Genetics and Genome Biology, Department of Pediatrics, The Hospital for Sick Children, and Department of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada.
Hum Mol Genet. 2011 Jan 1;20(1):1-15. doi: 10.1093/hmg/ddq427. Epub 2010 Nov 1.
Myotonic dystrophy (DM1) affects multiple organs, shows age-dependent progression and is caused by CTG expansions at the DM1 locus. We determined the DM1 CpG methylation profile and CTG length in tissues from DM1 foetuses, DM1 adults, non-affected individuals and transgenic DM1 mice. Analysis included CTCF binding sites upstream and downstream of the CTG tract, as methylation-sensitive CTCF binding affects chromatinization and transcription of the DM1 locus. In humans, in a given foetus, expansions were largest in heart and smallest in liver, differing by 40-400 repeats; in adults, the largest expansions were in heart and cerebral cortex and smallest in cerebellum, differing by up to 5770 repeats in the same individual. Abnormal methylation was specific to the mutant allele. In DM1 adults, heart, liver and cortex showed high-to-moderate methylation levels, whereas cerebellum, kidney and skeletal muscle were devoid of methylation. Methylation decreased between foetuses and adults. Contrary to previous findings, methylation was not restricted to individuals with congenital DM1. The expanded repeat demarcates an abrupt boundary of methylation. Upstream sequences, including the CTCF site, were methylated, whereas the repeat itself and downstream sequences were not. In DM1 mice, expansion-, tissue- and age-specific methylation patterns were similar but not identical to those in DM1 individuals; notably in mice, methylation was present up- and downstream of the repeat, but greater upstream. Thus, in humans, the CpG-free expanded CTG repeat appears to maintain a highly polarized pattern of CpG methylation at the DM1 locus, which varies markedly with age and tissues.
强直性肌营养不良症（DM1）影响多个器官，具有年龄依赖性进展，由 DM1 基因座上的 CTG 扩展引起。我们确定了 DM1 胎儿、DM1 成人、非患者个体和转基因 DM1 小鼠组织中的 DM1 CpG 甲基化谱和 CTG 长度。分析包括 CTG 道上下游的 CTCF 结合位点，因为甲基化敏感的 CTCF 结合会影响 DM1 基因座的染色质化和转录。在人类中，在给定的胎儿中，扩张在心脏中最大，在肝脏中最小，相差 40-400 个重复；在成人中，最大的扩张在心脏和大脑皮层，最小的在小脑，同一个体中相差高达 5770 个重复。异常甲基化是突变等位基因特有的。在 DM1 成人中，心脏、肝脏和皮层显示出高低度甲基化水平，而小脑、肾脏和骨骼肌则没有甲基化。甲基化在胎儿和成人之间减少。与之前的发现相反，甲基化不限于先天性 DM1 个体。扩展重复划定了甲基化的突然边界。上游序列，包括 CTCF 位点，被甲基化，而重复本身和下游序列则没有。在 DM1 小鼠中，扩张、组织和年龄特异性甲基化模式与 DM1 个体相似但不完全相同；值得注意的是，在小鼠中，甲基化存在于重复的上下游，但上游更多。因此，在人类中，无 CpG 的扩展 CTG 重复似乎在 DM1 基因座上维持着高度极化的 CpG 甲基化模式，该模式随年龄和组织变化显著。
