Nucleosome positioning in A549 cells before/after NME2 induction
Ontology highlight
ABSTRACT:
ORGANISM(S): Homo sapiens
PROVIDER: GSE40363 | GEO | 2014/08/04
SECONDARY ACCESSION(S): PRJNA174034
REPOSITORIES: GEO
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Project description:Previous studies have analyzed patterns of transcription, transcription factor (TF) binding or mapped nucleosome occupancy across the genome. These suggest that the three aspects are genetically connected but the cause and effect relationships are still unknown. For example, physiologic TF binding studies involve many TFs, consequently, it is difficult to assign nucleosome reorganization to the binding site occupancy of any particular TF. Therefore, several aspects remain unclear: does TF binding influence nucleosome (re)organizations locally (in close vicinity of their binding sites) or impact the chromatin landscape at a more global level; are all or only a fraction of TF binding a result of reorganization in nucleosome occupancy; finally, do all TF binding and associated nucleosome occupancy changes result in altered gene expression? With these in mind, we sought to study a single TF that induces physiological changes, and following characterization of the two states (before and after induction of the TF) we determined: (a) genomic binding sites of the TF, (b) promoter nucleosome occupancy and (c) transcriptome profiles, independently in both conditions. Results demonstrate that TF binding influences expression of the target gene only when it is coupled to nucleosome repositioning at or close to its binding site, and not when transcription factor binding occurs without local associated nucleosome reorganization. The nature of interaction between TF binding and nucleosomes and what extent it influences transcription
2014-08-04 | E-GEOD-40363 | biostudies-arrayexpress
Project description:It is widely believed that reorganization of nucleosomes result in availability of transcription factor (TF) binding sites for eukaryotic gene regulation. Recent findings also show TFs induced during physiological perturbations can alter nucleosome occupancy to facilitate DNA binding. Although, these suggest a close relationship between TF binding and nucleosomes, the nature of this interaction, or to what extent it influences transcription is not clear. Moreover, since physiological perturbations induced multiple TFs, relatively direct effect of any TF on nucleosome occupancy remains poorly addressed. With these in mind, we used a single TF to induce physiological changes and following characterization of the two states (before and after induction of the TF) we determined: (a) genome wide binding sites of the TF, (b) promoter nucleosome occupancy and (c) transcriptome profiles, independently in both conditions. We find only ~20% of TF binding results from nucleosome repositioning - interestingly, almost all corresponding genes were transcriptionally altered. Whereas, when TF-occupancy was independent of nucleosome repositioning only a small fraction of corresponding genes were expressed/repressed. These observations suggest a model where TF occupancy leads to transcriptional change only when coupled with nucleosome repositioning in close proximity. This, to our knowledge, for the first time also helps explain why genome wide TF occupancy (e.g., from ChIP-sequencing) typically overlaps with only a small fraction of genes that change expression. The nature of interaction between TF binding and nucleosomes and what extent it influences transcription
2014-08-04 | E-GEOD-40300 | biostudies-arrayexpress
Project description:It is widely believed that reorganization of nucleosomes result in availability of binding sites that engage transcription factors during eukaryotic gene regulation. Recent findings, on the other hand, suggest that transcription factors induced as a result of physiological perturbations directly (or in association with chromatin modifiers) may alter nucleosome occupancy to facilitate DNA binding. Although, together these suggest a close relationship between transcription factor binding and nucleosome reorganization, the nature of the inter-dependency, or to what extent it influences regulatory transcription is not clear. Moreover, since most studies used physiolgical pertubations that induced multiple transcription factor chromatin modifiers, the relatively local (or direct) effect of transcription factor binding on nucleosome occupancy remains unclear. With these in mind, we used a single transcription factor to induce physiological changes, representing metastatic (aggressive cancer) and the corresponding non-metastatic state, in human cancer cells. Following characterization of the two states (before and after induction of the transcription factor) we determined: (a) genome wide binding sites of the transcription factor, (b) promoter nucleosome occupancy and (c) transcriptome profiles, independently in both conditions. Interestingly, we find only ~20% of TF binding results from nucleosome reorganization - however, almost all corresponding genes were transcriptionally altered. Whereas, in cases where TF-occupancy was independent of nucleosome repositioning (in close vicinity), or co-occurred with nucleosomes, only a small fraction of the corresponding genes were expressed/repressed. Together, these indicate a model where TF occupancy only when coupled with nucleosome repositioning in close proximity is transcriptionally active. This, to our knowledge, for the first time also helps explain why genome wide TF occupancy (e.g., from ChIP-seq) is typically associated with only a small fraction of genes that change expression. For expression profiling of cells in NME2-induced conditions, A549 cells were transfected with pcDNA-NME2-MYC or pcDNA-MYC (control). RNA was isolated from the cells 48h after transfection using the trizol method (Sigma) as per manufacturerM-bM-^@M-^Ys protocol. Total RNA was processed to hybridize to Illumina Human HT-12 v4 Expression BeadChip as per manufacturerM-bM-^@M-^Ys instructions. Three biological replicates were averaged and data was analyzed using BeadStudio (P <0.05 of fold change).
