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Immunoglobulin enhancers increase RNA polymerase 2 stalling at somatic hypermutation target sequences [GRO-seq]

ABSTRACT: Somatic hypermutation (SHM) drives the genetic diversity of immunoglobulin genes in activated B cells and supports the generation of antibodies with increased affinity for antigen. SHM is targeted to Ig genes by their enhancers (DIVACs; diversification activators) but how the enhancers mediate this activity is unknown. We show that DIVACs that strongly stimulate SHM increase the phosphorylation of RNA polymerase 2 (Pol2) and Pol2 occupancy in the mutating gene with little or no accompanying increase in elongation-competent Pol2 or production of full length transcripts, indicating the accumulation of stalled Pol2. DIVAC-induced stalling is weakly associated with an increase in the detection of single-stranded DNA bubbles in the mutating target gene. We did not find evidence for anti-sense transcription or an association of H3K27ac with DIVAC activity in the mutating gene. These findings argue for a connection between Pol2 stalling and cis-acting targeting elements in the context of SHM and thus define a mechanistic basis for locus-specific targeting of SHM in the genome. Our results suggest that DIVACs make the target gene a suitable platform for AID-mediated mutation without the need for increasing transcriptional output.

ORGANISM(S): Gallus gallus

PROVIDER: GSE180176 | GEO | 2021/10/22

REPOSITORIES: GEO

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Immunoglobulin enhancers increase RNA polymerase 2 stalling at somatic hypermutation target sequences [ChIP-Seq]

Project description:Somatic hypermutation (SHM) drives the genetic diversity of immunoglobulin genes in activated B cells and supports the generation of antibodies with increased affinity for antigen. SHM is targeted to Ig genes by their enhancers (DIVACs; diversification activators) but how the enhancers mediate this activity is unknown. We show that DIVACs that strongly stimulate SHM increase the phosphorylation of RNA polymerase 2 (Pol2) and Pol2 occupancy in the mutating gene with little or no accompanying increase in elongation-competent Pol2 or production of full length transcripts, indicating the accumulation of stalled Pol2. DIVAC-induced stalling is weakly associated with an increase in the detection of single-stranded DNA bubbles in the mutating target gene. We did not find evidence for anti-sense transcription or an association of H3K27ac with DIVAC activity in the mutating gene. These findings argue for a connection between Pol2 stalling and cis-acting targeting elements in the context of SHM and thus define a mechanistic basis for locus-specific targeting of SHM in the genome. Our results suggest that DIVACs make the target gene a suitable platform for AID-mediated mutation without the need for increasing transcriptional output.

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Immunoglobulin enhancers increase RNA polymerase 2 stalling at somatic hypermutation target sequences

Project description:Immunoglobulin enhancers increase RNA polymerase 2 stalling at somatic hypermutation target sequences

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Immunoglobulin enhancers increase RNA polymerase 2 stalling at somatic hypermutation target sequences [GRO-seq]

Project description:Immunoglobulin enhancers increase RNA polymerase 2 stalling at somatic hypermutation target sequences [GRO-seq]

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Immunoglobulin enhancers increase RNA polymerase 2 stalling at somatic hypermutation target sequences [ChIP-Seq]

Project description:Immunoglobulin enhancers increase RNA polymerase 2 stalling at somatic hypermutation target sequences [ChIP-Seq]

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Topologically Associated Domains Delineate Susceptibility to Somatic Hypermutation

Project description:Somatic hypermutation (SHM) introduces point mutations into immunoglobulin (Ig) genes of activated B cells to support the process of antibody affinity maturation but also causes "off-target" mutations in other parts of the genome. We have used sensitive lentiviral SHM reporter vectors and a mutationally active human B cell line to identify dozens of regions of the genome that are intrinsically susceptible to SHM ("hot" regions) and many hundreds of regions that are resistant to SHM ("cold" regions). Hot and cold regions are frequently contained within topologically associated domains (TADs). Comparison of hot and cold TADs reveals that while overall levels of transcription are equal, hot TADs are enriched for NIPBL (a component of the cohesin loader), super enhancers, markers of paused/stalled RNA polymerase 2, and multiple transcription factors implicated in B cell development and targeting of SHM. We demonstrate that at least some hot TADs contain enhancer elements that possess SHM targeting activity and that insertion of a strong Ig SHM-targeting element into a cold TAD renders it hot. Our findings lead to a model for SHM susceptibility involving the cooperative action of cis-acting SHM targeting elements and the dynamic and architectural properties of TADs.

