Biphasic Activation of Fyn Kinase upon Fertilization of the Sea Urchin Egg

AbstractFertilization results in the tyrosine phosphorylation of several egg proteins within minutes of sperm–egg binding and inhibitor studies have shown that tyrosine kinase activity is required for many aspects of egg activation. The present study demonstrates the presence of p59c-fynkinase in the sea urchin egg and examines the effect of fertilization on the activity of this enzyme. Fertilization had little effect on Fyn kinase activity during the first 2 min after insemination; however, activity had increased approximately eightfold between 5 and 15 min postinsemination. This initial, rapid increase in kinase activity was followed by a period of slightly elevated kinase activity, which was two- to threefold higher than that in the unfertilized egg. Bindin, as well as various parthenogenic agents known to activate the calcium- and pH-mediated pathways of egg activation, failed to elicit any change in enzyme activity, indicating that activation of the kinase required sperm-induced egg activation. However, phorbol ester treatment did induce a slow increase in kinase activity within 30 to 60 min of administration. These findings indicate that the p59fynkinase is activated within minutes of fertilization and may play a role in the egg activation process