Genome-scale ChIP-chip analysis using 10,000 human cells.
ABSTRACT: The technique of chromatin immunoprecipitation (ChIP) is a powerful method for identifying in vivo DNA binding sites of transcription factors and for studying chromatin modifications. Unfortunately, the large number of cells needed for the standard ChIP protocol has hindered the analysis of many biologically interesting cell populations that are difficult to obtain in large numbers. New ChIP methods involving the use of carrier chromatin have been developed that allow the one-gene-at-a-time analysis of very small numbers of cells. However such methods are not useful if the resultant sample will be applied to genomic microarrays or used in ChIP-sequencing assays. Therefore, we have miniaturized the ChIP protocol such that as few as 10,000 cells (without the addition of carrier reagents) can be used to obtain enough sample material to analyze the entire human genome. We demonstrate the reproducibility of this MicroChIP technique using 2.1 million feature high-density oligonucleotide arrays and antibodies to RNA polymerase II and to histone H3 trimethylated on lysine 27 or lysine 9.
Project description:Genome-wide location analysis of histone modifications and transcription factor binding relies on chromatin immunoprecipitation (ChIP) assays. These assays are, however, time-consuming and require large numbers of cells, hindering their application to the analysis of many interesting cell types. We report here a fast microChIP (muChIP) assay for 1,000 cells in combination with microarrays to produce genome-scale surveys of histone modifications. muChIP-chip reliably reproduces data obtained by large-scale assays: H3K9ac and H3K9m3 enrichment profiles are conserved and nucleosome-free regions are revealed.
Project description:Much effort has been devoted to understand how chromatin modification regulates development and disease. Despite recent progress, however, it remains difficult to obtain high-quality epigenomic maps using chromatin-immunoprecipitation-coupled deep sequencing (ChIP-seq) in samples with low-cell numbers. Here, we present an Atlantis dsDNase-based technology, aFARP-ChIP-seq, that provides accurate profiling of genome-wide histone modifications in as few as 100 cells. By mapping histone lysine trimethylation (H3K4me3) and acetylation (H3K27Ac) in group I innate lymphoid cells (ILC1) sorted from different tissues in parallel, aFARP-ChIP-seq uncovers putative active promoter and enhancer landscapes of several tissue-specific Natural Killer cells (NK) and ILC1. aFARP-ChIP-seq is also highly effective in mapping transcription factor binding sites in small number of cells. Thus, aFARP-ChIP-seq offers multiplexing mapping of both epigenome and transcription factor binding sites using a small number of cells.
Project description:Chromatin immunoprecipitation (ChIP) is a powerful technique for studying protein-DNA interactions. Drawbacks of current ChIP assays however are a requirement for large cell numbers, which limits applicability of ChIP to rare cell samples, and/or lengthy procedures with limited applications. There are to date no protocols for fast and parallel ChIPs of post-translationally modified histones from small cell numbers or biopsies, and importantly, no protocol allowing for investigations of transcription factor binding in small cell numbers. We report here the development of a micro (micro) ChIP assay suitable for up to nine parallel quantitative ChIPs of modified histones or RNA polymerase II from a single batch of 1000 cells. MicroChIP can also be downscaled to monitor the association of one protein with multiple genomic sites in as few as 100 cells. MicroChIP is applicable to small fresh tissue biopsies, and a cross-link-while-thawing procedure makes the assay suitable for frozen biopsies. Using MicroChIP, we characterize transcriptionally permissive and repressive histone H3 modifications on developmentally regulated promoters in human embryonal carcinoma cells and in osteosarcoma biopsies. muChIP creates possibilities for multiple parallel and rapid transcription factor binding and epigenetic analyses of rare cell and tissue samples.
Project description:Chromatin immunoprecipitation followed by next generation sequencing (ChIP-seq) is a key technique in chromatin research. Although heavily applied, existing ChIP-seq protocols are often highly fine-tuned workflows, optimized for specific experimental requirements. Especially the initial steps of ChIP-seq, particularly chromatin shearing, are deemed to be exceedingly cell-type-specific, thus impeding any protocol standardization efforts. Here we demonstrate that harmonization of ChIP-seq workflows across cell types and conditions is possible when obtaining chromatin from properly isolated nuclei. We established an ultrasound-based nuclei extraction method (NEXSON: Nuclei EXtraction by SONication) that is highly effective across various organisms, cell types and cell numbers. The described method has the potential to replace complex cell-type-specific, but largely ineffective, nuclei isolation protocols. By including NEXSON in ChIP-seq workflows, we completely eliminate the need for extensive optimization and sample-dependent adjustments. Apart from this significant simplification, our approach also provides the basis for a fully standardized ChIP-seq and yields highly reproducible transcription factor and histone modifications maps for a wide range of different cell types. Even small cell numbers (?10,000 cells per ChIP) can be easily processed without application of modified chromatin or library preparation protocols.
