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Enhancer Regulation of Transcriptional Bursting Parameters Revealed by Forced Chromatin Looping.

ABSTRACT: Mammalian genes transcribe RNA not continuously, but in bursts. Transcriptional output can be modulated by altering burst fraction or burst size, but how regulatory elements control bursting parameters remains unclear. Single-molecule RNA FISH experiments revealed that the ?-globin enhancer (LCR) predominantly augments transcriptional burst fraction of the ?-globin gene with modest stimulation of burst size. To specifically measure the impact of long-range chromatin contacts on transcriptional bursting, we forced an LCR-?-globin promoter chromatin loop. We observed that raising contact frequencies increases burst fraction but not burst size. In cells in which two developmentally distinct LCR-regulated globin genes are cotranscribed in cis, burst sizes of both genes are comparable. However, allelic co-transcription of both genes is statistically disfavored, suggesting mutually exclusive LCR-gene contacts. These results are consistent with competition between the ?-type globin genes for LCR contacts and suggest that LCR-promoter loops are formed and released with rapid kinetics.

SUBMITTER: Bartman CR

PROVIDER: S-EPMC4842148 | biostudies-literature | 2016 Apr

REPOSITORIES: biostudies-literature

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Enhancer Regulation of Transcriptional Bursting Parameters Revealed by Forced Chromatin Looping.

Bartman Caroline R CR Hsu Sarah C SC Hsiung Chris C-S CC Raj Arjun A Blobel Gerd A GA

Molecular cell 20160407 2

Mammalian genes transcribe RNA not continuously, but in bursts. Transcriptional output can be modulated by altering burst fraction or burst size, but how regulatory elements control bursting parameters remains unclear. Single-molecule RNA FISH experiments revealed that the β-globin enhancer (LCR) predominantly augments transcriptional burst fraction of the β-globin gene with modest stimulation of burst size. To specifically measure the impact of long-range chromatin contacts on transcriptional b ...[more]

PMID: 27067601

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Project description:BACKGROUND:Genome-wide association studies (GWASs) have identified single-nucleotide polymorphisms (SNPs) that may be genetic factors underlying Alzheimer's disease (AD). However, how these AD-associated SNPs (AD SNPs) contribute to the pathogenesis of this disease is poorly understood because most of them are located in non-coding regions, such as introns and intergenic regions. Previous studies reported that some disease-associated SNPs affect regulatory elements including enhancers. We hypothesized that non-coding AD SNPs are located in enhancers and affect gene expression levels via chromatin loops. METHODS:To characterize AD SNPs within non-coding regions, we extracted 406?AD SNPs with GWAS p-values of less than 1.00?×?10-?6 from the GWAS catalog database. Of these, we selected 392 SNPs within non-coding regions. Next, we checked whether those non-coding AD SNPs were located in enhancers that typically regulate gene expression levels using publicly available data for enhancers that were predicted in 127 human tissues or cell types. We sought expression quantitative trait locus (eQTL) genes affected by non-coding AD SNPs within enhancers because enhancers are regulatory elements that influence the gene expression levels. To elucidate how the non-coding AD SNPs within enhancers affect the gene expression levels, we identified chromatin-chromatin interactions by Hi-C experiments. RESULTS:We report the following findings: (1) nearly 30% of non-coding AD SNPs are located in enhancers; (2) eQTL genes affected by non-coding AD SNPs within enhancers are associated with amyloid beta clearance, synaptic transmission, and immune responses; (3) 95% of the AD SNPs located in enhancers co-localize with their eQTL genes in topologically associating domains suggesting that regulation may occur through chromatin higher-order structures; (4) rs1476679 spatially contacts the promoters of eQTL genes via CTCF-CTCF interactions; (5) the effect of other AD SNPs such as rs7364180 is likely to be, at least in part, indirect through regulation of transcription factors that in turn regulate AD associated genes. CONCLUSION:Our results suggest that non-coding AD SNPs may affect the function of enhancers thereby influencing the expression levels of surrounding or distant genes via chromatin loops. This result may explain how some non-coding AD SNPs contribute to AD pathogenesis.

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Enhancer Regulation of Transcriptional Bursting Parameters Revealed by Forced Chromatin Looping.

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Enhancer Regulation of Transcriptional Bursting Parameters Revealed by Forced Chromatin Looping.

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