Abstract
BackgroundMetamorphic climax is the crucial stage of amphibian metamorphosis responsible for the morphological and functional changes for landing. This developmental period is most sensitive to environmental changes and pollution. Understanding its metabolic basis and requirements has great significance to ecological and toxicological researches. Rana omeimontis tadpoles are unique model for investigating this issue, as their liver has the dual role of metabolic regulation and fat storage.ResultsUsing a combined approach of transcriptomics and metabolomics, we revealed the metabolic reorganization during natural and T3-driven metamorphic climax by reconstructing the metabolic networks in the liver and tail of Rana omeimontis tadpoles. In metamorphic tadpoles, the metabolic flux from the apoptotic tail replaced hepatic fat storage as metabolic fuel, resulting in increased hepatic amino acid and fat level. In the liver, amino acid catabolism (transamination and urea cycle) was upregulated along with energy metabolism (TCA cycle and oxidative phosphorylation), while the carbohydrate and lipid catabolism (glycolysis, pentose phosphate pathway/PPP and β-oxidation) were decreased. Meanwhile, the hepatic glycogen phosphorylation and gluconeogenesis were upregulated, and the carbohydrate flux likely flowed into the synthesis of glycan units (e.g., UDP-glucuronate). In the tail, glycolysis, β-oxidation, and transamination were all downregulated, accompanied by synchronous downregulation of energy production and consumption. The glycogenolysis was maintained in the tail, and the carbohydrate flux likely flowed into both PPP and the synthesis of glycan units (e.g., UDP-glucuronate and UDP-glucosamine). Interestingly, the fatty acid elongation and desaturation, as well as the synthesis of bioactive lipid (e.g., prostaglandins) were encouraged in the tail during metamorphic climax. Protein synthesis was downregulated in both the liver and tail. The significance of these metabolic adjustments and their potential regulation mechanism were discussed.ConclusionThe energic strategy and anabolic requirements during metamorphic climax were revealed at molecular level. Amino acid has increased contribution to energy metabolism during metamorphic climax. Carbohydrate anabolism is more intensively required than protein synthesis for the body construction of the froglet. The tail plays a critical role in anabolism and even metabolic regulation. These findings would deepen our understanding on the requirement and proceeding of amphibian metamorphosis.