SOX4 regulates gonad morphogenesis and promotes male germ cell differentiation in mice

The group C SOX transcription factors SOX4, −11 and −12 play important and mutually overlapping roles in development of a number of organs. Here, we examined the role of SoxC genes during gonadal development in mice. All three genes were expressed in developing gonads of both sexes, predominantly in somatic cells, with Sox4 being most strongly expressed. Sox4 deficiency resulted in elongation of both ovaries and testes, and an increased number of testis cords. While female germ cells entered meiosis normally, male germ cells showed reduced levels of differentiation markers Nanos2 and Dnmt3l and increased levels of pluripotency genes Cripto and Nanog, suggesting that SOX4 may normally act to restrict the pluripotency period of male germ cells and ensure their proper differentiation. Finally, our data reveal that SOX4 (and, to a lesser extent, SOX11 and −12) repressed transcription of the sex-determining gene Sox9 via an upstream testis-specific enhancer core (TESCO) element in fetal gonads, raising the possibility that SOXC proteins may function as transcriptional repressors in a context-dependent manner. •SoxC genes are expressed in mouse fetal gonads, predominantly in somatic cells.•SOX4 activity influences organ shape in developing ovaries and testes.•SOX4 activity also promotes the differentiation of male germ cells.•SOX4 both activates and represses transcription depending on context.