Post-testicular modifications and maturation events occurring in the sperm

Abstract

In general, post-testicular maturation events occurring in sperm are controlled by factors expressed in the luminal fluid within the epididymis. This indicates that the sperm interacts with the ductal epithelial cells and that these interactions are continuously maintained throughout the passage of the sperm along the male and female reproductive tracts until the time of fertilization. The sperm maturation-related molecules secreted in the epididymis have recently been designated as epididymosomes (Sullivan et al. 2007). The direct and indirect interactions between sperm and the epithelial cells help to protect and stabilize the sperm components, and they suppress early activation of sperm motility and membrane fusion. These interactions facilitate the functional maturation of the sperm, leading to capacitation and the acrosome reaction. Functional impairment of the epithelial cells lining the male and female reproductive tracts causes obstruction of the epididymal passage and restricts the migration ability of the sperm; this has been demonstrated in cases of failed expression of the carnitine transporter (OCTN2) gene (Toshimori et al. 1999).