Epididymal Sperm Transport and Fertilization

Abstract

In order to acquire progressive motility, complete maturation and compaction of chromatin, regulate their volume, and acquire molecules necessary for fertilization, spermatozoa released from the testis must transit through the epididymis, a long convoluted tubule that connects the efferent ducts to the vas deferens, where they undergo several molecular modifications. Sperm modifications occurring during transit in the three segments that compose the epididymis (caput, corpus, and cauda) are accomplished by epididymal epithelium secretions, including epididymosomes (extracellular microvesicles enriched in cholesterol and proteins), miRNA, and other macromolecules. Epididymal pH and electrolytes composition of the luminal fluid are also important for a correct sperm maturation. Epididymal secretions are regulated by a variety of factors, mostly androgens and estrogens, to create a different luminal environment in each epididymal segment supporting progressive sperm maturation and allowing maintenance of sperm viability and motility during storage in the cauda. Finally, epididymal contraction allows sperm emission at ejaculation. Overall, the role of epididymis on the development of sperm functions is essential for male reproduction, and alterations in any of its functions may lead to subfertility or infertility. Due to its importance for a successful male reproductive function, the epididymis appears to be a promising target for post-testicular male contraception.