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

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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).