Estradiol-17β Stimulates the Renewal of Spermatogonial Stem Cells in Males

In this work, we examined the functions of the female hormone “estrogen” on spermatogenesis of the Japanese eel (Anguilla japonica).Estradiol-17β (E2), a natural estrogen in vertebrates, was present in the serum and its receptor was expressed in the testis during the whole process of spermatogenesis. Spermatogonial stem cell renewal was promoted by E2implantation but was suppressed by tamoxifen (an antagonist of estrogen). In vitro,10 pg/ml of E2was sufficient to induce spermatogonial stem cell division in cultured testicular tissue, therefore confirming the in vivoobservations. These results clearly show that estrogen is an indispensable “male hormone” in the early spermatogenetic cycle.