Sites of estrogen uptake in embryonic Trachemys scripta, a turtle with temperature-dependent sex determination.

Female sex determination can be induced in embryonic red-eared slider turtles (Trachemys scripta) by exogenous estrogen, as well as by incubation at warm temperature. In the present study, estrogen target areas were identified in embryos before (stage 15), during (stage 18), and after (stage 22) the critical period for sex determination. Both hyperfilm and emulsion autoradiography were used to localize tritium accumulation after the injection of radiolabeled 17 beta-estradiol. Site-specific tritium-labelling was found at all stages, notably in the mesonephros at stage 15, in the mesonephros and oviduct at stage 18, and in the mesonephros, oviduct, and the interrenal gland at stage 22. Few if any cells in the gonad were tritium-labeled at any stage. The large number of estrogen-concentrating cells in the mesonephros and interrenal and the lack of binding to gonadal tissues indicates that estrogen action on gonadal differentiation during the period of sex determination may be indirect.