Thyroid Hormone Regulation of Sertoli Cell Proliferation may be Mediated through the Cell Cycle Inhibitors p27Kip1 and p21Cip1

The Sertoli cell is the somatic cell of the seminiferous epithelium that supports all stages of male germ cell development from spermatogonia to fully mature spermatozoa. Sertoli cells support a relatively fixed number of germ cells, though the specific number of germ cells supported by each Sertoli cell varies with species. Therefore, the number of Sertoli cells in the adult testis establishes the magnitude of sperni production, and factors that control Sertoli cell proliferation and establishment of the aduft population are of critical interest. Sertoli cell proliferation begins fetally and persists for variable periods after birth, depending on the species. In rats and mice Sertoli cells rapidly proliferate neonatally then ceases by about the time of weaning, thus establishing the adult Sertoli cell population.