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Cryotherapy is one of the most common treatments for trauma or fatigue in the field of sports medicine. However, the molecular biological effects of acute cold exposure on skeletal muscle remain unclear. Therefore, we used zebrafish, which have recently been utilized as an animal model for skeletal muscle, to comprehensively investigate and selectively clarify the time-course changes induced by cryotherapy. Zebrafish were exposed intermittently to cold stimulation three times for 15 min each. Thereafter, skeletal muscle samples were collected after 15 min and 1, 2, 4, and 6 h. mRNA sequencing revealed the involvement of trim63a, fbxo32, fbxo30a, and klhl38b in "protein ubiquitination" from the top 10 most upregulated genes. Subsequently, we examined the time-course changes of the four genes by quantitative PCR, and their expression peaked 2 h after cryotherapy and returned to baseline after 6 h. Moreover, the proteins encoded by trim63a and fbxo32 (muscle-specific RING finger protein 1 [MuRF1] and muscle atrophy F-box, respectively), which are known to be major genes encoding E3 ubiquitin ligases, were examined by western blotting, and MuRF1 expression displayed similar temporal changes as trim63a expression. These findings suggest that acute cold exposure transiently upregulates E3 ubiquitin ligases, especially MuRF1; thus, cryotherapy may contribute to the treatment of trauma or fatigue by promoting protein processing., Competing Interests: Declaration of competing interest The authors have no conflict of interest to declare., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Recently, fasting has been spotlighted from a healthcare perspective. However, the de-tailed biological mechanisms and significance by which the effects of fasting confer health benefits are not yet clear. Due to certain advantages of the zebrafish as a vertebrate model, it is widely utilized in biological studies. However, the biological responses to nutrient metabolism within zebrafish skeletal muscles have not yet been amply reported. Therefore, we aimed to reveal a gene expression profile in zebrafish skeletal muscles in response to fasting-refeeding. Accordingly, mRNA-sequencing and bioinformatics analysis were performed to examine comprehensive gene expression changes in skeletal muscle tissues during fasting-refeeding. Our results produced a novel set of nutrition-related genes under a fasting-refeeding protocol. Moreover, we found that five genes were dramatically upregulated in each fasting (for 24 h) and refeeding (after 3 h), exhibiting a rapid response to the provided conditional changes. The assessment of the gene length revealed that the gene set whose expression was elevated only after 3 h of refeeding had a shorter length, suggesting that nutrition-related gene function is associated with gene length. Taken together, our results from the bioinformatics analyses provide new insights into biological mechanisms induced by fasting-refeeding conditions within zebrafish skeletal muscle.