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Séminaire

  • Génomes

    • Vendredi 13 novembre 11:00-12:00 - Ines DRINNENBERG - Institut Curie, Paris

      Evolution of centromeres : Conserved functions but diverse architectures

      Résumé : Despite their essentiality for faithful chromosome segregation, centromere architectures are diverse among eukaryotes and embody two main configurations : mono- and holocentromeres, referring respectively to a localized or unrestricted distribution of centromeric activity. Previous studies revealed that holocentricity in many insects strongly coincides with the loss of the otherwise essential centromeric marker CenH3 (CENP-A), suggesting a molecular link between the two events.
      Here, we aim to characterize this unique CenH3-deficient chromosome segregation pathway. Using proteomic and genomic approaches in Bombyx mori (silk moth) cell lines, we aim to determine the mechanism of CenH3-independent kinetochore assembly that led to the establishment of their holocentric architecture.
      In this context, we have recently identified additional inner kinetochore components including CENP-T and determined their contribution to kinetochore assembly independent of CenH3. In addition, we also leveraged the identification of these kinetochore components against which we also generated antibodies to map and characterize the centromeres of B. mori. This uncovered a robust correlation between centromere profiles and regions of low chromatin dynamics found anywhere along the chromosome. Transcriptional perturbation experiments showed that centromeres become excluded from regions of active chromatin but can form de novo in regions where chromatin activity is low. The identified link to chromatin dynamics helps to discuss the plasticity of centromere identity. In this context, our study points to a novel mechanism of centromere formation that occurs in a manner recessive to the chromosome-wide chromatin landscape rather than being defined by the presence of CenH3. Based on similar profiles observed in additional Lepidoptera, we propose an evolutionarily conserved mechanism that underlies the establishment of holocentromeres through loss of a specified centromere.

      Contact : Daan NOORDERMEER <daan.noordermeer i2bc.paris-saclay.fr>

      Lieu : Auditorium - bâtiment 21 - campus de Gif-sur-Yvette

      Article

    • Mardi 17 novembre 15:58-16:58 - Pierre Mandin - Laboratoire de Chimie Bactérienne UMR 7283

      A sRNA “ménage à trois” : Three sRNAs control Fe-S biogenesis in response to oxygen and iron stresses

      Résumé : Fe-S clusters are essential and ubiquitous cofactors involved in a plethora of reactions. Despite their usefulness, Fe-S clusters are extremely sensitive to oxidative stress and iron starvation. Fe-S biogenesis regulation is therefore crucial for cell viability. In E. coli, two main machineries are involved in Fe-S cluster production : ISC, the housekeeping system, and SUF, which is expressed under stress. IscR, itself an Fe-S cluster containing protein, is a transcriptional regulator that induces the synthesis of either system in function of its concentration and of its Fe-S cluster bound state.
      We show here that three sRNAs, FnrS, OxyS and RyhB regulate Fe-S biogenesis by controlling IscR concentration and activity. FnrS is expressed during anaerobiosis and directly represses IscR translation by binding the iscR mRNA. OxyS is induced by oxidative stress and activates IscR translation by a yet undefined mechanism. Finally, RyhB, which is expressed during iron starvation, was shown to repress the isc machinery. We show here that in this way RyhB indirectly controls IscR Fe-S maturation state and activity. To our knowledge this is the first case of a triple regulation by sRNAs happening at both transcriptional, post transcriptional and post-translational levels through direct and indirect mechanisms. We are currently exploring how these sRNAs control dynamically Fe-S biogenesis and help the cell face stressful conditions. In any case, such an exquisite control clearly puts IscR and Fe-S biogenesis at the very heart of stress response control by sRNAs.
      Séminaire en visio réservé aux membres de l’I2BC (lien sur l’agenda intranet)

      Article

  • I2BC

    • Vendredi 6 novembre 11:00-12:30 - Mart Krupovic - Institut Pasteur, Paris

      Living on the edge : the secrets of archaeal viruses

      Résumé : Viruses of archaea represent one of the most enigmatic parts of the virosphere. Most of the characterized archaeal viruses infect extremophilic hosts and display remarkable diversity of virion morphotypes, many of which have never been observed among bacteriophages or viruses of eukaryotes. However, recent environmental studies have shown that archaeal viruses are widespread also in moderate soil and marine ecosystems, where they play an important ecological role by influencing the turnover of microbial communities, with a global impact on the carbon and nitrogen cycles. During the seminar, I will present the recent advances in our understanding of the genomic and morphological diversity of archaeal viruses and the mechanisms of virus-host interactions in Archaea. I will highlight some of the molecular adaptations underlying the stability of archaeal viruses in extremely hot acidic environments. Finally, I will examine the potential origins and evolution of archaeal viruses and discuss their place in the global virosphere.

