In the male genital ridge, transient Sry expression causes supporting cells to differentiate into Sertoli cells which then act as the organizing center for testis differentiation. Point mutations or deletions in the human or mouse Sry coding region can lead to female development in XY individuals. Sertoli cells also act to prevent gonocytes from differentiating prematurely. They produce the enzyme CYP26B1 to counteract surrounding retinoic acid. Retinoic acid acts as a signal to the gonocytes to enter meiosis. The gonocyte and Sertoli cells have been shown to form gap and desmosomelike junctions as well as adherins junctions composed of cadherins and connexins. To differentiate into spermatogonia, the gonocytes must lose their junctions to Sertoli cells and become migratory once again. They migrate to the basement membrane of the seminiferous cord and differentiate.
