Transcription factor Ascl2 promotes geminal center B cell responses through directly regulating AID transcription
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ABSTRACT:
ORGANISM(S): Mus musculus
PROVIDER: GSE169416 | GEO | 2021/03/30
REPOSITORIES: GEO
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Project description:Somatic hypermutation (SHM) and class switch recombination (CSR) increase the affinity and diversify the effector functions of antibodies during immune responses. Although SHM and CSR are fundamentally different, their independent roles in regulating B cell fate have been difficult to uncouple because a single enzyme, activation-induced cytidine deaminase (encoded by Aicda), initiates both reactions. Here, we used a combination of Aicda and antibody mutant alleles that separate the effects of CSR and SHM on polyclonal immune responses. We found that class-switching to IgG1 biased the fate choice made by B cells, favoring the plasma cell over memory cell fate without significantly affecting clonal expansion in the germinal center (GC). In contrast, SHM reduced the longevity of memory B cells by creating polyreactive specificities that were selected against over time. Our data define the independent contributions of SHM and CSR to the generation and persistence of memory in the antibody system.
2016-10-19 | GSE76865 | GEO
Project description:Somatic hypermutation (SHM) and class switch recombination (CSR) increase the affinity and diversify the effector functions of antibodies during immune responses. Although SHM and CSR are fundamentally different, their independent roles in regulating B cell fate have been difficult to uncouple because a single enzyme, activation-induced cytidine deaminase (encoded by Aicda), initiates both reactions. Here, we used a combination of Aicda and antibody mutant alleles that separate the effects of CSR and SHM on polyclonal immune responses. We found that class-switching to IgG1 biased the fate choice made by B cells, favoring the plasma cell over memory cell fate without significantly affecting clonal expansion in the germinal center (GC). In contrast, SHM reduced the longevity of memory B cells by creating polyreactive specificities that were selected against over time. Our data define the independent contributions of SHM and CSR to the generation and persistence of memory in the antibody system.
2016-10-19 | GSE76864 | GEO
Project description:Most human B cell lymphomas (B-NHL) are derived from germinal centers (GCs), the structure where B-cells undergo class switch recombination (CSR) and somatic hypermutation (SHM) and are selected for high-affinity antibody production. The pathogenesis of B-NHL is associated with distinct genetic lesions, including chromosomal translocations and aberrant somatic hypermutation, which appear to arise from mistakes occurring during CSR and SHM. To ascertain the role of CSR and SHM in lymphomagenesis, we crossed three oncogene-driven (MYC, BCL6, MYC/BCL6) mouse models of B cell lymphoma with mice lacking activation-induced cytidine deaminase (AID), the enzyme required for both processes. We show that AID deficiency prevents BCL6-dependent, GC-derived B-NHL, while it has no impact on the formation of MYC-driven, pre-GC lymphomas. Accordingly, abrogation of AID is associated with the disappearance of both CSR- and SHM-mediated structural alterations, including cMYC-IgH chromosomal translocations and aberrant SHM. These results demonstrate that AID is required for GC-derived lymphomagenesis, providing direct support to the notion that errors in AID-mediated antigen-receptor gene modification events represent major contributors to the pathogenesis of human B-NHL. Keywords: Phenotypic characterization of tumors developing in oncogene-driven mouse models of lymphomas
2007-11-01 | GSE9249 | GEO
Project description:Class switch recombination (CSR) and somatic hypermutation (SHM) are antibody gene diversification reactions occurring in mature B cells that are essential for protective humoral immunity. CSR and SHM are initiated following activation by the antigen, and are dependent on efficient induction of activation-induced cytidine deaminase (AID). Therefore, mature B cell viability and fitness are crucial to mount effective immune responses. Here, we identified PDGFA-associated protein 1 (Pdap1) as an essential regulator of cellular homeostasis in mature B cells. Pdap1 deficiency leads to sustained expression of the integrated stress response (ISR) effector activating transcription factor 4 (Atf4) and induction of the ISR transcriptional program, increased cell death, and defective AID expression. As a consequence, loss of Pdap1 reduces germinal center B cell formation and impairs CSR and SHM. Thus, Pdap1 protects mature B cells against chronic ISR activation, and ensures efficient antibody diversification by promoting their survival and optimal function.
