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  • Génomes

    • Vendredi 11 janvier 11:00-12:00 - Pierre Therizols - Institut Jean-Bernard – Hôpital St. Louis

      Dual role of the histone variant H3.3 in embryonic stem cells

      Résumé : The 3D organisation of the chromatin has emerged as an important contributor to genome regulation. Nuclear periphery and pericentromeric centromeric clusters are essential landmarks that contribute to the compartmentalisation of heterochromatin and directly regulates important processes such as transcription or DNA repair.
      Several epigenetic transitions occur during early embryogenesis. Between the morula and blastula stages, parental DNA methylation is erased. This hypomethylated phase leads to a massive reorganisation of DNA repeat-associated heterochromatin. Later, upon embryo implantation, nuclear periphery associated heterochromatin is reorganised, 1,600 genes gain or lose association with the nuclear envelope upon transcriptional activation or repression.
      In this presentation, we identify the histone variant H3.3 as an important factor for the nuclear organisation in embryonic stem cells (ESCs). H3.3 is a histone H3 variant playing a dual role by regulating both euchromatin and heterochromatin. H3.3 is essential for early development, but its exact role remains elusive.
      In the first part, we show that H3.3 is an important factor for heterochromatin reorganisation in ground-state ESCs. Upon DNA demethylation, we observe a clustering of pericentromeric heterochromatin. This clustering correlates with the recruitment of H3.3 and its chaperone Daxx and we demonstrate that their recruitment to major-satellite is sufficient to mediate pericentric heterochromatin clustering. Interestingly, in Daxx knock-out cell lines pericentromeric heterochromatin fails to cluster properly and peripheral heterochromatin is lost. These heterochromatin defects lead to severe growth defect after few days. Altogether, our results suggest Daxx and H3.3 maintain heterochromatin homeostasis in absence of DNA methylation.
      In the second part, we highlight another role for H3.3 during ESCs differentiation. We find a strong correlation between lamina-associated domains repositioning and H3.3 deposition or depletion. By using TALE mediated epigenome editing, we observe that H3.3 chaperone recruitment is sufficient to decondense the Nrp1 gene and to relocate it away from the nuclear periphery.
      Contact : Daan Noordermeer <daan.noordermeer>

      Lieu : Salle des séminaires- bâtiment 26 - Campus CNRS de Gif-sur-Yvette


    • Jeudi 17 janvier 11:00-12:00 - Javier Lopez-Garrido - University of California, San Diego

      On how the genome shapes the spore

      Résumé : Bacillus subtilis is a bacterium with a simple developmental pathway leading to spore formation under conditions of nutrient limitation. Sporulation starts with an asymmetric cell division event, called polar septation, giving rise to two cells with different sizes and developmental fates : the smaller forespore, which becomes the metabolically dormant spore, and the larger mother cell, which dies after sporulation. Polar septation generates asymmetry that is harnessed by the activation of cell specific transcription factors that define the developmental fates of each cell. It also has a dramatic topological consequence, namely, the forespore chromosome is trapped at the middle of the sporulation septum. Spore formers have evolved a system to deal with this topological problem : a membrane protein, called SpoIIIE, is recruited to the point where the chromosome is trapped, and catalyzes the transport the chromosome from the mother cell to the forespore to guarantee that a complete genome is packed in the spore. In this talk, I will present genetic, fluorescence microscopy and cryo-electron microscopy experiments to dissect organization of the SpoIIIE DNA translocation complex. I will also show how chromosome translocation impacts forespore shape. Our results illustrate how simple biophysical interactions between core cellular components contribute to the shape of the spore.
      Contact : Yoshiharu YAMAICHI <yoshiharu.yamaichi>

      Lieu : Bibliothèque- bâtiment 34 - Campus CNRS de Gif-sur-Yvette


    • Vendredi 25 janvier 11:00-12:00 - Nathalie Beaujean - Stem Cell & Brain Institute – Lyon

