Escape from X inactivation is directly modulated by Xist non-coding RNA [methylation]

X-chromosome inactivation silences one copy of the X-chromosome in female cells, but a number of genes escapes this inactivation. We asked whether increased levels of Xist RNA, the molecular actor driving X-inactivation, impacts expression levels of escapees. To this end, we performed DNA methylation profiling of X-linked genes in clonal neural progenitor cell lines with transgenes that allow for the overexpression of Xist on the inactive X chromosome. We perform Xist overexpression experiments for up to three weeks and also test the reversibility of Xist overexpression using washout experiments. Overall design: Clonal neural progenitor cell lines were generated by differentiating first generation hybrid embryonic stem cells (from a C57BL6/J x CAST/EiJ cross). All cell lines carry an inactive B6 X chromosome and a doxycycline-inducible transgene on the Xi. Doxycyclin treatment for 7 and 21 days was performed in the E6 cell line and allele-specific DNA methylation was measured. Furthermore, washing out doxycycline was analyzed to assess reversibility.