The role of testicular germ cell apoptosis during equine spermatogenesis
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
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
Advisor:Forrest, David W.; Varner, Dickson D.; Blanchard, Terry L.; Johnson, Larry
School:Texas A&M University
School Location:USA - Texas
Source Type:Master's Thesis
Keywords:apoptosis spermatogenesis stallion
Date of Publication:12/01/2005