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SH2 domain-mediated activation of an SRC family kinase is not required to initiate Ca²⁺ release at fertilization in mouse eggs

Department of Cell Biology, University of Connecticut Health Center, 263 Farmington Avenue, Farmington, Connecticut 06032, USA

Correspondence should be addressed to L M Mehlmann or L A Jaffe; Email: lmehlman{at}neuron.uchc.edu or ljaffe{at}neuron.uchc.edu

SRC family kinases (SFKs) function in initiating Ca²⁺ release at fertilization in several species in the vertebrate evolutionary line, but whether they play a similar role in mammalian fertilization has been uncertain. We investigated this question by first determining which SFK proteins are expressed in mouse eggs, and then measuring Ca²⁺ release at fertilization in the presence of dominant negative inhibitors. FYN and YES proteins were found in mouse eggs, but other SFKs were not detected; based on this, we injected mouse eggs with a mixture of FYN and YES Src homology 2 (SH2) domains. These SH2 domains were effective inhibitors of Ca²⁺ release at fertilization in starfish eggs, but did not inhibit Ca²⁺ release at fertilization in mouse eggs. Thus the mechanism by which sperm initiate Ca²⁺ release in mouse eggs does not depend on SH2 domain-mediated activation of an SFK. We also tested the small molecule SFK inhibitor SU6656, and found that it became compartmentalized in the egg cytoplasm, thus suggesting caution in the use of this inhibitor. Our findings indicate that although the initiation of Ca²⁺ release at fertilization of mammalian eggs occurs by a pathway that has many similarities to that in evolutionarily earlier animal groups, the requirement for SH2 domain-mediated activation of an SFK is not conserved.

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