Vendredi 2 juillet 2010 à 14h30

Claude THERMES

Centre de Génétique Moléculaire
Référent du pôle Génomique Fonctionnelle / Responsable PF séquençage haut débit IMAGIF

Plateforme de séquençage haut débit IMAGIF : présentation et perspectives

Contacts : Olivier Espéli (01 69 82 32 14) - Claude Thermes (01 69 82 38 28)

Lien vers le pôle Génomique Fonctionnelle d'Imagif

Vendredi 25 juin 2010 à 11h30

Emmanuel FARGE

Mécanique et Génétique du Développement Embryonnaire
UMR 168, Institut Curie, Paris

Mechanical cues in embryonic and tumor development gene expression

Invité par Annie Sainsard-Chanet (01 69 82 43 70)

Résumé

Embryonic development is a coordination of multi-cellular biochemical patterning and morphogenetic movements.
Last decades revealed the close control of Myosin-II dependent biomechanical morphogenesis by patterning gene expression. Here we describe the reverse control of developmental gene expression and of Myosin-II patterning by the mechanical strains developed by morphogenetic movements, recently revealed at Drosophila gastrulation through mechano-transduction processes involving the Armadillo/b-catenin and the down-stream of Fog Rho pathways. We describe the innovative magnetic tweezers tools we have set up to measure and apply physiological strains and forces in vivo, from the inside of the tissue, to modulate and mimic morphogenetic movements in living embryos. We discuss the incidence in tumor development, and perspective in evolution, of the mechanical control of master genes expression.

Vendredi 18 juin 2010 à 14h30

Sarah LAMBERT

Institut Curie-Centre National de la Recherche Scientifique, UMR3348
Réponse cellulaire aux perturbations de la réplication

Homologous recombination restarts blocked replication forks
at the expense of genome rearrangements by template exchange

Invitée par Mireille Bétermier (01 69 82 31 64)

Résumé

Template switching induced by stalled replication forks has recently been proposed to underlie complex genomic rearrangements. However, the resulting models are not supported by robust physical evidence. Here we analysed replication and recombination intermediates in a well defined fission yeast system that blocks converging forks. We show that, in response to fork arrest, chromosomal rearrangements result from Rad52-dependent nascent strand template exchange occurring during fork restart. This template exchange occurs by both Rad51-dependent and independent mechanisms.
We demonstrate that Rqh1, the BLM homologue, limits Rad51-dependent template exchange without affecting fork restart. In contrast we report that the Srs2 helicase promotes both fork restart and template exchange. Our data demonstrate that template exchange occurs during recombination-dependent fork restart at the expense of genome rearrangements and emphasise the important role of HR in replication restart and the replicative mechanisms responsible for genome rearrangements.

Vendredi 11 juin 2010 à 14h30

Sandra DUHARCOURT

Institut de Biologie de l'Ecole Normale Supérieure - Génomique Fonctionnelle
CNRS UMR8197 INSERM U1024

Epigenetic regulation of the genome:
RNA-directed DNA elimination in the ciliate Paramecium tetraurelia

Invitée par Linda Sperling (01 69 82 32 09)

Résumé

There has been debate about whether promiscuous transcription in eukaryotes produce functional RNAs or simply represent transcriptional noise. In ciliates, genome-wide transcription of both germline and somatic genomes has been implicated in epigenetic programming of the zygotic genome. In these organisms, the massive and reproducible genome rearrangements that occur during zygote development are known to be epigenetically controlled by homology-dependent maternal effects.
We have obtained experimental evidence that has revealed the regulatory roles of two classes of ncRNAs in this process: (i) the piRNA-like scnRNAs, which seem to be produced from the entire germline genome; and (ii) longer transcripts from the somatic genome, which enable the selection of specific scnRNAs. This suggests that genome-wide transcription apparently serves to mediate non-Mendelian inheritance of rearrangement patterns across sexual generations. RNA-directed DNA elimination in ciliates share many conserved features with the formation of heterochromatin and their study will likely reveal general principles applicable to the understanding of genome organization in all other eukaryotes.

