Mammalian sperm-egg recognition: does fertilin beta have a major role to play?

The advent of simple in vitro fertilisation techniques has provided the reproductive biologist with an invaluable system for assaying sperm fertilising ability. In particular, they provide a useful way of identifying and characterising gamete-specific proteins that play a role in sperm-egg interactions, and in recent years, a growing number of sperm surface proteins have been identified that appear to be involved in these processes. Fertilin beta was one of the first sperm membrane proteins to be implicated in egg interactions and it has been proposed that this is mediated by means of binding of its disintegrin-like domain to cognate integrin receptors on the egg plasma membrane. A recent paper in Science by Cho and colleagues [Cho et al. 1998. Fertilisation defects in sperm from mice lacking fertilin beta. Science 281: 1857-1859 (Ref. 1)] provides preliminary data on a fertilin beta knockout mouse. Whilst fertilin beta null males had greatly reduced fertility, somewhat surprisingly, this could be largely attributed to causes other than impaired binding to the egg plasma membrane.