A developmental switch in H4 acetylation upstream of Xist plays a role in X chromosome inactivation
O'Neill LP., Keohane AM., Lavender JS., McCabe V., Heard E., Avner P., Brockdorff N., Turner BM., Annunziato AT.
By performing immunoprecipitation assays of chromatin from the X inactivation center, it was determined that the upstream region of Xist is uniquely hyperacetylated in XX female ES cells, but not in male cells or in mutant cells in which the P1/P2 promoters of Xist have been deleted from one of the X chromosomes. Hyperacetylation declines during development, concomitant with X inactivation, but is not absolutely required for Xi to be inactivated. It is proposed that hyperacetylation of the 5' region of Xist facilitates the promoter switch that results in the stabilization of the Xist transcript, and ultimately X inactivation in cis. It is also suggested that the absence of 5' hyperacetylation of Xist in males protects the single X chromosome from promoter switching, and thus from inactivation.