Xist RNA Dependent and Independent Mechanisms Regulate Dynamic X Chromosome Inactivation in B Lymphocytes [CUTandRUN_PRC2]

X-chromosome inactivation (XCI) maintenance in female B cells is dynamic (dXCI), where naïve cells lack cytological enrichment of Xist RNA and heterochromatic marks on the inactive X-chromosome (Xi), and these marks re-localize after stimulation. Here, we report the epigenetic profiling of silencing (H3K27me3, H2AK119Ub, H3K9me3, DNA methylation (DNAm)) and activating (H3K27ac) marks on the Xi during dXCI and investigate the requirement for Xist RNA in maintaining the Xi epigenetic landscape. We find that the Xi in naïve B cells is depleted for H2AK119Ub and H3K9me3 but enriched for DNAm and H3K27me3 which maintain an epigenetic memory of transcriptional silencing dependent on Xist RNA. Upon stimulation, Xist-independent H3K27me3 and Xist-dependent H2AK119Ub modifications accumulate across the Xi. Thus, naïve B cells maintain an epigenetic memory of silencing in the absence of Xist RNA localization via retention of DNAm and H3K27me3, and both H3K27me3 and H2AK119Ub accumulate on the Xi post-stimulation in an Xist-dependent and -independent manner. These data have critical implications for understanding molecular mechanisms underlying female-biased immune responses.