2014-08-04 | E-GEOD-40194 | biostudies-arrayexpress
Project description:It is widely believed that reorganization of nucleosomes result in availability of transcription factor (TF) binding sites for eukaryotic gene regulation. Recent findings also show TFs induced during physiological perturbations can alter nucleosome occupancy to facilitate DNA binding. Although, these suggest a close relationship between TF binding and nucleosomes, the nature of this interaction, or to what extent it influences transcription is not clear. Moreover, since physiological perturbations induced multiple TFs, relatively direct effect of any TF on nucleosome occupancy remains poorly addressed. With these in mind, we used a single TF to induce physiological changes and following characterization of the two states (before and after induction of the TF) we determined: (a) genome wide binding sites of the TF, (b) promoter nucleosome occupancy and (c) transcriptome profiles, independently in both conditions. We find only ~20% of TF binding results from nucleosome repositioning - interestingly, almost all corresponding genes were transcriptionally altered. Whereas, when TF-occupancy was independent of nucleosome repositioning only a small fraction of corresponding genes were expressed/repressed. These observations suggest a model where TF occupancy leads to transcriptional change only when coupled with nucleosome repositioning in close proximity. This, to our knowledge, for the first time also helps explain why genome wide TF occupancy (e.g., from ChIP-sequencing) typically overlaps with only a small fraction of genes that change expression.
2014-08-04 | GSE40300 | GEO
Project description:It is widely believed that reorganization of nucleosomes result in availability of binding sites that engage transcription factors during eukaryotic gene regulation. Recent findings, on the other hand, suggest that transcription factors induced as a result of physiological perturbations directly (or in association with chromatin modifiers) may alter nucleosome occupancy to facilitate DNA binding. Although, together these suggest a close relationship between transcription factor binding and nucleosome reorganization, the nature of the inter-dependency, or to what extent it influences regulatory transcription is not clear. Moreover, since most studies used physiolgical pertubations that induced multiple transcription factor chromatin modifiers, the relatively local (or direct) effect of transcription factor binding on nucleosome occupancy remains unclear. With these in mind, we used a single transcription factor to induce physiological changes, representing metastatic (aggressive cancer) and the corresponding non-metastatic state, in human cancer cells. Following characterization of the two states (before and after induction of the transcription factor) we determined: (a) genome wide binding sites of the transcription factor, (b) promoter nucleosome occupancy and (c) transcriptome profiles, independently in both conditions. Interestingly, we find only ~20% of TF binding results from nucleosome reorganization - however, almost all corresponding genes were transcriptionally altered. Whereas, in cases where TF-occupancy was independent of nucleosome repositioning (in close vicinity), or co-occurred with nucleosomes, only a small fraction of the corresponding genes were expressed/repressed. Together, these indicate a model where TF occupancy only when coupled with nucleosome repositioning in close proximity is transcriptionally active. This, to our knowledge, for the first time also helps explain why genome wide TF occupancy (e.g., from ChIP-seq) is typically associated with only a small fraction of genes that change expression.
2014-08-04 | GSE40194 | GEO
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.
