Dunican Donncha S, Ruzov Alexey, Hackett Jamie A, Meehan Richard R
Human Genetics Unit, MRC, Western General Hospital, Crewe Road, and Genes and Development Group, School of Biomedical Sciences, The University of Edinburgh, Edinburgh EH4 2XU, UK.
Development. 2008 Apr;135(7):1295-302. doi: 10.1242/dev.016402. Epub 2008 Feb 27.
We previously reported that the maintenance cytosine methyltransferase xDnmt1 is essential for gene silencing in early Xenopus laevis embryos. In the present study, we show that silencing is independent of its catalytic function and that xDnmt1 possesses an intrinsic transcription repression function. We show that reduction of xDnmt1p by morpholino (xDMO) injection prematurely activates gene expression without global changes in DNA methylation before the mid-blastula transition (MBT). Repression of xDnmt1p target genes can be reimposed in xDMO morphants with an mRNA encoding a catalytically inactive form of human DNMT1. Moreover, target gene promoter analysis indicates that silencing is not reliant on dynamic changes in DNA methylation. We demonstrate that xDnmt1 can suppress transcription activator function and can be specifically localised to non-methylated target promoters. These data imply that xDnmt1 has a major silencer role in early Xenopus development before the MBT as a direct transcription repressor protein.
我们之前报道过,维持性胞嘧啶甲基转移酶xDnmt1对于非洲爪蟾早期胚胎中的基因沉默至关重要。在本研究中,我们表明基因沉默独立于其催化功能,并且xDnmt1具有内在的转录抑制功能。我们发现,通过注射吗啉代寡核苷酸(xDMO)降低xDnmt1p的水平会在囊胚中期转换(MBT)之前过早激活基因表达,而DNA甲基化并无全局性变化。在注射xDMO的胚胎中,用编码无催化活性形式的人DNMT1的mRNA可以重新施加对xDnmt1p靶基因的抑制。此外,靶基因启动子分析表明,基因沉默并不依赖于DNA甲基化的动态变化。我们证明,xDnmt1可以抑制转录激活因子的功能,并且可以特异性地定位于未甲基化的靶启动子。这些数据表明,在MBT之前的非洲爪蟾早期发育中,xDnmt1作为一种直接的转录抑制蛋白具有主要的沉默作用。