Dr.Lambert and Dr.Goode will study a block to polyspermy in the Ascidian egg. According to their model, the sperm bind to glycosides on the vitelline coat of the egg. An increase in the number of sperm binding to the vitelline coat is followed by a rapid decline. This decline in binding helps insure that only a single sperm enters the egg. Sperm binding is inhibited by the Na+-dependent release of a glycosidase that modifies the vitelline coat sperm receptors. They hypothesize that the glycosidase is initially linked to the egg membrane and is rapidly discharged at fertilization. The fact that detergents and Phospholipase C can free the enzyme from the unfertilized egg suggest that the enzyme is linked to a membrane phospholipid. Their model includes linkage of the glycosidase to a phosphatidylcholine and the Na+-dependent activation of a phospholipase that causes enzyme release. The glycosidase and phospholipase will be isolated and extensively characterized. Antibodies will be prepared to both proteins for ultrastructural enzyme localization. The mechanism of release will be probed through the use of phospholipase agonists and antagonists and also through the direct measurement of phospholipase activity in unfertilized and fertilized eggs. The role of G proteins and ions in Ascidian egg activation will also be probed. %%% Although millions of sperm are produced for each egg, if more than a single sperm enters the egg,cleavage is grossly abnormal and death is inevitable. As a consequence, blocking the entry of additional sperm is of critical importance to fertility. Dr.Lambert and Dr. Goode will further the understanding of this phenomenon by studying the molecular details of sperm entry and blocking in the Ascidian system.
