Developmental Biology, Volume 256, Issue 2 , 15 April 2003, Pages 367-378
Andrew F. Giusti (a)(b)(c)(1)(2), Forest J. O'Neill (c)(1), Kyo Yamasu (d), Kathy R. Foltz (c) and Laurinda A. Jaffe (a)(b)
(a) Department of Physiology, University of Connecticut Health Center, Farmington, CT 06032, USA
(b) Marine Biological Laboratory, Woods Hole, MA 02543, USA
(c) Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, CA 93106, USA
(d) Department of Regulation Biology, Saitama University, Saitama, Saitama 338-8570, Japan
Received 16 August 2002; revised 3 December 2002; accepted 11 January 2003; Available online 8 March 2003.
(1) These authors contributed equally to this work.
(2) Present address: Remedyne Corporation, 2219 Bath Street, Santa Barbara, CA 93105, USA.
Egg activation at fertilization requires the release of Ca2+ from the egg's endoplasmic reticulum, and recent evidence has indicated that a Src family kinase (SFK) may function in initiating this signaling pathway in echinoderm eggs. Here, we identify and characterize a SFK from the sea urchin Strongylocentrotus purpuratus, SpSFK1. SpSFK1 RNA is present in eggs, and an antibody made against a SpSFK1 peptide recognizes an ~58-kDa egg membrane-associated protein in eggs of S. purpuratus as well as another sea urchin Lytechinus variegatus. Injection of both species of sea urchin eggs with dominant-interfering Src homology 2 domains of SpSFK1 delays and reduces the release of Ca2+ at fertilization. Injection of an antibody against SpSFK1 into S. purpuratus eggs also causes a small increase in the delay between sperm-egg fusion and Ca2+ release. In contrast, when injected into eggs of L. variegatus, this same antibody has a dramatic stimulatory effect: it causes PLC-dependent Ca2+ release like that occurring at fertilization. Correspondingly, in lysates of L. variegatus eggs, but not S. purpuratus eggs, the antibody stimulates SFK activity. Injection of L. variegatus eggs with another antibody that recognizes the L. variegatus egg SFK also causes PLC-dependent Ca2+ release like that at fertilization. These results indicate that activation of a Src family kinase present in sea urchin eggs is necessary to cause Ca2+ release at fertilization and is capable of stimulating Ca2+ release in the unfertilized egg via PLC, as at fertilization.
Author Keywords: Fertilization; Src family kinase; Calcium; Egg activation
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