1,721,008 research outputs found
Manipulation des nucléotides par la bactérie intracellulaire obligatoire Chlamydia trachomatis
No full textChlamydia trachomatis est une bactérie intracellulaire obligatoire qui infecte les cellules épithéliales humaines du tractus uro-génital. Ce pathogène est connu comme étant l'infection sexuellement transmissible la plus courante. Certaines souches peuvent aussi infecter la conjonctive oculaire, qui peut évoluer en trachome, constituant la principale cause de cécité d'origine bactérienne. Le développement intracellulaire de la bactérie dans un compartiment membranaire, appelé inclusion, au sein du cytoplasme de la cellule a rendu C. trachomatis dépendant de l'hôte pour l'acquisition des nucléosides triphosphates (NTP), les éléments constitutifs de l'ARN et de l'ADN (sous la forme de désoxynucléotides, dNTP). Les membranes n'étant pas perméables aux nucléotides, ces métabolites, ou leurs précurseurs, sont transportés par des transporteurs spécifiques. Seuls les transporteurs de NTP bactériens, Npt1 et Npt2, ont été identifiés pour importer les NTP de l'inclusion vers les bactéries, ce qui soulève la question de savoir comment les nucléotides de l'hôte deviennent accessibles dans l'inclusion. Cette thèse porte sur deux aspects principaux : premièrement, les stratégies mises en œuvre par C. trachomatis pour accéder aux nucléotides de l'hôte, et deuxièmement, la caractérisation de la protéine bactérienne CtMazG, qui présente une fonction hypothétique de nucléotide pyrophosphohydrolase. Dans la cellule hôte, les nucléotides sont synthétisés par deux voies : la voie de sauvetage, qui synthétise des nucléotides (formes phosphorylées de nucléosides) à partir de nucléosides importés, et la voie de novo, où les nucléotides sont synthétisés à partir d'autres métabolites cellulaires. Nos données démontrent que les deux voies de synthèse des nucléotides contribuent à l'approvisionnement de C. trachomatis. De plus, nous montrons que les nucléotides, et non les nucléosides, sont importés dans l'inclusion. Cependant, nos efforts pour identifier les transporteurs responsables de cet import ont été infructueux.En parallèle, nous avons exploré le rôle de la protéine bactérienne CtMazG dans l'infection par C. trachomatis. Nous avons confirmé l'activité pyrophosphohydrolase de nucléotides, en particulier pour les dNTP puriques (dATP et dGTP), ce qui entraîne la génération de formes monophosphate de désoxynucléosides puriques. Nos données montrent que CtMazG est nécessaire au développement optimal de la bactérie et que son absence résulte en l'accumulation de mutations. Dans plusieurs autres organismes, le rôle de MazG dans la préservation du génome est lié à sa spécialisation vis-à-vis de nucléotides oxydés, mais ce n'est pas le cas de CtMazG. Nos données suggèrent plutôt que CtMazG équilibre les niveaux relatifs de dNTP, participant par ce biais à la fidélité de l'étape de réplication du génome. CtMazG a en outre un rôle important pour l'entrée des bactéries dans leur phase proliférative, là encore possiblement en équilibrant les dNTP.En conclusion, ce projet a permis de mieux comprendre des stratégies employées par C. trachomatis pour accéder aux nucléotides de l'hôte et d'élucider le rôle d'une enzyme bactérienne modulant les dNTP dans le développement de C. trachomatis.Chlamydia trachomatis is an obligate intracellular bacterium that infects human epithelial cells of the urogenital tract. This pathogen is known as the most common sexually transmitted infection. Certain strains can also infect the ocular conjunctiva, which can develop into trachoma, the leading cause of bacterial blindness.The intracellular development of the bacterium in a membrane compartment, called an inclusion, within the cell cytoplasm has made C. trachomatis dependent on the host for the acquisition of nucleoside triphosphates (NTP), the building blocks of RNA and DNA (in the form of deoxynucleotides, dNTP). As membranes are not permeable to nucleotides, these metabolites, or their precursors, are transported by specific transporters. Only bacterial NTP transporters, Npt1 and Npt2, have been identified to import NTP from the inclusion into bacteria, raising the question of how host nucleotides become accessible in the inclusion.This thesis focuses on two main aspects: firstly, the strategies implemented by C. trachomatis to access host nucleotides, and secondly, the characterization of the bacterial protein CtMazG, which exhibits a hypothetical nucleotide pyrophosphohydrolase function. In the host cell, nucleotides are synthesized by two pathways: the salvage pathway, which synthesizes nucleotides (phosphorylated forms of nucleosides) from imported nucleosides, and the de novo pathway, where nucleotides are synthesized from other cellular metabolites. Our data demonstrate that both nucleotide synthesis pathways contribute to the supply of C. trachomatis. In addition, we show that nucleotides, not nucleosides, are imported into the inclusion. However, our efforts to identify the transporters responsible for this import were unsuccessful.In parallel, we explored the role of the bacterial protein CtMazG in C. trachomatis infection. We confirmed the nucleotide pyrophosphohydrolase activity, particularly for purine dNTPs (dATP and dGTP), leading to the generation of monophosphate