Incomplete X-inactivation initiated by a hypomorphic Xist allele in the mouse. Mus musculus

Mammals have evolved a mechanism to compensate for the difference in the number of X chromosome genes between XX females and XY males by inactivating one of the two X chromosomes in females. This X chromosome inactivation phenomenon is triggered by Xist gene, which is essential for X-inactivation to occur in cis. We demonstrate that an Xist mutant, XistIVS, is unique in that it retains a partial function to silence the X chromosome, which would provide an opportunity to dissect the molecular mechanism of Xist RNA-mediated chromosome silencing. Overall design: To study the effect of XistIVS mutation on silencing of X-linked genes, global expression levels of X-linked genes were measured in mutant and control cells. We used female trophoblast stem (TS) cells carrying XistIVS mutation and gene expression was assayed using microarray containing 572 probes corresponding most of the X-linked genes. Then the result was compared with that obtained from wild-type control cells.

哺乳动物已演化出一种补偿机制，用以抵消XX雌性与XY雄性间X染色体(X chromosome)基因数量的差异——该机制通过使雌性两条X染色体中的一条发生失活来实现。该X染色体失活(X chromosome inactivation)现象由Xist基因(Xist gene)启动，该基因对于X染色体失活的顺式(cis)发生不可或缺。本研究证实，Xist突变体XistIVS具有独特性：其仍保留了部分沉默X染色体的功能，这为解析Xist RNA介导的染色体沉默的分子机制提供了重要契机。实验整体设计：为探究XistIVS突变对X连锁(X-linked)基因沉默的影响，本研究检测了突变细胞与对照细胞中X连锁基因的全局表达水平。本研究采用携带XistIVS突变的雌性滋养层干细胞(trophoblast stem cells, TS cells)，通过包含572个探针(probe)的微阵列(microarray)芯片完成基因表达检测，该芯片覆盖绝大多数X连锁基因。随后将所得结果与野生型(wild-type)对照细胞的检测结果进行比对分析。