Ovotestes in B6-XXSxr sex-reversed mice.

The sex-reversed mutation Sxr results in XX males. In the absence of any other mutations, testis differentiation in XXSxr fetuses is essentially normal and only one report of an XXSxr fetus with ovotestes is in the literature. We report that 84% (21/25) of 13 days postcoitum XXSxr fetuses on the B6 inbred genomic background have ovotestes. Ovotestes were found in fetuses from both Sxra and Sxrb variants. Examination of fetuses older than 13 dpc suggests that the presence of ovotestes is transient in most fetuses. However, one overt hermaphrodite was identified after birth. The development of ovotestes is associated with the inbred background and is exacerbated by the dominant spotting oncogene allele KitW-42J. We propose that spreading of X-inactivation into the Sxr region resulting in loss of Sry expression is more extensive in B6-Sxr strains.