Simple SummaryHibernating animals reduce their metabolic rate through a variety of transcriptional, translational, and post-translational regulation methods to survive in extreme environments with an overall reduction in their body’s activity levels. Histone methylation is a mechanism that regulates gene expression at the transcriptional level, and specific histone methylation and demethylation modifications can either inactivate or activate gene transcription. In this study, we focused on the hibernation ofPelodiscus sinensis(P. sinensis) as an experimental model and studied the changes in the physiological metabolism index, histones, and related genes on growth and development under conditions of artificially induced hibernation. Although this paper lacks further evidence thatP. sinensishas been induced into a deep hibernation state, cold torpor is perhaps a more accurate description. The changes in physiological indexes, transcription level, mRNA relative expression, protein localization, relative protein expression, and enzyme activity associated with histone and histone (demethylation) genes in various tissues were analyzed under hibernating and normal conditions. The results provide insight into the adaptative mechanism ofP. sinensisto its environment.AbstractPelodiscus sinensis(P. sinensis) is a commonly cultivated turtle species with a habit of hibernation. To study the changes in histone expression and methylation ofP. sinensisduring hibernation induction, a model was established by artificial induction. Physiological and metabolic indices were measured, and the expression and localization of histone (H1,H2A,H2B,H3, andH4) and methylation-related genes (ASH2L,KMT2A,KMT2E,KDM1A,KDM1B, andKDM5A) were measured by quantitative PCR, immunohistochemistry, and Western blot analysis. The results indicated that the metabolism, antioxidation index, and relative expression of histone methyltransferase were significantly decreased (p< 0.05), whereas the activity and expression of histone demethyltransferase were significantly increased (p< 0.05). Although our results showed significant changes in physiological and gene expression after hibernation induction, we could not confirm thatP. sinensisentered deep hibernation. Therefore, for the state after cooling-induced hibernation, cold torpor might be a more accurate description. The results indicate that theP. sinensiscan enter cold torpor through artificial induction, and the expression of histones may promote gene transcription. Unlike histones expressed under normal conditions, histone methylation may activate gene transcription during hibernation induction. Western blot analysis revealed that theASH2LandKDM5Aproteins were differentially expressed in the testis at different months (p< 0.05), which may perform a role in regulating gene transcription. The immunohistochemical localization ofASH2LandKDM5Ain spermatogonia and spermatozoa suggests thatASH2LandKDM5Amay perform a role in mitosis and meiosis. In conclusion, this study is the first to report changes in histone-related genes in reptiles, which provides insight for further studies on the physiological metabolism and histone methylation regulation ofP. sinensisduring the hibernation induction and hibernation period.