (Fz/PCP) signalling into polarized centriole positioning in Drosophila wings. It was shown that centrioles are polarized in pupal wing cells as a readout of PCP signalling, with both gain and loss-of-function Fz/PCP signalling affecting centriole polarization. Importantly, loss or gain of centrioles does not affect Fz/PCP establishment, implicating centriolar positioning as a conserved PCP-readout, likely downstream of PCP-regulated actin polymerization. Together with vertebrate data, these results suggest a unifying model of centriole/cilia positioning as a common downstream effect of PCP signalling from flies to mammals.

Nagel, A. C., Szawinski, J., Zimmermann, M. and Preiss, A. (2016). Drosophila Cyclin G is a regulator of the Notch signalling Pathway during wing development. PLoS One 11: e0151477. PubMed ID: 26963612
Summary:
Notch activity is required for proper wing vein differentiation which is hampered in mutants of either the receptor Notch, the ligand Delta or the antagonist Hairless. Moreover, the Notch pathway is involved in several aspects of Drosophila oogenesis as well. This study has identified Drosophila Cyclin G (CycG) as a molecular interaction partner of Hairless, the major antagonist in the Notch signalling pathway. Loss of CycG was shown before to cause female sterility and to disturb the architecture of the egg shell. Nevertheless, Notch dependent processes during oogenesis appeared largely unaffected in cycG mutant egg chambers. Loss of CycG modified the dominant wing phenotypes of Notch, Delta and Hairless mutants. Whereas the Notch loss of function phenotype was ameliorated by a loss of CycG, the phenotypes of either Notch gain of function or of Delta or Hairless loss of function were enhanced. In contrast, loss of CycG had only a minor effect on the wing vein phenotype of mutants affecting the EGFR signalling pathway emphasizing the specificity of the interaction of CycG and Notch pathway members.

Orme, M. H., et al. (2016). The unconventional myosin CRINKLED and its mammalian orthologue MYO7A regulate caspases in their signalling roles. Nat Commun 7: 10972. PubMed ID: 26960254
Summary:
Caspases provide vital links in non-apoptotic regulatory networks controlling inflammation, compensatory proliferation, morphology and cell migration. How caspases are activated under non-apoptotic conditions and process a selective set of substrates without killing the cell remain enigmatic. This study found that the Drosophila unconventional myosin Crinkled (Ck) selectively interacts with the initiator caspase DRONC and regulates some of its non-apoptotic functions. Loss of CK in the arista, border cells or proneural clusters of the wing imaginal discs affects DRONC-dependent patterning. The data indicate that CK acts as substrate adaptor, recruiting Shaggy46/GSK3-β to DRONC, thereby facilitating caspase-mediated cleavage and localized modulation of kinase activity. Similarly, the mammalian CK counterpart, MYO7A, binds to and impinges on CASPASE-8, revealing a new regulatory axis affecting receptor interacting protein kinase-1 (RIPK1)>CASPASE-8 signalling. Together, these results expose a conserved role for unconventional myosins in transducing caspase-dependent regulation of kinases, allowing them to take part in specific signalling events.

Lindstrom, R., Lindholm, P., Kallijarvi, J., Palgi, M., Saarma, M. and Heino, T. I. (2016). Exploring the Conserved role of MANF in the unfolded protein response in Drosophila melanogaster. PLoS One 11: e0151550. PubMed ID: 26975047
Summary:
Disturbances in the homeostasis of endoplasmic reticulum (ER) referred to as ER stress is involved in a variety of human diseases. ER stress activates unfolded protein response (UPR), a cellular mechanism the purpose of which is to restore ER homeostasis. Previous studies show that Mesencephalic Astrocyte-derived Neurotrophic Factor (MANF) is an important novel component in the regulation of UPR. In vertebrates, MANF is upregulated by ER stress and protects cells against ER stress-induced cell death. Biochemical studies have revealed an interaction between mammalian MANF and GRP78, the major ER chaperone promoting protein folding. This study discovered that the upregulation of MANF expression in response to drug-induced ER stress is conserved between Drosophila and mammals. Additionally, by using a genetic in vivo approach genetic interactions was found between Drosophila Manf and genes encoding for Drosophila homologues of GRP78, PERK and XBP1, the key components of UPR. These data suggest a role for Manf in the regulation of Drosophila UPR.