Vendredi 28 mai 2010 à 14h30

Alessandro A. SARTORI

Institute of Molecular Cancer Research, University of Zurich, Zurich, Switzerland

CtIP: An evolutionarily conserved protein involved in DNA double-strand break repair

Invité par Mireille Bétermier (01 69 82 31 64)

Résumé

Cells have evolved two major pathways to repair DNA double-strand breaks (DSBs): non-homologous end-joining (NHEJ) and homologous recombination (HR). While NHEJ is the predominant pathway during G1 and does not require sequence homology, accurate repair of DSBs by HR is restricted to S/G2 and requires extensive 5’?3’ resection of DNA ends to generate 3’ ssDNA tails followed by strand invasion of a homologous template. Investigation of the molecular mechanisms of DNA end resection has recently gained much attention and a two-step model has been postulated for human cells: First, CtIP and the MRE11 complex cooperate in the removal of a few nucleotides from the 5’ end (“end-trimming”). In a second step, these intermediates are further resected by two alternative pathways involving either EXO1 or BLM, allowing efficient RAD51 nucleoprotein filament formation. In the first part of my seminar, I would like to present some of our new data showing that CtIP, through its ability to physically and functionally interact with EXO1, coordinates DNA end resection in human cells.
The apparent absence of any conserved 'nuclease' domain within CtIP is quite puzzling, giving its essential role in DNA end resection throughout eukaryotic evolution. We therefore decided to set out a more thorough structure-function analysis of the CtIP homolog found in Paramecium tetraurelia (PtCtIP). Thus, in the second part of this seminar, I would like to discuss our latest data on the biochemical properties of PtCtIP and give an outlook on how this knowledge may guide us to design novel therapeutic approaches for the treatment of cancer.

Vendredi 7 mai 2010 à 14h30

Bénédicte DELAVAL

University of Massachussetts Medical School, Program of Molecular Medicine
Worcester MA - USA

Centrosome defects in disease: Mitotic dysfunction, a novel mechanism for generating ciliopathies

Invitée par Bénédicte Michel (01 69 82 32 29)

Résumé

Centrosomes contribute to spindle organization and orientation in mitosis and mediate primary cilia assembly in non-cycling cells but their role in ciliopathies is poorly understood. Ciliopathies and associated cyst formation have long been associated exclusively with cilia disruption but recent results also suggest the involvement of misoriented cell division in cystogenesis. Cilia have been proposed to influence the orientation of cell division through the regulation of the planar cell polarity pathway. However, the molecular mechanism for misoriented cell division in ciliopathies remains unclear.
To understand the role of centrosomes in ciliopathies, we depleted well-characterized centrosome proteins in human cells and zebrafish embryos. We show here that depletion of centrin2 leads to ciliopathy in zebrafish and induces cilia and mitotic defects in vivo. This finding suggests that not only cilia disruption, but also defects occurring in mitosis may participate in the global ciliopathy phenotype including kidney cyst formation.
Interestingly, many cilia proteins including intraflagellar transport proteins (IFT), well characterized for their essential role in primary cilia assembly in non-cycling cells and their involvement in ciliopathies, also localize to spindle poles in mitosis. This suggests that they could also play a direct role in mitosis. To test this hypothesis, we depleted the cilia protein IFT88, well characterized for its function in cilia, both in cultured cells and zebrafish embryos. We show here that depletion of IFT88 induces mitotic defects in both systems, most notably, loss of astral microtubules leading to spindle misorientation and consequently misoriented cell division. We further show that, at the molecular level, IFT88 functions in mitosis as part of a dynein1-mediated transport system. This transport system is required for spindle poles localization of microtubule nucleating components (g tubulin and EB1) that are essential for proper astral microtubule nucleation and consequently spindle orientation.
This work uncovers for the first time a function for an IFT protein in mitosis. This unanticipated mitotic function for a cilia protein reveals a novel molecular mechanism for misorientation of cell division following cilia protein disruption. More importantly, this work suggest common mechanisms for generating ciliopathies following centrosome and cilia proteins depletion, challenges the current cilia-based model for cystogenesis, and thus has the potential to radically change the way we think about the etiology of ciliopathies.

