Genetic and pharmacological reactivation of the mammalian inactive X chromosome
Genetic and pharmacological reactivation of the mammalian inactive X chromosome
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DOI：
10.1073/pnas.1413620111
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发表时间：
2014-09-02
影响因子：
11.1
通讯作者：
Green, Michael R.
中科院分区：
文献类型：
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作者：
Bhatnagar, Sanchita;Zhu, Xiaochun;Green, Michael R.
X染色体失活(XCI)是雌性哺乳动物体细胞中一条X染色体的随机转录沉默，是确保X连锁基因在两性中平等表达的一种机制。XCI在顺式基因中是由非编码的Xist RNA启动的，它覆盖着产生XCI的非活性X染色体(XI)。然而，调节XCI的反式作用因素在很大程度上仍不清楚。在这里，我们进行大规模的RNA干扰筛选，以确定组成细胞信号和转录调节因子(XCIF)的反式作用XCI因子，包括DNA甲基转移酶DNMT1。XCIF的表达模式解释了分化后XCI的选择性发病。XCIF的功能至少部分是通过促进Xist对XI的表达和/或本地化。令人惊讶的是，我们发现DNMT1通常是一个转录抑制因子，是Xist转录的激活因子。其中两个XCIF的小分子抑制剂可以可逆地重新激活XI，这对Rett综合征和其他显性X连锁疾病的治疗具有重要意义。其中一个XCIF的纯合子小鼠，stanniocalcin 1(STC1)，有预期的XCI缺陷，但令人惊讶的是表型正常。值得注意的是，X连锁基因在雌性stc1(-/-)小鼠中没有过度表达，这表明存在一种机制(S)，可以弥补持续的XCI缺陷来调节X连锁基因的表达。
X-chromosome inactivation (XCI), the random transcriptional silencing of one X chromosome in somatic cells of female mammals, is a mechanism that ensures equal expression of X-linked genes in both sexes. XCI is initiated in cis by the noncoding Xist RNA, which coats the inactive X chromosome (Xi) from which it is produced. However, trans-acting factors that mediate XCI remain largely unknown. Here, we perform a large-scale RNA interference screen to identify trans-acting XCI factors (XCIFs) that comprise regulators of cell signaling and transcription, including the DNA methyltransferase, DNMT1. The expression pattern of the XCIFs explains the selective onset of XCI following differentiation. The XCIFs function, at least in part, by promoting expression and/or localization of Xist to the Xi. Surprisingly, we find that DNMT1, which is generally a transcriptional repressor, is an activator of Xist transcription. Small-molecule inhibitors of two of the XCIFs can reversibly reactivate the Xi, which has implications for treatment of Rett syndrome and other dominant X-linked diseases. A homozygous mouse knockout of one of the XCIFs, stanniocalcin 1 (STC1), has an expected XCI defect but surprisingly is phenotypically normal. Remarkably, X-linked genes are not overexpressed in female Stc1(-/-) mice, revealing the existence of a mechanism(s) that can compensate for a persistent XCI deficiency to regulate X-linked gene expression.