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  • Génomes

    • Vendredi 21 avril 2017 11:00-12:00 - Dr Kazufumi MOCHIZUKI - Institute of Human Genetics (IGH) CNRS-University of Montpellier UMR9002 Montpellier

      Small RNA-mediated trans-generational genome comparison and trans-recognition network in Tetrahymena DNA elimination

      Résumé : Small RNAs are used to silence transposable elements (TEs) in many eukaryotes, which use surprisingly diverse evolutionary solutions to identify TEs. We have previously reported that in the ciliated protozoan Tetrahymena thermophile, small RNA-mediated comparison of the germline and somatic genomes underlies identification of TE-related sequences, which are then eliminated from the soma. In addition, we recently found an additional layer of small RNA-mediated identification of TE-related sequences in Tetrahymena. We found that a limited set of Internal Eliminated Sequences (IESs) containing potentially active TEs produces a class of small RNAs that recognize not only the IESs from which they are derived but also other IESs in trans. This trans-recognition triggers the expression of yet another novel class of small RNAs that identify other IESs. Therefore, TE-related sequences in Tetrahymena are robustly targeted for elimination by a genome-wide trans-recognition network accompanied by a chain reaction of small RNA production. In this presentation, I will discuss our latest picture of small RNA-directed DNA elimination with two “trans” mechanisms : small RNA-mediated trans-generational genome comparison and trans-recognition network.

      Lieu : Auditorium - Bâtiment 21, campus de gif


  • B3S

    • Mercredi 26 avril 2017 11:00-12:00 - Eric Durand - LISM, Marseille

      Multi-scale & integrated architecture of the type VI secretion system (T6SS) In Gram-negative species

      Résumé : Eric utilises an integrated structural biology approach for the multi-scale studies of the structure, assembly and function of the Type VI Secretion System from enteroaggregative E. coli, which is an important determinant in the pathogen’s competitiveness, adaptation, and virulence. Over the last years, he has made a remarkable progress and important contributions to the literature on the subject and will present us the latest advances from his group and the field. The talk will be of great interest to structural biologists specialising in diverse methods (X-tallography, cryo-EM, SAXS and structural MS), microbiologists and cell biologists interested in host-pathogen interactions.

      The type VI secretion system (T6SS) is a multi-protein secretory machine shown to be implicated in inter-bacterial competition through the delivery of antibacterial toxins with peptidoglycan, lipid or DNA hydrolysis activities directly into the target cell [1]. This machine is composed of 13 different subunits, categorized in three different complexes (i-iii). A cytoplasmic tubular structure that is related to bacteriophage contractile tails (TTC, i)) is built on an assembly platform (baseplate or BPC, ii)) and is anchored to the cell envelope by a membrane complex (MC, iii).
      The tail is composed of a puncturing device wrapped by a contractile sheath. In our laboratory, we have demonstrated that the model bacterium and important pathogen Enteroaggregative E. coli (EAEC) utilizes the T6SS machinery to kill other gram-negative bacteria [2]. This mechanism involves cell-to-cell and prolonged contacts between predator and prey bacterial cells. Prey lysis occurs rapidly, in a few tens of seconds after the contraction of the T6SS tail sheath.
      We recently succeeded to purify the membrane complex (MC), a 1.7 MDa structure that is composed of 10 copies of three proteins : TssJ, -L, and –M. Using negative stain electron microscopy, we collected tens of thousands of images of the complex in different orientation and reconstructed the membrane complex with a resolution of 11.6 A [3]. We were then able to connect this MC to the rest of the machinery by isolating a complex between TssJLM and the first protein to interact with the MC, namely TssA [4]. This study shed light on the function of TssA and demonstrated for the first time a direct association between the cytoplasmic protein TssA and the membrane embedded TssJLM MC complex.
      Our research project is dedicated to understand the structure, assembly and functioning of the T6SS in EAEC, as a model organism. The project is based on multiscale and integrated studies of this macromolecular nanomachine, integrating several approaches :
      - Cellular scale : fluorescence microscopy, sub-cellular localisation of protein complexes (100-1000 Å), cryo-electron tomography (ECT : 20-60 Å)
      - From mid to near-atomic resolution : (Cryo)-electron microscopy and SAXS (3.5-25 Å).
      - Atomic resolution : X-ray crystallography (< 3.5 Å).
      - “Amino acid” resolution : CX-MS and site-directed mutagenesis.
      The presentation will focus on our latest studies that all aim at understanding and deciphering cellular-scale behaviours – namely bacterial competition, pathogenesis/virulence, toxins secretion – at the molecular scale.

      [1] Durand E, Cambillau C, Cascales E, Journet L. 2014. VgrG, Tae, Tle, and beyond : the versatile arsenal of Type VI secretion effectors. Trends Microbiol. Sep ;22(9):498-507
      [2] Brunet YR, Espinosa L, Harchouni S, Mignot T, Cascales E. 2013. Imaging type VI secretion-mediated bacterial killing. Cell Rep. 3:36-41
      [3] Durand E, Nguyen VS, Zoued A, Logger L, Péhau-Arnaudet G, Aschtgen M-S, Spinelli S, Desmyter A, Bardiaux B, Dujeancourt A, Roussel A, Cambillau C, Cascales E and Fronzes R. 2015. Biogenesis and structure of a bacterial Type VI secretion membrane core complex. Nature. Jul 30 ;523(7562):555-60.
      [4] Zoued A*, Durand E*,*, Brunet YR, Spinelli S, Douzi B, Guzzo M, Flaugnatti N, Legrand P, Journet L, Fronzes R, Mignot T, Cambillau C, Cascales E. Priming and polymerization of a bacterial contractile tail structure. Nature. 2016 Mar 3 ;531(7592):59-63.

      Lieu : Bibliothèque - Bâtiment 13, campus de gif


Journée de département

  • Microbiologie

    • Vendredi 28 avril 2017 09:00-18:00 -

      Journée microbiologie

      Résumé : Cette année, la thématique de la journée portera sur : Interactions des micro-organismes avec l’environnement/hôte.
      Pour les personnes extérieur à l’I2BC, l’inscription est gratuite mais obligatoire avant le 18 avril 2017 sur le lien :

      Lieu : Auditorium - Bâtiment 21, campus de gif


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