抄録
During amphibian fertilization, sperm bind to vitelline envelope (VE) that surrounds an egg, and undergo acrosome-reaction that enables sperm to penetrate the VE. Sperm-egg fusion activates an egg and resumes the cell cycle. Despite considerable lines of evidence, molecular mechanisms of fertilization remain to be elucidated because of the conflicting results. To understand molecular mechanism of sperm-egg ineraction, we have characterized a 26 kDa Ca2+-binding protein, Xenopus dicalcin, in Xenopus eggs. Xenopus dicalcin is localized prominently in the VE of Xenopus eggs, and dicalcin binds to protein cores of two constituent glycoproteins in a Ca2+-dependent manner. Since these two VE glycoproteins are considered to function as sperm-receptors, we tested the effect of dicalcin on sperm-VE binding and fertilization in vitro. Preincubation of eggs with recombinant dicalcin reduced the number of sperm that bound to VE as well as the efficiency of fertilization. In contrast, inhibition of intrinsic dicalcin by preincubation of anti-dicalcin antibody increased sperm-binding to VE and the efficiency of fertilization. These results indicated that dicalcin inhibits sperm-egg interaction and subsequent fertilization. [J Physiol Sci. 2008;58 Suppl:S141]
