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


Friday, July 31st, 2015

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Holly, R. M., Mavor, L. M., Zuo, Z. and Blankenship, J. T. (2015). A rapid, membrane-dependent pathway directs furrow formation through RalA in the early Drosophila embryo. Development 142: 2316-2328. PubMed ID: 26092850
Plasma membrane furrow formation is crucial in cell division and cytokinesis. Furrow formation in early syncytial Drosophila embryos is exceptionally rapid, with furrows forming in as little as 3.75 min. This study used 4D imaging to identify furrow formation, stabilization, and regression periods, and identified a rapid, membrane-dependent pathway that is essential for plasma membrane furrow formation in vivo. Myosin II function is thought to provide the ingression force for cytokinetic furrows, but the role of membrane trafficking pathways in guiding furrow formation is less clear. It was demonstrated that a membrane trafficking pathway centered on Ras-like protein A (RalA) is required for fast furrow ingression in the early fly embryo. RalA function is absolutely required for furrow formation and initiation. In the absence of RalA and furrow function, chromosomal segregation is aberrant and polyploid nuclei are observed. RalA localizes to syncytial furrows, and mediates the movement of exocytic vesicles to the plasma membrane. Sec5, which is an exocyst complex subunit and localizes to ingressing furrows in wild-type embryos, becomes punctate and loses its cortical association in the absence of RalA function. Rab8 also fails to traffic to the plasma membrane and accumulates aberrantly in the cytoplasm in RalA disrupted embryos. RalA localization precedes F-actin recruitment to the furrow tip, suggesting that membrane trafficking might function upstream of cytoskeletal remodeling. These studies identify a pathway, which stretches from Rab8 to RalA and the exocyst complex, that mediates rapid furrow formation in early Drosophila embryos.

González-Morales, N., Mendoza-Ortíz, M.Á., Blowes, L.M., Missirlis, F. and Riesgo-Escovar, J.R. (2015). Ferritin is required in multiple tissues during Drosophila melanogaster development. PLoS One 10: e0133499. PubMed ID: 26192321
In Drosophila, iron is stored in the cellular endomembrane system inside a protein cage formed by 24 ferritin subunits of two types (Fer1HCH and Fer2LCH) in a 1:1 stoichiometry. In larvae, ferritin accumulates in the midgut, hemolymph, garland, pericardial cells and in the nervous system. This study presents analyses of embryonic phenotypes for mutations in Fer1HCH, Fer2LCH and in both genes simultaneously. Mutations in either gene or deletion of both genes results in a similar set of cuticular embryonic phenotypes, ranging from non-deposition of cuticle to defects associated with germ band retraction, dorsal closure and head involution. A fraction of ferritin mutants have embryonic nervous systems with ventral nerve cord disruptions, misguided axonal projections and brain malformations. Ferritin mutants die with ectopic apoptotic events. Furthermore, it was shown that ferritin maternal contribution, which varies reflecting the mother's iron stores, is used in early development. The study also evaluated phenotypes arising from the blockage of COPII transport from the endoplasmic reticulum to the Golgi apparatus, feeding the secretory pathway, plus analysis of ectopically expressed and fluorescently marked Fer1HCH and Fer2LCH. Overall, these results are consistent with insect ferritin combining three functions: iron storage, intercellular iron transport, and protection from iron-induced oxidative stress. These functions are required in multiple tissues during Drosophila embryonic development.

Buffolo, M., Batista Possidonio, A. C., Mermelstein, C. and Araujo, H. (2015). A conserved role for calpains during myoblast fusion. Genesis [Epub ahead of print]. PubMed ID: 26138338
Myoblast fusion is a key step during skeletal muscle differentiation as it enables the formation of contractile fibers. Calpains have been implicated in some aspects of myogenesis in mammals, but whether they exert a conserved function during myoblast fusion has not been investigated. Calpain function in two models of myogenesis were studied: in vitro analysis of chick myogenic cultures and in vivo analysis of Drosophila muscle development. First it was shown that Calpain A is important for fly muscle function. In addition, Calpain A knockdown reduced lateral body wall muscle length and width, as well as the number of nuclei in dorsal oblique muscles, consistent with fewer cells fusing to form fibers. Treatment of chick cultures with a selective Calpain inhibitor led to the formation of thinner myotubes containing a reduced number of nuclei, consistent with decreased myoblast fusion. Dynamic changes in IκBα labeling and transfection with a dominant-negative IκBα suggest a role for the NFκB pathway during chick myogenesis and a possible role of Calpains in attenuating NFκB signals that restrict myoblast fusion. These data suggest that different model organisms may be used to study the role of Calpains in regular myogenesis and Calpain-related muscular degenerative disorders.

Eltsov, M., Dube, N., Yu, Z., Pasakarnis, L., Haselmann-Weiss, U., Brunner, D. and Frangakis, A. S. (2015). Quantitative analysis of cytoskeletal reorganization during epithelial tissue sealing by large-volume electron tomography. Nat Cell Biol 17: 605-614. PubMed ID: 25893916
The closure of epidermal openings is an essential biological process that causes major developmental problems such as spina bifida in humans if it goes awry. At present, the mechanism of closure remains elusive. Therefore, this study reconstructed a model closure event, dorsal closure in fly embryos, by large-volume correlative electron tomography.A comprehensive, quantitative analysis of the cytoskeletal reorganization, enabling separated epidermal cells to seal the epithelium, is presented. After establishing contact through actin-driven exploratory filopodia, cells use a single lamella to generate 'roof tile'-like overlaps. These shorten to produce the force, 'zipping' the tissue closed. The shortening overlaps lack detectable actin filament ensembles but are crowded with microtubules. Cortical accumulation of shrinking microtubule ends suggests a force generation mechanism in which cortical motors pull on microtubule ends as for mitotic spindle positioning. In addition, microtubules orient filopodia and lamellae before zipping. This 4D electron microscopy picture describes an entire developmental process and provides fundamental insight into epidermal closure.

Buckalew, R., Finley, K., Tanda, S. and Young, T. (2015). Evidence for internuclear signaling in Drosophila embryogenesis. Dev Dyn [Epub ahead of print]. PubMed ID: 26033666
Syncytial nuclei in Drosophila embryos undergo their first 13 divisions nearly synchronously. In the last several cell cycles, these division events travel across the anterior-posterior axis of the syncytial blastoderm in a wave. The phenomenon is well documented but the underlying mechanisms are not yet understood. Timing and positional data obtained from in vivo imaging of Drosophila embryos was studied. The statistical properties were determined of the distribution of division times within and across generations with the null hypothesis that timing of division events is an independent random variable for each nucleus. Timing data was compared with a model of Drosophila cell cycle regulation that does not include internuclear signaling, and to a universal model of phase-dependent signaling to determine the probable form of internuclear signaling in the syncytial embryo. It is concluded that the statistical variance of division times is lower than one would expect from uncoordinated activity. In fact, the variance decreases between the 10th and 11th divisions, which demonstrates a contribution of internuclear signaling to the observed synchrony and division waves. This comparison with a coupled oscillator model leads to the conclusion that internuclear signaling must be of Response/Signaling type with a positive impulse.

McCarthy, G. D., Drewell, R. A. and Dresch, J. M. (2015). Global sensitivity analysis of a dynamic model for gene expression in Drosophila embryos. PeerJ 3: e1022. PubMed ID: 26157608
It is well known that gene regulation is a tightly controlled process in early organismal development. However, the roles of key processes involved in this regulation, such as transcription and translation, are less well understood, and mathematical modeling approaches in this field are still in their infancy. In recent studies, biologists have taken precise measurements of protein and mRNA abundance to determine the relative contributions of key factors involved in regulating protein levels in mammalian cells. This study approached this question from a mathematical modeling perspective. A simple dynamic mathematical model was used that incorporates terms representing transcription, translation, mRNA and protein decay, and diffusion in an early Drosophila embryo. A global sensitivity analyses was performed on this model using various different initial conditions and spatial and temporal outputs. The results indicate that transcription and translation are often the key parameters to determine protein abundance. This observation is in close agreement with the experimental results from mammalian cells for various initial conditions at particular time points, suggesting that a simple dynamic model can capture the qualitative behavior of a gene. Additionally, it was found that parameter sensitivites are temporally dynamic, illustrating the importance of conducting a thorough global sensitivity analysis across multiple time points when analyzing mathematical models of gene regulation.

Thursday, July 30

Larkin, A., Chen, M.Y., Kirszenblat, L., Reinhard, J., van Swinderen, B. and Claudianos, C. (2015). Neurexin-1 regulates sleep and synaptic plasticity in Drosophila melanogaster. Eur J Neurosci [Epub ahead of print]. PubMed ID: 26201245
Neurexins are cell adhesion molecules important for synaptic plasticity and homeostasis, though links to sleep have not yet been investigated. This study examined effects of neurexin-1 perturbation on sleep in Drosophila, showing that neurexin-1 nulls display fragmented sleep and altered circadian rhythm. Conversely, over-expression of neurexin-1 can increase and consolidate night-time sleep. This is not solely due to developmental effects as it can be induced acutely in adulthood, and is coupled with evidence for synaptic growth. Timing of over-expression can differentially impact sleep patterns, with specific night-time effects. These results show that neurexin-1 is dynamically involved in synaptic plasticity and sleep in Drosophila. Neurexin-1 and a number of its binding partners have been repeatedly associated with mental health disorders, including autism spectrum disorders, schizophrenia and Tourette syndrome, all of which are also linked to altered sleep patterns. How and when plasticity-related proteins such as neurexin-1 function during sleep can provide vital information on the interaction between synaptic homeostasis and sleep, paving the way for more informed treatments of human disorders.

Styczynska-Soczka, K. and Jarman, A. P. (2015). The Drosophila homologue of Rootletin is required for mechanosensory function and ciliary rootlet formation in chordotonal sensory neurons. Cilia 4: 9. PubMed ID: 26140210
In vertebrates, rootletin is the major structural component of the ciliary rootlet and is also part of the tether linking the centrioles of the centrosome. Rootletin function has not been explored in Drosophila. In the Drosophila embryo, Rootletin is expressed exclusively in cell lineages of type I sensory neurons, the only somatic cells bearing a cilium. Expression is strongest in mechanosensory chordotonal neurons. Knock-down of Rootletin results in loss of ciliary rootlet in these neurons and severe disruption of their sensory function. However, the sensory cilium appears largely normal in structure and in localisation of proteins suggesting no strong defect in ciliogenesis. No evidence was found for a defect in cell division. The role of Rootletin as a component of the ciliary rootlet is conserved in Drosophila. In contrast, lack of a general role in cell division is consistent with lack of centriole tethering during the centrosome cycle in Drosophila. Although the evidence is consistent with an anchoring role for the rootlet, severe loss of mechanosensory function of chordotonal (Ch) neurons upon Rootletin knock-down may suggest a direct role for the rootlet in the mechanotransduction mechanism itself.

Ng, F.S. and Jackson, F.R. (2015). The ROP vesicle release factor is required in adult Drosophila glia for normal circadian behavior. Front Cell Neurosci 9: 256. PubMed ID: 26190976
It is known that endocytosis and/or vesicle recycling mechanisms are essential in adult Drosophila glial cells for the neuronal control of circadian locomotor activity. The goal of this study was to identify specific glial vesicle trafficking, recycling, or release factors that are required for rhythmic behavior. From a glia-specific, RNAi-based genetic screen, eight glial factors were identified and were found to be required for normally robust circadian rhythms in either a light-dark cycle or in constant dark conditions. In particular, it was shown that conditional knockdown of the ROP vesicle release factor in adult glial cells results in arrhythmic behavior. Immunostaining for ROP reveals reduced protein in glial cell processes and an accumulation of the Par Domain Protein 1ε (PDP1ε) clock output protein in the small lateral clock neurons. These results suggest that glia modulate rhythmic circadian behavior by secretion of factors that act on clock neurons to regulate a clock output factor. 

Lee, Y., Moon, S.J., Wang, Y. and Montell, C. (2015). A Drosophila gustatory receptor required for strychnine sensation. Chem Senses [Epub ahead of print]. PubMed ID: 26187906
Strychnine is a potent, naturally occurring neurotoxin that effectively protects plants from animal pests by deterring feeding behavior. In insects, such as the fruit fly, Drosophila melanogaster, bitter-tasting aversive compounds are detected primarily through a family of gustatory receptors (GRs), which are expressed in gustatory receptor neurons. Multiple GRs that eliminate the behavioral avoidance to several bitter compounds, with the exception of strychnine, have been previously described. This study reports the identity of a strychnine receptor, referred to as GR47a. A mutation in Gr47a, eliminates strychnine repulsion and strychnine-induced action potentials. GR47a is narrowly tuned, as the responses to other avoidance compounds are unaffected in the mutant animals. This analysis supports an emerging model that Drosophila GRs fall broadly into two specificity classes-one class is comprised of core receptors that are broadly required, whereas the other class, which includes GR47a, consists of narrowly tuned receptors that define chemical specificity.

Harris, R.M., Pfeiffer, B.D., Rubin, G.M. and Truman, J.W. (2015). Neuron hemilineages provide the functional ground plan for the Drosophila ventral nervous system. Elife [Epub ahead of print]. PubMed ID: 26193122
Drosophila central neurons arise from neuroblasts that generate neurons in a pair-wise fashion, with the two daughters providing the basis for distinct A and B hemilineage groups. Thirty three postembryonically-born hemilineages contribute over 90% of the neurons in each thoracic hemisegment. This study devised genetic approaches to define the anatomy of most of these hemilineages and to assess their functional roles using the heat-sensitive channel dTRPA1. The simplest hemilineages contain local interneurons and their activation causes tonic or phasic leg movements lacking interlimb coordination. The next level is hemilineages of similar projection cells that drive intersegmentally coordinated behaviors such as walking. The highest level involves hemilineages whose activation elicits complex behaviors such as takeoff. These activation phenotypes indicate that the hemilineages vary in their behavioral roles with some contributing to local networks for sensorimotor processing and others having higher order functions of coordinating these local networks into complex behavior.

Evans, T.A., Santiago, C., Arbeille, E. and Bashaw, G.J. (2015). Robo2 acts in trans to inhibit Slit-Robo1 repulsion in pre-crossing commissural axons. Elife 4. PubMed ID: 26186094
During nervous system development, commissural axons cross the midline despite the presence of repellant ligands. In Drosophila, commissural axons avoid premature responsiveness to the midline repellant Slit by expressing the endosomal sorting receptor Commissureless, which reduces surface expression of the Slit receptor Roundabout1 (Robo1). This study describes a distinct mechanism to inhibit Robo1 repulsion and promote midline crossing, in which Roundabout2 (Robo2) binds to and prevents Robo1 signaling. Unexpectedly, it was found that Robo2 is expressed in midline cells during the early stages of commissural axon guidance, and that over-expression of Robo2 can rescue robo2-dependent midline crossing defects non-cell autonomously. It was shown that the extracellular domains required for binding to Robo1 are also required for Robo2's ability to promote midline crossing, in both gain-of-function and rescue assays. These findings indicate that at least two independent mechanisms to overcome Slit-Robo1 repulsion in pre-crossing commissural axons have evolved in Drosophila.

Wednesday, July 29

Kwok, R.S., Li, Y.H., Lei, A.J., Edery, I. and Chiu, J.C. (2015). The catalytic and non-catalytic functions of the Brahma chromatin-remodeling protein collaborate to fine-tune circadian transcription in Drosophila. PLoS Genet 11: e1005307. PubMed ID: 26132408
This study identifies the Brahma (Brm) complex as a regulator of the Drosophila clock. In Drosophila, CLOCK (CLK) is the master transcriptional activator driving cyclical gene expression by participating in an auto-inhibitory feedback loop that involves stimulating the expression of the main negative regulators, period (per) and timeless (tim). BRM functions catalytically to increase nucleosome density at the promoters of per and tim, creating an overall restrictive chromatin landscape to limit transcriptional output during the active phase of cycling gene expression. In addition, the non-catalytic function of BRM regulates the level and binding of CLK to target promoters and maintains transient RNAPII stalling at the per promoter, likely by recruiting repressive and pausing factors. By disentangling its catalytic versus non-catalytic functions at the promoters of CLK target genes, this study uncovers a multi-leveled mechanism in which BRM fine-tunes circadian transcription.

Sanulli, S., et al. (2015). Jarid2 methylation via the PRC2 complex regulates H3K27me3 deposition during cell differentiation. Mol Cell 57: 769-783. PubMed ID: 25620564
Polycomb Group (PcG) proteins maintain transcriptional repression throughout development, mostly by regulating chromatin structure. Polycomb Repressive Complex 2 (PRC2), a component of the Polycomb machinery, is responsible for the methylation of histone H3 lysine 27 (H3K27me2/3). Jarid2 was previously identified as a cofactor of PRC2, regulating PRC2 targeting to chromatin and its enzymatic activity. Deletion of Jarid2 leads to impaired orchestration of gene expression during cell lineage commitment. This study reveals an unexpected crosstalk between Jarid2 and PRC2, with Jarid2 being methylated by PRC2. This modification is recognized by the Eed (see Drosophila Extra Sexcombs) core component of PRC2 and triggers an allosteric activation of PRC2's enzymatic activity. Jarid2 methylation is shown to be important to promote PRC2 activity at a locus devoid of H3K27me3 and for the correct deposition of this mark during cell differentiation. These results uncover a regulation loop where Jarid2 methylation fine-tunes PRC2 activity depending on the chromatin context.

Morán, T., Bernués, J. and Azorín, F. (2015). The Drosophila histone demethylase dKDM5/LID regulates hematopoietic development. Dev Biol [Epub ahead of print]. PubMed ID: 26183107
dKDM5/LID regulates transcription of essential developmental genes and, thus, is required for different developmental processes. This study reports the essential contribution of dKDM5/LID to hematopoiesis in Drosophila. The study shows that dKDM5/LID is abundant in hemocytes and that its depletion induces over-proliferation and differentiation defects of larval hemocytes and disrupts organization of the actin cytoskeleton. It was also shown that dKDM5/LID regulates expression of key factors of hematopoietic development. In particular, dKDM5/LID depletion up-regulates expression of several transcription factors involved in hemocytes proliferation and differentiation as well as of several small-GTPases that link signaling effectors to actin cytoskeleton formation and dynamics.

Chen, C. C., et al. (2015). Establishment of centromeric chromatin by the CENP-A assembly factor CAL1 requires FACT-mediated transcription. Dev Cell 34: 73-84. PubMed ID: 26151904
Centromeres are essential chromosomal structures that mediate accurate chromosome segregation during cell division. Centromeres are specified epigenetically by the heritable incorporation of the centromeric histone H3 variant CENP-A. While many of the primary factors that mediate centromeric deposition of CENP-A are known, the chromatin and DNA requirements of this process have remained elusive. This study uncovered a role for transcription in Drosophila CENP-A deposition. Using an inducible ectopic centromere system that uncouples CENP-A deposition from endogenous centromere function and cell-cycle progression, CENP-A assembly by its loading factor, CAL1, was shown to require RNAPII-mediated transcription of the underlying DNA. This transcription depends on the CAL1 binding partner FACT, but not on CENP-A incorporation. This work establishes RNAPII passage as a key step in chaperone-mediated CENP-A chromatin establishment and propagation.

Tuesday, July 28th

Turkel, N., Portela, M., Poon, C., Li, J., Brumby, A.M. and Richardson, H.E. (2015). Cooperation of the BTB-Zinc finger protein, Abrupt, with cytoskeletal regulators in Drosophila epithelial tumorigenesis. Biol Open [Epub ahead of print]. PubMed ID: 26187947
The deregulation of cell polarity or cytoskeletal regulators is a common occurrence in human epithelial cancers. Moreover, there is accumulating evidence in human epithelial cancer that BTB-ZF genes, such as Bcl6 and ZBTB7A, are oncogenic. Previous studies on Drosophila melanogaster have identified a cooperative interaction between a mutation in the apico-basal cell polarity regulator Scribble (Scrib) and overexpression of the BTB-ZF protein Abrupt (Ab). This study shows that co-expression of ab with actin cytoskeletal regulators, RhoGEF2 or Src64B, in the developing eye-antennal epithelial tissue results in the formation of overgrown amorphous tumours, whereas ab and DRac1 co-expression leads to non-cell autonomous overgrowth. Together with ab, these genes affect the expression of differentiation genes, resulting in tumours locked in a progenitor cell fate. Finally, the study shows that the expression of two mammalian genes related to ab, Bcl6 and ZBTB7A, which are oncogenes in mammalian epithelial cancers, significantly correlate with the upregulation of cytoskeletal genes or downregulation of apico-basal cell polarity neoplastic tumour suppressor genes in colorectal, lung and other human epithelial cancers. Altogether, this analysis reveals that upregulation of cytoskeletal regulators cooperate with Abrupt in Drosophila epithelial tumorigenesis, and that high expression of human BTB-ZF genes, Bcl6 and ZBTB7A, shows significant correlations with cytoskeletal and cell polarity gene expression in specific epithelial tumour types. This highlights the need for further investigation of the cooperation between these genes in mammalian systems

Thomas, S., Fisher, K. H., Snowden, J. A., Danson, S. J., Brown, S. and Zeidler, M. P. (2015). Methotrexate is a JAK/STAT pathway inhibitor. PLoS One 10: e0130078. PubMed ID: 26131691
The JAK/STAT pathway transduces signals from multiple cytokines and controls haematopoiesis, immunity and inflammation. There is a need for effective low cost treatments. This study used the low-complexity Drosophila melanogaster pathway to screen for small molecules that modulate JAK/STAT signalling. This screen identified methotrexate and the closely related aminopterin as potent suppressors of STAT activation. Methotrexate was shown to suppress human JAK/STAT signalling, without affecting other phosphorylation-dependent pathways. Furthermore, methotrexate significantly reduces STAT5 phosphorylation in cells expressing JAK2 V617F, a mutation associated with most human MPNs. Methotrexate acts independently of dihydrofolate reductase (DHFR) and is comparable to the JAK1/2 inhibitor ruxolitinib. However, cells treated with methotrexate still retain their ability to respond to physiological levels of the ligand erythropoietin. It is concluded that aminopterin and methotrexate act as competitive inhibitors of DHFR. Methotrexate is also widely used at low doses to treat inflammatory and immune-mediated conditions including rheumatoid arthritis. In this low-dose regime, folate supplements are given to mitigate side effects by bypassing the biochemical requirement for DHFR. Although independent of DHFR, the mechanism-of-action underlying the low-dose effects of methotrexate is unknown. Given that multiple pro-inflammatory cytokines signal through the pathway, it is suggested that suppression of the JAK/STAT pathway is likely to be the principal anti-inflammatory and immunosuppressive mechanism-of-action of low-dose methotrexate. In addition, it is suggested that patients with JAK/STAT-associated haematological malignancies may benefit from low-dose methotrexate treatments. These findings represent an important development with significant cost-saving future potential.

Hentze, J. L., Carlsson, M. A., Kondo, S., Nassel, D. R. and Rewitz, K. F. (2015). The neuropeptide Allatostatin A regulates metabolism and feeding decisions in Drosophila. Sci Rep 5: 11680. PubMed ID: 26123697
Coordinating metabolism and feeding is important to avoid obesity and metabolic diseases, yet the underlying mechanisms, balancing nutrient intake and metabolic expenditure, are poorly understood. Several mechanisms controlling these processes are conserved in Drosophila, where homeostasis and energy mobilization are regulated by the glucagon-related adipokinetic hormone (AKH) and the Drosophila insulin-like peptides (DILPs). This study provides evidence that the Drosophila neuropeptide Allatostatin A (AstA) regulates AKH and DILP signaling. The AstA receptor gene, Dar-2, is expressed in both the insulin and AKH producing cells. Silencing of Dar-2 in these cells results in changes in gene expression and physiology associated with reduced DILP and AKH signaling and animals lacking AstA accumulate high lipid levels. This suggests that AstA is regulating the balance between DILP and AKH, believed to be important for the maintenance of nutrient homeostasis in response to changing ratios of dietary sugar and protein. Furthermore, AstA and Dar-2 are regulated differentially by dietary carbohydrates and protein and AstA-neuronal activity modulates feeding choices between these types of nutrients. These results suggest that AstA is involved in assigning value to these nutrients to coordinate metabolic and feeding decisions, responses that are important to balance food intake according to metabolic needs.

