Ki. Sato et al., Tyrosine kinase-dependent activation of phospholipase C gamma is required for calcium transient in Xenopus egg fertilization, DEVELOP BIO, 224(2), 2000, pp. 453-469
In a previous study (K.-I. Sate et al., 1999, Dev. Biol. 209, 308-320), we
presented evidence that a Src-related protein-tyrosine kinase (PTK), named
Xyk, may act upstream of the calcium release in fertilization of the Xenopu
s egg. In the present study, we examined whether PTK activation of phosphol
ipase C gamma (PLC gamma) plays a role in the fertilization-induced calcium
signaling. Immunoprecipitation studies show that Xenopus egg PLC gamma is
tyrosine phosphorylated and activated within a few minutes after fertilizat
ion but not after A23187-induced egg activation. Consistently, we observed
a fertilization-induced association of PLC gamma with Xyk activity that was
not seen in A23187-activated eggs. A Src-specific PTK inhibitor, PP1, bloc
ked effectively the fertilization-induced association of PLC gamma with Xyk
activity and up-regulation of PLC gamma, when microinjected into the egg.
In addition, a PLC inhibitor, U-73122, inhibited sperm-induced inositol 1,4
,5-trisphosphate production and the calcium transient and subsequent calciu
m-dependent events such as cortical contraction, elevation of fertilization
envelope, and tyrosine dephosphorylation of p42 MAP kinase, all of which w
ere also inhibited by PP1. On the other hand, A23187 could cause the calciu
m response and calcium-dependent events in eggs injected with PP1 or U-7312
2. These results support the idea that Xenopus egg fertilization requires S
rc-family PTK-dependent PLC gamma activity that acts upstream of the calciu
m-dependent signaling pathway. (C) 2000 Academic Press.