Hydrogen peroxide induces Src family tyrosine kinase-dependent activation of Xenopus eggs

Fertilization is accompanied by a rapid and transient calcium release in eg gs, which is required for the onset of zygotic developmental program or 'eg g activation'. Recently, it was found that Src family tyrosine kinase (SFK) -dependent phospholipase C (PLC) activity is necessary for the calcium tran sience in fertilized Xenopus eggs. The present study demonstrates that hydr ogen peroxide (H2O2) stimulates protein-tyrosine phosphorylation in Xenopus eggs, which occurs primarily in the egg cortex of the animal hemisphere as revealed by indirect immunofluorescence study. Egg SFK was found to be upr egulated by H2O2 while the SFK-specific inhibitor PP1 effectively blocked H 2O2-induced tyrosine phosphorylation. As in fertilized eggs, PLC gamma, but not She, was tyrosine-phosphorylated in H2O2-treated eggs. H2O2 also cause d inositol 1,4,5-trisphosphate (IP3) production and sustained calcium relea se. Alter limited application of H2O2, elevated SFK activity and tyrosine p hosphorylation were quickly reversed. Under such conditions, eggs showed co rtical contraction and dephosphorylation of p42 MAP kinase, both of which a re indicative of egg activation. These egg activation events, as well as H2 O2-induced IP3 production and calcium release, were sensitive to PP1 and PL C inhibitor U-73122. Together, the present study demonstrated that H2O2 can mimic, at least in part, early events of Xenopus egg activation that requi re an SFK-dependent PLC pathway.