Department of Molecular Biology, Massachusetts General Hospital, Boston, MA, USA.
Department of Genetics, Harvard Medical School, Boston, MA, USA.
Nat Cell Biol. 2020 Sep;22(9):1116-1129. doi: 10.1038/s41556-020-0558-0. Epub 2020 Aug 17.
How allelic asymmetry is generated remains a major unsolved problem in epigenetics. Here we model the problem using X-chromosome inactivation by developing "BioRBP", an enzymatic RNA-proteomic method that enables probing of low-abundance interactions and an allelic RNA-depletion and -tagging system. We identify messenger RNA-decapping enzyme 1A (DCP1A) as a key regulator of Tsix, a noncoding RNA implicated in allelic choice through X-chromosome pairing. DCP1A controls Tsix half-life and transcription elongation. Depleting DCP1A causes accumulation of X-X pairs and perturbs the transition to monoallelic Tsix expression required for Xist upregulation. While ablating DCP1A causes hyperpairing, forcing Tsix degradation resolves pairing and enables Xist upregulation. We link pairing to allelic partitioning of CCCTC-binding factor (CTCF) and show that tethering DCP1A to one Tsix allele is sufficient to drive monoallelic Xist expression. Thus, DCP1A flips a bistable switch for the mutually exclusive determination of active and inactive Xs.
等位基因不对称性是如何产生的，这在表观遗传学中仍然是一个未解决的主要问题。在这里，我们通过开发“BioRBP”来模拟 X 染色体失活的问题，这是一种酶 RNA 蛋白质组学方法，能够探测低丰度的相互作用和等位基因 RNA 耗竭和标记系统。我们确定信使 RNA 脱帽酶 1A (DCP1A) 是 Tsix 的关键调节因子，Tsix 是一种非编码 RNA，通过 X 染色体配对参与等位基因选择。DCP1A 控制 Tsix 的半衰期和转录延伸。耗尽 DCP1A 会导致 X-X 对的积累，并扰乱了 Xist 上调所需的单等位基因 Tsix 表达的转变。虽然 DCP1A 的缺失会导致超配对，但迫使 Tsix 降解可以解决配对问题，并使 Xist 上调成为可能。我们将配对与 CCCTC 结合因子 (CTCF) 的等位基因分配联系起来，并表明将 DCP1A 连接到一个 Tsix 等位基因上足以驱动单等位基因 Xist 的表达。因此，DCP1A 为活性和非活性 X 染色体的相互排斥决定翻转了一个双稳态开关。
