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Séminaire

  • Génomes

    • Vendredi 15 janvier 10:00-11:00 - Hidetoshi Saze - Okinawa Institute of Science and Technology, Plant Epigenetics Unit

      Epigenetic regulation of intragenic transposons and gene transcription in plant genomes

      Résumé : Genomes of higher eukaryotes contain a large number of transposable elements (TEs), that are often silenced by epigenetic mechanisms, such as histone modifications and DNA methylation. Although TE silencing adversely affects expression of nearby genes, recent studies revealed the presence of intragenic TEs marked by repressive epigenetic marks within transcriptionally permissive chromatin environments. However, molecular mechanism underlying the regulation of intragenic TEs and their potential impacts on gene expression are still poorly understood. We analyzed genome-wide distribution and epigenetic regulation of intragenic TEs in the genomes of Arabidopsis and rice, and revealed that the repressive chromatin state of intragenic TEs is critical for proper transcription and splicing of associated genes. Our study provides new insights into how intragenic TEs affect the transcriptional landscape of the plant genomes, and suggests the importance of epigenetic mechanisms for regulation of TEs within transcriptional gene units.


      Contact : Yoshiharu.YAMAICHI

      Lieu : Visio

      Article

    • Vendredi 22 janvier 10:00-11:00 - Masayuki Su'etsugu - Rikkyo University

      In vitro amplification of mega-sized circular DNA and its applications

      Résumé : We have reconstituted an entire replication cycle of the Escherichia coli circular chromosome with 26 proteins that catalyze initiation, fork progression, Okazaki-fragment maturation, and decatenation. Because decatenation provides supercoiled monomers that are competent for the next round of replication initiation, the cycle repeats autonomously and continuously. This Replication-Cycle Reaction (RCR) can propagate large circular DNA up to 1 Mbp. We further developed a multiple-DNA fragment assembly reaction, termed RA (Recombination Assembly). Using a two-step enzymatic reaction, RA-RCR, we have successfully constructed a 27 kb plasmid from 50 fragments. RA-RCR thus provides a powerful cell-free tool to generate large circular DNA without relying on conventional cell-based cloning.


      Contact : Yoshiharu.YAMAICHI

      Lieu : Visio

      Article

    • Vendredi 29 janvier 11:00-12:00 - Anjana Badrinarayanan - National Centre for Biological Sciences (TIFR), Bangalore, India

      Searching for homology : in vivo mechanism of bacterial homologous recombination

      Résumé : Structural Maintenance of Chromosome (SMC) proteins play central roles in chromosome dynamics across domains of life. While their function in chromosome organization and segregation in bacteria is well-characterized, their contribution to pathways of genome integrity maintenance is less understood. Here, I will present recent work from my group showing evidence for requirement of the highly conserved SMC protein, RecN, in mediating homology search and repair in vivo during double-strand break (DSB) repair. Using quantitative live cell imaging, we follow temporal and spatial dynamics of the recombinase, RecA, after induction of a single DSB on the chromosome of Caulobacter crescentus. We find that the RecA-nucleoprotein filament is mobile and moves in a directional manner across the length of the cell, undergoing several such cycles until homology search is complete. These dynamics are independent of the presence of a repair template. Instead, such large-scale translocations of the filament as well as remodeling of its architecture is driven by RecN. We show that filament dynamics is lost in the absence of RecN. Rates of RecA loading or integrity of the RecA-nucleoprotein filament are unaffected in the absence of RecN. Together, our data suggest that RecN arrives after RecA has loaded at the break, following which it triggers RecA filament mobility via its ATPase cycle. Our findings are consistent with a model where symmetry breaking by RecN likely acts as the driver for directional RecA filament translocation. Such symmetry breaking highlights a conserved feature of SMC proteins across domains of life, irrespective of their specific functions in modulating chromosome dynamics.
      Contact : Yoshiharu.YAMAICHI i2bc.paris-saclay.fr