Futran, A. S., Kyin, S., Shvartsman, S. Y. and Link, A. J. (2015). Mapping the binding interface of ERK and transcriptional repressor Capicua using photocrosslinking. Proc Natl Acad Sci U S A 112: 8590-8595. PubMed ID: 26124095
Extracellular signal-regulated kinase (ERK; Rolled in Drosophila) coordinates cellular responses to a range of stimuli by phosphorylating its numerous substrates. One of these substrates, Capicua (Cic), is a transcriptional repressor that was first identified in Drosophila and has been implicated in a number of human diseases. This study used a chemical biology approach to map the binding interface of ERK and Cic. The noncanonical amino acid p-azidophenylalanine (AzF) was introduced into the ERK-binding region of Drosophila Cic, and photocrosslinking and tandem mass spectrometry were used to pinpoint its binding site on ERK. The ERK-binding region of human Cic was also identified, and it was shown to bind to the same site on ERK despite lacking conservation with the Drosophila Cic binding region. Finally, the amino acids involved in human Cic binding to ERK were mapped using AzF-labeled ERK. These results reveal the molecular details of the ERK-Cic interaction and demonstrate that the photocrosslinking approach is complementary to existing methods for mapping kinase-substrate binding interfaces.

Monday, July 27th

Lenhart, K.F. and DiNardo, S. (2015). Somatic cell encystment promotes abscission in germline stem cells following a regulated block in cytokinesis. Dev Cell [Epub ahead of print]. PubMed ID: 26143993
In many tissues, the stem cell niche must coordinate behavior across multiple stem cell lineages. How this is achieved is largely unknown. This study identifies delayed completion of cytokinesis in germline stem cells (GSCs) as a mechanism that regulates the production of stem cell daughters in the Drosophila testis. Through live imaging, it was shown that a secondary F-actin ring is formed through regulation of Cofilin activity to block cytokinesis progress after contractile ring disassembly (GSCs delay cytokinesis in two distinct phases). The duration of this block is controlled by Aurora B kinase. Additionally, a requirement for somatic cell encystment of the germline in promoting GSC abscission was identified. The study suggests that this non-autonomous role promotes coordination between stem cell lineages. These findings reveal the mechanisms by which cytokinesis is inhibited and reinitiated in GSCs and why such complex regulation exists within the stem cell niche.

Levine, M.T., Vander Wende, H.M. and Malik, H.S. (2015). Mitotic fidelity requires transgenerational action of a testis-restricted HP1. Elife 4. PubMed ID: 26151671
Sperm-packaged DNA must undergo extensive reorganization to ensure its timely participation in embryonic mitosis. Whereas maternal control over this remodeling is well described, paternal contributions are virtually unknown. This study shows that Drosophila melanogaster males lacking Heterochromatin Protein 1E (HP1E) sire inviable embryos that undergo catastrophic mitosis. In these embryos, the paternal genome fails to condense and resolve into sister chromatids in synchrony with the maternal genome. This delay leads to a failure of paternal chromosomes, particularly the heterochromatin-rich sex chromosomes, to separate on the first mitotic spindle. Remarkably, HP1E is not inherited on mature sperm chromatin. Instead, HP1E primes paternal chromosomes during spermatogenesis to ensure faithful segregation post-fertilization. This transgenerational effect suggests that maternal control is necessary but not sufficient for transforming sperm DNA into a mitotically competent pronucleus. Instead, paternal action during spermiogenesis exerts post-fertilization control to ensure faithful chromosome segregation in the embryo.

Intra, J., Concetta, V., Daniela, C., Perotti, M. E. and Pasini, M. E. (2015). Drosophila sperm surface α-l-fucosidase interacts with the egg coats through its core fucose residues. Insect Biochem Mol Biol 63: 133-143. PubMed ID: 26101846
Fucose and α-l-fucosidases have fundamental function(s) during gamete interactions. An α-l-fucosidase has been detected as transmembrane protein on the surface of spermatozoa of eleven Drosophila species. Immunofluorescence labeling showed that the protein is localized in the sperm plasma membrane over the acrosome and the tail, in Drosophila melanogaster. In the present study, efforts were made to analyze with solid phase assays the oligosaccharide recognition ability of fruit fly sperm α-l-fucosidase with defined carbohydrate chains that can functionally mimic egg glycoconjugates. The results showed that α-l-fucosidase bound to fucose residue and in particular it prefers N-glycans carrying core α1,6-linked fucose and core α1,3-linked fucose in N-glycans carrying only a terminal mannose residue. No binding was detected when α-l-fucosidase was pre-incubated with fucoidan, a polymer of α-l-fucose and the monosaccharide fucose. Furthermore, egg labeling with anti-horseradish peroxidase, that recognized only core α1,3-linked fucose, correlates with α-l-fucosidase micropylar binding. Collectively, these data support the hypothesis of the potential role of this glycosidase in sperm-egg interactions in Drosophila.

Smendziuk, C. M., Messenberg, A., Vogl, W. and Tanentzapf, G. (2015). Bi-directional gap junction-mediated Soma-Germline communication is essential for spermatogenesis. Development [Epub ahead of print]. PubMed ID: 26116660
Soma-germline interactions play conserved essential roles in regulating cell proliferation, differentiation, patterning, and homeostasis in the gonad. In the Drosophila testis, secreted signalling molecules of the JAK-STAT, Hedgehog, BMP, and EGF pathways are used to mediate germline-soma communication. This study demonstrates that gap junctions may also mediate direct, bi-directional signalling between the soma and germline. When gap junctions between the soma and germline are disrupted, germline differentiation is blocked and germline stem cells are not maintained. In the soma, gap junctions are required to regulate proliferation and differentiation. Localization and RNAi-mediated knockdown studies reveal that gap junctions in the fly testis are heterotypic channels containing Zpg/Inx4 and Inx2 on the germline and the soma side, respectively. Overall, these results show that bi-directional gap junction-mediated signalling is essential to coordinate the soma and germline to ensure proper spermatogenesis in Drosophila. Moreover, this study shows that stem cell maintenance and differentiation in the testis are directed by gap junction-derived cues.

Sunday, July 26th

Uchiyama, T., Koike, R., Yuma, Y., Okamoto, K., Arimoto-Kobayashi, S., Suzuki, T. and Negishi, T. (2015). Somatic-cell mutation induced by short exposures to cigarette smoke in urate-null, oxidative stress-sensitive Drosophila. Mutagenesis [Epub ahead of print]. PubMed ID: 26138228
A urate-null strain of Drosophila is hypersensitive to cigarette smoke (CS), and it has been suggested that CS induces oxidative stress in Drosophila because uric acid is a potent antioxidant. This study used a new Drosophila strain (y v ma-l; mwh) to examine the mutagenicity induced by gaseous-phase CS; these flies are urate-null due to a mutation in ma-l, and they are heterozygous for multiple wing hair (mwh), a mutation that functions as a marker for somatic-cell mutation. In an assay with this newly developed strain, a superoxide anion-producing weed-killer, paraquat, exhibited significant mutagenicity; in contrast, paraquat was hardly mutagenic with a wild-type strain. Drosophila larvae were exposed to CS for 2, 4 or 6h, and then kept at 25 degrees C on instant medium until adulthood. After eclosion, mutant spots, which consisted of mutant hairs on wings, were scored. The number of mutant spots increased significantly in an exposure time-dependent manner in the urate-null females (ma-l -/-), but not in the urate-positive females (ma-l+/-). This study showed that short-term exposure to CS was mutagenic in this in vivo system. In addition, suggestive data was obtained regarding reactive oxygen species production in larva after CS exposure using the fluorescence probe H2DCFDA. These results suggest that oxidative damage, which might be countered by uric acid, was partly responsible for induction of somatic cell mutations in Drosophila larvae exposed to CS.

Hardy, C. M., Birse, R. T., Wolf, M. J., Yu, L., Bodmer, R. and Gibbs, A. G. (2015). Obesity-associated cardiac dysfunction in starvation-selected Drosophila melanogaster. Am J Physiol Regul Integr Comp Physiol: [Epub ahead of print]. PubMed ID: 26136533
There is a clear link between obesity and cardiovascular disease, but the complexity of this interaction in mammals makes it difficult to study. Among the animal models used to investigate obesity-associated diseases, Drosophila melanogaster has emerged as an important platform of discovery. In the laboratory, Drosophila can be made obese through lipogenic diets, genetic manipulations and adaptation to evolutionary stress. While dietary and genetic changes that cause obesity in flies have been demonstrated to induce heart dysfunction, there have been no reports investigating how obesity affects the heart in laboratory-evolved populations. This paper studied replicated populations of Drosophila that had been selected for starvation resistance for over 65 generations. These populations evolved characteristics that closely resemble hallmarks of metabolic syndrome in mammals. Starvation-selected Drosophila have dilated hearts with impaired contractility. This phenotype appears to be correlated with large fat deposits along the dorsal cuticle, which alter the anatomical position of the heart. A strong relationship was demonstrated between fat storage and heart dysfunction, as dilation and reduced contractility can be rescued through prolonged fasting. Unlike other Drosophila obesity models, the starvation-selected lines do not exhibit excessive lipid deposition within the myocardium and rather store excess triglycerides in large lipid droplets within the fat body. These findings provide a new model to investigate obesity-associated heart dysfunction.

Chou, C. C., Alexeeva, O. M., Yamada, S., Pribadi, A., Zhang, Y., Mo, B., Williams, K. R., Zarnescu, D. C. and Rossoll, W. (2015). PABPN1 suppresses TDP-43 toxicity in ALS disease models. Hum Mol Genet [Epub ahead of print]. PubMed ID: 26130692
TAR DNA-binding protein 43 (TDP-43; see Drosophila TDP-43) is a major disease protein in amyotrophic lateral sclerosis (ALS) and related neurodegenerative diseases. Both the cytoplasmic accumulation of toxic ubiquitinated and hyperphosphorylated TDP-43 fragments and the loss of normal TDP-43 from the nucleus may contribute to the disease progression by impairing normal RNA and protein homeostasis. Therefore, both the removal of pathological protein and the rescue of TDP-43 mislocalization may be critical for halting or reversing TDP-43 proteinopathies. This study reports poly(A)-binding protein nuclear 1 (PABPN1) as a novel TDP-43 interaction partner that acts as a potent suppressor of TDP-43 toxicity. Overexpression of full-length PABPN1 but not a truncated version lacking the nuclear localization signal protects from pathogenic TDP-43-mediated toxicity, promotes the degradation of pathological TDP-43 and restores normal solubility and nuclear localization of endogenous TDP-43. Reduced levels of PABPN1 enhances the phenotypes in several cell culture and Drosophila models of ALS and results in the cytoplasmic mislocalization of TDP-43. Moreover, PABPN1 rescues the dysregulated stress granule (SG) dynamics and facilitates the removal of persistent SGs in TDP-43-mediated disease conditions. These findings demonstrate a role for PABPN1 in rescuing several cytopathological features of TDP-43 proteinopathy by increasing the turnover of pathologic proteins.

Calap-Quintana, P., Soriano, S., Llorens, J. V., Al-Ramahi, I., Botas, J., Molto, M. D. and Martinez-Sebastian, M. J. (2015). TORC1 inhibition by rapamycin promotes antioxidant defences in a Drosophila model of Friedreich's ataxia. PLoS One 10: e0132376. PubMed ID: 26158631
Friedreich's ataxia (FRDA), the most common inherited ataxia in the Caucasian population, is a multisystemic disease caused by a significant decrease in the frataxin level. To identify genes capable of modifying the severity of the symptoms of frataxin depletion, a candidate genetic screen was performed in a Drosophila RNAi-based model of FRDA. Genetic reduction in TOR Complex 1 (TORC1; see Tor) signalling was found to improve the impaired motor performance phenotype of FRDA model flies. Pharmacologic inhibition of TORC1 signalling by rapamycin also restored this phenotype and increased the lifespan and ATP levels. Furthermore, rapamycin reduced the altered levels of malondialdehyde + 4-hydroxyalkenals and total glutathione of the model flies. The rapamycin-mediated protection against oxidative stress is due in part to an increase in the transcription of antioxidant genes mediated by cap-n-collar (Drosophila ortholog of Nrf2). These results suggest that autophagy is indeed necessary for the protective effect of rapamycin in hyperoxia. Rapamycin increased the survival and aconitase activity of model flies subjected to high oxidative insult, and this improvement was abolished by the autophagy inhibitor 3-methyladenine. These results point to the TORC1 pathway as a new potential therapeutic target for FRDA and as a guide to finding new promising molecules for disease treatment.

Niehues, S., et al. (2015). Impaired protein translation in Drosophila models for Charcot-Marie-Tooth neuropathy caused by mutant tRNA synthetases. Nat Commun 6: 7520. PubMed ID: 26138142
Dominant mutations in five tRNA synthetases cause Charcot-Marie-Tooth (CMT) neuropathy, suggesting that altered aminoacylation function underlies the disease. However, previous studies showed that loss of aminoacylation activity is not required to cause CMT. This study presents a Drosophila model for CMT with mutations in glycyl-tRNA synthetase (GARS). Expression of three CMT-mutant GARS proteins induces defects in motor performance and motor and sensory neuron morphology, and shortens lifespan. Mutant GARS proteins display normal subcellular localization but markedly reduce global protein synthesis in motor and sensory neurons, or when ubiquitously expressed in adults, as revealed by FUNCAT and BONCAT. Translational slowdown is not attributable to altered tRNA(Gly) aminoacylation, and cannot be rescued by Drosophila Gars overexpression, indicating a gain-of-toxic-function mechanism. Expression of CMT-mutant tyrosyl-tRNA synthetase also impairs translation, suggesting a common pathogenic mechanism. Finally, genetic reduction of translation is sufficient to induce CMT-like phenotypes, indicating a causal contribution of translational slowdown to CMT.

Balasov, M., Akhmetova, K. and Chesnokov, I. (2015). Drosophila model of Meier-Gorlin syndrome based on the mutation in a conserved C-Terminal domain of Orc6. Am J Med Genet A. PubMed ID: 26139588
Meier-Gorlin syndrome (MGS) is an autosomal recessive disorder characterized by microtia, primordial dwarfism, small ears, and skeletal abnormalities. Patients with MGS often carry mutations in the genes encoding the components of the pre-replicative complex such as Origin Recognition Complex (ORC) subunits Orc1, Orc4, Orc6, and helicase loaders Cdt1 and Cdc6. Orc6 is an important component of ORC and has functions in both DNA replication and cytokinesis. Mutation in conserved C-terminal motif of Orc6 associated with MGS impedes the interaction of Orc6 with core ORC. In order to study the effects of MGS mutation in an animal model system. MGS mutation was introduced in Orc6, and a Drosophila model of MGS was established. Mutant flies die at third instar larval stage with abnormal chromosomes and DNA replication defects. The lethality can be rescued by elevated expression of mutant Orc6 protein. Rescued MGS flies are unable to fly and display multiple planar cell polarity defects.

Saturday, July 25th

Kim, M., et al. (2015). Drosophila Gyf/GRB10 interacting GYF protein is an autophagy regulator that controls neuron and muscle homeostasis. Autophagy: [Epub ahead of print]. PubMed ID: 26086452
Autophagy is a process essential for eliminating ubiquitinated protein aggregates and dysfunctional organelles. Defective autophagy is associated with various degenerative diseases such as Parkinson disease. Through a genetic screening in Drosophila, this study identified CG11148, whose product is orthologous to GIGYF1 (GRB10 interacting GYF protein 1) and GIGYF2 in mammals, as a new autophagy regulator; the gene is hereafter refered to as Gyf. Silencing of Gyf completely suppressed the effect of Atg1-Atg13 activation in stimulating autophagic flux and inducing autophagic eye degeneration. Although Gyf silencing did not affect Atg1-induced Atg13 phosphorylation or Atg6-Pi3K59F (class III PtdIns3K)-dependent Fyve puncta formation, it inhibited formation of Atg13 puncta, suggesting that Gyf controls autophagy through regulating subcellular localization of the Atg1-Atg13 complex. Gyf silencing also inhibited Atg1-Atg13-induced formation of Atg9 puncta, which is accumulated upon active membrane trafficking into autophagosomes. Gyf-null mutants also exhibited substantial defects in developmental or starvation-induced accumulation of autophagosomes and autolysosomes in the larval fat body. Furthermore, heads and thoraxes from Gyf-null adults exhibited strongly reduced expression of autophagosome-associated Atg8a-II compared to wild-type (WT) tissues. The decrease in Atg8a-II was directly correlated with an increased accumulation of ubiquitinated proteins and dysfunctional mitochondria in neuron and muscle, which together led to severe locomotor defects and early mortality. These results suggest that Gyf-mediated autophagy regulation is important for maintaining neuromuscular homeostasis and preventing degenerative pathologies of the tissues. Since human mutations in the GIGYF2 locus were reported to be associated with a type of familial Parkinson disease, the homeostatic role of Gyf-family proteins is likely to be evolutionarily conserved.

Yang, S., Long, L. H., Li, D., Zhang, J. K., Jin, S., Wang, F. and Chen, J. G. (2015). β-Guanidinopropionic acid extends the lifespan of Drosophila melanogaster via an AMP-activated protein kinase-dependent increase in autophagy. Aging Cell [Epub ahead of print]. PubMed ID: 26120775
Previous studies have demonstrated that AMP-activated protein kinase (AMPK) controls autophagy through the mammalian target of rapamycin (mTOR) and Unc-51 like kinase 1 (ULK1/Atg1) signaling, which augments the quality of cellular housekeeping, and that β-guanidinopropionic acid (β-GPA), a creatine analog, leads to a chronic activation of AMPK. However, the relationship between β-GPA and aging remains elusive. In this study, it was hypothesized that feeding β-GPA to adult Drosophila produces the lifespan extension via activation of AMPK-dependent autophagy. It was found that dietary administration of β-GPA at a concentration higher than 900 mm induced a significant extension of the lifespan of Drosophila melanogaster in repeated experiments. Furthermore, it was found that Atg8 protein, the homolog of microtubule-associated protein 1A/1B-light chain 3 (LC3) and a biomarker of autophagy in Drosophila, was significantly upregulated by β-GPA treatment, indicating that autophagic activity plays a role in the effect of β-GPA. On the other hand, when the expression of Atg5 protein, an essential protein for autophagy, was reduced by RNA interference (RNAi), the effect of β-GPA on lifespan extension was abolished. Moreover, it was found that AMPK was also involved in this process. β-GPA treatment significantly elevated the expression of phospho-T172-AMPK levels, while inhibition of AMPK by either AMPK-RNAi or compound C significantly attenuated the expression of autophagy-related proteins and lifespan extension in Drosophila. Taken together, these results suggest that β-GPA can induce an extension of the lifespan of Drosophila via AMPK-Atg1-autophagy signaling pathway.

Colin, J., Garibal, J., Clavier, A., Szuplewski, S., Risler, Y., Milet, C., Gaumer, S., Guenal, I. and Mignotte, B. (2015). Screening of suppressors of bax-induced cell death identifies Glycerophosphate oxidase-1 as a mediator of debcl-induced apoptosis in Drosophila. Genes Cancer 6: 241-253. PubMed ID: 26124923
Members of the Bcl-2 family are key elements of the apoptotic machinery. In mammals, this multigenic family contains about twenty members, which either promote or inhibit apoptosis. The mammalian pro-apoptotic Bcl-2 family member Bax is very efficient in inducing apoptosis in Drosophila, allowing the study of bax-induced cell death in a genetic animal model. This study reports the results of the screening of a P[UAS]-element insertion library performed to identify gene products that modify the phenotypes induced by the expression of bax in Drosophila melanogaster. Seventeen putative modifiers involved in various function or process were isolated: the ubiquitin/proteasome pathway; cell growth, proliferation and death; pathfinding and cell adhesion; secretion and extracellular signaling; metabolism and oxidative stress. The brat gene belongs to a group of suppressors, which is implicated in cell growth, proliferation or death. Other identified genes are involved in carbohydrate metabolism, such as Gpo-1. This result is in agreement with the evidence that Bcl-2 family proteins, in addition to their well characterized function in cell death, also play roles in metabolic processes in particular at the level of energetic metabolism. Most of these suppressors also inhibit debcl-induced phenotypes, suggesting that the activities of both proteins can be modulated in part by common signaling or metabolic pathways. Among these suppressors, Glycerophosphate oxidase-1 is found to participate in debcl-induced apoptosis by increasing mitochondrial reactive oxygen species accumulation.

Qi, Y., Liu, H., Daniels, M. P., Zhang, G. and Xu, H. (2015). Loss of Drosophila i-AAA protease, dYME1L, causes abnormal mitochondria and apoptotic degeneration. Cell Death Differ [Epub ahead of print]. PubMed ID: 26160069
Mitochondrial AAA (ATPases Associated with diverse cellular Activities) proteases i-AAA (intermembrane space-AAA) and m-AAA (matrix-AAA) are closely related and have major roles in inner membrane protein homeostasis. Mutations of m-AAA proteases are associated with neuromuscular disorders in humans. However, the role of i-AAA in metazoans is poorly understood. This study generated a deletion affecting Drosophila i-AAA, dYME1L (dYME1Ldel). Mutant flies exhibited premature aging, progressive locomotor deficiency and neurodegeneration that resemble some key features of m-AAA diseases. dYME1Ldel flies displayed elevated mitochondrial unfolded protein stress and irregular cristae. Aged dYME1Ldel flies had reduced complex I (NADH/ubiquinone oxidoreductase) activity, increased level of reactive oxygen species (ROS), severely disorganized mitochondrial membranes and increased apoptosis. Furthermore, inhibiting apoptosis by targeting dOmi (Drosophila Htra2/Omi) or DIAP1, or reducing ROS accumulation suppressed retinal degeneration. The results suggest that i-AAA is essential for removing unfolded proteins and maintaining mitochondrial membrane architecture. Loss of i-AAA leads to the accumulation of oxidative damage and progressive deterioration of membrane integrity, which might contribute to apoptosis upon the release of proapoptotic molecules such as dOmi. Containing ROS level could be a potential strategy to manage mitochondrial AAA protease deficiency.

Friday, July 24th

Green, E. W., O'Callaghan, E. K., Hansen, C. N., Bastianello, S., Bhutani, S., Vanin, S., Armstrong, J. D., Costa, R. and Kyriacou, C. P. (2015). Drosophila circadian rhythms in seminatural environments: Summer afternoon component is not an artifact and requires TrpA1 channels. Proc Natl Acad Sci U S A 112: 8702-8707. PubMed ID: 26124142
Under standard laboratory conditions of rectangular light/dark cycles and constant warm temperature, Drosophila melanogaster show bursts of morning (M) and evening (E) locomotor activity and a "siesta" in the middle of the day. These M and E components have been critical for developing the neuronal dual oscillator model in which clock gene expression in key cells generates the circadian phenotype. However, under natural European summer conditions of cycling temperature and light intensity, an additional prominent afternoon (A) component that replaces the siesta is observed. This component has been described as an "artifact" of the TriKinetics locomotor monitoring system that is used by many circadian laboratories world wide. Using video recordings, this study shows that the A component is not an artifact, neither in the glass tubes used in TriKinetics monitors nor in open-field arenas. By studying various mutants in the visual and peripheral and internal thermo-sensitive pathways, it was revealed that the M component is predominantly dependent on visual input, whereas the A component requires the internal thermo-sensitive channel Transient receptor potential A1 (TrpA1). Knockdown of TrpA1 in different neuronal groups reveals that the reported expression of TrpA1 in clock neurons is unlikely to be involved in generating the summer locomotor profile, suggesting that other TrpA1 neurons are responsible for the A component. Studies of circadian rhythms under seminatural conditions therefore provide additional insights into the molecular basis of circadian entrainment that would otherwise be lost under the usual standard laboratory protocols.

