Gamete recognition: sperm proteins that interact with the egg zona pellucida

The gamete recognition and initial binding processes that are crucial for t he success of mammalian fertilization are mediated by moieties associated w ith the extracellular matrix of the egg (the zona pellucida) and the head o f the fertilizing spermatozoon The zona proteins involved have been charact erized in some detail, with ZP3 and ZP2 generally acknowledged to be respon sible for the initial (primary) and secondary interactions, respectively. H owever, the identity of the complementary molecules on the sperm surface is highly contentious and remains unresolved. This review summarizes the curr ent knowledge and controversies in this research area. The credentials of s ome of the major candidates and the probability of the involvement of multi ple sperm receptors with different binding characteristics are assessed. Re solving this very important gap in our understanding is an essential prereq uisite to understanding fully the molecular and signal transduction events that cause sperm acrosomal exocytosis. Such fundamental information is also imperative for the development of novel forms of contraception (or sterili zation) targeted against specific sperm epitopes. Moreover, this informatio n may contribute to our understanding of certain types of male infertility.