Development, Vol 120, Issue 12 3463-3472, Copyright © 1994 by Company of Biologists

JOURNAL ARTICLES

Signal transduction during shrimp oocyte activation by extracellular Mg2+: roles of inositol 1,4,5- trisphosphate, tyrosine kinases and G-proteins

L. L. Lindsay and W. H. Clark, Jr

Oocytes of the shrimp Sicyonia ingentis are naturally activated upon contact with seawater Mg2+. We investigated the mechanism of Mg2+-induced intracellular Ca2+ release and cortical contraction through treatment of oocytes with various activators and inhibitors of signal transduction pathways. Injection of oocytes with the second messenger inositol 1,4,5-trisphosphate resulted in an immediate rise in intracellular Ca2+ and normal cortical contraction. By contrast, injection of the GTP analog guanosine 5'-O-(3'-thiotriphosphate) to activate G-proteins did not affect intracellular Ca2+ levels but did induce cortical contraction. Tyrosine kinase inhibitors (tyrphostin and staurosporine) suppressed the Mg2+-induced Ca2+ rise and contraction, and the inhibition could be overcome by injection with inositol 1,4,5-trisphosphate. Immunoprecipitation of phosphotyrosine- containing proteins from oocyte lysates showed that a 110x103 Mr protein was phosphorylated within seconds of oocyte exposure to Mg2+, and tyrphostin inhibited the phosphorylation of this protein. Pretreatment of oocytes with the protease trypsin abolished their ability to release Ca2+ in response to extracellular Mg2+, indicating a role for a cell surface protein during normal oocyte activation; treated oocytes could be rescued by inositol 1,4,5-trisphosphate injection. These results suggest that S. ingentis oocytes are activated through a Mg2+ 'receptor' which activates a tyrosine kinase and results in the production of inositol 1,4,5-trisphosphate to release intracellular Ca2+ stores and induce cortical contraction. A G-protein/GTPase may also be involved in the pathway leading to cortical contraction.

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				R Deguchi, K Osanai, and M Morisawa Extracellular Ca2+ entry and Ca2+ release from inositol 1,4,5-trisphosphate-sensitive stores function at fertilization in oocytes of the marine bivalve Mytilus edulis Development, January 11, 1996; 122(11): 3651 - 3660. [Abstract] [PDF]