GONADAL SEX REVERSAL OF THE DEVELOPING MARSUPIAL OVARY IN-VIVO AND IN-VITRO

Undifferentiated tammar wallaby ovaries were transplanted under the sk in of male pouch young during the period of mitotic division of the XX germ cells. After 25 days, all the germ cells had disappeared and the ovaries contained seminiferous-like cords, Similarly, undifferentiate d ovaries cultured for 4 days with recombinant human Mullerian-inhibit ing substance (rhMIS) also contained well-differentiated seminiferous- like cords and few or no surviving germ cells. The majority of control s cultured without rhMIS developed as normal ovaries. However, in a fe w control ovaries seminiferous-like cords developed in those regions o f the ovaries that were partially necrotic and contained few germ cell s. These results strongly suggest that sex-reversal of the tammar ovar y is the direct result of loss of mitotic germ cells, rather than an e ffect of MIS on female somatic cells. MIS is apparently toxic to these female germ cells in mitosis, but not to male germ cells in mitosis. Thus, in normal development in the tammar, the presence of XX germ cel ls in the ovary inhibits the formation of seminiferous cords so that t he gonad develops as an ovary.