      Lieu : Visio - https://uvsq-fr.zoom.us/j/92861689942?pwd=N3h2alA1VWcrUTNvenNrb2pNWWk0Zz09

      Notes de dernières minutes : Ce séminaire est donné dans le cadre d’un enseignement de M2 hébergé par l’I2BC. Contact : Ombeline Rossier (ombeline.rossier@i2bc.paris-saclay.fr)

      Article

  • Microbiologie

    • Vendredi 6 novembre 09:30-10:30 - Olivier BORKOWSKI - Institut Pasteur, Paris

      Relationship between gene expression and host physiology in bacteria and yeast

      Résumé : My scientific interest, from my PhD to my current work, focuses on the relationship between cell physiology and gene expression. During my PhD, I worked on B. subtilis to understand the impact of growth rate on protein production using a system-oriented approach. Then, during my postdocs, I focused on the impact of protein production on the growth rate. I developed a method to predict the cost of heterologous protein production using cell-free systems (in vitro expression) and models of the translation process. In parallel, I used synthetic biology approaches to build :
      -  Genetic circuits sensing the changes in cell physiology in different growth phases to control protein production in E. coli using genetic logic gates
      -  Autonomous "feedback control" circuits to sense and reduce the weight of resource competition between the host and synthetic circuits
      I also coupled cell-free systems and active learning to maximize protein production and highlight the critical resources limiting gene expression in vitro. Today, I am working on active learning as a general tool to assist the design of genetic circuits in S. cerevisiae.
      I am currently developing a project to build a platform to easily express and study gene expression of difficult to grow/transform non-model organisms. Non-model organisms represent the vast majority of bacteria in nature and are poorly understood. On the contrary, it is now fast and easy to express gene by adding DNA in cell-free expression systems. The literature contains a collection of well-established protocols to obtain cell-free systems from multiple model bacteria.
      This project aims to use these cell-free systems and a library of plasmids to emulate the transcription machineries of “uncultivable” organisms. Such approach will be adaptable to a variety of new organisms as long as the genes involved in the transcription processes are well-annotated to build the suitable plasmids library. Eventually, with this platform, I should be able to express complete genomes to provide large transcriptome datasets and identify new genes, regulations and pathways but also to develop new genetic tools to manipulate these organisms.

      Lieu : En visio

      Article

  • B3S

    • Vendredi 6 novembre 11:00-12:00 - Valérie Biou - Laboratoire de Biologie Physico-Chimique des Protéines Membranaires, Institut de Biologie Physico-Chimique

      Energy supply of heme import in bacteria : Cryo-EM structures of two membrane complexes

      Résumé : Gram negative bacteria import iron from their host cells via a two-membrane spanning complex energised by a TonB-like complex in the inner membrane. We solved the structures of two partners of TonB from Serratia marcescens : ExbB pentamer and its complex with ExbD. The structures show the detailed location of the partners and exhibit differences with respect to the E. coli complex.

      Lieu : Amphithéatre de Neurospin, CEA Saclay - https://joliot.cea.fr/drf/joliot/Pages/Entites_de_recherche/neurospin/Plan-neurospin.aspx

      Article

    • Mardi 17 novembre 11:30-13:30 - Dorit Hanein - Institut Pasteur, Paris

      Coupling molecular activation and its functional output through 4d multiscale imaging - Correlative light and cryogenic cellular tomography studies

      Résumé :

      How do cells employ large, macromolecular machineries in cellular processes ?
      Despite of their key roles in every biological process and accumulated knowledge of composition and interactions, how nanomachine assemblies are organized in cells remains a mystery, and simplified schematic “cartoons” are currently our primary source of information. This is a knowledge gap given the importance in development, cancer biology, and tissue engineering. Specifically today, in which pathogens are taking hold on these machineries to promote their own survival, inflicting havoc on their unwilling host.
      I plan on presenting how we can move beyond “cartoon biology” and generate quantitative, (sub)nanometer-scale, three-dimensional structures of various molecular machineries in their native environment and in well-defined functional states. I will describe progress towards a technology platform that combines a unique set of state-of-the art light and cryogenic electron microscopy technologies, mechanical engineering, and protein expertise to provide a direct sub-nanometer scale definition on how these nano-machines structurally adapts to collectively response to changes in the environment, and thus provide clues on how to avert their malfunction in disease or infection. 
       
      Invited by Julie Ménétrey
       
      Due to Covid-19 the seminar will be online : https://us02web.zoom.us/j/82680525715

      Lieu : Webinar

      Article

    • Jeudi 19 novembre 11:00-12:00 - Jacqueline CHERFILS - Laboratoire de Biologie et Pharmacologie Appliquée, Ecole Normale Supérieure Paris-Saclay

      Peripheral membrane signalling by small GTPases : mechanisms and inhibition

      Résumé : Séminaire en visio :
      https://bbb.i2bc.paris-saclay.fr/b/mar-3z7-zg6

      Article

    • Mercredi 25 novembre 11:00-12:00 - Tobias Madl - Univ. Graz, Autriche

      Regulation of FOX transcription factors by b-catenin

      Résumé :

