Practice question

Maintenance of testicular fate throughout life requires continuous repression of ovarian program by Sox9, Sox8, Dmrt1 and Fgf9. Sox9 persists in adult Sertoli cells binding regulatory regions of Foxl2 and Wnt4 preventing reactivation, thereby blocking granulosa transdifferentiation. Dmrt1 independently antagonizes Foxl2, while in females Foxl2 antagonizes Dmrt1 maintaining ovary. Conditional ablation of Sox9 in adult XY gonads leads to upregulation of Wnt4/β-catenin and transformation toward granulosa-like cells with ectopic Foxl2, illustrating guardianship role. Therefore Sox9 critical for maintaining testes by blocking ovarian development.