Roles of Intracellular Cyclic AMP Signal Transduction in the Capacitation and Subsequent Hyperactivation of Mouse and Boar Spermatozoa

It is not until accomplishment of a variety of molecular changes during the transitthrough the female reproductive tract that mammalian spermatozoa are capable ofexhibiting highly activated motility with asymmetric whiplash beating of the flagella(hyperactivation) and undergoing acrosomal exocytosis in the head (acrosomereaction). These molecular changes of the spermatozoa are collectively termedcapacitation and promoted by bicarbonate, calcium and cholesterol acceptors. Suchcapacitation-promoting factors can stimulate intracellular cyclic AMP (cAMP) signaltransduction in the spermatozoa. Meanwhile, hyperactivation and the acrosome reactionare essential to sperm fertilization with oocytes and are apparently triggered by asufficient increase of intracellular Ca²⁺ in the sperm flagellum and head,respectively. Thus, it is necessary to investigate the relationship between cAMPsignal transduction and calcium signaling cascades in the spermatozoa for the purposeof understanding the molecular basis of capacitation. In this review, I cover updatedinsights regarding intracellular cAMP signal transduction, the acrosome reaction andflagellar motility in mammalian spermatozoa and then account for possible roles ofintracellular cAMP signal transduction in the capacitation and subsequenthyperactivation of mouse and boar spermatozoa.