INVOLVEMENT OF PHOSPHOLIPASE C-GAMMA-1 IN MOUSE EGG ACTIVATION-INDUCED BY A TRUNCATED FORM OF THE C-KIT TYROSINE KINASE PRESENT IN SPERMATOZOA

Microinjection of a truncated form of the c-kit tyrosine kinase presen t in mouse spermatozoa (tr-kit) activates mouse eggs parthenogenetical ly, and tr-kit-induced egg activation is inhibited by preincubation wi th an inhibitor of phospholipase C (PLC) (Sette, C., A. Bevilacqua, A. Bianchini, F. Mangia, R, Geremia, and F. Rossi. 1997. Development [Ca mb.]. 124:2267-2274). Coinjection of glutathione-S-transferase (GST) f usion proteins containing the src-homology (SH) domains of the gamma 1 isoform of PLC (PLC gamma 1) competitively inhibits tr-kit-induced eg g activation. A GST fusion protein containing the SH3 domain of PLC ga mma 1 inhibits egg activation as efficiently as the whole SH region, w hile a GST fusion protein containing the two SH2 domains is much less effective. A GST fusion protein containing the SH3 domain of the Grb2 adaptor protein does not inhibit tr-kit-induced egg activation, showin g that the effect of the SH3 domain of PLC gamma 1 is specific. Tr-kit -induced egg activation is also suppressed by co-injection of antibodi es raised against the PLC gamma 1 SH domains, but not against the PLCy 1 COOH-terminal region. In transfected COS cells, coexpression of PLC gamma 1 and tr-kit increases diacylglycerol and inositol phosphate pro duction, and the phosphotyrosine content of PLC gamma 1 with respect t o cells expressing PLC gamma 1 alone. These data indicate that tr-kit activates PLCy1, and that the SH3 domain of PLC gamma 1 is essential f or tr-kit-induced egg activation.