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

The gamete recognition and initial binding processes that are crucial for the success of mammalian fertilization are mediated by moieties associated with the extracellular matrix of the egg (the zona pellucida) and the head of the fertilizing spermatozoon. The zona proteins involved have been characterized in some detail, with ZP3 and ZP2 generally acknowledged to be responsible for the initial (primary) and secondary interactions, respectively. However, the identity of the complementary molecules on the sperm surface is highly contentious and remains unresolved. This review summarizes the current knowledge and controversies in this research area. The credentials of some of the major candidates and the probability of the involvement of multiple sperm receptors with different binding characteristics are assessed. Resolving this very important gap in our understanding is an essential prerequisite 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 sterilization) targeted against specific sperm epitopes. Moreover, this information may contribute to our understanding of certain types of male infertility.