Shibata S, Wakayama T, Yokota T
Department of Stem Cell Biology, Graduate School of Medicine, Kanazawa University, Kanazawa, Japan.
Cytogenet Genome Res. 2008;121(2):96-101. doi: 10.1159/000125834. Epub 2008 Jun 9.
Nuclear transfer ES (ntES) cells are established from cloned blastocysts generated by somatic cell nuclear transfer and are expected to be an important resource for regenerative medicine. However, cloned mammals, generated by similar methods, show various abnormalities, which suggest disordered gene regulation. Random X chromosome inactivation (XCI) has been observed to take place in cloned female mouse embryos, but XCI does not necessarily occur according to Xce strength, a genetic element that determines the likelihood of each X chromosome to be inactivated. This observation suggests incomplete reprogramming of epigenetic marks related to XCI. Here, we investigated XCI in ntES cell lines, which were established using differentiated embryoid bodies that originated from a female mouse ES cell line. We examined Xist RNA localization, histone modifications in the Xist locus, and XCI choice. We did not find substantial differences between the ntES lines and their parental ES line. This suggests that the Xist locus and the epigenetic marks involved in XCI are reprogrammed by nuclear transfer and subsequent ntES cell establishment. In contrast to skewed XCI in cloned mice, our observations indicate that normal XCI choice takes place in ntES cells, which supports the goal of safe therapeutic cloning for clinical use.
核移植胚胎干细胞（ntES细胞）是由体细胞克隆囊胚建立而来，有望成为再生医学的重要资源。然而，通过类似方法产生的克隆哺乳动物表现出各种异常，这表明基因调控紊乱。已观察到克隆的雌性小鼠胚胎中会发生随机X染色体失活（XCI），但XCI不一定根据Xce强度发生，Xce是一种决定每条X染色体失活可能性的遗传元件。这一观察结果表明与XCI相关的表观遗传标记重编程不完全。在此，我们研究了ntES细胞系中的XCI，这些细胞系是使用源自雌性小鼠胚胎干细胞系的分化胚体建立的。我们检测了Xist RNA定位、Xist基因座中的组蛋白修饰以及XCI选择。我们未在ntES细胞系与其亲本胚胎干细胞系之间发现实质性差异。这表明Xist基因座和参与XCI的表观遗传标记通过核移植及随后的ntES细胞建立得以重编程。与克隆小鼠中倾斜的XCI不同，我们的观察结果表明ntES细胞中发生正常的XCI选择，这支持了临床安全治疗性克隆的目标。
