[The mechanism of gonadal differentiation]

The steroid-hormone dependent sexual development presupposes the already sex-specific differentiated gonads. The H-Y antigen is held responsible for the primary differentiation of the indifferent gonadal anlage towards testicular organization. Studies on the function of H-Y antigen, using gonadal cells in vitro, have shown that in the presence of H-Y antigen the gonad differentiates into testicular, in its absence into ovarian structures, independent of whether the sex chromosomes are XX or XY. The gonads of both sexes are endowed with a specific H-Y receptor, other tissues are not. The bipotency of the gonadal anlage arises from this character. Some disorders of sexual development presumably go back to mutations affecting the genetic control of the H-Y gene and the function of H-Y antigen, respectively. It is discussed that the Y chromosome may have a mere regulatory function and not include the H-Y gene. Thus, the primary differentiation of the gonad should be dependent exclusively on whether or not the H-Y gene is active.