基因內(nèi)的甲基化作用

DNA甲基化在通過其對(duì)基因表達(dá)的效應(yīng)來保持細(xì)胞身份中扮演重要角色。5'啟動(dòng)子的甲基化抑制基因表達(dá)，而基因內(nèi)的DNA甲基化（即甲基化過程發(fā)生在一個(gè)基因體本身的內(nèi)部）作用的研究卻不是很多，仍然存在爭議。

Although it is known that the methylation of DNA in 5′ promoters suppresses gene expression, the role of DNA methylation in gene bodies is unclear1, 2, 3, 4, 5. In mammals, tissue- and cell type-specific methylation is present in a small percentage of 5′ CpG island （CGI） promoters, whereas a far greater proportion occurs across gene bodies, coinciding with highly conserved sequences5, 6, 7, 8, 9, 10. Tissue-specific intragenic methylation might reduce3, or, paradoxically, enhance transcription elongation efficiency1, 2, 4, 5. Capped analysis of gene expression （CAGE） experiments also indicate that transcription commonly initiates within and between genes11, 12, 13, 14, 15. To investigate the role of intragenic methylation, we generated a map of DNA methylation from the human brain encompassing 24.7 million of the 28 million CpG sites. From the dense, high-resolution coverage of CpG islands, the majority of methylated CpG islands were shown to be in intragenic and intergenic regions, whereas less than 3% of CpG islands in 5′ promoters were methylated.

現(xiàn)在，一個(gè)基于測(cè)序技術(shù)的、來自人腦的下一代DNA甲基化圖已構(gòu)建成功，其覆蓋面達(dá)到的程度。將這幅圖與小鼠和人的組蛋白甲基化的腦組織Chip-seq及基因表達(dá)結(jié)合起來，凸顯了基因內(nèi)甲基化在調(diào)控基因體內(nèi)的組織特異性啟動(dòng)子中所起的一個(gè)主要作用以及在5'啟動(dòng)子中所起的一個(gè)次要作用（其作用之小出乎意料）。