University of Geneva - Faculty of Medicine

The phylum of Apicomplexa includes more than five thousands species of obligate intracellular protozoan parasites, among them some important pathogens such as the Plasmodium spp., the etiologic agent of malaria, or Toxoplasma gondii responsible for toxoplasmosis in humans and animals. Host cell invasion and egress from the infected cells are essential events for these obligate intracellular parasites. Host cell entry is powered by gliding motility and is initiated by the attachment and reorientation of the polarized parasites such that the apical secretory organelles (micronemes and rhoptries) sequentially discharge their contents at the point of contact with host cell. The coccidian-subgroup of Apicomplexa possesses a dynamic organelle called the conoïd. This motile organelle is positioned at the extreme apical pole of the zoite and consisting of a unique polymer of tubulin fibers. The conoïd extrudes over the host cell plasma membrane during glinding, invasion and egress. Conoïd protrusion is sensitive to cytochalasin D and can be induced by calcium ionophore or ethanol treatment in vitro. The class XIV myosin TgMyoH exhibits 3 ATS (alpha tubulin suppressor) domains and 6 to 8 putative IQ motifs and localizes to the apical polar ring of the conoïd by high-resolution microscopy. Here we described conditional knockouts of TgMyoH and established the essential role of this motor for parasite survival. Detailed phenotypic analysis of the mutants revealed that TgMyoH is involved in a global cytoskeleton rearrangement allowing the first step of the parasite motility, and essential for invasion, and egress.