Germ cell genotype controls cell cycle during spermatogenesis in the rat

Spermatogenesis is one of the most productive self-renewing systems in the body: on the order of 10(7) spermatozoa are produced daily per gram of test is tissue. In each mammalian species, the time required for completion of t he process is unique and unalterable. Because the process is supported by s omatic Sertoli cells, it has generally been thought that cell-cell interact ion between germ and Sertoli cells controls the duration of cell cycles and cellular organization. We have used the newly developed technique of sperm atogonial transplantation to examine which cell type(s) determines the rate at which germ cells proceed through spermatogenesis. Rat germ cells were t rans-planted into a mouse testis, and the mouse was killed 12.9-13 days aft er administration of a single dose of [H-3]thymidine. The most advanced rat cell type labeled was the pachytene spermatocyte at stages VI-VIII of the spermatogenic cycle. In animals given only rat cells, some endogenous sperm atogenesis of the mouse recovered. The most advanced labeled mouse cell typ es in recipients killed 12.9-13 days after administration of a single dose of [H-3]thymidine were meiotic cells or young spermatids, which is consiste nt with a spermatogenic cycle length comparable to the 8.6 days reported fo r the mouse. The same results were obtained if a mixture of rat and mouse c ells were transplanted. There existed two separate timing regimens for germ cell development in the recipient mouse testis; one of rat and one of mous e duration. Rat germ cells that were supported by mouse Sertoli cells alway s differentiated with cell cycle timing characteristic of the rat and gener ated the spermatogenic structural pattern of the rat, demonstrating that th e cell differentiation process of spermatogenesis is regulated by germ cell s alone.