One of the two X chromosomes in female mammals is inactivated by the noncodingXistRNA. In mice, X chromosome inactivation (XCI) is regulated by the antisense RNATsix, which repressesXiston the active X chromosome. In the absence ofTsix, PRC2-mediated histone H3 lysine 27 trimethylation (H3K27me3) is established over theXistpromoter. Simultaneous disruption ofTsixand PRC2 leads to derepression ofXistand in turn silencing of the single X chromosome in male embryonic stem cells. Here, we identified histone H3 lysine 36 trimethylation (H3K36me3) as a modification that is recruited byTsixcotranscriptionally and extends over theXistpromoter. Reduction of H3K36me3 by expression of a mutated histone H3.3 with a substitution of methionine for lysine at position 36 causes a significant derepression ofXist. Moreover, depletion of the H3K36 methylaseSetd2leads to upregulation ofXist, suggesting H3K36me3 as a modification that contributes to the mechanism ofTsixfunction in regulating XCI. Furthermore, we found that reduction of H3K36me3 does not facilitate an increase in H3K27me3 over theXistpromoter, indicating that additional mechanisms exist by whichTsixblocks PRC2 recruitment to theXistpromoter.
Histone H3 Lysine 36 Trimethylation Is Established over theXistPromoter by AntisenseTsixTranscription and Contributes to RepressingXistExpression