Clinical Ramifications of Apoptosis in the Human Testis

Abstract

In mammals, multiplication of germ cells in the testis is always accompanied by degeneration of some of the proliferating cells. During spermatogenesis, germ cell death occurs spontaneously at various phases of germ cell development, and in consequence the seminiferous epithelium yields fewer spermatozoa than would be anticipated from spermatogonial proliferations (1–3). Germ cell deletion during normal spermatogenesis has been estimated to result in the loss of up to 75% of the potential numbers of mature sperm cells in the adult testis (2, 4, 5). Detailed analyses of germ cell degeneration have been published (1–3, 5–7); morphometric analyses of semithin sections of perfusion-fixed testes have indicated that the loss of germ cells is greatest during the mitoses of type A2, A3, and A4 spermatogonia and during the first meiotic division. No degeneration occurs in type Al spermatogonia, or in intermediate of type B spermatogonia (7, 8). The mitotic and meiotic division take place at distinct stages of the cycle of the seminiferous epithelium (often referred to as the spermatogenic cycle). Therefore, spontaneously degenerating cells can normally be found only at certain stages: at stages II to VII few if any cells degenerate, whereas stages XIII to I show considerable germ cell degeneration (3, 7, 8).