Molecular Genetic Studies on the Physiological Function and Disorders of DNA Methylation

CpG二核苷酸的甲基化在表观遗传基因组调控中起着核心作用，其缺陷导致先天性疾病和癌症。我们已经研究了DNA甲基转移酶（DNMTs）和甲基-CpG结合蛋白（MBD蛋白）的功能和紊乱，并发现以下内容。1.通过敲除小鼠DNMT 3A基因，DNMT，在一个种系特异性的方式，我们发现，这种酶是必不可少的父亲和母亲的印记。2.测定DNMT 3A和DNMT 3B的酶性质和靶特异性。3.在日本ICE综合征家族中发现了DNMT 3B的新突变。我们还发现了一例在DNMT 3B中没有突变的ICE病例，这表明了该疾病的异质性。4.我们报道了一种新的与印记有关的疾病，即父亲14二体，其特征是钟形胸部和波浪形肋骨。5.我们发现MBD 1通过两条独立的途径抑制转录并形成抑制性染色质：1）一条途径是由转录介质MCAF/AM和组蛋白甲基转移酶SETDB 1/ESET形成的复合物介导的; 2）另一条途径涉及组蛋白甲基转移酶Suv 39、组蛋白去乙酰化酶HDAC 1/2和异染色质蛋白HP 1。6.与a.测定含甲基化CpG的DNA分子。7.发现导致Rett综合征的McCP 2突变损害其抑制转录和形成抑制性染色质的能力。8.我们报道了MBD 1与甲基化嘌呤DNA糖基化酶协同促进碱基切除修复。总而言之，我们的发现极大地增加了我们对DNA甲基化和转录抑制机制以及DNA甲基化相关疾病病理学的了解。

Methylation of CpG dinucleotides plays a central role in the epigenetic genome regulation, and its defects cause congenital disorders and cancers. We have studied the functions and disorders of DNA methyltransferases (DNMTs) and methyl-CpG-binding proteins (MBD proteins) and found the followings. 1.By knocking out mouse DNMT3A, a de novo-type. DNMT, in a germline-specific manner, we found that this enzyme is essential for paternal and maternal imprinting. 2.Enzymatic properties and target specificities of DNMT3A and DNMT3B were determined. 3.New mutations of DNMT3B were identified in Japanese families with ICE syndrome. We also found an ICE case with no mutation in DNMT3B, which suggests the heterogeneity of the disease. 4.We reported that paternal disomy 14 is a new imprinting-related disorder characterized by bell-shaped chest and wavy ribs. 5.We found that MBD1 represses transcription and forms repressive chromatin through two independent pathways: 1) one mediated by a complex formed with a transcriptional mediator MCAF/AM and a histone methyltransferase SETDB1/ESET; 2) the other involving a histone methyltransferase Suv39, a histone deacetylase HDAC1/2 and a heterochromatin protein HP1. 6.The tertiary structure of the DNA binding domain of MBD1 complexed with a. methylated-CpG-containing DNA molecule was determined. 7.The mutations of McCP2 causing Rett syndrome were found to impair its ability to repress transcription and to form repressive chromatin. 8.We reported that MBD1 promotes base excision repair in cooperation with a methylated-purine DNA glycosylase. All together, our findings have greatly increased our knowledge on the mechanisms of DNA methylation and transcriptional repression through it and the pathology of DNA methylation-associated disorders.