Crisp proteins and sperm chemotaxis: discovery in amphibians and explorations in mammals.

Crisp proteins appear to play multiple roles in the life history of sperm. One of these roles is to act as a sperm chemoattractant. Allurin, a 21 kDa Crisp protein rapidly released from the egg jelly of at least two frogs, X. laevis and X. tropicalis, elicits directed motility in both homospecific and heterospecific sperm. In X. tropicalis, allurin is coded for by the newly documented Crisp A gene. Recently, the observation that allurin can also elicit chemotaxis in mouse sperm raises the question of whether allurin-like proteins might act as sperm chemoattractants in mammals. Although an allurin gene has yet to be documented in mammals, Crisp proteins truncated post-translationally appear to exist in both the male and female reproductive tract of mammals.