X-inactivation pattern in the epididymis of sex-reversed mice heterozygous for testicular feminization.

Female mice heterozygous for testicular feminization were sex-reversed by means of the autosomal sex reversal mutation {Sxr). Due to X-inactivation, the blastemata for male sex organs in these animals are composed of a mixture of cells, carrying either the wildtype X chromosome or the X chromosome affected with Tfm in an active state. Thus, the two types of cells are sensitive to androgens or insensitive to androgens, respectively. This mosaic could be demonstrated in the epididymis on a cellular level. Segments of undifferentiated Tfm cells were found alternating with normally differentiated wild-type cells. The ultrastructural appearance of the mosaic is described.