      Lieu : Visio

      Article

  • Microbiologie

    • Mardi 12 janvier 11:00-12:00 - Emilie Lesur - Equipe Synthèse de Molécules et de Macromolécules Bioactives, ICMMO

      Sondes à base de tréhalose et d’acides mycoliques pour l’étude de la biogénèse de la membrane des Corynebacteriales

      Lieu : Visio - Lien Visio disponible sur l’intranet ou sur demande (communication i2bc.paris-saclay.fr)

      Article

    • Mardi 26 janvier 11:30-12:30 - Marie-Joelle Virolle - Equipe Métabolisme Energétique des Streptomyces

      Impact of phosphate concentration on membranous phospholipid composition of two Streptomyces model strains, Streptomyces lividans and Streptomyces coelicolor

      Lieu : Lien Visio disponible sur l’intranet ou sur demande (communication@i2bc.paris-saclay.fr)

      Article

  • cytoskeleton club

    • Mardi 12 janvier 11:30-13:00 - Olivia du Roure - PMMH, Paris

      Cytoskeleton club - Pinching the cortex of live cells reveals myosin II dependent thickness instabilities

      Résumé : The cell cortex is a contractile actin meshwork, which determines cell shape and is essential for cell mechanics, migration and division. Because the cortical thickness is below optical resolution, it has been generally considered as a thin uniform elastic and contractile layer. Using two mutually attracted magnetic beads, one inside the cell and the other in the extracellular medium, we pinch the cortex of dendritic cells and provide an accurate and time resolved measure of its thickness. Moreover this allows for a direct characterization of the cell cortex mechanics. Our observations draw a new picture of the cell cortex as a highly dynamic layer, harboring large fluctuations in its third dimension due to actomyosin contractility. We propose that the cortex dynamics might be responsible for the fast shape changing capacity of highly contractile cells that use amoeboid-like migration.
      Link to attend the webinar : https://us02web.zoom.us/j/84972283883

      Lieu : Webinar

      Article

Soutenance

  • Virologie

    • Lundi 11 janvier 14:00-18:00 - Clémence Taisne - Equipe Autophagie et immunité antivirale

      Détournement de la machinerie autophagique par le cytomégalovirus humain : conséquences sur sa multiplication

      Résumé : Le cytomégalovirus humain (HCMV)appartient à la famille des Herpesviridae. Ce virus est responsable d’infections congénitales et d’infections graves chez les personnes immunodéprimées. Nous avons précédemment montré l’interaction entre le HCMV et l’autophagie, un processus cellulaire de dégradation et de recyclage. Ce processus est constitutif et permet le maintien de l’homéostasie cellulaire. L’autophagie est induite en cas de stress et peut être utilisée par la cellule pour se défendre des infections virales ou bactériennes. Nous avons montré que le HCMV induit la formation de structures autophagiques mais que le virus bloque l’étape finale du processus pour empêcher sa propre dégradation. Afin de caractériser le rôle de l’autophagie sur la multiplication virale, nous avons utilisé une approche génétique qui a montré que l’autophagie était bénéfique pour la multiplication du HCMV.
      Nous avons donc établi des lignées cellulaires stables, déficientes ou invalidées pour des protéines autophagiques (ULK1, BECN1, ATG5,
      LC3B et ATG4B). Grâce à ces outils, nous avons ensuite étudié comment l’autophagie module les différentes étapes du cycle du HCMV, à savoir : l’entrée, la synthèse protéique, la réplication du génome, l’assemblage et la sortie des virus. Nos résultats montrent que les protéines de l’autophagie sont présentes et agissent au niveau du compartiment d’assemblage viral dans le cytoplasme. Plusieurs de ces protéines sont conservées au sein des particules virales extracellulaires, notamment LC3 et ATG5. L’ensemble de nos résultats démontrent que le HCMV détourne les membranes autophagiques pour acquérir son enveloppe ce qui semble favoriser son infectivité et sa propagation.

      Lieu : A définir en fonction de la situation sanitaire

      Article

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