Project description:Endogenous retroviruses (ERVs) have provided an evolutionary advantage in the diversification of transcript regulation and are thought to be involved in the establishment of extraembryonic tissues during development. However, silencing of these elements remains critical for the maintenance of genome stability. Here, we define a new chromatin state that is uniquely characterized by the combination of the histone variant H3.3 and H3K9me3, two chromatin ‘marks’ that have previously been considered to belong to fundamentally opposing chromatin states. H3.3/H3K9me3 heterochromatin is fundamentally distinct from ‘canonical’ H3K9me3 heterochromatin that has been under study for decades and this unique functional interplay of a histone variant and a repressive histone mark is crucial for silencing ERVs in ESCs. Our study solidifies the emerging notion that H3.3 is not a histone variant associated exclusively with “active” chromatin and further suggests that its incorporation at unique heterochromatic regions may be central to its function during development and the maintenance of genome stability. RNA-seq analysis of three embryonic stem cell lines WT, H3.3 KO1, and H3.3 KO2)
Project description:Polycomb repressive complex 2 (PRC2) regulates gene expression during lineage specification through trimethylation of lysine 27 on histone H3 (H3K27me3). In Drosophila, polycomb binding sites are dynamic chromatin regions coupled to incorporation of the histone variant H3.3. Here we show in mouse embryonic stem cells (ESCs) that H3.3 is required for proper establishment of H3K27me3 at the promoters of developmentally regulated genes. These promoters show reduced dynamics as determined by deposition of de novo synthesized histones, associated with reduced PRC2 occupancy. H3.3-depleted ESCs show upregulation of extraembryonic trophectoderm, as well as misregulation of other developmental genes upon differentiation. Our data demonstrate the importance of H3.3 incorporation in ESCs and suggest that changes in chromatin dynamics in its absence lead to misregulation of gene expression during differentiation. Moreover, our findings lend support to the emerging notion that H3.3 has multiple functions in distinct genomic locations that are not always correlated with an “active” chromatin state. Native ChIP analysis of three histone post-translational modifications (H3K4me3, H3K27me3, H3K27ac) in two mouse embryonic stem cell (ESC) lines (control and H3.3-depleted). Inputs sequenced as control. Native ChIP analysis of H3.3B-HA in control and Suz12-/- ESCs. Crosslinking ChIP analysis of histone H3 using a general H3 antibody in two ESC lines (control and H3.3-depleted). Crosslinking ChIP analysis Hira, UTX, and Jmjd3 in wild type and H3.3 KO ESCs.
