Institute of Biochemistry, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario K1S 5B6, Canada.
Comp Biochem Physiol Part D Genomics Proteomics. 2020 Jun;34:100660. doi: 10.1016/j.cbd.2020.100660. Epub 2020 Feb 1.
The red eared slider turtle (Trachemys scripta elegans) is a champion vertebrate facultative anaerobe, capable of surviving for several months under conditions of exceptionally low oxygen availability. The ability of the turtle to facilitate this impressive tolerance to oxygen restriction is accomplished through a dramatic reduction in non-essential cellular processes. This is done in an attempt to conserve limited ATP stores and match demand in the anoxic state, with ATP supplied primarily through anaerobic glycolysis. Determining both the non-essential and the essential cellular processes that are deemed to be anoxia-responsive in the turtle has been an intense area of study over the past few decades. As a result, recent advancements have established the influence of global metabolic controls, such as post-transcriptional and post-translational regulation of gene expression in anoxia adaptation. A remaining question is whether or not epigenetic-level regulatory mechanisms are also utilized to allow for local control over gene expression. Recently, research has begun to document lysine methylation as an anoxia-responsive post-translational histone modification, as the activities of a number of methyl-lysine regulatory enzymes are extraordinarily sensitive to oxygen availability. As a result, oxygen-dependent methyl-lysine regulatory enzymes have been of particular interest to several recent studies of animal oxygen sensitivity, including the freshwater turtle. This review will introduce the concept of lysine methylation as an oxygen-sensitive protein modification as well as a prospectus on how this modification may contribute to anoxia tolerance in the turtle.
红耳滑龟（Trachemys scripta elegans）是一种擅长进行兼性厌氧呼吸的脊椎动物冠军，能够在极低氧气供应的情况下生存数月。龟类之所以能够显著耐受缺氧，是因为其显著减少了非必需的细胞过程。这是为了保存有限的 ATP 储存并在缺氧状态下匹配需求，其中 ATP 主要通过无氧糖酵解提供。在过去几十年中，确定在龟类中被认为对缺氧有反应的非必需和必需细胞过程一直是一个密集的研究领域。因此，最近的进展确立了全球代谢控制的影响，例如在缺氧适应中的基因表达的转录后和翻译后调控。一个悬而未决的问题是，是否还利用了表观遗传水平的调节机制来允许对基因表达进行局部控制。最近，研究开始将赖氨酸甲基化为一种对缺氧有反应的翻译后组蛋白修饰，因为许多甲基赖氨酸调节酶的活性对氧气可用性非常敏感。因此，依赖于氧的甲基赖氨酸调节酶一直是对动物氧气敏感性的几个最近研究的特别关注，包括淡水龟。这篇综述将介绍赖氨酸甲基化为一种氧敏感的蛋白质修饰的概念，以及这种修饰如何有助于龟类的耐缺氧能力。
