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  • Génomes

    • Vendredi 14 juin 11:00-12:00 - Romain MERCIER - Institute of Microbiology of the Mediterranean, Marseille, France

      Molecular basis of Twitching motility regulation in Myxococcus xanthus

      Résumé : In living organisms, surface cell movements are essential for environmental exploration and multicellular development, and are also at the basis of cancer cell dissemination. In Bacteria, surface cell movements are mediated by a class of widespread nanomachines called Type-IV Pili (TFP). TFP-based motility (or twitching), is at the root of highly cooperative cell movements, which on pathogens allow host colonization and biofilm formation. Despite an extensive knowledge on TFPs molecular structure, the determinants and regulations that convert TFPs into highly efficient motility machines remain largely unknown. In the model organism Myxococcus xanthus, TFP-driven group movements promote predation on prey bacteria and the formation of multicellular fruiting bodies (biofilm). Here, we will present the discovery of a new cytoplasmic platform that regulates TFP activity. We will also discuss how this cytoplasmic platform might orchestrate Twitching motility in M. xanthus.

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

      Article

    • Vendredi 21 juin 11:00-12:00 - Lori A. PILE - Department of Biological Sciences, Wayne State University, Detroit, Michigan, USA

      Determination of gene regulatory and metabolic networks by an essential histone modifying complex

      Résumé : Regulation of the spatial and temporal patterns of gene expression is central to every aspect of organismal development, normal physiological function and is directly linked to numerous diseases. Histone modifying enzymes that add or remove histone marks regulate chromatin structure to promote or repress gene activity. Among the key complexes that regulate the epigenetic signatures on histones is the SIN3 histone modifying complex, which contains both a deacetylase and a demethylase enzyme. How these factors coordinately regulate expression of specific gene sets to control cell proliferation and developmental transitions is largely unknown. Through analysis of chromosomal localization patterns and gene expression profiles, we determined genome-wide functional regulatory activity of the two major isoforms of Drosophila SIN3. Because we found that both isoforms regulate genes encoding key metabolic enzymes, we next identified metabolites controlled by SIN3. These experiments have uncovered SIN3 controlled gene and metabolic networks linking epigenetic regulation by SIN3 to central carbon metabolism necessary for cellular energy production.

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

      Article

    • Vendredi 28 juin 10:00-11:00 - Yves GAUDIN - I2BC

      Negri bodies are viral factories with properties of liquid organelles

      Résumé : Replication and assembly of many viruses occur in viral factories which are specialized intracellular compartments formed during viral infection. For rabies virus, those viral factories are called Negri bodies (NBs). NBs are cytoplasmic inclusion bodies in which viral RNAs (mRNAs as well as genomic and antigenomic RNAs) are synthesized. NBs are spherical, they can fuse together and can reversibly deform when encountering a physical barrier. All these characteristics are similar to those of eukaryotic membrane-less liquid organelles which contribute to the compartmentalization of the cell interior. Indeed, the liquid nature of NBs has been confirmed by FRAP experiments. The co-expression of rabies virus nucleoprotein N and phosphoprotein P is sufficient to induce the formation of cytoplasmic inclusions recapitulating NBs properties. Remarkably, P and N have features similar to those of cellular proteins involved in liquid organelles formation : N is an RNA binding protein and P contains intrinsically disordered domains. An overview of the literature indicates that formation of liquid viral factories by phase separation is probably common among Mononegavirales. This allows specific recruitment and concentration of viral proteins. Finally, as virus-associated molecular patterns recognized by cellular sensors of RNA virus replication are probably essentially present in the viral factory, there should be a subtle interplay (which remains to be characterized) between those liquid structures and the cellular proteins which trigger the innate immune response.

      Lieu : Bibliothèque - bâtiment 34 - campus de Gif-sur-Yvette

      Article

  • Biologie Cellulaire

    • Vendredi 7 juin 11:30-12:30 - James CASTELLI-GAIR HOMBRIA - CABD, Sevilla, Espagne

      Comparison of the trachea and the endocrine gland development of Drosophila as a model to study divergent evolution of organogenesis

      Résumé : We have discovered that, despite being functionally and morphologically different, the tracheae and the endocrine organs controlling insect metamorphosis are homologous structures that develop from a serially repeated structure. In the cephalic segments, JAK/STAT signalling collaborating with anterior Hox genes induces the metameric structure to develop into the endocrine glands required for moulting and metamorphosis. In the trunk segments, JAK/STAT signalling collaborating with central and posterior Hox genes induces the formation of respiratory trachea.
      The development of trachea and endocrine organs initiates with the invagination of the polarized epithelial cells. The morphological divergence occurs shortly after invagination, when activation of Snail in the endocrine primordia induces an epithelial to mesenchymal transition (EMT). New genetic evidence suggests that the head endoskeletal elements are also derived from the same metamerically repeated structure.
      Our data are important because : (1) they uncover the genetic and developmental mechanisms for ring gland morphogenesis and (2) indicate that the head endoskeleton, the respiratory tracheal organs and two main endocrine glands arose through a process of divergent evolution from an ectodermal repeated structure that lead to extremely different morphological and functional organs.

