Chen Taiping, Ueda Yoshihide, Dodge Jonathan E, Wang Zhenjuan, Li En
Cutaneous Biology Research Center and Cardiovascular Research Center, Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts 02129, USA.
Mol Cell Biol. 2003 Aug;23(16):5594-605. doi: 10.1128/MCB.23.16.5594-5605.2003.
We have previously shown that the DNA methyltransferases Dnmt3a and Dnmt3b carry out de novo methylation of the mouse genome during early postimplantation development and of maternally imprinted genes in the oocyte. In the present study, we demonstrate that Dnmt3a and Dnmt3b are also essential for the stable inheritance, or "maintenance," of DNA methylation patterns. Inactivation of both Dnmt3a and Dnmt3b in embryonic stem (ES) cells results in progressive loss of methylation in various repeats and single-copy genes. Interestingly, introduction of the Dnmt3a, Dnmt3a2, and Dnmt3b1 isoforms back into highly demethylated mutant ES cells restores genomic methylation patterns; these isoforms appear to have both common and distinct DNA targets, but they all fail to restore the maternal methylation imprints. In contrast, overexpression of Dnmt1 and Dnmt3b3 failed to restore DNA methylation patterns due to their inability to catalyze de novo methylation in vivo. We also show that hypermethylation of genomic DNA by Dnmt3a and Dnmt3b is necessary for ES cells to form teratomas in nude mice. These results indicate that genomic methylation patterns are determined partly through differential expression of different Dnmt3a and Dnmt3b isoforms.
我们之前已经表明，DNA甲基转移酶Dnmt3a和Dnmt3b在植入后早期发育过程中对小鼠基因组进行从头甲基化，并在卵母细胞中对母源印记基因进行从头甲基化。在本研究中，我们证明Dnmt3a和Dnmt3b对于DNA甲基化模式的稳定遗传或“维持”也是必不可少的。胚胎干细胞（ES细胞）中Dnmt3a和Dnmt3b的失活导致各种重复序列和单拷贝基因中甲基化的逐渐丧失。有趣的是，将Dnmt3a、Dnmt3a2和Dnmt3b1亚型重新导入高度去甲基化的突变ES细胞中可恢复基因组甲基化模式；这些亚型似乎有共同的和不同的DNA靶点，但它们都未能恢复母源甲基化印记。相比之下，Dnmt1和Dnmt3b3的过表达未能恢复DNA甲基化模式，因为它们无法在体内催化从头甲基化。我们还表明，Dnmt3a和Dnmt3b对基因组DNA的超甲基化对于ES细胞在裸鼠中形成畸胎瘤是必要的。这些结果表明，基因组甲基化模式部分是通过不同Dnmt3a和Dnmt3b亚型的差异表达来决定的。
