Female development in mammals is regulated by Wnt-4 signalling

In the mammalian embryo, both sexes are initially morphologically Indisting uishable: specific hormones are required for sex-specific development. Mull erian inhibiting substance and testosterone secreted by the differentiating embryonic testes result in the loss of female (Mullerian) or promotion of male (Wolffian) reproductive duct development, respectively. The signalling molecule Wnt-4 is crucial for female sexual development. At birth, sexual development in males with a mutation in Wnt-4 appears to be normal; however , Wnt-4-mutant females are masculinized-the Mullerian duct is absent white the Wolffian duct continues to develop. Wnt-4 is initially required in both sexes for formation of the Mullerian duct, then Wnt-4 in the developing ov ary appears to suppress the development of Leydig cells; consequently, Wnt- 4-mutant females ectopically activate testosterone biosynthesis. Wnt-4 may also be required for maintenance of the female germ line. Thus, the establi shment of sexual dimorphism is under the control of both local and systemic signals.