Multiple Myosins Are Required to Coordinate Actin Assembly with Coat Compression during Compensatory Endocytosis

Actin is involved in endocytosis in organisms ranging from yeast to mammals. In activated Xenopus eggs, exocytosing cortical granules (CGs) are surrounded by actin "coats," which compress the exocytosing compartments, resulting in compensatory endocytosis. Here, we examined the roles of two myosins in actin coat compression. Myosin-2 is recruited to exocytosing CGs late in coat compression. Inhibition of myosin-2 slows coat compression without affecting actin assembly. This differs from phenotype induced by inhibition of actin assembly, where exocytosing CGs are trapped at the plasma membrane (PM) completely. Thus, coat compression is likely driven in part by actin assembly itself, but it requires myosin-2 for efficient completion. In contrast to myosin-2, the long-tailed myosin-1e is recruited to exocytosing CGs immediately after egg activation. Perturbation of myosin-1e results in partial actin coat assembly and induces CG collapse into the PM. Intriguingly, simultaneous inhibition of actin assembly and myosin-1e prevents CG collapse. Together, the results show that myosin-1e and myosin-2 are part of an intricate machinery that coordinates coat compression at exocytosing CGs.