Differentially methylated CpG island within human XIST mediates alternative P2 transcription and YY1 binding
Differentially methylated CpG island within human XIST mediates alternative P2 transcription and YY1 binding
复制标题
DOI：
10.1186/s12863-014-0089-4
复制
发表时间：
2014-09-09
期刊：
影响因子：
2.9
通讯作者：
Brown, Carolyn J.
中科院分区：
文献类型：
--
作者：
Chapman, Andrew G.;Cotton, Allison M.;Brown, Carolyn J.
背景：X染色体失活使女性的一条X染色体沉默，使男性的单条X染色体获得剂量补偿。虽然大多数基因在非活动的X染色体上是沉默的，但长非编码RNA XIST的基因在活动的X染色体上是沉默的，并在与XIST RNA相关的非活动的X染色体上表达，从而触发染色体的沉默。在小鼠中，Xist的另一个启动子P2也是YY1结合的部位，它被证明是Xist RNA和染色体DNA之间的纽带。在人类中，与小鼠Xist激活的初始事件有许多不同，包括在胚胎外组织中缺乏功能性反义调控因子TSix，以及缺乏严格的父系失活，这促使我们研究人类XIST基因的调节区。结果：我们证明XIST中的女性特异性DNA酶高敏感部位是非激活的X染色体特异性的，并与来自内部P2启动子的转录相关。P2位于CpG岛上，该岛在男性和女性之间存在差异甲基化，并与保守的YY1结合位点重叠，这些结合位点仅结合在非甲基化的非活性X染色体上。然而，YY1结合不足以驱动P2的表达或建立DHS，这可能需要一个发育特异的因子。结论：XIST中差异甲基化的DNA酶超敏感位点标志着另一种功能未知的启动子P2的位置，因为它缺少对沉默至关重要的A重复序列。此外，这个区域将YY1结合在未甲基化的非活性X染色体上，YY1的缺失会解除XIST RNA的束缚，并减少XIST的转录。
Background: X-chromosome inactivation silences one X chromosome in females to achieve dosage compensation with the single X chromosome in males. While most genes are silenced on the inactive X chromosome, the gene for the long non-coding RNA XIST is silenced on the active X chromosome and expressed from the inactive X chromosome with which the XIST RNA associates, triggering silencing of the chromosome. In mouse, an alternative Xist promoter, P2 is also the site of YY1 binding, which has been shown to serve as a tether between the Xist RNA and the DNA of the chromosome. In humans there are many differences from the initial events of mouse Xist activation, including absence of a functional antisense regulator Tsix, and absence of strictly paternal inactivation in extraembryonic tissues, prompting us to examine regulatory regions for the human XIST gene.Results: We demonstrate that the female-specific DNase hypersensitivity site within XIST is specific to the inactive X chromosome and correlates with transcription from an internal P2 promoter. P2 is located within a CpG island that is differentially methylated between males and females and overlaps conserved YY1 binding sites that are only bound on the inactive X chromosome where the sites are unmethylated. However, YY1 binding is insufficient to drive P2 expression or establish the DHS, which may require a development-specific factor. Furthermore, reduction of YY1 reduces XIST transcription in addition to causing delocalization of XIST.Conclusions: The differentially methylated DNase hypersensitive site within XIST marks the location of an alternative promoter, P2, that generates a transcript of unknown function as it lacks the A repeats that are critical for silencing. In addition, this region binds YY1 on the unmethylated inactive X chromosome, and depletion of YY1 untethers the XIST RNA as well as decreasing transcription of XIST.