Yi Sun

Abstract :

Babesia divergens is an hemoprotozoan Apicomplexa that infects mainly cattle and which is transmitted by the tick Ixodes ricinus. The general goal of my PhD work is to improve the knowledge on B. divergens invasion of erythrocyte at the cellular (invasion steps) and molecular levels (caracterization of proteins involved). The study of intra- and interspecific conservation of the genes related to the invasion process should give insights into the species-specific steps of Babesia-erythrocyte interactions. In that goal, I have collaborated to the resdescription of B. capreoli, a B. divergens phylogenetically related species. The overlapping host range and the relatedness of these two close species are key advantages for the study of host specificity. I therefore characterized in B. capreoli the gene Bcp37/41, an ortholog of the merozoite surface antigen Bd37 of B. divergens. Despite a high intra- and inter-specific polymorphism, the conservation in these two orthologs of residues potentially involved in parasite adhesion to red blood cell suggests their non specific interaction with the erythrocyte. To further study B. divergens-erythrocyte interactions, an invasion test was set up and used to demonstrate the speed of the invasion process (less than 45s) and the possibility of the simultaneous invasion of one RBC by two merozoites. This test has been used to study rap-1 (rhoptry-associatedprotein 1) expression in the course of the cell cycle. RAP-1 localization in rhoptry bulbs, its role in invasion and its low genetic polymorphism have also been determined.

Key words :

Babesia divergens, Babesia capreoli, invasion, erythrocyte, apical complex, Bd37, RAP-1, Polymorphism