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Hyperdynamic plasticity of chromatin proteins in pluripotent embryonic stem cells.

ABSTRACT: Differentiation of embryonic stem (ES) cells from a pluripotent to a committed state involves global changes in genome expression patterns. Gene activity is critically determined by chromatin structure and interactions of chromatin binding proteins. Here, we show that major architectural chromatin proteins are hyperdynamic and bind loosely to chromatin in ES cells. Upon differentiation, the hyperdynamic proteins become immobilized on chromatin. Hyperdynamic binding is a property of pluripotent cells, but not of undifferentiated cells that are already lineage committed. ES cells lacking the nucleosome assembly factor HirA exhibit elevated levels of unbound histones, and formation of embryoid bodies is accelerated. In contrast, ES cells, in which the dynamic exchange of H1 is restricted, display differentiation arrest. We suggest that hyperdynamic binding of structural chromatin proteins is a functionally important hallmark of pluripotent ES cells that contributes to the maintenance of plasticity in undifferentiated ES cells and to establishing higher-order chromatin structure.

SUBMITTER: Meshorer E

PROVIDER: S-EPMC1868458 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Histone variants and their chaperones are key regulators of eukaryotic transcription, and are critical for normal development. The histone variant H3.3 has been shown to play important roles in pluripotency and differentiation, and although its genome-wide patterns have been investigated, little is known about the role of its dynamic turnover in transcriptional regulation. To elucidate the role of H3.3 dynamics in embryonic stem cell (ESC) biology, we generated mouse ESC lines carrying a single copy of a doxycycline (Dox)-inducible HA-tagged version of H3.3, and monitored the rate of incorporation of the HA-tagged variant by ChIP-seq at varying time points following Dox induction. Active H3K4me3-enriched genes display high turnover dynamics in transcription start sites (TSS); H3K27me3-enriched genes have a lower turnover dynamics in the TSS, but higher turnover rates in gene bodies; developmental bivalent genes marked by both H3K4me3 and H3K27me3 show a mixed behavior with high TSS dynamics and high gene body dynamics, especially in genes bound by both PRC1 and PRC2. In contrast, genes proximal to super-enhancers show the most reduced gene-body turnover dynamics, while genes proximal to other enhancers show no unique pattern. In RA-treated cells, while the overall profile in expressed genes remains largely unaltered over the TSS and gene body, a significant and dramatic decrease in turnover occurs at the -1 nucleosome position immediately before the TSS, revealing a hyperdynamic nucleosome in promoters of genes expressed in ESCs. We suggest that histone turnover dynamics provides an additional mechanism involved in expression regulation, that gene-body turnover dynamics is distinct from that of promoter regions, and that a hyperdynamic -1 nucleosome marks promoters in ESCs. Our data provide evidence for regional regulation of H3.3 turnover in ESC promoters, and calls for testing, in high resolution, the dynamic behavior of additional histone variants and other structural chromatin proteins.

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Hyperdynamic plasticity of chromatin proteins in pluripotent embryonic stem cells.

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