LES SEMINAIRES AU CGM en 2004

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16/09
F.-X. Barre

Pierre Léopold
Institut de Signalisation, Biologie du Développement et Cancer, UMR6543 CNRS, Parc Valrose, Nice

Résumé :
Most animals are developmentally programmed to grow to a characteristic adult size. The size of an organ is also intrinsically programmed, as is each individual cell size. Understanding how animal growth is controlled is a major goal in biological research. Our recent work has established that the /Drosophila/ fat body (functionally equivalent to the vertebrate liver) coordinates organismal growth with nutritional information, through a sensor mechanism implying both TOR and IGF/insulin signaling pathways, the main regulators of cell growth. Ongoing experiments aiming to characterize this humoral control of growth will be presented.

Sam Butcher
University of Wisconsin-Madison USA

Résumé :
Intron removal in nuclear precursor-messenger RNA is catalyzed through two transesterification reactions by a multi-megaDalton ribonucleoprotein machine called the spliceosome. A complex between U2 and U6 small nuclear RNAs (snRNAs) forms the catalytic core of the spliceosome. We have completed an NMR structural analysis of a protein-free U2-U6 complex from yeast. The observed folding of the U2-U6 complex is a four helix junction. The base pairing of the catalytically important AGC triad extends the U6 intramolecular stem-loop (U6 ISL), and the NMR structure of this RNA reveals striking structural similarities with domain 5 of group II self-splicing introns. A dynamic analysis of the U6 ISL reveals a base flipping motion at the critical U80 residue. We hypothesize that the four way junction conformation and the base flipping motion are relevant to the first step of splicing.

Brigitte Meunier
Wolfson Institute, University College, London, UK

Résumé :
Le complexe bc1 (ou complexe III) de la chaine respiratoire mitochondriale catalyse le transfert d'electrons de l'ubiquinol au cytochrome c et la translocation de proton a travers la membrane mitochondriale interne. L'enzyme est composee de 10-11 sous-unites dont une, le cytochrome b, est codee par l'ADN mitochondrial. Le complexe est la cible de d'agents anti-microbiens utilises en medecine et agriculture. De nombreuses mutations de resistance aux inhibiteurs ont ete detectees dans le cytochrome b d'organismes pathogenes apres traitement. De plus une vingtaine de mutations du cytochrome b ont ete reportees chez des patients atteints de maladies neuromusculaires. Nous utilisons la levure, Saccharomyces cereviseae, comme modele pour caracteriser l'effet de ces mutations et determiner les bases moleculaires des deficiences respiratoires et des resistances. Nous etudions egalement l'effet de l'inhibition du complexe bc1 sur l'expression genomique par 'DNA microarray'.

Doron Rapaport
Institut für Physiologische Chemie der Ludwig-Maximilians-Universität München

Résumé :
The outer membranes of mitochondria and chloroplasts are distinguished by the presence of beta-barrel membrane proteins. The other biological membrane known to harbour beta-barrel proteins is the outer membrane of gram-negative bacteria. In mitochondria these proteins fulfil a variety of functions like transport of small molecules (porin/VDAC), translocation of proteins (Tom40) and regulation of mitochondrial morphology (Mdm10). These proteins are nuclear-encoded, synthesized in the cytosol, targeted to mitochondria as chaperone-bound species, recognized by the translocase of the outer membrane (TOM complex) and then inserted into the outer membrane where they assemble into functional oligomers. We recently identified a protein complex that is essential for the topogenesis of mitochondrial outer membrane beta-barrel proteins (TOB complex). Known constituents of this complex are Tob55, Tob38 and Mas37; the first two are essential for yeast cell viability. The functions of the TOB complex and of its components are discussed. Interestingly, important elements of the topogenesis of beta-barrel membrane proteins have been conserved during evolution of mitochondria from endosymbiotic bacterial ancestors.

Fred Heffron
Department of Molecular Microbiology and Immunology Oregon Health and Science University

Résumé :
Visitez le site de Fred Heffron : http://www.ohsu.edu/microbiology/heffron.html

Michael Boutros
German Cancer Research Center, Heidelberg, Germany

Résumé :
Michael has recently developed with Norbert Perrimon (Boston) the methodology to perform genome wide RNAi screens using the Drosophila Schneider Cell line. He has now his own lab at Heidelberg where he is using this powerful technic to dissect signaling cascades.
For additional information: http://boutros.info/lab/index.html

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Jacques Daniel
CNRS-CGM, Gif

Résumé :

Richard ffrench-Constant
Department of Biology & Biochemistry University of Bath, UK

Résumé :
We will examine the impact of molecular biology on our understanding of traits of adaptive advantage using examples from Batesian mimicry, insecticide resistance and insect parasitism
Richard ffrench-Constant nous parlera de Photorhabdus, une bactérie qui vit en symbiose avec des nématodes et est pathogène pour les insectes (papillons). Cette bactérie utilise le nématode comme vecteur pour pénétrer au sein de l'insecte. L'étude des facteurs de virulence des bactéries entomopathogènes (ex toxines) est en pleine expansion avec des applications possibles dans le bio-contrôle des insectes ravageurs .