Tuesday, April 5th

Philippe, A.S., Jeanson, R., Pasquaretta, C., Rebaudo, F., Sueur, C. and Mery, F. (2016). Genetic variation in aggregation behaviour and interacting phenotypes in Drosophila. Proc Biol Sci 283 (1827). PubMed ID: 27009219
Summary:
This study used a combination of approaches to study how genetic variation and social environment interact to influence aggregation dynamics in Drosophila. The study used two different natural lines of Drosophila that arise from a polymorphism in the foraging gene (rovers and sitters). Groups of flies were placed in a heated arena. Flies could freely move towards one of two small, cooler refuge areas. In groups of the same strain, sitters were found to have a greater tendency to aggregate. The observed behavioural variation was based on only two parameters: the probability of entering a refuge and the likelihood of choosing a refuge based on the number of individuals present. Aggregation behaviour of each line was strongly affected by the presence of the other strain, without changing the decision rules used by each. Individuals obeying local rules shaped complex group dynamics via a constant feedback loop between the individual and the group. This study could help to identify the circumstances under which particular group compositions may improve individual fitness through underlying aggregation mechanisms under specific environmental conditions. 

Wijesekera, T.P., Saurabh, S and Dauwalder, B. (2016). Juvenile hormone is required in adult males for Drosophila courtship. PLoS One 11: e0151912. PubMed ID: 27003411
Summary:
Juvenile Hormone (JH) has a prominent role in the regulation of insect development. Much less is known about its roles in adults, although functions in reproductive maturation have been described. In adult females, JH has been shown to regulate egg maturation and mating. To examine a role for JH in male reproductive behavior, this study generated males with reduced levels of Juvenile Hormone Acid O-Methyl Transferase (JHAMT) and tested them for courtship. JHAMT regulates the last step of JH biosynthesis in the Corpora Allata (CA), the organ of JH synthesis. Males with reduced levels of JHAMT show a reduction in courtship that can be rescued by application of Methoprene, a JH analog, shortly before performing the courtship assays. In agreement with this, reducing JHAMT conditionally in mature flies leads to courtship defects that are rescuable by Methoprene. The same result is also observed when the CA are conditionally ablated by the expression of a cellular toxin. These findings demonstrate that JH plays an important physiological role in the regulation of male mating behavior.

Mohammad, F., Aryal, S., Ho, J., Stewart, J.C., Norman, N.A., Tan, T.L., Eisaka, A. and Claridge-Chang, A. (2016). Ancient anxiety pathways influence Drosophila defense behaviors. Curr Biol [Epub ahead of print]. PubMed ID: 27020741
Summary:
Anxiety helps us anticipate and assess potential danger in ambiguous situations; however, the anxiety disorders are the most prevalent class of psychiatric illness. Anxiety research makes wide use of three rodent behavioral assays-elevated plus maze, open field, and light/dark box-that present a choice between sheltered and exposed regions. Exposure avoidance in anxiety-related defense behaviors has been confirmed to be a correlate of rodent anxiety by treatment with known anxiety-altering agents and is now used to characterize anxiety systems. Modeling anxiety with a small neurogenetic animal would further aid the elucidation of its neuronal and molecular bases. Drosophila neurogenetics research has elucidated the mechanisms of fundamental behaviors and implicated genes that are often orthologous across species. In an enclosed arena, flies stay close to the walls during spontaneous locomotion, a behavior proposed to be related to anxiety. This study tested this hypothesis with manipulations of the GABA receptor, serotonin signaling, and stress. The effects of these interventions were strikingly concordant with rodent anxiety, verifying that these behaviors report on an anxiety-like state. Application of this method was able to identify several new fly anxiety genes. The presence of conserved neurogenetic pathways in the insect brain identifies Drosophila as an attractive genetic model for the study of anxiety and anxiety-related disorders, complementing existing rodent systems.

Thibert, J., Farine, J. P., Cortot, J. and Ferveur, J. F. (2016). Drosophila food-associated pheromones: Effect of experience, genotype and antibiotics on larval behavior. PLoS One 11: e0151451. PubMed ID: 26987117
Summary:
Animals ubiquitously use chemical signals to communicate many aspects of their social life. These chemical signals often consist of environmental cues mixed with species-specific signals-pheromones-emitted by conspecifics. During their life, insects can use pheromones to aggregate, disperse, choose a mate, or find the most suitable food source on which to lay eggs. Before pupariation, larvae of several Drosophila species migrate to food sources depending on their composition and the presence of pheromones. Some pheromones derive from microbiota gut activity and these food-associated cues can enhance larval attraction or repulsion. To explore the mechanisms underlying the preference (attraction/repulsion) to these cues and clarify their effect, this study manipulated factors potentially involved in larval response. In particular, it was found that the (1) early exposure to conspecifics, (2) genotype, and (3) antibiotic treatment changed D. melanogaster larval behavior. Generally, larvae-tested either individually or in groups-strongly avoided food processed by other larvae. Compared to previous reports on larval attractive pheromones, the data suggest that such attractive effects are largely masked by food-associated compounds eliciting larval aversion. The antagonistic effect of attractive vs. aversive compounds could modulate larval choice of a pupariation site and impact the dispersion of individuals in nature.

