Xie S, Wang Z, Okano M, Nogami M, Li Y, He W W, Okumura K, Li E
Cardiovascular Research Center, Massachusetts General Hospital, Department of Medicine, Harvard Medical School, Charlestown, MA 02129, USA.
Gene. 1999 Aug 5;236(1):87-95. doi: 10.1016/s0378-1119(99)00252-8.
DNA methylation plays an important role in animal development and gene regulation. In mammals, several genes encoding DNA cytosine methyltransferases have been identified. DNMT1 is constitutively expressed and is required for the maintenance of global methylation after DNA replication. In contrast, the murine Dnmt3 family genes appear to be developmentally regulated and behave like de novo DNA methyltransferases in vitro. In this study, we have cloned human DNMT3A and DNMT3B that encode full-length DNMT3A and DNMT3B proteins with 98% and 94% amino acid sequence identity to their murine homologues. The DNMT3A and DNMT3B show high homology in the carboxy terminal catalytic domain and contain a conserved cysteine-rich region, which shares homology with the X-linked ATRX gene of the SNF2/SWI family. We have mapped human DNMT3A and DNMT3B to chromosomes 2p23 and 20q11.2 respectively, and determined the DNMT3B genomic structure. We further show that DNMT3A expression is ubiquitous and can be readily detected in most adult tissues, whereas DNMT3B is expressed at very low levels in most tissues except testis, thyroid and bone marrow. Significantly, both DNMT3A and DNMT3B expression is elevated in several tumor cell lines to levels comparable to DNMT1. The cloning of the human DNMT3 genes will facilitate further biochemical and genetic studies of their functions in establishment of DNA methylation patterns, regulation of gene expression and tumorigenesis.
DNA甲基化在动物发育和基因调控中发挥着重要作用。在哺乳动物中，已鉴定出几个编码DNA胞嘧啶甲基转移酶的基因。DNMT1持续表达，是DNA复制后维持整体甲基化所必需的。相比之下，小鼠Dnmt3家族基因似乎受发育调控，在体外表现得像从头DNA甲基转移酶。在本研究中，我们克隆了人类DNMT3A和DNMT3B，它们编码的全长DNMT3A和DNMT3B蛋白与小鼠同源物的氨基酸序列同一性分别为98%和94%。DNMT3A和DNMT3B在羧基末端催化结构域显示出高度同源性，并包含一个保守的富含半胱氨酸区域，该区域与SNF2/SWI家族的X连锁ATRX基因具有同源性。我们已将人类DNMT3A和DNMT3B分别定位到染色体2p23和20q11.2，并确定了DNMT3B的基因组结构。我们进一步表明，DNMT3A表达普遍存在，在大多数成年组织中很容易检测到，而DNMT3B在除睾丸、甲状腺和骨髓外的大多数组织中表达水平非常低。值得注意的是，在几种肿瘤细胞系中，DNMT3A和DNMT3B的表达均升高至与DNMT1相当的水平。人类DNMT3基因的克隆将有助于进一步对其在DNA甲基化模式建立、基因表达调控和肿瘤发生中的功能进行生化和遗传学研究。
