Function of valois in germ plasm assembly and posterior development of Drosophila melanogaster

We report the cloning and characterization of valois (vls), a posterior group gene of Drosophila melanogaster , which was initially identified in a screen for female steriles. Three EMS alleles of vls contain premature stop codons in the open reading frame. Sequence analyses show the presence of WD domains in Vls and find significant similarity with the human MEP50 protein which is involved in the assembly of the splicing machinery. We did not find evidence that this function is conserved in flies yet.We created a null mutant for vls, which shows a maternal effect lethal phenotype accompanied by posterior polarity defects in the embryos. Hemizygous vlsEMS females show a weaker, partially maternal-effect lethal and a fully penetrant grandchildless phenotype. The posterior localization of Vasa is disrupted in vlsnull ovaries, but the initial distribution of Oskar protein and mRNA appear normal. However, levels of the Short Oskar isoform responsible for pole plasm assembly are greatly reduced and Vasa appears to be differently modified post-translationally. Furthermore, a Vls::GFP fusion protein is detected all throughout oogenesis in the nurse cell and oocyte cytoplasm. Taken together, these data suggest that Vls is a cytoplasmic protein involved in the transport or activation of Vasa at the posterior of the oocyte essential for the accumulation of Short Osk

Molecular Bases of Cell–Cell Junctions Stability and Dynamics

Epithelial cell–cell junctions are formed by apical adherens junctions (AJs), which are composed of cadherin adhesion molecules interacting in a dynamic way with the cortical actin cytoskeleton. Regulation of cell–cell junction stability and dynamics is crucial to maintain tissue integrity and allow tissue remodeling throughout development. Actin filament turnover and organization are tightly controlled together with myosin-II activity to produce mechanical forces that drive the assembly, maintenance, and remodeling of AJs. In this review, we will discuss these three distinct stages in the lifespan of cell–cell junctions, using several developmental contexts, which illustrate how mechanical forces are generated and transmitted at junctions, and how they impact on the integrity and the remodeling of cell–cell junctions

Organisation spatiale de l'adhérence intercellulaire par le cytosquelette d'actine dans l'épithélium embryonnaire de drosophile

L'adhérence intercellulaire, responsable de la cohésion des tissus, est maintenue par les protéines transmembranaires E-Cadhérines (E-Cad) qui sont liées dynamiquement via b- et a-Caténine au cytosquelette d'actine. afin de mieux comprendre comment cette interaction dynamique stabilise l'adhérence et comment les molécules E-Cad sont distribuées à la surface des cellules, j'ai utilisé au cours de ma thèse l'épithélium embryonnaire de drosophile. Mes travaux mettent en évidence deux nivaux de contrôle de l'adhérence par l'actine. Des filaments d'actine qui se renouvellent lentement maintiennent localement les molécules E-card en agrégats stables. D'autres filaments, qui se renouvellent rapidement, contrôlent la localisation de ces agréagats en les immobilisant par un mécanisme d'ancrage impliquant a-Caténine. mes travaux identifient la principale fonction de a-Caténine dans le contrôle de l'adhérence et démontrent que d'adhérence est organisée spatialement à la surface cellulaire.Intercellular adhesion, crucial for tissue cohesion, is maintained by E-Cadherin (E-Cad) transmembrane proteins which are dynamically linked to the actin cytoskeleton via b- and a-Catenin. To understand how this dynamic interaction stabilizes adhesion and how E-Cad molecules are distributed at the cell surface, i have used drosophila embryonic epithelial cells during my phD. My work reveals two levels of control of adhesion by actin. One population of actin filaments with a slow turnover maintains locally E-Card molecules in stable aggregates. Another population of filaments, with rapid turnover, controls the localization of these aggregates by immobilizing them by an anchoring mechanism which involves a-Catenin. This work identifies the main function of a-Catenin in adhesion control and demonstrates that adhesion is spacially organized at the cell surfaceAIX-MARSEILLE2-BU Sci.Luminy (130552106) / SudocSudocFranceF

Circadian rhythms in neuronal activity propagate through output circuits

International audienceTwenty-four hour rhythms in behavior are organized by a network of circadian pacemaker neurons. Rhythmic activity in this network is generated by intrinsic rhythms in clock neuron physiology and communication between clock neurons. However, it is poorly understood how the activity of a small number of pacemaker neurons is translated into rhythmic behavior of the whole animal. To understand this, we screened for signals that could identify circadian output circuits in Drosophila melanogaster. We found that leucokinin neuropeptide (LK) and its receptor (LK-R) were required for normal behavioral rhythms. This LK/LK-R circuit connects pacemaker neurons to brain areas that regulate locomotor activity and sleep. Our experiments revealed that pacemaker neurons impose rhythmic activity and excitability on LK- and LK-R-expressing neurons. We also found pacemaker neuron–dependent activity rhythms in a second circadian output pathway controlled by DH44 neuropeptide–expressing neurons. We conclude that rhythmic clock neuron activity propagates to multiple downstream circuits to orchestrate behavioral rhythms

