The role of testicular germ cell apoptosis during equine spermatogenesis
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Apoptosis in testicular germ cells has been demonstrated in many species. Features of apoptosis reported in other species were used to confirm use of the TUNEL assay in stallion testes. Eight stallions with normal testicular size and semen quality were evaluated to determine the germ cell types and stages where apoptosis most commonly occurs. Mean numbers of TUNEL-positive germ cells per 100 Sertoli cell nuclei were highest in stages IV and V of the seminiferous epithelial cycle corresponding to meiotic divisions of primary spermatocytes and mitotic proliferation of B1 and B2 spermatogonia. Round and elongated spermatids were labeled less frequently by the TUNEL assay. To examine the relationships between germ cell apoptotic rate and spermatogenic efficiency, seminal traits were assessed to classify stallions into normal or reduced quality semen groups. Apoptotic rates were higher for stages IV-VI and stage VIII seminiferous tubules in stallions with reduced semen quality. Daily sperm production (DSP) per gram and per testis were lower for stallions with reduced semen quality. Regression analyses revealed negative linear relationships for germ cell apoptotic rate with DSP/g, DSP/testis, daily sperm output, progressively motile sperm and morphologically normal sperm in ejaculates. Mean circulating concentrations of inhibin were lower for stallions ejaculating reduced quality semen. Apoptotic rate was negatively correlated with concentrations of inhibin and estradiol-17b and positively correlated with concentrations of LH and FSH. To study germ cell apoptosis and formation of the Sertoli cell barrier during the initiation of spermatogenesis, tubule development was classified based on lumen score. Formation of a seminiferous tubule lumen was consistent with events leading to development of a Sertoli cell barrier. A primary wave of apoptosis removed early differentiating germ cell types prior to the formation of a tubule lumen facilitating both the formation of a tubule lumen and a Sertoli cell barrier. A second wave of apoptosis occurred after the formation of a lumen but before seminiferous tubule cross-sections contained a full complement of germ cells. In conclusion, apoptosis is an essential mechanism during normal spermatogenesis. Apoptosis also accounts for low numbers of normal sperm seen in the ejaculates of some stallions.
Heninger, Noah Leland, III (2005). The role of testicular germ cell apoptosis during equine spermatogenesis. Doctoral dissertation, Texas A&M University. Texas A&M University. Available electronically from