Direct and mediated effects of testosterone: analysis of sex reversed mosaic mice heterozygous for testicular feminization.

Sex reversed mice are XX males carrying on one of their X chromosomes a translocation of the sex determining region of the Y (Cattanach's Sxr factor). The phenotype corresponds to the Klinefelter syndrome in man. The X linked Tfm (testicular feminization) mutation in the mouse is a frame shift in the androgen receptor gene leading to complete androgen insensitivity. Due to random X inactivation, sex reversed mice heterozygous for Tfm, are mosaics composed of a variable proportion of androgen insensitive X Tfm and androgen sensitive X+ wildtype cells. In the intersexual genital tract, Tfm cells are maintained as undifferentiated cells in the epididymal duct. To the distorted prostate lobes and bulbourethral glands they contribute some lobules of indifferent urethral glands. A large contribution of Tfm cells allows downgrowth of Wolffian and Müllerian ducts to form a vagina. In the external genitalia the stimulatory effect of testosterone is reduced leading to various degrees of feminization correlating with the proportion of Tfm cells present. In the mosaics effects of testosterone, mediated by local growth factors from the wildtype to the Tfm cells, can be distinguished from direct effects expressed only in the wildtype cells. Mediated effects are embryonic induction and morphogenesis of male organs and postnatal maintenance of organ structure and proliferation. The direct effect is cellular differentiation.