Shen Yin, Matsuno Youko, Fouse Shaun D, Rao Nagesh, Root Sierra, Xu Renhe, Pellegrini Matteo, Riggs Arthur D, Fan Guoping
Department of Human Genetics, Geffen School of Medicine, and Departments of Pathology and Laboratory Medicine and Molecular Cell and Developmental Biology, University of California, Los Angeles, CA 90095, USA.
Proc Natl Acad Sci U S A. 2008 Mar 25;105(12):4709-14. doi: 10.1073/pnas.0712018105. Epub 2008 Mar 13.
X chromosome inactivation (XCI) is an essential mechanism for dosage compensation of X-linked genes in female cells. We report that subcultures from lines of female human embryonic stem cells (hESCs) exhibit variation (0-100%) for XCI markers, including XIST RNA expression and enrichment of histone H3 lysine 27 trimethylation (H3K27me3) on the inactive X chromosome (Xi). Surprisingly, regardless of the presence or absence of XCI markers in different cultures, all female hESCs we examined (H7, H9, and HSF6 cells) exhibit a monoallelic expression pattern for a majority of X-linked genes. Our results suggest that these established female hESCs have already completed XCI during the process of derivation and/or propagation, and the XCI pattern of lines we investigated is already not random. Moreover, XIST gene expression in subsets of cultured female hESCs is unstable and subject to stable epigenetic silencing by DNA methylation. In the absence of XIST expression, approximately 12% of X-linked promoter CpG islands become hypomethylated and a portion of X-linked alleles on the Xi are reactivated. Because alterations in dosage compensation of X-linked genes could impair somatic cell function, we propose that XCI status should be routinely checked in subcultures of female hESCs, with cultures displaying XCI markers better suited for use in regenerative medicine.
X染色体失活（XCI）是雌性细胞中X连锁基因剂量补偿的重要机制。我们报告称，来自女性人胚胎干细胞（hESC）系的传代培养物在XCI标记物方面表现出差异（0 - 100%），包括XIST RNA表达以及失活X染色体（Xi）上组蛋白H3赖氨酸27三甲基化（H3K27me3）的富集。令人惊讶的是，无论不同培养物中是否存在XCI标记物，我们检测的所有女性hESC（H7、H9和HSF6细胞）对于大多数X连锁基因都表现出单等位基因表达模式。我们的结果表明，这些已建立的女性hESC在衍生和/或传代过程中已经完成了XCI，并且我们研究的细胞系的XCI模式已经不是随机的。此外，培养的女性hESC亚群中的XIST基因表达不稳定，并且会受到DNA甲基化导致的稳定表观遗传沉默。在没有XIST表达的情况下，约12%的X连锁启动子CpG岛会发生低甲基化，并且Xi上的一部分X连锁等位基因会被重新激活。由于X连锁基因剂量补偿的改变可能损害体细胞功能，我们建议在女性hESC的传代培养物中常规检查XCI状态，具有XCI标记物的培养物更适合用于再生医学。
