Practice question

Testis determination initiates when Sry protein briefly expressed in XY bipotential gonads binds testis-specific enhancer of Sox9 together with Sf1, triggering dramatic Sox9 upregulation in pre-Sertoli precursors. Elevated Sox9 establishes feed-forward loop involving Fgf9 and prostaglandin D2 maintaining high Sox9 and repressing β-catenin/Wnt4 ovarian signals. Sox9 subsequently activates Dhh for Leydig specification, Amh for Müllerian regression and collagen genes organizing testis cords and supporting germ cell quiescence. Without Sry, Sox9 remains low permitting ovarian differentiation via Wnt4, β-catenin and Foxl2 pathways.