5-Hydroxymethylcytosine-mediated active demethylation is required for mammalian neuronal differentiation and function.
5-Hydroxymethylcytosine-mediated active demethylation is required for mammalian neuronal differentiation and function.
复制标题
DOI：
10.7554/elife.66973
复制
发表时间：
2021-12-17
期刊：
影响因子：
7.7
通讯作者：
Heintz N
中科院分区：
文献类型：
--
作者：
Stoyanova E;Riad M;Rao A;Heintz N
虽然哺乳动物神经元中积累了高水平的5-羟甲基胞嘧啶(5hmC)，但我们对其在终末分化中的作用或作为活跃的DNA去甲基化的中间体的了解并不完整。我们报道了在小鼠肌肉中发育的有丝分裂后浦肯野细胞(PC)的DNA甲基化和羟甲基化、染色质可及性和组蛋白标记的高分辨率定位。我们的数据揭示了PC转录和表观遗传程序之间的新关系，并发现了一类在末端分化过程中同时丢失5-甲基胞嘧啶(5mC)和5hmC的基因。从有丝分裂后的PC中删除5hmC编写器Tet1、TET2和Tet3可以防止调节域和基因体中5mC和5hmC的丢失，并阻碍转录和表观遗传的发育转变。我们的数据表明，Tet介导的活性DNA去甲基化在体内发生，而获得成体PC的精确分子特性需要在分化的最后阶段持续将5mC氧化到5hmC。在出生时，哺乳动物的大脑包含数百亿个神经元。虽然数量不会随着动物的成长而增加很多，但它们的大小和结构有许多戏剧性的变化。这些变化允许神经元相互交流，发展成网络，并学习成人大脑的任务。这些变化发生的一种方式是在每个神经元的DNA上积累化学标记，这些标记有助于指示哪些基因启动，哪些基因关闭。标记DNA最常见的方法之一是在四种DNA碱基之一胞嘧啶的基础上添加一种称为甲基的化学基团。这个过程被称为甲基化。当发生甲基化时，胞嘧啶变成5-甲基胞嘧啶，或简称5mC。2009年，研究人员在大脑的DNA中发现了另一种修饰：5-羟甲基胞嘧啶，简称5HmC。当一组称为Tet羟基酶的蛋白质将5mC转化为5hmC时，这种修饰就会出现。通常情况下，将5mC转换为5hmC有助于细胞在分裂和扩张之前去除DNA上的标记。这一点很重要，因为新生成的细胞需要能够积累它们自己的甲基化标记，以正确地发挥它们的作用。然而，大脑中的神经元在出生后积累了5hmC，此时细胞不再分裂，这表明神经元可能需要5hmC才能成熟。Stoyanova等人。通过跟踪从出生到成年期DNA中发生的化学变化，开始确定小鼠神经元是否需要5hmC来获得它们的成体特征。他们测试的一些小鼠正常产生5hmC，而另一些则缺乏在特定类别的神经元中制造Tet蛋白所需的基因，阻止它们在分化过程中将5mC转化为5hmC。结果表明，如果5hmC在出生后第一周不能持续产生，神经元就不会正常成熟。这是因为神经元需要开启和关闭正确的基因才能正确分化，而这只有在一些基因中积累了5hmC，而其他基因中5hmC和5mC被移除时才会发生。这些数据突出了Tet蛋白在准备去除标记方面的作用，Tet蛋白将5mC转化为5hmC，并表明主动去除这些标记对神经元分化至关重要。鉴于5HmC在神经元发育中的作用，这个系统中的问题可能会导致大脑紊乱。进一步的研究旨在了解细胞是如何控制5hmC水平的，这可能会带来改善大脑健康的新方法。研究还表明，如果分裂细胞失去制造5hmC的能力，它们可能会癌变。未来的工作可能会更多地解释这种情况是如何发生的，以及为什么会发生。
Although high levels of 5-hydroxymethylcytosine (5hmC) accumulate in mammalian neurons, our knowledge of its roles in terminal differentiation or as an intermediate in active DNA demethylation is incomplete. We report high-resolution mapping of DNA methylation and hydroxymethylation, chromatin accessibility, and histone marks in developing postmitotic Purkinje cells (PCs) in Mus musculus. Our data reveal new relationships between PC transcriptional and epigenetic programs, and identify a class of genes that lose both 5-methylcytosine (5mC) and 5hmC during terminal differentiation. Deletion of the 5hmC writers Tet1, Tet2, and Tet3 from postmitotic PCs prevents loss of 5mC and 5hmC in regulatory domains and gene bodies, and hinders transcriptional and epigenetic developmental transitions. Our data demonstrate that Tet-mediated active DNA demethylation occurs in vivo, and that acquisition of the precise molecular properties of adult PCs require continued oxidation of 5mC to 5hmC during the final phases of differentiation. At birth, the mammalian brain contains tens of billions of neurons. Although the number does not increase much as the animal grows, there are many dramatic changes to their size and structure. These changes allow the neurons to communicate with one another, develop into networks, and learn the tasks of the adult brain. One way that these changes occur is by the accumulation of chemical marks on each neuron’s DNA that help dictate which genes switch on, and which turn off. One of the most common ways that DNA can be marked is through the addition of a chemical group called a methyl group to one of the four DNA bases, cytosine. This process is called methylation. When methylation occurs, cytosine becomes 5-methylcytosine, or 5mC for short. In 2009, researchers found another modification present in the DNA in the brain: 5-hydroxymethylcytosine, or 5hmC. This modification appears when a group of proteins called the Tet hydroxylases turn 5mC into 5hmC. Converting 5mC to 5hmC normally helps cells remove marks on their DNA before they divide and expand. This is important because the newly generated cells need to be able to accumulate their own methylation marks to perform their roles properly. However, neurons in the brain accumulate 5hmC after birth, when the cells are no longer dividing, indicating that 5hmC may be required for the neurons to mature. Stoyanova et al. set out to determine whether mouse neurons need 5hmC to get their adult characteristics by tracking the chemical changes that occur in DNA from birth to adulthood. Some of the mice they tested produced 5hmC normally, while others lacked the genes necessary to make the Tet proteins in a specific class of neurons, preventing them from converting 5mC to 5hmC as they differentiate. The results reveal that neurons do not mature properly if 5hmC is not produced continuously following the first week of life. This is because neurons need to have the right genes switched on and off to differentiate correctly, and this only happens when 5hmC accumulates in some genes, while 5hmC and 5mC are removed from others. The data highlight the role of the Tet proteins, which convert 5mC into 5hmC, in preparing the marks for removal and demonstrate that active removal of these marks is essential for neuronal differentiation. Given the role of 5hmC in the development of neurons, it is possible that problems in this system could contribute to brain disorders. Further studies aimed at understanding how cells control 5hmC levels could lead to new ways to improve brain health. Research has also shown that if dividing cells lose the ability to make 5hmC, they can become cancerous. Future work could explain more about how and why this happens.