Bretman, A., Fricke, C., Westmancoat, J.D. and Chapman, T. (2016). Effect of competitive cues on reproductive morphology and behavioral plasticity in male fruitflies. Behav Ecol 27: 452-461. PubMed ID: 27004011
Summary:
Phenotypic plasticity will be favored whenever there are significant fitness benefits of responding to environmental variation. The extent and nature of the plasticity that evolves depends on the rate of environmental fluctuations and the capacity to track and respond to that variability. Reproductive environments represent one arena in which changes can be rapid. The finding that males of many species show morphological, physiological, and behavioral plasticity in response to premating and postmating reproductive competition (RC) suggests that plasticity is broadly beneficial. The developmental environment is expected to accurately predict the average population level of RC but to be a relatively poor indicator of immediate RC at any particular mating. Therefore, this study predicts that manipulation of average RC during development should cause a response in plasticity "set" during development (e.g., size of adult reproductive structures), but not in flexible plasticity determined by the immediate adult environment (e.g., behavioral plasticity in mating duration). This prediction was tested in Drosophila melanogaster males by manipulating 2 independent cues of average RC during development: 1) larval density and 2) the presence or absence of adult males within larval culture vials. Consistent with the prediction, both manipulations result in the development of males with significantly larger adult accessory glands (although testis size decreases when males are added to culture vials). There is no effect on adult plasticity (mating duration, extended mating in response to rivals). The results suggest that males have evolved independent responses to long- and short-term variation in RC.

Dubowy, C., Moravcevic, K., Yue, Z., Wan, J. Y., Van Dongen, H. P. and Sehgal, A. (2016). Genetic dissociation of daily sleep and sleep following thermogenetic sleep deprivation in Drosophila.Sleep [Epub ahead of print]. PubMed ID: 26951392
Summary:
Sleep rebound - the increase in sleep that follows sleep deprivation (SD) - is a hallmark of homeostatic sleep regulation. This, this study developed an efficient thermogenetic method of inducing SD in Drosophila that produces a strong rebound. To develop a thermogenetic method of SD suitable for screening, different populations of wake-promoting neurons labeled by Gal4 drivers were thermogenetically stimulated. Thermogenetic activation of neurons marked by the c584-Gal4 driver produces both strong sleep loss and a substantial rebound that is more subject to genetic regulation and more consistent within genotypes than rebound following mechanical or caffeine-induced SD. This driver was then used to induce SD in a screen of 1,741 mutagenized lines generated by the Drosophila Gene Disruption Project. Flies were subjected to 9 h of SD during the dark period and released from SD 3 h before lights-on. Recovery was measured over the 15 h following SD. Following identification of lines with reduced sleep rebound, baseline sleep and sleep depth was characterized before and after SD. Two lines were identified that consistently exhibit a blunted increase in the duration and depth of sleep after thermogenetic SD. Neither of the two genotypes has reduced total baseline sleep. Statistical analysis across all screened lines shows that genotype is a strong predictor of recovery sleep, independent from effects of genotype on baseline sleep. These data show that rebound sleep following thermogenetic SD can be genetically separated from sleep at baseline. This suggests that genetically controlled mechanisms of sleep regulation not manifest under undisturbed conditions contribute to sleep rebound following thermogenetic SD.

Monday, April 4th

Ng, B. F., Selvaraj, G. K., Mateos, C. S., Grosheva, I., Alvarez-Garcia, I., Martin-Bermudo, M. D. and Palacios, I. M. (2016). Alpha-Spectrin and integrins act together to regulate actomyosin and columnarization, and to maintain a mono-layered follicular epithelium. Development [Epub ahead of print]. PubMed ID: 26952981
Summary:
This study reports the role of Spectrins during epithelia morphogenesis using the Drosophila follicular epithelium (FE). α-Spectrin and β-Spectrin are shown to be are essential to maintain a mono-layered FE, but, contrary to previous work, Spectrins are not required to control proliferation. Furthermore, spectrin mutant cells show differentiation and polarity defects only in the ectopic layers of stratified epithelia, similar to integrin mutants. These results identify α-Spectrin and integrins as novel regulators of apical constriction-independent cell elongation, as α-spectrin and integrin cells fail to columnarize. Finally, increasing and reducing the activity of the Rho1-myosin-II pathway enhances and decreases multi-layering of α-spectrin cells, respectively. Similarly, higher myosin-II activity enhances the integrin multi-layering phenotype. This work identifies a primary role for α-Spectrin in controlling cell shape, perhaps by modulating actomyosin. All together, it is suggested that a functional Spectrin-Integrin complex is essential to balance adequate forces, in order to maintain a mono-layered epithelium.

