Regulation of the starfish sperm acrosome reaction by cGMP, pH, cAMP and Ca2+
Published: 1 July 2008
Midori Matsumoto1,*, Osamu Kawase1,2, M. Sadiqul Islam1, Masahiro Naruse1, Shin-Nosuke Watanabe1, Riho Ishikawa1 and Motonori Hoshi3
1Department of Biosciences and Informatics, Keio University Kouhoku-ku, Yokohama, 2Obihiro University of Agriculture and Veterinary Medicine, Inada-cho, Obihiro, Hokkaido and 3The Open University of Japan, Mihama-ku, Chiba City, Japan
In the starfish, Asterias amurensis, three components in the jelly coat of eggs, namely acrosome reaction-inducing substance (ARIS), Co-ARIS and asterosap, act in concert on homologous spermatozoa to induce the acrosome reaction (AR). Molecular recognition between the sperm surface molecules and the egg jelly molecules must underlie signal transduction events triggering the AR. Asterosap is a sperm-activating molecule, which stimulates rapid synthesis of intracellular cGMP, pH and Ca2+. This transient elevation of Ca2+ level is caused by a K+-dependent Na+/Ca2+ exchanger, and the increase of intracellular pH is sufficient for ARIS to induce the AR. The concerted action of ARIS and asterosap could induce elevate intracellular cAMP levels in starfish sperm and the sustained increase in [Ca2+], which is essential for the AR. The signaling pathway induced by these factors seems to be synergistically regulated to trigger the AR in starfish sperm.
invertebrate fertilization, cyclic nucleotides, signal transduction, ion channel, spermatozoa