The wood frog is one of the few freeze-tolerance vertebrates. This is accomplished in part by the accumulation of cryoprotectant glucose, metabolic rate depression, and stress response activation. These may be achieved by mechanisms such as DNA methylation, which is typically associated with transcriptional repression. Hyperglycemia is also associated with modifications to epigenetic profiles, indicating an additional role that the high levels of glucose play in freeze tolerance. We sought to determine whether DNA methylation is affected during freezing exposure, and whether this is due to the wood frog's response to hyperglycemia. We examined global DNA methylation and DNA methyltransferases (DNMTs) in the liver and muscle of frozen and glucose-loaded wood frogs. The results showed that levels of 5-methylcytosine (5mC) increased in the muscle, suggesting elevated DNA methylation during freezing. DNMT activities also decreased in muscle during thawing, glucose loading, and in vitro glucose experiments. Liver DNMT activities were similar to muscle; however, a varied response to DNMT levels and a decrease in 5mC highlight the metabolic role the liver plays during freezing. Glucose was also shown to decrease DNMT activity levels in the wood frog, in vitro, elucidating a potentially novel regulatory mechanism. Together these results suggest an interplay between freeze tolerance and hyperglycemic regulation of DNA methylation.

中文翻译：

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耐冻脊椎动物中的DNA甲基化和DNA甲基转移酶的调控。

木蛙是为数不多的耐寒脊椎动物之一。这部分是通过冷冻保护剂葡萄糖的积累，代谢率下降和应激反应激活来实现的。这些可以通过诸如DNA甲基化之类的机制来实现，该机制通常与转录抑制相关。高血糖症也与表观遗传学特征的改变有关，表明高水平的葡萄糖在抗冻性中起着另外的作用。我们试图确定冷冻暴露期间DNA甲基化是否受到影响，以及这是否归因于蛙蛙对高血糖症的反应。我们检查了冷冻和葡萄糖加载的青蛙的肝脏和肌肉中的整体DNA甲基化和DNA甲基转移酶（DNMT）。结果表明，肌肉中5-甲基胞嘧啶（5mC）的水平升高，提示冷冻过程中DNA甲基化升高。在解冻，葡萄糖负荷和体外葡萄糖实验过程中，肌肉中的DNMT活性也降低。肝脏的DNMT活性与肌肉相似。但是，对DNMT水平的不同反应和5mC的降低突显了肝脏在冷冻过程中的代谢作用。还显示了葡萄糖在体外可降低木蛙中DNMT活性水平，阐明了潜在的新型调节机制。这些结果共同表明，冷冻耐受性与DNA甲基化的高血糖调节之间存在相互作用。对DNMT水平的不同反应和5mC的降低突出了肝脏在冷冻过程中所起的代谢作用。还显示了葡萄糖在体外可降低木蛙中DNMT活性水平，阐明了潜在的新型调节机制。这些结果共同表明，冷冻耐受性与DNA甲基化的高血糖调节之间存在相互作用。对DNMT水平的不同反应和5mC的降低突出了肝脏在冷冻过程中所起的代谢作用。还显示了葡萄糖在体外可降低木蛙中DNMT活性水平，阐明了潜在的新型调节机制。这些结果共同表明，冷冻耐受性与DNA甲基化的高血糖调节之间存在相互作用。