Lundi 3 mai 2010 à 14h00

Salle de conférences, bâtiment 23-24
Centre de Génétique Moléculaire
CNRS Gif-sur-Yvette

Asma KHAMMARI

Analyse génétique de l'apoptose des cellules polaires de l'ovaire de Drosophile

Soutenance de Thèse de Doctorat - Université Pierre et Marie Curie

Vendredi 30 avril 2010 à 14h30

Bernard LOPEZ

Laboratoire d'étude des Mécanismes de la Recombinaison, UMR CEA/CNRS 217
Institut de Radiobiologie Cellulaire et Moléculaire, Fontenay-aux-Roses

Contrôle de la stabilité du génome, signalisation AKT1 et cancer du sein

Invité par Bénédicte Michel (01 69 82 32 29)

Résumé

Un réseau coordonnant la réponse des cellules aux dommages à l’ADN (DDR : DNA damage response) et la ségrégation des chromosomes, assure la duplication et le maintien de la stabilité du génome. Un défaut dans chacun des partenaires de ce réseau aboutit à de l’instabilité génétique et à une prédisposition tumorale. Cependant, on peut souligner que de très nombreux cancers se développent en absence d’exposition à des stress génotoxiques exogènes forts. Il est donc remarquable que l’activation de la DDR a été trouvée à un stade précancéreux, dans des cellules non-traitées; cette activation de la DDR est interprétée comme le résultat d’un stress réplicatif spontanée. Les fourches de réplication de l’ADN sont régulièrement bloquées par une variété de stress. Dans tous les organismes étudiés, la recombinaison homologue (RH) est essentielle pour la réactivation des fourches de réplication bloquées.
Nous avons analysé différents processus impliqués dans le maintien de la stabilité du génome dans des cellules de mammifères déficientes pour les RH, non-traitées, i.e. en absence de stress exogènes : nous montrons que la vitesse d’élongation des fourches de réplication est ralentie, que la duplication des centrosomes est altérée et que les ségrégations mitotiques sont affectées. Afin de montrer que ces 3 types d’évènements sont liés, nous traitons les cellules sauvages avec des perturbateurs de la réplication et étudions les conséquences sur la duplication des centrosomes et sur la ségrégation mitotique. Comme ces défauts se produisent spontanément dans les cellules RH-, nous analysons l’impact du stress endogènes (stress oxydant) sur la réplication, la duplication des centrosomes et sur la ségrégation mitotique. Les données mettent en exergue l’importance du stress endogène pour l’instabilité génétique endogène et donc la prédisposition tumorale des cellules déficientes en RH, telles que celles porteuses de mutations dans BRCA2.
Des mutations germinales dans 10 gènes peuvent conduire à une prédisposition héréditaire au cancer du sein et de l’ovaire. Parmi ces 10 gènes 9 sont directement impliqués dans la DDR (BRCA1 et BRCA2 sont les plus fréquemment mutés). Cependant la grande majorité des cancers du sein sont des formes sporadiques. Alors se pose la question du statut de la DDR dans les formes sporadiques de cancer du sein. La kinase oncogénique AKT1, qui contrôle la voie de signalisation PI3K/AKT1/PTEN est trouvée suractivée dans 50 % des cancers du sein sporadiques. J’essayerais de vous convaincre que l’activation d’AKT1 conduit à une séquestration cytoplasmique de BRCA1 et donc à un phénotype de type BRCA- (sans mutation du gène). Ces données révèlent les connections moléculaires entre les cancers du sein sporadiques et héréditaires. BRCA1 a été décrit comme affectant le NHEJ. Donc nous poserons la question de l’impact d’AKT1 sur le NHEJ.
Pour analyser le NHEJ nous avons développé un substrat intrachromosomique. Nous avons ainsi caractérisé une voie moléculaire alternative (A-NHEJ) au NHEJ canonique (C-NHEJ) KU/XRCC4 dépendant. Nous montrons que MRE11 peut être impliqué dans les 2 voies (C-NHEJ et A-NHEJ). L’initiation de la voie NHEJ sera discutée.

