Sperm Capacitation and Acrosome Reaction in Mammalian Sperm

Physiological changes that endow mammalian sperm with fertilizing capacity are known as sperm capacitation. As part of capacitation, sperm develop an asymmetrical flagellar beating known as hyperactivation and acquire the ability to undergo the acrosome reaction. Together, these processes promote fertilizing competence in sperm. At the molecular level, capacitation involves a series of signal transduction events which include activation of cAMP-dependent phosphorylation pathways, removal of cholesterol, hyperpolarization of the sperm plasma membrane, and changes in ion permeability. In recent years, new technologies have aided in the study of sperm signaling molecules with better resolution, at both spatial and temporal levels, unraveling how different cascades integrate and cooperate to render a fertilizing sperm. Despite this new information, the molecular mechanisms connecting capacitation with acrosomal exocytosis and hyperactivation are not well understood. This review brings together results obtained in mammalian species in the field of sperm capacitation with special focus on those pathways involved in the preparation to undergo the acrosomal reaction.