Differential loss of histone H3 isoforms mono-, di- and tri-methylated at lysine 4 during X-inactivation in female embryonic stem cells.
Silencing of genes on one of the two female X chromosomes early in development helps balance expression of X-linked genes between XX females and XY males and involves chromosome-wide changes in histone variants and modifications. Mouse female embryonic stem (ES) cells have two active Xs, one of which is silenced on differentiation, and provide a powerful model for studying the dynamics of X inactivation. Here, we use immunofluorescence microscopy of metaphase chromosomes to study changes in H3 mono-, di- or tri-methylated at lysine 4 (H3K4mel, -2 or -3) on the inactivating X (Xi) in female ES cells. H3K4me3 is absent from Xi in approximately 25% of chromosome spreads by day 2 of differentiation and in 40-50% of spreads by days 4-6, making it one of the earliest detectable changes on Xi. In contrast, loss of H3K4me2 occurs 1-2 days later, when histone acetylation also diminishes. Remarkably, H3K4mel is depleted on both (active) X chromosomes in undifferentiated female ES cells, and on the single X in males, and remains depleted on Xi. Consistent with this, chromatin immunoprecipitation reveals differentiation-related reductions in H3K4me2 and H3K4me3 at the promoter regions of genes undergoing X-inactivation in female ES cells, but no comparable change in H3K4me1.
O'Neill
Laura P
LP
Chromatin and Gene Expression Group, Institute of Biomedical Research, University of Birmingham Medical School, Birmingham B15 2TT, UK.
Spotswood
Hugh T
HT
Fernando
Milan
M
Turner
Bryan M
BM
D000818:Animals; D002454:Cell Differentiation / Q000235:genetics; D004303:Dosage Compensation, Genetic; D053595:Embryonic Stem Cells / Q000166:cytology / Q000378:metabolism*; D044127:Epigenesis, Genetic; D005260:Female; D005455:Fluorescent Antibody Technique; D006657:Histones / Q000235:genetics / Q000378:metabolism*; D047468:Immunoprecipitation; D017404:In Situ Hybridization, Fluorescence; D008239:Lysine / Q000378:metabolism*; D008677:Metaphase / Q000235:genetics; D008745:Methylation; D051379:Mice; D049951:X Chromosome Inactivation
D006657:Histones; D008239:Lysine