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Coregulation of transcription factor binding and nucleosome occupancy through DNA features of mammalian enhancers.

ABSTRACT: Transcription factors (TFs) preferentially bind sites contained in regions of computationally predicted high nucleosomal occupancy, suggesting that nucleosomes are gatekeepers of TF binding sites. However, because of their complexity mammalian genomes contain millions of randomly occurring, unbound TF consensus binding sites. We hypothesized that the information controlling nucleosome assembly may coincide with the information that enables TFs to bind cis-regulatory elements while ignoring randomly occurring sites. Hence, nucleosomes would selectively mask genomic sites that can be contacted by TFs and thus be potentially functional. The hematopoietic pioneer TF Pu.1 maintained nucleosome depletion at macrophage-specific enhancers that displayed a broad range of nucleosome occupancy in other cell types and in reconstituted chromatin. We identified a minimal set of DNA sequence and shape features that accurately predicted both Pu.1 binding and nucleosome occupancy genome-wide. These data reveal a basic organizational principle of mammalian cis-regulatory elements whereby TF recruitment and nucleosome deposition are controlled by overlapping DNA sequence features.

SUBMITTER: Barozzi I

PROVIDER: S-EPMC4048654 | biostudies-literature | 2014 Jun

REPOSITORIES: biostudies-literature

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Coregulation of transcription factor binding and nucleosome occupancy through DNA features of mammalian enhancers.

Barozzi Iros I Simonatto Marta M Bonifacio Silvia S Yang Lin L Rohs Remo R Ghisletti Serena S Natoli Gioacchino G

Molecular cell 20140508 5

Transcription factors (TFs) preferentially bind sites contained in regions of computationally predicted high nucleosomal occupancy, suggesting that nucleosomes are gatekeepers of TF binding sites. However, because of their complexity mammalian genomes contain millions of randomly occurring, unbound TF consensus binding sites. We hypothesized that the information controlling nucleosome assembly may coincide with the information that enables TFs to bind cis-regulatory elements while ignoring rando ...[more]

PMID: 24813947

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Project description:In mammalian cells transcription factors (TFs) preferentially bind sites contained in regions of high nucleosomal occupancy, as determined by nucleotide-dependent computational analysis. This observation suggests that nucleosomes may act as gatekeepers of TF binding sites. We hypothesized that in mammalian genomes the information controlling nucleosome assembly may partially coincide with the information that enables TFs to recognize cognate sites in cis-regulatory elements while ignoring the myriad of non-functional, randomly occurring consensus binding sites. This way, nucleosome-mediated masking would be coupled to TF binding site functionality. The hematopoietic master regulator Pu.1 maintained nucleosome depletion at macrophage-specific enhancers that were otherwise occupied by nucleosomes in other cell types and in reconstituted chromatin. We identified a minimal set of DNA sequence and shape features that predicted Pu.1 binding with 78% accuracy. The same features predicted nucleosome occupancy in cells where Pu.1 was not expressed with higher accuracy than specifically designed models. Control of nucleosome deposition by DNA sequence and shape features that also specify TF consensus site functionality may allow maintaining the gatekeeper function of nucleosomes during evolution of cis-regulatory elements. Chromatin immuno-precipitations of the transcription factor Pu.1 followed by multiparallel sequencing performed in murine bone marrow-derived macrophages. Experiments carried out in cells infected either with a retroviral vector containing a short hairpin targeting Pu.1 or with the empty vector as control. The shPU.1 hairpin (sequence available upon request) was selected among five designed using a publicly available software (http://katahdin.mssm.edu/siRNA) and was cloned in a modified version of TtRMPVIR inducible retroviral vector (Genbank HQ456318) in which the puromycin resistance gene was inserted. The empty vector, containing an sh-Renilla sequence, was used as control. Chromatin immuno-precipitations of the transcription factor PU.1 binding to in vitro reconstituted chromatin followed by multiparallel sequencing Micrococcal nuclease digestion of chromatin extracted from bone marrow derived macrophages followed by multiparallel sequencing . Experiments were carried out in untreated cells (4 replicates) and cells infected either with a retroviral vector containing a short hairpin targeting Pu.1 or with the empty vector as control (2 replicates). The shPU.1 hairpin (sequence available upon request) was selected among five designed using a publicly available software (http://katahdin.mssm.edu/siRNA) and was cloned in a modified version of TtRMPVIR inducible retroviral vector (Genbank HQ456318) in which the puromycin resistance gene was inserted. The empty vector, containing an sh-Renilla sequence, was used as control. Micrococcal nuclease digestion of in vitro reconstituted chromatin followed by multiparallel sequencing

Project description:BackgroundDivergence of transcription factor binding sites is considered to be an important source of regulatory evolution. The associations between transcription factor binding sites and phenotypic diversity have been investigated in many model organisms. However, the understanding of other factors that contribute to it is still limited. Recent studies have elucidated the effect of chromatin structure on molecular evolution of genomic DNA. Though the profound impact of nucleosome positions on gene regulation has been reported, their influence on transcriptional evolution is still less explored. With the availability of genome-wide nucleosome map in yeast species, it is thus desirable to investigate their impact on transcription factor binding site evolution. Here, we present a comprehensive analysis of the role of nucleosome positioning in the evolution of transcription factor binding sites.ResultsWe compared the transcription factor binding site frequency in nucleosome occupied regions and nucleosome depleted regions in promoters of old (orthologs among Saccharomycetaceae) and young (Saccharomyces specific) genes; and in duplicate gene pairs. We demonstrated that nucleosome occupied regions accommodate greater binding site variations than nucleosome depleted regions in young genes and in duplicate genes. This finding was confirmed by measuring the difference in evolutionary rates of binding sites in sensu stricto yeasts at nucleosome occupied regions and nucleosome depleted regions. The binding sites at nucleosome occupied regions exhibited a consistently higher evolution rate than those at nucleosome depleted regions, corroborating the difference in the selection constraints at the two regions. Finally, through site-directed mutagenesis experiment, we found that binding site gain or loss events at nucleosome depleted regions may cause more expression differences than those in nucleosome occupied regions.ConclusionsOur study indicates the existence of different selection constraint on binding sites at nucleosome occupied regions than at the nucleosome depleted regions. We found that the binding sites have a different rate of evolution at nucleosome occupied and depleted regions. Finally, using transcription factor binding site-directed mutagenesis experiment, we confirmed the difference in the impact of binding site changes on expression at these regions. Thus, our work demonstrates the importance of composite analysis of chromatin and transcriptional evolution.

Dataset Information

Coregulation of transcription factor binding and nucleosome occupancy through DNA features of mammalian enhancers.

Publications

Coregulation of transcription factor binding and nucleosome occupancy through DNA features of mammalian enhancers.

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