Department of Hematology, University Hospital Regensburg, Franz-Josef-Strauss-Allee 11, 93042 Regensburg, Germany.
Genome Biol. 2010;11(6):R63. doi: 10.1186/gb-2010-11-6-r63. Epub 2010 Jun 18.
In mammals, the dynamics of DNA methylation, in particular the regulated, active removal of cytosine methylation, has remained a mystery, partly due to the lack of appropriate model systems to study DNA demethylation. Previous work has largely focused on proliferating cell types that are mitotically arrested using pharmacological inhibitors to distinguish between active and passive mechanisms of DNA demethylation.
We explored this epigenetic phenomenon in a natural setting of post-mitotic cells: the differentiation of human peripheral blood monocytes into macrophages or dendritic cells, which proceeds without cell division. Using a global, comparative CpG methylation profiling approach, we identified many novel examples of active DNA demethylation and characterized accompanying transcriptional and epigenetic events at these sites during monocytic differentiation. We show that active DNA demethylation is not restricted to proximal promoters and that the time-course of demethylation varies for individual CpGs. Irrespective of their location, the removal of methylated cytosines always coincided with the appearance of activating histone marks.
Demethylation events are highly reproducible in monocyte-derived dendritic cells from different individuals. Our data suggest that active DNA demethylation is a precisely targeted event that parallels or follows the modification of histones, but is not necessarily coupled to alterations in transcriptional activity.
在哺乳动物中，DNA 甲基化的动态变化，特别是胞嘧啶甲基化的有调控的、活跃的去除，一直是一个谜，部分原因是缺乏适当的模型系统来研究 DNA 去甲基化。以前的工作主要集中在增殖细胞类型上，这些细胞通过使用药理抑制剂有丝分裂来区分 DNA 去甲基化的主动和被动机制。
我们在有丝分裂后细胞的自然环境中探索了这种表观遗传现象：人外周血单核细胞分化为巨噬细胞或树突状细胞，这个过程不进行细胞分裂。我们使用全局、比较性 CpG 甲基化分析方法，在单核细胞分化过程中，在这些位点鉴定了许多新的主动 DNA 去甲基化的例子，并对其伴随的转录和表观遗传事件进行了特征描述。我们表明，主动 DNA 去甲基化不仅限于近端启动子，而且个别 CpG 的去甲基化时间进程也不同。无论它们的位置如何，甲基化胞嘧啶的去除总是与激活组蛋白标记的出现相吻合。
来自不同个体的单核细胞衍生的树突状细胞中的去甲基化事件高度可重复。我们的数据表明，主动 DNA 去甲基化是一个精确靶向的事件，与组蛋白的修饰平行或紧随其后，但不一定与转录活性的改变相关。
