ABSTRACT
The Y chromosome from certain populations of M. m. domesticus is incapable of normal testis determination in the B6 inbred strain resulting in XY hermaphrodites or XY females (XYDOM sex reversal). B6 consomic strains have been developed with either transient (B6-YAKR) or severe (B6-YTIR) XYDOM sex reversal. We report that a point mutation, the dominant white spotting oncogene allele, KitW-42J, exacerbates XYDOM sex reversal. In B6-YAKR, penetrance of the trait is low; however, in B6-YTIR, KitW-42J exacerbated sex reversal to such an extent that almost all XY progeny developed into females. The exacerbation of sex reversal was not linked to retardation of early fetal growth or reduction of testis size. Furthermore, semiquantitative RT-PCR for the testis-determining gene, Sry, suggests that exacerbation of sex reversal in B6-YTIR is not due to blockade of Sry expression, a substantial delay in initiation of Sry expression, or exceptionally low levels of Sry mRNAs. We propose that KitW-42J enhances sex reversal by adversely affecting a critical step in testis differentiation that is downstream of Sry.
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