Inherent to the mammalian spermatogenetic process, spermatozoa exiting the male gonad have features that make them unique in terms of structure and physiology. Through the meiotic process, the male germ cell becomes haploid and during late

GReD Laboratory, CNRS UMR 6293, INSERM U1013, Clermont Universit√©, 24, avenue des Landais, Aubiere 63171, France e-mail: [email protected]

A. Agarwal et al. (eds.), Studies on Men's Health and Fertility, Oxidative Stress 95

in Applied Basic Research and Clinical Practice, DOI 10.1007/978-1-61779-776-7_5, © Springer Science+Business Media, LLC 2012

spermatogenesis undergoes a spectacular program of cell differentiation in which among many changes the size of its nucleus is reduced to about one-tenth that in a somatic cell. This is permitted by the gradual replacement of testicular histones, first by transition proteins, and then by smaller positively charged molecules called protamines. This compacted state of the sperm chromatin signs the end of transcriptional activity in the male germ cell. In addition, supporting Sertoli cells engulf most of the residual cytoplasm of the male gamete as well as the subcellular organelles that normally sustain cell metabolic activity, especially protein translation. Finally, the late events of spermatogenesis also give this cell an engine and propeller in the form of a flagellar structure connected to the mitochondria-containing sperm midpiece. Although these dramatic structural modifications elegantly and efficiently serve the purpose of fertilization, they have direct consequences on the subsequent physiology of spermatozoa. The absence of transcription/translation events in this now silent cell makes it unable to elicit any kind of response when challenged by external and/or internal stressors. This nonresponsive situation is aggravated by the fact that being devoid of most of its cytoplasm the sperm cell is consequently devoid of the cytosolic tools (molecules and/or enzymes) that usually serve to protect somatic cells. Thus, at the end of spermatogenesis, spermatozoa are particularly fragile and have to rely on their environment both to mature and survive. One of the multiple tasks of the epididymis luminal environment is to provide efficient protection for transiting and stored spermatozoa.

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