forms of purine deoxynucleosides. Our data show that CtMazG is necessary for optimal bacterial development, and that its absence results in the accumulation of mutations. In many other organisms, MazG's role in genome preservation is linked to its specialization in oxidized nucleotides, but this is not the case for CtMazG. Instead, our data suggest that CtMazG balances the relative levels of dNTP, thereby contributing to the fidelity of the genome replication step. CtMazG also plays an important role in the entry of bacteria into their proliferative phase, again possibly by balancing dNTP.In conclusion, this project has enabled us to gain a better understanding of the strategies employed by C. trachomatis to access host nucleotides, and to elucidate the role of a bacterial enzyme modulating dNTP in the development of C. trachomatis
Identificaion and characterization of a novel early effector protein of Chlamydia trachomatis
No full textC. trachomatis est une bactérie Gram-négative intracellulaire obligatoire et un pathogène humain. Première cause de maladie sexuellement transmissible d'origine bactérienne, elle est également responsable, dans les pays en développement, d'infections oculaires pouvant conduire à la cécité (trachome). Son cycle de développement bi-phasique a lieu au sein d'un compartiment appelé inclusion. Grâce à un système de sécrétion de type 3 (SST3), Chlamydia sécrète des protéines dans le cytosol de la cellule afin de promouvoir sa survie et sa multiplication. Ces protéines sont désignées sous le terme d'effecteurs.C. trachomatis is an obligate intracellular Gram-negative bacteria and a human pathogen. It is the most prevalent cause of sexually transmitted diseases of bacterial origin and a leading cause of preventable blindness in the developing world. During their biphasic developmental cycle the bacteria remains in a membrane-bounded cellular compartment called an inclusion. Using a type 3 secretion system (T3SS) they translocate effector proteins inside the cytosol of the cell to promote its survival and multiplication.The aim of the PhD was to study the function of CT622, a hypothetic protein from C. trachomatis. We showed that CT622 is an effector protein from the T3SS and that it is secreted early during the infection. We identified a bacterial protein that binds to CT622, and we showed that it acts as a chaperone, stabilizing CT622 and enhancing its secretion. We obtained bacteria lacking CT622 expression, thus demonstrating that CT622 is not essential for bacterial growth in vitro. However, preliminary studies indicate that in the absence of CT622 bacterial development is delayed and T3SS is defective.We identified several molecules interacting with CT622: geranylgeranyl diphosphate, Rab39 and Atg16L1 proteins. Future work will aim at understanding how these identified interactions, or other bacterial or cellular partners still to be discovered, contribute to the establishment of a niche favorable to bacterial development
The chlamydial OTU domain-containing protein ChlaOTU is an early type III secretion effector targeting ubiquitin and NDP52
Get PDFChlamydia are obligate intracellular pathogens. Upon contact with the host, they use type III secretion to deliver proteins into the cell, thereby triggering actin-dependent entry and establishing the infection. We observed that Chlamydia caviae elicited a local and transient accumulation of ubiquitinated proteins at the entry sites, which disappeared within 20 min. We investigated the mechanism for the rapid clearance of ubiquitin. We showed that the OTU-like domain containing protein CCA00261, predicted to have deubiquitinase activity, was detected in infectious particles and was a type III secretion effector. This protein is present in several Chlamydia strains, including the human pathogen Chlamydia pneumoniae, and we further designate it as ChlaOTU. We demonstrated that ChlaOTU bound ubiquitin and NDP52, and we mapped these interactions to distinct domains. NDP52 was recruited to Chlamydia entry sites and was dispensable for infection and for bacterial growth. ChlaOTU functioned as a deubiquitinase in vitro. Heterologousexpression of ChlaOTU reduced ubiquitin accumulation at the entry sites, while a catalytic mutant of the deubiquitinase activity had the opposite effect. Altogether, we have identified a novel secreted protein of chlamydiae. ChlaOTU targets both ubiquitin and NDP52 and likely participates in the clearance of ubiquitin at the invasion sites.Fil: Furtado, Ana Rita. Institut Pasteur. Unité de Biologie des Interactions Cellulaires; FranciaFil: Essid, Miriam. Institut Pasteur. Unité de Biologie des Interactions Cellulaires; FranciaFil: Perrinet, Stéphenie. Institut Pasteur. Unité de Biologie des Interactions Cellulaires; FranciaFil: Balaña, Maria Eugenia. Institut Pasteur. Unité de Biologie des Interactions Cellulaires; Francia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Ciencias y Tecnología "Dr. Cesar Milstein"; ArgentinaFil: Yoder, Nicholas. Nine Cambridge Center. Whitehead Institute for Biomedical Research; Estados UnidosFil: Dehoux, Pierre. Institut Pasteur. Plateforme Intégration et Analyse Génomique; FranciaFil: Subtil, Agathe. Institut Pasteur. Unité de Biologie des Interactions Cellulaires; Franci
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
- …
