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Abstract
The final stages of sperm differentiation occur outside the gonad, in the epididymal
tubule. These last maturation steps, essential to the quality of spermatozoa, are
not under the genomic control of the germ cells. A series of sequential interactions
with the epididymal fluid, mostly specific proteins present in the lumen of different
regions, are believed to induce the final steps of sperm maturation. In order to provide
the luminal changes required for this maturation to occur, the epithelium may resort
to two basic mechanisms: absorption and secretion. Far from being a uniform channel,
the epididymal duct is a canal with highly specialized regional differentiation of
its epithelial ultrastructure and its secretory and absorptive functions. This review
focuses on the ultrastructural characteristic of the epithelial cells, their specific
secretory activity according to the epididymal regions and their eventual role in
sperm maturation of the boar. The chronology of the changes that occur in and on the
sperm and in the surrounding environment are described. Relationships between the
highly regionalized epididymal activities, sperm characteristics linked to their survival
and fertility potential are also presented in this review.