DNA hypermethylation enhanced telomerase reverse transcriptase expression in human induced pluripotent stem cells. Homo sapiens

During reprogramming into human induced pluripotent stem cell (iPSCs), several stem cell marker genes are induced, such as OCT-4, NANOG, SALL4, and TERT. OCT-4, NANOG, and SALL4 gene expression can be regulated by DNA methylation. Their promoters become hypomethylated in iPSCs during reprogramming, leading to their induced expression. However, epigenetic regulation of the TERT gene remains unclear. In this study, we focused on epigenetic regulation of the human TERT gene and identified a differentially methylated region (DMR) at a distal region in the TERT promoter between human iPSCs and their parental somatic cells. Interestingly, the TERT-DMR was highly methylated in iPSCs, but low-level methylation was observed in their parental somatic cells. Region-specific, methylated-promoter assays showed that the methylated TERT-DMR up-regulated the promoter activity in iPSCs. In addition, Lamin B1 accumulated at the TERT-DMR in iPSCs, but not in their parent somatic cells. These results suggested that the TERT transcription was enhanced by DNA methylation at the TERT-DMR via binding to nuclear lamina during reprogramming. Our findings shed light on a new functional aspect of DNA methylation in gene expression. Overall design: Bisulphite converted DNA from the samples were hybridized to the Illumina Infinium Human Methylation450K Beadchip

在将体细胞重编程为人类诱导多能干细胞（iPSCs）的过程中，会诱导多种干细胞标志物基因的表达，例如OCT-4、NANOG、SALL4与TERT。OCT-4、NANOG及SALL4的基因表达可受DNA甲基化调控：在重编程过程中，这些基因的启动子区域在iPSCs中发生低甲基化，进而诱导其表达上调。然而，目前关于TERT基因的表观遗传调控机制仍未明确。本研究聚焦于人类TERT基因的表观遗传调控，在人类iPSCs与其亲本体细胞的TERT启动子远端区域，鉴定出一处差异甲基化区域（DMR）。值得注意的是，该TERT-DMR在iPSCs中呈现高甲基化状态，而在亲本体细胞中仅检测到低水平甲基化。区域特异性甲基化启动子实验结果显示，甲基化的TERT-DMR可上调iPSCs中的启动子活性。此外，核纤层蛋白B1（Lamin B1）在iPSCs的TERT-DMR区域发生富集，而在亲本体细胞中则无此富集现象。上述结果表明，在重编程过程中，TERT的转录可通过TERT-DMR处的DNA甲基化结合核纤层而得到增强。本研究的发现为DNA甲基化在基因表达调控中的全新功能维度提供了新的研究视角。整体实验设计：将样本中的亚硫酸氢盐转化DNA与Illumina Infinium人类甲基化450K芯片进行杂交。