Department of Anatomy and Cell Biology, Indiana University School of Medicine Indianapolis, IN, USA.
Agricultural and Biological Engineering, Bindley Bioscience Center, Purdue University West Lafayette, IN, USA.
Front Genet. 2014 Mar 10;5:46. doi: 10.3389/fgene.2014.00046. eCollection 2014.
DNA methylation 5-methylcytosine (5mC) predicts a compacting chromatin inaccessible to transcription. The discovery of 5-hydroxymethylcytosine (5hmC), which is derived from 5mC, adds a new dimension to the mechanism and role of DNA methylation in epigenetics. Genomic evidence indicates that the 5hmC is located in the alternate regions to 5mC. However, the nature of 5hmC, as compared with classical 5mC remains unclear. Observing the mouse brain through embryonic development to the adult, first, we found that 5hmC is not merely an intermediate metabolite of demethylation, but is long lasting, chromatically distinct, and dynamically changing during neurodevelopment. Second, we found that 5hmC distinctly differs from 5mC in its chromatin affiliation during neural stem cell (NSC) development. Thirdly, we found both 5mC and 5hmC to be uniquely polarized and dynamic through the NSC development. 5mC was found to progressively polarize with MBD1 and MeCP2, and recruits H3K9me3 and H3K27me3; while 5hmC progressively co-localizes with MBD3 and recruits H3K4me2. Critical differential binding of 5mC with MBD1, and 5hmC with MBD3 was validated by Resonance Energy Transfer technique FLIM-FRET. This transition and polarization coincides with neuroprogenitor differentiation. Finally, at the time of synaptogenesis, 5mC gradually accumulates in the heterochromatin while 5hmC accumulates in the euchromatin, which is consistent with the co-localization of 5hmC with PolII, which mediates RNA transcription. Our data indicate that 5mC and 5hmC are diverse in their functional interactions with chromatin. This diversity is likely to contribute to the versatile epigenetic control of transcription mediating brain development and functional maintenance of adult brain.
DNA 甲基化 5-甲基胞嘧啶（5mC）预测了一种致密的染色质，转录因子无法接近。5-羟甲基胞嘧啶（5hmC）的发现增加了 DNA 甲基化在表观遗传学中的机制和作用的新维度，它来源于 5mC。基因组证据表明，5hmC 位于 5mC 的替代区域。然而，与经典的 5mC 相比，5hmC 的性质仍不清楚。通过观察胚胎发育到成年期的小鼠大脑，我们首先发现 5hmC 不仅仅是去甲基化的中间代谢产物，而是在神经发育过程中持久存在、染色质明显不同且动态变化的。其次，我们发现 5hmC 在神经干细胞（NSC）发育过程中的染色质关联与 5mC 明显不同。第三，我们发现 5mC 和 5hmC 在 NSC 发育过程中都呈现独特的极化和动态变化。5mC 随着 MBD1 和 MeCP2 的逐渐极化，招募 H3K9me3 和 H3K27me3；而 5hmC 则随着 MBD3 的逐渐极化，招募 H3K4me2。通过共振能量转移技术 FLIM-FRET 验证了 5mC 与 MBD1 的关键差异结合，以及 5hmC 与 MBD3 的关键差异结合。这种转变和极化与神经祖细胞分化同时发生。最后，在突触发生时，5mC 逐渐积累在异染色质中，而 5hmC 则积累在常染色质中，这与介导 RNA 转录的 5hmC 与 PolII 的共定位一致。我们的数据表明，5mC 和 5hmC 在与染色质的功能相互作用方面存在多样性。这种多样性可能有助于转录的多功能表观遗传控制，从而调节大脑发育和成年大脑的功能维持。
