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Abstract：
Epigenetic defects caused by hereditary or de novo mutations are implicated in various human diseases. It remains uncertain whether correcting the underlying mutation can reverse these defects in patient cells. Here we show by the analysis of myotonic dystrophy type 1 (DM1)-related locus that in mutant human embryonic stem cells (hESCs), DNA methylation and H3K9me3 enrichments are completely abolished by repeat excision (CTG2000 expansion), whereas in patient myoblasts (CTG2600 expansion), repeat deletion fails to do so. This distinction between undifferentiated and differentiated cells arises during cell differentiation, and can be reversed by reprogramming of gene-edited myoblasts. We demonstrate that abnormal methylation in DM1 is distinctively maintained in the undifferentiated state by the activity of the de novo DNMTs (DNMT3b in tandem with DNMT3a). Overall, the findings highlight a crucial difference in heterochromatin maintenance between undifferentiated (sequence-dependent) and differentiated (sequence-independent) cells, thus underscoring the role of differentiation as a locking mechanism for repressive epigenetic modifications at the DM1 locus.
摘要：
由遗传或从头突变引起的表观遗传缺陷与各种人类疾病有关。纠正潜在突变是否可以逆转患者细胞中的这些缺陷仍不确定。在这里，我们通过分析肌强直性营养不良1型（DM1）相关基因座，在突变的人胚胎干细胞（hESC）中，DNA甲基化和H3K9me3富集被重复切除（CTG2000扩增）完全废除，而在患者成肌细胞（CTG2600扩增）中，重复删除失败。未分化和分化细胞之间的这种区别出现在细胞分化过程中，并且可以通过基因编辑的成肌细胞的重编程来逆转。我们证明，DM1中的异常甲基化通过从头DNMT（DNMT3b与DNMT3a串联）的活性在未分化状态下被独特地维持。总的来说,这些发现强调了未分化（序列依赖性）和分化（序列依赖性）细胞之间异染色质维持的关键差异，从而强调了分化作为DM1基因座抑制性表观遗传修饰的锁定机制的作用。
