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Chromatin decouples promoter threshold from dynamic range.

ABSTRACT: Chromatin influences gene expression by restricting access of DNA binding proteins to their cognate sites in the genome. Large-scale characterization of nucleosome positioning in Saccharomyces cerevisiae has revealed a stereotyped promoter organization in which a nucleosome-free region (NFR) is present within several hundred base pairs upstream of the translation start site. Many transcription factors bind within NFRs and nucleate chromatin remodelling events which then expose other cis-regulatory elements. However, it is not clear how transcription-factor binding and chromatin influence quantitative attributes of gene expression. Here we show that nucleosomes function largely to decouple the threshold of induction from dynamic range. With a series of variants of one promoter, we establish that the affinity of exposed binding sites is a primary determinant of the level of physiological stimulus necessary for substantial gene activation, and sites located within nucleosomal regions serve to scale expression once chromatin is remodelled. Furthermore, we find that the S. cerevisiae phosphate response (PHO) pathway exploits these promoter designs to tailor gene expression to different environmental phosphate levels. Our results suggest that the interplay of chromatin and binding-site affinity provides a mechanism for fine-tuning responses to the same cellular state. Moreover, these findings may be a starting point for more detailed models of eukaryotic transcriptional control.

SUBMITTER: Lam FH

PROVIDER: S-EPMC2435410 | biostudies-literature | 2008 May

REPOSITORIES: biostudies-literature

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Chromatin decouples promoter threshold from dynamic range.

Lam Felix H FH Steger David J DJ O'Shea Erin K EK

Nature 20080416 7192

Chromatin influences gene expression by restricting access of DNA binding proteins to their cognate sites in the genome. Large-scale characterization of nucleosome positioning in Saccharomyces cerevisiae has revealed a stereotyped promoter organization in which a nucleosome-free region (NFR) is present within several hundred base pairs upstream of the translation start site. Many transcription factors bind within NFRs and nucleate chromatin remodelling events which then expose other cis-regulato ...[more]

PMID: 18418379

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Project description:In multicellular organisms, transcription regulation is one of the central mechanisms modelling lineage differentiation and cell-fate determination. Transcription requires dynamic chromatin configurations between promoters and their corresponding distal regulatory elements. It is believed that their communication occurs within large discrete foci of aggregated RNA polymerases termed transcription factories in three-dimensional nuclear space. However, the dynamic nature of chromatin connectivity has not been characterized at the genome-wide level. Here, through a chromatin interaction analysis with paired-end tagging approach using an antibody that primarily recognizes the pre-initiation complexes of RNA polymerase II, we explore the transcriptional interactomes of three mouse cells of progressive lineage commitment, including pluripotent embryonic stem cells, neural stem cells and neurosphere stem/progenitor cells. Our global chromatin connectivity maps reveal approximately 40,000 long-range interactions, suggest precise enhancer-promoter associations and delineate cell-type-specific chromatin structures. Analysis of the complex regulatory repertoire shows that there are extensive colocalizations among promoters and distal-acting enhancers. Most of the enhancers associate with promoters located beyond their nearest active genes, indicating that the linear juxtaposition is not the only guiding principle driving enhancer target selection. Although promoter-enhancer interactions exhibit high cell-type specificity, promoters involved in interactions are found to be generally common and mostly active among different cells. Chromatin connectivity networks reveal that the pivotal genes of reprogramming functions are transcribed within physical proximity to each other in embryonic stem cells, linking chromatin architecture to coordinated gene expression. Our study sets the stage for the full-scale dissection of spatial and temporal genome structures and their roles in orchestrating development.

Project description:In multicellular organisms, transcription regulation is one of the central mechanisms modelling lineage differentiation and cell-fate determination. Transcription requires dynamic chromatin configurations between promoters and their corresponding distal regulatory elements. It is believed that their communication occurs within large discrete foci of aggregated RNA polymerases termed transcription factories in three-dimensional nuclear space. However, the dynamic nature of chromatin connectivity has not been characterized at the genome-wide level. Here, through a chromatin interaction analysis with paired-end tagging approach using an antibody that primarily recognizes the pre-initiation complexes of RNA polymerase II, we explore the transcriptional interactomes of three mouse cells of progressive lineage commitment, including pluripotent embryonic stem cells, neural stem cells and neurosphere stem/progenitor cells. Our global chromatin connectivity maps reveal approximately 40,000 long-range interactions, suggest precise enhancer?promoter associations and delineate cell-type-specific chromatin structures. Analysis of the complex regulatory repertoire shows that there are extensive colocalizations among promoters and distal-acting enhancers. Most of the enhancers associate with promoters located beyond their nearest active genes, indicating that the linear juxtaposition is not the only guiding principle driving enhancer target selection. Although promoter?enhancer interactions exhibit high cell-type specificity, promoters involved in interactions are found to be generally common and mostly active among different cells. Chromatin connectivity networks reveal that the pivotal genes of reprogramming functions are transcribed within physical proximity to each other in embryonic stem cells, linking chromatin architecture to coordinated gene expression. Our study sets the stage for the full-scale dissection of spatial and temporal genome structures and their roles in orchestrating development.

Project description:Serum-to-2i interconversion of mouse Embryonic Stem Cells (mESCs) is a valuable in vitro model for early embryonic development. To assess whether 3D chromatin organization changes during this transition, we established Capture Hi-C with target-sequence enrichment of DNase I hypersensitive sites. We detected extremely long-range intra- and inter-chromosomal interactions between a small subset of H3K27me3 marked bivalent promoters involving the Hox clusters in serum grown cells. Notably, these promoter-mediated interactions are not present in 2i ground-state pluripotent mESCs but appear upon further development into primed-like serum mESCs. Reverting serum mESCs to ground-state 2i mESCs removes these promoter-promoter interactions in a spatiotemporal manner. H3K27me3, which is largely absent at bivalent promoters in ground-state 2i mESCs, is necessary but not sufficient to establish these interactions, as confirmed by Capture Hi-C on Eed-/- serum mESCs. Our results implicate H3K27me3 and PRC2 as critical players in chromatin alteration during priming of ESCs for differentiation. To study dynamics in chromatin architecture and to characterize long-range interaction, we performed Hi-C using DpnII as the restriction enzyme, potentially reaching a genome-wide coverage at a less than 1Kb resolution. We subsequently performed enrichment of interaction by a target capture similar to the exome sequencing approach. We enriched for DNaseI hyper-sensitive sites (DHSâs) in chromatin from mESCs. Probes were designed against the union of all DHSâs of Serum and 2i mESCs. Capture Hi-C reveals Extremely Long-Range Interactions (ELRI) in Serum but not in 2i ESCs. We observed H3K27me3 as a prominent characteristic, but not exclusive feature of ELRI loci in Serum mESCs. To further elucidate the involvement of constituents of PRC1 and PRC2 in ELRI, we performed ChIP-seq experiment on Suz12 and Ring1B during serum-to-2i transition. In addition, RNA-seq was performed to compare the expression levels of genes.

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Chromatin decouples promoter threshold from dynamic range.

Publications

Chromatin decouples promoter threshold from dynamic range.

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