Jeudi 22 avril 2010 à 11h30

Pr. Steve J.  BUSBY

Prokaryotic gene regulation,
School of Biosciences, University of Birmingham, UK

Regulation at simple and complex bacterial promoters

Invité par Frédéric Boccard (01 69 82 32 20)

Résumé :

Lien vers la page Web

Vendredi 16 avril 2010 à 14h30

Pr. Fevzi DALDAL

Department of Biology, Plant Science Institute,
University of Pennsylvania, Philadelphia, USA

Cytochrome c biogenesis: The Ccm System and DegP

Invité par Soufian Ouchane (01 69 82 31 65)

Résumé

Cytochromes of c-type contain covalently attached hemes that are formed via thioether bonds between the vinyls of heme b and cysteines of the C1XXC2H motifs of apocytochromes. In various organisms, this post-translational modification relies on membrane-associated specific biogenesis proteins, referred to as cytochrome c maturation systems. A highly complex version of these systems, Ccm or System I, is found in Gram-negative bacteria, archaea and plant mitochondria. I will review the Ccm components that can be categorized into three conserved modules, describe emerging functional interactions between the Ccm components, the role of periplasmic protease DegP in this process , and present a mechanistic view of the molecular basis of ubiquitous vinyl-2~Cys1 and vinyl-4~Cys2 heme b-apocytochrome c thioether bonds in c-type cytochromes.

Mercredi 14 avril 2010 à 14h00

Salle de conférences, bâtiment 26
Centre de Génétique Moléculaire
CNRS Gif-sur-Yvette

Bahia Khalfaoui Hassani

Oxydases terminales chez la bactérie pourpre Rubrivivax gelatinosus :
rôle et mise en place dans la membrane

Soutenance de Thèse de Doctorat - Université Paris-Sud 11

Vendredi 9 avril 2010 à 14h30

Gaël CRISTOFARI

Ecole Normale Supérieure de Lyon/Université Nice-Sophia Antipolis
Laboratoire de Biologie et Pathologie des Génomes, INSERM U998 - CNRS UMR 6267, Lyon

Jumping genes in humans

Invité par Antonin Morillon (01 69 82 38 82 / 36 38)

Résumé

Retrotransposons are a class of highly repetitive sequences, which are very abundant in the human genome. They disperse by an RNA-based copy-and-paste mechanism, called retrotransposition. This process can drive profound genome rearrangements. Although generally silent, they are expressed in germ cells, in the early embryo, and in embryonic stem cells, which occasionally results in genetic diseases. Retrotransposons are also massively re-expressed in the large majority of cancers, but the importance and consequences of retrotransposition in human tumors have been poorly studied. Somatic retrotransposition is difficult to track in human tissue due to the highly repetitive and dispersed nature of these elements. We are developing approaches to understand how retrotransposons can participate in the normal and pathological remodeling of the human genome and how they are controlled by their host.

Vendredi 2 avril 2010 à 14h30

Laurent PERRIN

Institut de Biologie du Développement de Marseille-Luminy

Differentiation of the heart: a fly perspective

Invité par Jacques Montagne (01 69 82 32 24)

Résumé

A great number of reports have unravelled the transcription factors and signalling pathways that control the formation of the cardiovascular system. These classical investigations have demonstrated a clear conservation of genetic control, from Drosophila to mammals. However, what these pathways control in terms of downstream gene networks, and how they dynamically interact to control the successive steps that progressively drive the differentiation of cardiomyocytes, largely remains unknown.
Our research projects use genetics and genomics to decipher cardiac Regulatory Networks involved in cardiac cell differentiation in fly. Our approach also includes the development of bio informatics tools to unravel the cis regulatory code from set of co expressed genes. In addition, we are interested in understanding how cardiac function is acquired downstream the cardiac regulatory network: eg how effectors genes “realize” the differentiation program.  Reverse genetic screens are under way to identify genes involved in acquisition and regulation of cardiac function.

Vendredi 26 mars 2010 à 14h30

Bernard  DE  MASSY

Institut de Génétique Humaine, CNRS UPR 1142, Montpellier

The PRDM9 Zinc finger array specifies meiotic recombination hotspots in humans and mice

Invité par Mireille Bétermier (01 69 82 31 64)

Résumé

Meiotic recombination events are non-randomly distributed and cluster into narrow regions of the genome (1-2Kb), defined as hotspots. Our lab is interested in understanding the mechanism and regulation of meiotic recombination in mice. Using various approaches, we have recently shown that hotspot localization is controlled by the Prdm9 gene. PRDM9 has a PR/SET domain (histone methyl transferase) and a zinc finger array interacting with the DNA. Our results show that the DNA sequence specificity mediated by the zinc fingers is a key determinant of the distribution of meiotic recombination events. These observations have wide implications on the basis and uses of genetic maps, and on genome evolution.