Project description:BACKGROUND: Chromatin immunoprecipitation coupled with high-throughput DNA sequencing (ChIP-seq) offers high resolution, genome-wide analysis of DNA-protein interactions. However, current standard methods require abundant starting material in the range of 1-20 million cells per immunoprecipitation, and remain a bottleneck to the acquisition of biologically relevant epigenetic data. Using a ChIP-seq protocol optimised for low cell numbers (down to 100,000 cells/IP), we examined the performance of the ChIP-seq technique on a series of decreasing cell numbers. RESULTS: We present an enhanced native ChIP-seq method tailored to low cell numbers that represents a 200-fold reduction in input requirements over existing protocols. The protocol was tested over a range of starting cell numbers covering three orders of magnitude, enabling determination of the lower limit of the technique. At low input cell numbers, increased levels of unmapped and duplicate reads reduce the number of unique reads generated, and can drive up sequencing costs and affect sensitivity if ChIP is attempted from too few cells. CONCLUSIONS: The optimised method presented here considerably reduces the input requirements for performing native ChIP-seq. It extends the applicability of the technique to isolated primary cells and rare cell populations (e.g. biobank samples, stem cells), and in many cases will alleviate the need for cell culture and any associated alteration of epigenetic marks. However, this study highlights a challenge inherent to ChIP-seq from low cell numbers: as cell input numbers fall, levels of unmapped sequence reads and PCR-generated duplicate reads rise. We discuss a number of solutions to overcome the effects of reducing cell number that may aid further improvements to ChIP performance.
Project description:BACKGROUND:The introduction of pathology tissue-chromatin immunoprecipitation (PAT-ChIP), a technique allowing chromatin immunoprecipitation (ChIP) from formalin-fixed paraffin-embedded (FFPE) tissues, has extended the application of chromatin studies to clinical patient samples. However, extensive crosslinking introduced during routine tissue fixation of clinical specimens may hamper the application of PAT-ChIP to genome-wide studies (PAT-ChIP-Seq) from archived tissue samples. The reduced efficiency in chromatin extraction from over-fixed formalin archival samples is the main hurdle to overcome, especially when low abundant epigenetic marks (e.g., H3K4me3) are investigated. RESULTS:We evaluated different modifications of the original PAT-ChIP protocol to improve chromatin isolation from FFPE tissues. With this aim, we first made extensive usage of a normal human colon specimen fixed at controlled conditions (24 h, 48 h, and 72 h) to mimic the variability of tissue fixation that is most frequently found in archived samples. Different conditions of chromatin extraction were tested applying either diverse sonication protocols or heat-mediated limited reversal of crosslinking (LRC). We found that, if compared with canonical PAT-ChIP protocol, LRC strongly increases chromatin extraction efficiency, especially when 72-h fixed FFPE samples are used. The new procedure, that we named enhanced PAT-ChIP (EPAT-ChIP), was then applied at genome-wide level using an archival sample of invasive breast carcinoma to investigate H3K4me3, a lowly abundant histone modification, and H3K27me3 and H3K27ac, two additional well-known histone marks. CONCLUSIONS:EPAT-ChIP procedure improves the efficiency of chromatin isolation from FFPE samples allowing the study of long time-fixed specimens (72 h), as well as the investigation of low distributed epigenetic marks (e.g., H3K4me3) and the analysis of multiple histone marks from low amounts of starting material. We believe that EPAT-ChIP will facilitate the application of chromatin studies to archived pathology samples, thus contributing to extend the current understanding of cancer epigenomes and enabling the identification of clinically useful tumor biomarkers.
