Samuel PICHON

Ph.D., University of Poitiers (France), 2009

MS Biology, evolution and control of populations, University of Tours (France), 2005

Dissertation

  • Title : Type IV secretion system and ankyrin domain-containing proteins in Wolbachia-arthropods interactions.
  • Supervisors: Prof. Pierre Grève and Prof. Didier Bouchon.
  • Defended on 2009, December the 15th.

Summary

Wolbachia are intracellular Gram-negative bacteria that are reproductive manipulators of many arthropods. In the isopod Armadillidium vulgare, the Wolbachia wVulC strain induces male feminization. Here, we characterized two vir operons which are expressed in all host tissues and which encode a type IV secretion system (T4SS) used to translocate bacterial effectors into host cytoplasm. Gene organization and sequence comparison in 37 Wolbachia strains highlighted the high conservation of both vir operons and their importance for the biology of the bacteria. We also identified in the on-going assembly of the wVulC genome, 66 ankyrin domain-encoding genes. Ankyrin motifs are known to mediate protein-protein interactions in eukaryotic organisms and thus are suggested to mediate in Wolbachia the interaction with host molecules. We showed that one of the three copies of the wVulC pk2 gene is only expressed in feminizing strains but not in the three strains inducing cytoplasmic incompatibility in terrestrial isopods. The associated Pk2 protein could be involved in male feminization. We thus tested the interaction between three T4SS proteins and five ankyrins (including Pk2) via the yeast two-hybrid and CRAfT (Cre-recombinase Reporter Assay for Translocation) methods. None of the five ankyrin proteins were revealed to be secreted by the wVulC strain. Nevertheless, this promising approach may enable us to identify Wolbachia effectors.

Keywords:Host-parasite interaction, Wolbachia, Secretion System, Ankyrin domain-containing proteins, Feminization, Cytoplasmic incompatibility, Bacterial effectors, Crustacean isopod.

Teaching

  • 2005-2008: Teaching Assistant at the University of Poitiers (246 Contact Hours).
  • 2008-2009: Assistant Lecturer at the University of Poitiers (269 Contact Hours).

Selected publications

  • Félix C., S. Pichon, C. Braquart-Varnier, H. Braig, L. Chen, R.A. Garrett, G. Martin and P. Grève (2008). Characterization and transcriptional analysis of two gene clusters for a type IV secretion machinery in Wolbachia of Armadillidium vulgare. Research in Microbiology, 159, 6, 481-485.
  • Cordaux R., S. Pichon, A. Ling, P. Pérez, C. Delaunay, F. Vavre, D. Bouchon and P. Grève (2008). Intense transpositional activity of insertion sequences in an ancient obligate endosymbiont. Molecular Biology and Evolution, 25, 9, 1889-1896.
  • Pichon S., Bouchon D., Cordaux R., Chen L., Garrett R.A. and P. Grève. Conservation of the Type IV Secretion System throughout Wolbachia evolution. Biochemical and Biophysical Research Communications 385: 557-562.

Contact

Email : samuel_pichon@hotmail.com

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