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.

Most testicular features undergo major circannual variation in seasonal breeding species. Although the ultimate cause of these variations is known to be the photoperiod in most cases, very little is known about the genetic mechanisms by which these changes are modulated in the testis. Many genes involved in testis development are known to be expressed in the adult testis as well. Since these genes encode genetic regulatory factors, it is reasonable to suspect that they could play some role in the control of the adult testis function. Using immunological detection techniques and RT-Q-PCR, we have studied the spatio-temporal expression pattern of WT1, SF1, SOX9, AMH, and DMRT1 in 4 representative stages of the circannual cycle of the testes of Talpa occidentalis, a mole species with strict seasonal reproduction. AMH is not expressed at any stage of the cycle, showing that inactive adult testes are functionally different from pre-pubertal, juvenile ones. The continuous presence of primary spermatocytes may explain the permanent repression of AMH in the mole testis. WT1 and SF1 are down-regulated and SOX9 is up-regulated in regressed mole testes, suggesting that the modulation of the expression of these genes may be involved in the control of circannual gonad variation. Furthermore, SOX9 and DMRT1 show clear spermatogenic stage-dependent expression patterns. Both genes are expressed more intensely during the proliferative stages of spermatogonia, although SOX9 expression is limited to Sertoli cells, whereas DMRT1 is expressed in both Sertoli and spermatogonial cells. Available data suggest that intratesticular levels of testosterone could regulate circannual spermatogenic variations of seasonal breeders by modulating the expression of DMRT1 to control spermatogonial proliferation.