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Bach2 regulates AID-mediated immunoglobulin gene conversion and somatic hypermutation in DT40 B cells

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Role of Dot1L and H3K79 methylation in regulating somatic hypermutation of immunoglobulin genes

Project description:Somatic hypermutation (SHM) and class switch recombination (CSR) of the immunoglobulin (Ig) genes allow B cells to make antibodies that protect us against a wide variety of pathogens. SHM is mediated by activation induced deaminase (AID), occurs at a million times higher frequency than other mutations in the mammalian genome and is largely restricted to the variable (V) and switch (S) regions of Ig genes. Using the Ramos human Burkitt’s lymphoma cell line, we find that H3K79me2/3 and its methyltransferase Dot1L are more abundant on the V region than the constant (C) region which does not undergo mutation. In primary naïve mouse B cells examined ex vivo, the H3K79me2/3 modification appears constitutively in the donor Sμ and is inducible in the recipient Sγ1 upon CSR stimulation. Knockout (KO) and inhibition of Dot1L in Ramos cells significantly reduces V region mutation and the abundance of H3K79me2/3 on the V region and is associated with a decrease of Pol II and its S2 phosphorylated form at the IgH locus. KO of Dot1L also decreases the abundance of BRD4 and CDK9 (a subunit of P-TEFb complex) on the V region and this is accompanied by decreased nascent transcripts throughout the IgH gene. Treatment with JQ1 (inhibitor of BRD4) or DRB (inhibitor of CDK9) decreased SHM and the abundance of Pol II S2P at the IgH locus. With all these factors playing a role in transcription elongation, our studies extend our insights into the chromatin context and dynamics of transcription required for SHM.

2021-02-28 | GSE167873 | GEO

HIRA-dependent H3.3 deposition and its modification H3.3K36me3 facilitate somatic hypermutation of immunoglobulin genes by maintaining the proper chromatin state and transcription

Project description:The H3.3 histone variant and its chaperone HIRA are involved in active transcription but their detailed roles in regulating somatic hypermutation (SHM) of immunoglobulin variable regions in human B cells is not yet fully understood. In this study we show that, knockout (KO) of HIRA significantly decreased SHM and changed the mutation pattern of the variable region of immunoglobulin heavy chain (IGH) in the human Ramos B cell line without changing the levels of AID and other major proteins known to be involved in SHM. Except for H3K79me2/3, many factors related to active transcription, including H3.3, were substantively decreased in HIRA KO cells and this was accompanied by decreased nascent transcription in IGH locus. The abundance of ZMYND11 that specifically binds to H3.3K36me3 on the Ig locus was also reduced in the HIRA KO. Somewhat surprisingly HIRA loss increased the chromatin accessibility of Ig V region locus. Furthermore, stable expression of ectopic H3.3G34V and H3.3G34R mutants that inhibit both the trimethylation of H3.3K36 and the recruitment of ZMYND11 significantly reduced SHM in Ramos cells, while the H3.3K79M did not. Consistent with HIRA KO, the H3.3G34V mutant also decreased the occupancy of various elongation factors and of ZMYND11 on the IGH variable and downstream switching regions. Our results reveal an unrecognized role of HIRA and the H3.3K36me3 modification in SHM and extend our knowledge of how transcription coupled chromatin structure and accessibility contribute to SHM in human B cells.

2021-07-29 | GSE180899 | GEO

Immunoglobulin enhancers increase RNA polymerase 2 stalling at somatic hypermutation target sequences

Project description:This SuperSeries is composed of the SubSeries listed below.

2021-10-22 | GSE180178 | GEO

Deciphering the importance of the palindromic architecture of the immunoglobulin heavy chain 3â?? regulatory region.

Project description:The IgH 3â?? regulatory region (3â??RR) controls class switch recombination (CSR) and somatic hypermutation (SHM) in B cells. The mouse 3â??RR contains four enhancer elements with hs1,2 flanked by inverted repeated sequences and the center of a 25-kb palindrome bounded by two hs3 enhancer inverted copies (hs3a and hs3b). hs4 lies downstream of the palindrome. Evolution maintained in mammals this unique palindromic arrangement suggesting that it is functionally significant. We report that deconstructing the palindromic IgH 3â??RR strongly impacts its function even when enhancers are preserved. CSR and IgH transcription appear poorly dependent from the 3â??RR architecture and are more or less preserved provided 3â??RR enhancers are present. By contrast, an â??architectural effectâ?? significantly lowers VH germline transcription, AID recruitment and SHM. In conclusion, this work indicates that the IgH 3â??RR does not simply pile up enhancer units but also optimally expose them into a functional architecture of crucial importance. RNAseq analysis of B-cell splenocytes with (S=stimulated) or without (R=resting) LPS activation from wt, delta2leftPAL, and deltaIRIS mice.

2016-02-08 | E-GEOD-76359 | biostudies-arrayexpress

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