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Génome et facteurs de virulence d'un polydnavirus d'hyménoptère parasitoïde

Abstract : The hymenoptera Cotesia congregata (Microgastrinae ; Braconidae) lays its eggs inside its host, a caterpillar of the lepidoptera Manduca sexta (Noctuidae ; Sphingidae) and introduces bracovirus (CcBV) particles, containing 30 double-stranded DNA circles. The viral genes carried by these circles encode for a range of proteins expressed in the tissues of the parasitized caterpillar. These viral proteins play an essential role for succesful parasitism. Viral gene expression leads to host physiology modifications such as alteration of immunity allowing the parasitoid larvae to develop. Additionnally, the parasitized host undergo a prewandering developmental arrest.
The characterization of bracovirus genome has advanced and allowed the discovery of many gene families. The introduction of this thesis summarizes up-to-date knowledge about insect immunity and bracoviral genes potentially involved in host physiology control.
During my thesis, sequencing and genome analyses demonstrated that the CcBV genome is composed of 30 double-stranded DNA circles coding for 9 multigenic families (Espagne et al 2004) comprising the protein tyrosine phosphatase (PTP) family (27 genes) (Provost et al 2004), the cystatin family (3 genes) (Espagne et al soumis) and the ankyrin motif encoding genes (6 genes) (Pennacchio et al en préparation). The detailed characterisation of the viral PTP gene family was performed. Field inversion gel electrophoresis (FIGE) allowed to physically localize PTP genes on the viral genome. Their expression was analysed on different host tissues by a multiplex RT PCR approach. Biochemical activity tests of 2 PTPs were performed by in vitro production using the baculovirus expression system.
Globally, genes of the described families are expressed in the parasitized host and some proteins have the biochemical function predicted by their conserved domains, suggesting these proteins play a role in the host physiological modifications induced by parasitism.
The characterization of viral genes expressed in the host is a key step toward further identification of the role of each protein in host physiology alteration.
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Submitted on : Thursday, October 5, 2006 - 8:45:53 AM
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Bertille Provost. Génome et facteurs de virulence d'un polydnavirus d'hyménoptère parasitoïde. Biochimie [q-bio.BM]. Université François Rabelais - Tours, 2004. Français. ⟨tel-00103667⟩

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