Mediation of CTCF transcriptional insulation by DEAD-box RNA-binding protein p68 and steroid receptor RNA activator SRA
Ontology highlight
ABSTRACT: CCCTC-binding factor (CTCF) is a DNA-binding protein that plays important roles in chromatin organization, though the mechanism by which CTCF carries out these functions is not fully understood. Recent studies show that CTCF recruits the cohesin complex to insulator sites and that cohesin is required for insulator activity. Here we have shown that the DEAD box RNA helicase p68 (DDX5) and its associated noncoding RNA, steroid receptor RNA activator (SRA), form a complex with CTCF that is essential for insulator function. p68 was detected at CTCF sites in the IGF2/H19 imprinted control region (ICR) as well as other genomic CTCF sites. In vivo depletion of SRA or p68 reduced CTCF-mediated insulator activity at the IGF2/H19 ICR, increased levels of IGF2 expression, and increased interactions between the endodermal enhancer and IGF2 promoter. p68/SRA also interacts with members of the cohesin complex. Depletion of either p68 or SRA does not affect CTCF binding to its genomic sites, but it does reduce cohesin binding. The results suggest that p68/SRA stabilizes the interaction of cohesin with CTCF, by binding to both, and is required for proper insulator function.
Project description:CCCTC-binding factor (CTCF) is a DNA-binding protein that plays important roles in chromatin organization, though the mechanism by which CTCF carries out these functions is not fully understood. Recent studies show that CTCF recruits the cohesin complex to insulator sites and that cohesin is required for insulator activity. Here we have shown that the DEAD box RNA helicase p68 (DDX5) and its associated noncoding RNA, steroid receptor RNA activator (SRA), form a complex with CTCF that is essential for insulator function. p68 was detected at CTCF sites in the IGF2/H19 imprinted control region (ICR) as well as other genomic CTCF sites. In vivo depletion of SRA or p68 reduced CTCF-mediated insulator activity at the IGF2/H19 ICR, increased levels of IGF2 expression, and increased interactions between the endodermal enhancer and IGF2 promoter. p68/SRA also interacts with members of the cohesin complex. Depletion of either p68 or SRA does not affect CTCF binding to its genomic sites, but it does reduce cohesin binding. The results suggest that p68/SRA stabilizes the interaction of cohesin with CTCF, by binding to both, and is required for proper insulator function. Identification of p68-binding sites in Hela cells using ChIP-Seq.
Project description:Chromosome segregation in mitosis and meiosis depends on sister chromatid cohesion mediated by cohesin complexes. Mutation of cohesin and other cohesion proteins causes transcriptional and developmental defects in animals and humans, but the molecular cause of these phenotypes is unknown. Here we describe 8811 cohesin binding sites in the human genome and show that the CCCTC-binding factor (CTCF) is associated with 88% of these. CTCF is dispensable for loading of cohesin onto DNA but is required for enrichment of cohesin at its binding sites. We provide evidence that cohesin is required for the role of CTCF sites in insulating promoters from distant enhancers. Like CTCF, cohesin is located on the maternal but not on the paternal allele of the H19 imprinting control region (ICR) and is required for imprinting of the H19-Igf2 locus. We find that cohesin is widely expressed in mammalian tissues, consistent with a cohesionindependent role in regulating gene expression. We propose that cohesin functions as a transcriptional insulator and speculate that subtle deficiencies in this function may be the cause of "cohesinopathies" such as Cornelia de Lange and Roberts syndrome. Keywords: ChIP-chip analysis
Project description:The insulator model explains the workings of the H19 and Igf2 domain in the soma, where insulation of the Igf2 promoter from its enhancers occurs by CTCF in the maternally inherited unmethylated chromosome but not the paternally inherited methylated allele. The molecular mechanism that targets paternal methylation imprint establishment to the imprinting control region (ICR) in the male germline is unknown. We tested the function of a prospermatogonia-specific broad low-level transcription in this process using mouse genetics. Paternal imprint establishment was abnormal when transcription was stopped at the entry point to the ICR. The germline epimutation persisted into the paternal allele of the soma, resulting in reduced Igf2 in fetal organs, and reduced fetal growth, consistent with the insulator model and IGF2’s role as fetal growth factor. In summary, broad low-level transcription through the ICR initiates paternal imprint establishment at the H19/Igf2 ICR in the male germ line, with implications for Silver-Russell syndrome. The superseries contains RNAseq and ChIPseq data from 15.5 dpc fetal male germ cells that carry the RNA terminator cassette and also from control wild type mice.
