Cellular biology of capacitation and the acrosome reaction

For successful fertilization in mammals, spermatozoa must complete capacitation and then undergo the acrosome reaction, an exocytotic process that allows cells to bind to and then penetrate the zona pellucida. After penetration has been achieved, acrosome-reacted cells are capable of fusing with the oocyte plasma membrane, thereby activating the oocyte and setting in train the completion of the second meiotic division and the initiation of the metabolic events that will sustain early embryonic development. Current evidence indicates that mechanisms controlling the intracellular Ca2+ concentration [Ca2+]i play pivotal roles in controlling sperm fertilizing ability; it is these mechanisms which will be discussed here.