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Genome-wide discovery of active regulatory elements and transcription factor footprints in Caenorhabditis elegans using DNase-seq

ABSTRACT: Deep sequencing of size-selected DNaseI-treated chromatin (DNase-seq) allows high resolution measurement of chromatin accessibility to DNaseI cleavage, permitting identification of de novo active cis regulatory modules (CRMs) and individual transcription factor (TF) binding sites. We adapted DNase-seq to nuclei isolated from C. elegans embryos and L1 arrest larvae to generate high-resolution maps of TF binding. Over half of embryonic DNaseI hypersensitive sites (DHS) were annotated in noncoding sequences, with 23% in intergenic, 11% promoter regions and 21% in introns, with similar statistics in data collected from L1 arrest larvae. Noncoding DHS exhibit high evolutionary sequence conservation and are enriched in marks of enhancer activity and transcription. We validated noncoding DHS against a previously investigated set of enhancers from myo-2, myo-3, hlh-1, elt-2 and lin-26/lir-1 gene loci and recapitulated 15 of 17 known enhancers in these loci. We then mined the DNase-seq data to identify putative active CRMs and TF footprints. Our DNase-seq data could also be used to improve predictions of tissue-specific expression compared to motifs alone. In a pilot functional test, 10 of 15 DHS from pha-4, icl-1 and ceh-13 drove reporter gene expression in transgenic C. elegans. Overall, we provide experimental annotation of 26,644 putative CRMs in the embryo containing 55,890 TF footprints, and 15,841 putative CRMs in the L1 arrest larvae containing 32,685 TF footprints.

ORGANISM(S): Caenorhabditis elegans

PROVIDER: GSE97425 | GEO | 2017/08/01

SECONDARY ACCESSION(S): PRJNA381766

REPOSITORIES: GEO

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Project description:Distant enhancer elements are a major source of specificity in mammalian gene expression. Although enhancers that regulate broad developmental decisions and inducible gene expression have been studied extensively, little is known about regulatory elements that govern monogenic and monoallelic expression. Here, using high throughput epigenetic and genetic techniques we identified a plethora of distant enhancers that regulate monoallelic olfactory receptor (OR) gene expression. Potential OR enhancers have unique, cell type specific epigenetic marks that distinguish them from other neuronal enhancers and correlate with enhancer activity in vivo. Using sequence capture to enrich for these sequences we identified Dnase-protected footprints that reveal novel regulatory sequences and transcription factors required for OR gene activation. Our experiments provide insight to the regulation of OR expression, and describe novel principles and methodologies towards the understanding of transcriptional mechanisms that generate cellular diversity. In vivo examination of H3K79me3 enrichment and DNAse protected footprints on olfactory receptor enhancer sequences. We performed ChIP-seq on native chromatin isolated from the mouse olfactory epithelium using antibodies against H3K79me3. To sequence accessible regions of the genome we treated nuclei with limiting amounts of DNAse I to digest accessible chromatin and perform Dnase Hypersensitivity (DHS)-seq. In the olfactory epithelium, the H enhancer – the first described enhancer for olfactory receptors has a well-defined DNAse I hypersensitivity peak and is flanked by high levels of H3K79me3. We find other intergenic sequences nearby olfactory receptor genes that share the same chromatin signature, and test their function in vivo. TO uncover transcription factor footprints on olfactory receptor enhancers we performed sequence capture of the DHS-seq library to enrich for these sequences. We find multiple DNAse-protected sequences and perform motif analysis on transcription factor footprints to reveal factors involved in olfactory receptor gene regulation.

Dataset Information

Genome-wide discovery of active regulatory elements and transcription factor footprints in Caenorhabditis elegans using DNase-seq

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