Short description:

The purpose of the epididymis remains mysterious and the reasons for the sperm’s extensive journey is perplexing. If a sperm were human-sized, its week or two trek through the epididymis would be ~2,750 kilometers. Testicular sperm, and those collected from the upper epididymal regions from both mice and men are competent for reproduction when injected using intracytoplasmic sperm injection (ICSI), demonstrating their reproductive competence. With advances in assisted reproductive technologies (ART), men without any sperm in their ejaculates are able to conceive through the application of sophisticated sperm-retrieval protocols and ICSI from epididymal sources. ART success rates are higher with epididymal sperm than with testicular ones, suggesting post-testicular maturation. Noteworthy investigations using primarily bull or mouse epididymal isolates have found important regional differences in gene expression patterns, proteins, and post-translational modifications, as well as epididymosomes, important vesicles found in the epididymal lumen. Here we show sperm maturation occurring within the epididymis involves a previously unappreciated event. The sperm centriole-pair persist with the sperm after release into the lumen of testicular tubules and as they travel into the epididymis head. Nearly all sperm have centrioles in the caput, and first the distal and then the proximal centrioles are destroyed as they pass through the corpus to reach the cauda epididymis on their transit to the vas deferens. The destruction of these centrioles is neither accelerated in young males nor slowed in older ones, though individual variabilities are found. Further, caput sperm with intact centriole pairs are unable to nucleate microtubules when introduced into metaphase-II oocytes. The term ‘Zombie centrioles’ recently introduced by Khire et al., seems apt to describe these non-functional centrioles awaiting their disassembly in the male reproductive tract.

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Abstract taken from PubMed

Abstract:

The fertilizing sperm's lengthiest unchartered voyage is through the longest, least-investigated organ in a man's body - the Epididymis. Over six meters long in men, ~80 meters in stallions and over one-hundred times a mouse's body length, there are few functions known aside from sperm storage and nutrition. While spermatogenesis is completed in the testes, here we demonstrate sperm centriole reduction occurs within the epididymis. Investigations of GFP-CENTR mice and controls demonstrate both the presence of centriole pairs in the upper caput region of the epididymis and, the destruction, first, of the distal and, then, of the proximal centriole as the sperm transits to the cauda and vas deferens in preparation for its climactic release. These centrioles can neither recruit γ-tubulin nor nucleate microtubules when eggs are inseminated or microinjected, yet numerous maternally-nucleated cytasters are found. These sperm centrioles appear as vestigial basal bodies, destroyed in the mid-to-lower corpus. Post-testicular sperm maturation, in which sperm centrioles found in the caput are destroyed prior to ejaculation, is a newly discovered function for the epididymis.

Link to the paper on PubMed