Ma X S, Wang X G, Qin L, Song C L, Lin F, Song J M, Zhu C C, Liu H L
College of Animal Science and Technology, Nanjing Agricultural University, Nanjing, China.
College of Animal Science and Technology, Nanjing Agricultural University, Nanjing, China
Genet Mol Res. 2014 Oct 27;13(4):8632-9. doi: 10.4238/2014.October.27.2.
The developmental dynamics of DNA methylation events have been well studied. Active demethylation of the paternal genome occurs in the zygote, passive demethylation occurs during cleavage stages, and de novo methylation occurs by the blastocyst stage. It is believed that the paternal genome has lower levels of methylation during early development than the maternal genome. However, in this study, we provide direct and indirect evidence of genome-wide de novo DNA methylation of the paternal genome after the first cell cycle in mouse embryos. Although very little methylation was detected within the male pronucleus in zygotes, an intense methylation signal was clearly visible within the androgenetic 2-cell embryos. Moreover, the DNA methylation level of the paternal genome in the post-zygotic metaphase embryos was similar to that of the maternal genome. Using indirect immunofluorescence with an antibody to methylated lysine 9 in histone H3, we provided new evidence to support the concept of spatial compartmentalization of parental genomes in 2-cell mouse embryos. Nevertheless, the transient segregation of parental genomes was not observed by determining the DNA methylation distribution in the 2-cell embryos even though DNA methylation asymmetry between the maternal and paternal pronucleus existed in the 1-cell stage. The disappearance of separate immunofluorescence signals of 5-methyl cytosine in the 2-cell embryos might be attributed to the de novo methylation of the paternal genome during the first mitotic cycle.
DNA甲基化事件的发育动力学已得到充分研究。父本基因组的主动去甲基化发生在合子中，被动去甲基化发生在卵裂阶段，而从头甲基化则发生在囊胚阶段。据信，在早期发育过程中，父本基因组的甲基化水平低于母本基因组。然而，在本研究中，我们提供了直接和间接证据，证明小鼠胚胎第一个细胞周期后父本基因组发生了全基因组范围的从头DNA甲基化。虽然在合子的雄原核内检测到的甲基化很少，但在孤雄二细胞胚胎内可见强烈的甲基化信号。此外，合子后中期胚胎中父本基因组的DNA甲基化水平与母本基因组相似。使用针对组蛋白H3中甲基化赖氨酸9的抗体进行间接免疫荧光，我们提供了新的证据来支持小鼠二细胞胚胎中亲本基因组空间分隔的概念。然而，尽管在单细胞阶段母本和父本原核之间存在DNA甲基化不对称，但通过确定二细胞胚胎中的DNA甲基化分布，未观察到亲本基因组的短暂分离。二细胞胚胎中5-甲基胞嘧啶单独免疫荧光信号的消失可能归因于第一个有丝分裂周期中父本基因组的从头甲基化。
