GSE119066
Perturbed maintenance of transcriptional repression on the inactive X-chromosome in the mouse brain after XIST deletion
The long noncoding RNA, Xist, is critical for initiation and establishment of X- chromosome inactivation during embryogenesis in mammals but it is unclear whether its continued expression is required for maintaining X inactivation in vivo.  By using an inactive X chromosome-linked MeCP2-GFP reporter, which allowed us to enumerate reactivation events in the mouse brain even when they occur in very few cells, we found that deletion of Xist in the brain after establishment of X chromosome inactivation leads to reactivation in 2-5% of neurons and in a smaller fraction of astrocytes. In contrast to global loss of both H3 lysine 27 tri-methylation (H3K27m3) and histone H2A lysine 119 monoubiquitylation (H2AK119ub1) we observed upon Xist deletion, alterations in CpG methylation were subtle, and this was mirrored by only minor alterations in X- chromosome-wide gene expression levels.  Our results demonstrate that Xist is required for maintaining tight transcriptional repression on the inactive X-chromosome and that partial loss of X-dosage compensation in the absence of Xist in the brain is well tolerated. Overall design: high throughput sequencing-based assessment of mRNA and DNA methylation levels in mice deleted for XIST after transcriptional silencing on the X chromosome has been established; 5 RNA seq samples and 3 LpnPI DNA samples from mice deleted for XIST; 3 RNA seq and 2 LpnPI DNA samples from control mice with intact XIST