Woichansky, I., Beretta, C. A., Berns, N. and Riechmann, V. (2016). Three mechanisms control E-cadherin localization to the zonula adherens. Nat Commun 7: 10834. PubMed ID: 26960923
Summary:
E-cadherin localization to the zonula adherens is fundamental for epithelial differentiation but the mechanisms controlling localization are unclear. Using the Drosophila follicular epithelium, E-cadherin transport was genetically dissected in an in vivo model. Three mechanisms were distinguished mediating E-cadherin accumulation at the zonula adherens. Two membrane trafficking pathways deliver newly synthesized E-cadherin to the plasma membrane. One is Rab11 dependent and targets E-cadherin directly to the zonula adherens, while the other transports E-cadherin to the lateral membrane. Lateral E-cadherin reaches the zonula adherens by endocytosis and targeted recycling. This pathway is dependent on RabX1, which provides a functional link between early and recycling endosomes. Moreover, lateral E-cadherin is transported to the zonula adherens by an apically directed flow within the plasma membrane. Differential activation of these pathways could facilitate cell shape changes during morphogenesis, while their misregulation compromises cell adhesion and tissue architecture in differentiated epithelia.

Aurich, F. and Dahmann, C. (2016). A mutation in fat2 uncouples tissue elongation from global tissue rotation. Cell Rep 14: 2503-2510. PubMed ID: 26972006
Summary:
Global tissue rotation was proposed as a morphogenetic mechanism controlling tissue elongation. In Drosophila ovaries, global tissue rotation of egg chambers coincides with egg chamber elongation. Egg chamber rotation was put forward to result in circumferential alignment of extracellular fibers. These fibers serve as molecular corsets to restrain growth of egg chambers perpendicular to the anteroposterior axis, thereby leading to the preferential egg chamber elongation along this axis. The atypical cadherin Fat2 (Kugelei) is required for egg chamber elongation, rotation, and the circumferential alignment of extracellular fibers. This study generated a truncated form of Fat2 that lacks the entire intracellular region. fat2 mutant egg chambers expressing this truncated protein fail to rotate yet display normal extracellular fiber alignment and properly elongate. These data suggest that global tissue rotation, even though coinciding with tissue elongation, is not a necessary prerequisite for elongation.

Davidson, A., Parton, R. M., Rabouille, C., Weil, T. T. and Davis, I. (2016). Localized translation of gurken/TGF-α mRNA during axis specification is controlled by access to Orb/CPEB on processing bodies. Cell Rep 14: 2451-2462. PubMed ID: 26947065
Summary:
In Drosophila oocytes, gurken/TGF-α mRNA is essential for establishing the future embryonic axes. gurken remains translationally silent during transport from its point of synthesis in nurse cells to its final destination in the oocyte, where it associates with the edge of processing bodies. This study shows that, in nurse cells, gurken is kept translationally silent by the lack of sufficient Orb/CPEB, its translational activator. Processing bodies in nurse cells have a similar protein complement and ultrastructure to those in the oocyte, but they markedly less Orb and do not associate with gurken mRNA. Ectopic expression of Orb in nurse cells at levels similar to the wild-type oocyte dorso-anterior corner at mid-oogenesis is sufficient to cause gurken mRNA to associate with processing bodies and translate prematurely. It is proposed that controlling the spatial distribution of translational activators is a fundamental mechanism for regulating localized translation.

Sunday, April 3rd

Fogarty, C. E., Diwanji, N., Lindblad, J. L., Tare, M., Amcheslavsky, A., Makhijani, K., Bruckner, K., Fan, Y. and Bergmann, A. (2016). Extracellular reactive oxygen species drive apoptosis-induced proliferation via Drosophila macrophages. Curr Biol [Epub ahead of print]. PubMed ID: 26898463
Summary:
Apoptosis-induced proliferation (AiP) is a compensatory mechanism to maintain tissue size and morphology following unexpected cell loss during normal development, and may also be a contributing factor to cancer and drug resistance. In apoptotic cells, caspase-initiated signaling cascades lead to the downstream production of mitogenic factors and the proliferation of neighboring surviving cells. In epithelial cells of Drosophila imaginal discs, the Caspase-9 ortholog Dronc drives AiP via activation of Jun N-terminal kinase (JNK); however, the specific mechanisms of JNK activation remain unknown. This study shows that caspase-induced activation of JNK during AiP depends on an inflammatory response. This is mediated by extracellular reactive oxygen species (ROSs) generated by the NADPH oxidase Duox in epithelial disc cells. Extracellular ROSs activate Drosophila macrophages (hemocytes), which in turn trigger JNK activity in epithelial cells by signaling through the tumor necrosis factor (TNF) ortholog Eiger. It is proposed that in an immortalized ("undead") model of AiP, signaling back and forth between epithelial disc cells and hemocytes by extracellular ROSs and TNF/Eiger drives overgrowth of the disc epithelium. These data illustrate a bidirectional cell-cell communication pathway with implication for tissue repair, regeneration, and cancer.