Visitez le site de l'équipe : http://staff.bath.ac.uk/bssrfc/

Sven SAUPE
Institut de Biochimie et de Génétique Cellulaires, UMR 5095 CNRS-Université de Bordeaux 2

Résumé :
La protéine HET-s du champignon filamenteux Podospora anserina est une protéine prion, c’est a dire une protéine infectieuse capable de propager un état conformationel altéré. Cette protéine est impliquée dans le déclenchement d’une réaction de mort cellulaire. Nous avons pu établir que la protéine HET-s forme des assemblages supramoléculaires de type amyloide. Il s’agit a présent de documenter les modifications structurales qui accompagnent la transition vers la forme prion pour élucider dans le détail le mécanisme de propagation de la forme amyloide infectieuse de la protéine HET-s.

François-Xavier BARRE
LMGM, CNRS, Toulouse

Résumé :
Chromosome replication and cell division are two critical steps in the life cycle of any cell. Equally important is that cell division does not take place before the DNA has been successfully replicated and distributed. In eukaryotic cells, this is achieved by the existence of rmitotic checkpoints. In prokaryotic cells, however, cell division can be initiated before the process of chromosome segregation is completed. In bacteria with circular chromosomes, this occurs at least each time chromosome dimers are formed by homologous recombination .
Such chromosome dimer cannot be segregated and stay trapped in the closing septum. They are eventually resolved by the addition of a crossover by the XerCD recombinases at a specific site on the chromosome, dif. Under these circumstances, chromosome segregation depends on a cell division protein, FtsK, which pumps DNA through the closing septum.
DNA translocation by FtsK is oriented by small polarized DNA sequences on the chromosome to allow for the equal distribution of genetic information in the two daughter cells. This process is also required to bring the XerCD-dif chromosome dimer resolution complex in contact with its activator: FtsK
Visitez le site de l'équipe de F.-X. Barre : http://www-lmgm.biotoul.fr//index-fr.html

Dr Jane MELLOR
Department of Biochemistry - Oxford - UK

Résumé :
The concept of poised RNAPII at the 5' regions of regulated genes is well established. We have been determining how poised RNAPII is regulated and show that differential K4 methylation is essential. Monomethylation of K4 is required to poise RNAPII while trimethylation leads to efficient and timely release of polymerase from the poise. Both marks work through the recruitment of factors.
The Isw1 chromatin remodelling ATPase, the transcription factor Fkh1 and the CTD kinase Kin28 lead to poising of polymerase while a complex and interdependent series of histone tail modifications leads to the recruitment of the SWI/SNF chromatin remodelling ATPase and release of polymerase. There pathways will be reviewed during the seminar.We have begun to uncover two new modes of gene regulation that require poised RNAPII (with CTD phosphorylated at Ser5) and have some evidence that poising may be regulated by the same factors that regulate RNAPII at active genes. The first is a gene loop in which poised RNAPII links the 5' and 3' regions of both actively transcribed genes and genes poised for expression. The second situation is at the silent mating type locus HMR where Isw1 and Fkh1 dependent poising of RNAPII at the locus is required for silencing.

Prof Pat HIGGINS
Howell Heflin Center for Human Genetics Birmingham, AL, USA

Bruno KLAHOLZ
IGBMC, Strasbourg

Alberto ROSA
Institute for Medical Research (INIMEC-CONICET), Argentina,
and Basic Medical Sciences Program, Washington State University Spokane, USAg

Jean-René MARTIN
NAMC du CNRS, Université Paris-sud, Orsay

Dr Marie-Odile FAUVARQUE
CEA-Grenoble - Département de Dynamique et Réponse Cellulaire

Professeur Pierre CAPY
"Populations, Génétique, Evolution", CNRS, Gif-sur-Yvette

François TADDEI
Hôpital Necker, Paris

David LEACH
University of Edinburgh

Résumé :
Mis-folded DNA is a threat to genome stability, as it is a substrate for polymerase slippage leading to deletions and potentially to other rearrangements. I will discuss the pathways leading to DNA mis-folding and the pathways that have evolved to remove mis-folded DNA from the E. coli genome. Since the proteins that mediate these pathways are conserved from E. coli to humans, we believe that our conclusions have general applicability to the management of DNA and for the maintenance of genome stability.

Véronique MOREL
Department of Genetics, University of Cambridge

Résumé :
À mi-parcours de l'embryogenèse de la drosophile, l'épiderme embryonnaire dorsal est discontinu. La fermeture dorsale (FD) est un processus de morphogenèse épithéliale au cours duquel les deux bords de l'épiderme embryonnaire migrent dorsalement et se soudent. La polarisation des cellules épidermales les plus dorsales (DME) dans le plan de l'épiderme constitue une étape décisive au bon déroulement de la FD. En effet, une FD anormale est observée lorsque cette polarisation est perturbée en absence d'activité wingless (wg) ou dishevelled (dsh). L'étude de la contribution de Wg à la polarisation des cellules DME montre que Wg joue un rôle permissif et que cette fonction passe par l'activation de la voie de signalisation Wingless dépendante de la bcaténine. De manière surprenante, la voie de signalisation Wingless dite de Polarité Cellulaire Planaire n'est pas requise pour la polarisation des cellules DME.

Marc BARTOLI
Généthon, Evry

Professor Hermann VAN TILBEURGH
Laboratoire d'Enzymologie et Biologie Structurales, CNRS, Gif-sur-Yvette

Patrick O'FARREL
UCSF, San Francisco

Professor Richard COGDELL
IBLS, Div. of Biochemistry & Molecular Biology, University of Glasgow

Justine COLLIER
Institut de Génétique et Microbiologie, Université Paris Sud, Orsay

Antonin MORILLON
Department of Biochemistry, University of Oxford, England