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© The Rockefeller University Press, 0021-9525/1997//1303 $5.00
The Journal of Cell Biology, Volume 138, Number 6, , 1997 1303-1311

Article

Calcium Release at Fertilization in Starfish Eggs Is Mediated by Phospholipase C{gamma}



David J. Carroll*, Chodavarapu S. Ramarao*, Lisa M. Mehlmann*, Serge Roche{ddagger}, Mark Terasaki*, and Laurinda A. Jaffe*

* Department of Physiology, University of Connecticut Health Center, Farmington, Connecticut 06032; and {ddagger} Institut National de la Santé et de la Recherche Medicale CJF9207, Faculté de Pharmacie 15, F-34060 Montpellier, France

Although inositol trisphosphate (IP3) functions in releasing Ca2+ in eggs at fertilization, it is not known how fertilization activates the phospholipase C that produces IP3. To distinguish between a role for PLC{gamma}, which is activated when its two src homology-2 (SH2) domains bind to an activated tyrosine kinase, and PLCβ, which is activated by a G protein, we injected starfish eggs with a PLC{gamma} SH2 domain fusion protein that inhibits activation of PLC{gamma}. In these eggs, Ca2+ release at fertilization was delayed, or with a high concentration of protein and a low concentration of sperm, completely inhibited. The PLC{gamma}SH2 protein is a specific inhibitor of PLC{gamma} in the egg, since it did not inhibit PLCβ activation of Ca2+ release initiated by the serotonin 2c receptor, or activation of Ca2+ release by IP3 injection. Furthermore, injection of a PLC{gamma} SH2 domain protein mutated at its phosphotyrosine binding site, or the SH2 domains of another protein (the phosphatase SHP2), did not inhibit Ca2+ release at fertilization. These results indicate that during fertilization of starfish eggs, activation of phospholipase C{gamma} by an SH2 domain-mediated process stimulates the production of IP3 that causes intracellular Ca2+ release.

Abbreviations used in this paper: GST, glutathione-S-transferase; IP3, inositol trisphosphate; PLC, phospholipase C; PIP2, phosphatidylinositol 4,5-bisphosphate.

Address all correspondence to David J. Carroll or Laurinda A. Jaffe, Department of Physiology, University of Connecticut Health Center, Farmington, CT 06032. Tel.: (860) 679-2661. Fax: (860) 679-1661. E-mail: ljaffe{at}neuron.uchc.edu

D.J. Carroll's present address is Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, CA 93106. e-mail: carroll{at}lifesci.lscf.ucsb.edu


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