Hydroxysteroid dehydrogenase activity associated with sexual differentiation in embryos of the turtle Trachemys...

Many turtles exhibit temperature-dependent sex determination. We have examined the hypothesis that incubation temperature causes a differential expression of steroidogenic enzymes in embryonic turtles. The activities of three steroidogenic enzymes were studied histochemically in turtle (Trachemys scripta) embryos at different developmental stages: sexually undifferentiated (Stage 15), differentiating (Stage 17), and differentiated (Stage 26; i.e., hatchling). Steroidogenic enzymes were detected in several tissues prior to, during, and after gonadal differentiation in embryos incubated at both male-producing and female-producing temperatures. In all embryos, ene-5-3 beta-hydroxysteroid dehydrogenase (HSDH) was detected only in adrenal tissue. 3 alpha-HSDH was localized in adrenal tissue, as well as in the mesonephros and liver. 17 beta-HSDH was evident in mesonephric, hepatic, and gut tissues. In hatchlings, ene-5-3 beta-HSDH and 3 alpha-HSDH were evident in the adrenal gland, whereas 3 alpha-HSDH and 17 beta-HSDH were present in the mesonephros and liver. While there was some variation in the activities of these enzymes during development, no temperature-specific pattern was apparent. At no stage were the enzymes observed in genital ridge/gonad. Our results show that T. scripta embryos possess enzymes necessary for steroid hormone synthesis. The segregated distributions of the enzymes suggest that a multi-organ regulatory system may mediate embryonic steroidogenesis. Our results do not indicate the genital ridge/gonad the principle site of steroid synthesis, although it may possess other enzymes that influence steroidogenesis.