Maguire, S. E., Rhoades, S., Chen, W. F., Sengupta, A., Yue, Z., Lim, J. C., Mitchell, C. H., Weljie, A. M. and Sehgal, A. (2015). Independent effects of GABA Transaminase (GABAT) on metabolic and sleep homeostasis. J Biol Chem [Epub ahead of print]. PubMed ID: 26124278
Breakdown of the major sleep promoting neurotransmitter, gamma-aminobutyric acid (GABA), in the GABA shunt generates catabolites that may enter the TCA cycle, but it is unknown whether catabolic by-products of the GABA shunt actually support metabolic homeostasis. In Drosophila, the loss of the specific enzyme that degrades GABA, GABA Transaminase (GABAT; CG7433), increases sleep, and this study shows that it also affects metabolism such that flies lacking GABAT fail to survive on carbohydrate media. Expression of GABAT in neurons or glia rescues this phenotype, indicating a general metabolic function for this enzyme in the brain. As GABA degradation produces two catabolic products, glutamate and succinic semialdehyde (SSA), attempts were made to determine which was responsible for the metabolic phenotype. Through genetic and pharmacological experiments, glutamate, rather than SSA, was determined to account for the metabolic phenotype of gabat mutants. This is supported by biochemical measurements of catabolites in wild-type and mutant animals. Using in vitro labeling assays, inhibition of GABAT was found to affect energetic pathways. Interestingly, it was also observed that gaba mutants display a general disruption in bioenergetics as measured by altered levels of TCA cycle intermediates, NAD+/NADH, and ATP levels. Finally, it is reported that the effects of GABAT on sleep do not depend upon glutamate, indicating that GABAT regulates metabolic and sleep homeostasis through independent mechanisms. These data indicate a role of the GABA shunt in the development of metabolic risk and suggest that neurological disorders caused by altered glutamate or GABA may be associated with metabolic disruption.

Krause Pham, C. and Ray, A. (2015). Conservation of olfactory avoidance in Drosophila species and identification of repellents for Drosophila suzukii. Sci Rep 5: 11527. PubMed ID: 26098542
Flying insects use olfaction to navigate towards fruits in complex odor environments with remarkable accuracy. Some fruits change odor profiles substantially during ripening and related species can prefer different stages. In Drosophila species attractive odorants have been studied extensively, but little is understood about the role of avoidance pathways. In order to examine the role of the avoidance cue CO2 emitted from fruit on behavior of two species with different ripening stage preferences, this study investigated the CO2-detection pathway in Drosophila melanogaster and Drosophila suzukii, a harmful pest of fruits. Avoidance to CO2 is not conserved in D. suzukii suggesting a behavioral adaptation that could facilitate attraction to younger fruit with higher CO2 emission levels. Known innate avoidance pathways were investigated from five species at different evolutionary distances: D. melanogaster, D. yakuba, D. suzukii, D. pseudoobscura and D. virilis. Surprisingly, only DEET shows strong repellency across all species, whereas CO2, citronellal and ethyl 3-hydroxybutyrate show only limited conservation. These findings led to a test of recently discovered safe DEET substitutes, and one was identified that protects fruits from D. suzukii thus providing a new behavioral strategy for controlling agricultural pests.

Ratliff, E. P., et al. (2015). Aging and Autophagic Function Influences the Progressive Decline of Adult Drosophila Behaviors. PLoS One 10: e0132768. PubMed ID: 26182057
Multiple neurological disorders are characterized by the abnormal accumulation of protein aggregates and the progressive impairment of complex behaviors. Drosophila studies demonstrate that middle-aged wild-type flies (WT, ~4-weeks) exhibit a marked accumulation of neural aggregates that is commensurate with the decline of the autophagy pathway. However, enhancing autophagy via neuronal over-expression of Atg8a (Atg8a-OE) reduces the age-dependent accumulation of aggregates. This study assessed basal locomotor activity profiles for single- and group-housed male and female WT flies and observed that only modest behavioral changes occurred by 4-weeks of age, with the noted exception of group-housed male flies. Male flies in same-sex social groups exhibit a progressive increase in nighttime activity. Infrared videos show aged group-housed males (4-weeks) are engaged in extensive bouts of courtship during periods of darkness, which is partly repressed during lighted conditions. Together, these nighttime courtship behaviors were nearly absent in young WT flies and aged Atg8a-OE flies. These results and previous results suggest that middle-aged male flies develop impairments in olfaction, which could contribute to the dysregulation of courtship behaviors during dark time periods. As Drosophila age, they develop early behavior defects that are coordinate with protein aggregate accumulation in the nervous system. In addition, the nighttime activity behavior is preserved when neuronal autophagy is maintained (Atg8a-OE flies). Thus, environmental or genetic factors that modify autophagic capacity could have a positive impact on neuronal aging and complex behaviors.

Thursday, July 23rd

Huylmans, A.K. and Parsch, J. (2015). Variation in the X:autosome distribution of male-biased genes among Drosophila melanogaster tissues and its relationship with dosage compensation. Genome Biol Evol [Epub ahead of print]. PubMed ID: 26108491
To better understand the chromosomal distribution of sex-biased genes in various tissues, this study used a common analysis framework to analyze microarray and RNA-seq data comparing male and female gene expression in individual tissues (brain, Malpighian tubule, gonads), composite structures (head, gonadectomized carcass), and whole flies. Although there are relatively few sex-biased genes in the brain, there is a strong and highly significant enrichment of male-biased genes on the X chromosome. A weaker enrichment of X-linked male-biased genes is seen in the head, suggesting that most of this signal comes from the brain. In all other tissues, there is either no departure from the random expectation or a significant paucity of male-biased genes on the X chromosome. The brain and head also differ from other tissues in that their male-biased genes are significantly closer to binding sites of the dosage compensation complex. The study proposes that the interplay of dosage compensation and sex-specific regulation can explain the observed differences between tissues and reconcile disparate results reported in previous studies.

Johnson, W. C., Ordway, A. J., Watada, M., Pruitt, J. N., Williams, T. M. and Rebeiz, M. (2015). Genetic changes to a transcriptional silencer element confers phenotypic diversity within and between Drosophila species. PLoS Genet 11: e1005279. PubMed ID: 26115430
The modification of transcriptional regulation has become increasingly appreciated as a major contributor to morphological evolution. However, the role of negative-acting control elements (e.g. silencers) in generating morphological diversity has been generally overlooked relative to positive-acting "enhancer" elements. The highly variable body coloration patterns among Drosophilid insects represents a powerful model system in which the molecular alterations that underlie phenotypic diversity can be defined. In a survey of pigment phenotypes among geographically disparate Japanese populations of Drosophila auraria, a remarkable degree of variation was discovered in male-specific abdominal coloration. In testing the expression patterns of the major pigment-producing enzymes, phenotypes were found that were uniquely correlated with differences in the expression of ebony, a gene required for yellow-colored cuticle. Assays of ebony's transcriptional control region indicated that a lightly pigmented strain harbored cis-regulatory mutations that caused correlated changes in its expression. Through a series of chimeric reporter constructs between light and dark strain

Zhang, T., et al. (2015). Mitf is a master regulator of the v-ATPase forming an Mitf/v-ATPase/TORC1 control module for cellular homeostasis. J Cell Sci [Epub ahead of print]. PubMed ID: 26092939
The v-ATPase is a fundamental eukaryotic enzyme central to cellular homeostasis. Although its impact on key metabolic regulators such as TORC1 (see Drosophila Tor) is well-documented, knowledge of mechanisms that regulate v-ATPase activity is limited. This study reports that the Drosophila transcription factor Mitf is a master regulator of this holoenzyme. Mitf directly controls transcription of all 15 v-ATPase components through M-box cis-sites and this coordinated regulation impacts holoenzyme activity in vivo. In addition, through the v-ATPase, Mitf promotes the activity of TORC1, which in turn negatively regulates Mitf. Evidence is provided that Mitf, v-ATPase and TORC1 form a negative regulatory loop that maintains each of these important metabolic regulators in relative balance. Interestingly, direct regulation of v-ATPase genes by human MITF also occurs in cells of the melanocytic lineage, showing mechanistic conservation in the regulation of the v-ATPase by MITF-TFE proteins in fly and mammals. Collectively, this evidence points to an ancient Mitf/v-ATPase/TORC1 module that serves as a dynamic modulator of metabolism for cellular homeostasis.

Abe, N., Dror, I., Yang, L., Slattery, M., Zhou, T., Bussemaker, H. J., Rohs, R. and Mann, R. S. (2015). Deconvolving the recognition of DNA shape from sequence. Cell 161: 307-318. PubMed ID: 25843630
Protein-DNA binding is mediated by the recognition of the chemical signatures of the DNA bases and the 3D shape of the DNA molecule. Because DNA shape is a consequence of sequence, it is difficult to dissociate these modes of recognition. This study teased them apart in the context of Hox-DNA binding by mutating residues that, in a co-crystal structure, only recognize DNA shape. Complexes made with these mutants lose the preference to bind sequences with specific DNA shape features. Introducing shape-recognizing residues from one Hox protein to another swapped binding specificities in vitro and gene regulation in vivo. Statistical machine learning revealed that the accuracy of binding specificity predictions improves by adding shape features to a model that only depends on sequence, and feature selection identified shape features important for recognition. Thus, shape readout is a direct and independent component of binding site selection by Hox proteins.

Wednesday, July 22nd

Zhou, Q. and Bachtrog, D. (2015). Ancestral chromatin configuration constrains chromatin evolution on differentiating sex chromosomes in Drosophila. PLoS Genet 11: e1005331. PubMed ID: 26114585
Sex chromosomes evolve distinctive types of chromatin from a pair of ancestral autosomes that are usually euchromatic. In Drosophila, the dosage-compensated X becomes enriched for hyperactive chromatin in males (mediated by H4K16ac), while the Y chromosome acquires silencing heterochromatin (enriched for H3K9me2/3). Drosophila autosomes are typically mostly euchromatic but the small dot chromosome has evolved a heterochromatin-like milieu (enriched for H3K9me2/3) that permits the normal expression of dot-linked genes, but which is different from typical pericentric heterochromatin. In Drosophila busckii, the dot chromosomes have fused to the ancestral sex chromosomes, creating a pair of 'neo-sex' chromosomes. Genomic, transcriptomic and epigenomic data was collected from D. busckii, to investigate the evolutionary trajectory of sex chromosomes from a largely heterochromatic ancestor. The neo-sex chromosomes formed <1 million years ago, but nearly 60% of neo-Y linked genes have already become non-functional. Expression levels are generally lower for the neo-Y alleles relative to their neo-X homologs, and the silencing heterochromatin mark H3K9me2, but not H3K9me3, is significantly enriched on silenced neo-Y genes. Despite rampant neo-Y degeneration, it was found that the neo-X is deficient for the canonical histone modification mark of dosage compensation (H4K16ac), relative to autosomes or the compensated ancestral X chromosome, possibly reflecting constraints imposed on evolving hyperactive chromatin in an originally heterochromatic environment. Yet, neo-X genes are transcriptionally more active in males, relative to females, suggesting the evolution of incipient dosage compensation on the neo-X. The data show that Y degeneration proceeds quickly after sex chromosomes become established through genomic and epigenetic changes.

Liu, F. G., Tsaur, S. C. and Huang, H. T. (2015). Biogeography of Drosophila (Diptera: Drosophilidae) in East and Southeast Asia. J Insect Sci 15 [Epub ahead of print]. PubMed ID: 26078303
The causes of high biological diversity in biodiversity hotspots have long been a major subject of study in conservation biology. To investigate this matter, a phylogeographic study was conducted of five Drosophila species from East and Southeast Asia: Drosophila albomicans Duda, D. formosana Duda, D. immigrans Sturtevant, D. melanogaster Meigen, and D. simulans Sturtevant. 185 samples were collected from 28 localities in eight countries. From each collected individual, the autosomal extra sex comb gene (esc) and seven mitochondrial genes were sequenced, including nicotinamide adenine dinucleotide hydrate-reductase dehydrogenase subunit 4 (ND4), ND4L, tRNA-His, tRNA-Pro, tRNA-Thr, partial ND5, and partial ND6. Phylogenetic analyses using maximum- likelihood and Bayesian methods revealed interesting population structure and identified the existence of two distinct D. formosana lineages (Southeast Asian and Taiwanese populations). Genetic differentiation among groups of D. immigrans suggests the possibility of endemic speciation in Taiwan. In contrast, D. melanogaster remained one extensively large population throughout East and Southeast Asia, including nearby islets. A molecular clock was used to estimate divergence times, which were compared with past geographical events to infer evolutionary scenarios. The findings suggest that interglacial periods may have caused population isolation, thus enhancing population differentiation more strongly for some of the Drosophila species. The population structure of each Drosophila species in East and Southeast Asia has been influenced by past geographic events.

Tobler, R., Hermisson, J. and Schlotterer, C. (2015). Parallel trait adaptation across opposing thermal environments in experimental Drosophila melanogaster populations. Evolution [Epub ahead of print]. PubMed ID: 26080903
Thermal stress is a pervasive selective agent in natural populations that impacts organismal growth, survival and reproduction. Drosophila melanogaster exhibits a variety of putatively adaptive phentotypic responses to thermal stress in natural and experimental settings; however, accompanying assessments of fitness are typically lacking. This study quantified changes in fitness and known thermal tolerance traits in replicated experimental D. melanogaster populations following more than 40 generations of evolution to either cyclic cold or hot temperatures. By evaluating fitness for both evolved populations alongside a reconstituted starting population, the evolved populations were shown to be the best adapted within their respective thermal environments. More strikingly, the evolved populations exhibited increased fitness in both environments and improved resistance to both acute heat and cold stress. This unexpected parallel response appeared to be an adaptation to the rapid temperature changes that drove the cycling thermal regimes, as parallel fitness changes were not observed when tested in a constant thermal environment. These results add to a small but growing group of studies that demonstrate the importance of fluctuating temperature changes for thermal adaptation and highlight the need for additional work in this area.

Condon, C., Acharya, A., Adrian, G. J., Hurliman, A. M., Malekooti, D., Nguyen, P., Zelic, M. H. and Angilletta, M. J. (2015). Indirect selection of thermal tolerance during experimental evolution of Drosophila melanogaster. Ecol Evol 5: 1873-1880. PubMed ID: 26140203
Natural selection alters the distribution of a trait in a population and indirectly alters the distribution of genetically correlated traits. Long-standing models of thermal adaptation assume that trade-offs exist between fitness at different temperatures; however, experimental evolution often fails to reveal such trade-offs. This study shows that adaptation to benign temperatures in experimental populations of Drosophila melanogaster resulted in correlated responses at the boundaries of the thermal niche. Specifically, adaptation to fluctuating temperatures (16-25 °C) decreased tolerance of extreme heat. Surprisingly, flies adapted to a constant temperature of 25 °C had greater cold tolerance than did flies adapted to other thermal conditions, including a constant temperature of 16 °C. As the populations were never exposed to extreme temperatures during selection, divergence of thermal tolerance likely reflects indirect selection of standing genetic variation via linkage or pleiotropy. No relationship was found between heat and cold tolerances in these populations. The results show that the thermal niche evolves by direct and indirect selection, in ways that are more complicated than assumed by theoretical models.

Tuesday, July 21st

Sandoval, H., Yao, C. K., Chen, K., Jaiswal, M., Donti, T., Lin, Y. Q., Bayat, V., Xiong, B., Zhang, K., David, G., Charng, W. L., Yamamoto, S., Duraine, L., Graham, B. H. and Bellen, H. J. (2014). Mitochondrial fusion but not fission regulates larval growth and synaptic development through steroid hormone production. Elife 3. PubMed ID: 25313867
Mitochondrial fusion and fission affect the distribution and quality control of mitochondria. This study shows that Marf (Mitochondrial associated regulatory factor), is required for mitochondrial fusion and transport in long axons. Moreover, loss of Marf leads to a severe depletion of mitochondria in neuromuscular junctions (NMJs). Marf mutants also fail to maintain proper synaptic transmission at NMJs upon repetitive stimulation, similar to Drp1 fission mutants. However, unlike Drp1, loss of Marf leads to NMJ morphology defects and extended larval lifespan. Marf is required to form contacts between the endoplasmic reticulum and/or lipid droplets (LDs) and for proper storage of cholesterol and ecdysone synthesis in ring glands. Interestingly, human Mitofusin-2 rescues the loss of LD but both Mitofusin-1 and Mitofusin-2 are required for steroid-hormone synthesis. These data show that Marf and Mitofusins share an evolutionarily conserved role in mitochondrial transport, cholesterol ester storage and steroid-hormone synthesis.

Devireddy, S., Liu, A., Lampe, T. and Hollenbeck, P. J. (2015). The organization of mitochondrial quality control and life cycle in the nervous system in vivo in the absence of PINK1. J Neurosci 35: 9391-9401. PubMed ID: 26109662
This study evaluated the roles of PINK1 mitochondrial kinase, and Parkin E3 ubiquitin ligase in targeting depolarized mitochondria for degradation in vivo, using quantitative measurements of mitochondria in Drosophila nervous system. The hypotheses was tested that impairment of mitochondrial quality control via suppression of PINK1 function should produce failures of turnover, accumulation of senescent mitochondria in the axon, defects in mitochondrial traffic, and a significant shift in the mitochondrial fission-fusion steady state. Although mitochondrial membrane potential was diminished by PINK1 deletion, the predicted increases in mitochondrial density or length in axons were not seen. Loss of PINK1 also produced specific, directionally balanced defects in mitochondrial transport, without altering the balance between stationary and moving mitochondria. Somatic mitochondrial morphology was also compromised. These results strongly circumscribe the possible mechanisms of PINK1 action in the mitochondrial life cycle and also raise the possibility that mitochondrial turnover events that occur in cultured embryonic axons might be restricted to the cell body in vivo, in the intact nervous system.

McMillan, B. J., Schnute, B., Ohlenhard, N., Zimmerman, B., Miles, L., Beglova, N., Klein, T. and Blacklow, S. C. (2015). A tail of two sites: a bipartite mechanism for recognition of Notch ligands by Mind bomb E3 ligases. Mol Cell 57: 912-924. PubMed ID: 25747658
Mind bomb (Mib) proteins (see Drosophila Mind bomb) are large, multi-domain E3 ligases that promote ubiquitination of the cytoplasmic tails of Notch ligands. This ubiquitination step marks the ligand proteins for epsin-dependent endocytosis, which is critical for in vivo Notch receptor activation. This study presents crystal structures of the substrate recognition domains of Mib1, both in isolation and in complex with peptides derived from Notch ligands. The structures, in combination with biochemical, cellular, and in vivo assays, show that Mib1 contains two independent substrate recognition domains that engage two distinct epitopes from the cytoplasmic tail of the ligand Jagged1 (see Drosophila Serrate), one in the intracellular membrane proximal region and the other near the C terminus. Together, these studies provide insights into the mechanism of ubiquitin transfer by Mind bomb E3 ligases, illuminate a key event in ligand-induced activation of Notch receptors, and identify a potential target for therapeutic modulation of Notch signal transduction in disease.

Matis, M., Russler-Germain, D. A., Hu, Q., Tomlin, C. J. and Axelrod, J. D. (2014). Microtubules provide directional information for core PCP function. Elife 3: e02893. PubMed ID: 25124458
Planar cell polarity (PCP) signaling controls the polarization of cells within the plane of an epithelium. Two molecular modules composed of Fat(Ft) / Dachsous(Ds) / Four-jointed(Fj) and a 'PCP-core' including Frizzled(Fz) and Dishevelled(Dsh) contribute to polarization of individual cells. How polarity is globally coordinated with tissue axes is unresolved. Consistent with previous results, this study found that the Ft/Ds/Fj-module has an effect on a microtubule (MT)-cytoskeleton. Evidence is provided for the model that the Ft/Ds/Fj-module provides directional information to the core-module through this MT organizing function. Ft/Ds/Fj-dependent initial polarization of the apical MT-cytoskeleton is shown to occur prior to global alignment of the core-module, reveal that the anchoring of apical non-centrosomal MTs at apical junctions is polarized. Directional trafficking of vesicles containing Dsh was observed to depend on Ft. The feasibility of this model was demonstrated by mathematical simulation. Together, these results support the hypothesis that Ft/Ds/Fj provides a signal to orient core PCP function via MT polarization.

Graves, J., Markman, S., Alegranti, Y., Gechtler, J., Johnson, R. I., Cagan, R. and Ben-Menahem, D. (2015). The LH/CG receptor activates canonical signaling pathway when expressed in Drosophila. Mol Cell Endocrinol [Epub ahead of print]. PubMed ID: 26112185
G-protein coupled receptors (GPCRs) and their ligands provide precise tissue regulation and are therefore often restricted to specific animal phyla. For example, the gonadotropins and their receptors are crucial for vertebrate reproduction but absent from invertebrates. In mammals, LHR mainly couples to the PKA signaling pathway, and CREB is the major transcription factor of this pathway. This study presents the results of expressing elements of the human gonadotropin system in Drosophila. Specifically, transgenic Drosophila were generated expressing the human LH/CG receptor (denoted as LHR), a constitutively active form of LHR, and an hCG analog. Activation-dependent signaling by LHR was demonstrated to direct Drosophila phenotypes including lethality and specific midline defects; these phenotypes were due to LHR activation of PKA/CREB pathway activity. That the LHR can act in an invertebrate demonstrates the conservation of factors required for GPCR function among phylogenetically distant organisms. This novel gonadotropin model may assist the identification of new modulators of mammalian fertility by exploiting the powerful genetic and pharmacological tools available in Drosophila.

Borg, R. M., Bordonne, R., Vassallo, N. and Cauchi, R. J. (2015). Genetic interactions between the members of the SMN-Gemins complex in Drosophila. PLoS One 10: e0130974. PubMed ID: 26098872
The SMN-Gemins complex is composed of Gemins 2-8, Unrip and the Survival motor neuron (SMN) protein. Despite multiple genetic studies, the Gemin proteins have not been identified as prominent modifiers of SMN-associated mutant phenotypes. This study used of the Drosophila model organism to investigate whether viability and motor phenotypes associated with a hypomorphic Gemin3 mutant are enhanced by changes in the levels of SMN, Gemin2 and Gemin5 brought about by various genetic manipulations. Modifier effect is shown by all three members of the minimalistic fly SMN-Gemins complex within the muscle compartment of the motor unit. Interestingly, muscle-specific overexpression of Gemin2 was by itself sufficient to depress normal motor function and its enhanced upregulation in all tissues leads to a decline in fly viability. The toxicity associated with increased Gemin2 levels is conserved in the yeast S. pombe in which it was found that the cytoplasmic retention of Sm proteins, likely reflecting a block in the snRNP assembly pathway, is a contributing factor. It is proposed that a disruption in the normal stoichiometry of the SMN-Gemins complex depresses its function with consequences that are detrimental to the motor system.

Monday, July 20th

Egenriether, S. M., Chow, E. S., Krauth, N. and Giebultowicz, J. M. (2015). Accelerated food source location in aging Drosophila. Aging Cell [Epub ahead of print] PubMed ID: 26102220
Adequate energy stores are essential for survival, and sophisticated neuroendocrine mechanisms evolved to stimulate foraging in response to nutrient deprivation. Food search behavior is usually investigated in young animals, and it is not known how aging alters this behavior. To address this question in Drosophila melanogaster, the ability to locate food by olfaction was investigated in young and old flies using a food-filled trap. As aging is associated with a decline in motor functions, learning, and memory, it was expected that aged flies would take longer to enter the food trap than their young counterparts. Surprisingly, old flies located food with significantly shorter latency than young ones. Robust food search behavior was associated with significantly lower fat reserves and lower starvation resistance in old flies. Food-finding latency (FFL) was shortened in young wild-type flies that were starved until their fat was depleted but also in heterozygous chico mutants with reduced insulin receptor activity and higher fat deposits. Conversely, food trap entry was delayed in old flies with increased insulin signaling. These results suggest that the difference in FFL between young and old flies is linked to age-dependent differences in metabolic status and may be mediated by reduced insulin signaling.

Zhang, S., Ross, K. D., Seidner, G. A., Gorman, M. R., Poon, T. H., Wang, X., Keithley, E. M., Lee, P. N., Martindale, M. Q., Joiner, W. J. and Hamilton, B. A. (2015). Nmf9 encodes a highly conserved protein important to neurological function in mice and flies. PLoS Genet 11: e1005344. PubMed ID: 26131556
Many protein-coding genes identified by genome sequencing remain without functional annotation or biological context. This study defines a novel protein-coding gene, Nmf9, based on a forward genetic screen for neurological function. ENU-induced and genome-edited null mutations in mice produce deficits in vestibular function, fear learning and circadian behavior, which correlated with Nmf9 expression in inner ear, amygdala, and suprachiasmatic nuclei. Homologous genes from unicellular organisms and invertebrate animals predict interactions with small GTPases, but the corresponding domains are absent in mammalian Nmf9. Intriguingly, homozygotes for null mutations in the Drosophila homolog, wide awake, show profound locomotor defects and premature death, while heterozygotes show striking effects on sleep and activity phenotypes. These results link a novel gene orthology group to discrete neurological functions, and show conserved requirement across wide phylogenetic distance and domain level structural changes.

