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Dauba A, Khamlichi AA. Long-Range Control of Class Switch Recombination by Transcriptional Regulatory Elements. Front Immunol 2021; 12:738216. [PMID: 34594340 PMCID: PMC8477019 DOI: 10.3389/fimmu.2021.738216] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2021] [Accepted: 08/17/2021] [Indexed: 01/18/2023] Open
Abstract
Immunoglobulin class switch recombination (CSR) plays a crucial role in adaptive immune responses through a change of the effector functions of antibodies and is triggered by T-cell-dependent as well as T-cell-independent antigens. Signals generated following encounter with each type of antigen direct CSR to different isotypes. At the genomic level, CSR occurs between highly repetitive switch sequences located upstream of the constant gene exons of the immunoglobulin heavy chain locus. Transcription of switch sequences is mandatory for CSR and is induced in a stimulation-dependent manner. Switch transcription takes place within dynamic chromatin domains and is regulated by long-range regulatory elements which promote alignment of partner switch regions in CSR centers. Here, we review recent work and models that account for the function of long-range transcriptional regulatory elements and the chromatin-based mechanisms involved in the control of CSR.
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Affiliation(s)
- Audrey Dauba
- Institut de Pharmacologie et de Biologie Structurale, IPBS, Université de Toulouse, CNRS, Université Paul Sabatier, Toulouse, France
| | - Ahmed Amine Khamlichi
- Institut de Pharmacologie et de Biologie Structurale, IPBS, Université de Toulouse, CNRS, Université Paul Sabatier, Toulouse, France
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2
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Oudinet C, Braikia FZ, Dauba A, Khamlichi AA. Mechanism and regulation of class switch recombination by IgH transcriptional control elements. Adv Immunol 2020; 147:89-137. [PMID: 32981636 DOI: 10.1016/bs.ai.2020.06.003] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Class switch recombination (CSR) plays an important role in humoral immunity by generating antibodies with different effector functions. CSR to a particular antibody isotype is induced by external stimuli, and occurs between highly repetitive switch (S) sequences. CSR requires transcription across S regions, which generates long non-coding RNAs and secondary structures that promote accessibility of S sequences to activation-induced cytidine deaminase (AID). AID initiates DNA double-strand breaks (DSBs) intermediates that are repaired by general DNA repair pathways. Switch transcription is controlled by various regulatory elements, including enhancers and insulators. The current paradigm posits that transcriptional control of CSR involves long-range chromatin interactions between regulatory elements and chromatin loops-stabilizing factors, which promote alignment of partner S regions in a CSR centre (CSRC) and initiation of CSR. In this review, we focus on the role of IgH transcriptional control elements in CSR and the chromatin-based mechanisms underlying this control.
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Affiliation(s)
- Chloé Oudinet
- Institut de Pharmacologie et de Biologie Structurale, IPBS, Université de Toulouse, Toulouse, France; Institut de Pharmacologie et de Biologie Structurale, CNRS, Université Paul Sabatier, Toulouse, France
| | - Fatima-Zohra Braikia
- Institut de Pharmacologie et de Biologie Structurale, IPBS, Université de Toulouse, Toulouse, France; Institut de Pharmacologie et de Biologie Structurale, CNRS, Université Paul Sabatier, Toulouse, France
| | - Audrey Dauba
- Institut de Pharmacologie et de Biologie Structurale, IPBS, Université de Toulouse, Toulouse, France; Institut de Pharmacologie et de Biologie Structurale, CNRS, Université Paul Sabatier, Toulouse, France
| | - Ahmed Amine Khamlichi
- Institut de Pharmacologie et de Biologie Structurale, IPBS, Université de Toulouse, Toulouse, France; Institut de Pharmacologie et de Biologie Structurale, CNRS, Université Paul Sabatier, Toulouse, France.
