Influence of the mesonephros on the development of fetal mouse ovaries following transplantation into adult male and female mice.

We previously reported that fetal mouse ovaries frequently develop testicular structure following transplantation into adult male mice. The mechanism involved in gonadal sex reversal of ovarian grafts is not known. In the present study, we examined the influence of the adjacent mesonephros on development of the ovarian grafts. The results show that (1) when fetal ovaries were transplanted with the attached mesonephros, the frequency of ovotestis development was higher in male hosts than in female hosts, (2) the fetal ovaries that had been separated from mesonephros developed testicular structures more frequently than those with the mesonephros, and the incidence of ovotestis development was comparable in male and female hosts, (3) removal of the cranial or caudal half of the mesonephros resulted in a similar frequency of ovotestis development, and (4) when fetal ovaries were separated and reattached to the mesonephros, they developed testicular structures at a frequency similar to that of ovaries left attached to the mesonephros, and the sex of mesonephroi reattached to ovarian grafts did not influence the incidence of ovotestis development. These findings suggest that fetal ovaries can develop testicular structures after transplantation regardless of the sex of host, and that the adjacent mesonephros protects ovarian grafts from masculinizing stimuli more efficiently in female host than male hosts.