Multiple intracellular signals coordinate structural dynamics in the sea urchin egg cortex at fertilization.

Fertilization of the sea urchin egg is accompanied by a sequence of structural changes in the egg cortex that include exocytosis, endocytosis, and microvillar growth. This architectural reorganization is coordinated by two intracellular signals: a rapid, transient rise in cytosolic free calcium and a slower, longer lasting increase in cytoplasmic pH. In this report we provide ultrastructural views of these events in quick-frozen eggs and discuss their relationship to the calcium and pH signals.