Actinomyosin-based motility and organelles biogenesis in Apicomplexa

Orateur : Dominique Soldati-Favre (Dep. of Microbiology and Molecular Medecine, Univ. of Geneva, Switzerland)

BBIO531K : The phylum Apicomplexa includes a large and diverse group of obligate intracellular parasites that lack normal appendages for locomotion such as cilia and flagella and instead the invasive stages use gliding motility to power their migration across biological barriers, invade host cells and egress from infected cells. The conserved molecular machinery that generates motion, the glideosome, involves the action of signaling molecules, myosin motor complexes, regulators of actin dynamics, adhesins and proteases. The glideosome is tightly spatiotemporally regulated and subjected to extensive posttranslational modifications. The Apicomplexans also share myosin motors implicated in other fundamental biological processes. Toxoplasma gondii myosin H is a class XIV motor expressed exclusively in the coccidian subgroup of Apicomplexa. TgMyoH localizes to the conoid and plays a key role in invasion and egress. In T. gondii, the segregation of the apicoplast occurs early during endodyogeny and coincides with nuclear division and daughter cell budding. This organelle is anchored to the centrosomes and associates with the mitotic spindle. Several experimental approaches that perturb actin dynamics lead to a severe impairment in apicoplast inheritance. The class XXIII myosin F has been identified as a key motor associated to this process. Additionally, TgMyoF also impacts on targeting the rhoptries to apical tip of the parasites due to a critical role in repositioning of the centrosomes during parasite division. In contrast to the apicoplast, rhoptries are formed de novo at a late stage of cell division, presumably by vesicular budding from the Golgi apparatus. These specialized secretory organelles not only contribute to moving junction- and parasitophorous vacuole membrane- formation but also send effector molecules into the host cell and critically impact on virulence. The implication of a myosin motor in anchoring rhoptries to the apical pole of the parasites might be connected the armadillo repeat only (ARO), an acylated protein, which is distributed at the surface of the rhoptries and has a vital function in invasion but not in egress.

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