Pegoraro, M., Picot, E., Hansen, C. N., Kyriacou, C. P., Rosato, E. and Tauber, E. (2015). Gene expression associated with early and late chronotypes in Drosophila melanogaster. Front Neurol 6: 100. PubMed ID: 26097463
The circadian clock provides the temporal framework for rhythmic behavioral and metabolic functions. In the modern era of industrialization, work, and social pressures, clock function is jeopardized, and can result in adverse and chronic effects on health. Understanding circadian clock function, particularly individual variation in diurnal phase preference (chronotype), and the molecular mechanisms underlying such chronotypes may lead to interventions that could abrogate clock dysfunction and improve human (and animal) health and welfare. Preliminary studies suggested that fruit-flies, like humans, can be classified as early rising "larks" or late rising "owls," providing a convenient model system for these types of studies. Strains of flies were identified showing increased preference for morning emergence (Early or E) from the pupal case, or more pronounced preference for evening emergence (Late or L). Pupae were sampled the day before eclosion (fourth day after pupariation) at 4 h intervals in the E and L strains, and differences were examined in gene expression by RNA-seq. This study has identified differentially expressed transcripts between the E and L strains, which provide candidate genes for subsequent studies of Drosophila chronotypes and their human orthologs.

Paulk, A.C., Kirszenblat, L., Zhou, Y. and van Swinderen, B. (2015). Closed-loop behavioral control increases coherence in the fly brain. J Neurosci 35: 10304-10315. PubMed ID: 26180205
This study questioned whether activity in the fruit fly brain is different during closed-loop behavior, compared with passive viewing of a stimulus. To address this question, the study used a procedure to record local field potential (LFP) activity across the fly brain while flies were controlling a virtual object through their movement on an air-supported ball. The virtual object was flickered at a precise frequency (7 Hz), creating a frequency tag that allowed tracking of brain responses to the object while animals were behaving. Following experiments under closed-loop control, the same stimulus was replayed to the fly in open loop, such that it could no longer control the stimulus. Identical receptive fields and similar strength of frequency tags were found across the brain for the virtual object under closed loop and replay. However, when comparing central versus peripheral brain regions, it was found that brain responses are differentially modulated depending on whether flies are in control or not. Additionally, coherence of LFP activity in the brain increases when flies are in control, compared with replay, even if motor behavior is similar. This suggests that processes associated with closed-loop control promote temporal coordination in the insect brain.

Sunday, July 19th

Menger, K. E., James, A. M., Cocheme, H. M., Harbour, M. E., Chouchani, E. T., Ding, S., Fearnley, I. M., Partridge, L. and Murphy, M. P. (2015). Fasting, but not aging, dramatically alters the redox status of cysteine residues on proteins in Drosophila melanogaster. Cell Rep 11: 1856-1865. PubMed ID: 26095360
Altering the redox state of cysteine residues on protein surfaces is an important response to environmental challenges. Although aging and fasting alter many redox processes, the role of cysteine residues is uncertain. To address this, a redox proteomic technique, oxidative isotope-coded affinity tags (OxICAT), was used to assess cysteine-residue redox changes in Drosophila melanogaster during aging and fasting. This approach enabled simultaneous identification and quantification of the redox state of several hundred cysteine residues in vivo. Cysteine residues within young flies had a bimodal distribution with peaks at approximately 10% and approximately 85% reversibly oxidized. Surprisingly, these cysteine residues did not become more oxidized with age. In contrast, 24 hr of fasting dramatically oxidized cysteine residues that were reduced under fed conditions while also reducing cysteine residues that were initially oxidized. It is concluded that fasting, but not aging, dramatically alters cysteine-residue redox status in D. melanogaster.

Wong, A.C., Luo, Y., Jing, X., Franzenburg, S., Bost, A. and Douglas, A.E. (2015). The host as driver of the microbiota in the gut and external environment of Drosophila melanogaster. Appl Environ Microbiol [Epub ahead of print]. PubMed ID: 26150460
Time-dependent changes of the microbial communities in the food are strongly influenced by the presence and abundance of Drosophila. When germ-free Drosophila eggs were aseptically added to non-sterile food, the microbiota in the food and flies converge to a composition dramatically different from fly-free food, showing that Drosophila has microbiota-independent effects on the food microbiota. The microbiota in both the flies that developed from unmanipulated eggs (bearing microorganisms) and the associated food is dominated by the most abundant bacteria on the eggs, demonstrating effective vertical transmission via surface contamination of eggs. Food co-inoculated with a four-species defined bacterial community of Acetobacter and Lactobacillus revealed the progressive elimination of Lactobacillus from the food bearing few or no Drosophila, indicative of antagonistic interactions between Acetobacter and Lactobacillus. Drosophila at high densities ameliorates the Acetobacter/Lactobacillus antagonism, enabling Lactobacillus to persist. This study on Drosophila demonstrates how animals can have major, coordinated effects on the composition of microbial communities in the gut and immediate environment.

Shih, H.W., Wu, C.L., Chang, S.W., Liu, T.H., Sih-Yu Lai, J., Fu, T.F., Fu, C.C. and Chiang, A.S. (2015). Parallel circuits control temperature preference in Drosophila during ageing. Nat Commun 6: 7775. PubMed ID: 26178754
The detection of environmental temperature and regulation of body temperature are integral determinants of behaviour for all animals. These functions become less efficient in aged animals, particularly during exposure to cold environments, yet the cellular and molecular mechanisms are not well understood. This study identifies an age-related change in the temperature preference of adult fruit flies that results from a shift in the relative contributions of two parallel mushroom body (MB) circuits-the β'- and β-systems. The β'-circuit primarily controls cold avoidance through dopamine signalling in young flies, whereas the β-circuit increasingly contributes to cold avoidance as adult flies age. Elevating dopamine levels in β'-afferent neurons of aged flies restores cold sensitivity, suggesting that the alteration of cold avoidance behaviour with ageing is functionally reversible. These results provide a framework for investigating how molecules and individual neural circuits modulate homeostatic alterations during the course of senescence.

Le Bourg, E., Gauthier, T. and Colinet, H. (2015). Feeding on frozen live yeast has some deleterious effects in Drosophila melanogaster. Exp Gerontol [Epub ahead of print]. PubMed ID: 26163343
Many experiments have shown that dietary restriction, for instance by removing live yeast or modifying the protein/carbohydrate ratio, can modulate lifespan, fecundity, resistance to severe stresses and behaviour in Drosophila melanogaster flies. This study tested whether feeding flies with frozen yeast rather than with fresh yeast could have some effect on these traits, the other components of the food being similar in the two groups. Freezing altered live yeast quality and flies feeding on frozen yeast lived slightly less (males), were less fecund at older ages, and poorly resisted to some severe stresses (cold and starvation), no negative effect being observed on resistance to heat. It seems that, like in humans, feeding on a low quality food can negatively impact healthspan and that an appropriate food is not only a food with optimal number of calories and appropriate ratios of proteins, carbohydrates, and fat.

Saturday, July 18th

Panda, D., Gold, B., Tartell, M. A., Rausch, K., Casas-Tinto, S. and Cherry, S. (2015). The transcription factor FoxK participates with Nup98 to regulate antiviral gene expression. MBio 6. PubMed ID: 25852164
Upon infection, pathogen recognition leads to a rapidly activated gene expression program that induces antimicrobial effectors to clear the invader. Nup98 has been shown to regulate the expression of a subset of rapidly activated antiviral genes to restrict disparate RNA virus infections in Drosophila by promoting RNA polymerase occupancy at the promoters of these antiviral genes. How Nup98 specifically targets these loci was unclear. In a genome-wide RNA interference (RNAi) screen, a relatively understudied forkhead transcription factor, FoxK, was identified as active against Sindbis virus (SINV) in Drosophila. This study found that FoxK is active against the panel of viruses that are restricted by Nup98, including SINV and vesicular stomatitis virus (VSV). Mechanistically, FoxK coordinately regulates the Nup98-dependent expression of antiviral genes. Depletion of FoxK significantly reduces Nup98-dependent induction of antiviral genes and reduces the expression of a forkhead response element-containing luciferase reporter. Together, these data show that FoxK-mediated activation of gene expression is Nup98 dependent. These studies were extended to mammalian cells, and it was found that the mammalian ortholog FOXK1 is antiviral against two disparate RNA viruses, SINV and VSV, in human cells. Interestingly, FOXK1 also plays a role in the expression of antiviral genes in mammals: depletion of FOXK1 attenuates virus-inducible interferon-stimulated response element (ISRE) reporter expression. Overall, these results demonstrate a novel role for FOXK1 in regulating the expression of antiviral genes, from insects to humans. This study has demonstrated that Nup98 cooperates with the transcription factor FoxK to regulate this gene expression program. Depletion of FoxK specifically reduces the induction of Nup98-dependent genes. Further, it was found that the antiviral function of FoxK is conserved, as the human ortholog FOXK1 is also antiviral and regulates gene expression from virus-induced promoters. Although other forkhead transcription factors have been implicated in immunity, a role for FoxK in antiviral defense was previously unappreciated. These findings reveal a conserved and novel role for FoxK in coordinating with Nup98 to promote a robust and complex antiviral transcriptional response.

Webster, C.L., Waldron, F.M., Robertson, S., Crowson, D., Ferrari, G., Quintana, J.F., Brouqui, J.M., Bayne, E.H., Longdon, B., Buck, A.H., Lazzaro, B.P., Akorli, J., Haddrill, P.R. and Obbard, D.J. (2015). The discovery, distribution, and evolution of viruses associated with Drosophila melanogaster. PLoS Biol 13: e1002210. PubMed ID: 26172158
Drosophila melanogaster is a valuable invertebrate model for viral infection and antiviral immunity, and is a focus for studies of insect-virus coevolution. This study uses a metagenomic approach to identify more than 20 previously undetected RNA viruses and a DNA virus associated with wild D. melanogaster. These viruses not only include distant relatives of known insect pathogens but also novel groups of insect-infecting viruses. By sequencing virus-derived small RNAs, it was shown that the viruses represent active infections of Drosophila. It was found that the RNA viruses differ in the number and properties of their small RNAs, and both siRNAs and a novel miRNA from the DNA virus were detected. Analysis of small RNAs also allowed identification of putative viral sequences that lack detectable sequence similarity to known viruses. By surveying >2,000 individually collected wild adult Drosophila, it was shown that more than 30% of D. melanogaster carry a detectable virus, and more than 6% carry multiple viruses. However, despite a high prevalence of the Wolbachia endosymbiont-which is known to be protective against virus infections in Drosophila-the study could not detect any relationship between the presence of Wolbachia and the presence of any virus. Using publicly available RNA-seq datasets, it was shown that the community of viruses in Drosophila laboratories is very different from that seen in the wild, but that some of the newly discovered viruses are nevertheless widespread in laboratory lines and are ubiquitous in cell culture. By sequencing viruses from individual wild-collected flies it was shown that some viruses are shared between D. melanogaster and D. simulans. These results provide an essential evolutionary and ecological context for host-virus interaction in Drosophila, and the newly reported viral sequences will help develop D. melanogaster further as a model for molecular and evolutionary virus research.

Beebe, K., Park, D., Taghert, P. H. and Micchelli, C. A. (2015). The Drosophila pro-secretory transcription factor dimmed is dynamically regulated in adult enteroendocrine cells and protects against gram-negative infection. G3 (Bethesda) [Epub ahead of print]. PubMed ID: 25999585
The endocrine system employs peptide hormone signals to translate environmental changes into physiological responses. The diffuse endocrine system embedded in the gastrointestinal barrier epithelium is one of the largest and most diverse endocrine tissues. Furthermore, it is the only endocrine tissue in direct physical contact with the microbial environment of the gut lumen. However, it remains unclear how this sensory epithelium responds to specific pathogenic challenges in a dynamic and regulated manner. This study demonstrates that the enteroendocrine cells of the adult Drosophila melanogaster midgut display a transient, sensitive, and systemic induction of the pro-secretory factor dimmed (dimm) in response to the Gram-negative pathogen Pseudomonas entomophila (Pe). In enteroendocrine cells, dimm controls the levels of the targets Phm, dcat-4 and the peptide hormone, Allatostatin A. Finally, dimm was identified as a host factor that protects against Pe infection and controls the expression of antimicrobial peptides. It is proposed that dimm provides "gain" in enteroendocrine output during the adaptive response to episodic pathogen exposure.

Ghosh, S., Singh, A., Mandal, S. and Mandal, L. (2015). Active hematopoietic hubs in Drosophila adults generate hemocytes and contribute to immune response. Dev Cell 33(4):478-88. PubMed ID: 25959225
Blood cell development in Drosophila shares significant similarities with vertebrate. The conservation ranges from biphasic mode of hematopoiesis to signaling molecules crucial for progenitor cell formation, maintenance, and differentiation. Primitive hematopoiesis in Drosophila ensues in embryonic head mesoderm, whereas definitive hematopoiesis happens in larval hematopoietic organ, the lymph gland. This organ, with the onset of pupation, ruptures to release hemocytes into circulation. It is believed that the adult lacks a hematopoietic organ and survives on the contribution of both embryonic and larval hematopoiesis. However, these studies revealed a surge of blood cell development in the dorsal abdominal hemocyte clusters of adult fly. These active hematopoietic hubs are capable of blood cell specification and can respond to bacterial challenges. The presence of progenitors and differentiated hemocytes embedded in a functional network of Laminin A and Pericardin within this hematopoietic hub projects it as a simple version of the vertebrate bone marrow (Ghosh, 2015).

Friday, June 17th

Ostrowski, D., Kahsai, L., Kramer, E.F., Knutson, P. and Zars, T. (2015). Place memory retention in Drosophila. Neurobiol Learn Mem [Epub ahead of print]. PubMed ID: 26143995
Some memories last longer than others, with some lasting a lifetime. Using several approaches memory phases have been identified. How are these different phases encoded, and do these different phases have similar temporal properties across learning situations? Place memory in Drosophila using the heat-box provides an excellent opportunity to examine the commonalities of genetically-defined memory phases across learning contexts. This study determines optimal conditions to test place memories that last up to three hours. An aversive temperature of 41°C was identified as critical for establishing a long-lasting place memory. Interestingly, adding an intermittent-training protocol only slightly increased place memory when intermediate aversive temperatures were used, and slightly extended the stability of a memory. Genetic analysis of this memory identified four genes as critical for place memory within minutes of training. The role of the rutabaga type I adenylyl cyclase was confirmed, and the latheo Orc3 origin of recognition complex component, the novel gene encoded by pastrel, and the small GTPase rac were all identified as essential for normal place memory. Examination of the dopamine and ecdysone receptor (DopEcR) did not reveal a function for this gene in place memory. When compared to the role of these genes in other memory types, these results suggest that there are genes that have both common and specific roles in memory formation across learning contexts. Importantly, contrasting the timing for the function of these four genes, plus a previously described role of the radish gene, in place memory with the temporal requirement of these genes in classical olfactory conditioning reveals variability in the timing of genetically-defined memory phases depending on the type of learning.

Bivik, C., Bahrampour, S., Ulvklo, C., Nilsson, P., Angel, A., Fransson, F., Lundin, E., Renhorn, J. and Thor, S. (2015). Novel genes involved in controlling specification of Drosophila FMRFamide neuropeptide cells. Genetics [Epub ahead of print]. PubMed ID: 26092715
The expression of neuropeptides is often extremely restricted in the nervous system, making them powerful markers for addressing cell specification. In the developing Drosophila ventral nerve cord, only six cells, the Ap4 neurons, out of some 10,000 neurons, express the neuropeptide FMRFamide (FMRFa). Each Ap4/FMRFa neuron is the last-born cell generated by an identifiable and well-studied progenitor cell; neuroblast 5-6 (NB5-6T). The restricted expression of FMRFa and the wealth of information regarding its gene regulation and Ap4 neuron specification, makes FMRFa a valuable readout for addressing many aspects of neural development. To this end, this paper describes a forward genetic screen utilizing an Ap4-specific FMRFa-eGFP transgenic reporter as a read-out. Systems identified in this screen included Polycomb group and Hox genes, columnar and segment polarity genes, temporal and NB identity genes, chromatin modification factors, cell fate determinants, axonal retrograde transport/BMP and Notch signaling factors, asymmetric cell division factors, chromosome condensation, cytokinesis, proteolysis and cell cycle factors, and RNA processing and Toll, Wnt and EGFR signaling factors. Novel alleles were isolated for previously known FMRFa regulators, confirming the validity of the screen. In addition, novel essential genes were identified, including several with previously undefined functions in neural development. This identification of genes affecting most major steps required for successful terminal differentiation of Ap4 neurons provides a comprehensive view of the genetic flow controlling the generation of highly unique neuronal cell types in the developing nervous system.

Kruttner, S., Traunmuller, L., Dag, U., Jandrasits, K., Stepien, B., Iyer, N., Fradkin, L. G., Noordermeer, J. N., Mensh, B. D. and Keleman, K. (2015). Synaptic Orb2A bridges memory acquisition and late memory consolidation in Drosophila. Cell Rep 11: 1953-1965. PubMed ID: 26095367
To adapt to an ever-changing environment, animals consolidate some, but not all, learning experiences to long-term memory. In mammals, long-term memory consolidation often involves neural pathway reactivation hours after memory acquisition. It is not known whether this delayed-reactivation schema is common across the animal kingdom or how information is stored during the delay period. This study shows that, during courtship suppression learning, Drosophila exhibits delayed long-term memory consolidation. It is also shown that the same class of dopaminergic neurons engaged earlier in memory acquisition is also both necessary and sufficient for delayed long-term memory consolidation. Furthermore, evidence is presented that, during learning, the translational regulator Orb2A tags specific synapses of mushroom body neurons for later consolidation. Consolidation involves the subsequent recruitment of Orb2B and the activity-dependent synthesis of CaMKII. Thus, these results provide evidence for the role of a neuromodulated, synapse-restricted molecule bridging memory acquisition and long-term memory consolidation in a learning animal.

Schulze, A., Gomez-Marin, A., Rajendran, V. G., Lott, G., Musy, M., Ahammad, P., Deogade, A., Sharpe, J., Riedl, J., Jarriault, D., Trautman, E. T., Werner, C., Venkadesan, M., Druckmann, S., Jayaraman, V. and Louis, M. (2015). Dynamical feature extraction at the sensory periphery guides chemotaxis. Elife 4. PubMed ID: 26077825
Behavioral strategies employed for chemotaxis have been described across phyla, but the sensorimotor basis of this phenomenon has seldom been studied in naturalistic contexts. This study examined how signals experienced during free olfactory behaviors are processed by first-order olfactory sensory neurons (OSNs) of the Drosophila larva. OSNs were found to be able to act as differentiators that transiently normalize stimulus intensity-a property potentially derived from a combination of integral feedback and feed-forward regulation of olfactory transduction. In olfactory virtual reality experiments, it is reported that high activity levels of the OSN suppress turning, whereas low activity levels facilitate turning. Using a generalized linear model, this study explains how peripheral encoding of olfactory stimuli modulates the probability of switching from a run to a turn. The work clarifies the link between computations carried out at the sensory periphery and action selection underlying navigation in odor gradients.

Thursday, July 16th

Reimão-Pinto, M.M., Ignatova, V., Burkard, T.R., Hung, J.H., Manzenreither, R.A., Sowemimo, I., Herzog, V.A., Reichholf, B., Fariña-Lopez, S. and Ameres, S.L. (2015). Uridylation of RNA hairpins by Tailor confines the emergence of microRNAs in Drosophila. Mol Cell [Epub ahead of print]. PubMed ID: 26145176
Uridylation of RNA species represents an emerging theme in post-transcriptional gene regulation. In the microRNA pathway, such modifications regulate small RNA biogenesis and stability in plants, worms, and mammals. This study reports Tailor, an uridylyltransferase that is required for the majority of 3' end modifications of microRNAs in Drosophila and predominantly targets precursor hairpins. Uridylation modulates the characteristic two-nucleotide 3' overhang of microRNA hairpins, which regulates processing by Dicer-1 and destabilizes RNA hairpins. Tailor preferentially uridylates mirtron hairpins, thereby impeding the production of non-canonical microRNAs. Mirtron selectivity is explained by primary sequence specificity of Tailor, selecting substrates ending with a 3' guanosine. In contrast to mirtrons, conserved Drosophila precursor microRNAs are significantly depleted in 3' guanosine, thereby escaping regulatory uridylation. These data support the hypothesis that evolutionary adaptation to Tailor-directed uridylation shapes the nucleotide composition of precursor microRNA 3' ends. Hence, hairpin uridylation may serve as a barrier for the de novo creation of microRNAs in Drosophila.

Bortolamiol-Becet, D., Hu, F., Jee, D., Wen, J., Okamura, K., Lin, C.J., Ameres, S.L. and Lai, E.C. (2015). Selective suppression of the splicing-mediated microRNA pathway by the terminal uridyltransferase Tailor. Mol Cell [Epub ahead of print]. PubMed ID: 26145174
Several terminal uridyltransferases (TUTases) are known to modulate small RNA biogenesis and/or function via diverse mechanisms. This study demonstrates that Drosophila splicing-derived pre-miRNAs (mirtrons) are efficiently modified by the previously uncharacterized TUTase, Tailor. Tailor is necessary and sufficient for mirtron hairpin uridylation, and this modification inhibits mirtron biogenesis. Genome-wide analyses demonstrate that mirtrons are dominant Tailor substrates, and three features contribute to substrate specificity. First, reprogramming experiments show Tailor preferentially identifies splicing-derived miRNAs. Second, in vitro tests indicate Tailor prefers substrate hairpins over mature miRNAs. Third, Tailor exhibits sequence preference for 3'-terminal AG, a defining mirtron characteristic. The study supports the notion that Tailor preferentially suppresses biogenesis of mirtrons, an evolutionarily adventitious pre-miRNA substrate class. Moreover, preferential activity of Tailor on 3'-G canonical pre-miRNAs and specific depletion of such loci from the pool of conserved miRNAs are detected. Thus, Tailor activity may have had collateral impact on shaping populations of canonical miRNAs.

Ishizu, H., Iwasaki, Y.W., Hirakata, S., Ozaki, H., Iwasaki, W., Siomi, H. and Siomi, M.C. (2015). Somatic primary piRNA biogenesis driven by cis-acting RNA elements and trans-acting Yb. Cell Rep [Epub ahead of print]. PubMed ID: 26166564
Primary piRNAs in Drosophila ovarian somatic cells arise from piRNA cluster transcripts and the 3' UTRs of a subset of mRNAs, including Traffic jam (Tj) mRNA. However, it is unclear how these RNAs are determined as primary piRNA sources. This study identifies a cis-acting 100-nt fragment in the Tj 3' UTR that is sufficient for producing artificial piRNAs from unintegrated DNA. These artificial piRNAs are effective in endogenous gene transcriptional silencing. Yb, a core component of primary piRNA biogenesis center Yb bodies, directly binds the Tj-cis element. Disruption of this interaction markedly reduces piRNA production. Thus, Yb is the trans-acting partner of the Tj-cis element. Yb-CLIP reveals that Yb binding correlates with somatic piRNA production but Tj-cis element downstream sequences produce few artificial piRNAs. The study thus proposes that Yb determines primary piRNA sources through two modes of action: primary binding to cis elements to specify substrates and secondary binding to downstream regions to increase diversity in piRNA populations.

Han, B. W., Wang, W., Li, C., Weng, Z. and Zamore, P. D. (2015). piRNA-guided transposon cleavage initiates Zucchini-dependent, phased piRNA production. Science 348: 817-821. PubMed ID: 25977554
PIWI-interacting RNAs (piRNAs) protect the animal germ line by silencing transposons. Primary piRNAs, generated from transcripts of genomic transposon "junkyards" (piRNA clusters), are amplified by the "ping-pong" pathway, yielding secondary piRNAs. This study reports that secondary piRNAs, bound to the PIWI protein Ago3, can initiate primary piRNA production from cleaved transposon RNAs. The first ~26 nucleotides (nt) of each cleaved RNA becomes a secondary piRNA, but the subsequent ~26 nt become the first in a series of phased primary piRNAs that bind Piwi, allowing piRNAs to spread beyond the site of RNA cleavage. The ping-pong pathway increases only the abundance of piRNAs, whereas production of phased primary piRNAs from cleaved transposon RNAs adds sequence diversity to the piRNA pool, allowing adaptation to changes in transposon sequence.

