The initial round of spermatogenesis in rats, occurring during the first to sixth weeks of postnatal life, is a key process in the development of sexual maturation and testicular competence. During this first round of spermatogenesis, a phase of increased apoptosis has been observed, culminating at 3 wk of age in the rat and often exhibiting a distinct localization, probably involving spermatocytes to a greater degree than spermatogonia. In the case of the adult testis, apoptosis occurs primarily in stages XII-XIV and I of spermatogenesis, during which differentiating type A spermatogonia, zygotene, both early and late pachytene spermatocytes, and meiotically dividing cells are eliminated by this process.
Such germ cell apoptosis in the immature testis appears to be necessary for the normal maturation process associated with spermatogenesis, but to our knowledge, its physiological significance has not yet been elucidated in detail. For transgenic mice in which Bax, a proapoptotic member of the Bcl-2 family of proteins, has been ‘‘knocked out,’’ the early wave of apoptosis is eliminated, resulting in the accumulation of spermatogonia and spermatocytes as well as infertility. proventil inhaler