Kimura H, Suetake I, Tajima S
Institute for Protein Research, Osaka University, Suita, Osaka, 565-0871, Japan.
J Biochem. 1999 Jun;125(6):1175-82. doi: 10.1093/oxfordjournals.jbchem.a022401.
In vertebrates, DNA methylation plays an important role in the regulation of gene expression and embryogenesis. DNA methyltransferase, which catalyzes the introduction of a methyl group at the 5th position of cytosine in the CpG sequence, is highly accumulated in mouse oocytes and is excluded from nuclei [Carlson et al. (1992) Genes Dev. 6, 2536-2541]. In this study, we examined the expression level and localization of Xenopus DNA methyltransferase in oocytes during oogenesis. The DNA methyltransferase protein was detectable in stage III oocytes and increased thereafter, until the oocytes had matured. The rate of DNA methyltransferase synthesis rapidly increased after stage IV oocytes. Different from in mouse oocytes, DNA methyltransferase was equally distributed in the nuclear and post-nuclear fractions, in stage VI oocytes. DNA methyltransferase translocated into nuclei was uniformly localized in the nuclear matrix, and the accumulated DNA methyltransferase in stage VI nuclei had DNA methylation activity.
在脊椎动物中，DNA甲基化在基因表达调控和胚胎发育过程中发挥着重要作用。DNA甲基转移酶催化在CpG序列中胞嘧啶的第5位引入甲基基团，在小鼠卵母细胞中高度积累且被排除在细胞核外[卡尔森等人（1992年），《基因与发育》，6卷，2536 - 2541页]。在本研究中，我们检测了非洲爪蟾DNA甲基转移酶在卵子发生过程中卵母细胞内的表达水平和定位。在III期卵母细胞中可检测到DNA甲基转移酶蛋白，此后其表达量增加，直至卵母细胞成熟。IV期卵母细胞后，DNA甲基转移酶的合成速率迅速增加。与小鼠卵母细胞不同，在VI期卵母细胞中，DNA甲基转移酶在细胞核和核后组分中均匀分布。转移到细胞核内的DNA甲基转移酶均匀地定位于核基质中，并且在VI期细胞核中积累的DNA甲基转移酶具有DNA甲基化活性。