      Lieu : Bibliothèque - bâtiment 34 - campus de Gif-sur-Yvette

      Article

    • Lundi 17 juin 11:00-12:00 - Hannetz ROSCHZTTARDTZ - Université de Santiago, Chili

      THE DIVERSE IRON DISTRIBUTION IN EUDICOTYLEDONEAE SEEDS : FROM ARABIDOPSIS TO QUINOA

      Résumé : Increased iron content in seeds is an important agronomic trait. This is due to the relevance of this element in seed production, embryo development, and seedling germination and growth, as well as in human nutrition. Seeds accumulate iron during embryo maturation stages of embryogenesis. Using Arabidopsis thaliana as model plant, it has been described that mature embryos accumulate iron within a specific cell layer, the endodermis. This distribution pattern was conserved in most of the analyzed members from Brassicales, with the exception of basal Vasconcellea pubescens that also showed elevated amounts of iron in cortex cells. To determine whether the V. pubescens iron distribution was indicative of a wider pattern in non-Brassicales Eudicotyledoneae, we studied iron distribution pattern in different embryos belonging to plant species from different Orders from Eudicotyledoneae and one basal from Magnoliidae. The results indicate that iron distribution in A. thaliana embryo is an extreme case of apomorphic character found in Brassicales, not-extensive to the rest of Eudicotyledoneae.
      Main publications :
      - Ibeas MA, Grant-Grant S, Coronas MF, Vargas-Perez JI, Navarro N, Abreu I, Castillo-Michel H, Avalos-Cembrano N, Paez Valencia J, Perez F, Gonzalez-Guerrero M, Roschzttardtz H (2018) The Diverse Iron Distribution in Eudicotyledoneae Seeds : From Arabidopsis to Quinoa. Front Plant Sci 9 : 1985
      - Tissot N, Robe K, Gao F, Grant-Grant S, Boucherez J, Bellegarde F, Maghiaoui A, Marcelin R, Izquierdo E, Benhamed M, Martin A, Vignols F, Roschzttardtz H, Gaymard F, Briat JF, Dubos C (2019) Transcriptional integration of the responses to iron availability in Arabidopsis by the bHLH factor ILR3. New Phytol. doi : 10.1111/nph.15753
      - Spitzer C, Li F, Buono R, Roschzttardtz H, Chung T, Zhang M, Osteryoung KW, Vierstra RD, Otegui MS (2015) The endosomal protein CHARGED MULTIVESICULAR BODY PROTEIN1 regulates the autophagic turnover of plastids in Arabidopsis. Plant Cell 27 : 391-402
      - Roschzttardtz H, Paez-Valencia J, Dittakavi T, Jali S, Reyes FC, Baisa G, Anne P, Gissot L, Palauqui JC, Masson PH, Bednarek SY, Otegui MS (2014) The VASCULATURE COMPLEXITY AND CONNECTIVITY gene encodes a plant-specific protein required for embryo provasculature development. Plant Physiol 166 : 889-902
      - Roschzttardtz H, Seguela-Arnaud M, Briat JF, Vert G, Curie C (2011) The FRD3 citrate effluxer promotes iron nutrition between symplastically disconnected tissues throughout Arabidopsis development. Plant Cell 23 : 2725-2737
      - Roschzttardtz H, Grillet L, Isaure MP, Conejero G, Ortega R, Curie C, Mari S (2011) Plant cell nucleolus as a hot spot for iron. J Biol Chem 286 : 27863-27866
      - Roschzttardtz H, Conejero G, Curie C, Mari S (2009) Identification of the endodermal vacuole as the iron storage compartment in the Arabidopsis embryo. Plant Physiol 151 : 1329-1338
      - Roschzttardtz H, Fuentes I, Vasquez M, Corvalan C, Leon G, Gomez I, Araya A, Holuigue L, Vicente-Carbajosa J, Jordana X (2009) A nuclear gene encoding the iron-sulfur subunit of mitochondrial complex II is regulated by B3 domain transcription factors during seed development in Arabidopsis. Plant Physiol 150 : 84-95

