Regulation of protein phosphorylation during sperm capacitation

Abstract

Work from several laboratories is beginning to elucidate the molecular basis of sperm capacitation, leading to a unified model of this extratesticular maturational event. Several questions of considerable importance must now be addressed. First, how is cholesterol movement from the sperm plasma membrane regulated, and how does that movement initiate intracellular signaling? Second, what is the mechanism by which the cAMP/PK- A pathway is stimulated, and how does stimulation of this pathway lead to cross talk and up-regulation of protein tyrosine phosphorylation? Finally, what is the nature of the substrates that are phosphorylated on tyrosine residues, and how does the phosphorylation of these substrates impact on the major end-points of capacitation, e.g., hyperactivation of motility, competence to undergo a regulated acrosome, reaction, and fertilization? Such signaling processes underlying capacitation appear to be quite unique and therefore warrant continued investigation.