Function of a sea urchin egg Src family kinase in initiating [Ca.sup.2+] release at fertilization

Egg activation at fertilization requires the release of [Ca.sup.2+] from the egg's endoplasmic reticulum, and recent evidence has indicated that a Src family kinase (SFK) may function in initiating this signaling pathway in echinoderm eggs. Here, we identify and characterize a SFK from the sea urchin Strongylocentrotus purpuratus, SpSFK1. SpSFK1 RNA is present in eggs, and an antibody made against a SpSFK1 peptide recognizes an ~58-kDa egg membrane-associated protein in eggs of S. purpuratus as well as another sea urchin Lytechinus variegatus. Injection of both species of sea urchin eggs with dominant-interfering Src homology 2 domains of SpSFK1 delays and reduces the release of [Ca.sup.2+] at fertilization. Injection of an antibody against SpSFK1 into S. purpuratus eggs also causes a small increase in the delay between sperm-egg fusion and [Ca.sup.2+] release. In contrast, when injected into eggs of L. variegatus, this same antibody has a dramatic stimulatory effect: it causes PLC[gamma]-dependent [Ca.sup.2+] release like that occurring at fertilization. Correspondingly, in lysates of L. variegatus eggs, but not S. purpuratus eggs, the antibody stimulates SFK activity. Injection of L. variegatus eggs with another antibody that recognizes the L. variegatus egg SFK also causes PLC[gamma]-dependent [Ca.sup.2+] release like that at fertilization. These results indicate that activation of a Src family kinase present in sea urchin eggs is necessary to cause [Ca.sup.2+] release at fertilization and is capable of stimulating [Ca.sup.2+] release in the unfertilized egg via PLC% as at fertilization. Keywords: Fertilization; Src family kinase; Calcium; Egg activation