Molecular Medicine Laboratory, Faculty of Medicine and Research Institute, Rambam Health Care Campus and Rappaport, Technion - Israel Institute of Technology, Haifa, Israel.
Epigenetics. 2011 Jan;6(1):63-75. doi: 10.4161/epi.6.1.13390. Epub 2011 Jan 1.
Human induced pluripotent stem (hiPS) cells provide therapeutic promises, as well as a potent in vitro model for studying biological processes which take place during human embryonic development and subsequent differentiation in normal and disease states. The epigenetic characteristics of iPS cells are reprogrammed to the embryonic state at which they acquire pluripotency. In addition, telomeres in hiPS cell must elongate sufficiently to provide the necessary replicative potential. Recent studies have demonstrated that the epigenetic characteristics of telomeric and subtelomeric regions are pivotal in regulating telomere length. Here we study telomere length, subtelomeric DNA methylation and telomeric-repeat-containing RNA (TERRA) expression in several hiPS cell clones derived from normal neonatal foreskin fibroblasts. We find that telomeres lengthen significantly in hiPS cells in comparison to the parental fibroblast source, and progressively shorten after differentiation back into fibroblast-like cells, concomitantly with telomerase activation and down-regulation, respectively. Subtelomeres in hiPS cells were found to be generally hypermethylated in comparison to the parental source. However bisulfite analysis revealed that at several subtelomeres examined, methylation levels differed between hiPS clones and that both de novo methylation and demethylation processes occurred during telomere reprogramming. Notably, although subtelomeres were in general very highly methylated, TERRA levels were elevated in hiPS cells, albeit to different degrees in the various clones. TERRA elevation may reflect enhanced stability or impaired degradation in hiPS cells, and/or alternatively, increased transcription from the hypomethylated subtelomeres. We suggest that TERRA may play a role in regulation of appropriate telomere function and length in hiPS cells.
人类诱导多能干细胞 (hiPS) 提供了治疗的潜力，同时也是研究人类胚胎发育过程中以及在正常和疾病状态下随后分化过程中发生的生物学过程的强大体外模型。iPS 细胞的表观遗传特征被重新编程为胚胎状态，在此状态下它们获得多能性。此外，hiPS 细胞中的端粒必须充分延长以提供必要的复制潜力。最近的研究表明，端粒和端粒附近区域的表观遗传特征在调节端粒长度方面起着关键作用。在这里，我们研究了来自正常新生儿包皮成纤维细胞的几个 hiPS 细胞克隆中端粒长度、端粒附近 DNA 甲基化和端粒重复 RNA（TERRA）的表达。我们发现，与亲本成纤维细胞来源相比，hiPS 细胞中端粒显著延长，并且在分化回成纤维样细胞后逐渐缩短，分别伴随着端粒酶的激活和下调。与亲本来源相比，hiPS 细胞中端粒附近通常呈高甲基化状态。然而，亚硫酸氢盐分析显示，在检查的几个端粒附近，甲基化水平在 hiPS 克隆之间存在差异，并且在端粒重编程过程中发生了从头甲基化和去甲基化过程。值得注意的是，尽管端粒附近通常高度甲基化，但 TERRA 水平在 hiPS 细胞中升高，尽管在不同的克隆中升高程度不同。TERRA 升高可能反映了 hiPS 细胞中稳定性增强或降解受损，或者替代地，从低甲基化的端粒附近转录增强。我们认为，TERRA 可能在 hiPS 细胞中端粒功能和长度的适当调节中发挥作用。
