Wong Nicholas C, Wong Lee H, Quach Julie M, Canham Paul, Craig Jeffrey M, Song Jenny Z, Clark Susan J, Choo K H Andy
Chromosome Research Laboratory, Murdoch Childrens Research Institute, Royal Children's Hospital, Parkville, Victoria, Australia.
PLoS Genet. 2006 Feb;2(2):e17. doi: 10.1371/journal.pgen.0020017. Epub 2006 Feb 10.
DNA methylation is a hallmark of transcriptional silencing, yet transcription has been reported at the centromere. To address this apparent paradox, we employed a fully sequence-defined ectopic human centromere (or neocentromere) to investigate the relationship between DNA methylation and transcription. We used sodium bisulfite PCR and sequencing to determine the methylation status of 2,041 CpG dinucleotides distributed across a 6.76-Mbp chromosomal region containing a neocentromere. These CpG dinucleotides were associated with conventional and nonconventional CpG islands. We found an overall hypermethylation of the neocentric DNA at nonconventional CpG islands that we designated as CpG islets and CpG orphans. The observed hypermethylation was consistent with the presence of a presumed transcriptionally silent chromatin state at the neocentromere. Within this neocentric chromatin, specific sites of active transcription and the centromeric chromatin boundary are defined by DNA hypomethylation. Our data demonstrate, for the first time to our knowledge, a correlation between DNA methylation and centromere formation in mammals, and that transcription and "chromatin-boundary activity" are permissible at the centromere through the selective hypomethylation of pockets of sequences without compromising the overall silent chromatin state and function of the centromere.
DNA甲基化是转录沉默的一个标志，但据报道着丝粒处存在转录现象。为了解决这一明显的矛盾，我们采用了一个完全序列定义的异位人类着丝粒（或新着丝粒）来研究DNA甲基化与转录之间的关系。我们使用亚硫酸氢钠PCR和测序来确定分布在一个包含新着丝粒的6.76兆碱基染色体区域内的2041个CpG二核苷酸的甲基化状态。这些CpG二核苷酸与传统和非传统的CpG岛相关。我们发现新着丝粒DNA在我们称为CpG小岛和CpG孤子的非传统CpG岛上总体呈高甲基化。观察到的高甲基化与新着丝粒处推测的转录沉默染色质状态的存在一致。在这种新着丝粒染色质中，活跃转录的特定位点和着丝粒染色质边界由DNA低甲基化定义。据我们所知，我们的数据首次证明了哺乳动物中DNA甲基化与着丝粒形成之间的相关性，并且通过序列区域的选择性低甲基化，着丝粒处允许转录和“染色质边界活性”，而不会损害着丝粒整体沉默染色质状态和功能。