Jeudi 18 mars 2010 à 11h30

Katja WASSMANN

Cell Division and Associated Checkpoints
UMR 7622 CNRS, Biologie du Développement UPMC

Precocious APC/C activation in mouse oocytes expressing a mutant form of the SAC kinase Mps1

Invitée par Olivier Espéli (01 69 82 32 14)

Résumé

Sexual reproduction requires the generation of haploid male and female gametes through two consecutive meiotic cell divisions. In meiosis I, paired chromosomes, and not paired sister chromatids such as in mitosis and meiosis II are separated into two daughter cells. This first meiotic division is rather error prone in mammalian oocytes, which has severe consequences: Missegregation events in female meiosis I can lead to the development of trisomies in humans, or to the spontaneous abortion of aneuploid embryos. We are interested in elucidating how chromosome segregation is regulated in mammalian female meiosis I. We use mouse oocytes as the model system closest to human oocytes. We and others have shown previously that the spindle assembly checkpoint or SAC, which assures correct chromosome segregation in mitosis, is also functional in meiosis I in mouse oocytes.
Reducing the levels of the SAC protein Mad2 leads to accelerated anaphase I onset and increased chromosome loss. Our efforts are currently focalised on the SAC kinase Mps1. I will present our results on progression through meiosis I and chromosome segregation in mouse oocytes expressing only a mutant form of Mps1. How components of the SAC interfere with normal cell cycle progression in meiosis I will be discussed.

Vendredi 19 février 2010 à 14h30

Michel CHARBONNEAU

UMR CNRS n°5239, Ecole Normale Supérieure de Lyon

Maintenance of genome integrity by telomere stability
and mitotic cell cycle checkpoint

Invité par Bénédicte Michel (01 69 82 32 29)

Résumé

Telomeres, the ends of linear chromosomes, contain repeated TG-rich DNA sequences which, in dividing cells, must be constantly replenished in order to avoid chromosome erosion and, hence, genomic instability. Moreover, unprotected telomeres are prone to end-to-end fusions. Telomerase, a specialized reverse transcriptase with a built-in RNA template or, in the absence of telomerase, alternative pathways of telomere maintenance are required for continuous cell proliferation in actively dividing cells as well as in cancerous cells. The challenge is to keep these free DNA ends masked from nucleolytic attacks, while also allowing the recruitment of telomerase at intervals. Specialized telomeric proteins protect the telomere ends from degradation and some of them also function in telomerase recruitment or other aspects of telomere length homeostasis.
We will describe novel pathways of telomeric DNA damage signaling by Replication Protein A in budding yeast. We will also introduce a novel pathway of telomerase-independent telomere maintenance, the ILT pathway. Finally, we will describe new projects on the role of the Cohesin complex in telomeric DNA damage signaling and repair.

Vendredi 5 février 2010 à 14h30

Michel WERNER

Laboratoire Régulation de l'Expression des Gènes et Epigénétique (LREGE),
Service de Biologie Intégrative et Génétique Moléculaire (SBIGeM),
Institut de Biologie et Technologies - Saclay (iBiTec-S)

Genome-wide mechanisms of transcription in yeast and mouse

Invité par Laurent Kuras (01 69 82 38 31)

Résumé

The genomes of eukaryotes is transcribed by three RNA polymerases (Pol). Pol I transcribes the large ribosomal RNAs. Pol II transcribes the protein-coding genes and a large number of small RNA while Pol III transcribes tRNAs, the 5S ribosomal RNAs and a small number of small RNAs of diverse functions.
Pol II transcription is highly regulated in response to the environment or to developmental programs. An important step in the regulation of transcription consists in the recruitment of Pol II itself to promoters. New insights into the role of the Mediator of transcription activation in this process will be presented.
The mammalian Pol III-transcribed genome has only been defined by bioinformatics analysis. We have used ChIP-Seq analysis to look at the distribution of Pol III and its transcription factors in mouse ES cells. Results of these experiments will be presented.

