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Distributed probing of chromatin structure in vivo reveals pervasive chromatin accessibility for expressed and non-expressed genes during tissue differentiation in C. elegans.

ABSTRACT: Tissue differentiation is accompanied by genome-wide changes in the underlying chromatin structure and dynamics, or epigenome. By controlling when, where, and what regulatory factors have access to the underlying genomic DNA, the epigenome influences the cell's transcriptome and ultimately its function. Existing genomic methods for analyzing cell-type-specific changes in chromatin generally involve two elements: (i) a source for purified cells (or nuclei) of distinct types, and (ii) a specific treatment that partitions or degrades chromatin by activity or structural features. For many cell types of great interest, such assays are limited by our inability to isolate the relevant cell populations in an organism or complex tissue containing an intertwined mixture of other cells. This limitation has confined available knowledge of chromatin dynamics to a narrow range of biological systems (cell types that can be sorted/separated/dissected in large numbers and tissue culture models) or to amalgamations of diverse cell types (tissue chunks, whole organisms).Transgene-driven expression of DNA/chromatin modifying enzymes provides one opportunity to query chromatin structures in expression-defined cell subsets. In this work we combine in vivo expression of a bacterial DNA adenine methyltransferase (DAM) with high throughput sequencing to sample tissue-specific chromatin accessibility on a genome-wide scale. We have applied the method (DALEC: Direct Asymmetric Ligation End Capture) towards mapping a cell-type-specific view of genome accessibility as a function of differentiated state. Taking advantage of C. elegans strains expressing the DAM enzyme in diverse tissues (body wall muscle, gut, and hypodermis), our efforts yield a genome-wide dataset measuring chromatin accessibility at each of 538,000 DAM target sites in the C. elegans (diploid) genome.Validating the DALEC mapping results, we observe a strong association between observed coverage by nucleosomes and low DAM accessibility. Strikingly, we observed no extended regions of inaccessible chromatin for any of the tissues examined. These results are consistent with "local choreography" models in which differential gene expression is driven by intricate local rearrangements of chromatin structure rather than gross impenetrability of large chromosomal regions.

SUBMITTER: Sha K

PROVIDER: S-EPMC3091661 | biostudies-literature | 2010 Aug

REPOSITORIES: biostudies-literature

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Distributed probing of chromatin structure in vivo reveals pervasive chromatin accessibility for expressed and non-expressed genes during tissue differentiation in C. elegans.

Sha Ky K Gu Sam G SG Pantalena-Filho Luiz C LC Goh Amy A Fleenor Jamie J Blanchard Daniel D Krishna Chaya C Fire Andrew A

BMC genomics 20100806

<h4>Background</h4>Tissue differentiation is accompanied by genome-wide changes in the underlying chromatin structure and dynamics, or epigenome. By controlling when, where, and what regulatory factors have access to the underlying genomic DNA, the epigenome influences the cell's transcriptome and ultimately its function. Existing genomic methods for analyzing cell-type-specific changes in chromatin generally involve two elements: (i) a source for purified cells (or nuclei) of distinct types, an ...[more]

PMID: 20691096

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Project description:BackgroundThe challenge in extracting genome-wide chromatin features from limiting clinical samples poses a significant hurdle in identification of regulatory marks that impact the physiological or pathological state. Current methods that identify nuclease accessible chromatin are reliant on large amounts of purified nuclei as starting material. This complicates analysis of trace clinical tissue samples that are often stored frozen. We have developed an alternative nuclease based procedure to bypass nuclear preparation to interrogate nuclease accessible regions in frozen tissue samples.ResultsHere we introduce a novel technique that specifically identifies Tissue Accessible Chromatin (TACh). The TACh method uses pulverized frozen tissue as starting material and employs one of the two robust endonucleases, Benzonase or Cyansase, which are fully active under a range of stringent conditions such as high levels of detergent and DTT. As a proof of principle we applied TACh to frozen mouse liver tissue. Combined with massive parallel sequencing TACh identifies accessible regions that are associated with euchromatic features and accessibility at transcriptional start sites correlates positively with levels of gene transcription. Accessible chromatin identified by TACh overlaps to a large extend with accessible chromatin identified by DNase I using nuclei purified from freshly isolated liver tissue as starting material. The similarities are most pronounced at highly accessible regions, whereas identification of less accessible regions tends to be more divergence between nucleases. Interestingly, we show that some of the differences between DNase I and Benzonase relate to their intrinsic sequence biases and accordingly accessibility of CpG islands is probed more efficiently using TACh.ConclusionThe TACh methodology identifies accessible chromatin derived from frozen tissue samples. We propose that this simple, robust approach can be applied across a broad range of clinically relevant samples to allow demarcation of regulatory elements of considerable prognostic significance.

Dataset Information

Distributed probing of chromatin structure in vivo reveals pervasive chromatin accessibility for expressed and non-expressed genes during tissue differentiation in C. elegans.

Publications

Distributed probing of chromatin structure in vivo reveals pervasive chromatin accessibility for expressed and non-expressed genes during tissue differentiation in C. elegans.

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