Drosophila valois encodes a divergent WD protein that is required for Vasa localization and Oskar protein accumulation

valois (vls) was identified as a posterior group gene in the initial screens for Drosophila maternal-effect lethal mutations. Despite its early genetic identification, it has not been characterized at the molecular level until now. We show that vls encodes a divergent WD domain protein and that the three available EMS-induced point mutations cause premature stop codons in the vls ORF. We have generated a null allele that has a stronger phenotype than the EMS mutants. The vlsnull mutant shows that vls+ is required for high levels of Oskar protein to accumulate during oogenesis, for normal posterior localization of Oskar in later stages of oogenesis and for posterior localization of the Vasa protein during the entire process of pole plasm assembly. There is no evidence for vls being dependent on an upstream factor of the posterior pathway, suggesting that Valois protein (Vls) instead acts as a co-factor in the process. Based on the structure of Vls, the function of similar proteins in different systems and our phenotypic analysis, it seems likely that vls may promote posterior patterning by facilitating interactions between different molecules

A two-tiered mechanism for stabilization and immobilization of E-cadherin

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Temporal Patterning of Neuroblasts Controls Notch-Mediated Cell Survival through Regulation of Hid or Reaper

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Evolution of Ovipositor Length in Drosophila suzukii Is Driven by Enhanced Cell Size Expansion and Anisotropic Tissue Reorganization Pupal morphogenesis of the ovipositor

International audienceGraphical Abstract Highlights d D. suzukii has evolved a bigger egg-laying organ compared to D. melanogaster d The inter-species size difference arises during a short development time window d The fine-tuning of shared cellular processes drives this difference in morphogenesis d The rate of cell apical area expansion and the tissue shape anisotropy have evolved In Brief The fruit pest species Drosophila suzukii has evolved a bigger egg-laying organ compared to D. melanogaster. Green et al. show that the fine-tuning of shared cellular processes-namely, the rate of cell apical area expansion and the tissue shape anisotropy-drives the change in size and shape of the egg-laying organ of D. suzukii

Map positions of third chromosomal female sterile and lethal mutations of Drosophila melanogaster

Chromosomal mutations induced by ethyl methanesulfonate (EMS) treatment can cause female sterility or maternal-effect lethality in Drosophila. EMS is particularly useful to researchers because it creates mutations independent of position effects. However, because researchers have little control over the chromosomal site of mutation, post-mutagenic genetic mapping is required to determine the cytological location of the mutation. To make a valuable set of mutants more useful to the research community, we have mapped the uncharacterized part of the female-sterile – maternal-effect lethal Tübingen collection. We mapped 49 female-sterile – maternal-effect lethal alleles and 72 lethal alleles to individual deficiency intervals on the third chromosome. In addition, we analyzed the phenotype of ovaries resulting from female sterile mutations. The observed phenotypes range from tumorous ovaries and early blocks in oogenesis, to later blocks, slow growth, blocks in stage 10, to apparently full development of the ovary. The mapping and phenotypic characterization of these 121 mutations provide the necessary information for the researcher to consider a specific mutant as a candidate for their gene of interest.Key words: Drosophila melanogaster, oogenesis, female sterile, maternal-effect lethal, EMS-induced mutations

Evolution of Multiple Sensory Systems Drives Novel Egg-Laying Behavior in the Fruit Pest Drosophila suzukii

International audienceThe rise of a pest species represents a unique opportunity to address how species evolve new behaviors and adapt to novel ecological niches [1]. We address this question by studying the egg-laying behavior of Drosophila suzukii, an invasive agricultural pest species that has spread from Southeast Asia to Europe and North America in the last decade [2]. While most closely related Drosophila species lay their eggs on decaying plant substrates, D. suzukii oviposits on ripening fruit, thereby causing substantial economic losses to the fruit industry [3-8]. D. suzukii has evolved an enlarged, serrated ovipositor that presumably plays a key role by enabling females to pierce the skin of ripe fruit [9]. Here, we explore how D. suzukii selects oviposition sites, and how this behavior differs from that of closely related species. We have combined behavioral experiments in multiple species with neurogenetics and mutant analysis in D. suzukii to show that this species has evolved a specific preference for oviposition on ripe fruit. Our results also establish that changes in mechanosensation, olfaction, and presumably gustation have contributed to this ecological shift. Our observations support a model in which the emergence of D. suzukii as an agricultural pest is the consequence of the progressive modification of several sensory systems, which collectively underlie a radical change in oviposition behavior