Practice question

Testicular organogenesis requires sequential action of Sry and Sox9 in supporting cell lineage. Sry provides transient trigger in XY genital ridge elevating Sox9 above threshold in pre-Sertoli cells; Sox9 then sustains expression via Fgf9-Pgd2 positive feedback, forms Sox9/Fgfr2 loop and represses ovarian β-catenin pathway. Sox9 activates Dhh for Leydig differentiation, Amh for Müllerian regression and extracellular matrix components forming basal lamina of testis cords. Combined functions establish Sertoli niche, induce quiescence of XY germ cells and vascular pattern. Deletion of either causes XY sex reversal.