A genetic model for sex determination, controlled by a balance of antagonistic pathways. In XY gonads, Sry triggers upregulation of Sox9, leading to Sertoli cell commitment and testicular differentiation. Sertoli cell differentiation is a result of the establishment of a positive feedback loop between Sox9 and secretion of Fgf9 (and also PGD2; not shown), which act in a paracrine manner to recruit additional Sertoli cells. In XX gonads, two independent signaling pathways involving the Rspo1/Wnt4/β-catenin pathway and Foxl2 tilt the balance towards the female side and silence Sox9 and Fgf9. Arrows indicate stimulation; T bars indicate inhibition.
Nef and Vassalli Journal of Biology 2009 8:74 doi:10.1186/jbiol173