Calcium Release at Fertilization in Starfish Eggs Is Mediated by Phospholipase Cγ |
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Authors: | David J Carroll Chodavarapu S Ramarao Lisa M Mehlmann Serge Roche Mark Terasaki and Laurinda A Jaffe |
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Institution: | *Department of Physiology, University of Connecticut Health Center, Farmington, Connecticut 06032; and ?Institut National de la Santé et de la Recherche Medicale CJF9207, Faculté de Pharmacie 15, F-34060 Montpellier, France |
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Abstract: | 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 PLCγ, 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 PLCγ SH2 domain fusion protein that inhibits activation of PLCγ. 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 PLCγSH2 protein is a specific inhibitor of PLCγ 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 PLCγ 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 Cγ by an SH2 domain-mediated process stimulates the production of IP3 that causes intracellular Ca2+ release. |
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