Levayer, R., Dupont, C. and Moreno, E. (2016). Tissue crowding induces caspase-dependent competition for space. Curr Biol [Epub ahead of print]. PubMed ID: 26898471
Summary:
Regulation of tissue size requires fine tuning at the single-cell level of proliferation rate, cell volume, and cell death. Whereas the adjustment of proliferation and growth has been widely studied, the contribution of cell death and its adjustment to tissue-scale parameters have been so far much less explored. Recently, it was shown that epithelial cells could be eliminated by live-cell delamination in response to an increase of cell density. Cell delamination was supposed to occur independently of caspase activation and was suggested to be based on a gradual and spontaneous disappearance of junctions in the delaminating cells. Studying the elimination of cells in the midline region of the Drosophila pupal notum, this study found that, contrary to what was suggested before, Caspase 3 activation precedes and is required for cell delamination. Yet, using particle image velocimetry, genetics, and laser-induced perturbations, this study confirmed that local tissue crowding is necessary and sufficient to drive cell elimination and that cell elimination is independent of known fitness-dependent competition pathways. Accordingly, activation of the oncogene Ras in clones was sufficient to compress the neighboring tissue and eliminate cells up to several cell diameters away from the clones. Mechanical stress has been previously proposed to contribute to cell competition. These results provide the first experimental evidences that crowding-induced death could be an alternative mode of super-competition, namely mechanical super-competition, independent of known fitness markers, that could promote tumor growth.

Hwangbo, D. S., Biteau, B., Rath, S., Kim, J. and Jasper, H. (2016). Control of apoptosis by Drosophila DCAF12. Dev Biol [Epub ahead of print]. PubMed ID: 26972874
Summary:
Regulated Apoptosis (Programmed Cell Death, PCD) maintains tissue homeostasis in adults, and ensures proper growth and morphogenesis of tissues during development of metazoans. Accordingly, defects in cellular processes triggering or executing apoptotic programs have been implicated in a variety of degenerative and neoplastic diseases. This study reports the identification of DCAF12, an evolutionary conserved member of the WD40-motif repeat family of proteins, as a new regulator of apoptosis in Drosophila. DCAF12 is required for Diap1 cleavage in response to pro-apoptotic signals, and is thus necessary and sufficient for RHG (Reaper, Hid, and Grim)-mediated apoptosis. Loss of DCAF12 perturbs the elimination of supernumerary or proliferation-impaired cells during development, and enhances tumor growth induced by loss of neoplastic tumor suppressors, highlighting the wide requirement for DCAF12 in PCD.

Fang, X., Zhou, J., Liu, W., Duan, X., Gala, U., Sandoval, H., Jaiswal, M. and Tong, C. (2016). Dynamin regulates autophagy by modulating lysosomal function. J Genet Genomics 43: 77-86. PubMed ID: 26924690
Summary:
Autophagy is a central lysosomal degradation pathway required for maintaining cellular homeostasis and its dysfunction is associated with numerous human diseases. To identify players in autophagy, this study tested approximately 1200 chemically induced mutations on the X chromosome in Drosophila fat body clones and discovered that shibire (shi) plays an essential role in starvation-induced autophagy. shi encodes a dynamin protein required for fission of clathrin-coated vesicles from the plasma membrane during endocytosis. Shi was shown to be dispensable for autophagy initiation and autophagosome-lysosome fusion, but required for lysosomal/autolysosomal acidification. Other endocytic core machinery components like clathrin and AP2 play similar but not identical roles in regulating autophagy and lysosomal function as dynamin. Previous studies suggested that dynamin directly regulates autophagosome formation and autophagic lysosome reformation (ALR) through its excision activity. This study provides evidence that dynamin also regulates autophagy indirectly by regulating lysosomal function.

