Phorbol Ester Induces Elevation of the Vitelline Coat of Eggs of the Ascidian Halocynthia roretzi: (phorbol ester/ascidian egg/vitelline coat/trypsin-like enzyme/calmodulin).

Elevation of the vitelline coat of eggs of the ascidian, Halocynthia roretzi, was induced by 12-O-tetradecanoylphorbol-13-acetate or phorbol-12, 13-didecanoate, but not by their 4-epimers. After elevation of the vitelline coat in this way, eggs were unable to undergo cleavage on addition of sperm. This elevation of the vitelline coat by phorbol esters was inhibited by specific inhibitors of trypsin-like enzyme, calmodulin, phospholipase A , and protein kinase C. In association with elevation of the vitelline coat, a trypsin-like enzyme was released from the eggs. The properties of this enzyme were similar to those of the enzyme released by calcium ionophore, which also induced elevation of the vitelline coat, suggesting that similar exocytosis of intracellular granules occurred in both cases. Calmodulin, possibly involved in the elevation process, was isolated from eggs and characterized.