Transcriptomic responses of liver and skeletal muscle to prolonged cold and heat acclimation in the narrow-mouth frog Kaloula borealis

Global climate change is increasing the intensity and frequency of thermal extremes, posing substantial physiological challenges for amphibians. However, tissue-specific molecular responses and shared responses across tissues to prolonged thermal acclimation remain poorly understood. In this study, the narrow-mouth frog ( Kaloula borealis ) was acclimated at 4 °C, 25 °C, and 35 °C for four weeks, and comparative transcriptomic analyses were performed on liver and skeletal muscle. Cold acclimation led to markedly larger transcriptional responses than heat acclimation in both tissues, with 7,727 and 5,440 differentially expressed genes (DEGs) identified in the liver and skeletal muscle, respectively, compared with 648 and 842 DEGs under heat acclimation. Functional enrichment analysis revealed that upregulated genes under cold acclimation in the liver were enriched in energy sensing and cellular stress responses, particularly the AMPK and FoxO signaling pathways, whereas genes involved in steroid biosynthesis, retinol metabolism, and carbohydrate metabolism were downregulated, consistent with transcriptional shifts associated with metabolic suppression during winter hibernation. Heat acclimation was characterized by increased expression of genes involved in endoplasmic reticulum protein processing, unfolded protein response, and translation-related processes, whereas several lipid metabolic pathways showed reduced transcriptional activity. Across both thermal treatments, upregulated genes in the liver were enriched in PPAR signaling and taurine metabolism, whereas upregulated genes in skeletal muscle were involved in TNF signaling and antigen processing. Mfuzz clustering further identified temperature-dependent expression patterns associated with innate immunity and lysosome-mediated degradation. These results demonstrate that prolonged cold and heat acclimation elicit distinct and tissue-specific transcriptional responses in K. borealis . The liver primarily exhibited transcriptional signatures related to metabolic regulation, whereas skeletal muscle showed comparatively greater changes in immune- and stress-associated pathways. These findings deepen our understanding of tissue-specific and shared regulatory mechanisms underlying thermal acclimation in amphibians.