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

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. 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.