      Lieu : Bibliothèque - bâtiment 34 - campus de Gif-sur-Yvette

      Article

    • Vendredi 21 juin 11:30-12:30 - Aeid IGBARIA - COSS Laboratory, Université de Rennes

      ER resident proteins reflux, a functional ER surveillance mechanism during stress and disease

      Résumé : Diverse perturbations to endoplasmic reticulum (ER) functions compromise the proper folding and structural maturation of secretory proteins causing ER stress. Recently, we found that diverse ER stress regimes cause properly folded, ER-resident eroGFP (and other ER luminal proteins) to “reflux” back to the reducing environment of the cytosol as intact, folded proteins. By performing a comprehensive genetic screen in Saccharomyces cerevisiae, we found that ER protein reflux during ER stress requires specific chaperones and cochaperones residing in both the ER and the cytosol. Chaperone mediated ER protein reflux proceeds more vigorously when ER-associated degradation (ERAD) factors are crippled, suggesting that reflux may work in parallel with ERAD. Finally, we found that ER protein reflux is conserved in mammalian cells, regulated by the IRE1a kinase/endoribonuclease and may play preeminent role in human diseases. In summary, chaperone-mediated ER protein reflux may play as a conserved protein quality control process that evolved to maintain secretory pathway homeostasis during ER protein-folding stress.

      Lieu : Bibliothèque - bâtiment 34 - campus de Gif-sur-Yvette

      Article

  • Virologie

    • Mardi 18 juin 14:00-15:00 - Emiliano RICCI - Laboratoire de Biologie et Modélisation de la Cellule, ENS Lyon

      Global impact of translation on mRNA stability in T cells and macrophages and a potential role for UTRs in its modulation

      Résumé : Post-transcriptional control is crucial for regulating protein expression, both basally and in response to extracellular cues. Proper signal transduction requires tight control of both response induction and termination. While much work has gone into understanding how mRNAs are translationally upregulated to boost protein expression during signaling, much less is known about how such responses are terminated. One way protein expression might be attenuated following translational activation is by targeting mRNAs to translation-dependent degradation (TDD), thus making any increase in protein expression self-limiting. The extent to which TDD is a general mechanism for limiting protein expression is currently unknown.
      Here we describe a comprehensive analysis of basal and signal-dependent gene expression in primary mouse T cells and macrophages. In order to measure the impact of TDD in regulating gene expression, we performed RNA-Seq, PAS-Seq and ribosome profiling to monitor RNA levels, 3’UTR length, translational efficiency, and RNA degradation transcriptome-wide, both before and after activation of T cells and macrophages. Our data surprisingly indicate that most unstable mRNAs are decayed to some extent in a translation-dependent manner, both in resting and activated cells. Interestingly, the extent of TDD is inversely correlated to the length of the 5’UTR and 3’UTR but not to that of the coding sequence. Furthermore, ribosome density also appears to explain the extend of TDD but in a biphasic manner. These unexpected observations highlight the strong interconnection that exists between mRNA translation and untranslated regions in regulating mRNA decay.

      Lieu : Salle de réunion - bâtiment 14 - campus de Gif-sur-Yvette

      Article

  • Microbiologie

    • Mardi 18 juin 11:30-12:30 - Véronique Fontaine - Université Libre de Bruxelles

      Looking for mycobacterial GroEL1 functions

      Résumé : Tuberculosis is a disease with high morbidity and mortality rates in the world, caused by slow-growing mycobacteria, mainly Mycobacterium tuberculosis. The chaperone GroEL1, also known as Cpn60.1, was recently shown to play a key role in several mycobacterial functions, including persistency in the host, bacterial virulence, and even antimicrobial resistance. Although the molecular mechanisms of action of this protein are multiple, and still not totally elucidated, GroEL1 interaction with metallic ions and lipids is further puzzling the picture.

