CAPACITATION AS A REGULATORY EVENT THAT PRIMES SPERMATOZOA FOR THE ACROSOME REACTION AND FERTILIZATION

Capacitation is defined as the series of transformations that spermato zoa normally undergo during their migration through the female genital tract, in order to reach and bind to the zona pellucida, undergo the acrosome reaction, and fertilize the egg. During this process, extensi ve changes occur in all sperm compartments (head and flagellum; membra ne, cytosol, cytoskeleton), factors originating from epididymal fluid and seminal plasma are lost or redistributed and membrane lipids and p roteins are reorganized; ion fluxes induce biochemical modifications a nd controlled amounts of reactive oxygen species are generated; sperma tozoa develop hyperactivated motility; and complex signal transduction mechanisms are initiated. The main purpose of capacitation is to ensu re that spermatozoa reach the eggs at the appropriate time and in the appropriate state to fertilize these eggs, by finely controlling the r ate of the changes necessary to prime spermatozoa and by activating al l the mechanisms needed for the subsequent acrosome reaction. The reve rsibility of some of the mechanisms leading to sperm capacitation may therefore be a very important aspect of the fine regulation and perfec t timing of this process.