A screen for reactivation of MeCP2 on the inactive X-chromosome identifies BMP/TGF-b superfamily as a regulator of maintenance of XIST expression. Mus musculus

X-chromosome inactivation (XCI) is an epigenetic phenomenon that renders one of the two X-chromosomes in female cells transcriptionally silent, ensuring that X-linked gene dosage matches that in males, who have only one copy of the X chromosome. When a mutation of an X-linked gene is heterozygous, as it is in most girls with Rett syndrome, a neurodevelopmental disorder caused by a mutation MeCP2 gene, the presence of the mutated allele on the active X chromosome entails transcriptional inactivation of the wild type allele on the inactive X, resulting in complete loss of gene function. Reactivation of the silenced wild-type copy of MeCP2 therefore presents a potential therapeutic strategy for Rett syndrome. To identify genes that silence MeCP2 on the Xi that could prove useful therapeutic targets, we carried out a screen for genes whose downregulation reactivated a MeCP2 reporter on the Xi. The 30 genes we have identified comprise seven functional groups revealing a genetic circuitry required for maintenance of X-chromosome inactivation in differentiated cells and a large number of targets suitable for pharmacologic intervention. Overall design: select for shRNAs that activate MeCP2 on inactive X that has been fused to Hygromycin-resistance gene