Practice question

Testis determination is suppressed primarily by ovarian Wnt4/β-catenin/Rspo1 canonical pathway in mammals. In XX gonads secreted Wnt4 binds Frizzled and Lrp5/6, signals via Disheveled inhibiting destruction complex of β-catenin. Accumulated β-catenin represses Sox9 enhancer and Fgf9 proliferative loop, prevents Sertoli specification and blocks formation of male-specific coelomic vessel dependent on Fgf9. It also induces Follistatin to inhibit coelomic vessel formation and steroidogenesis. When pathway disrupted in XX embryos, testes-like structures develop with Sertoli cells, illustrating active repressive function of β-catenin/Wnt4 axis.