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

      Article

  • B3S

    • Jeudi 6 juin 11:00-12:00 - Sandra de Macedo Ribeiro - Instituto de Biologia Molecular e Celular – IBMC, Porto, Portugal

      Dissecting the ataxin-3 aggregation pathways

      Résumé : Machado-Joseph disease is a neurodegenerative disorder caused by expansion the polyQ tract of ataxin-3 (Atx3). This protein contains a globular Josephin domain (JD) and a C-terminal tail containing the polyQ segment. Aggregation of Atx3 is well characterized and is critically dependent on early self-assembly events modulated by the JD. Biophysical studies unveiled Atx3 multistep aggregation pathway, but structural and mechanistic details of the aggregation process are still lacking. To provide a time-resolved perspective on Atx3 aggregation pathway(s), Atx3 self-assembly was monitored by dynamic light scattering, Thioflavin-T fluorescence, size exclusion chromatography and Electron Microscopy. Those studies were combined with biophysical modeling and experimental determination of equilibrium dissociation constants to provide an unprecedented quantitative perspective of the Atx3 aggregation mechanisms. The talk will discuss how experimental and theoretical approaches permit the identification of deviations from the simple nucleation-polymerization mechanism and suggest the presence of Atx3 aggregation pathways parallel to amyloid fibrillation. This knowledge is critical to understand the mechanisms underlying the effect of different Atx3 binding molecules for on- and off- pathway aggregation steps.
      Contact : Julie Ménétrey

      Lieu : Bibliothèque - Bâtiment 34, campus de Gif-sur-Yvette

      Article

  • cytoskeleton club

    • Mardi 11 juin 11:30-12:30 -

      Cytoskeleton club - Internal seminar

      Lieu : Bibliothèque - bât. 34

      Article

Soutenance

  • Génomes

    • Lundi 3 juin 14:30-17:00 - Jean-Yves Thuret - Equipe Sénescence et Stabilité Génomique, I2BC

      Mécanismes de la sénescence induite par l’oncogène B-Raf-V600E, Nouvelles approches sénolytiques

      Lieu : Salle des séminaires, Bât. 144 - CEA Saclay

      Article

  • Biologie Cellulaire

    • Mardi 18 juin 14:00-17:00 - Amanda Martin Barranco - I2BC, équipe Approches Intégratives du Transport des Ions

      Role of the protein HIR2 and the Plasma membrane microdomains in the control of Fe acquisition, using Arabidopsis thaliana as a model plant

      Résumé : Iron is an essential nutrient for plant growth and development. In Arabidopsis thaliana, the transporter IRT1, which allows iron absorption through the epidermic cells of the root, is a major actor in iron nutrition. Despite of it, IRT1 also transports the non-iron metals zinc (Zn), manganese (Mn) and cobalt (Co). These metals are considered as the secondary substrates of IRT1, and therefore this transporter is considered as poorly specific. Our laboratory has recently uncover that these secondary substrates regulate IRT1 endocytosis. In order to uncover the different proteins that can be implicated in the traffic or in the regulation of IRT1 activity, we have proceeded to perform IRT1 immnopurifications, followed by mass spectrometry analyses. This approach has allowed us to produce a first interactome list of IRT1. Among the proteins that interact with IRT1, we have isolated AHA2 and FRO2, both well known in the process of iron acquisition in Arabidopsis, and also a SPFH domain containing protein known as HIR2. Although it is known that HIR2 is contained in membrane microdomains in Arabidopsis, its function is still to determine. Nevertheless, in the animal kingdom, SPFH domain containing proteins have been proposed as implicated in the formation of membrane microdomains. This is specially the case of the specific SPFH domain containing proteins known as Flotillins, which have the ability to mediate endocytosis in animals as in plants.
      After validation of the interaction between IRT1 and FRO2/AHA2/HIR2 by different complementary approaches, we have microscopically analyzed the intracellular dynamics of these proteins. Our results suggest the existence of a protein complex that reunites the three major actors of iron homeostasis in Arabidopsis : IRT1, FRO2 and AHA2. We suspect that the main function of this complex is to optimize the process of iron absorption in the root. In spite of what is known for IRT1 and despite being part of a same complex, FRO2 and AHA2 are not massively endocytosed in response to a non-iron metal excess (Zn, Mn, Co). Furthermore, we have shown that FRO2 and AHA2 are ubiquitinated, although their ubiquitination is also independent of the concentration of the non-iron metals, unlike the ubiquitination of IRT1. Finally, using reverse genetic approaches, we have been able to show that HIR2 is implicated in the maintenance of the iron homeostasis. Indeed, hir2 mutants are extremely sensitive to lack of Fe, even though they present posttranslational deregulations that result in the an overaccumulation of the protein IRT1. We are currently trying to determine how HIR2 regulates the dynamics and/or the stability of IRT1 inside the cell. HIR2 could be assuring the recruiting of IRT1,or the recruitment of the whole iron acquisition complex, into specific membrane microdomains. On the other hand, HIR2 could be implicated in a new pathway of internalization of IRT1, independent of clathrin.

