In addition, pronounced staining of gonocytes or spermatogonia, with no stage-de-pendency, was present at all ages. Because these groups of cells were also discovered to be particularly prone to apo-ptosis, it appears likely that in the immature testis, Bax regulates apoptosis in two distinct types of germ cells (i.e., the stem cells and midpachytene spermatocytes).
This conclusion is rather interesting in light of the disturbance in spermatogenesis associated with Bax. During the pubertal development of mice containing a targeted deletion of the antiapoptotic Bax, overproduction of spermatogonia, hyperplasia of the seminiferous tubule, and a block in the normal maturation of preleptotene spermatocytes are observed, resulting in later atrophy of the seminiferous epithelium. The midpachytene and prelep-totene spermatocytes are nursed by the same Sertoli cell during spermatogenic stages VII-VIII (Fig. 3) in both the rat and mouse. Thus, some correlation may exist between apoptosis in midpachytene spermatocytes and further maturation of preleptotene spermatocytes. The observation here that expression of Bax is localized to an advanced type of spermatocyte may explain why spermatogenesis in the Bax-deficient mouse can progress to such a relatively advanced state before permanent disruption of its organization and induction of Bax-independent apoptosis.