Project description:Catalytic activity of the ISWI family of remodelers is critical for nucleosomal organization and transcription factor binding, including the insulator protein CTCF. To define which subcomplex mediates these diverse functions we phenotyped a panel of isogenic mouse stem cell lines each lacking one of six ISWI accessory subunits. Individual deletions of either CERF, RSF1, ACF, WICH or NoRC subcomplexes only moderately affect the chromatin landscape, while removal of the NURF-specific subunit BPTF leads to drastic reduction in chromatin accessibility and Snf2h ATPase localization around CTCF sites. While this reduces distances to the adjacent nucleosomes it only modestly impacts CTCF binding itself. In absence of accessibility, the insulator function of CTCF is nevertheless impaired resulting in lower occupancy of cohesin and cohesin-loading factors, and reduced insulation at these sites, highlighting the need of NURF-mediated remodeling for open chromatin and proper CTCF function. Our comprehensive analysis reveals a specific role for NURF in mediating Snf2h localization and chromatin opening at bound CTCF sites showing that local accessibility is critical for cohesin binding and insulator function.
Project description:Enhancer function is frequently investigated piecemeal using truncated reporter assays or single deletion analysis, thus it remains unclear to what extent their function is influenced by surrounding genomic context. Using our Big-IN technology for targeted integration of large DNAs, we analyzed the regulatory architecture of the Igf2/H19 locus, a paradigmatic model of enhancer selectivity. We assembled payloads containing a 157-kb functional Igf2/H19 locus and engineered mutations to genetically direct CTCF occupancy at the imprinting control region (ICR) that switches the target gene of the H19 enhancer cluster. Contrasting the activity of payloads delivered to the endogenous locus or to a safe harbor locus (Hprt) revealed that the functional elements comprising the Igf2/H19 locus are highly sensitive to their native context. Exchanging components of the Igf2/H19 locus with the well-studied Sox2 locus showed that the H19 enhancer cluster in particular functioned poorly out of context, and required its native surroundings to activate Sox2 expression. Conversely, the Sox2 locus control region (LCR) could activate both Igf2 and H19 outside its native context, but its activity was only partially modulated by CTCF occupancy at the ICR. Analysis of regulatory DNA actuation across different cell types revealed that, while the H19 enhancers are tightly coordinated within their native locus, the Sox2 LCR acts more independently. We show that these enhancer clusters typify broader classes of loci genome-wide. Our results show that unexpected dependencies may influence even the most studied functional elements, and our synthetic regulatory genomics approach permits large-scale manipulation of complete loci to investigate how locus architecture relates to function.
Project description:Enhancer function is frequently investigated piecemeal using truncated reporter assays or single deletion analysis, thus it remains unclear to what extent their function is influenced by surrounding genomic context. Using our Big-IN technology for targeted integration of large DNAs, we analyzed the regulatory architecture of the Igf2/H19 locus, a paradigmatic model of enhancer selectivity. We assembled payloads containing a 157-kb functional Igf2/H19 locus and engineered mutations to genetically direct CTCF occupancy at the imprinting control region (ICR) that switches the target gene of the H19 enhancer cluster. Contrasting the activity of payloads delivered to the endogenous locus or to a safe harbor locus (Hprt) revealed that the functional elements comprising the Igf2/H19 locus are highly sensitive to their native context. Exchanging components of the Igf2/H19 locus with the well-studied Sox2 locus showed that the H19 enhancer cluster in particular functioned poorly out of context, and required its native surroundings to activate Sox2 expression. Conversely, the Sox2 locus control region (LCR) could activate both Igf2 and H19 outside its native context, but its activity was only partially modulated by CTCF occupancy at the ICR. Analysis of regulatory DNA actuation across different cell types revealed that, while the H19 enhancers are tightly coordinated within their native locus, the Sox2 LCR acts more independently. We show that these enhancer clusters typify broader classes of loci genome-wide. Our results show that unexpected dependencies may influence even the most studied functional elements, and our synthetic regulatory genomics approach permits large-scale manipulation of complete loci to investigate how locus architecture relates to function.
