Dynamique Cellulaire - Développement - Association de Biologie ...

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14h50-15h15 associated GW-bodies D. WEIL ; weil@vjf.cnrs.fr Sylvie Souquere, Stéphanie Mollet, Michel Kress, François Dautry, Gérard Pierron, Dominique Weil. CNRS Institut André Lwoff Villejuif Stress granules are cytoplasmic ribonucleoprotein granules formed following various stresses: oxidative, heat shock, UV. They contain untranslated mRNAs along with RNA binding proteins, translation initiation factors and proteins of the small ribosomal subunit. In fluorescence microscopy, stress granules are frequently seen adjacent to P-bodies, which are ribonucleoprotein granules of smaller size involved in mRNA degradation and storage. We have previously shown in live cells that stress granules often assemble at the vicinity of pre-existing P-bodies, suggesting that these two compartments are structurally related. Here we show by electron microscopy that P-bodies have a fibrillar compact structure, while stress granules are loosely organised and fibrillo-granular. Stress granule formation appears restricted to cells in which polysomes are disrupted into monosomes. In situ hybridization indicates an unbalanced ratio of 18S versus 28S rRNA in stress granules, and reveals that they contain only a minor fraction of the cellular arrested mRNAs. Finally, even when in close-contact with P-bodies, both domains are keeping their ultrastructural identities. Fredrecic Gilleron (Leica) : Les cryométhodes à l’appui des microscopies corrélatives 15h15-15h45 Pause-café et Posters 15h45-16h10 La clathrine est un nouvel activateur du complexe Wave 16h10-16h35 Jérémie GAUTIER ; gautier@lebs.cnrs-gif.fr Jérémie J. Gautier , Lamia Bouslama-Oueghlani, Emmanuel Derivery, Arnaud Echard, Helen Beilinson,Wolfgang Faigle, Damarys Loew, Daniel Louvard, Buzz Baum, and Alexis Gautreau Lab. “Complex Assemblies and Morphogenesis” CNRS UPR3082 Laboratoire d’Enzymologie et Biochimie Structurales, Bât. 34 Avenue de la Terrasse 91198 Gif-sur-Yvette Cedex France. Institut Curie, Centre de Recherche CNRS UMR144 Lab. “Cell Morphogenesis and Intracellular Signaling” 26 rue d’Ulm, 75248 Paris Cedex 05, France. Institut Curie, Centre de Recherche Lab. “Proteomic Mass Spectrometry” 26 rue d’Ulm, 75248 Paris Cedex 05, France. MRC Laboratory for Molecular Cell Biology and Dept of Cell and Developmental Biology, University College London, Gower St London WC1E 6BT, UK La migration cellulaire requiert des projections de la membrane plasmique appelées lamellipodes et ruffles. Le complexe Scar/Wave est essentiel à la formation de ces projections. Il alterne entre une conformation inactive dans le cytosol et une conformation active à la membrane qui génère un réseau branché de filaments d’actine via l’activation du complexe Arp2/3. Dans le but d’identifier de nouveaux facteurs contrôlant l’activation du complexe Scar/Wave, nous avons réalisé un double crible en cellules de Drosophile. L’analyse protéomique à identifié des partenaires potentiels du complexe. L’analyse de génomique fonctionnelle à identifié des gènes donnant le même phénotype que le complexe Scar/Wave après déplétion par ARN interférence. De manière surprenante, le croisement des deux listes à conduit à l’identification d’une seule molécule, la clathrine. La clathrine interagit avec le complexe Scar/Wave dans des cellules de Drosophile et humaines. La déplétion de la clathrine induit un défaut de formation des projections membranaires associé à un défaut de recrutement du complexe Scar/Wave à la membrane. A l’inverse, le ciblage de la clathrine à la membrane s’accompagne d’un recrutement du complexe Scar/Wave et potentialise la formation de projections membranaires. Ces résultats démontrent un nouveau rôle de la clathrine dans le recrutement du complexe Scar/Wave au cours de son cycle d’activation. Functional analysis of Longevity Assurance Gene homologs (LOHs) in Arabidopsis Diana MOLINO ; dmolino@versailles.inra.fr Molino D., Bellec Y., Boutin GP, Marion J., Gissot L, Moreau P., Faure JD Laboratoire de Biologie Cellulaire INRA Versailles Sphingolipids were found in yeast and mammals to be essentials in several basic cellular functions such as endocytosis, protein transport, cell proliferation, apoptosis and stress responses. A key step of the sphingolipid biosynthetic pathway is the acylation of long chain bases (LCBs) catalyzed by the sphingoid base N-acyl transferase or Ceramide synthase. Ceramide synthases were found to be involved in cell proliferation and cell death in many organisms including plants. However, their precise cellular functions are still poorly known in plants. Three Longevity homologues (LOHs) have Association de Biologie Cellulaire du Grand campus http://biocell.cnrs-gif.fr 8