Vendredi 29 janvier 2010 à 14h30

Nynke DEKKER

Kavli Institute of NanoScience, TU Delft
The Netherlands

Manipulating nucleic acids with photons and magnets: real-time dynamics in biology

Invitée par Olivier Espéli (01 69 82 32 14)

Résumé

We employ single-molecule techniques to study DNA- and RNA-protein interactions, and have focused on processes related to topology, transcription, and replication. For example, we have examined the mechanisms of Type I Topoisomerases (Koster et al., Nature 2005), their interaction with chemotherapeutic drugs and concomitant implications for the replication fork (Koster et al., Nature 2007). I will briefly review recent progress in technique development, and highlight recent results.

Subsequently, I will describe in more detail our work on RNA and RNA-protein interactions. We have developed a number of nanoscale techniques to monitor the structure of RNA and its mechanical properties.  Quite recently, we have extended their use to the real-time polymerization dynamics of RdRPs, examining the model RdRP from Bacteriophage ?6 during its transcription mode. We quantify its pausing behavior and speculate on its ability to switch RNA strands.

Lab Webpage

Vendredi 22 janvier 2010 à 14h30

Pawel GOLIK

Department of Genetics and Biotechnology, University of Warsaw,
Warsaw, Poland

PPR proteins in yeast mitochondria - from molecular biology to evolution and systems biology

Invité par Nathalie Bonnefoy (01 69 82 31 75)

Résumé

Pentatricopeptide repeat (PPR) proteins form the largest known RNA-binding protein family and are found in all eukaryotes, being particularly abundant in higher plants. PPR proteins localize mostly in mitochondria and chloroplasts, where they modulate organellar genome expression on the posttranscriptional level. 
The seminar presents the results of functional analysis of Dmr1p - a S. cerevisiae PPR protein involved in mitochondrial rRNA biogenesis. Results of an in-depth evolutionary analysis of the PPR family in sequenced yeast genomes are also presented, together with some conclusions about system-level properties of the mitochondrial gene expression machinery.

Vendredi 15 janvier 2010 à 14h30 - Salle de conférences du bâtiment 26

Christine ALLMANG

Architecture et Réactivité de l’ARN, Université de Strasbourg, CNRS,
Institut de Biologie Moléculaire et Cellulaire, Strasbourg

Un mécanisme commun pour l’assemblage des sn(o)RNP et des ARNm de sélénoprotéines

Invitée par Laurent Chavatte (01 69 82 32 13)

Résumé

Les sélénoprotéines jouent un rôle clé dans la protection contre le stress oxydant, la maturation de l’hormone thyroïdienne et du spermatozoïde et le développement du muscle. Le sélénium est incorporé dans les sélénoprotéines sous la forme de l’acide aminé sélénocystéine (Sec). Celui-ci est codé par un codon UGASec, habituellement l’un des codons de terminaison de la traduction. L’incorporation de sélénocystéine fait appel à un mécanisme de recodage co-traductionnel particulièrement complexe qui met en oeuvre une machinerie moléculaire spécialisée.
Nous avons récemment démontré que l’assemblage correct des mRNP de sélénoprotéines, pré-requis à leur traduction, obéissait étonnamment aux mêmes règles que celui d’autres complexes ARN-protéines (RNP) essentiels de la cellule tels que les petits ARN nucléolaires (snoRNP, impliqués dans la biogenèse du ribosome), la télomerase (essentielle à l’intégrité chromosomique) et les petits ARN nucléaires (snRNP, appartenant au complexe d’épissage). L’assemblage fait appel à un complexe supramoléculaire lié au chaperon protéique HSP90, conservé de la levure à l’homme et d’importance fondamentale pour la cellule (Boulon et al., J Cell Biol. 2008). L’analyse de la formation des mRNP de sélénoprotéines nous a permis de mettre en évidence d’autres similitudes insoupçonnées avec les sn/snoRNP, tant du point de vue de la composition protéique des RNP, de la maturation de la coiffe des ARNm de sélénoprotéines que du mode d’assemblage.