SIGNAL-TRANSDUCTION DURING FERTILIZATION - STUDIES WITH PROTEASES ANDHETEROLOGOUS RECEPTORS

Recent investigations of fertilization have indicated the importance o f signaling pathways in the egg that are initiated by cell surface rec eptors. The evidence includes: (1) stimulation of heterologous recepto rs (mammalian) in starfish eggs, leading to activation of both early ( e.g., Ca2+ release) and late (e.g., DNA synthesis) events of fertiliza tion (Shilling et al., 1994); and (2) activation of eggs by external t reatment with specific proteases (Carroll and Jaffe, 1995). Heterologo us receptor-induced activation involves phospholipase C (PLC). This en zyme may be activated by a G-protein mediated pathway (PLC-beta) or a tyrosine kinase receptor pathway (PLC-gamma). There have been other me chanisms for egg activation proposed, which will not be discussed here , such as the introduction of a ''cytoplasmic factor'' by the sperm. i nto the egg (Swann, 1990). We propose a multi-subunit receptor complex as the mediator of the activating signal from sperm, with properties similar to those of other receptor-mediated signal transduction pathwa ys.