Cell：新技术揭示DNA密码中的5-羟甲基胞嘧啶隐秘信息

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由于缺少在全基因组范围内，对5-羟甲基胞嘧啶（5hmC）进行单个碱基水平分辨率的作图手段，对5hmC的研究一直进展缓慢。5月17日Cell杂志在线发表了Chuan He研究组的研究论文“Base-Resolution Analysis of 5-Hydroxymethylcytosine in the Mammalian Genome”将这一研究方向推进了一大步。

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传统的亲和纯化手段不能准确定位5hmC，也不能确定它在每一修饰位点的相对丰度。Chuan He等人运用Tet辅助的重亚硫酸盐测序（TAB-Seq）技术，与传统的重亚硫酸盐测序技术结合,在基因组范围内以单个碱基的分辨率对5hmC进行作图，并确定5hmC与5mC的相对丰度。

将这一技术应用于胚胎干细胞，他们不仅证实了5hmC在哺乳动物基因组中广泛分布，而且显示5hmC位点更易于出现在某些特殊序列当中，并具有在两条DNA链分布的不对称性。

他们还发现邻近转录因子结合的DNA位点存在高水平的5hmC和低水平的5mC。此外，5hmC分布水平在不同功能序列元件之间差异也很大。这提示5hmC的修饰和保持在这些元件之间的机制是不同的。 
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<a title="" href="http://dx.doi.org/10.1016/j.cell.2012.04.027" target="_blank">doi:10.1016/j.cell.2012.04.027</a>
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<div>Base-Resolution Analysis of 5-Hydroxymethylcytosine in the Mammalian Genome</div>
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<div>Miao Yu,Gary C. Hon,Keith E. Szulwach,Chun-Xiao Song,Liang Zhang,Audrey Kim,Xuekun Li,Qing Dai,Yin Shen,Beomseok Park,Jung-Hyun Min,Peng Jin, Bing Ren, and Chuan He</div>
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<div>The study of 5-hydroxylmethylcytosines (5hmC) has been hampered by the lack of a method to map it at single-base resolution on a genome-wide scale. Affinity purification-based methods cannot precisely locate 5hmC nor accurately determine its relative abundance at each modified site. We here present a genome-wide approach, Tet-assisted bisulfite sequencing (TAB-Seq), that when combined with traditional bisulfite sequencing can be used for mapping 5hmC at base resolution and quantifying the relative abundance of 5hmC as well as 5mC. Application of this method to embryonic stem cells not only confirms widespread distribution of 5hmC in the mammalian genome but also reveals sequence bias and strand asymmetry at 5hmC sites. We observe high levels of 5hmC and reciprocally low levels of 5mC near but not on transcription factor-binding sites. Additionally, the relative abundance of 5hmC varies significantly among distinct functional sequence elements, suggesting different mechanisms for 5hmC deposition and maintenance.</div>
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 <br/>来源：生物谷

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