The Mouse A/HeJ Y Chromosome: Another Good Y Gone Bad

In both humans and mice there are numerous reports of Y chromosome abnormalities that interfere with sex determination. Recent studies in the mouse of one such mutation have identified Y chromosome nondisjunction during preimplantation development as the cause of abnormal testis determination that results in a high frequency of true hermaphroditism. We report here that the mouse Y chromosome from the A/HeJ inbred strain induces similar aberrations in sex determination. Our analyses provide evidence, however, that the mechanism underlying these aberrations is not Y chromosome nondisjunction. On the basis of our findings, we postulate that a mutation at or near the centromere affects both the segregation and sex-determining properties of the A/HeJ Y chromosome. This Y chromosome adds to the growing list of Y chromosome aberrations in humans and mice. In both species, the centromere of the Y is structurally and morphologically distinct from the centromeres of all other chromosomes. We conclude that these centromeric features make the human and mouse Y chromosomes extremely sensitive to minor structural alterations, and that our studies provide yet another example of a good Y chromosome gone 'bad.'