Saturday, April 2nd

Burnouf, S., Grönke, S., Augustin, H., Dols, J., Gorsky, M.K., Werner, J., Kerr, F., Alic, N., Martinez, P. and Partridge, L. (2016). Deletion of endogenous Tau proteins is not detrimental in Drosophila. Sci Rep 6: 23102. PubMed ID: 26976084
Summary:
Human Tau (hTau) is a highly soluble and natively unfolded protein that binds to microtubules within neurons. Its dysfunction and aggregation into insoluble paired helical filaments is involved in the pathogenesis of Alzheimer's disease (AD), constituting, together with accumulated β-amyloid (Aβ) peptides, a hallmark of the disease. Deciphering both the loss-of-function and toxic gain-of-function of hTau proteins is crucial to further understand the mechanisms leading to neurodegeneration in AD. As the fruit fly Drosophila melanogaster expresses Tau proteins (dTau) that are homologous to hTau, this study aimed to better comprehend dTau functions by generating a specific tau knock-out (KO) fly line using homologous recombination. It was observed that the specific removal of endogenous dTau proteins does not lead to overt, macroscopic phenotypes in flies. Indeed, survival, climbing ability and neuronal function are unchanged in tau KO flies. In addition, any overt positive or negative effect of dTau removal on human Aβ-induced toxicity were not found. Altogether, these results indicate that the absence of dTau proteins has no major functional impact on flies, and suggest that the tau KO strain is a relevant model to further investigate the role of dTau proteins in vivo, thereby giving additional insights into hTau functions.

Gorsky, M. K., Burnouf, S., Dols, J., Mandelkow, E. and Partridge, L. (2016). Acetylation mimic of lysine 280 exacerbates human Tau neurotoxicity in vivo. Sci Rep 6: 22685. PubMed ID: 26940749
Summary:
Dysfunction and accumulation of the microtubule-associated human Tau (hTau) protein into intraneuronal aggregates is observed in many neurodegenerative disorders including Alzheimer's disease (AD). Reversible lysine acetylation has recently emerged as a post-translational modification that may play an important role in the modulation of hTau pathology. Acetylated hTau species have been observed within hTau aggregates in human AD brains and multi-acetylation of hTau in vitro regulates its propensity to aggregate. However, whether lysine acetylation at position 280 (K280) modulates hTau-induced toxicity in vivo is unknown. This study generated new Drosophila transgenic models of hTau pathology to evaluate the contribution of K280 acetylation to hTau toxicity, by analysing the respective toxicity of pseudo-acetylated (K280Q) and pseudo-de-acetylated (K280R) mutant forms of hTau. It was observed that mis-expression of pseudo-acetylated K280Q-hTau in the adult fly nervous system potently exacerbated fly locomotion defects and photoreceptor neurodegeneration. In addition, modulation of K280 influenced total hTau levels and phosphorylation without changing hTau solubility. Altogether, these results indicate that pseudo-acetylation of the single K280 residue is sufficient to exacerbate hTau neurotoxicity in vivo, suggesting that acetylated K280-hTau species contribute to the pathological events leading to neurodegeneration in AD.

Parkinson, W. M., Dookwah, M., Dear, M. L., Gatto, C. L., Aoki, K., Tiemeyer, M. and Broadie, K. (2016). Neurological roles for phosphomannomutase type 2 in a new Drosophila congenital disorder of glycosylation disease model. Dis Model Mech [Epub ahead of print]. PubMed ID: 26940433
Summary:
The most common Congenital disorders of glycosylation (CDGs), CDG-Ia or PMM2-CDG, arises from phosphomannomutase type 2 (PMM2) mutations. This study reports the generation and characterization of the first Drosophila PMM2-CDG model. CRISPR-generated Drosophila pmm2 null mutants display severely disrupted glycosylation and early lethality, while RNAi-targeted neuronal PMM2 knockdown results in a strong shift in pauci-mannose glycan abundance, progressive incoordination and later lethality, closely paralleling human CDG-Ia symptoms of shortened lifespan, movement impairments and defective neural development. Analyses of the well-characterized Drosophila neuromuscular junction (NMJ) reveal synaptic glycosylation loss accompanied by structural architecture and functional neurotransmission defects. NMJ synaptogenesis is driven by intercellular signals traversing an extracellular synaptomatrix co-regulated by glycosylation and matrix metalloproteinases (MMPs). Specifically, Wnt Wingless (Wg) trans-synaptic signaling depends on the heparan sulfate proteoglycan (HSPG) co-receptor Dally-like protein (Dlp), which is regulated by synaptic MMP activity. Loss of synaptic MMP2, Wg ligand, Dlp co-receptor and downstream trans-synaptic signaling occurs with PMM2 knockdown. Taken together, this Drosophila CDG disease model provides a new avenue for the dissection of cellular and molecular mechanisms underlying neurological impairments and a means to discover and test novel therapeutic treatment strategies.
Sun, X., et al. (2016). Melatonin attenuates hLRRK2-induced sleep disturbances and synaptic dysfunction in a Drosophila model of Parkinson's disease. Mol Med Rep [Epub ahead of print]. PubMed ID: 26985725
Summary:
Sleep problems are the most common non-motor symptoms in Parkinson's disease (PD), and are more difficult to treat than the motor symptoms. In the current study, the role of human leucine-rich repeat kinase 2 (hLRRK2), the most common genetic cause of PD, was investigated with regards to sleep problems, and the therapeutic potential of melatonin in hLRRK2-associated sleep problems was explored in Drosophila. hLRRK2 was selectively expressed in the mushroom bodies (MBs) in Drosophila and sleep patterns were measured using the Drosophila Activity Monitoring System. MB expression of hLRRK2 resulted in sleep problems, presynaptic dysfunction as evidenced by reduced miniature excitatory postsynaptic current (mEPSC) and excitatory postsynaptic potential (EPSP) frequency, and excessive synaptic plasticity such as increased axon bouton density. Treatment with melatonin at 4 mM significantly attenuated the sleep problems and rescued the reduction in mEPSC and EPSP frequency in the hLRRK2 transgenic flies. The present study demonstrates that MB expression of hLRRK2 in flies recapitulates the clinical features of the sleep disturbances in PD, and that melatonin attenuates hLRRK2-induced sleep disorders and synaptic dysfunction, suggesting the therapeutic potential of melatonin in PD patients carrying LRRK2 mutations.

