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  • Génomes

    • Vendredi 1er février 11:00-12:00 - Eugene Gladyshev - Institut Pasteur

      Recombination-independent recognition of DNA homology for meiotic silencing in Neurospora crassa

      Résumé : Homologous chromosome pairing represents a critical aspect of meiosis in nearly all sexually reproducing organisms. While in some species this process depends on the formation of double-strand DNA breaks, in the others it can proceed (partially or completely) in the apparent absence of DNA breakage and recombination. The nature of a mechanism that can identify intact homologous chromosomes represents a fundamental question in molecular biology. Using “meiotic silencing by unpaired DNA” (MSUD) in Neurospora crassa as a model system, we demonstrate the existence of a cardinally new solution to the problem of DNA homology recognition during meiosis. Here we take advantage of the unique ability of MSUD to detect and silence (by RNA interference) any relatively short fragment of genomic DNA present on only one of the two homologous chromosomes. Specifically, we show that MSUD does not require the function of eukaryotic RecA proteins (Rad51/Dmc1) and the type II topoisomerase-like protein Spo11. We further show that MSUD can recognize patterns of weak interspersed homology in which triplet units of sequence identity are arrayed with a periodicity of 11 base-pairs. In doing so, MSUD shares its basis for homology recognition with “repeat-induced point mutation” (RIP), a prototypical genome-defense phenomenon that is activated in premeiotic nuclei of N. crassa and many other filamentous fungi. Taken together, these results reveal the role of a recombination-independent homology-directed process in guiding the expression of small interfering RNAs and, more broadly, suggest that meiotic chromosomes can be evaluated for homology at the base-pair resolution by a mechanism that operates on intact DNA double helices.
      Contact : Fabienne Malagnac <fabienne.malagnac>

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


    • Vendredi 15 février 11:30-12:30 - Martial Marbouty - Institut Pasteur

      Contact genomic : a new tool to study microbial communities and unveil mobile elements - bacteria relationships in mammalian gut microbiota

      Résumé : Metagenome sequence analysis relies principally on compositional approaches, which hypothesise that sequences sharing similar characteristics (GC%, codon bias, coverage-covariation... etc.) should share the same cellular compartment. Although these approaches have generated important results, they remain somehow limited and do not allow the full characterization and understanding of the genetic composition of a complex microbial population. Contact genomics, which aimed at exploiting the 3D physical signature of genomes to solve their sequence, has the potential to alleviate or improve some of these caveats. To explore the genomic content of bacterial populations at a new level of resolution, we have recently developed meta3C (Marbouty et al. 2014), a derivative protocol of the chromosome conformation capture (3C ; Dekker et al. 2002) assay that aims at deciphering the average 3D organization of a genome. Using controlled mixes of bacterial or yeast species, we showed that the frequent collisions experienced by DNA molecules sharing similar cellular compartments can be measured through meta3C and conveniently used to assemble larger scaffolds of the genomes present in a metapopulation.
      Here I will present data obtained from different samples of mammalian gut microbiota (Marbouty et al. 2017). Meta3C allows unveiling hundreds of genomic compartments, hence species. Moreover, Meta3C allows to link mobile genetic element sequences to their bacterial host and provide a convenient way to study interactions between genomic entities in a complex population. I will discuss the different ways to explore this network and the results in light of the promising potential of the approach for future applications.
      Contact : Mireille Bétermier <mireille.betermier>

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

      Notes de dernières minutes : CHANGE OF TIME : now it starts at 11h30 (instead of 11h00)


    • Vendredi 22 février 11:00-12:00 - Frédéric Checler - Institut de Pharmacologie Moléculaire et Cellulaire, Sophia-Antipolis

      Presenilins-PINK1 functional interplay governs mitophagic response

      Résumé : The amyloid cascade hypothesis postulates that the overload of canonical Aß could be a key event in Alzheimer’s disease (AD) setting and progression. One of the histological stigmata consistently reported in AD brain consists in the alteration of mitochondrial physiology and dynamics. Such feature also stands in other neurodegenerative pathologies including Parkinson’s disease. However, little was known concerning the molecular mechanisms underlying these dysfunctions. We have recently delineated a functional interplay linking presenilins also referred to as -secretase, the enzyme responsible for the production of amyloid peptides that accumuate in AD-affected brains, and Pink-1, one of the proteins responsible for a subset of autosomal recessive cases of Parkinson’s disease (FPD). We show that this molecular dialogue drives mitophagic response. Further, we establish that parkin (another FPD-linked protein) acts upstream of Pink-1 to control its function in a PS-dependent manner. Overall, our studies established a novel function of PS that explains, at least in part, the mechanistic defects underlying mitochondrial dysfunctions observed in AD and confirmed our hypothesis of a molecular dialogue and functional interplay between proteins involved in distinct neurodegenerative pathologies.
      1- GOIRAN T., et al. (2018) Biological Psychiatry, 83, 416-427

      Lieu : Auditorium I2BC - Bâtiment 21, Campus de Gif-sur-Yvette


  • B3S

    • Mardi 19 février 11:00-12:30 - Ricardo Cesar Guerrero Ferreira - ETH Zürich, Dept. Biosysteme Basel, Mattenstrasse 26, 4058 Basel (Switzerland)

      The structure of alpha-synuclein fibrils by cryo-electron microscopy

      Résumé : Synucleinopathies are progressive disorders characterized by the presence of intracellular inclusions such as Lewy bodies and Lewy neurites which contain alpha-synuclein fibrils. Using cryo-electron microscopy techniques we determined the structure of these fibrils at high resolution. The fibril core, the non-amyloid component region, and the residues responsible for the interaction of the two component protofilaments are well resolved in the EM maps and the corresponding atomic models. We propose a mechanism of fibril elongation, growth and stability. Our results also provide valuable insights to support the rational design of molecules for diagnosis and treatment of synucleinopathies.

      Lieu : Auditorium I2BC - Bât. 21, Campus de Gif-sur-Yvette


  • cytoskeleton club

    • Mardi 12 février 11:30-13:00 - Carsten Janke - Institut Curie, UMR CNRS 3348, Orsay

      Cytoskeleton club - Controlling microtubule functions with the tubulin code

      Résumé : The tubulin code is a signalling mechanism that, by modulating the properties of single tubulin units of microtubules, controls and fine-tunes microtubule functions in cells. The code is generated by the expression of alternative tubulin genes, called ‘isotypes’, and by the generation of a range of complex posttranslational modifications. Polyglutamylation, polyglycylation and detyrosination are modifications localized at the outer surface of microtubules, and are therefore likely to regulate the interactions with microtubule-associated proteins. Enzymes that catalyse those modifications are members of an evolutionary conserved family of tubulin tyrosine ligase like proteins (TTLL), whereas reverse enzymes (until present only deglutamylases have been identified) are members of the cytosolic carboxy peptidase family (CCP). Our current work on mouse models for glutamylation and glycylation has revealed an important role of polyglutamylation in neurodegeneration, which is most likely mediated by alterations of neuronal transport. Glycylation plays a key role in stabilizing cilia and flagella, and is also important for primary cilia. Moreover, both polyglutamylation and polyglycylation play a key role in male fertility. Strikingly, the often subtle cellular phenotypes generated by altered tubulin modifications translate into serious defects on the organism level, such as neurodegeneration or male infertility, which underpins the emerging importance of the tubulin code in human pathologies.
      Contact : Julie Ménétrey

      Lieu : Bibliothèque - bât. 34


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