Serological and cytological evidence for increased Y-chromosome related material in Sxr,XY (sex-reversed carrier, male) mice.

In order to define the nature of the genetic lesion which gave rise to Sxr, the sex-limited autosomal dominant sex reversal condition in the mouse, cytological and serological studies were carried out comparing Sxr,XY (males carrying the sex-reversal gene) and normal XY male mice. Cytotoxic H-Y antisera were absorbed by splenocytes or sperm from both Sxr,XY and normal XY male mice. Our results indicate that for both types of tissue, Sxr,XY cells absorbed consistently greater amounts of cytotoxic activity than did normal XY cells. Whole-mount electron micrographs as well as light micrographs of silver-stained spermatocytes suggest that during meiotic prophase in Sxr,XY males, the paracentromeric region of the normal Y chromosome pairs with a supernumerary Y chromosomal fragment. This fragment can be identified as one of Y chromosomal origin by its thickened axial core. Taken together, our findings support the notion that the Sxr syndrome in the mouse can be due to a supernumerary Y chromosomal fragment containing male determining factors (including one or more H-Y structural or regulatory genes) rather than to a constitutive autosomal mutation.