TYROSINE PHOSPHORYLATION OF THE EGG RECEPTOR FOR SPERM AT FERTILIZATION

Gamete interaction triggers a variety of responses within the egg, col lectively referred to as egg activation. In addition to the hallmarks of calcium release and fertilization envelope elevation, there are cyt oskeletal rearrangements, protein tyrosine phosphorylation, and an inc rease in pH, among others. The ultimate goal of these concerted activa tion events is entry of the newly fertilized egg into the cell cycle. However, the molecular mechanisms which promote downstream cell activa tion events remain poorly understood. One model suggests that sperm de liver an ''activating factor'' upon fusion with the egg plasma membran e, while a second model proposes that the egg receptor for sperm trans duces a signal that mediates a cascade of subsequent events. It also i s possible that multiple pathways are activated. As a first step towar d testing the hypothesis of receptor-mediated signal transduction, we have investigated the tyrosine phosphorylation state of the sea urchin egg receptor for sperm using specific antibodies. The present work in dicates that the sperm receptor is phosphorylated by an egg cortical t yrosine kinase in response to sperm or purified ligand (bindin) bindin g. Maximal phosphorylation was reached within 20 sec. These data suppo rt the hypothesis that the sperm receptor is a gamete recognition prot ein which responds to ligand binding and focus attention on the questi on of the role of this tyrosine phosphorylation signal in egg activati on. (C) 1994 Academic Press, Inc.