Wednesday, July 15th

Palumbo, V., et al. (2015). Misato controls mitotic microtubule generation by stabilizing the tubulin chaperone protein-1 complex. Curr Biol 25: 1777-1783. PubMed ID: 26096973
Mitotic spindles are primarily composed of microtubules (MTs), generated by polymerization of α- and β-Tubulin hetero-dimers. Defects in Tubulin polymerization dramatically affect spindle formation and disrupt chromosome segregation. Recently studies have described a role for the product of the conserved misato (mst) gene in regulating mitotic MT generation in flies, but the molecular function of Mst remains unknown. This study used affinity purification mass spectrometry (AP-MS) to identify interacting partners of Mst in the Drosophila embryo. Mst was shown to associate stoichiometrically with the hetero-octameric Tubulin Chaperone Protein-1 (TCP-1) complex, with the hetero-hexameric Tubulin Prefoldin complex, and with proteins having conserved roles in generating MT-competent Tubulin. RNAi-mediated in vivo depletion of any TCP-1 subunit phenocopies the effects of mutations in mst or the Prefoldin-encoding gene merry-go-round (mgr), leading to monopolar and disorganized mitotic spindles containing few MTs. Crucially, it was demonstrated that Mst, but not Mgr, is required for TCP-1 complex stability and that both the efficiency of Tubulin polymerization and Tubulin stability are drastically compromised in mst mutants. Moreover, structural bioinformatic analyses indicate that Mst resembles the three-dimensional structure of Tubulin monomers and might therefore occupy the TCP-1 complex central cavity. Collectively, these results suggest that Mst acts as a co-factor of the TCP-1 complex, playing an essential role in the Tubulin-folding processes required for proper assembly of spindle MTs.

Benmimoun, B., Polesello, C., Haenlin, M. and Waltzer L. (2015). The EBF transcription factor Collier directly promotes Drosophila blood cell progenitor maintenance independently of the niche. Proc Natl Acad Sci U S A [Epub ahead of print]. PubMed ID: 26150488
The maintenance of stem or progenitor cell fate relies on intrinsic factors as well as local cues from the cellular microenvironment and systemic signaling. In the lymph gland, an hematopoietic organ in Drosophila larva, a group of cells called the Posterior Signaling Centre (PSC), whose specification depends on the EBF transcription factor Collier (Col) and the HOX factor Antennapedia (Antp), has been proposed to form a niche required to maintain the pool of hematopoietic progenitors (prohemocytes). In contrast with this model, this study shows that genetic ablation of the PSC does not cause an increase in blood cell differentiation or a loss of blood cell progenitors. Furthermore, although both col and Antp mutant larvae are devoid of PSC, the massive prohemocyte differentiation observed in col mutant is not phenocopied in Antp mutant. Interestingly, beside its expression in the PSC, Col is also expressed at low levels in prohemocytes and it was shown that this expression persists in PSC-ablated and Antp mutant larvae. Moreover, targeted knockdown and rescue experiments indicate that Col expression is required in the prohemocytes to prevent their differentiation. Together, this study shows that the PSC is dispensable for blood cell progenitor maintenance and reveals the key role of the conserved transcription factor Col as an intrinsic regulator of hematopoietic progenitor fate.

Schuster, K.J. and Smith-Bolton, R.K. (2015). Taranis protects regenerating tissue from fate changes induced by the wound response in Drosophila. Dev Cell [Epub ahead of print]. PubMed ID: 26096735
Regenerating tissue must replace lost structures with cells of the proper identity and function. How regenerating tissue establishes or maintains correct cell fates during regrowth is an open question. This study identified a gene, taranis, that is essential for maintaining proper cell fate in damaged and regenerating Drosophila wing imaginal discs but that is dispensable for these fates in normal wing development. In regenerating tissue with reduced levels of Taranis, expression of the posterior selector gene engrailed is silenced through an autoregulatory silencing mechanism that requires the PRC1 component polyhomeotic, resulting in a transformation of posterior tissue into anterior tissue late in regeneration. An essential component of the wound response, JNK signaling, induces this misregulation of engrailed expression. Taranis can suppress these JNK-induced cell fate changes without interfering with JNK signaling activity. Thus, taranis protects regenerating tissue from deleterious side effects of wound healing and regeneration.

Etournay, R., Popovic, M., Merkel, M., Nandi, A., Blasse, C., Aigouy, B., Brandl, H., Myers, G., Salbreux, G., Julicher, F. and Eaton, S. (2015). Interplay of cell dynamics and epithelial tension during morphogenesis of the pupal wing. Elife 4. PubMed ID: 26102528
How tissue shape emerges from the collective mechanical properties and behavior of individual cells is not understood. This study combined experiment and theory to study this problem in the developing wing epithelium of Drosophila. At pupal stages, the wing-hinge contraction contributes to anisotropic tissue flows that reshape the wing blade. This study quantitatively accounts for this wing-blade shape change on the basis of cell divisions, cell rearrangements and cell shape changes. Cells both generate and respond to epithelial stresses during this process, and the nature of this interplay was shown to specify the pattern of junctional network remodeling that changes wing shape. Patterned constrains exerted on the tissue by the extracellular matrix are key to force the tissue into the right shape. This study presents a continuum mechanical model that quantitatively describes the relationship between epithelial stresses and cell dynamics, and how their interplay reshapes the wing.

Tuesday, July 14th

Otani, T., Oshima, K., Kimpara, A., Takeda, M., Abdu, U. and Hayashi, S. (2015). A transport and retention mechanism for the sustained distal localization of Spn-F-IKKepsilon during Drosophila bristle elongation. Development 142: 2338-2351. PubMed ID: 26092846
Stable localization of the signaling complex is essential for the robust morphogenesis of polarized cells. Cell elongation involves molecular signaling centers that coordinately regulate intracellular transport and cytoskeletal structures. In Drosophila bristle elongation, the protein kinase IKKepsilon is activated at the distal tip of the growing bristle and regulates the shuttling movement of recycling endosomes and cytoskeletal organization. However, how the distal tip localization of IKKepsilon is established and maintained during bristle elongation is unknown. This study demonstrates that IKKepsilon distal tip localization is regulated by Spindle-F (Spn-F), which is stably retained at the distal tip and functions as an adaptor linking IKKepsilon to cytoplasmic dynein. Javelin-like (Jvl) is a key regulator of Spn-F retention. In jvl mutant bristles, IKKepsilon and Spn-F initially localize to the distal tip but fail to be retained there. In S2 cells, particles that stain positively for Jvl or Spn-F move in a microtubule-dependent manner, whereas Jvl and Spn-F double-positive particles are immobile, indicating that Jvl and Spn-F are transported separately and, upon forming a complex, immobilize each other. These results suggest that polarized transport and selective retention regulate the distal tip localization of the Spn-F-IKKepsilon complex during bristle cell elongation.

Chen, G. Y., Arginteanu, D. F. and Hancock, W. O. (2015). Processivity of the kinesin-2 KIF3A results from rear head gating and not front head gating. J Biol Chem 290: 10274-10294. PubMed ID: 25657001
The kinesin-2 family motor KIF3A/B works together with dynein to bidirectionally transport intraflagellar particles, melanosomes, and neuronal vesicles. Compared with kinesin-1, kinesin-2 is less processive, and its processivity is more sensitive to load, suggesting that processivity may be controlled by different gating mechanisms. This study used stopped-flow and steady-state kinetics experiments, along with single-molecule and multimotor assays to characterize the entire kinetic cycle of a KIF3A homodimer that exhibits motility similar to that of full-length KIF3A/B. Upon first encounter with a microtubule, the motor rapidly exchanges both mADP and mATP. When adenosine 5'-[(β,γ)-imido]triphosphate was used to entrap the motor in a two-head-bound state, exchange kinetics were unchanged, indicating that rearward strain in the two-head-bound state does not alter nucleotide binding to the front head. A similar lack of front head gating was found when intramolecular strain was enhanced by shortening the neck linker domain from 17 to 14 residues. In single-molecule assays in ADP, the motor dissociates at 2.1 s-1, 20-fold slower than the stepping rate, demonstrating the presence of rear head gating. In microtubule pelleting assays, the KD(Mt) is similar in ADP and ATP. The data and accompanying simulations suggest that, rather than KIF3A processivity resulting from strain-dependent regulation of nucleotide binding (front head gating), the motor spends a significant fraction of its hydrolysis cycle in a low affinity state but dissociates only slowly from this state. This work provides a mechanism to explain differences in the load-dependent properties of kinesin-1 and kinesin-2.

Lerit, D.A., Jordan, H.A., Poulton, J.S., Fagerstrom, C.J., Galletta, B.J., Peifer, M. and Rusan, N.M. (2015). Interphase centrosome organization by the PLP-Cnn scaffold is required for centrosome function. J Cell Biol 210: 79-97. PubMed ID: 26150390
Pericentriolar material (PCM) mediates the microtubule (MT) nucleation and anchoring activity of centrosomes. A scaffold organized by Centrosomin (Cnn) serves to ensure proper PCM architecture and functional changes in centrosome activity with each cell cycle. This study investigates the mechanisms that spatially restrict and temporally coordinate centrosome scaffold formation. Focusing on the mitotic-to-interphase transition in Drosophila melanogaster embryos, it was shown that the elaboration of the interphase Cnn scaffold defines a major structural rearrangement of the centrosome. The study identifies an unprecedented role for Pericentrin-like protein (PLP), which localizes to the tips of extended Cnn flares, to maintain robust interphase centrosome activity and promote the formation of interphase MT asters required for normal nuclear spacing, centrosome segregation, and compartmentalization of the syncytial embryo. These data reveal that Cnn and PLP directly interact at two defined sites to coordinate the cell cycle-dependent rearrangement and scaffolding activity of the centrosome to permit normal centrosome organization, cell division, and embryonic viability.

Hannezo, E., Dong, B., Recho, P., Joanny, J. F. and Hayashi, S. (2015). Cortical instability drives periodic supracellular actin pattern formation in epithelial tubes. Proc Natl Acad Sci U S A [Epub ahead of print]. PubMed ID: 26077909
An essential question of morphogenesis is how patterns arise without preexisting positional information. Cytoskeletal flows in the cell cortex have been identified as a key mechanism of molecular patterning at the subcellular level. Studies have suggested that biological polymers such as actomyosin gels have the property to self-organize. This study reports that the regular spacing pattern of supracellular actin rings in the Drosophila tracheal tubule is governed by a self-organizing principle. A simple biophysical model is proposed where pattern formation arises from the interplay of myosin contractility and actin turnover. The hypotheses of the model was validated using photobleaching experiments, and it is reported that the formation of actin rings is contractility dependent. Moreover, genetic and pharmacological perturbations of the physical properties of the actomyosin gel modify the spacing of the pattern, as the model predicted. In addition, the model posited a role of cortical friction in stabilizing the spacing pattern of actin rings. Consistently, genetic depletion of apical extracellular matrix caused strikingly dynamic movements of actin rings, mirroring the model prediction of a transition from steady to chaotic actin patterns at low cortical friction. These results therefore demonstrate quantitatively that a hydrodynamical instability of the actin cortex can trigger regular pattern formation and drive morphogenesis in an in vivo setting.

Monday, July 13th

Slack, C., Alic, N., Foley, A., Cabecinha, M., Hoddinott, M.P. and Partridge, L. (2015). The Ras-Erk-ETS-signaling pathway is a drug target for longevity. Cell [Epub ahead of print]. PubMed ID: 26119340
Identifying the molecular mechanisms that underlie aging and their pharmacological manipulation are key aims for improving lifelong human health. This study identifies a critical role for Ras-Erk-ETS signaling in aging in Drosophila. It was shown that inhibition of Ras is sufficient for lifespan extension downstream of reduced insulin/IGF-1 (IIS) signaling. Moreover, direct reduction of Ras or Erk activity leads to increased lifespan. The study identifies the E-twenty six (ETS) transcriptional repressor, Anterior open (Aop), as central to lifespan extension caused by reduced IIS or Ras attenuation. Importantly, it demonstrates that adult-onset administration of the drug trametinib, a highly specific inhibitor of Ras-Erk-ETS signaling, can extend lifespan. This discovery of the Ras-Erk-ETS pathway as a pharmacological target for animal aging, together with the high degree of evolutionary conservation of the pathway, suggests that inhibition of Ras-Erk-ETS signaling may provide an effective target for anti-aging interventions in mammals.

Lee, J. E., et al. Defective Hfp-dependent transcriptional repression of dMYC is fundamental to tissue overgrowth in Drosophila XPB models. Nat Commun 6: 7404. PubMed ID: 26074141
Nucleotide excision DNA repair (NER) pathway mutations cause neurodegenerative and progeroid disorders (xeroderma pigmentosum (XP), Cockayne syndrome (CS) and trichothiodystrophy (TTD)), which are inexplicably associated with (XP) or without (CS/TTD) cancer. Moreover, cancer progression occurs in certain patients, but not others, with similar C-terminal mutations in the XPB helicase subunit of transcription and NER factor TFIIH. Mechanisms driving overproliferation and, therefore, cancer associated with XPB mutations are currently unknown. In this study using Drosophila models, evidence is provided that C-terminally truncated Hay/XPB alleles enhance overgrowth dependent on reduced abundance of RNA recognition motif protein Hfp/FIR, which transcriptionally represses the MYC oncogene homologue, dMYC. The data demonstrate that dMYC repression and dMYC-dependent overgrowth in the Hfp hypomorph is further impaired in the C-terminal Hay/XPB mutant background. Thus, it is predicted that defective transcriptional repression of MYC by the Hfp orthologue, FIR, might provide one mechanism for cancer progression in XP/CS.

Laye, M. J., Tran, V., Jones, D. P., Kapahi, P. and Promislow, D. E. (2015). The effects of age and dietary restriction on the tissue-specific metabolome of Drosophila. Aging Cell [Epub ahead of print]. PubMed ID: 26085309
Dietary restriction (DR) is a robust intervention that extends lifespan and slows the onset of age-related diseases in diverse organisms. This study examined changes in the metabolome from the head, thorax, abdomen, and whole body at multiple ages in Drosophila fed either a nutrient-rich ad libitum (AL) or nutrient-restricted (DR) diet. Multivariate analysis clearly separates the metabolome by diet in different tissues and different ages. DR significantly altered the metabolome and, in particular, slowed age-related changes in the metabolome. Interestingly, interacting metabolites were observed whose correlation coefficients, but not mean levels, differed significantly between AL and DR. The number and magnitude of positively correlated metabolites was greater under a DR diet. Furthermore, there was a decrease in positive metabolite correlations as flies aged on an AL diet. Conversely, DR enhanced these correlations with age. Metabolic set enrichment analysis identified several known (e.g., amino acid and NAD metabolism) and novel metabolic pathways that may affect how DR effects aging. The results suggest that network structure of metabolites is altered upon DR and may play an important role in preventing the decline of homeostasis with age.

Rogers, R. P. and Rogina, B. (2015). The role of INDY in metabolism, health and longevity. Front Genet 6: 204. PubMed ID: 26106407
Indy (I'm Not Dead Yet) encodes the fly homolog of a mammalian SLC13A5 plasma membrane transporter. INDY is expressed in metabolically active tissues functioning as a transporter of Krebs cycle intermediates with the highest affinity for citrate. Decreased expression of the Indy gene extends longevity in Drosophila and C. elegans. Reduction of INDY or its respective homologs in C. elegans and mice induces metabolic and physiological changes similar to those observed in calorie restriction. It is thought that these physiological changes are due to altered levels of cytoplasmic citrate, which directly impacts Krebs cycle energy production as a result of shifts in substrate availability. Citrate cleavage is a key event during lipid and glucose metabolism; thus, reduction of citrate due to Indy reduction alters these processes. With regards to mammals, mice with reduced Indy (mIndy-/-) also exhibit changes in glucose metabolism, mitochondrial biogenesis and are protected from the negative effects of a high calorie diet. Together, these data support a role for Indy as a metabolic regulator, which suggests INDY as a therapeutic target for treatment of diet and age-related disorders such as Type II Diabetes and obesity.

Wise, A., Tenezaca, L., Fernandez, R. W., Schatoff, E., Flores, J., Ueda, A., Zhong, X., Wu, C. F., Simon, A. F. and Venkatesh, T. (2015). Drosophila mutants of the autism candidate gene neurobeachin (rugose) exhibit neuro-developmental disorders, aberrant synaptic properties, altered locomotion, impaired adult social behavior and activity patterns. J Neurogenet: 1-34. PubMed ID: 26100104
Autism spectrum disorder (ASD) is a neurodevelopmental disorder in humans characterized by complex behavioral deficits, including intellectual disability, impaired social interactions and hyperactivity. ASD exhibits a strong genetic component with underlying multi-gene interactions. Candidate gene studies have shown that the neurobeachin gene is disrupted in human patients with idiopathic autism. The gene for neurobeachin (NBEA) spans the common fragile site FRA 13A and encodes a signal scaffold protein. In mice, NBEA has been shown to be involved in the trafficking and function of a specific subset of synaptic vesicles. rugose (rg) is the Drosophila homologue of the mammalian and human neurobeachin. Previous genetic and molecular analyses have shown that rg encodes an A kinase anchor protein (DAKAP 550), which interacts with components of the EGFR and Notch mediated signaling pathways, facilitating cross-talk between these and other pathways. This study presents functional data from studies on the larval neuromuscular junction that reveal abnormal synaptic architecture and physiology. In addition, adult rg loss-of-function mutants exhibit defective social interactions, impaired habituation, aberrant locomotion and hyperactivity. These results demonstrate that Drosophila neurobeachin (rugose) mutants exhibit phenotypic characteristics reminiscent of human ASD and thus could serve as a genetic model for studying autism spectrum disorders.

Bargiela, A., Cerro-Herreros, E., Fernandez-Costa, J. M., Vilchez, J. J., Llamusi, B. and Artero, R. (2015). Increased autophagy and apoptosis contribute to muscle atrophy in a myotonic dystrophy type 1 Drosophila model. Dis Model Mech 8: 679-690. PubMed ID: 26092529
Muscle mass wasting is one of the most debilitating symptoms of myotonic dystrophy type 1 (DM1) disease, ultimately leading to immobility, respiratory defects, dysarthria, dysphagia and death in advanced stages of the disease. In order to study the molecular mechanisms leading to the degenerative loss of adult muscle tissue in DM1, an inducible Drosophila model of expanded CTG trinucleotide repeat toxicity was generated that resembles an adult-onset form of the disease. Heat-shock induced expression of 480 CUG repeats in adult flies resulted in a reduction in the area of the indirect flight muscles. In these model flies, reduction of muscle area was concomitant with increased apoptosis and autophagy. Inhibition of apoptosis or autophagy mediated by the overexpression of DIAP1, mTOR (also known as Tor) or muscleblind, or by RNA interference (RNAi)-mediated silencing of autophagy regulatory genes, achieved a rescue of the muscle-loss phenotype. In fact, mTOR overexpression rescued muscle size to a size comparable to that in control flies. These results were validated in skeletal muscle biopsies from DM1 patients in which it was found downregulated autophagy and apoptosis repressor genes, and also in DM1 myoblasts where increased autophagy was found. These findings provide new insights into the signaling pathways involved in DM1 disease pathogenesis.

Sudmeier, L. J., Howard, S. P. and Ganetzky, B. (2015). A Drosophila model to investigate the neurotoxic side effects of radiation exposure. Dis Model Mech 8: 669-677. PubMed ID: 26092528
Children undergoing cranial radiation therapy (CRT) for CNS malignancies are at increased risk for neurological deficits later in life. Using Drosophila as a model, wild-type third-instar larvae were irradiated with single doses of gamma-radiation, and the percentage that survived to adulthood was determined. Motor function of surviving adults was examined with a climbing assay, and longevity was assessed by measuring lifespan. Neuronal cell death was assayed by using immunohistochemistry in adult brains. Irradiating late third-instar larvae at a dose of 20 Gy or higher impaired the motor activity of surviving adults. A dose of 40 Gy or higher resulted in a precipitous reduction in the percentage of larvae that survive to adulthood. A dose-dependent decrease in adult longevity was paralleled by a dose-dependent increase in activated Death caspase-1 (Dcp1) in adult brains. Survival to adulthood and adult lifespan were more severely impaired with decreasing larval age at the time of irradiation. Differences in genotype confered phenotypic differences in radio-sensitivity for developmental survival and motor function. This work demonstrates the usefulness of Drosophila to model the toxic effects of radiation during development.

Sheik Mohideen, S., Yamasaki, Y., Omata, Y., Tsuda, L. and Yoshiike, Y. (2015). Nontoxic singlet oxygen generator as a therapeutic candidate for treating tauopathies. Sci Rep 5: 10821. PubMed ID: 26027742
Methylene blue (MB) inhibits the aggregation of tau, a main constituent of neurofibrillary tangles. However, MB's mode of action in vivo is not fully understood. MB treatment reduced the amount of sarkosyl-insoluble tau in Drosophila that express human wild-type tau. MB concurrently ameliorated the climbing deficits of transgenic tau flies to a limited extent and diminished the climbing activity of wild-type flies. MB also decreased the survival rate of wild-type flies. Based on its photosensitive efficacies, it was surmised that singlet oxygen generated through MB under light might contribute to both the beneficial and toxic effects of MB in vivo. Rose bengal (RB) was identified that suppressed tau accumulation and ameliorated the behavioral deficits to a lesser extent than MB. Unlike MB, RB did not reduce the survival rate of flies. These findings indicate that singlet oxygen generators with little toxicity may be suitable drug candidates for treating tauopathies.

Sunday, July 12th

Slocumb, M.E., Regalado, J.M., Yoshizawa, M., Neely, G.G., Masek, P., Gibbs, A.G. and Keene, A.C. (2015). Enhanced sleep is an evolutionarily adaptive response to starvation stress in Drosophila. PLoS One 10: e0131275. PubMed ID: 26147198
Animals maximize fitness by modulating sleep and foraging strategies in response to changes in nutrient availability. Wild populations of the fruit fly Drosophila melanogaster display highly variable levels of starvation and desiccation resistance that differ in accordance with geographic location, nutrient availability, and evolutionary history. Further, flies potently modulate sleep in response to changes in food availability, and selection for starvation resistance enhances sleep, revealing strong genetic relationships between sleep and nutrient availability. To determine the genetic and evolutionary relationship between sleep and nutrient deprivation, this study assessed sleep in flies selected for desiccation or starvation resistance. While starvation resistant flies have higher levels of triglycerides, desiccation resistant flies have enhanced glycogen stores, indicative of distinct physiological adaptations to food or water scarcity. Strikingly, selection for starvation resistance, but not desiccation resistance, leads to increased sleep, indicating that enhanced sleep is not a generalized consequence of higher energy stores. Thermotolerance is not altered in starvation or desiccation resistant flies, providing further evidence for context-specific adaptation to environmental stressors. F2 hybrid flies were generated by crossing starvation selected flies with desiccation selected flies, and the relationship between nutrient deprivation and sleep was examined. Hybrids exhibit a positive correlation between starvation resistance and sleep, while no interaction was detected between desiccation resistance and sleep, revealing that prolonged sleep provides an adaptive response to starvation stress. Therefore, these findings demonstrate context-specific evolution of enhanced sleep in response to chronic food deprivation, and provide a model for understanding the evolutionary relationship between sleep and nutrient availability.

