Role of signaling pathways in regulating the capacitation of mammalian spermatozoa.

Mammalian testicular spermatozoa are immotile and incompetent for fertilization. They acquire motility during epididymal maturation and fertilizing ability during a second phase of maturation in the female reproductive tract, termed as capacitation. Capacitation was discovered independently by Austin and Cang in early 1950s and was defined as the obligate period of residency of spermatozoa in the female reproductive tract, which confers on the spermatozoa the ability to fertilize an oocyte. Over the years, the definition of capacitation has changed and it has been recognized as a complex phenomenon, which is correlated with changes associated with the spermatozoa in the female tract. These alterations in metabolism, intracellular ion concentration, membrane fluidity, intracellular pH, cAMP concentration and concentration of reactive oxygen species, ultimately make the spermatozoa fertilization-competent. The molecular basis of capacitation is poorly understood despite the fact that it is an important event preceding fertilization. This review presents our current understanding of the signaling events involved in the process of capacitation.