Department of Animal Biotechnology, College of Animal Bioscience and Technology, Konkuk University, 120 Neungdong-ro, Gwangjin-gu, Seoul 133-702, Republic of Korea.
J Cell Sci. 2013 Jun 1;126(Pt 11):2516-24. doi: 10.1242/jcs.122754. Epub 2013 Mar 22.
Induced pluripotent stem cells (iPSCs), generated from somatic cells by overexpression of transcription factors Oct4, Sox2, Klf4 and c-Myc have the same characteristics as pluripotent embryonic stem cells (ESCs). iPSCs reprogrammed from differentiated cells undergo epigenetic modification during reprogramming, and ultimately acquire a similar epigenetic state to that of ESCs. In this study, these epigenetic changes were observed in reprogramming of uniparental parthenogenetic somatic cells. The parthenogenetic pattern of imprinted genes changes during the generation of parthenogenetic maternal iPSCs (miPSCs), a process referred to as pluripotent reprogramming. We determined whether altered imprinted genes are maintained or revert to the parthenogenetic state when the reprogrammed cells are redifferentiated into specialized cell types. To address this question, we redifferentiated miPSCs into neural stem cells (miPS-NSCs) and compared them with biparental female NSCs (fNSCs) and parthenogenetic NSCs (pNSCs). We found that pluripotent reprogramming of parthenogenetic somatic cells could reset parthenogenetic DNA methylation patterns in imprinted genes, and that alterations in DNA methylation were maintained even after miPSCs were redifferentiated into miPS-NSCs. Notably, maternally methylated imprinted genes (Peg1, Peg3, Igf2r, Snrpn and Ndn), whose differentially methylated regions were fully methylated in pNSCs, were demethylated and their expression levels were found to be close to the levels in normal biparental fNSCs after reprogramming and redifferentiation. Our findings suggest that pluripotent reprogramming of parthenogenetic somatic cells followed by redifferentiation leads to changes in DNA methylation of imprinted genes and the reestablishment of gene expression levels to those of normal biparental cells.
诱导多能干细胞（iPSCs）是通过过表达转录因子 Oct4、Sox2、Klf4 和 c-Myc 从体细胞中产生的，具有与多能胚胎干细胞（ESCs）相同的特征。重编程过程中，从分化细胞中重编程的 iPSCs 经历表观遗传修饰，最终获得与 ESCs 相似的表观遗传状态。在这项研究中，观察到单亲生殖体细胞核重编程过程中的这些表观遗传变化。单亲生殖印迹基因的模式在单亲生殖母源 iPSCs（miPSCs）的产生过程中发生变化，这一过程被称为多能重编程。我们确定了当重编程细胞重新分化为特化细胞类型时，改变的印迹基因是否被维持或恢复到单亲生殖状态。为了解决这个问题，我们将 miPSCs 重新分化为神经干细胞（miPS-NSCs），并将其与双亲性雌性 NSCs（fNSCs）和单亲生殖 NSCs（pNSCs）进行比较。我们发现，单亲生殖体细胞的多能重编程可以重置印迹基因中的单亲生殖 DNA 甲基化模式，并且在 miPSCs 重新分化为 miPS-NSCs 后，DNA 甲基化的改变仍然得以维持。值得注意的是，母源甲基化印迹基因（Peg1、Peg3、Igf2r、Snrpn 和 Ndn）的差异甲基化区域在 pNSCs 中完全甲基化，在重编程和重新分化后被去甲基化，其表达水平接近正常双亲性 fNSCs 的水平。我们的研究结果表明，单亲生殖体细胞的多能重编程，继之以重新分化，导致印迹基因的 DNA 甲基化发生变化，并重新建立基因表达水平，使其恢复为正常双亲性细胞的水平。
