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Front. Endocrinol. | doi: 10.3389/fendo.2018.00059

Characteristics of the Epididymal Luminal Environment Responsible for Sperm Maturation and Storage

 Wei Zhou1,  Geoffry N. De Iuliis1, Matthew D. Dun2, 3 and  Brett Nixon1*
  • 1School of Environmental and Life Sciences, University of Newcastle, Australia
  • 2Faculty of Health and Medicine, University of Newcastle, Australia
  • 3School of Biomedical Sciences and Pharmacy, Hunter Medical Research Institute, Australia

The testicular spermatozoa of all mammalian species are considered functionally immature owing to their inability to swim in a progressive manner and engage in productive interactions with the cumulus oocyte complex. The ability to express these key functional attributes develops progressively during the cells’ descent through the epididymis, a highly specialized ductal system that forms an integral part of the male reproductive tract. The functional maturation of the spermatozoon is achieved via continuous interactions with the epididymal luminal microenvironment and remarkably, occurs in the complete absence of de novo gene transcription or protein translation. Compositional analysis of the luminal fluids collected from the epididymis of a variety of species has revealed the complexity of this milieu, with a diversity of inorganic ions, proteins, and small non-coding RNA transcripts having been identified to date. Notably, both the quantitative and qualitative profile each of these different luminal elements display substantial segment-to-segment variation which in turn contribute to the regionalized functionality of this long tubule. Thus, spermatozoa acquire functional maturity in the proximal segments before being stored in a quiescent state in the distal segment in preparation for ejaculation. Such marked division of labor is achieved via the combined secretory and absorptive activity of the epithelial cells lining each segment. Here, we review our current understanding of the molecular mechanisms that exert influence over the unique intraluminal environment of the epididymis, with a particular focus on vesicle-dependent mechanisms that facilitate intracellular communication between the epididymal soma and maturing sperm cell population.

Keywords: Epididymis, Sperm Maturation, Intracellular communication, Protein trafficking, apocrine secretion, merocrine secretion, epididymosome, dynamin

Received: 14 Dec 2017; Accepted: 09 Feb 2018.

Edited by:

Marc Yeste, University of Girona, Spain

Reviewed by:

Robert Sullivan, Laval University, Canada
Jean-Louis DACHEUX, UMR7247 Physiologie de la reproduction et des comportements (PRC), France  

Copyright: © 2018 Zhou, De Iuliis, Dun and Nixon. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Prof. Brett Nixon, University of Newcastle, School of Environmental and Life Sciences, Callaghan, NSW, Australia, brett.nixon@newcastle.edu.au