2020-06-19 | GSE141876 | GEO
Project description:The transcription factor Bach2 is required for germinal center formation and somatic hypermutation (SHM) of immunoglobulins, both central to an efficient antibody-mediated immune response. Activation-induced cytidine deaminase (AID) initiates SHM and CSR in germinal centers and has potential to induce human B cell lymphoma. To understand the role of Bach2 in AID-mediated immunoglobulin gene diversification processes, we established a Bach2-deficient DT40 B cell line. We show that in addition to allowing SHM, Bach2 drives immunoglobulin gene conversion (GCV), an important AID-dependent antibody gene diversification process. We demonstrate that Bach2 promotes GCV by increasing the expression of AID. Importantly, we found that the regulation of AID is independent of Blimp-1 and that Bach2-deficient cells have altered expression of several genes regulating AID expression, stability and function. These results demonstrate that Bach2 has a previously unappreciated role in the production of high-affinity antibodies.
2017-03-27 | GSE92430 | GEO
Project description:Changes in DNA methylation are required for the formation of germinal centers (GC), but the mechanisms of such changes are poorly understood. Activation-induced cytidine deaminase (AID) has been recently implicated recently in DNA demethylation through its deaminase activity coupled with DNA repair. We investigated the epigenetic function of AID in vivo in germinal center B cells (GCB) isolated from wild type (WT) and AID-deficient (Aicda-/-) mice. We determined that the transit of B cells through the GC is associated with marked locus-specific loss of methylation and increased methylation diversity, both of which are lost in Aicda-/- animals. Differentially methylated cytosines (DMCs) between GCB and naïve B cells (NB) are enriched in genes that are targeted for somatic hypermutation (SHM) by AID and these genes form networks required for B cell development and proliferation. Finally, we observed significant conservation of AID-dependent epigenetic reprogramming between mouse and human B cells. ERRBS and RNA-seq of wild type and Aicda knockout murine naive and germinal center B cells. ERRBS of human naive and germinal center B cells
2015-09-15 | E-GEOD-71702 | biostudies-arrayexpress
Project description:The activation induced cytosine deaminase (AID) mediates diversification of B cell immunoglobulin genes by the three distinct yet related processes of somatic hypermutation (SHM), class switch recombination (CSR), and gene conversion (GCV). SHM occurs in germinal center B cells, and the transcription factor Bcl6 is a key regulator of the germinal center B cell gene expression program, including expression of AID. To test the hypothesis that Bcl6 function is important for the process of SHM, we compared WT chicken DT40 B cells, which constitutively perform SHM/GCV, to their Bcl6-deficient counterparts. We found that Bcl6-deficient DT40 cells were unable to perform SHM and GCV despite enforced high level expression of AID and substantial levels of AID in the nucleus of the cells. To gain mechanistic insight into the GCV/SHM dependency on Bcl6, transcriptional features of a highly expressed SHM target gene were analyzed in Bcl6-sufficient and -deficient DT40 cells. No defect was observed in the accumulation of single stranded DNA in the target gene as a result of Bcl6 deficiency. In contrast, association of Spt5, an RNA polymerase II (Pol II) and AID binding factor, was strongly reduced at the target gene body relative to the transcription start site in Bcl6-deficient cells as compared to WT cells. However, partial reconstitution of Bcl6 function substantially reconstituted Spt5 association with the target gene body but did not restore detectable SHM. Our observations suggest that in the absence of Bcl6, Spt5 fails to associate efficiently with Pol II at SHM targets, perhaps precluding robust AID action on the SHM target DNA. Our data also suggest, however, that Spt5 binding is not sufficient for SHM of a target gene even in DT40 cells with strong expression of AID. Sequencing of the IgL V region and mutationally active GFP transgene in WT, Bcl6-/- Pax5R, and Bcl6-/- Pax5R Bcl6R chicken DT40 cells for evidence of AID dependent mutations. ChIP-seq proiles of RNA Pol II, Spt5, and pSer5 Pol II at a GFP transgene in WT, Bcl6-/- Pax5R, and Bcl6-/- Pax5R Bcl6R chicken DT40 cells.
