Explore of the regulatory factors involved in the nitrogen metabolic conversion in the ontogeny of amphibians

During amphibian metamorphosis, the liver begins to synthesize the urea cycle enzymes necessary to create urea from carbon dioxide and ammonia. We explored the regulatory factor involved in a shift of nitrogen metabolism from ammonotelic to ureotelic. The expression of carbamoyl phosphate synthetase 1 （CPS1) mRNA was first detected at st.47 tadpoles, suggesting that early tadpole produces and excretes urea. We examined the mRNA expression changes in glucocorticoid receptor （GR), CREB, HNF3α, and C/EBPαduring ontogeny. In the results, GR expression was markedly increased in st.44-45 tadpole. We also revealed that corticosterone treatment for Xenopus tadpole （st.44) increased the expression level of CPS I mRNA. Accordingly, CPS I expression （urea synthesis) in early tadpole of Xenopus laevis appears to be mediated by corticosterone and its receptor （GR).