Role of Apoptosis and Cell Proliferation in the Testicular Dynamics of Seasonal Breeding Mammals: A Study in the Iberian Mole, Talpa occidentalis1

Apoptosis and cell proliferation are two important cellular processes known to be involved in the normal functioning of the testis in nonseasonally breeding mammals, but there is some controversy concerning their roles in the gonads of males from seasonally breeding species. We have studied the processes of apoptosis and cell proliferation in the testes of males of the Iberian mole (Talpa occidentalis), a species showing a strict seasonal reproduction pattern. Both males and females are sexually active during the winter and completely inactive in the summer, with two transitional periods, in the autumn and the spring. Adult males from these four reproductive stages were captured, and their testes were immunohistochemically studied for the presence of apoptotic and proliferation molecular markers as well for other testicular and meiotic cell-specific markers. We found that apoptosis varies in a season-dependent manner in the testes of male moles, affecting mainly late zygotene and pachytene cells during the period of sexual inactivity, but it does not differentially affect the number of Sertoli cells. More interestingly, apoptosis is not responsible for the massive germ-cell depletion occurring during mole testis regression. In addition, a wave of spermatogonial cell proliferation appears to restore the number of spermatogonia lost during the period of testis inactivity. According to current knowledge, data from moles indicate that mammals do not form a homogeneous group regarding the mechanisms by which the cell-content dynamics are regulated in the testes of males from seasonally breeding species.