Fig. 1.

Capacitation and fertilization. (A) As a result of capacitation, sperm develop hyperactivated motility, the ability to respond to chemotactic signals and acrosome reaction-inducing signals. Capacitated sperm penetrate the cumulus and reach the zona pellucida. Contact with the zona pellucida triggers acrosome reactions, permitting sperm to penetrate to the oocyte surface and fuse with the oocyte. Multiple steps in this process are controlled by capacitation. (B) Simple model of CFTR function during capacitation, in which HCO₃⁻ entry through CFTR stimulates an sAC/PKA cascade leading to the activation of downstream effectors and to capacitation. It is unresolved whether this pathway can fully account for the modulation of sperm function during capacitation and of how CFTR conductance is controlled to drive this cascade.