Figure 7. A proposed model for formation of the genital ridge.

Formation of the testis or ovary begins when Gata4-dependent thickening of the coelomic epithelium gives rise to the genital ridge. LHX9 and SF1, acting downstream of GATA4, are subsequently induced, promoting growth and maintenance of the genital ridge. WT1 and EMX2 (not shown), though widely expressed in the genital ridge, are not dependent on Gata4 and likely function in parallel to support growth and maintenance of the genital ridge. The genital ridge then develops as either an ovary or a testis, depending on the sex chromosome constitution of the embryo.