Vasques Luciana R, Stabellini Raquel, Xue Fei, Tian X Cindy, Soukoyan Marina, Pereira Lygia V
Depto Biologia and Centro de Estudos do Genoma Humano, Instituto de Biociências, Universidade de São Paulo, São Paulo, SP, Brazil.
DNA Res. 2005;12(5):373-8. doi: 10.1093/dnares/dsi013. Epub 2006 Jan 11.
X chromosome inactivation (XCI) in human and mice involves XIST/Xist gene expression from the inactive X (Xi) and repression from the active X (Xa). Repression of the XIST/Xist gene on the Xa has been associated with methylation of its 5' region. In mice, Dnmt1 has been shown to be involved in the methylation and transcriptional repression of Xist on Xa. We examined maintenance of XIST gene repression on Xa in HCT116 cell lines knockout for either DNMT1 or DNMT3B and for DNMT1 and DNMT3B simultaneously. Methylation of the XIST promoter and XIST transcriptional repression is sustained in DNMT1-, DNMT3B- and DNMT1/DNMT3B knockout cells. Despite global DNA demethylation, the double knockout cells present only partial demethylation of the XIST promoter, which is not sufficient for gene reactivation. In contrast, global DNA demethylation with 5-aza-2'-deoxycytidine leads to XIST expression. Therefore, in these human cells maintenance of XIST methylation is controlled differently than global genomic methylation and in the absence of both DNMT1 and DNMT3B.
人类和小鼠中的X染色体失活（XCI）涉及来自失活X染色体（Xi）的XIST/Xist基因表达以及来自活性X染色体（Xa）的抑制。Xa上XIST/Xist基因的抑制与其5'区域的甲基化有关。在小鼠中，已证明Dnmt1参与Xa上Xist的甲基化和转录抑制。我们检测了在HCT116细胞系中，分别敲除DNMT1或DNMT3B以及同时敲除DNMT1和DNMT3B时，Xa上XIST基因抑制的维持情况。在DNMT1、DNMT3B以及DNMT1/DNMT3B敲除细胞中，XIST启动子的甲基化和XIST转录抑制得以维持。尽管发生了全基因组DNA去甲基化，但双敲除细胞中XIST启动子仅呈现部分去甲基化，这不足以使基因重新激活。相比之下，用5-氮杂-2'-脱氧胞苷进行全基因组DNA去甲基化会导致XIST表达。因此，在这些人类细胞中，XIST甲基化的维持与全基因组甲基化的控制方式不同，且是在DNMT1和DNMT3B均缺失的情况下。