      Transcription factors harbour defined intrinsically disordered regulatory regions, which raises the question of how they mediate binding to structured co-regulators and how this regulates activity. Here, we present a detailed molecular regulatory mechanism of Forkhead box transcription factors by the structured transcriptional co-regulator β-catenin. We find that the largely disordered regions of FOXP2 and FOXO4 bind β-catenin through multiple defined interaction sites, and this is regulated by post-translational modifications. In Case of FOXO4, binding of β-catenin competes with the auto-inhibitory interaction of the FOXO4 disordered region with its DNA-binding forkhead domain, and thereby enhances FOXO4 transcriptional activity. Furthermore, we show how regulators can switch between different transcription complexes, for example between anti-proliferative FOXO and pro-proliferative Wnt/TCF/LEF signalling. Together these data illustrate how the interplay of intrinsically disordered regions, post-translational modifications and co-factor binding contribute to transcription factor function.


      Selected publications on that topic :
      - Nonclassical nuclear localization signals mediate nuclear import of CIRBP.
      Bourgeois B, et al. Proc Natl Acad Sci U S A. 2020.
      doi : 10.1073/pnas.1918944117
      - Probing Surfaces in Dynamic Protein Interactions.
      Spreitzer E, et al. J Mol Biol. 2020.
      doi : 10.1016/j.jmb.2020.02.032
      - Regulation of cellular senescence via the FOXO4-p53 axis.
      Bourgeois B, Madl T. FEBS Lett. 2018.
      doi : 10.1002/1873-3468.13057
      - Phase Separation of FUS Is Suppressed by Its Nuclear Import Receptor and Arginine Methylation.
      Hofweber M, et al. Cell. 2018.
      doi : 10.1016/j.cell.2018.03.004


      CV :
      https://forschung.medunigraz.at/fodok/suchen.person_uebersicht?sprache_in=en&ansicht_in=&menue_id_in=101&id_in=80568

      Lieu : Visio-BBB - https://bbb.i2bc.paris-saclay.fr/b/the-rp2-hmf

      Article

  • cytoskeleton club

    • Mardi 10 novembre 09:00-18:00 - Sophie Martin, Thomas Surrey, Juliette Azimzadeh, Carsten Janke, Matthieu Piel, Marie-Emilie Terret

      Paris Cytoskeleton Day

      Résumé : The Paris Cytoskeleton Day is a scientific one-day symposium open to all types of cytoskeletal components and all types of approaches.
      The meeting will be fully virtual, yet lively and interactive, with ample time for discussions after each talk.
      During the breaks following the 2 keynote talks, you will have the opportunity to chat in smaller groups with the keynote speakers.
       
      The full program of the Paris Cytoskeleton Day can be found here : https://pcd2020.sciencesconf.org/resource/page/id/1
       
      Registration is free of charge, but mandatory.
      You have until the 6th of November to register, at https://pcd2020.sciencesconf.org/registration
       
      Organizing committee :
      Renata Basto (Curie), Véronique Brodu (IJM), Arnaud Echard (Pasteur), Antoine Jégou (IJM), Guillaume Romet-Lemonne (IJM)

      Lieu : Webinar

      Article

Soutenance

  • Génomes

    • Vendredi 27 novembre 14:30-17:30 - Olivier Arnaiz - Equipe Réarrangements programmés du génome

      Annotation des génomes de paramécies

      Résumé :
      Les nouvelles technologies de séquençage (NGS) ont révolutionné nos approches de la génomique.
      De nombreux génomes d’organismes ont été séquencés et assemblés. Le décryptage de l’information qu’ils contiennent (annotation) est plus que jamais une étape cruciale. Dans ce manuscrit, je vais me focaliser sur l’impact qu’ont eu les NGS sur l’annotation des génomes de paramécies, et notamment l’annotation de gènes et d’éléments transposables (ET).
      La paramécie est un eucaryote unicellulaire possédant deux types de noyaux. Un noyau germinal (MIC) utilisé pour transmettre l’information génétique à la génération sexuelle suivante, et un noyau somatique (MAC) assurant l’expression des gènes. Les caractéristiques particulières des gènes de paramécies m’ont incité à développer une chaîne de procédures dédiée à leur annotation, utilisant des données ARN-seq.
      A chaque cycle sexuel, le MAC parental est perdu et un nouveau MAC est généré à partir d’un MIC impliquant des réarrangements programmés de génome et notamment de l’élimination d’ADN portant des ET et de petites séquences à copie unique appelées IES (Internal Eliminated Sequence). Nous avons développé le logiciel ParTIES, utilisant des données ADN-seq, pour identifier les -45 000 IES du génome de Pararamecium tetraurelia et montré que les IES sont des reliques d’ET. Une série de trois duplications globales de génome (WGD) anciennes mais encore visible, pendant l’histoire évolutive de la lignée, nous a permis de décrire la dynamique d’invasion et d’évolution des ET à l’origine des IES.

      Lieu : Visio - https://eu.bbcollab.com/guest/0157bdbadfc940e29445882ec6385ea2

      Article

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