2016-02-21 | E-GEOD-77141 | biostudies-arrayexpress
Project description:The activation induced cytosine deaminase (AID) mediates diversification of B cell immunoglobulin genes by the three distinct yet related processes of somatic hypermutation (SHM), class switch recombination (CSR), and gene conversion (GCV). SHM occurs in germinal center B cells, and the transcription factor Bcl6 is a key regulator of the germinal center B cell gene expression program, including expression of AID. To test the hypothesis that Bcl6 function is important for the process of SHM, we compared WT chicken DT40 B cells, which constitutively perform SHM/GCV, to their Bcl6-deficient counterparts. We found that Bcl6-deficient DT40 cells were unable to perform SHM and GCV despite enforced high level expression of AID and substantial levels of AID in the nucleus of the cells. To gain mechanistic insight into the GCV/SHM dependency on Bcl6, transcriptional features of a highly expressed SHM target gene were analyzed in Bcl6-sufficient and -deficient DT40 cells. No defect was observed in the accumulation of single stranded DNA in the target gene as a result of Bcl6 deficiency. In contrast, association of Spt5, an RNA polymerase II (Pol II) and AID binding factor, was strongly reduced at the target gene body relative to the transcription start site in Bcl6-deficient cells as compared to WT cells. However, partial reconstitution of Bcl6 function substantially reconstituted Spt5 association with the target gene body but did not restore detectable SHM. Our observations suggest that in the absence of Bcl6, Spt5 fails to associate efficiently with Pol II at SHM targets, perhaps precluding robust AID action on the SHM target DNA. Our data also suggest, however, that Spt5 binding is not sufficient for SHM of a target gene even in DT40 cells with strong expression of AID.
2016-02-21 | GSE77141 | GEO
Project description:Somatic hypermutation (SHM) and class switch recombination (CSR) of immunoglobulin (Ig) genes are genomic modification events that occur in germinal center (GC) B cells and are initiated through deamination of cytidine to uracil by activation induced cytidine deaminase (AID). Resulting uracil-guanine (U-G) mismatches are subsequently processed by low-fidelity base-excision (BER) and mismatch repair (MMR) pathways to yield mutations and DNA strand lesions. Although off-target AID activity also contributes to oncogenic point mutations and chromosome translocations associated with B cell lymphomas, the role of downstream AID-associated DNA repair pathways in the pathogenesis of these lymphomas is unknown. Here, we show that simultaneous BER and MMR deficiency causes genomic instability and a shorter latency to the development of a BCL6-driven GC B cell lymphoma. In contrast, loss of BER alone is highly protective against B cell transformation while loss of MMR fosters the development of a variety of malignancies. These findings lend insight into a complex interplay between AID-associated BER and MMR pathways that produces a net protective effect against GC B cell lymphomagenesis. Representative B cell lymphomas from 3 IµHABcl6, 6 IµHABcl6 Ung-/- Msh2-/-, and 5 IµHABcl6 Msh2-/- mice were analyzed in this study. Total RNA was extracted from frozen tumor cells and processed according to Illumina standard protocols.
2015-12-08 | E-GEOD-48304 | biostudies-arrayexpress
Project description:During a germinal center (GC) response, B cells diversify their immunoglobulin (Ig) genes by somatic hyper-mutation (SHM) and undergo clonal expansion and positive selection thereby enabling the generation of higher affinity antibodies. We have analyzed the genomic states underlying GC B cell dynamics by single cell RNA-Seq. Profiling of antigen specific GC B cells during the peak of the response, revealed four distinctive genomic states characterized by antigen presentation, apoptotic, mitochondrial and mitotic gene expression modules. Intersection of genomic states and Ig heavy-chain (Igh) class-switch trajectory suggested that mitochondrial machinery is utilized to support class-switch recombination (CSR). Furthermore, by analyzing the transcriptomes of B cells with varying affinity BCR sequences that assembled from single-cell RNA-seq data through a novel algorithm, we show that high affinity GC B cells manifest enhanced mitotic and BCR signaling transduction, but compromised antigen processing and presentation gene expression modules. Thus, we are developing a comprehensive framework of the genomic states and molecular pathways underlying GC B cell dynamics.
2018-03-10 | GSE79096 | GEO