Unknown,Transcriptomics,Genomics,Proteomics

Dataset Information

Orientation-Specific Joining of AID-initiated DNA Breaks Promotes Antibody Class Switching

ABSTRACT: During B cell development, RAG endonuclease cleaves immunoglobulin heavy chain (IgH) V, D, and J gene segments and orchestrates their fusion as deletional events that assemble a V(D)J exon in the same transcriptional orientation as adjacent Cμ constant region exons. In mice, six additional sets of constant region exons (CHs) lie 100-200kb downstream in the same transcriptional orientation as V(D)J and Cμ exons. Long repetitive switch (S) regions precede Cμ and downstream CHs. In mature B cells, class switch recombination (CSR) generates different antibody classes by replacing Cμ with a downstream CH. Activation Induced Cytidine Deaminase (AID) initiates CSR by promoting deamination lesions within Sμ and a downstream acceptor S region; these lesions are converted into DNA double strand breaks (DSBs) by general DNA repair factors. Productive CSR must occur in a deletional orientation by joining the upstream end of an Sμ DSB to the downstream end of an acceptor S region DSB. However, the relative frequency of deletional to inversional CSR junctions had not been measured. Thus, whether orientation-specific joining is a programmed mechanistic feature of CSR as it is for V(D)J recombination and, if so, how this is achieved was unknown. To address this question, we adapted high throughput genome wide translocation sequencing (HTGTS) into a highly sensitive DSB end-joining assay and applied it to endogenous AID-initiated S region DSBs. We find that CSR indeed is programmed to occur in a productive deletional orientation and does so via an unprecedented mechanism that involves in cis IgH organizational features in combination with frequent S region DSBs initiated by AID. We further implicate ATM-dependent DSB response (DSBR) factors in enforcing this mechanism and provide a solution to the enigma of why CSR is so reliant on the 53BP1 DSBR factor. We performed high-throughput genome-wide translocation sequencing (HTGTS) with different B cell genotypes that induces either I-SceI or AID-initiated DSBs as bait to study their joining pattern to AID-initiated S region breaks Please note that the 'ΔSγ1_2xI/ΔSµ_2xI-3' raw data files were analyzed twice with different reference assemblies to address specific points, and associated with both 'ΔSγ1_2xI_ΔSµ_2xI-3'.txt and Sγ1_2xI_ΔSµ_2xI-3'_trans-Sm.txt processed data files. As for the reference genome mm9_129_IgHC, it is a custom built generated based on mm9 (Bl6 line based mouse genome) and the partial genome sequence of another mouse line 129sv. It is not currently available in any public database however can be easily obtained either from the authors or self-built using information provided in the associated manuscript.

ORGANISM(S): Mus musculus

SUBMITTER: Junchao Dong

PROVIDER: E-GEOD-71005 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Orientation-specific joining of AID-initiated DNA breaks promotes antibody class switching.

Dong Junchao J Panchakshari Rohit A RA Zhang Tingting T Zhang Yu Y Hu Jiazhi J Volpi Sabrina A SA Meyers Robin M RM Ho Yu-Jui YJ Du Zhou Z Robbiani Davide F DF Meng Feilong F Gostissa Monica M Nussenzweig Michel C MC Manis John P JP Alt Frederick W FW

Nature 20150826 7567

During B-cell development, RAG endonuclease cleaves immunoglobulin heavy chain (IgH) V, D, and J gene segments and orchestrates their fusion as deletional events that assemble a V(D)J exon in the same transcriptional orientation as adjacent Cμ constant region exons. In mice, six additional sets of constant region exons (CHs) lie 100-200 kilobases downstream in the same transcriptional orientation as V(D)J and Cμ exons. Long repetitive switch (S) regions precede Cμ and downstream CHs. In mature B ...[more]

PMID: 26308889

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Project description:Classical non-homologous end-joining (C-NHEJ) is a major mammalian DNA double strand break (DSB) repair pathway. Core C-NHEJ factors, such as XRCC4, are required for joining DSB intermediates of the G1 phase-specific V(D)J recombination reaction in progenitor lymphocytes. Core factors also contribute to joining DSBs in cycling mature B-lineage cells, including DSBs generated during antibody class switch recombination (CSR) and DSBs generated by ionizing radiation (IR). The XLF C-NHEJ factor is dispensable for V(D)J recombination in normal cells, but, due to functional redundancy, is absolutely required for this process in cells deficient for the ATM DSB response factor. The recently identified PAralogue of XRCC4 and XLF (PAXX) factor has homology to these two proteins and variably contributes to IR-induced DSB repair in human and chicken cells. We now report that PAXX is dispensable for joining V(D)J recombination DSBs in G1-arrested mouse pro-B cell lines, dispensable for joining CSR-associated DSBs in a cycling mouse B cell line, and dispensable for normal IR-resistance in both G1-arrested and cycling pro-B lines. However, we find that combined deficiency for PAXX and XLF in G1-arrested pro-B lines abrogates DSB joining during V(D)J recombination and sensitizes the cells to IR exposure. Thus, PAXX provides core C-NHEJ factor-associated functions in the absence of XLF and vice versa in G1-arrested Pro-B cell lines. Finally, we also find that PAXX-deficiency has no impact on V(D)J recombination DSB joining in ATM-deficient pro-B lines. We discuss implications of these findings with respect to potential PAXX and XLF functions in C-NHEJ. Examination of CSR Switch mu-to-alpha junctions from mu bait DSBs using LAM-HTGTS and Illumina Miseq. Two clones of PAXX-/- and XLF-/- and 1 clone of Ligase4-/- were derived from the parental CH12F3 line; the second Ligase4-/- clone was acquired from Keifei Yu. Two clones of XLF-/-PAXX-/-CH12 cells were derived from one of the PAXX-/- clones. Three biological replicates were analyzed for each clone.

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 m constant region (Cm), allowing generation of mIgH chain transcripts and IgM-class antibodies1. Mouse IgH class switch recombination (CSR) replaces Cmwith 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 Sm 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 (iEm)/Sm 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 Sm and target S regions near the 3’IgHRR for CSR. In CH12F3 B lymphoma cells, inactivation of the constitutively active Ia-promoter abrogates looping and CSR to Sa, while activating transcription, looping, and CSR to upstream S regions. CBEs inserted upstream of Ia in convergent orientation with 3’IgH CBEs generate sub-loops that activate inversional Sa 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.

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 Cwith 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.

Dataset Information

Orientation-Specific Joining of AID-initiated DNA Breaks Promotes Antibody Class Switching

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Orientation-specific joining of AID-initiated DNA breaks promotes antibody class switching.

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