Activation of Src-family PTK activity at fertilization: role of the SH2 domain

The role of Src-family protein tyrosine kinases (SFKs) in egg activation has been established, in large part, by the observation that GST fusion proteins encoding the SH2 domain of Src or Fyn suppress the sperm-induced calcium transient and cause polyspermy in marine invertebrate eggs. These fusion proteins are thought to act as dominant-negative inhibitors of SFK function; however, the mechanism by which they work is not known. The objective of the present study was to test the hypothesis that fusion proteins containing the above SH2 domains prevent activation of SFKs in response to fertilization. A single cell assay was developed that allows estimation of SFK activity in eggs injected with the GST-Fyn-SH2 fusion protein. The results demonstrate that the GST-Fyn-SH2 fusion protein prevents fertilization induced stimulation of SFK activity at concentrations that also suppress the sperm-induced calcium transient in zebrafish eggs. (C) 2003 Elsevier Inc. All rights reserved.