M.S.

Production traits and disease resistance are believed to be under the control of many genes, i.e. quantitative trait loci (QTL). The objective of the present study was to establish a methodology for identifying DNA markers which are associated with QTL in chickens using an alternative approach to the traditional linkage analysis. A systematic screening approach was designed to search a chicken liver cDNA library for clones which revealed polymorphisms associated with traits. In the first stage of the experiment, a total of 92 cDNA clones were subjected to restriction fragment length polymorphism (RFLP) analysis. About 33% and 22% of the clones revealed DNA polymorphisms at MspI and TaqI restriction sites, respectively. Subsequently, DNA polymorphisms which responded to selection were identified by comparing RFLP frequencies in divergently selected strains of chickens. About 60% of the RFLPs responded to selection for egg production traits and/or Marek's disease (MD) resistance. Trait associations of these RFLPs were then studied by selectively genotyping individuals at the extremes of trait distributions, followed by an analysis of individuals in the entire population and statistical evaluation. Finally, RFLP regions of DNA markers were characterized and PCR assays for rapid RFLP screening were developed. DNA markers in two genes were identified and characterized by this methodology. One was a marker in the chicken mitochondrial genome which arose from a nucleotide substitution (T to C) in the NADH subunit IV gene. Statistical analysis for typing random individual samples from the strains showed that this DNA polymorphism was associated with mature body weight and egg specific gravity which is a strong indicator for egg shell thickness. Other analyzed markers were located in the chicken mitochondrial phospho-enolpyruvate carboxykinase (PEPCK-M). Using the cDNA of this gene as a probe, southern blotting revealed a highly polymorphic band pattern. Statistical analy

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Le virus de la maladie de Marek (MDV) est un α-herpèsvirus aviaire responsable de lymphomes chez la poule. En absence de virions libres détectables en culture cellulaire, il est couramment admis que ce virus se dissémine uniquement de cellule à cellule par un mécanisme non identifié à ce jour. Mon travail de thèse comprenait 3 parties. La première avait pour objectif d’étudier la contribution des contacts cellulaires et de possibles virions extracellulaires dans la dissémination de MDV. La seconde partie visait à étudier le rôle du cytosquelette d’actine dans la dissémination intercellulaire du MDV et l’implication des voies de signalisation des RhoGTPases. J’ai montré que l’activité de la voie Rho-ROCK favorise la dissémination du MDV au contraire de la voie Rac-PAK. Un possible lien entre la dissémination du MDV et les jonctions adhérentes, maintenues par l’activité de la voie Rho-ROCK, est discuté. Enfin, la troisième partie avait pour but le développement d’un nouveau test de dissémination entre cellules sur un cycle viral unique. Pour cela, j’ai construit un virus MDV rapporteur inductible et des lignées cellulaires aviaires exprimant une flippase. / Marek’s disease virus (MDV) is an avian α-herpesvirus which is responsible for lymphomas in chicken. In absence of detectable cell-free virions in cell culture, it is well admit that this virus only spread from cell-to-cell. The involved mechanisms remain unknown. My thesis work was divided in three parts. The objectives of the first one were to study the contribution of cell contacts and of potential extracellular infectious virions on MDV spread. The second part aimed at studying the role of the actin cytoskeleton in MDV intercellular spread and the involvement of RhoGTPase signaling pathways. I showed that the Rho-ROCK signaling pathway promotes the dissemination in contrast to the Rac-PAK signaling pathway. A possible link between MDV spread and adherens junctions, maintained by Rho-ROCK signaling, is discussed. The third and last part had the purpose to develop a new assay of MDV spread between cells on a single viral cycle. For this, I built an inducible reporter MDV virus and avian cell lines expressing a flippase.