Quantitative Analysis of Spermatogenesis and Apoptosis in the Common Marmoset (Callithrix jacchus) Reveals High Rates of Spermatogonial Turnover and High

Spermatogenesis is characterized by the succession in time and space of specific germ cell associations (stages). There can be a single stage (e.g., rodents and some macaques) or more than one stage (e.g., chimpanzee and human) per tubular cross section. We analyzed the organization of the seminiferous epi-thelium and quantified testicular germ cell production and ap-optosis in a New World primate, the common marmoset (Cal-lithrix jacchus). Tubule cross sections contained more than one stage, and the human six-stage system could be applied to mar-moset spermatogenesis. Stereological (optical disector) analysis (n 5 5) revealed high spermatogenic efficiency during meiosis and no loss of spermatids during spermiogenesis. The conversion of type A to type B spermatogonia was several-fold higher than that reported for other primates. Highest apoptotic rates were found for S-phase cells (20%) and 4C cells (15%) by flow cy-tometric analysis (n 5 6 animals); histological analysis con-firmed spermatogonial apoptosis. Haploid germ cell apoptosis was,2%. Marmoset spermatogenesis is very efficient and in-volves substantial spermatogonial proliferation. The prime de-terminants of germ cell production in primates appear to be proliferation and survival of spermatogonia rather than the ef-ficiency of meiotic divisions. Based on the organizational simi-larities, common marmosets could provide a new animal model for experimental studies of human spermatogenesis. apoptosis, gametogenesis, meiosis, spermatogenesis, teste