Impact of epididymal maturation on the tyrosine phosphorylation patterns exhibited by rat spermatozoa

As mammalian spermatozoa migrate through the epididymis, they acquire functionality characterized by the potential to ex-press coordinated movement and the competence to undergo capacitation. The mechanisms by which spermatozoa gain the ability to capacitate during epididymal transit are poorly under-stood. The purpose of this study was to investigate the impact of epididymal maturation on the signal transduction pathways regulating tyrosine phosphorylation, because this process is thought to be central to the attainment of a capacitated state and expression of hyperactivated motility. Western blot and im-munocytochemical analyses demonstrated that epididymal mat-uration in vivo is associated with a progressive loss of phospho-tyrosine residues from the sperm head. As cells pass from the caput to the cauda epididymis, tyrosine phosphorylation be-comes confined to a narrow band at the posterior margin of the acrosomal vesicle. Epididymal maturation of rat spermatozoa was also associated with an acquired competence to respond to high levels of intracellular cAMP by phosphorylating tyrosine residues on the sperm tail. Immature caput spermatozoa were incapable of exhibiting this response, despite the apparent avail-ability of cAMP and protein kinase A. These findings help to clarify the biochemical changes associated with the functional maturation of spermatozoa during epididymal transit. sperm, sperm capacitation/acrosome reactio