Incorrect statement about genital ridge determination?
Designating Rspo1 as promoter of testis pathway is incorrect because genetic evidence firmly places Rspo1 in ovarian network. Rspo1 synergizes with Wnt4 to activate β-catenin signaling, promoting granulosa differentiation and directly repressing Sox9/Fgf9 male program. Loss-of-function in humans and mice results in XX masculinization, appearance of Sertoli cells, androgen production and ovotestes, not testicular failure. Gain of Rspo1 activity antagonizes testis cord formation. Testis pathway instead relies on Sry, Sox9, Fgf9, Dmrt1 and Dhh. Therefore Rspo1 belongs to ovary-promoting module alongside Wnt4, Foxl2 and β-catenin.
Ref: Gilbert, Developmental Biology, 12th ed., Chapter 6: Incorrect assignment of Rspo1 function; ovarian pathway genes.