Mund Cora, Musch Tanja, Strödicke Martin, Assmann Birte, Li En, Lyko Frank
Research Group Epigenetics, Deutsches Krebsforschungszentrum, Im Neuenheimer Feld 580, 69120 Heidelberg, Germany.
Biochem J. 2004 Mar 15;378(Pt 3):763-8. doi: 10.1042/BJ20031567.
DNA methyltransferases (Dnmts) mediate the epigenetic modification of eukaryotic genomes. Mammalian DNA methylation patterns are established and maintained by co-operative interactions among the Dnmt proteins Dnmt1, Dnmt3a and Dnmt3b. Owing to their simultaneous presence in mammalian cells, the activities of individual Dnmt have not yet been determined. This includes a fourth putative Dnmt, namely Dnmt2, which has failed to reveal any activity in previous assays. We have now established transgenic Drosophila strains that allow for individual overexpression of all known mouse Dnmts. Quantitative analysis of genomic cytosine methylation levels demonstrated a robust Dnmt activity for the de novo methyltransferases Dnmt3a and Dnmt3b. In addition, we also detected a weak but significant activity for Dnmt2. Subsequent methylation tract analysis by genomic bisulphite sequencing revealed that Dnmt3 enzymes preferentially methylated CpG dinucleotides in a processive manner, whereas Dnmt2 methylated isolated cytosine residues in a non-CpG dinucleotide context. Our results allow a direct comparison of the activities of mammalian Dnmts and suggest a significant functional specialization of these enzymes.
DNA甲基转移酶（Dnmts）介导真核生物基因组的表观遗传修饰。哺乳动物的DNA甲基化模式是由Dnmt蛋白Dnmt1、Dnmt3a和Dnmt3b之间的协同相互作用建立和维持的。由于它们同时存在于哺乳动物细胞中，单个Dnmt的活性尚未确定。这其中包括第四个假定的Dnmt，即Dnmt2，它在之前的检测中未显示出任何活性。我们现已建立了转基因果蝇品系，可使所有已知的小鼠Dnmts进行个体过表达。对基因组胞嘧啶甲基化水平的定量分析表明，从头甲基转移酶Dnmt3a和Dnmt3b具有强大的Dnmt活性。此外，我们还检测到Dnmt2具有微弱但显著的活性。随后通过基因组亚硫酸氢盐测序进行的甲基化片段分析表明，Dnmt3酶以连续方式优先甲基化CpG二核苷酸，而Dnmt2在非CpG二核苷酸背景下甲基化孤立的胞嘧啶残基。我们的结果使得能够直接比较哺乳动物Dnmts的活性，并表明这些酶具有显著的功能特化。
