Phalloidin inhibits cortical granule exocytosis and ooplasmic segregation in loach eggs.

Injections of phalloidin under the surface of loach eggs, followed by activation of the eggs in tap water, result in local inhibition of cortical granule (CG) exocytosis. Light and electron microscopy revealed that in the region where exocytosis is inhibited the thickness of the microfilamentous cortex (MC) separating CGs from the plasma membrane (PM) is increased significantly, and many CGs are detached and have moved away from the MC. Injections of phalloidin also inhibit ooplasmic segregation in fertilized eggs. The experiments suggest that in intact eggs the MC represents a physical barrier to CG exocytosis, and that interactions of the MC with the PM and CGs are crucial for the retention of CGs near the sites of fusion.