Practice question

Sox9 promotes testis pathway not only by activating male genes but also by antagonizing ovarian Wnt4/β-catenin signaling creating mutually exclusive fates. Sox9 binds and represses promoters of Wnt4 and Foxl2 and interferes with β-catenin transcriptional activity via competition for co-activators and direct protein interaction. This mutual repression creates bistable switch ensuring exclusive adoption of one gonadal identity. In XY gonads high Sox9 blocks Wnt4 preventing Follistatin expression and allowing testis-specific vasculature. Conversely Wnt4/β-catenin represses Sox9 in XX, illustrating reciprocal inhibition essential for sexual dimorphism.