Expression pattern and histone acetylation of energy metabolic genes in Xenopus laevis liver in response to diet statuses

Adult male Xenopus laevis can tolerate months of fasting by catabolizing carbohydrates and lipids

The African clawed frog, Xenopus laevis, has been reported to tolerate long-term fasting without dormancy. However, the strategies for energy acquisition during fasting are unclear in this species. We performed 3- and 7-month fasting experiments to investigate how the metabolism of male X. laevis changes during long-term fasting. We found that the levels of several serum biochemical parameters, such as glucose, triglycerides, and free fatty acids, as well as liver glycogen were reduced after 3 months of fasting, whereas after 7 months of fasting, triglyceride levels were reduced, and fat body wet weight was lower than that of fed group indicating the onset of lipid catabolism. In addition, transcript levels of gluconeogenic genes, such as pck1, pck2, g6pc1.1, and g6pc1.2, were increased in the livers of animals fasted for 3 months, suggesting upregulation of gluconeogenesis. Our results raise the possibility that male X. laevis can tolerate much longer fasting than previously reported by utilizing several energy storage molecules. Further investigation of the effects of prolonged fasting on the metabolic switches from carbohydrates to lipids or amino acids in X. laevis is required.

Waking the sleeping dragon: gene expression profiling reveals adaptive strategies of the hibernating reptile Pogona vitticeps

Background

Hibernation is a physiological state exploited by many animals exposed to prolonged adverse environmental conditions associated with winter. Large changes in metabolism and cellular function occur, with many stress response pathways modulated to tolerate physiological challenges that might otherwise be lethal. Many studies have sought to elucidate the molecular mechanisms of mammalian hibernation, but detailed analyses are lacking in reptiles. Here we examine gene expression in the Australian central bearded dragon (Pogona vitticeps) using mRNA-seq and label-free quantitative mass spectrometry in matched brain, heart and skeletal muscle samples from animals at late hibernation, 2 days post-arousal and 2 months post-arousal.

Results

We identified differentially expressed genes in all tissues between hibernation and post-arousal time points; with 4264 differentially expressed genes in brain, 5340 differentially expressed genes in heart, and 5587 differentially expressed genes in skeletal muscle. Furthermore, we identified 2482 differentially expressed genes across all tissues. Proteomic analysis identified 743 proteins (58 differentially expressed) in brain, 535 (57 differentially expressed) in heart, and 337 (36 differentially expressed) in skeletal muscle. Tissue-specific analyses revealed enrichment of protective mechanisms in all tissues, including neuroprotective pathways in brain, cardiac hypertrophic processes in heart, and atrophy protective pathways in skeletal muscle. In all tissues stress response pathways were induced during hibernation, as well as evidence for gene expression regulation at transcription, translation and post-translation.

Conclusions

These results reveal critical stress response pathways and protective mechanisms that allow for maintenance of both tissue-specific function, and survival during hibernation in the central bearded dragon. Furthermore, we provide evidence for multiple levels of gene expression regulation during hibernation, particularly enrichment of miRNA-mediated translational repression machinery; a process that would allow for rapid and energy efficient reactivation of translation from mature mRNA molecules at arousal. This study is the first molecular investigation of its kind in a hibernating reptile, and identifies strategies not yet observed in other hibernators to cope stress associated with this remarkable state of metabolic depression.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5750-x) contains supplementary material, which is available to authorized users.