Filograna, R., et al. (2016). SOD-mimetic M40403 is protective in cell and fly models of paraquat toxicity: Implications for Parkinson disease. J Biol Chem. PubMed ID: 26953346
Summary:
Parkinson disease is a debilitating and incurable neurodegenerative disorder, affecting approximately 1-2% of people over sixty-five years old. Oxidative damage is considered to play a central role in the progression of Parkinson disease and strong evidence links chronic exposure to the pesticide paraquat with the incidence of the disease, most probably through the generation of oxidative damage. This work demonstrated in human SH-SY5Y neuroblastoma cells the beneficial role of superoxide dismutase (SOD) enzymes against paraquat-induced toxicity, as well as the therapeutic potential of the SOD-mimetic compound M40403. Having verified the beneficial effects of superoxide dismutation in cells, the effects were then evaluated using Drosophila melanogaster as in vivo model. Besides protecting against the oxidative damage induced by paraquat treatment, these data demonstrated that in Drosophila M40403 was able to compensate for the loss of endogenous SOD enzymes, acting both at a cytosolic and mitochondrial level. Because previous clinical trials have indicated that the M40403 molecule is well tolerated in humans, this study may have important implication for the treatment of Parkinson disease.

Lehmann, S., Costa, A. C., Celardo, I., Loh, S. H. and Martins, L. M. (2016). Parp mutations protect against mitochondrial dysfunction and neurodegeneration in a PARKIN model of Parkinson's disease. Cell Death Dis 7: e2166. PubMed ID: 27031963
Summary:
The co-enzyme nicotinamide adenine dinucleotide (NAD+) is an essential co-factor for cellular energy generation in mitochondria as well as for DNA repair mechanisms in the cell nucleus involving NAD+-consuming poly (ADP-ribose) polymerases (PARPs). Mitochondrial function is compromised in animal models of Parkinson's disease (PD) associated with Parkin mutations. This study uncovered alterations in NAD+ salvage metabolism in Drosophila parkin mutants. A dietary supplementation with the NAD+ precursor nicotinamide rescues mitochondrial function and is neuroprotective. Further, by mutating Parp in parkin mutants, it was shown that this increases levels of NAD+ and its salvage metabolites. This also rescues mitochondrial function and suppresses dopaminergic neurodegeneration. It is concluded that strategies to enhance NAD+ levels by administration of dietary precursors or the inhibition of NAD+-dependent enzymes, such as PARP, that compete with mitochondria for NAD+ could be used to delay neuronal death associated with mitochondrial dysfunction.

