Testicular cell differentiation in fetal mouse ovaries following transplantation into adult male mice.

Testicular development is a complicated process involving differentiation and arrangement of several cell types. To analyze the process of testicular organization we examined the sequence of the appearance of testicular structures induced in fetal ovaries following transplantation. Fetal mouse ovaries on the twelfth day of gestation were transplanted beneath the kidney capsules of adult male mice. They continued to develop morphologically as ovaries until the eleventh day after transplantation, when seminiferous cord formation and testosterone production began in addition to follicle development (ovotestes). Between the eleventh and fourteenth day after transplantation, ovarian grafts frequently contained transitional structures consisting of Sertoli cells, pregranulosa cells, a third type of cells which show intermediate characteristics between Sertoli and pregranulosa cells, and oocytes enclosed by common basal lamina. Leydig cells or peritubular myoid cells were not found in the transitional area, whereas these cells were present around seminiferous cords composed only of Sertoli cells. Oocytes were absent or degenerated in the well-developed seminiferous cords. The present findings suggest that, in ovarian grafts, pregranulosa cells can differentiate into Sertoli cells, which are responsible for the organization of the seminiferous cords, degeneration of oocytes, and differentiation of other testicular somatic cell types.