The Allure of Egg for Sperm

Abstract

Although sperm binding proteins on the inner layers of the extracellular matrix of vertebrate eggs have received a good deal of attention, sperm attractants in the outer jelly area have been detected in bioassays, but have not been identified. Now Olson et al. have purified a sperm chemoattractant from the egg jelly of Xenopus eggs. The protein, which they name allurin, turns out to have sequence similarity to members of the CRISP (cysteine-rich secretory protein) family. The new results indicate that CRISP family members escort or guide sperm on their voyage from the testes to the egg. The CRISP protein TPX-1 functions to promote adhesion of sperm to Sertoli cells in the testes. During maturation in the epididymis, sperm bind another set of CRISP proteins, the acidic epididymal secretory proteins, or AEGs. And finally, they encounter the new CRISP member, allurin, the first to be identified as a product of the female. The authors suggest that receptors on the surface of the sperm likely sense a gradient in the concentration of allurin that guides the sperm to their target. J. H. Olson, X. Xiang, T. Ziegert, A. Kittelson, A. Rawls, A. L. Bieber, D. E. Chandler. Allurin, a 21-kDa sperm chemoattractant from Xenopus egg jelly, is related to mammalian sperm-binding proteins. Proc. Natl. Acad. Sci. U.S.A. 98 , 11205-11210 (2001). [Abstract] [Full Text]