Remarkable metabolic reorganization and altered metabolic requirements in frog metamorphic climax
Background Metamorphic climax is the crucial stage of amphibian metamorphosis responsible for the morphological and functional changes necessary for transition to a terrestrial habitat. This developmental period is sensitive to environmental changes and pollution. Understanding its metabolic basis and requirements is significant for ecological and toxicological research. Rana omeimontis tadpoles are a useful model for investigating this stage as their liver is involved in both metabolic regulation and fat storage.
Results We used a combined approach of transcriptomics and metabolomics to study the metabolic reorganization during natural and T3-driven metamorphic climax in the liver and tail of Rana omeimontis tadpoles. The metabolic flux from the apoptotic tail replaced hepatic fat storage as metabolic fuel, resulting in increased hepatic amino acid and fat levels. 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) decreased. The hepatic glycogen phosphorylation and gluconeogenesis were upregulated, and the carbohydrate flux was used for 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. 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). 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 are discussed.
Conclusion The energic strategy and anabolic requirements during metamorphic climax were revealed at the molecular level. Amino acid made an increased contribution to energy metabolism during metamorphic climax. Carbohydrate anabolism was essential for the body construction of the froglets. The tail was critical in anabolism including synthesizing bioactive metabolites. These findings increase our understanding of amphibian metamorphosis and provide background information for ecological, evolutionary, conservation, and developmental studies of amphibians.
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Additional file 1: Liver and tail metabolites tables.
Additional file 2: Figure S1 Overview of the transcriptomes of control and T3-treated tadpoles. (A) Unigene length distribution. (B) Gene expression correlations between samples. (C–D) Volcano plots showing the DEGs of liver (C) and tail (D) metabolomes between control and T3-treated tadpoles. Figure S2 Liver size of control and T3-treated tadpoles. ***, p < 0.001. Figure S3 Scatter plots of PCAs based on liver (A) and tail (B) metabolomes of pro-metamorphic (stage 30-31) and T3-driven metamorphic tadpoles. Figure S4 Transcriptional variation of genes involved in primary bile acid biosynthesis and steroid metabolism in the liver. *, p < 0.05; **, p < 0.01; ***, p < 0.001. Figure S5 Transcriptional variation of genes with potential metabolic regulatory functions in the liver and tail. *, p < 0.05. Figure S6 Arachidonic acid metabolism highlighted by tail DEGs between control and T3-treated tadpoles. Figure S7 Variation of glutamine levels during metamorphic climax. Different letters denote significant differences between groups (p < 0.05), as shown by the Student–Newman–Keuls post hoc test after one-way ANOVA. *, p < 0.05. Figure S8 Transcriptional changes of genes involved in energy metabolism during metamorphic climax. (A) Transcriptional changes of genes involved in energy metabolism (TCA cycle and oxidative phosphorylation) in the liver. (B) Transcriptional changes of genes involved in TCA cycle in the tail. (C) Heatmap showing the transcriptional level of genes involved in oxidative phosphorylation in the tail. (D) Transcriptional changes of major energy consuming proteins in the tail. A positive logarithmic transformed fold change value means upregulation in T3-treated group, and vice versa; *, p < 0.05. PDH, pyruvate dehydrogenase; CS, citrate synthase; IDH, isocitrate dehydrogenase; 2-OGDH, 2-oxoglutarate dehydrogenase; SCL, succinyl-CoA ligase; SDH, succinate dehydrogenase; MDH, malate dehydrogenase; ND, NADH dehydrogenase; MCK, muscle creatine kinase; UCP, uncoupling protein.
Posted 21 Aug, 2020
On 08 Oct, 2020
On 17 Sep, 2020
Received 15 Sep, 2020
On 01 Sep, 2020
Received 01 Sep, 2020
On 31 Aug, 2020
Invitations sent on 30 Aug, 2020
On 17 Aug, 2020
On 16 Aug, 2020
On 16 Aug, 2020
Received 20 Jul, 2020
On 20 Jul, 2020
On 14 Jul, 2020
Received 26 Jun, 2020
On 11 Jun, 2020
Invitations sent on 29 May, 2020
On 24 May, 2020
On 23 May, 2020
On 23 May, 2020
On 22 May, 2020
Remarkable metabolic reorganization and altered metabolic requirements in frog metamorphic climax
Posted 21 Aug, 2020
On 08 Oct, 2020
On 17 Sep, 2020
Received 15 Sep, 2020
On 01 Sep, 2020
Received 01 Sep, 2020
On 31 Aug, 2020
Invitations sent on 30 Aug, 2020
On 17 Aug, 2020
On 16 Aug, 2020
On 16 Aug, 2020
Received 20 Jul, 2020
On 20 Jul, 2020
On 14 Jul, 2020
Received 26 Jun, 2020
On 11 Jun, 2020
Invitations sent on 29 May, 2020
On 24 May, 2020
On 23 May, 2020
On 23 May, 2020
On 22 May, 2020
Background Metamorphic climax is the crucial stage of amphibian metamorphosis responsible for the morphological and functional changes necessary for transition to a terrestrial habitat. This developmental period is sensitive to environmental changes and pollution. Understanding its metabolic basis and requirements is significant for ecological and toxicological research. Rana omeimontis tadpoles are a useful model for investigating this stage as their liver is involved in both metabolic regulation and fat storage.
Results We used a combined approach of transcriptomics and metabolomics to study the metabolic reorganization during natural and T3-driven metamorphic climax in the liver and tail of Rana omeimontis tadpoles. The metabolic flux from the apoptotic tail replaced hepatic fat storage as metabolic fuel, resulting in increased hepatic amino acid and fat levels. 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) decreased. The hepatic glycogen phosphorylation and gluconeogenesis were upregulated, and the carbohydrate flux was used for 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. 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). 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 are discussed.
Conclusion The energic strategy and anabolic requirements during metamorphic climax were revealed at the molecular level. Amino acid made an increased contribution to energy metabolism during metamorphic climax. Carbohydrate anabolism was essential for the body construction of the froglets. The tail was critical in anabolism including synthesizing bioactive metabolites. These findings increase our understanding of amphibian metamorphosis and provide background information for ecological, evolutionary, conservation, and developmental studies of amphibians.
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7