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

      Article

    • Lundi 24 juin 14:00-17:00 - Christophe Lefebvre - I2BC - Equipe Autophagie et Développement

      Interaction entre réticulum endoplasmique et Autophagie chez le nématode Caenorhabditis elegans

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

      Article

  • B3S

    • Jeudi 6 juin 14:00-18:00 - Fernando Raio Vilela - Equipe Gigant/Ménétrey

      Caractérisation structurale du recrutement de JIP3 par la Kinésine-1

      Résumé : Le transport intracellulaire de cargos est un processus critique au sein des cellules eucaryotes, et notamment au niveau des neurones, pour contrôler différentes fonctions dont la maturation et la transmission synaptique. La kinésine-1 est un moteur moléculaire capable de transporter différents types de cargos, comme des organelles, des vésicules ou des assemblages macromoléculaires le long des microtubules. La kinésine-1 est un hétérotétramère constitué d’un homodimère de chaînes lourdes (KHC) associé à deux chaînes légères (KLC) ; les deux chaînes, KHC et KLC étant capables de recruter des cargos. L’un des premiers cargos de la kinésine-1 à avoir été identifié sont les protéines JIP3/4 (JNK-Interacting Protein 3/4) ; elles jouent aussi un rôle de protéines adaptatrices pour le transport d’autres cargos de la kinésine-1. La kinésine-1 recrute les protéines JIP3/4 de deux façons distinctes et indépendantes (i) via KHC et (ii) via KLC. Le recrutement de JIP3/4 par KHC et KLC est capable, via des mécanismes moléculaires distincts, d’activer la motilité de la kinésine-1 et donc de contrôler le transport intracellulaire dans lequel elle est impliquée et les fonctions associées au sein des neurones.
      Au cours de mon travail de thèse, j’ai contribué à caractériser par des approches bio-informatiques, biochimiques/biophysiques et structurales, les deux modes de recrutement des protéines JIP3/4 par la kinésine-1 : (i) via KHC et (ii) via KLC. Ce travail a permis d’apporter des nouveaux éléments pour comprendre le mode de recrutement de ces protéines cargos/adaptatrices par la kinésine-1, mais aussi de mieux comprendre les mécanismes moléculaires de son activation par les protéines JIP3/4. Nous avons également étudié l’interaction de JIP3 avec un moteur moléculaire de l’actine, la MyosineVa, en raison de l’homologie de structure élevée entre un domaine de JIP3 et un domaine de RILPL2, cargo de la MyosineVa.
       
      Mots clés : Kinésine-1 ; JIP3 ; transport intracellulaire ; MyosineVa ; Biologie Structurale Intégrative
       
      Contact : Julie Ménétrey, Paola Llinas

      Lieu : Bibliothèque - Bâtiment 34, campus de Gif-sur-Yvette

      Article

    • Mardi 18 juin 10:00-12:00 - Agathe Urvoas - I2BC - Equipe Modélisation et Ingénierie des Protéines

      Ingénierie par évolution dirigée d’une famille de protéines artificielles à motifs structuraux répétés : les alphaReps - conception, caractérisation et applications

      Résumé : L’ingénierie d’ossatures protéiques par des approches d’évolution dirigée permet d’obtenir de nouvelles structures protéiques fixant spécifiquement des molécules cibles choisies. Une famille de protéines artificielles à motifs structuraux répétés, nommées αRep a été développée. Les αReps sont des protéines particulièrement stables et faciles à produire sous forme recombinante en comparaison avec les protéines dérivées d’anticorps classiquement utilisées. A partir d’une banque comportant plus d’un milliard de variants, il est possible de sélectionner des αReps fixant spécifiquement, à haute affinité (KD de l’ordre du nM au μM) des cibles protéiques d’intérêt. Les applications de ces protéines artificielles ont été explorées : en biochimie structurale pour aider à la cristallogenèse, en biologie cellulaire pour le développement de traceurs intracellulaires ou pour le développement de biosenseurs génériques, en chimie avec la conception de métalloenzymes artificielles par couplage de complexes organométalliques mais également en physique pour la reconnaissance de surfaces non biologiques et la morphosynthèse de nanoparticules.
      La modularité des αReps assimilables à des briques de Lego® moléculaire ouvre la voie à des constructions combinatoires pouvant conduire par exemple à l’ingénierie de voies métaboliques artificielles, à des assemblages protéiques fonctionnalisés ou encore à des outils d’interaction allostériques.

      Lieu : Salle Edgar Lederer - Bât. 430, Campus d’Orsay

      Article

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