      Epigenetic reprogramming of rabbit stem cells

      Résumé : Abstract
      Pluripotency is the term used to describe the ability of a stem cell to give rise to all cell types in mature organisms. Two main types of pluripotent stem cells (PSCs) have been described : naïve and primed. The naïve pluripotent state is characteristic of mouse embryonic stem cells (mESCs) and developmentally corresponds to the early epiblast component of the blastocyst stage (just before implantation). Under appropriate conditions, mESCs exhibit unlimited self-renewal capacity while retaining the attributes of preimplantation epiblast identity and potency – especially the ability to generate chimeras.
      On the other hand, in non-rodent species, including humans, it is challenging to capture this original “embryonic” state of pluripotency in PSCs that are mostly in the primed state. In particular, the scarcity of primate embryos makes it difficult to address this issue. As a surrogate model, the rabbit is perfectly suited to explore the nature and mechanisms of acquisition and maintenance of pluripotency in the epiblast cells and ESCs. We therefore explore naïve pluripotency in the rabbit.
      We characterised the transcriptome of the rabbit epiblast throughout pre-implantation development using single-cell analysis. We observed a transcriptomic continuum of pluripotency in vivo specific to the rabbit, although we observed many similarities to the mouse. We also identified new genes and rabbit-specific markers of naïve pluripotency that could be used for reprogramming conventional rabbit PSCs to naïve-state pluripotency ; in particular genes related to the epigenome reprogramming occurring during embryonic development such as the histone acetyltransferase Kat8. We are now implementing new strategies using the identified markers to reprogram rabbit PSCs towards the naïve state. These results will allow us to judge the state of pluripotency of rabbit PSCs we will derive in vitro, as compared to the embryo.
      Contact : Daan Noordermeer <daan.noordermeer>

      Lieu : Bibliothèque- bâtiment 34 - Campus CNRS de Gif-sur-Yvette


  • Virologie

    • Mercredi 16 janvier 11:00-12:00 - Gilles Truan - Laboratoire d'Ingénierie des Systèmes Biologiques et des Procédés (LISBP), Toulouse

      Analysis of the large conformational changes of the NADPH cytochrome P450 reductase by SAXS, NMR and incorporation of non-natural amino acids, fluorophore labeling and FRET techniques

      Résumé : NADPH cytochrome P450 reductase (CPR) is a multidomain protein that transfers electrons from NADPH to a series of electron acceptors. CPR comprises one FAM and one FAD domains that contains the flavins, responsible for the various electrons transfer steps. Large conformational changes have been evidenced in CPR. They trigger the movements of the FMN and FAD domains that are mandatory to promote electron transfers to acceptors. We have demonstrated that CPR is actually in a rapid conformational equilibrium between two states by SAXS and NMR. We recently produced CPR having incorporated two different unnatural amino acids (cyclopropene-L-lysine and p-propargyloxy-L-phenylalanine) in the two catalytic domains. These amino acids were directly derivatized with Cy3 and Cy5, thus producing CPR molecules bearing two different fluorophores. The talk will be centered on the development of the technique as well as the preliminary results obtained in single molecule microscopy FRET.

      Lieu : bâtiment à préciser - Campus de Gif-sur-Yvette


  • Club Bioinformatique

    • Lundi 14 janvier 11:00-12:30 -

      Club Bioinformatique, génomique et biologie des systèmes

      Résumé :

      Orateur : Olivier Arnaiz (équipe Réarrangements programmés du génome, I2BC) : "Modification du transcriptome de Paramecium après altération des réarrangements du génome."
      Orateur : Jean-Christophe Aude (équipe Bio-Informatique Moléculaire, I2BC) : "R avancé dans l’environnement informatique de l’I2BC : retour d’expérience, outils/package de programmation"
      Note : Cette présentation s’adresse tout particulièrement aux personnes utilisant R (donc connaissant déjà le langage) dans le cadre de leur recherche. L’objectif sera de partager un retour d’expérience sur l’environnement informatique et les outils systèmes permettant un usage efficace de R. En ce qui concerne R lui même, on présentera quelques packages clés (principalement ceux de rstudio) et j’introduirai des méthodes d’optimisation en C++. Il ne sera pas nécessaire de disposer d’une machine ce sera en mode "démo" pour introduire les concepts.

      Lieu : Salle Kalogeropoulos - Bât. 400, Campus d’Orsay


  • cytoskeleton club

    • Mardi 8 janvier 11:30-13:00 - Claire Boulogne & Romain Le Bars - plateformes Imagerie-Gif - I2BC

      Cytoskeleton club

      Lieu : Bibliothèque - bât. 34


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