Control of the annual testicular cycle of the marbled-newt by p53, p21, and Rb gene products

p53, p21, and Rb are proteins with an important role in cell-cycle control. The expression and distribution of these gene products and the apoptotic rate were studied in the marbled-newt testis along the annual cycle to know the role of these factors in the control of spermatogenesis and glandular tissue formation. The study was carried out using Western blot analysis and immunohistochemistry. The results differed from those, previously reported in mammals showing constant spermatogenesis. Greater expression of p53 and p21 was found in the quiescence period and was detected in PCGs (primordial germ cells), spermatogonia, follicular, interstitial cells, and glandular tissue. Greater expression of Rb and phosph-Rb was present in the proliferation period, in PCGs, and spermatogonia. Apoptosis was only detected in secondary spermatogonia (quiescence and spermiogenesis periods) and primary spermatocytes (proliferation and spermiogenesis periods). In the quiescence period, the increase in p53 expression activates p21 expression, which inhibits Rb phosphorylation and arrests the cell cycle in G1. In the proliferation period and, in a lesser degree, in the spermiogenesis period, the expressions of p53 and p21 decrease and phosph-Rb increases, enhancing cell proliferation. These gene products do not seem to be related to apoptosis.