Project description:Enhancer function is frequently investigated piecemeal using truncated reporter assays or single deletion analysis, thus it remains unclear to what extent their function is influenced by surrounding genomic context. Using our Big-IN technology for targeted integration of large DNAs, we analyzed the regulatory architecture of the Igf2/H19 locus, a paradigmatic model of enhancer selectivity. We assembled payloads containing a 157-kb functional Igf2/H19 locus and engineered mutations to genetically direct CTCF occupancy at the imprinting control region (ICR) that switches the target gene of the H19 enhancer cluster. Contrasting the activity of payloads delivered to the endogenous locus or to a safe harbor locus (Hprt) revealed that the functional elements comprising the Igf2/H19 locus are highly sensitive to their native context. Exchanging components of the Igf2/H19 locus with the well-studied Sox2 locus showed that the H19 enhancer cluster in particular functioned poorly out of context, and required its native surroundings to activate Sox2 expression. Conversely, the Sox2 locus control region (LCR) could activate both Igf2 and H19 outside its native context, but its activity was only partially modulated by CTCF occupancy at the ICR. Analysis of regulatory DNA actuation across different cell types revealed that, while the H19 enhancers are tightly coordinated within their native locus, the Sox2 LCR acts more independently. We show that these enhancer clusters typify broader classes of loci genome-wide. Our results show that unexpected dependencies may influence even the most studied functional elements, and our synthetic regulatory genomics approach permits large-scale manipulation of complete loci to investigate how locus architecture relates to function.
Project description:Silver-Russell syndrome(SRS, OMIM 180860) is an imprinting disordermanifesting in fetal and postnatal growth retardation. Loss of methylation (LOM) is detected in the imprinting control region 1 (ICR1) that controls the H19/IGF2 domain, in about 65% of SRS cases. The cause of this epigenetic deficiency is unknown. It may affect the process of imprint establishment --de novo methylation of ICR1 in the male germ line. In the paralogous mouse locus this process involves DNA methyltransferase DNMT3A and H3K36me2 histone methyltransferase NSD1, but the mechanism that targets these enzymes to this ICR is unknown. Based on our genome-wide deep-sequencing data of transcription and DNA methylation, we hypothesized that low-level transcription is required in prospermatogonia for targeting H3K36me2 and de novo methylation to ICR. We truncated this transcript at the entry point to ICR by gene-targeting. In response, the establishment of DNA methylation imprint was incomplete. The sporadic LOM persisted from the male germ line into the paternal allele of the soma, resulting in reduced Igf2, and increased, biallelic H19 RNA in the fetal organs, consistent with the insulator model. Fetus weight was also variably reduced upon paternal transmission of this mutation, consistent with the role of IGF2 as a fetal growth factor. We identify low-level transcription-through as the mechanism that initiates paternal imprint establishment at the H19/Igf2 ICR in the male germ line. The findings predict that RNA-dependent imprint establishment may be affected in human fetuses resulting in sporadic hypomethylation of the ICR1 in SRS.
Project description:Catalytic activity of the ISWI family of remodelers is critical for nucleosomal organization and transcription factor binding, including the insulator protein CTCF. To define which subcomplex mediate these diverse functions we phenotyped a panel of isogenic mouse stem cell lines each lacking one of six ISWI accessory subunits. Individual deletions of either CERF, RSF1, ACF, WICH or NoRC subcomplexes cause only moderate effects on the chromatin landscape, while removal of the NURF specific subunit BPTF leads to drastic reduction in chromatin accessibility and Snf2h ATPase localization around CTCF sites. While this reduces distances to the adjacent nucleosomes it only modestly impacts CTCF binding itself. In absence of accessibility bound CTCF is nevertheless impaired in function resulting in lower occupancy of cohesin and cohesin-loading factors, and reduced insulation at these sites, highlighting the need of NURF-mediated remodeling for open chromatin and proper CTCF function. Our comprehensive analysis reveals a specific role for NURF in mediating Snf2h localization and chromatin opening at bound CTCF sites showing that local accessibility is critical for cohesin binding and insulator function.
Project description:Catalytic activity of the ISWI family of remodelers is critical for nucleosomal organization and transcription factor binding, including the insulator protein CTCF. To define which subcomplex mediate these diverse functions we phenotyped a panel of isogenic mouse stem cell lines each lacking one of six ISWI accessory subunits. Individual deletions of either CERF, RSF1, ACF, WICH or NoRC subcomplexes cause only moderate effects on the chromatin landscape, while removal of the NURF specific subunit BPTF leads to drastic reduction in chromatin accessibility and Snf2h ATPase localization around CTCF sites. While this reduces distances to the adjacent nucleosomes it only modestly impacts CTCF binding itself. In absence of accessibility bound CTCF is nevertheless impaired in function resulting in lower occupancy of cohesin and cohesin-loading factors, and reduced insulation at these sites, highlighting the need of NURF-mediated remodeling for open chromatin and proper CTCF function. Our comprehensive analysis reveals a specific role for NURF in mediating Snf2h localization and chromatin opening at bound CTCF sites showing that local accessibility is critical for cohesin binding and insulator function.