Luikenhuis S, Wutz A, Jaenisch R
Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02142, USA.
Mol Cell Biol. 2001 Dec;21(24):8512-20. doi: 10.1128/MCB.21.24.8512-8520.2001.
Expression of the Xist gene, a key player in mammalian X inactivation, has been proposed to be controlled by the antisense Tsix transcript. Targeted deletion of the Tsix promoter encompassing the DPXas34 locus leads to nonrandom inactivation of the mutant X, but it remains unresolved whether this phenotype is caused by loss of Tsix transcription or by deletion of a crucial DNA element. In this study we determined the role of Tsix transcription in random X inactivation by using mouse embryonic stem (ES) cells as a model system. Two approaches were chosen to modulate Tsix transcription with minimal disturbance of genomic sequences. First, Tsix transcription was functionally inhibited by introducing a transcriptional stop signal into the transcribed region of Tsix. In the second approach, an inducible system for Tsix expression was created. We found that the truncation of the Tsix transcript led to complete nonrandom inactivation of the targeted X chromosome. Induction of Tsix transcription during ES cell differentiation, on the other hand, caused the targeted chromosome always to be chosen as the active chromosome. These results for the first time establish a function for antisense transcription in the regulation of X inactivation.
Xist基因是哺乳动物X染色体失活过程中的关键因子，其表达被认为受反义转录本Tsix的调控。包含DPXas34位点的Tsix启动子靶向缺失会导致突变X染色体的非随机失活，但这种表型是由Tsix转录缺失还是关键DNA元件缺失引起的仍未明确。在本研究中，我们以小鼠胚胎干细胞（ES细胞）为模型系统，确定了Tsix转录在随机X染色体失活中的作用。我们选择了两种方法在最小程度干扰基因组序列的情况下调节Tsix转录。第一种方法是通过在Tsix转录区域引入转录终止信号来功能性抑制Tsix转录。第二种方法是构建一个Tsix表达的诱导系统。我们发现，Tsix转录本的截短导致靶向X染色体完全非随机失活。另一方面，在ES细胞分化过程中诱导Tsix转录会使靶向染色体总是被选为活性染色体。这些结果首次确立了反义转录在X染色体失活调控中的作用。
