Résumé : The asymmetric cell division cycle of the non-pathogenic Gram-negative bacterium Caulobacter crescentus provides a simple and genetically tractable system to dissect transcriptional regulatory cascades controlling cell cycle events. Additionally, as Caulobacter cells remodel their cell poles at defined times during the cell cycle, the implementation of cell polarity and its functional consequences can be conveniently studied. We have identified polarity factors in Caulobacter and are exploring how these factors act coordinately to control polar morphogenesis, and we are now exploring if they function similarly in related obligate intracellular pathogens.
Invitée par Yoshiharu YAMAICHI, Equipe Intégrité du génome et de la polarité cellulaire chez la bactérie
Lieu : Salle de séminaires - Bâtiment 26, campus de Gif
Résumé : Signaling nucleotides are key molecules in all domains of life and control fundamental processes including central metabolic or stress response processes as well as biofilm formation. c-di-AMP is one of the more recently discovered signaling molecules and is produced by a number of bacteria including pathogens such as Staphylococcus aureus. In S. aureus, c-di-AMP is important for bacterial growth, antibiotic resistance, osmotic and pH stress tolerance. The signaling nucleotide is synthesized from two molecules of ATP by the diadenylate cyclase DacA and degraded to pApA by the phosphodiesterase GdpP. Here, recent work on the identification and characterization of additional factors regulating cellular c-di-AMP levels will be discussed. In addition, data from genome-wide interaction screens leading to the identification of c-di-AMP specific receptor proteins will be presented.
Contact : lionello.bossi
Lieu : Bibliothèque - Bâtiment 34, campus de Gif
Résumé : Invité par Bénédicte Michel, équipe Stabilité de l’ADN bactérien
Lieu : Auditorium - Bâtiment 21, campus de gif
Résumé : Phages are the most abundant biological entities on Earth. They modulate bacterial populations either by lysing their hosts or by conferring selective advantages by contributing phage-encoded fitness factors. Consequently, phages play a critical role in host survival and pathogenicity, and in nutrient redistribution. The analysis of phage genomes in any environment provides insights into the physiological impact of viruses on the microbial community and human health. However, in most environments the function of over 70%, and sometimes greater than 95%, of phage-encoded genes cannot be predicted based on similarity to genes with known function currently in databases. This may be due either to extreme divergence from a common ancestor or to the presence of previously unidentified functions, structures, and/or protein folds. Accurate identification of viral-encoded functions would greatly improve annotation and understanding the contribution of phages in any environment.
We have developed machine learning tools that predict gene function independently of amino acid sequence alignments. The resulting predictions are being validated using structural methods (X-ray crystallography and EM), which have unveiled new protein folds. We are combining these approaches with phenotypic responses, biochemistry, and metabolomics to probe the functions of non-structural proteins encoded by phages, and uncovering new contributions to bacterial lifestyles, with implications for microbial communities and human health.
Lieu : Auditorium - Bâtiment 21, Campus de gif
Résumé : During the past decade, many studies shed light on cilia as sensory and motile organelles which play major roles in vertebrate development and homeostasis. The building and maintenance of all cilia is dependent upon a complex transport system referred to as the intraflagellar transport (IFT). This IFT system is composed of several adaptor complexes that are fundamental during ciliogenesis. The high number of IFT proteins in these complexes (almost 20 in the IFT complex B) indicates that the IFT proteins have different functions. Although work on several ciliated model systems have been able to help our understanding of IFT proteins functions, notably through temperature sensitive mutants, studies in mammalian systems remain challenging. Indeed, in mammals, the absence of most of the IFT subunits leads to absence of cilia formation, thus preventing us from gaining much insight in their ciliary role. Hence, it is fundamental to try to develop systems in which we can uncouple intraflagellar transport and primary cilia formation. To do that, we first reasoned that some proteins of the IFT complex might be absent in some ciliated organisms, revealing proteins that could be dispensable during cilia formation. This led to the discovery of the unique function of two IFT-B proteins, IFT25 and IFT27, which mouse mutants die at birth with hedgehog-like phenotypes but are able to form primary and motile cilia. Building on these results, we designed a cellular system using rapamycin-induced dimerization in order to sequester IFT proteins from their ciliary pool into other cell compartments and show that this might be a powerful tool to study IFT proteins.
Lieu : Auditorium - bâtiment 21 - Campus de Gif
Résumé : The last decade witnessed the discovery of four families of giant viruses infecting Acanthamoeba. They have genome encoding from 500 to 2000 genes, a large fraction of which encoding proteins of unknown origin. These unique proteins meant to recognize and manipulate the same building blocks as cells raise the question on their origin as well as the role viruses played in the cellular word evolution. The Mimiviridae and the Pandoraviridae are increasingly populated by members from very diverse habitats and are ubiquitous on the planet. The two other families were first isolated from a 30,000 years old permafrost sample and were named Pithovirus and Mollivirus sibericum. While we know that at least one modern relative of Pithovirus was spotted decade ago in Acanthamoeba cells, to date there is only one representative of the Molliviridae family. The study of their replicative cycle in their common host revealed a common strategy to infect Acanthamoeba, beginning with the spectacular opening of the virions followed by a fusion with the membrane of the host vacuole. Then the various giant virus families exhibit either cytoplasmic or nucleocytoplasmic replication cycles with a gradation in their dependency to the host nucleus. I will describe their respective cycles as observed by electron microscopy in the light of the viral and host protein expression dynamic. Giant viruses thus present very diverse physiologies, not correlated with virion’s morphologies and genome complexities.