Project description:The translocation t(15;17) generates the chimeric PML-RARalpha transcription factor that is the initiating event of acute promyelocytic leukemia. A global view of PML-RARalpha transcriptional functions was obtained by genome-wide binding and chromatin modification analyses combined with genome-wide expression data. Chromatin immunoprecipitation (ChIP)-chip experiments identified 372 direct genomic PML-RARalpha targets. A subset of these was confirmed in primary acute promyelocytic leukemia. Direct PML-RARalpha targets include regulators of global transcriptional programs as well as critical regulatory genes for basic cellular functions such as cell-cycle control and apoptosis. PML-RARalpha binding universally led to HDAC1 recruitment, loss of histone H3 acetylation, increased tri-methylation of histone H3 lysine 9, and unexpectedly increased trimethylation of histone H3 lysine 4. The binding of PML-RARalpha to target promoters and the resulting histone modifications resulted in mRNA repression of functionally relevant genes. Taken together, our results reveal that the transcription factor PML-RARalpha regulates key cancer-related genes and pathways by inducing a repressed chromatin formation on its direct genomic target genes.
Project description:Cross-talk between DNA methylation and histone modifications drives the establishment of composite epigenetic signatures and is traditionally studied using correlative rather than direct approaches. Here we present sequential ChIP-bisulfite-sequencing (ChIP- BS-seq) as an approach to quantitatively assess DNA methylation patterns associated with chromatin modifications or chromatin-associated factors directly. A chromatin- immunoprecipitation (ChIP)-capturing step is used to obtain a restricted representation of the genome occupied by the epigenetic feature of interest, for which a single-base resolution DNA methylation map is then generated. When applied to H3 lysine 27 tri- methylation (H3K27me3), we found that H3K27me3 and DNA methylation are compatible throughout most of the genome, except for CpG islands, where these two marks are mutually exclusive. Further ChIP-BS-seq-based analysis in Dnmt triple- knock-out (TKO) embryonic stem cells revealed that total loss of CpG methylation is associated with alteration of H3K27me3 levels throughout the genome: H3K27me3 in localized peaks is decreased while broad local enrichments (BLOCs) of H3K27me3 are formed. At an even broader scale, these BLOCs correspond to regions of high DNA methylation in wild-type ES cells, suggesting that DNA methylation prevents H3K27me3 deposition locally and at megabase scale. Our strategy provides an unique way of investigating global interdependencies between DNA methylation and other chromatin features. ChIP (chromatin immunoprecipitation) is followed by bisulfite conversion and deep sequencing to directly assess DNA methylation levels in captured chromatin fragments (ChIP-BS-seq). We used ChIP-BS-seq to study the potential global cross-talk between H3K27me3 and DNA methylation, which are both linked to repression. First, we used capturing of methylated DNA, followed by bisulfite-deep sequencing (MethylCap-BS-seq). Genomic DNA isolated from normal and tumor colon tissues was used for MethylCap-BS-seq as well as for conventional MethylCap-seq experiments. Second, we performed ChIP-BS-seq on H3K27me3, using HCT116 colon carcinoma cells. Third, to further study the relevance of the observations, we generated genome-wide profiles for H3K27me3 and DNA methylation by conventional ChIP-seq and MethylCap-seq, and RNA-seq, respectively. Finally, we performed H3K27me3-ChIP-BS-seq and MethylCap-seq on wild-type mouse ES cells as well as Dnmt-triple-knockout (TKO) mouse ES cells.
Project description:Chromatin immunoprecipitation followed by sequencing (ChIP-Seq) is the preferred approach to map histone modifications and identify cis-regulatory DNA elements throughout the genome. Multiple methods have been described to increase the efficiency of library preparation and to reduce hands-on time as well as costs. This review describes detailed steps to perform cell fixation, chromatin shearing, immunoprecipitation, and sequencing library preparation for a batch of 48-96 samples with small cell numbers. The protocol implements a semiautomated platform to reduce technical variability and improve signal-to-noise ratio as well as reduce hands-on time, thus allowing large-scale epigenetic studies of clinical samples with limited cell numbers.
Project description:We made Polycomb (PC) and histone H3 lysine 27 trimethylation (H3K27me3) chromatin binding maps in central brain tissue from 3rd instar larvae, allowing us to make a direct comparison to our 4C data (http://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE23166). Our results demonstrate that our PC and H3K27me3 maps are highly similar, and fit with previously identified hallmarks of PcG-bound chromatin, namely: PC and H3K27me3 co-occur in the genome as large contiguous domains that largely repress transcription of the underlying genes, which encode important regulators of development. Keywords: Genome binding/occupancy profiling by genome tiling array ChIP-chip experiments for H3K27me3 were performed in Drosophila larval brain tissue. Samples were hybridized to 380k NimbleGen arrays with 300 bp probe spacing.