Takeshima Hideyuki, Suetake Isao, Shimahara Hideto, Ura Kiyoe, Tate Shin-ichi, Tajima Shoji
Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka 565-0871.
J Biochem. 2006 Mar;139(3):503-15. doi: 10.1093/jb/mvj044.
In mammals, the resetting of DNA methylation patterns in early embryos and germ cells is crucial for development. De novo type DNA methyltransferases Dnmt3a and Dnmt3b are responsible for creating DNA methylation patterns during embryogenesis and in germ cells. Although their in vitro DNA methylation properties are similar, Dnmt3a and Dnmt3b methylate different genomic DNA regions in vivo. In the present study, we have examined the DNA methylation activity of Dnmt3a and Dnmt3b towards nucleosomes reconstituted from recombinant histones and DNAs, and compared it to that of the corresponding naked DNAs. Dnmt3a showed higher DNA methylation activity than Dnmt3b towards naked DNA and the naked part of nucleosomal DNA. On the other hand, Dnmt3a scarcely methylated the DNA within the nucleosome core region, while Dnmt3b significantly did, although the activity was low. We propose that the preferential DNA methylation activity of Dnmt3a towards the naked part of nucleosomal DNA and the significant methylation activity of Dnmt3b towards the nucleosome core region contribute to their distinct methylation of genomic DNA in vivo.
在哺乳动物中，早期胚胎和生殖细胞中DNA甲基化模式的重设对发育至关重要。从头型DNA甲基转移酶Dnmt3a和Dnmt3b负责在胚胎发生过程中和生殖细胞中创建DNA甲基化模式。尽管它们的体外DNA甲基化特性相似，但Dnmt3a和Dnmt3b在体内甲基化不同的基因组DNA区域。在本研究中，我们检测了Dnmt3a和Dnmt3b对由重组组蛋白和DNA重构的核小体的DNA甲基化活性，并将其与相应的裸露DNA的活性进行比较。Dnmt3a对裸露DNA和核小体DNA的裸露部分显示出比Dnmt3b更高的DNA甲基化活性。另一方面，Dnmt3a几乎不甲基化核小体核心区域内的DNA，而Dnmt3b则显著甲基化，尽管活性较低。我们认为，Dnmt3a对核小体DNA裸露部分的优先DNA甲基化活性以及Dnmt3b对核小体核心区域的显著甲基化活性有助于它们在体内对基因组DNA进行不同的甲基化。