Mattei, A. L., Riccio, M. L., Avila, F. W. and Wolfner, M. F. (2015). Integrated 3D view of postmating responses by the Drosophila melanogaster female reproductive tract, obtained by micro-computed tomography scanning. Proc Natl Acad Sci U S A 112(27):8475-80. PubMed ID: 26041806.
Physiological changes in females during and after mating are triggered by seminal fluid components in conjunction with female-derived molecules. In insects, these changes include increased egg production, storage of sperm, and changes in muscle contraction within the reproductive tract (RT). Such postmating changes have been studied in dissected RT tissues, but understanding their coordination in vivo requires a holistic view of the tissues and their interrelationships. This study used high-resolution, multiscale micro-computed tomography (CT) scans to visualize and measure postmating changes in situ in the Drosophila female RT before, during, and after mating. These studies reveal previously unidentified dynamic changes in the conformation of the female RT that occur after mating. The results also reveal how the reproductive organs temporally shift in concert within the confines of the abdomen. For example, chiral loops were observed in the uterus and in the upper common oviduct that relax and constrict throughout sperm storage and egg movement. Specific seminal fluid proteins or female secretions mediate some of the postmating changes in morphology. The morphological movements, in turn, can cause further changes due to the connections among organs. In addition, apparent copulatory damage occurred to the female intima, suggesting a mechanism for entry of seminal proteins, or other exogenous components, into the female's circulatory system. The 3D reconstructions provided by high-resolution micro-CT scans reveal how male and female molecules and anatomy interface to carry out and coordinate mating-dependent changes in the female's reproductive physiology.

Rovenko, B. M., Kubrak, O. I., Gospodaryov, D. V., Perkhulyn, N. V., Yurkevych, I. S., Sanz, A., Lushchak, O. V. and Lushchak, V. I. (2015). High sucrose consumption promotes obesity whereas its low consumption induces oxidative stress in Drosophila melanogaster. J Insect Physiol 79: 42-54. PubMed ID: 26050918
This paper studied the effects of sucrose in larval diet on development and metabolic parameters of adult flies. Larvae consumed more food at low sucrose diet, overeating with yeast. On high sucrose diet, larvae ingested more carbohydrates, despite consuming less food and obtaining less protein derived from yeast. High sucrose diet slowed down pupation and increased pupa mortality, enhanced levels of lipids and glycogen, increased dry body mass, decreased water content, i.e. resulted in obese phenotype. Furthermore, it suppressed reactive oxygen species-induced oxidation of lipids and proteins as well as the activity of superoxide dismutase. The activity of catalase was gender-related. In males, at all sucrose concentrations used catalase activity was higher than at its concentration of 0.25%, whereas in females sucrose concentration virtually did not influence the activity. High sucrose diet increased content of protein thiols and the activity of glucose-6-phosphate dehydrogenase. The increase in sucrose concentration also enhanced uric acid level in females, but caused opposite effects in males. Development on high sucrose diets was accompanied by elevated steady-state insulin-like peptide 3 mRNA level. Finally, carbohydrate starvation at yeast overfeeding on low sucrose diets resulted in oxidative stress reflected by higher levels of oxidized lipids and proteins accompanied by increased superoxide dismutase activity. Potential mechanisms involved in regulation of redox processes by carbohydrates are discussed.

Stetina, T., Kostal, V. and Korbelova, J. (2015). The role of inducible Hsp70, and other heat shock proteins, in adaptive complex of cold tolerance of the fruit fly (Drosophila melanogaster). PLoS One 10: e0128976. PubMed ID: 26034990
This paper analyzes the cold tolerance and the expression levels of 24 different mRNA transcripts of the Hsps complex and related genes in response to cold in two strains of D. melanogaster: the wild-type and the Hsp70- null mutant lacking all six copies of Hsp70 gene. Larvae of both strains showed similar patterns of Hsps complex gene expression in response to long-term cold-acclimation and during recovery from chronic cold exposures or acute cold shocks. No transcriptional compensation for missing Hsp70 gene was seen in Hsp70- strain. The cold-induced Hsps gene expression is most probably regulated by alternative splice variants C and D of the Heat Shock Factor. The cold tolerance in Hsp70- null mutants was clearly impaired only when the larvae were exposed to severe acute cold shock. No differences in mortality were found between two strains when the larvae were exposed to relatively mild doses of cold, either chronic exposures to 0 degrees C or acute cold shocks at temperatures down to -4 degrees C. It is concluded that up-regulated expression of a complex of inducible Hsps genes, and Hsp70 mRNA in particular, is tightly associated with cold-acclimation and cold exposure in D. melanogaster. Genetic elimination of Hsp70 up-regulation response has no effect on survival of chronic exposures to 0 degrees C or mild acute cold shocks, while it negatively affects survival after severe acute cold shocks at temperaures below -8 degrees C.

Nasiri Moghadam, N., Holmstrup, M., Manenti, T., Brandt Mouridsen, M., Pertoldi, C. and Loeschcke, V. (2015). The role of storage lipids in the relation between fecundity, locomotor activity, and lifespan of Drosophila melanogaster longevity-selected and control lines. PLoS One 10: e0130334. PubMed ID: 26115349
The contribution of insect fat body to multiple processes, such as development, metamorphosis, activity, and reproduction results in trade-offs between life history traits. In the present study, age-induced modulation of storage lipid composition in Drosophila melanogaster longevity-selected (L) and non-selected control (C) lines was studied and the correlation between total body fat mass and lifespan assessed. The trade-offs between fecundity, locomotor activity, and lifespan were re-evaluated from a lipid-related metabolic perspective. Fewer storage lipids in the L lines compared to the C lines supports the impact of body fat mass on extended lifespan. The higher rate of fecundity and locomotor activity in the L lines may increase the lipid metabolism and enhance the lipolysis of storage lipids, reducing fat reserves. The correlation between neutral lipid fatty acids and fecundity, as well as locomotor activity, varied across age groups and between the L and C lines. The fatty acids that correlated with egg production were different from the fatty acids that correlated with locomotor activity. The present study suggests that fecundity and locomotor activity may positively affect the lifespan of D. melanogaster through the inhibition of fat accumulation.

Terhzaz, S., Cabrero, P., Brinzer, R. A., Halberg, K. A., Dow, J. A. and Davies, S. A. (2015). A novel role of Drosophila cytochrome P450-4e3 in permethrin insecticide tolerance. Insect Biochem Mol Biol [Epub ahead of print]. PubMed ID: 26073628
The exposure of insects to xenobiotics, such as insecticides, triggers a complex defence response necessary for survival. This response includes the induction of genes that encode key Cytochrome P450 monooxygenase detoxification enzymes. Drosophila melanogaster Malpighian (renal) tubules are critical organs in the detoxification and elimination of these foreign compounds, so the tubule response induced by dietary exposure to the insecticide permethrin was examined. Expression of the gene encoding Cytochrome P450-4e3 (Cyp4e3) was significantly up-regulated by Drosophila fed on permethrin, and manipulation of Cyp4e3 levels, specifically in the principal cells of the Malpighian tubules, impacts significantly on the survival of permethrin-fed flies. Both dietary exposure to permethrin and Cyp4e3 knockdown cause a significant elevation of oxidative stress-associated markers in the tubules, including H2O2 and lipid peroxidation byproduct, HNE (4-hydroxynonenal). Thus, Cyp4e3 may play an important role in regulating H2O2 levels in the endoplasmic reticulum (ER) where it resides, and its absence triggers a JAK/STAT and NF-kappaB-mediated stress response, similar to that observed in cells under ER stress. This work increases understanding of the molecular mechanisms of insecticide detoxification and provides further evidence of the oxidative stress responses induced by permethrin metabolism.

Saturday, July 11th

Shorter, J., Couch, C., Huang, W., Carbone, M.A., Peiffer, J., Anholt, R.R. and Mackay, T.F. (2015). Genetic architecture of natural variation in Drosophila melanogaster aggressive behavior. Proc Natl Acad Sci U S A [Epub ahead of print]. PubMed ID: 26100892
Aggression is an evolutionarily conserved complex behavior essential for survival and the organization of social hierarchies. With the exception of genetic variants associated with bioamine signaling, which have been implicated in aggression in many species, the genetic basis of natural variation in aggression is largely unknown. Drosophila melanogaster is a favorable model system for exploring the genetic basis of natural variation in aggression. This study performed genome-wide association analyses using the inbred, sequenced lines of the Drosophila melanogaster Genetic Reference Panel (DGRP) and replicate advanced intercross populations derived from the most and least aggressive DGRP lines. Genes were identified that have been previously implicated in aggressive behavior as well as many novel loci, including gustatory receptor 63a (Gr63a), which encodes a subunit of the receptor for CO2, and genes associated with development and function of the nervous system. Although genes from the two association analyses are largely nonoverlapping, they map onto a genetic interaction network inferred from an analysis of pairwise epistasis in the DGRP. Mutations and RNAi knock-down alleles were used to functionally validate 79% of the candidate genes and 75% of the candidate epistatic interactions. Epistasis for aggressive behavior causes cryptic genetic variation in the DGRP that is revealed by changing allele frequencies in the outbred populations derived from extreme DGRP lines. This phenomenon may pertain to other fitness traits and species, with implications for evolution, applied breeding, and human genetics.

Rodrigues, M.A., et al. (2015). Drosophila melanogaster larvae make nutritional choices that minimize developmental time. J Insect Physiol [Epub ahead of print]. PubMed ID: 26149766
To gain insight into the the relationship between life history characters and foraging decisions, this study used a geometric framework for nutrition to assess how the protein and carbohydrate content of the larval diet affected key life history traits in Drosophila. In no-choice assays, survival from egg to pupae, female and male body size, and ovariole number - a proxy for female fecundity - are maximized at the highest protein to carbohydrate (P:C) ratio (1.5:1). In contrast, development time is minimized at intermediate P:C ratios, around 1:2. Next, the larvae were subjected to two-choice tests to determine how they regulate their protein and carbohydrate intake in relation to these life history traits. Larvae were found to target their consumption to P:C ratios that minimize development time. Finally, whether adult females also chose to lay their eggs in the P:C ratios that minimize developmental time was examined. Using a three-choice assay, adult females were found to preferentially lay their eggs in food P:C ratios that are suboptimal for all larval life history traits. These results demonstrate that D. melanogaster larvae make foraging decisions that trade-off developmental time with body size, ovariole number, and survival. In addition, adult females make oviposition decisions that do not appear to benefit the larvae. The study proposes that these decisions may reflect the living nature of the larval nutritional environment in rotting fruit. These studies illustrate the interaction between the nutritional environment, life history traits, and foraging choices in D. melanogaster, and lend insight into the ecology of their foraging decisions.

Herrero, A., Romanowski, A., Meelkop, E., Caldart, C., Schoofs, L. and Golombek, D. A. (2015). Pigment-dispersing factor (Pdf) signaling in the circadian system of Caenorhabditis elegans. Genes Brain Behav. PubMed ID: 26113231
The neuropeptide PDF (Pigment Dispersing Factor) is important for the generation and entrainment of circadian rhythms in the fruitfly Drosophila melanogaster. Recently two pdf homologs, pdf-1 and pdf-2, and a PDF receptor, pdfr-1, have been found in Caenorhabditis elegans and have been implicated in locomotor activity. This work studied the role of the PDF neuropeptide in the circadian system of C. elegans and found that both pdf-1 and pdf-2 mutants affect the normal locomotor activity outputs. In particular, loss of pdf-1 induced circadian arrhythmicity under both light-dark (LD) and constant dark (DD) conditions. These defects can be rescued by a genomic copy of the pdf-1 locus. These results indicate that PDF-1 is involved in rhythm generation and in the synchronization to LD cycles, since rhythmic patterns of activity rapidly disappear when pdf-1 mutants are recorded under both entrained and free running conditions. The role of PDF-2 and the PDF receptors is probably more complex and involves the interaction between the two pdf paralogues found in the nematode.

Mureli, S. and Fox, J. L. (2015). Haltere mechanosensory influence on tethered flight behavior in Drosophila. J Exp Biol [Epub ahead of print]. PubMed ID: 26113141
Tethered flies to examine the relationship between halteres and the visual system using wide-field motion or moving figures as visual stimuli. Haltere input was altered by surgically decreasing its mass, or by removing it entirely. Haltere removal does not affect the flies' ability to flap or steer their wings, but it does increase the temporal frequency at which they modify their wingbeat amplitude. Reducing the haltere mass decreases the optomotor reflex response to wide-field motion, and removing the haltere entirely does not further decrease the response. Decreasing the mass does not attenuate the response to figure motion, but removing the entire haltere does attenuate the response. When flies are allowed to control a visual stimulus in closed-loop conditions, haltereless flies fixate figures with the same acuity as intact flies, but cannot stabilize a wide-field stimulus as accurately as intact flies can. These manipulations suggest that the haltere mass is influential in wide-field stabilization, but less so in figure tracking. In both figure and wide-field experiments, responses to visual motion were observed with and without halteres, indicating that during tethered flight, intact halteres are not strictly necessary for visually-guided wing-steering responses. However, the haltere feedback loop may operate in a context-dependent way to modulate responses to visual motion.

Friday, July 10th

Yang, F., Zhao, R., Fang, X., Huang, H., Xuan, Y., Ma, Y., Chen, H., Cai, T., Qi, Y. and Xi, R. (2015). The RNA surveillance complex Pelo-Hbs1 is required for transposon silencing in the Drosophila germline. EMBO Rep [Epub ahead of print]. PubMed ID: 26124316
Silencing of transposable elements (TEs) in the metazoan germline is critical for genome integrity and is primarily dependent on Piwi proteins and associated RNAs, which exert their function through both transcriptional and posttranscriptional mechanisms. This study reports that the evolutionarily conserved Pelo (Dom34)-Hbs1 mRNA surveillance complex is required for transposon silencing in the Drosophila germline. In pelo mutant gonads, mRNAs and proteins of some selective TEs are up-regulated. Pelo is not required for piRNA biogenesis, and Pelo may function at the translational level to silence TEs: this function requires interaction with Hbs1, and overexpression of RpS30a partially reverts TE-silencing defects in pelo mutants. Interestingly, TE silencing and spermatogenesis defects in pelo mutants can also effectively be rescued by expressing the mammalian ortholog of Pelo. The study proposes that the Pelo-Hbs1 surveillance complex provides another level of defense against the expression of TEs in the germline of Drosophila and possibly all metazoa.

Simon, B., Masiewicz, P., Ephrussi, A. and Carlomagno, T. (2015). The structure of the SOLE element of oskar mRNA. RNA [Epub ahead of print]. PubMed ID: 26089324.
mRNA localization by active transport is a regulated process that requires association of mRNPs with protein motors for transport along either the microtubule or the actin cytoskeleton. oskar mRNA localization at the posterior pole of the Drosophila oocyte requires a specific mRNA sequence, termed the SOLE, which comprises nucleotides of both exon 1 and exon 2 and is assembled upon splicing. The SOLE folds into a stem-loop structure. Both SOLE RNA and the exon junction complex (EJC) are required for oskar mRNA transport along the microtubules by kinesin. The SOLE RNA likely constitutes a recognition element for a yet unknown protein, which either belongs to the EJC or functions as a bridge between the EJC and the mRNA. This study determined the solution structure of the SOLE RNA by Nuclear Magnetic Resonance spectroscopy. The SOLE forms a continuous helical structure, including a few noncanonical base pairs, capped by a pentanucleotide loop. The helix displays a widened major groove, which could accommodate a protein partner. In addition, the apical helical segment undergoes complex dynamics, with potential functional significance.

Lozano, J., Montanez, R. and Belles, X. (2015). MiR-2 family regulates insect metamorphosis by controlling the juvenile hormone signaling pathway. Proc Natl Acad Sci U S A 112: 3740-3745. PubMed ID: 25775510
Depletion of Dicer-1, the enzyme that catalyzes the final step of miRNA biosynthesis, prevents metamorphosis in Blattella germanica. However, the precise regulatory roles of miRNAs in the process have remained elusive. In the present work, Dicer-1 depletion has been shown to result in an increase of mRNA levels of Kruppel homolog 1 (Kr-h1), a juvenile hormone-dependent transcription factor that represses metamorphosis, and that depletion of Kr-h1 expression in Dicer-1 knockdown individuals rescues metamorphosis. It was also found that the 3'UTR of Kr-h1 mRNA contains a functional binding site for miR-2 family miRNAs (for miR-2, miR-13a, and miR-13b). These data suggest that metamorphosis impairment caused by Dicer-1 and miRNA depletion is due to a deregulation of Kr-h1 expression and that this deregulation is derived from a deficiency of miR-2 miRNAs. This was corroborated by treating the last nymphal instar of B. germanica with an miR-2 inhibitor, which impaired metamorphosis, and by treating Dicer-1-depleted individuals with an miR-2 mimic to allow nymphal-to-adult metamorphosis to proceed. Taken together, the data indicate that miR-2 miRNAs scavenge Kr-h1 transcripts when the transition from nymph to adult should be taking place, thus crucially contributing to the correct culmination of metamorphosis.

Michalski, D. and Steiniger, M. (2015). In vivo characterization of the Drosophila mRNA 3' end processing core cleavage complex. RNA [Epub ahead of print]. PubMed ID: 26081560
A core cleavage complex (CCC) consisting of CPSF73, CPSF100, and Symplekin is required for cotranscriptional 3' end processing of all metazoan pre-mRNAs, yet little is known about the in vivo molecular interactions within this complex. The CCC is a component of two distinct complexes, the cleavage/polyadenylation complex and the complex that processes nonpolyadenylated histone pre-mRNAs. RNAi-depletion of CCC factors in Drosophila culture cells causes reduction of CCC processing activity on histone mRNAs, resulting in read through transcription. In contrast, RNAi-depletion of factors only required for histone mRNA processing allows use of downstream cryptic polyadenylation signals to produce polyadenylated histone mRNAs. This study used Dmel-2 tissue culture cells stably expressing tagged CCC components to determine that amino acids 272-1080 of Symplekin and the C-terminal approximately 200 amino acids of both CPSF73 and CPSF100 are required for efficient CCC formation in vivo. Additional experiments reveal that the C-terminal 241 amino acids of CPSF100 are sufficient for histone mRNA processing indicating that the first 524 amino acids of CPSF100 are dispensable for both CCC formation and histone mRNA 3' end processing. CCCs containing deletions of Symplekin lacking the first 271 amino acids resulted in dramatic increased use of downstream polyadenylation sites for histone mRNA 3' end processing similar to RNAi-depletion of histone-specific 3' end processing factors FLASH, SLBP, and U7 snRNA. A model is proposed in which CCC formation is mediated by CPSF73, CPSF100, and Symplekin C-termini, and the N-terminal region of Symplekin facilitates cotranscriptional 3' end processing of histone mRNAs.

Thursday, July 9th

Strauss, A. L., Kawasaki, F. and Ordway, R. W. (2015). A distinct perisynaptic glial cell type forms tripartite neuromuscular synapses in the Drosophila adult. PLoS One 10: e0129957. PubMed ID: 26053860 .
Studies of Drosophila flight muscle neuromuscular synapses have revealed their tripartite architecture and established an attractive experimental model for genetic analysis of glial function in synaptic transmission. This study defined a new Drosophila glial cell type, designated peripheral perisynaptic glia (PPG), which resides in the periphery and interacts specifically with fine motor axon branches forming neuromuscular synapses. Identification and specific labeling of PPG was achieved through cell type-specific RNAi-mediated knockdown (KD) of a glial marker, Glutamine Synthetase 2 (GS2). In addition, comparison among different Drosophila neuromuscular synapse models from adult and larval developmental stages indicated the presence of tripartite synapses on several different muscle types in the adult. In contrast, PPG appear to be absent from larval body wall neuromuscular synapses, which do not exhibit a tripartite architecture but rather are imbedded in the muscle plasma membrane. Evolutionary conservation of tripartite synapse architecture and peripheral perisynaptic glia in vertebrates and Drosophila suggests ancient and conserved roles for glia-synapse interactions in synaptic transmission.

Muller, M., Genc, O. and Davis, G. W. (2015). RIM-binding protein links synaptic homeostasis to the stabilization and replenishment of high release probability vesicles. Neuron 85: 1056-1069. PubMed ID: 25704950.
This study defines activities of RIM-binding protein (RBP) that are essential for baseline neurotransmission and presynaptic homeostatic plasticity. At baseline, rbp mutants have a approximately 10-fold decrease in the apparent Ca(2+) sensitivity of release that this study attributes to (1) impaired presynaptic Ca(2+) influx, (2) looser coupling of vesicles to Ca(2+) influx, and (3) limited access to the readily releasable vesicle pool (RRP). During homeostatic plasticity, RBP is necessary for the potentiation of Ca(2+) influx and the expansion of the RRP. Remarkably, rbp mutants also reveal a rate-limiting stage required for the replenishment of high release probability (p) vesicles following vesicle depletion. This rate slows approximately 4-fold at baseline and nearly 7-fold during homeostatic signaling in rbp. These effects are independent of altered Ca(2+) influx and RRP size. It is proposed that RBP stabilizes synaptic efficacy and homeostatic plasticity through coordinated control of presynaptic Ca(2+) influx and the dynamics of a high-p vesicle pool.

Chang, L., Kreko-Pierce, T. and Eaton, B. A. (2015). The guanine exchange factor Gartenzwerg and the small GTPase Arl1 function in the same pathway with Arfaptin during synapse growth. Biol Open [Epub ahead of print]. PubMed ID: 26116655
The generation of neuronal morphology requires transport vesicles originating from the Golgi apparatus (GA) to deliver specialized components to the axon and dendrites. Drosophila Arfaptin is a membrane-binding protein localized to the GA that is required for the growth of the presynaptic nerve terminal. This study provides biochemical, cellular and genetic evidence that the small GTPase Arl1 and the guanine-nucleotide exchange factor (GEF) Gartenzwerg are required for Arfaptin function at the Golgi during synapse growth. These data define a new signaling pathway composed of Arfaptin, Arl1, and Garz, required for the generation of normal synapse morphology.

Lavieu, G., Dunlop, M. H., Lerich, A., Zheng, H., Bottanelli, F. and Rothman, J. E. (2014). The Golgi ribbon structure facilitates anterograde transport of large cargoes. Mol Biol Cell 25: 3028-3036. PubMed ID: 25103235
In mammalian cells, individual Golgi stacks fuse laterally to form the characteristic perinuclear ribbon structure. Yet the purpose of this remarkable structure has been an enigma. This study reports that breaking down the ribbon of mammalian cells strongly inhibits intra-Golgi transport of large cargoes without altering the rate of transport of smaller cargoes. In addition, insect cells that naturally harbor dispersed Golgi stacks have limited capacity to transport artificial oversized cargoes. These results imply that the ribbon structure is an essential requirement for transport of large cargoes in mammalian cells, and it is suggested that this is because it enables the dilated rims of cisternae (containing the aggregates) to move across the stack as they transfer among adjacent stacks within the ribbon structure.

Wednesday, July 8th

Langen, M., Agi, E., Altschuler, D.J., Wu, L.F., Altschuler, S.J. and Hiesinger, P.R. (2015). The developmental rules of neural superposition in Drosophila. Cell [Epub ahead of print]. PubMed ID: 26119341
Complicated neuronal circuits can be genetically encoded, but the underlying developmental algorithms remain largely unknown. This study describes a developmental algorithm for the specification of synaptic partner cells through axonal sorting in the Drosophila visual map. This approach combines intravital imaging of growth cone dynamics in developing brains of intact pupae and data-driven computational modeling. These analyses suggest that three simple rules (Rule 1: The Scaffolding Rule, Rule 2; The Extension Rule, and Rule 3; The Stop Rule) are sufficient to generate the seemingly complex neural superposition wiring of the fly visual map without an elaborate molecular matchmaking code. The computational model explains robust and precise wiring in a crowded brain region despite extensive growth cone overlaps and provides a framework for matching molecular mechanisms with the rules they execute. Finally, ordered geometric axon terminal arrangements that are not required for neural superposition are a side product of the developmental algorithm, thus elucidating neural circuit connectivity that remained unexplained based on adult structure and function alone.

Kis, V, Barti, B., Lippai, M. and Sass, M. (2015). Specialized cortex glial cells accumulate lipid droplets in Drosophila melanogaster. PLoS One 10: e0131250. PubMed ID: 26148013
Lipid droplets (LDs) are common organelles of the majority of eukaryotic cell types. Their biological significance has been extensively studied in mammalian liver cells and white adipose tissue. Although the central nervous system contains the highest relative amount and the largest number of different lipid species, neither the spatial nor the temporal distribution of LDs has been described. This study used the brain of the fruitfly, Drosophila melanogaster, to investigate the neuroanatomy of LDs. LDs were shown to be exclusively localised in glial cells but not in neurons in the larval nervous system. It was shown that the brain's LD pool, rather than being constant, changes dynamically during development and reaches its highest value at the beginning of metamorphosis. LDs are particularly enriched in cortex glial cells located close to the brain surface. These specialized superficial cortex glial cells contain the highest amount of LDs among glial cell types and encapsulate neuroblasts and their daughter cells. Superficial cortex glial cells, combined with subperineurial glial cells, express the Drosophila fatty acid binding protein (Dfabp), as was demonstrated through light- and electron microscopic immunocytochemistry. This is the first study that describes LD neuroanatomy in the Drosophila larval brain.