16h35-17h00 been found in Arabidopsis. We are investigating the role of LOHs enzymes and their sphingolipid products in plant development using a strategy based on pharmacological and genetic approaches. Seedlings treated with ceramide synthases inhibitor Fumonisin B1 (FB1) displayed altered roots growth under different nutrient and stress conditions. In vivo imaging of FB1-treated root cells, with various endomembrane and plasma membrane markers showed that subcellular trafficking and plasma membrane dynamics was modified. In particular sub-cellular distribution of membrane proteins will be discussed. Insertion mutants were also characterized for each LOH gene and their phenotypic analysis will be described. Finally, the LOH proteins were found to co-localized with ER markers (Marion et al. 2008). A model describing how ceramide synthesis and ceramide-derived molecules could be involved in membrane dynamics, sub-cellular protein distribution and cell division will be presented. Autophagy can rescue cellular but not developmental defects of endosomal maturation mutants. Abderazak DJEDDI ; abderazak.djeddi@cgm.cnrs-gif.fr Abderazak DJEDDI, Xavier MICHELET, Adriana ALBERTI and Renaud LEGOUIS. Centre de Génétique Moléculaire, CNRS, 91198 Gif-Sur-Yvette, France Endocytosis and autophagy are two major processes required for lysosome-dependant degradative pathway in eukaryotic cells. Endocytosis plays a key role in degrading and recycling extracellular and plasma membrane proteins and downregulating receptor-mediated signalling. Autophagy is responsible for non-selective intracellular components degradation allowing cell survival under starvation conditions and plays an essential role during C. elegans development. During autophagy, double-membrane vesicles named autophagosomes sequester cytoplasm and fuse with lysosomes. Our aim is to understand the interaction between autophagy and endocytosis during C. elegans development. We have previously demonstrated that the inactivation of Class E vps genes required for endosome maturation leads to various developmental defects ranging from embryonic lethality to no obvious phenotype. Using an RNAi approach against 9 vps-E genes we monitored the localisation of an endosomal and an autophagosomal marker respectively VPS-27::GFP and GFP::LGG-1. RNAi inactivation of lethal vps-E genes leads to an accumulation of enlarged endosomal structures and subsequently an increase of the autophagic process. Noticeably, the apparition of enlarged endosomes in vps-E mutants was not directly correlated with the stage of lethality which, in contrast was always concomitant with the increase of autophagy. We hypothesized that GFP::LGG-1 subcellular localisation in vps-E mutants could result either from autophagosomeslysosome defective fusion or from an indirect response to maintain homeostasis. In higher eukaryotes, autophagosomes are able to fuse with late endosomes, so we first asked whether autophagosomes and endosomes share common compartments. We have performed immunocolocalisation experiments of the autophagic marker GFP::LGG-1 with markers of early or late endosomes. No vesicle was positive for both markers neither in wild-type animals nor in vps-E mutants suggesting that there is no common compartment between autophagosomes and endosomes in C. elegans. Thus, the autophagosomal accumulation is not due to a blockage of phagosome-to-lysosome fusion. Next we used a genetic approach to analyse whether autophagy is responsible for lethality in vps-E mutants. Using RNAi , we induced or reduced the level of autophagy in several vps-E mutant backgrounds. We observed that an induction of autophagy may correct vps-E cellular defects while a reduction hastens cellular degradation. However an increase of autophagy could only delay but not suppress the lethal phenotype. According to these results we propose that in vps-E mutants autophagy is a secondary response in an attempt to preserve the homeostasis of the cell from endocytosis defects. Jeudi 28 Mai 2009 Session 3 - Signalisation Interaction entre signalisation IP3/Ca2+ et voie LET-413/DLG-1 9h00-9h25 pendant l'embryogenèse de C.elegans Christophe LEFEBVRE ; lefebvre@cgm.cnrs-gif.fr Christophe Lefebvre 1, Jennifer Pilipiuk 2, Tobias Wiesenfahrt 2, Olaf Bossinger 2 et Renaud Legouis 1. 1 Centre de Génétique Moléculaire, CNRS, UPR2167, 91198 Gif-sur-Yvette,Université Parissud,Orsay France. 2 Institute for Genetics, Heinrich-Heine-University, 40225 Düsseldorf, Germany. Les cellules épithéliales sont polarisées et présentent une compartimentation apico-basale délimitée par des jonctions serrées et des jonctions adhérentes. Ces jonctions sub-apicales jouent un rôle Association de Biologie Cellulaire du Grand campus http://biocell.cnrs-gif.fr 9
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