Friday, April 1st

Poon, C.L., Mitchell, K.A., Kondo, S., Cheng, L.Y. and Harvey, K.F. (2016). The Hippo pathway regulates neuroblasts and brain size in Drosophila melanogaster. Curr Biol [Epub ahead of print]. PubMed ID: 26996505
Summary:
This study shows that the conserved Hippo pathway, a key regulator of epithelial organ size, restricts neuroblast proliferative potential and neuronal cell number to regulate brain size. The inhibition of Hippo pathway activity via depletion of the core kinases Tao-1, Hippo, or Warts regulates several key characteristics of neuroblasts during postembryonic neurogenesis. The Hippo pathway is required to maintain timely entry and exit from neurogenesis by regulating both neuroblast reactivation from quiescence and the time at which neuroblasts undergo terminal differentiation. Further, it restricts neuroblast cell-cycle speed, specifies cell size, and alters the proportion of neuron types generated during postembryonic neurogenesis. Collectively, deregulation of Hippo signaling in neuroblasts causes a substantial increase in overall brain size. It was shown that these effects are mediated via the key downstream transcription co-activator Yorkie and that, indeed, Yorkie overexpression in neuroblasts is sufficient to cause brain overgrowth. These studies reveal a novel mechanism that controls stem cell proliferative potential during postembryonic neurogenesis to regulate brain size.

Barnstedt, O., Owald, D., Felsenberg, J., Brain, R., Moszynski, J. P., Talbot, C. B., Perrat, P. N. and Waddell, S. (2016). Memory-relevant mushroom body output synapses are cholinergic. Neuron 89: 1237-1247. PubMed ID: 26948892
Summary:
Memories are stored in the fan-out fan-in neural architectures of the mammalian cerebellum and hippocampus and the insect mushroom bodies. However, whereas key plasticity occurs at glutamatergic synapses in mammals, the neurochemistry of the memory-storing mushroom body Kenyon cell output synapses is unknown. This study demonstrates a role for acetylcholine (ACh) in Drosophila. Kenyon cells express the ACh-processing proteins ChAT and VAChT, and reducing their expression impairs learned olfactory-driven behavior. Local ACh application, or direct Kenyon cell activation, evokes activity in mushroom body output neurons (MBONs). MBON activation depends on VAChT expression in Kenyon cells and is blocked by ACh receptor antagonism. Furthermore, reducing nicotinic ACh receptor subunit expression in MBONs compromises odor-evoked activation and redirects odor-driven behavior. Lastly, peptidergic corelease enhances ACh-evoked responses in MBONs, suggesting an interaction between the fast- and slow-acting transmitters. Therefore, olfactory memories in Drosophila are likely stored as plasticity of cholinergic synapses.

Li, Q., Zhang, X., Hu, W., Liang, X., Zhang, F., Wang, L., Liu, Z. J. and Zhong, Y. (2016). Importin-7 mediates memory consolidation through regulation of nuclear translocation of training-activated MAPK in Drosophila. Proc Natl Acad Sci U S A [Epub ahead of print]. PubMed ID: 26929354
Summary:
Translocation of signaling molecules, MAPK in particular, from the cytosol to nucleus represents a universal key element in initiating the gene program that determines memory consolidation. Translocation mechanisms and their behavioral impact, however, remain to be determined. This study reports that a highly conserved nuclear transporter, Drosophila importin-7 (DIM-7), regulates import of training-activated MAPK for consolidation of long-term memory (LTM). Silencing DIM-7 functions results in impaired LTM, whereas overexpression of DIM-7 enhances LTM. This DIM-7-dependent regulation of LTM is confined to a consolidation time window and in mushroom body neurons. Image data show that bidirectional alteration in DIM-7 expression results in proportional changes in the intensity of training-activated MAPK accumulated within the nuclei of mushroom body neurons during LTM consolidation. Such DIM-7-regulated nuclear accumulation of activated MAPK is observed only in the training specified for LTM induction and determines the amplitude, but not the time course, of memory consolidation.

Cavey, M., Collins, B., Bertet, C. and Blau, J. (2016). Circadian rhythms in neuronal activity propagate through output circuits. Nat Neurosci [Epub ahead of print]. PubMed ID: 26928065
Summary:
Twenty-four hour rhythms in behavior are organized by a network of circadian pacemaker neurons. Rhythmic activity in this network is generated by intrinsic rhythms in clock neuron physiology and communication between clock neurons. However, it is poorly understood how the activity of a small number of pacemaker neurons is translated into rhythmic behavior of the whole animal. To understand this, a screen was carried out for signals that could identify circadian output circuits in Drosophila melanogaster. Leucokinin neuropeptide (LK) and its receptor (LK-R) were found to be required for normal behavioral rhythms. This LK/LK-R circuit connects pacemaker neurons to brain areas that regulate locomotor activity and sleep. These experiments revealed that pacemaker neurons impose rhythmic activity and excitability on LK- and LK-R-expressing neurons. Pacemaker neuron-dependent activity rhythms were also found in a second circadian output pathway controlled by DH44 neuropeptide-expressing neurons. It is concluded that rhythmic clock neuron activity propagates to multiple downstream circuits to orchestrate behavioral rhythms.

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