Lieu : Auditorium - Bâtiment 21, campus de Gif
Résumé : Identifying the function of every gene in all sequenced organisms is the major challenge of the post-genomic era and an obligate step for any systems biology approach. This objective is far from reached. By various estimates, at least 30-50% of the genes of any given organism are of unknown function, incorrectly annotated, or have only a generic annotation such as “ATPase”. Moreover, with 8000 genomes sequenced and 80,000 in the pipeline (http://www.genomeson.line.org), the numbers of unknown genes are increasing, and annotation errors are proliferating rapidly. For some gene families, 40% of the annotations are wrong. On the other side of the coin, there are still 1,900 known enzyme activities for which no corresponding gene has been identified and these numbers are also increasing. This biochemical knowledge is yet to be captured in genome annotations.
Using mainly a comparative genomic approach, we have linked gene and function for around 50 families related mainly to the fields of coenzyme metabolism, tRNA modification, protein modification and more recently metabolite repair. This approach integrates several types of data and uses filters, sieves, and associations to make predictions that can then be tested experimentally. An unknown gene’s function may thus be predicted from those of its associates : the ‘guilt by association’ principle. Associations that can be derived from whole genome datasets include : gene clustering, gene fusion events, phylogenetic occurrence profiles or signatures and shared regulatory sites. Post-genomic experimental sources such as protein interaction networks, gene expression profiles and phenomics data can also be used to find associations. In practice it is often ‘guilt by multiple association’ as genes can be associated in several ways, and analyzing more than one of these improves the accuracy of predictions.
We have applied these methods to decipher the synthesis and salvage pathways for two azapurine modifications of tRNA, Queuosine (Q) and Archaeosine (G+), made from the same precursor molecule PreQ0. This has led to the discovery of many unforeseen roles for PreQ0 derivatives that will be discussed. These include : 1) the fact that the queuine base is a forgotten vitamin in Eukaryotes that has to be salvaged from the diet or microflora ; 2) the discovery of links between Q and metal homeostasis in different kingdoms of life ; 3) to the identification of 7-deazapurine in bacterial and phage DNA as well as novel secondary metabolite clusters by miming genomes for novel preQ0 synthesis gene clusters.
Invité par l’équipe Microbiologie Moléculaire des Actinomycètes
Lieu : Salle de séminaires - Bâtiment 400, Campus de gif
Résumé : Les interférons de type I jouent un rôle central dans la mise en place d’une réponse immunitaire efficace contre les infections virales et les cellules tumorales. Pour identifier des composés modulateurs de la réponse interféron à visées thérapeutiques ou diagnostiques, nous avons développé différents systèmes de criblages à haut débit basés notamment sur le gène rapporteur luciférase. En criblant différentes banques de composés, dont la Chimiothèque Nationale, à l’aide de ces tests, nous avons pu isoler des molécules originales qui amplifient la réponse cellulaire à l’ADN cytosolique ou aux ARN viraux, en particulier des inhibiteurs de la voie de biosynthèse des pyrimidines. Si ces résultats ont permis d’établir une preuve de concept, nos travaux actuels visent au développement de tests plus physiologiques sur cellules primaires dans le but de faciliter à l’avenir le passage de l’in vitro à l’in vivo.
Lieu : Salle de séminaires - Bâtiment 14C, Campus de Gif
Résumé : MyosinV is an unconventional actin-based molecular motor that acts as a transporter or a tether for a variety of membrane cargoes. In the resting state MyosinV adopts an autoinhibited conformation, forming a cytosolic pool of inactive motors. Several Rab GTPases and their effectors directly bind and cooperate with MyosinV to regulate membrane trafficking. Structural studies of MyosinV motor and its complexes with interacting partners provide insights into the mechanism of the motor’s membrane recruitment and how that is coupled with myosin activation. Discovery and characterization of the direct interaction between the actin assembly regulator Spir and MyosinV, and Spir/MyosinV/Rab11 complex provide evidence for a synergic recruitment to promote both actin track generation and myosin motor activity in vesicle transport processes.
Invitée par Julie MENETREY, Equipe Biochimie Structurale des Microtubules, des Kinésines et de leurs Cargos. Vous pouvez contacter Julie pour rencontrer Olena Pylypenko
Lieu : Bibliothèque - Bâtiment 34, campus de Gif
Résumé : PS : Merci de prévenir Marie-Hélène Le Du quelques jours en avance si vous avez besoin d’un avis de rendez-vous pour entrer sur le site.
Lieu : Salle de réunion - Bâtiment 144, Campus de Saclay