Lin, W. Y., Williams, C., Yan, C., Koledachkina, T., Luedke, K., Dalton, J., Bloomsburg, S., Morrison, N., Duncan, K. E., Kim, C. C. and Parrish, J. Z. (2015). The SLC36 transporter Pathetic is required for extreme dendrite growth in Drosophila sensory neurons. Genes Dev 29: 1120-1135. PubMed ID: 26063572
Dendrites exhibit enormous diversity in form and can differ in size by several orders of magnitude even in a single animal. However, whether neurons with large dendrite arbors have specialized mechanisms to support their growth demands is unknown. To address this question, a genetic screen was conducted for mutations that differentially affected growth in neurons with different-sized dendrite arbors. From this screen, a mutant was identified that selectively affects dendrite growth in neurons with large dendrite arbors without affecting dendrite growth in neurons with small dendrite arbors or the animal overall. This mutant disrupts a putative amino acid transporter, Pathetic (Path), that localizes to the cell surface and endolysosomal compartments in neurons. Although Path is broadly expressed in neurons and nonneuronal cells, mutation of path impinges on nutrient responses and protein homeostasis specifically in neurons with large dendrite arbors but not in other cells. Altogether, these results demonstrate that specialized molecular mechanisms exist to support growth demands in neurons with large dendrite arbors and define Path as a founding member of this growth program.

Shankar, S., Chua, J. Y., Tan, K. J., Calvert, M. E., Weng, R., Ng, W. C., Mori, K. and Yew, J. Y. (2015). The neuropeptide tachykinin is essential for pheromone detection in a gustatory neural circuit. Elife 4. PubMed ID: 26083710
behavior of many organisms. However, little is known about the processing of taste pheromones in higher order brain centers. This study describes a male-specific gustatory circuit in Drosophila that underlies the detection of the anti-aphrodisiac pheromone (3R,11Z,19Z)-3-acetoxy-11,19-octacosadien-1-ol (CH503). Using behavioral analysis, genetic manipulation, and live calcium imaging, it was shown that Gr68a-expressing neurons on the forelegs of male flies exhibit a sexually-dimorphic physiological response to the pheromone and relay information to the central brain via peptidergic neurons. The release of tachykinin from 8-10 cells within the subesophageal zone is required for the pheromone-triggered courtship suppression. Taken together, this work describes a neuropeptide-modulated central brain circuit that underlies the programmed behavioral response to a gustatory sex pheromone. These results will allow further examination of the molecular basis by which innate behaviors are modulated by gustatory cues and physiological state.

Tuesday, July 7th

Jones, J. and Macdonald, P.M. (2015). Neurl4 contributes to germ cell formation and integrity in Drosophila. Biol Open [Epub ahead of print]. PubMed ID: 26116656
Primordial germ cells (PGCs) form at the posterior pole of the Drosophila embryo, and then migrate to their final destination in the gonad where they will produce eggs or sperm. Studies of the different stages in this process, including assembly of germ plasm in the oocyte during oogenesis, specification of a subset of syncytial embryonic nuclei as PGCs, and migration, have been informed by genetic analyses. Mutants have defined steps in the process, and the identities of the affected genes have suggested biochemical mechanisms. This study describes a novel PGC phenotype. When Neurl4 activity is reduced, newly formed PGCs frequently adopt irregular shapes and appear to bud off vesicles. PGC number is also reduced, an effect exacerbated by a separate role for Neurl4 in germ plasm formation during oogenesis. Like its mammalian homolog, Drosophila Neurl4 protein is concentrated in centrosomes and downregulates centrosomal protein CP110. Reducing CP110 activity suppresses the abnormal PGC morphology of Neurl4 mutants. These results extend prior analyses of Neurl4 in cultured cells, revealing a heightened requirement for Neurl4 in germ-line cells in Drosophila

Lopez-Panades, E., Gavis, E. R. and Casacuberta, E. (2015). Specific localization of the Drosophila telomere transposon proteins and RNAs, give insight in their behavior, control and telomere biology in this organism. PLoS One 10: e0128573. PubMed ID: 26068215.
Drosophila telomeres constitute a remarkable exception to the telomerase mechanism. Although maintaining the same cytological and functional properties as telomerase maintain telomeres, Drosophila telomeres embed the telomere retrotransposons whose specific and highly regulated terminal transposition maintains the appropriate telomere length in this organism. This study reports a detailed study of the localization of the main components that constitute the telomeres in Drosophila, HeT-A and TART RNAs and proteins. The results in wild type and mutant strains reveal localizations of HeT-A Gag and TART Pol that give insight in the behavior of the telomere retrotransposons and their control. TART Pol and HeT-A Gag only co-localize at the telomeres during the interphase of cells undergoing mitotic cycles. In addition, unexpected protein and RNA localizations with a well-defined pattern in cells such as the ovarian border cells and nurse cells, suggest possible strategies for the telomere transposons to reach the oocyte, and/or additional functions that might be important for the correct development of the organism. Finally, it has been possible to visualize the telomere RNAs at different ovarian stages of development in wild type and mutant lines, demonstrating their presence in spite of being tightly regulated by the piRNA mechanism.

Manning, L.A.1, Weideman, A.M., Peercy, B.E. and Starz-Gaiano, M. (2015). Tissue landscape alters adjacent cell fates during Drosophila egg development. Nat Commun 6: 7356. PubMed ID: 26082073
Extracellular signalling molecules control many biological processes, but the influence of tissue architecture on the local concentrations of these factors is unclear. This study examines this issue in the Drosophila egg chamber, where two anterior cells secrete Unpaired (Upd) to activate Signal transducer and activator of transcription (STAT) signalling in the epithelium. High STAT signalling promotes cell motility. Genetic analysis shows that all cells near the Upd source can respond. However, using upright imaging, surprising asymmetries in STAT activation patterns were shown, suggesting that some cells experience different Upd levels than predicted by their location. A three-dimensional mathematical model was developed to characterize the spatio-temporal distribution of the activator. Simulations show that irregular tissue domains can produce asymmetric distributions of Upd, consistent with results in vivo. Mutant analysis substantiates this idea. The study concludes that cellular landscape can heavily influence the effect of diffusible activators and should be more widely considered.

Nguyen, T.T.1 and Moehring, A.J. (2015).Accurate alternative measurements for female lifetime reproductive success in Drosophila melanogaster. PLoS One 10: e0116679. PubMed ID: 26125633
Fitness is an individual's ability to survive and reproduce, and is an important concept in evolutionary biology. However, accurately measuring fitness is often difficult, and appropriate fitness surrogates need to be identified. Lifetime reproductive success, the total progeny an organism can produce in their lifetime, is thought to be a suitable proxy for fitness, but the measure of an organism's reproductive output across a lifetime can be difficult or impossible to obtain. This study demonstrates that the short-term measure of reproductive success across five days provides a reasonable prediction of an individual's total lifetime reproductive success in Drosophila melanogaster. However, the lifetime reproductive success of a female that has only mated once is not correlated to the lifetime reproductive success of a female that is allowed to mate multiple times, demonstrating that these measures should not serve as surrogates nor be used to make inferences about one another. 

Monday, July 6th

Akagawa, H., Hara, Y., Togane, Y., Iwabuchi, K., Hiraoka, T. and Tsujimura, H. (2015). The role of the effector caspases drICE and dcp-1 for cell death and corpse clearance in the developing optic lobe in Drosophila. Dev Biol [Epub ahead of print]. PubMed ID: 26022392
In the developing Drosophila optic lobe, cell death occurs via apoptosis and in a distinctive spatio-temporal pattern of dying cell clusters. This study analyzed the role of effector caspases drICE and dcp-1 in optic lobe cell death and subsequent corpse clearance using mutants. Neurons in many clusters required either drICE or dcp-1 and each one was sufficient. This suggests that drICE and dcp-1 function in cell death redundantly. However, dying neurons in a few clusters strictly required drICE but not dcp-1, but required drICE and dcp-1 when drICE activity was reduced via hypomorphic mutation. In addition, analysis of the mutants suggests an important role of effecter caspases in corpse clearance. In both null and hypomorphic drICE mutants, greater number of TUNEL-positive cells were observed than in wild type, and many TUNEL-positive cells remained until later stages. Lysotracker staining showed that there was a defect in corpse clearance in these mutants. All the results suggested that drICE plays an important role in activating corpse clearance in dying cells, and that an additional function of effector caspases is required for the activation of corpse clearance as well as that for carrying out cell death.

Evans, I. R., Rodrigues, F. S., Armitage, E. L. and Wood, W. (2015). Draper/CED-1 mediates an ancient damage response to control inflammatory blood cell migration in vivo. Curr Biol 25: 1606-1612. PubMed ID: 26028435
Recent studies in zebrafish have shown that wound-induced H2O2 is detected by the redox-sensitive Src family kinase (SFK) Lyn within responding blood cells. This study shows the same signaling occurs in Drosophila inflammatory cells in response to wound-induced H2O2 with mutants for the Lyn homolog Src42A displaying impaired inflammatory migration to wounds. Activation of Src42A is necessary to trigger a signaling cascade within the inflammatory cells involving the ITAM domain-containing protein Draper-I (a member of the CED-1 family of apoptotic cell clearance receptors) and a downstream kinase, Shark, that is required for migration to wounds. The Src42A-Draper-Shark-mediated signaling axis is homologous to the well-established SFK-ITAM-Syk-signaling pathway used in vertebrate adaptive immune responses. Consequently, the results suggest that adaptive immunoreceptor-signaling pathways important in distinguishing self from non-self appear to have evolved from a more-ancient damage response. Furthermore, this changes the role of H2O2 from an inflammatory chemoattractant to an activator signal that primes immune cells to respond to damage cues via the activation of damage receptors such as Draper.

Mauvezin, C., Nagy, P., Juhasz, G. and Neufeld, T. P. (2015). Autophagosome-lysosome fusion is independent of V-ATPase-mediated acidification. Nat Commun 6: 7007. PubMed ID: 25959678.
The ATP-dependent proton pump V-ATPase ensures low intralysosomal pH, which is essential for lysosomal hydrolase activity. Based on studies with the V-ATPase inhibitor BafilomycinA1, lysosomal acidification is also thought to be required for fusion with incoming vesicles from the autophagic and endocytic pathways. This study shows that loss of V-ATPase subunits in the Drosophila fat body causes an accumulation of non-functional lysosomes, leading to a block in autophagic flux. However, V-ATPase-deficient lysosomes remain competent to fuse with autophagosomes and endosomes, resulting in a time-dependent formation of giant autolysosomes. In contrast, BafilomycinA1 prevents autophagosome-lysosome fusion in these cells, and this defect is phenocopied by depletion of the Ca(2+) pump SERCA, a secondary target of this drug. Moreover, activation of SERCA promotes fusion in a BafilomycinA1-sensitive manner. Collectively, these results indicate that lysosomal acidification is not a prerequisite for fusion, and that BafilomycinA1 inhibits fusion independent of its effect on lysosomal pH.

Zhang, Y., Cai, R., Zhou, R., Li, Y. and Liu, L. (2015). Tousled-like kinase mediated a new type of cell death pathway in Drosophila. Cell Death Differ [Epub ahead of print]. PubMed ID: 26088162
Programmed cell death (PCD) has an important role in sculpting organisms during development. However, much remains to be learned about the molecular mechanism of PCD. This study found that ectopic expression of tousled-like kinase (tlk) in Drosophila initiated a new type of cell death. Furthermore, the TLK-induced cell death is likely to be independent of the canonical caspase pathway and other known caspase-independent pathways. Genetically, atg2 RNAi could rescue the TLK-induced cell death, and this function of atg2 is likely distinct from its role in autophagy. In the developing retina, loss of tlk resulted in reduced PCD in the interommatidial cells (IOCs). Similarly, an increased number of IOCs was present in the atg2 deletion mutant clones. However, double knockdown of tlk and atg2 by RNAi did not have a synergistic effect. These results suggested that ATG2 may function downstream of TLK. In addition to a role in development, tlk and atg2 RNAi could rescue calcium overload-induced cell death. Together, these results suggest that TLK mediates a new type of cell death pathway that occurs in both development and calcium cytotoxicity.

Sunday, July 5th

Tokusumi, T., Tokusumi, Y., Hopkins, D. W. and Schulz, R. A. (2015). Bag of Marbles controls the size and organization of the Drosophila hematopoietic niche through interactions with the Insulin-like growth factor pathway and Retinoblastoma-family protein. Development [Epub ahead of print]. PubMed ID: 26041767
During Drosophila hematopoiesis, Bag of Marbles (Bam) is known to function as a positive regulator of hematopoietic progenitor maintenance in the lymph gland blood cell-forming organ. This study demonstrates a key function for Bam in cells of the lymph gland posterior signaling center (PSC), a cellular domain proven to function as a hematopoietic niche. Bam is expressed in PSC cells and gene loss-of-function results in PSC overgrowth and disorganization, indicating Bam plays a crucial role in controlling the proper development of the niche. It was previously shown that Insulin receptor (InR) pathway signaling was essential for proper PSC cell proliferation. This study analyzed PSC cell number in lymph glands that were double mutant for bam and InR pathway genes, and observed bam genetically interacts with pathway members in the formation of a normal PSC. The elF4A protein is a translation factor downstream of InR pathway signaling and functional knockdown of this critical regulator rescued the bam PSC overgrowth phenotype, further supporting the cooperative function of Bam with InR pathway members. Additionally, the Retinoblastoma-family protein (Rbf), a proven regulator of cell proliferation, is present in cells of the PSC, with this expression dependent on bam function. In contrast, perturbation of Decapentaplegic or Wingless signaling failed to affect Rbf niche cell expression. Together, these findings indicate InR pathway-Bam-Rbf functional interactions represent a newly identified means to regulate the correct size and organization of the PSC hematopoietic niche.

Venkatesan, A., Fan, J. Y., Nauman, C. and Price, J. L. (2015). A Doubletime nuclear localization signal mediates an interaction with Bride of Doubletime to promote circadian function. J Biol Rhythms [Epub ahead of print]. PubMed ID: 26082158
Doubletime (DBT) has an essential circadian role in Drosophila melanogaster because it phosphorylates Period (Per). To determine if DBT antagonism can produce distinct effects in the cytosol and nucleus, forms of a dominant negative DBTK/R with these 2 alternative localizations were produced. DBT has a putative nuclear localization signal (NLS), and mutation of this signal confers cytosolic localization of DBT in the lateral neurons of Drosophila clock cells in the brain. By contrast, addition of a strong NLS domain (e.g., SV40 NLS) to DBT's C terminus leads to more nuclear localization. Expression of DBTK/R with the mutated NLS (DBTK/R NLS-) using a timGAL4 driver does not alter the circadian period of locomotor activity. By contrast, expression of DBTK/R with the strong NLS (DBTK/R stNLS) lengthens period more strongly than DBTK/R, with damped oscillations of Per phosphorylation and localization. Both DBTK/R and DBTWT without the NLS fail to interact with Bride of Doubletime (BDBT) protein, which is related to FK506-binding proteins and shown to interact with DBT to enhance its circadian function. This result suggests that the DBTK/R NLS- has lost its dominant negative property because it does not form normal clock protein complexes. DBTWT proteins with the same changes (NLS- and stNLS) also produce equivalent changes in localization that do not produce opposite period phenotypes. Additionally, the lack of a dominant negative for the DBTK/R NLS- is not due to failure to localize to nuclei. Finally, bdbt RNAi increases the cytosolic localization of DBTK/R but not of DBTWT, suggesting a role for BDBT in DBT kinase-dependent nuclear localization of DBT.

Kang, S. W., Lee, E., Cho, E., Seo, J. H., Ko, H. W. and Kim, E. Y. (2015). Drosophila peptidyl-prolyl isomerase Pin1 modulates circadian rhythms via regulating levels of PERIOD. Biochem Biophys Res Commun. PubMed ID: 25998391.
In animal circadian clock machinery, the phosphorylation program of Period (Per) leads to the spatio-temporal regulation of diverse Per functions, which are crucial for the maintenance of approximately 24-hr circadian rhythmicity. The peptidyl-prolyl isomerase PIN1 modulates the diverse functions of its substrates by inducing conformational changes upon recognizing specific phosphorylated residues. This study shows that overexpression of Drosophila pin1, dodo (dod), lengthens the locomotor behavioral period. Using Drosophila S2 cells, it was demonstrated that Dod associates preferentially with phosphorylated species of Per, which delays the phosphorylation-dependent degradation of Per. Consistent with this, Per protein levels are higher in flies overexpressing dod. Taken together, it is suggested that Dod plays a role in the maintenance of circadian period by regulating Per metabolism.
Lim, B., Dsilva, C.J., Levario, T.J., Lu, H., Schüpbach, T., Kevrekidis, I.G. and Shvartsman, S.Y. (2015). Dynamics of inductive ERK signaling in the Drosophila embryo. Curr Biol [Epub ahead of print]. PubMed ID: 26096970
Transient activation of the highly conserved extracellular-signal-regulated kinase (ERK) establishes precise patterns of cell fates in developing tissues. Quantitative parameters of these transients are essentially unknown. This study provides a detailed quantitative picture of an ERK-dependent inductive signaling event in the early Drosophila embryo, an experimental system that offers unique opportunities for high-throughput studies of developmental signaling. Data analysis reveals a spatiotemporal pulse of ERK activation that is consistent with a model in which transient production of a short-ranged ligand feeds into a simple signal interpretation system. The pulse of ERK signaling acts as a switch in controlling the expression of the ERK target gene. The quantitative approach that leads to this model, based on the integration of data from fixed embryos and live imaging, can be extended to other developmental systems patterned by transient inductive signals.

Jevtov, I., et al. (2015). TORC2 mediates the heat stress response in Drosophila by promoting the formation of stress granules. J Cell Sci [Epub ahead of print]. PubMed ID: 26054799
The kinase TOR is found in two complexes, TORC1, involved in growth control, and TORC2 with less well defined roles. This study asked whether TORC2, disrupted by use of Rictor mutant flies, has a role in sustaining cellular stress. TORC2 inhibition in Drosophila was shown to lead to a reduced tolerance to heat stress. Accordingly, upon heat stress, both in the animal and Drosophila cultured S2 cells, TORC2 is activated and is required for the stability of its known target Akt/PKB. The phosphorylation of the stress activated protein kinases is not modulated by TORC2, nor is the heat-induced upregulation of heat shock proteins. Instead, it was shown, both in vivo and in cultured cells, that TORC2 is required for the assembly of heat-induced cytoprotective ribonucleoprotein particles, the pro-survival stress granules. These granules are formed in response to protein translation inhibition imposed by heat stress that appears less efficient in the absence of TORC2 function. It is proposed that TORC2 mediates heat resistance in Drosophila by promoting the cell autonomous formation of stress granules.

Kim, Y. J., Guzman-Hernandez, M. L., Wisniewski, E. and Balla, T. (2015). Phosphatidylinositol-phosphatidic acid exchange by Nir2 at ER-PM contact sites maintains phosphoinositide signaling competence. Dev Cell 33: 549-561. PubMed ID: 26028218
Sustained agonist-induced production of the second messengers InsP3 and diacylglycerol requires steady delivery of phosphatidylinositol (PtdIns) from its site of synthesis in the ER to the plasma membrane (PM) to maintain PtdIns(4,5)P2 levels. Similarly, phosphatidic acid (PtdOH), generated from diacylglycerol in the PM, has to reach the ER for PtdIns resynthesis. This study shows that the Drosophila RdgB homolog, Nir2, a presumed PtdIns transfer protein, not only transfers PtdIns from the ER to the PM but also transfers PtdOH to the opposite direction at ER-PM contact sites. PtdOH delivery to the ER is impaired in Nir2-depleted cells, leading to limited PtdIns synthesis and ultimately to loss of signaling from phospholipase C-coupled receptors. These studies reveal a unique feature of Nir2, namely its ability to serve as a highly localized lipid exchanger that ensures that PtdIns synthesis is matched with PtdIns(4,5)P2 utilization so that cells maintain their signaling competence.

Saturday, July 4th

Gottardo, M., Callaini, G. and Riparbelli, M.G. (2015). The Drosophila centriole: conversion of doublets to triplets within the stem cell niche. J Cell Sci [Epub ahead of print]. PubMed ID: 26092937
This study reports that two distinct centriole lineages exist in Drosophila: somatic centrioles usually composed of microtubule doublets and germ line centrioles characterized by triplets. Remarkably, the transition from doublets to triplets in the testis occurs within the stem cell niche with the formation of the C-tubule. It was demonstrated that the old mother centriole that stays in the apical cytoplasm of the male germline stem cells (GSCs) is invariably composed by triplets, whereas its daughter is always built by mixed doublets and triplets. This difference represents the first documentation of a structural asymmetry between mother and daughter centrioles in Drosophila GSCs and may reflect a correlation between the architecture of parent centrioles and their ability to recruit centrosomal proteins. It was also found that the old mother centriole is linked to the cell membrane by distinct projections that may play an important role in keeping its apical position during centrosome separation.

Hsiao, J. Y., Goins, L. M., Petek, N. A. and Mullins, R. D. (2015). Arp2/3 complex and cofilin modulate binding of tropomyosin to branched actin networks. Curr Biol 25: 1573-1582. PubMed ID: 26028436.
Tropomyosins are coiled-coil proteins that bind actin filaments and regulate multiple cytoskeletal functions, including actin network dynamics near the leading edge of motile cells. Tropomyosins inhibit actin nucleation by the Arp2/3 complex and prevent filament disassembly by cofilin. This study finds that the Arp2/3 complex and cofilin, in turn, regulate the binding of tropomyosin to actin filaments. Using fluorescence microscopy, this study showed that tropomyosin (non-muscle Drosophila Tm1A) polymerizes along actin filaments, starting from "nuclei" that appear preferentially on ADP-bound regions of the filament, near the pointed end. Tropomyosin fails to bind dendritic actin networks created in vitro by the Arp2/3 complex, in part because the Arp2/3 complex blocks pointed ends. Cofilin promotes phosphate dissociation and severs filaments, generating new pointed ends and rendering Arp2/3-generated networks competent to bind tropomyosin. Tropomyosin's attraction to pointed ends reveals a basic molecular mechanism by which lamellipodial actin networks are insulated from the effects of tropomyosin.

Inaba, M., Buszczak, M. and Yamashita, Y.M. (2015). Nanotubes mediate niche-stem-cell signalling in the Drosophila testis. Nature [Epub ahead of print]. PubMed ID: 26131929
Stem cell niches provide resident stem cells with signals that specify their identity. Niche signals act over a short range such that only stem cells but not their differentiating progeny receive the self-renewing signals. However, the cellular mechanisms that limit niche signalling to stem cells remain poorly understood. This study shows that the Drosophila male germline stem cells form previously unrecognized structures, microtubule-based nanotubes, which extend into the hub, a major niche component. Microtubule-based nanotubes are observed specifically within germline stem cell populations, and require intraflagellar transport proteins for their formation. The bone morphogenetic protein (BMP) receptor Tkv localizes to microtubule-based nanotubes. Perturbation of microtubule-based nanotubes compromises activation of Dpp signalling within germline stem cells, leading to germline stem cell loss. Moreover, Dpp ligand and Tkv receptor interaction is necessary and sufficient for microtubule-based nanotube formation. The study proposes that microtubule-based nanotubes provide a novel mechanism for selective receptor-ligand interaction, contributing to the short-range nature of niche-stem-cell signalling.

