Bloskie Tighe, Storey Kenneth B
Department of Biology, Carleton University, Ottawa, ON K1S 5B6, Canada.
Epigenomes. 2022 Jul 12;6(3):17. doi: 10.3390/epigenomes6030017.
Transcriptional suppression is characteristic of extreme stress responses, speculated to preserve energetic resources in the maintenance of hypometabolism. In recent years, epigenetic regulation has become heavily implicated in stress adaptation of many animals, including supporting freeze tolerance of the wood frog (Rana sylvatica). However, nervous tissues are frequently lacking in these multi-tissue analyses which warrants investigation. The present study examines the role of DNA methylation, a core epigenetic mechanism, in the response of wood frog brains to freezing. We use immunoblot analysis to track the relative expression of DNA methyltransferases (DNMT), methyl-CpG-binding domain (MBD) proteins and ten-eleven-translocation (TET) demethylases across the freeze-thaw cycle in R. sylvatica brain, including selected comparisons to freeze-associated sub-stresses (anoxia and dehydration). Global methyltransferase activities and 5-hmC content were also assessed. The data show coordinated evidence for DNA hypomethylation in wood frog brains during freeze-recovery through the combined roles of depressed DNMT3A/3L expression driving lowered DNMT activity and increased TET2/3 levels leading to elevated 5-hmC genomic content (p < 0.05). Raised levels of DNMT1 during high dehydration were also noteworthy. The above suggest that alleviation of transcriptionally repressive 5-mC DNA methylation is a necessary component of the wood frog freeze-thaw cycle, potentially facilitating the resumption of a normoxic transcriptional state as frogs thaw and resume normal metabolic activities.
转录抑制是极端应激反应的特征，据推测这是为了在维持低代谢状态时保存能量资源。近年来，表观遗传调控与许多动物的应激适应密切相关，包括支持木蛙（林蛙）的耐冻能力。然而，在这些多组织分析中，神经组织常常缺失，这值得研究。本研究考察了DNA甲基化（一种核心表观遗传机制）在木蛙大脑对冰冻反应中的作用。我们使用免疫印迹分析来追踪林蛙大脑在冻融循环过程中DNA甲基转移酶（DNMT）、甲基-CpG结合域（MBD）蛋白和十-十一易位（TET）去甲基化酶的相对表达，包括与冰冻相关的亚应激（缺氧和脱水）的选定比较。还评估了全局甲基转移酶活性和5-羟甲基胞嘧啶（5-hmC）含量。数据显示，在冻融恢复过程中，木蛙大脑中存在DNA低甲基化的协同证据，这是通过DNMT3A/3L表达降低导致DNMT活性降低以及TET2/3水平升高导致5-hmC基因组含量增加共同作用的结果（p < 0.05）。在高度脱水期间DNMT1水平升高也值得注意。上述结果表明，减轻转录抑制性的5-甲基胞嘧啶（5-mC）DNA甲基化是木蛙冻融循环的必要组成部分，可能有助于青蛙解冻并恢复正常代谢活动时恢复正常氧合转录状态。
