Gonadal sex differentiation, development up to sexual maturity and steroidogenesis in the skipper frog, Euphlyctis cyanophlyctis

Gonadal sex differentiation, development up to sexual maturity and steroidogenesis were studied in the Indian skipper frog, Euphlyctis cyanophlyctis. In stage 25 tadpoles, gonads contained a few yolk laden germ cells and somatic cells. Ovarian differentiation occurred at stage 27 with the initiation of meiosis. Interestingly, meiosis preceded the formation of a central lumen that was discernible at stage 28. Folliculogenesis in the developing ovary was observed at stage 29. Vitellogenesis was observed in the 3 months old frogs and the females attained sexual maturity around 4 months. Testicular differentiation occurred indirectly through an ovarian phase. In some animals, from stage 37 onwards, oocyte degeneration was observed that was completed around metamorphic climax. Concurrently, large numbers of mesonephric cells were invading the gonads. Around metamorphosis, reorganization of the germ and somatic cells into testicular cords was observed. Following metamorphosis, the formation of seminiferous tubules was observed in the 2 weeks old males. Meiosis in the developing testes was observed in 1.5 months old males. In 3 months old males, the testes contained all stages spermatogenesis including spermatozoa. Steroidogenesis in the developing gonads was studied by immunohistochemical localization of 3β-HSD enzyme. At stage 26, a few immunoreactive cells were seen in the kidneys (interrenal cells). However, during and after differentiation, gonads failed to show positive immunoreaction. In the developing ovary at stage 37, follicular cells surrounding the oocytes were positive for 3β-HSD immunoreactivity. In the ovaries of 3 months old females, follicular cells surrounding the vitellogenic oocytes and stromal cells were positive for 3β-HSD immunoreaction. E. cyanophlyctis exhibits undifferentiated type of gonadal differentiation, in which gonadal differentiation precedes steroidogenesis.

► Euphlyctis cyanophlyctis exhibits undifferentiated type of gonadal differentiation.
► Gonadal differentiation into ovaries occurs at stage 27 with the initiation of meiosis in the ovaries.
► Meiosis in the ovary precedes the formation of a central ovarian lumen.
► Testicular differentiation starts at stage 37 and completes within first 2 weeks of metamorphosis.
► Male and female frogs attain sexual maturity within 4 months following metamorphosis.
► Gonadal differentiation precedes gonadal steroidogenesis.