2014-05-08 | GSE50762 | GEO
Project description:Nucleosomes are the primary unit of chromatin structure and inhibit key intracellular interactions which regulate how eukaryotic genetic information is read, including transcription factor (TF) binding to DNA. In theory, the sterics of nucleosome-DNA interactions could inhibit TF binding to all nucleosome-bound DNA. In reality, however, nucleosome inhibition of TF binding is variable both across a genome and even within a single nucleosome. Prior studies have demonstrated that nucleosome occupancy, nucleosome positioning, TF binding site (TFBS) affinity & TFBS location can each influence TF targeting in vivo, however, this work has been largely correlative and no study has dissected collective from individual contributions of these important variables. Therefore, to address this deficiency, we have mapped genome-wide changes in chromatin structure and TF binding following experimental nucleosome depletion. Heuristic modeling of results confirmed that chromatin specification of TF targeting is a multivariate, context-specific, process, with most informative features originating from additive interactions between cis and trans variables. Additionally, we found compelling evidence that nucleosomes serve to inhibit intra-genic TF binding, as evidenced by an increasing number of sub-optimal TFBS occupied following nucleosome depletion. The majority of these conditional loci were located within open reading frames and parallel transcriptome analysis revealed their occurrence was linked to generation of intragenic cryptic transcripts. Together results support the idea that chromatin structure has evolved to coordinate specification of regulatory factor targeting & gene expression. Findings have functional relevance to emerging datasets on genetic and epigenetic variation in human disease states.
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Project description:Nucleosomes are the primary unit of chromatin structure and inhibit key intracellular interactions which regulate how eukaryotic genetic information is read, including transcription factor (TF) binding to DNA. In theory, the sterics of nucleosome-DNA interactions could inhibit TF binding to all nucleosome-bound DNA. In reality, however, nucleosome inhibition of TF binding is variable both across a genome and even within a single nucleosome. Prior studies have demonstrated that nucleosome occupancy, nucleosome positioning, TF binding site (TFBS) affinity & TFBS location can each influence TF targeting in vivo, however, this work has been largely correlative and no study has dissected collective from individual contributions of these important variables. Therefore, to address this deficiency, we have mapped genome-wide changes in chromatin structure and TF binding following experimental nucleosome depletion. Heuristic modeling of results confirmed that chromatin specification of TF targeting is a multivariate, context-specific, process, with most informative features originating from additive interactions between cis and trans variables. Additionally, we found compelling evidence that nucleosomes serve to inhibit intra-genic TF binding, as evidenced by an increasing number of sub-optimal TFBS occupied following nucleosome depletion. The majority of these conditional loci were located within open reading frames and parallel transcriptome analysis revealed their occurrence was linked to generation of intragenic cryptic transcripts. Together results support the idea that chromatin structure has evolved to coordinate specification of regulatory factor targeting & gene expression. Findings have functional relevance to emerging datasets on genetic and epigenetic variation in human disease states.
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Project description:Nucleosomes are the primary unit of chromatin structure and inhibit key intracellular interactions which regulate how eukaryotic genetic information is read, including transcription factor (TF) binding to DNA. In theory, the sterics of nucleosome-DNA interactions could inhibit TF binding to all nucleosome-bound DNA. In reality, however, nucleosome inhibition of TF binding is variable both across a genome and even within a single nucleosome. Prior studies have demonstrated that nucleosome occupancy, nucleosome positioning, TF binding site (TFBS) affinity & TFBS location can each influence TF targeting in vivo, however, this work has been largely correlative and no study has dissected collective from individual contributions of these important variables. Therefore, to address this deficiency, we have mapped genome-wide changes in chromatin structure and TF binding following experimental nucleosome depletion. Heuristic modeling of results confirmed that chromatin specification of TF targeting is a multivariate, context-specific, process, with most informative features originating from additive interactions between cis and trans variables. Additionally, we found compelling evidence that nucleosomes serve to inhibit intra-genic TF binding, as evidenced by an increasing number of sub-optimal TFBS occupied following nucleosome depletion. The majority of these conditional loci were located within open reading frames and parallel transcriptome analysis revealed their occurrence was linked to generation of intragenic cryptic transcripts. Together results support the idea that chromatin structure has evolved to coordinate specification of regulatory factor targeting & gene expression. Findings have functional relevance to emerging datasets on genetic and epigenetic variation in human disease states.
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