A role for myosin 1e in cortical granule exocytosis in Xenopus oocytes.

Xenopus oocytes undergo dynamic structural changes during maturation and fertilization. Among these, cortical granule exocytosis and compensatory endocytosis provide effective models to study membrane trafficking. This study documents an important role for myosin 1e in cortical granule exocytosis. Myosin 1e is expressed at the earliest stage that cortical granule exocytosis can be detected in oocytes. Prior to exocytosis, myosin 1e relocates to the surface of cortical granules. Overexpression of myosin 1e augments the kinetics of cortical granule exocytosis, whereas tail-derived fragments of myosin 1e inhibit this secretory event (but not constitutive exocytosis). Finally, intracellular injection of myosin 1e antibody inhibits cortical granule exocytosis. Further experiments identified cysteine string proteins as interacting partners for myosin 1e. As constituents of the membrane of cortical granules, cysteine string proteins are also essential for cortical granule exocytosis. Future investigation of the link between myosin 1e and cysteine string proteins should help to clarify basic mechanisms of regulated exocytosis.