British Heart Foundation Centre of Research Excellence, Department of Cardiology, King's College London, London SE5 9NU, UK.
King's Centre of Excellence for Mass Spectrometry, King's College London, London SE1 9NH, UK.
Nucleic Acids Res. 2018 Feb 16;46(3):1210-1226. doi: 10.1093/nar/gkx1197.
Graded levels of molecular oxygen (O2) exist within developing mammalian embryos and can differentially regulate cellular specification pathways. During differentiation, cells acquire distinct epigenetic landscapes, which determine their function, however the mechanisms which regulate this are poorly understood. The demethylation of 5-methylcytosine (5mC) is achieved via successive oxidation reactions catalysed by the Ten-Eleven-Translocation (Tet) enzymes, yielding the 5-hydroxymethylcytosine (5hmC) intermediate. These require O2 as a co-factor, and hence may link epigenetic processes directly to O2 gradients during development. We demonstrate that the activities of Tet enzymes display distinct patterns of [O2]-dependency, and that Tet1 activity, specifically, is subject to differential regulation within a range of O2 which is physiologically relevant in embryogenesis. Further, differentiating embryonic stem cells displayed a transient burst of 5hmC, which was both dependent upon Tet1 and inhibited by low (1%) [O2]. A GC-rich promoter region within the Tet3 locus was identified as a significant target of this 5mC-hydroxylation. Further, this region was shown to associate with Tet1, and display the histone epigenetic marks, H3K4me3 and H3K27me3, which are characteristic of a bivalent, developmentally 'poised' promoter. We conclude that Tet1 activity, determined by [O2] may play a critical role in regulating cellular differentiation and fate in embryogenesis.
哺乳动物胚胎发育过程中存在不同氧浓度梯度，这能调节细胞的特化途径。在分化过程中，细胞获得不同的表观遗传景观，从而决定其功能，但调控这一过程的机制尚不清楚。5-甲基胞嘧啶（5mC）的去甲基化是通过 Ten-Eleven-Translocation（Tet）酶催化的连续氧化反应实现的，生成 5-羟甲基胞嘧啶（5hmC）中间产物。这些反应需要 O2 作为辅助因子，因此可能将表观遗传过程直接与发育过程中的 O2 梯度联系起来。我们证明 Tet 酶的活性表现出明显的 O2 依赖性模式，特别是 Tet1 活性受到生理相关范围内 O2 浓度的差异调节。此外，分化的胚胎干细胞显示出 5hmC 的短暂爆发，这既依赖于 Tet1，也受到低氧（1%）的抑制。在 Tet3 基因座的 GC 丰富启动子区域被鉴定为 5mC 羟化的重要靶标。此外，该区域与 Tet1 相关，并显示出组蛋白表观遗传标记 H3K4me3 和 H3K27me3，这是一种二价的、发育“准备”的启动子的特征。我们的结论是，O2 决定的 Tet1 活性可能在调节胚胎发生中的细胞分化和命运中发挥关键作用。
