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

As mammalian spermatozoa migrate through the epididymis, they acquire funct ionality characterized by the potential to express coordinated movement and the competence to undergo capacitation. The mechanisms by which spermatozo a gain the ability to capacitate during epididymal transit are poorly under stood. The purpose of this study was to investigate the impact of epididyma l maturation on the signal transduction pathways regulating tyrosine phosph orylation, because this process is thought to be central to the attainment of a capacitated state and expression of hyperactivated motility. Western b lot and immunocytochemical analyses demonstrated that epididymal maturation in vivo is associated with a progressive loss of phosphotyrosine residues from the sperm head. As cells pass from the caput to the cauda epididymis, tyrosine phosphorylation becomes 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 o f intracellular cAMP by phosphorylating tyrosine residues on the sperm tail . Immature caput spermatozoa were incapable of exhibiting this response, de spite the apparent availability of cAMP and protein kinase A. These finding s help to clarify the biochemical changes associated with the functional ma turation of spermatozoa during epididymal transit.