Delay of testicular differentiation in the B6.YDOM ovotestis demonstrated by immunocytochemical staining for müllerian inhibiting substance

It has been found that when the Y chromosome from Mus musculus domesticus (YDOM) is placed onto the C57BL/6J (B6) mouse background, the XY progeny (B6.YDOM) develop ovaries or ovotestes but not normal testes during fetal life. We examined the ontogeny of the abnormal testicular differentiation in the B6.YDOM ovotestis by immunocytochemical staining for Mullerian inhibiting substance (MIS). We found that the B6.YDOM ovotestis initiated testicular differentiation later in development than did the control B6 testis. When the YDOM was transferred onto the SJL/J mouse background by crossing B6.YDOM males with SJL/J females, all XY progeny developed normal testes. The onset of testicular differentiation was at the same developmental stage as in the B6 male fetus. These results suggest that the delay of testicular differentiation is not due to the effect of the YDOM chromosome itself, but due to improper interaction of the testis-determining gene on the YDOM chromosome with autosomal genes of B6. In addition, we found a close correlation between the arrest of germ cells at the prespermatogonia stage and MIS production of adjacent somatic cells in the B6.YDOM ovotestis. This result may support the hypothesis that MIS is involved in the regulation of germ cell differentiation.