Yamazaki Yukiko, Fujita Toko C, Low Eleanor W, Alarcón Vernadeth B, Yanagimachi Ryuzo, Marikawa Yusuke
Institute for Biogenesis Research, Department of Anatomy and Reproductive Biology, University of Hawaii John A. Burns School of Medicine, Honolulu, HI 96822, USA.
Mol Reprod Dev. 2006 Feb;73(2):180-8. doi: 10.1002/mrd.20411.
During differentiation, somatic cell nuclei acquire unique patterns of epigenetic modifications, such as DNA methylation, which affect the transcriptional activity of specific genes. Upon transfer into oocytes, however, the somatic nucleus undergoes reprogramming of these epigenetic modifications to achieve pluripotency. Oct4 is one of the critical pluripotency regulators, and is expressed in the germ line, including the pluripotent early embryonic cells. Previous studies showed that the upstream regulatory sequences of the Oct4 gene are distinctly methylated in somatic cells, and the DNA methylation of the regulatory sequences suppresses the transcriptional activity. Thus, successful reprogramming of the somatic cell nucleus to gain pluripotency must be accompanied by the demethylation of the Oct4 regulatory sequences. Here, we investigated the methylation pattern of the Oct4 promoter during early development of cloned mouse embryos. We found that the Oct4 promoter was only gradually demethylated during the early cleavage stages and that the ineffective demethylation of the promoter was associated with developmental retardation. We also found that the upstream sequences of the other pluripotency regulators, namely Nanog, Sox2, and Foxd3, were considerably under-methylated in cumulus cells. These results suggest that the Oct4 gene, as compared to the other pluripotency regulators, needs to undergo extensive demethylation during nuclear reprogramming, and that the failure of such demethylation is associated with inefficient development of cloned somatic cell embryos.
在分化过程中，体细胞的细胞核会获得独特的表观遗传修饰模式，如DNA甲基化，这会影响特定基因的转录活性。然而，当转入卵母细胞后，体细胞核会经历这些表观遗传修饰的重编程以实现多能性。Oct4是关键的多能性调节因子之一，在生殖系中表达，包括多能性早期胚胎细胞。先前的研究表明，Oct4基因的上游调控序列在体细胞中明显甲基化，且调控序列的DNA甲基化会抑制转录活性。因此，体细胞的细胞核成功重编程以获得多能性必然伴随着Oct4调控序列的去甲基化。在此，我们研究了克隆小鼠胚胎早期发育过程中Oct4启动子的甲基化模式。我们发现Oct4启动子在早期卵裂阶段仅逐渐去甲基化，且启动子去甲基化无效与发育迟缓有关。我们还发现，其他多能性调节因子，即Nanog、Sox2和Foxd3的上游序列在卵丘细胞中甲基化程度相当低。这些结果表明，与其他多能性调节因子相比，Oct4基因在核重编程过程中需要经历广泛的去甲基化，且这种去甲基化的失败与克隆体细胞胚胎发育效率低下有关。