Kaushik, G., et al. (2015). Vinculin network-mediated cytoskeletal remodeling regulates contractile function in the aging heart. Sci Transl Med 7: 292ra299. PubMed ID: 26084806
The human heart is capable of functioning for decades despite minimal cell turnover or regeneration, suggesting that molecular alterations help sustain heart function with age. However, identification of compensatory remodeling events in the aging heart remains elusive. This study presents the cardiac proteomes of young and old rhesus monkeys and rats, from which it was shown that certain age-associated remodeling events within the cardiomyocyte cytoskeleton are highly conserved and beneficial rather than deleterious. Targeted transcriptomic analysis in Drosophila confirmed conservation and implicated vinculin as a unique molecular regulator of cardiac function during aging. Cardiac-restricted vinculin overexpression reinforced the cortical cytoskeleton and enhanced myofilament organization, leading to improved contractility and hemodynamic stress tolerance in healthy and myosin-deficient fly hearts. Moreover, cardiac-specific vinculin overexpression increased median life span by more than 150% in flies. A broad array of potential therapeutic targets and regulators of age-associated modifications, specifically for vinculin, are presented. These findings suggest that the heart has molecular mechanisms to sustain performance and promote longevity, which may be assisted by therapeutic intervention to ameliorate the decline of function in aging patient hearts.

Friday, July 3rd

Sun, K., Jee, D., de Navas, L. F., Duan, H. and Lai, E. C. (2015). Multiple in vivo biological processes are mediated by functionally redundant activities of Drosophila mir-279 and mir-996. PLoS Genet 11: e1005245. PubMed ID: 26042831.
Drosophila mir-279 has been reported as essential to restrict the emergence of CO2-sensing neurons, to maintain circadian rhythm, and to regulate ovarian border cells. The mir-996 locus is located near mir-279 and bears a similar seed, but they otherwise have distinct, conserved, non-seed sequences, suggesting their evolutionary maintenance for separate functions. Single and double deletion mutants were generated of the mir-279 and mir-996 hairpins, and cursory analysis suggested that mir-996 was dispensable. However, discrepancies in the strength of individual mir-279 deletion alleles led to the the finding that extant mir-279 mutants are deficient for mature mir-996, even though they retain its genomic locus. Therefore a panel of genomic rescue transgenes was engineered into the double deletion background, allowing a pure assessment of mir-279 and mir-996 requirements. Surprisingly, detailed analyses of viability, olfactory neuron specification, and circadian rhythm indicate that mir-279 is completely dispensable. Instead, an endogenous supply of either mir-279 or mir-996 suffices for normal development and behavior. Sensor tests of nine key mir-279/996 targets showed their similar regulatory capacities, although transgenic gain-of-function experiments indicate partially distinct activities of these miRNAs that may underlie that co-maintenance in genomes. Altogether, this study elucidated the unexpected genetics of this critical miRNA operon, and provides a foundation for their further study. More importantly, these studies demonstrate that multiple, vital, loss-of-function phenotypes can be rescued by endogenous expression of divergent seed family members, highlighting the importance of this miRNA region for in vivo function.

Montelli, S., Mazzotta, G., Vanin, S., Caccin, L., Corra, S., De Pitta, C., Boothroyd, C., Green, E. W., Kyriacou, C. P. and Costa, R. (2015). period and timeless mRNA splicing profiles under natural conditions in Drosophila melanogaster. J Biol Rhythms 30: 217-227. PubMed ID: 25994101.
Analysis of Drosophila circadian behavior under natural conditions has revealed a number of novel and unexpected features. This study focused on the oscillations of per and tim mRNAs and their posttranscriptional regulation and observe significant differences in molecular cycling under laboratory and natural conditions. In particular, robust per mRNA cycling from fly heads is limited to the summers, whereas tim RNA cycling is observed throughout the year. When both transcripts do cycle, their phases are similar, except for the very warmest summer months. The natural splicing profiles of per and tim transcripts were also studied and a clear relationship was observed between temperature and splicing. In natural conditions, the relationship between accumulation of the perspliced variant, low temperature, and the onset of the evening component of locomotor activity, first described in laboratory conditions, was also confirmed. Intriguingly, in the case of tim splicing, the opposite relationship was observed, with timspliced expression increasing at higher temperatures. A first characterization of the 4 different TIM protein isoforms (resulting from the combination of the natural N-terminus length polymorphism and the C-terminus alternative splicing) using the 2-hybrid assay showed that the TIMunspliced isoforms have a stronger affinity for CRY, but not for PER, suggesting that the tim 3' splicing could have physiological significance, possibly in temperature entrainment and/or adaptation to seasonal environments.

Hansen, H. T., Rasmussen, S. H., Adolph, S. K., Plass, M., Krogh, A., Sanford, J., Nielsen, F. C. and Christiansen, J. (2015). Drosophila Imp iCLIP identifies an RNA assemblage co-ordinating F-actin formation. Genome Biol 16: 123. PubMed ID: 26054396
Post-transcriptional RNA regulons ensure co-ordinated expression of monocistronic mRNAs encoding functionally related proteins. This study employed a combination of RIP-seq and short- and long-wave individual-nucleotide resolution crosslinking and immunoprecipitation (iCLIP) technologies in Drosophila cells to identify transcripts associated with cytoplasmic ribonucleoproteins (RNPs) containing the RNA-binding protein Imp. Extensive binding was found of Imp to 3'UTRs of transcripts that are involved in F-actin formation. A common denominator of the RNA-protein interface is the presence of multiple motifs with a central UA-rich element flanked by CA-rich elements. Experiments in single cells and intact flies reveal compromised actin cytoskeletal dynamics associated with low Imp levels. The former shows reduced F-actin formation and the latter exhibits abnormal neuronal patterning. This demonstrates a physiological significance of the defined RNA regulon. These data imply that Drosophila Imp RNPs may function as cytoplasmic mRNA assemblages that encode proteins which participate in actin cytoskeletal remodeling. Thus, they may facilitate co-ordinated protein expression in sub-cytoplasmic locations such as growth cones.

Ling, L., Ge, X., Li, Z., Zeng, B., Xu, J., Chen, X., Shang, P., James, A. A., Huang, Y. and Tan, A. (2015). MiR-2 family targets awd and fng to regulate wing morphogenesis in Bombyx mori. RNA Biol: [Epub ahead of print]. PubMed ID: 26037405
MicroRNAs (miRNAs) are post-transcriptional regulators that target specific mRNAs for repression and thus play key roles in many biological processes, including insect wing morphogenesis. miR-2 is an invertebrate-specific miRNA family that has been predicted in the fruit fly, Drosophila melanogaster, to be involved in regulating the Notch signaling pathway. This study shows that miR-2 plays a critical role in wing morphogenesis in the silkworm, Bombyx mori, a lepidopteran model insect. Transgenic over-expression of a miR-2 cluster using a Gal4/UAS system results in deformed adult wings, supporting the conclusion that miR-2 regulates functions essential for normal wing morphogenesis. Two genes, abnormal wing disc (awd) and fringe (fng), which are positive regulators in Notch signaling, are identified as miR-2 targets and validated by a dual-luciferase reporter assay. The relative abundance of both awd and fng expression products was reduced significantly in transgenic animals, implicating them in the abnormal wing phenotype. Furthermore, somatic mutagenesis analysis of awd and fng using the CRISPR/Cas9 system and knock-out mutants also resulted in deformed wings similar to those observed in the miR-2 over-expression transgenic animals. The critical role of miR-2 in Bombyx wing morphogenesis may provide a potential target in future lepidopteran pest control.

Chou, M. H., Hsieh, Y. C., Huang, C. W., Chen, P. H., Chan, S. P., Tsao, Y. P., Lee, H. H., Wu, J. T. and Chen, S. L. (2015). BCAS2 regulates Delta-Notch signaling activity through Delta pre-mRNA splicing in Drosophila wing development. PLoS One 10: e0130706. PubMed ID: 26091239
BCAS2 is essential for Drosophila viability and functions in pre-mRNA splicing. This study provides strong evidence that BCAS2 regulates the activity of Delta-Notch signaling via Delta pre-mRNA splicing. Depletion of dBCAS2 reduces Delta mRNA expression and leads to accumulation of Delta pre-mRNA, resulting in diminished transcriptions of Delta-Notch signaling target genes, such as cut and E(spl)m8. Furthermore, ectopic expression of human BCAS2 (hBCAS2) and Drosophila BCAS2 (dBCAS2) in a dBCAS2-deprived fly can rescue dBCAS2 depletion-induced wing damage to the normal phenotypes. These rescued phenotypes are correlated with the restoration of Delta pre-mRNA splicing, which affects Delta-Notch signaling activity. Additionally, overexpression of Delta can rescue the wing deformation by deprivation of dBCAS2; and the depletion of dBCAS2 can restore the aberrant eye associated with Delta-overexpressing retinas; providing supporting evidence for the regulation of Delta-Notch signaling by dBCAS2. Taken together, dBCAS2 participates in Delta pre-mRNA splicing that affects the regulation of Delta-Notch signaling in Drosophila wing development.

Wan, D., Zhang, Z. C., Zhang, X., Li, Q. and Han, J. (2015). X chromosome-linked intellectual disability protein PQBP1 associates with and regulates the translation of specific mRNAs. Hum Mol Genet [Epub ahead of print]. PubMed ID: 26002102

X chromosome-linked intellectual disability is a common developmental disorder, and mutations of the polyglutamine-binding protein 1 (PQBP1) gene have been linked to this disease. In addition to existing in the nucleus as a splicing factor, PQBP1 is also found in cytoplasmic RNA granules, where it associates with RNA-binding proteins. However, the roles of cytoplasmic PQBP1 are largely unknown. This study showed that the Drosophila homolog of PQBP1 (dPQBP1) is present in the cytoplasm of photoreceptor cells, and its loss results in defective rhabdomere morphogenesis, which is due to impaired Chaoptin translation. This study also showed that dPQBP1 regulates mRNA translation by interacting with dFMR1, which binds to specific mRNAs and facilitates their assembly into translating ribosomes, a function that is conserved for human PQBP1 and FMRP. These findings reveal the conserved function of PQBP1 in mRNA translation and provide molecular insights into the pathogenic mechanisms underlying Renpenning syndrome.

Thursday, July 2nd

Skalska, L., Stojnic, R., Li, J., Fischer, B., Cerda-Moya, G., Sakai, H., Tajbakhsh, S., Russell, S., Adryan, B. and Bray, S. J. (2015) Chromatin signatures at Notch-regulated enhancers reveal large-scale changes in H3K56ac upon activation. EMBO J [Epub ahead of print]. PubMed ID: 26069324.
The conserved Notch pathway functions in diverse developmental and disease-related processes, requiring mechanisms to ensure appropriate target selection and gene activation in each context. To investigate the influence of chromatin organisation and dynamics on the response to Notch signalling, this study partitioned Drosophila chromatin using histone modifications and established the preferred chromatin conditions for binding of Su(H), the Notch pathway transcription factor. Manipulating activity of a co-operating factor, Lozenge/Runx, showed that it can help facilitate these conditions. While many histone modifications were unchanged by Su(H) binding or Notch activation, rapid changes were detected in acetylation of H3K56 at Notch-regulated enhancers. This modification extended over large regions, required the histone acetyl-transferase CBP and was independent of transcription. Such rapid changes in H3K56 acetylation appear to be a conserved indicator of enhancer activation as they also occurred at the mammalian Notch-regulated Hey1 gene and at Drosophila ecdysone-regulated genes. This intriguing example of a core histone modification increasing over short timescales may therefore underpin changes in chromatin accessibility needed to promote transcription following signalling activation.

Shen, W., Wang, D., Ye, B., Shi, M., Zhang, Y. and Zhao, Z. (2015). A possible role of Drosophila CTCF in mitotic bookmarking and maintaining chromatin domains during the cell cycle. Biol Res 48: 27. PubMed ID: 26013116.
The CCCTC-binding factor (CTCF) is a highly conserved insulator protein that plays various roles in many cellular processes. CTCF is one of the main architecture proteins in higher eukaryotes, and in combination with other architecture proteins and regulators, also shapes the three-dimensional organization of a genome. Experiments show CTCF partially remains associated with chromatin during mitosis. However, the role of CTCF in the maintenance and propagation of genome architectures throughout the cell cycle remains elusive. This study performed a comprehensive bioinformatics analysis on public datasets of Drosophila CTCF (dCTCF). dCTCF-binding sites were characterized according to their occupancy status during the cell cycle, and three classes were identified: interphase-mitosis-common (IM), interphase-only (IO) and mitosis-only (MO) sites. Integrated function analysis showed dCTCF-binding sites of different classes might be involved in different biological processes, and IM sites were more conserved and more intensely bound. dCTCF-binding sites of the same class preferentially localized closer to each other, and were highly enriched at chromatin syntenic and topologically associating domains boundaries. These results revealed different functions of dCTCF during the cell cycle and suggested that dCTCF might contribute to the establishment of the three-dimensional architecture of the Drosophila genome by maintaining local chromatin compartments throughout the whole cell cycle.

Borsos, B. N., Pankotai, T., Kovacs, D., Popescu, C., Pahi, Z. and Boros, I. M. (2015). Acetylations of Ftz-F1 and histone H4K5 are required for the fine-tuning of ecdysone biosynthesis during Drosophila metamorphosis. Dev Biol [Epub ahead of print]. PubMed ID: 25959239
The molting during Drosophila development is tightly regulated by the ecdysone hormone. Several steps of the ecdysone biosynthesis have been already identified but the regulation of the entire process has not been clarified yet. Studies have shown that the dATAC histone acetyltransferase complex is necessary for the steroid hormone biosynthesis process. To reveal possible mechanisms controlled by dATAC assumptions were made that either dATAC may influence directly the transcription of Halloween genes involved in steroid hormone biosynthesis or it may exert an indirect effect on it by acetylating the Ftz-F1 transcription factor which regulates the transcription of steroid converting genes. This study shows that the lack of dATAC complex results in increased mRNA level and decreased protein level of Ftz-F1. In this context, decreased mRNA and increased protein levels of Ftz-F1 were detected upon treatment of Drosophila S2 cells with histone deacetylase inhibitor trichostatin A. Ftz-F1, the transcriptional activator of Halloween genes, is acetylated in S2 cells. In addition, ecdysone biosynthetic Halloween genes were found to be transcribed in S2 cells and their expression can be influenced by deacetylase inhibitors. Furthermore, H4K5 acetylation was detected at the regulatory regions of disembodied and shade Halloween genes, while H3K9 acetylation is absent on these genes. Based on these findings it is concluded that the dATAC HAT complex might play a dual regulatory role in Drosophila steroid hormone biosynthesis through the acetylation of Ftz-F1 protein and the regulation of the H4K5 acetylation at the promoters of Halloween genes.

Cenci, G., Ciapponi, L., Marzullo, M., Raffa, G.D., Morciano, P., Raimondo, D., Burla, R., Saggio, I. and Gatti, M. (2015). The analysis of pendolino (peo) mutants reveals differences in the fusigenic potential among Drosophila telomeres. PLoS Genet 11: e1005260. PubMed ID: 26110638
Drosophila telomeres are sequence-independent structures that are maintained by transposition to chromosome ends of three specialized retroelements (HeT-A, TART and TAHRE; collectively designated as HTT) rather than telomerase activity. Fly telomeres are protected by the terminin complex (HOAP-HipHop-Moi-Ver) that localizes and functions exclusively at telomeres and by non-terminin proteins that do not serve telomere-specific functions. Although all Drosophila telomeres terminate with HTT arrays and are capped by terminin, they differ in the type of subtelomeric chromatin. This study shows that mutations in pendolino (peo) cause telomeric fusions (TFs). The analysis of several peo mutant combinations shows that these TFs preferentially involve the Y, XR and 4th chromosome telomeres, a TF pattern never observed in the other 10 telomere-capping mutants so far characterized. peo encodes a non-terminin protein homologous to the E2 variant ubiquitin-conjugating enzymes. The Peo protein directly interacts with the terminin components, but peo mutations do not affect telomeric localization of HOAP, Moi, Ver and HP1a, suggesting that the peo-dependent telomere fusion phenotype is not due to loss of terminin from chromosome ends. peo mutants are also defective in DNA replication and PCNA recruitment. However, results suggest that general defects in DNA replication are unable to induce TFs in Drosophila cells. The study thus hypothesizes that DNA replication in Peo-depleted cells results in specific fusigenic lesions concentrated in heterochromatin-associated telomeres. Alternatively, it is possible that Peo plays a dual function being independently required for DNA replication and telomere capping.

Wednesday, July 1st

Guillermin, O., Perruchoud, B., Sprecher, S.G. and Egger, B. (2015). Characterization of Tailless functions during Drosophila optic lobe formation. Dev Biol [Epub ahead of print]. PubMed ID: 26111972
Brain development goes through phases of proliferative growth and differentiation to ensure the formation of correct number and variety of neurons. How and when naïve neuroepithelial cells decide to enter a differentiation pathway remains poorly understood. In the Drosophila visual system, four optic ganglia emerge from neuroepithelia of the inner (IPC) and outer (OPC) proliferation centers. This study demonstrates that the orphan nuclear receptor Tailless (Tll) is a key factor for the development of all optic ganglia. The study describes tll expression during larval optic lobe development in unprecedented detail and finds a spatiotemporally dynamic pattern. In the larval OPC, symmetrically dividing neuroepithelial cells transform into asymmetrically dividing medulla neuroblast and into lamina precursor cells in a precisely regulated fashion. Using genetic manipulations, it was found that tll is required for proper neuroepithelium morphology and neuroepithelial cell survival. It was shown that tll regulates the precise timing of the transition from neuroepithelial cells to medulla neuroblasts. In particular, however, it was demonstrated that tll has a crucial role for the specification of lamina precursor cells. The study proposes that the Tll/Tlx transcription factors have an evolutionary conserved role in regulating neural precursor cell states in the Drosophila optic lobe and in the mammalian retina.
Liu, T., Mahesh, G., Houl, J. H. and Hardin, P. E. (2015). Circadian activators are expressed days before they initiate clock function in late pacemaker neurons from Drosophila. J Neurosci 35: 8662-8671. PubMed ID: 26041931
Circadian pacemaker neurons in the Drosophila brain control daily rhythms in locomotor activity. These pacemaker neurons can be subdivided into early or late groups depending on whether rhythms in period (per) and timeless (tim) expression are initiated at the first instar (L1) larval stage or during metamorphosis, respectively. Because CLOCK-CYCLE (CLK-CYC) heterodimers initiate circadian oscillator function by activating per and tim transcription, a Clk-GFP transgene was used to mark when late pacemaker neurons begin to develop. It was surprising to see that CLK-GFP was already expressed in four of five clusters of late pacemaker neurons during the third instar (L3) larval stage. CLK-GFP is only detected in postmitotic neurons from L3 larvae, suggesting that these four late pacemaker neuron clusters are formed before the L3 larval stage. A GFP-cyc transgene was used to show that CYC, like CLK, is also expressed exclusively in pacemaker neurons from L3 larval brains, demonstrating that CLK-CYC is not sufficient to activate per and tim in late pacemaker neurons at the L3 larval stage. These results suggest that most late pacemaker neurons develop days before novel factors activate circadian oscillator function during metamorphosis.

Mencarelli, C. and Pichaud, F. (2015). Orthodenticle is required for the expression of principal recognition molecules that control axon targeting in the Drosophila retina. PLoS Genet 11: e1005303. PubMed ID: 26114289.
Parallel processing of neuronal inputs relies on assembling neural circuits into distinct synaptic-columns and layers. This is orchestrated by matching recognition molecules between afferent growth cones and target areas. Controlling the expression of these molecules during development is crucial but not well understood. The developing Drosophila visual system is a powerful genetic model for addressing this question. In this model system, the achromatic R1-6 photoreceptors project their axons in the lamina while the R7 and R8 photoreceptors, which are involved in colour detection, project their axons to two distinct synaptic-layers in the medulla. This study shows that the conserved homeodomain transcription factor Orthodenticle (Otd), which in the eye is a main regulator of rhodopsin expression, is also required for R1-6 photoreceptor synaptic-column specific innervation of the lamina. The data indicate that otd function in these photoreceptors is largely mediated by the recognition molecules flamingo (fmi) and golden goal (gogo). In addition, otd was found to regulate synaptic-layer targeting of R8. During this process, otd and the R8-specific transcription factor senseless/Gfi1 (sens) function as independent transcriptional inputs that are required for the expression of fmi, gogo and the adhesion molecule capricious (caps), which govern R8 synaptic-layer targeting. This work therefore demonstrates that otd is a main component of the gene regulatory network that regulates synaptic-column and layer targeting in the fly visual system.

Marmor-Kollet, N. and Schuldiner, O. (2015). Contrasting developmental axon regrowth and neurite sprouting of Drosophila mushroom body neurons reveals shared and unique molecular mechanisms. Dev Neurobiol. PubMed ID: 26037037
The molecular mechanisms regulating intrinsic axon growth potential during development or following injury remain largely unknown despite their vast importance. This study has established a neurite sprouting assay of primary cultured mushroom body (MB) neurons. This study used the MARCM technique to both mark and manipulate MB neurons, enabling quantification of the sprouting abilities of single WT and mutant neurons originating from flies at different developmental stages. Sprouting of dissociated MB neurons was dependent on wnd, the DLK ortholog, a conserved gene that is required for axon regeneration. Next, and as expected, the sprouting ability of adult MB neurons was found to be significantly decreased. In contrast, and surprisingly, it was found that pupal-derived neurons exhibit increased sprouting compared with neurons derived from larvae, suggesting the existence of an elevated growth potential state. The molecular requirements of neurite sprouting was then contrasted to developmental axon regrowth of MB neurons, a process that requires the nuclear receptor UNF acting via the target of rapamycin (TOR) pathway. Strikingly, it was found that while TOR was required for neurite sprouting, UNF was not. In contrast, PTEN was found to inhibit sprouting in adult neurons, suggesting that TOR is regulated by the PI3K/PTEN pathway during sprouting and by UNF during developmental regrowth. Interestingly, the PI3K pathway as well as Wnd were not required for developmental regrowth nor for initial axon outgrowth suggesting that axon growth during circuit formation, remodeling, and regeneration share some molecular components but differ in others.

Hernandez, K., Myers, L. G., Bowser, M. and Kidd, T. (2015). Genetic tools for the analysis of Drosophila stomatogastric nervous system development. PLoS One 10: e0128290. PubMed ID: 26053861
The Drosophila stomatogastric nervous system (SNS) is a compact collection of neurons that arises from the migration of neural precursors. This study describes genetic tools allowing functional analysis of the SNS during the migratory phase of development. GAL4 lines driven by fragments of the Ret promoter are described that yielded expression in a subset of migrating neural SNS precursors and also included a distinct set of midgut associated cells. Screening of additional GAL4 lines driven by fragments of the Gfrl/Munin, forkhead, twist and goosecoid (Gsc) promoters identified a Gsc fragment with expression from initial selection of SNS precursors until the end of embryogenesis. Inhibition of EGFR signaling using three identified lines disrupted the correct patterning of the frontal and recurrent nerves. To manipulate the environment traveled by SNS precursors, a FasII-GAL4 line with strong expression throughout the entire intestinal tract was identified. The transgenic lines described offer the ability to specifically manipulate the migration of SNS precursors and will allow the modeling and in-depth analysis of neuronal migration in ENS disorders such as Hirschsprung's disease.

Linneweber, G. A., Winking, M. and Fischbach, K. F. (2015). The cell adhesion molecules Roughest, Hibris, Kin of Irre and Sticks and Stones are required for long range spacing of the Drosophila wing disc sensory sensilla. PLoS One 10: e0128490. PubMed ID: 26053791
The development of external sensory organs requires complex cell-cell communication in order to give each cell a specific identity and to ensure a regular distributed pattern of the sensory bristles. In a variety of processes the heterophilic Irre Cell Recognition Module, consisting of the Neph-like proteins: Roughest, Kin of irre and of the Nephrin-like proteins: Sticks and Stones, Hibris, plays key roles in the recognition events of different cell types throughout development. In the present study these proteins are apically expressed in the adhesive belt of epithelial cells participating in sense organ development in a partially exclusive and asymmetric manner. Using mutant analysis the GAL4/UAS system, RNAi and gain of function an involvement was found of all four Irre Cell Recognition Module-proteins in the development of a highly structured array of sensory organs in the wing disc. The proteins secure the regular spacing of sensory organs showing partial redundancy and may function in early lateral inhibition events as well as in cell sorting processes. Comparisons with other systems suggest that the Irre Cell Recognition module is a key organizer of highly repetitive structures.

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