Genome-wide localization of Smc1, Smc3 and CTCF in mouse B cells.
Ontology highlight
ABSTRACT:
ORGANISM(S): Mus musculus
PROVIDER: GSE43594 | GEO | 2013/10/11
SECONDARY ACCESSION(S): PRJNA186794
REPOSITORIES: GEO
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Project description:High-throughput genome-wide translocation sequencing (HTGTS) is a robust approach to identify genome-wide translocation junctions. We performed HTGTS to study the fate of introduced c-myc DSBs in mouse splenic B cells activated for activation cytidine deaminase (AID)-dependent class switch recombination (CSR). We found frequent translocations of c-myc DSBs to AID-initiated DSBs in IgH switch regions in wild-type (WT) and ATM-deficient B cells. However, c-myc also translocated frequently to newly generated DSBs within a 35-megabase region downstream of IgH in ATM-deficient, but not WT, CSR-activated B cells. Moreover, we found such DSBs and translocations in activated B cells that did not express AID or undergo CSR. These findings indicate that ATM deficiency leads to formation of chromosome 12 dicentrics via RAG-initiated IgH DSBs in progenitor B cells and that these dicentrics can be propagated developmentally into mature B cells where they generate new DSBs downstream of IgH via breakage-fusion-bridge cycles.
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Project description:Immunoglobulin class switch recombination (CSR) is initiated by the transcription-coupled recruitment of activation induced cytidine deaminase (AID) to immunoglobulin switch (S) regions. During CSR, the IgH locus undergoes dynamic three-dimensional structural changes in which promoters, enhancers and S regions are brought to close proximity. Nevertheless, little is known about the underlying mechanisms. Here we conditionally inactivated in B cells the Med1 subunit of mediator, a complex implicated in transcription initiation and long-range enhancer/promoter loop formation. We find that Med1-deficiency results in defective CSR, reduced acceptor switch region transcription and that this correlates with reduced long-range interactions between the acceptor switch regions and the Em enhancer, as determined by 4C-Seq. Our results implicate the mediator complex in the mechanism of CSR and are consistent with a model in which Med1 facilitates the transcriptional activation of switch regions and their long-range contacts with the IgH locus enhancers during CSR. 4C-seq data in resting and activated WT and Med1 mutant B cells. 4C bait was designed in the Eu enhancer of the Igh locus on chromosome 12. Primer sequences: 5â TCTGTCCTAAAGGCTCTGAGA 3â and 5â GAACACAGAAGTATGTGTATGGA 3â.
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Project description:In a B lymphocyte immunoglobulin heavy chain locus (IgH), a developmentally assembled V(D)J exon encoding an antibody variable region lies upstream of exons encoding a constant region (C), allowing generation of IgH chain transcripts and IgM-class antibodies1. Mouse IgH class switch recombination (CSR) replaces Cwith one of 6 sets of constant region exons (CHs) that lie 100-200kb downstream1. Each CH is flanked upstream by a promoter, non-coding I-exon, and long repetitive switch (S) region1,2. Cytokines/activators induce specific I-promoter transcription and activation-induced cytidine deaminase (AID)2,3. AID is transcriptionally-targeted to initiate DNA breaks in S and activated downstream acceptor S regions, which are joined in deletional orientation to complete CSR4,5. 3’IgH regulatory region (3’IgHRR) enhancers control upstream I promoters and, thereby, CSR via linear competition involving I promoter/3’IgHRR interactions6-11. Here, we report that synapsis of regulatory elements, S regions and DSBs for CSR is achieved by chromatin loop extrusion. In naive B cells, 3’IgHRR enhancers and adjacent 3’IgH CTCF-binding elements (CBEs) interact via loop extrusion with the upstream Igh intronic enhancer (iE)/S locale to generate dynamic 200kb 3’Igh basal loop. In CSR-activated B cells, induced transcription from I-promoters within this basal loop generates dynamic sub-loops that directionally align S and target S regions near the 3’IgHRR for CSR. In CH12F3 B lymphoma cells, inactivation of the constitutively active I-promoter abrogates looping and CSR to S, while activating transcription, looping, and CSR to upstream S regions. CBEs inserted upstream of I in convergent orientation with 3’IgH CBEs generate sub-loops that activate inversional S CSR. In I-promoter-deleted CH12F3 cells, this ectopic CBE-based sub-loop inactivates upstream S region CSR, while transcriptionally activating non-S region sequences adjacent to the inserted CBEs for S synapsis and CSR. Together, our findings implicate chromatin loop extrusion in the “unprecedented mechanism”5 by which Igh organization in cis promotes orientation-specific CSR DSB joining.
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Project description:In a B lymphocyte immunoglobulin heavy chain locus (IgH), a developmentally assembled V(D)J exon encoding an antibody variable region lies upstream of exons encoding a constant region (C), allowing generation of IgH chain transcripts and IgM-class antibodies1. Mouse IgH class switch recombination (CSR) replaces Cwith one of 6 sets of constant region exons (CHs) that lie 100-200kb downstream1. Each CH is flanked upstream by a promoter, non-coding I-exon, and long repetitive switch (S) region1,2. Cytokines/activators induce specific I-promoter transcription and activation-induced cytidine deaminase (AID)2,3. AID is transcriptionally-targeted to initiate DNA breaks in S and activated downstream acceptor S regions, which are joined in deletional orientation to complete CSR4,5. 3’IgH regulatory region (3’IgHRR) enhancers control upstream I promoters and, thereby, CSR via linear competition involving I promoter/3’IgHRR interactions6-11. Here, we report that synapsis of regulatory elements, S regions and DSBs for CSR is achieved by chromatin loop extrusion. In naive B cells, 3’IgHRR enhancers and adjacent 3’IgH CTCF-binding elements (CBEs) interact via loop extrusion with the upstream Igh intronic enhancer (iE)/S locale to generate dynamic 200kb 3’Igh basal loop. In CSR-activated B cells, induced transcription from I-promoters within this basal loop generates dynamic sub-loops that directionally align S and target S regions near the 3’IgHRR for CSR. In CH12F3 B lymphoma cells, inactivation of the constitutively active I-promoter abrogates looping and CSR to S, while activating transcription, looping, and CSR to upstream S regions. CBEs inserted upstream of I in convergent orientation with 3’IgH CBEs generate sub-loops that activate inversional S CSR. In I-promoter-deleted CH12F3 cells, this ectopic CBE-based sub-loop inactivates upstream S region CSR, while transcriptionally activating non-S region sequences adjacent to the inserted CBEs for S synapsis and CSR. Together, our findings implicate chromatin loop extrusion in the “unprecedented mechanism”5 by which Igh organization in cis promotes orientation-specific CSR DSB joining.
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