The testis cords are precursors to the rete testis.

Activation of Fgf9 by SOX-9 starts vital processes in male development, such as the creation of testis cords and the multiplication of Sertoli cells.

SOX9 associates with Sf1 to increase the level of Anti-Müllerian hormone to repress female development while activating and forming a feedforward loop with FGF9, which creates the testis cords and is responsible for the proliferation of sertoli cells.

The absence of Fgf9 causes an individual, even an individual with X and Y chromosomes, to develop into a female, as it's needed to carry out important masculinizing developmental functions such as the multiplication of Sertoli cells and creation of the testis cords.