Regulation of Gonadal Differentiation in Frogs Derived from UV-irradiated Eggs(Developmental Biology)

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The gonadal differentiation in normal Rana nigromaculata was described and the process in animals derived from pressed and UV-irradiated eggs were examined and compared. The initial formation of medullae was basically the same (12 pairs of segments) in all primitive gonads of the normal (control) and UV-treated animals. The UV-treated animals, however, had fewer germ cells and medullary cells than the control. Ovarian development in normal larvae proceeded in cyclic rhythms, each cycle consisting of three steps : active proliferation of germ cells, growth of oocytes, and the swelling of secondary genital cavities (SGCs). In larvae derived from UV-irradiated eggs, ovaries (with a few germ cells) did not show the initial two steps in the first cycle, but in the second cycle the first step was observed. Consequently, germ cells became surrounded individually or in groups by the wall-cells (medullary cells) of SGCs, hence reducing the SGC volume. These ovaries were eventually masculinized more or less completely, and functional (fertile upon artificial insemination) sex-reversed frogs were produced. The results may suggest that the encounter of indifferent germ cells with medullary cells is necessary to induce the production of serologically detectable male (SDM) antigen as the underdeveloped ovaries kept the female characters until the stage when the encounter occurred.