Evidence that a starfish egg Src family tyrosine kinase associates with PLC-gamma 1 SH2 domains at fertilization

The initiation of calcium release at fertilization in the eggs of most anim als relies on the production of IP3, implicating the activation of phosphol ipase C, Recent work has demonstrated that injection of PLC-gamma SH2 domai n fusion proteins into starfish eggs specifically inhibits the initiation o f calcium release in response to sperm, indicating that PLC-gamma is necess ary for Ca2+ release at fertilization [Carroll et al. (1997) J. Cell Biol. 138, 1303-1311]. Here we investigate how PLC-gamma may be activated, by usi ng the PLC-gamma SH2 domain fusion protein as an affinity matrix to identif y interacting proteins. A tyrosine kinase activity and an egg protein of ca . M-r 58 K that is recognized by an antibody directed against Src family ty rosine kinases associate with PLC-gamma SH2 domains in a fertilization-depe ndent manner. These associations are detected by 15 s postfertilization, co nsistent with a function in releasing Ca2+. Calcium ionophore treatment of eggs did not cause association of the kinase activity or of the Src family protein with the PLC-gamma SH2 domains. These data identify an egg Src fami ly tyrosine kinase as a potential upstream regulator of PLC-gamma in the ac tivation of starfish eggs. (C) 1999 Academic Press.