SOX9 EXPRESSION DURING GONADAL DEVELOPMENT IMPLIES A CONSERVED ROLE FOR THE GENE IN TESTIS DIFFERENTIATION IN MAMMALS AND BIRDS

Heterozygous mutations in SOX9 lead to a human dwarfism syndrome, Camp omelic dysplasia. Consistent with a role in sex determination, we find that Sox9 expression closely follows differentiation of Sertoli cells in the mouse testis, in experimental sex reversal when fetal ovaries are grafted to adult kidneys and in the chick where there is no eviden ce for a Sry gene. Our results imply that Sox9 plays an essential role in sex determination, possibly immediately downstream of Sry in mamma ls, and that it functions as a critical Sertoli cell differentiation f actor, perhaps in all vertebrates.