Retinoids induce differentiation of type A spermatogonia in vitro: organ culture of mouse cryptorchid testes.

To study the effects of retinoids on testicular germ cell differentiation, especially on stem cells, artificially induced cryptorchid testes of adult mice were cultured in vitro inasmuch as they contain only stem cells, type A spermatogonia. We report here that retinol, retinal, retinol acetate, even retinoic acid, activated cell division in type A spermatogonia and stimulated them to differentiate. These findings are the first demonstration of the in vitro induction of early stage of spermatogenesis by retinoids and also retinoic acid, which is considered to be a biochemically inactive compound for mammalian testicular function.