miR-100 promotes the proliferation of spermatogonial stem cells via regulating Stat3

Micro RNAs play important roles during mammalian spermatogenesis, but the function(s) of specific miRNAs remain largely unknown. Here, we report that miR-100 is predominantly expressed in undifferentiated murine spermatogonia, including spermatogonial stem cells (SSCs). We utilized a miRNA mimic and inhibitor to knock down and overexpress miR-100 in cultured SSCs, respectively, finding that the miR-100 promotes the proliferation of SSCs in vitro. Furthermore, signals promoting SSC maintenance induced, whereas retinoic acid repressed, expression of miR-100. Stat3 expression was modulated by miR-100, with increased transcript and protein abundance in the presence of the miR-100 inhibitor versus reduced protein levels following miR-100 overexpression. Stat3 silencing also mimicked the reduced SSC proliferation phenotype associated with elevated miR-100 levels. Importantly, Stat3 silencing rescued the anti-proliferation capacity of miR-100 inhibitor on cultured SSCs. Given that the Stat3 3' untranslated region was not repressed by pre-miR-100 in a standard luciferase reporter assay, we suggest that miR-100 promotes SSC proliferation by indirect regulation of Stat3.