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Two modes of cis-activation of switch transcription by the IgH superenhancer. Proc Natl Acad Sci U S A 2019; 116:14708-14713. [PMID: 31266889 DOI: 10.1073/pnas.1902250116] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
B cell isotype switching plays an important role in modulating adaptive immune responses. It occurs in response to specific signals that often induce different isotype (I) promoters driving transcription of switch regions, located upstream of the Ig heavy chain (IgH) constant genes. The transcribed switch regions can recombine, leading to a change of the constant gene and, consequently, of antibody isotype. Switch transcription is controlled by the superenhancer 3' regulatory region (3'RR) that establishes long-range chromatin cis-interactions with I promoters. Most stimuli induce more than one I promoter, and switch transcription can occur on both chromosomes. Therefore, it is presently unknown whether induced I promoters compete for the 3'RR on the same chromosome. Here we performed single-chromosome RT-qPCR assays to examine switch transcription monoallelically in the endogenous context. We show that there are two modes of 3'RR-mediated activation of I promoters: coactivation and competition. The nature of the inducing signal plays a pivotal role in determining the mode of activation. Furthermore, we provide evidence that, in its endogenous setting, the 3'RR has a bidirectional activity. We propose that the coactivation and competition modes mediated by the 3'RR may have evolved to cope with the different kinetics of primary immune responses.
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Delgado-Benito V, Rosen DB, Wang Q, Gazumyan A, Pai JA, Oliveira TY, Sundaravinayagam D, Zhang W, Andreani M, Keller L, Kieffer-Kwon KR, Pękowska A, Jung S, Driesner M, Subbotin RI, Casellas R, Chait BT, Nussenzweig MC, Di Virgilio M. The Chromatin Reader ZMYND8 Regulates Igh Enhancers to Promote Immunoglobulin Class Switch Recombination. Mol Cell 2018; 72:636-649.e8. [PMID: 30293785 PMCID: PMC6242708 DOI: 10.1016/j.molcel.2018.08.042] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2018] [Revised: 07/01/2018] [Accepted: 08/25/2018] [Indexed: 01/18/2023]
Abstract
Class switch recombination (CSR) is a DNA recombination reaction that diversifies the effector component of antibody responses. CSR is initiated by activation-induced cytidine deaminase (AID), which targets transcriptionally active immunoglobulin heavy chain (Igh) switch donor and acceptor DNA. The 3′ Igh super-enhancer, 3′ regulatory region (3′RR), is essential for acceptor region transcription, but how this function is regulated is unknown. Here, we identify the chromatin reader ZMYND8 as an essential regulator of the 3′RR. In B cells, ZMYND8 binds promoters and super-enhancers, including the Igh enhancers. ZMYND8 controls the 3′RR activity by modulating the enhancer transcriptional status. In its absence, there is increased 3′RR polymerase loading and decreased acceptor region transcription and CSR. In addition to CSR, ZMYND8 deficiency impairs somatic hypermutation (SHM) of Igh, which is also dependent on the 3′RR. Thus, ZMYND8 controls Igh diversification in mature B lymphocytes by regulating the activity of the 3′ Igh super-enhancer. ZMYND8 is required for GLT of acceptor S regions and Class Switch Recombination ZMYND8 supports efficient somatic hypermutation of the Igh variable regions ZMYND8 binds B cell super-enhancers, including the 3′ Igh enhancer ZMYND8 modulates the transcriptional status and activity of the 3′ Igh enhancer
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Affiliation(s)
- Verónica Delgado-Benito
- Laboratory of DNA Repair and Maintenance of Genome Stability, The Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin 13125, Germany
| | - Daniel B Rosen
- Laboratory of Molecular Immunology, The Rockefeller University, New York, NY 10065, USA
| | - Qiao Wang
- Laboratory of Molecular Immunology, The Rockefeller University, New York, NY 10065, USA
| | - Anna Gazumyan
- Laboratory of Molecular Immunology, The Rockefeller University, New York, NY 10065, USA
| | - Joy A Pai
- Laboratory of Molecular Immunology, The Rockefeller University, New York, NY 10065, USA
| | - Thiago Y Oliveira
- Laboratory of Molecular Immunology, The Rockefeller University, New York, NY 10065, USA
| | - Devakumar Sundaravinayagam
- Laboratory of DNA Repair and Maintenance of Genome Stability, The Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin 13125, Germany
| | - Wenzhu Zhang
- Laboratory of Mass Spectrometry and Gaseous Ion Chemistry, The Rockefeller University, New York, NY 10065, USA
| | - Matteo Andreani
- Laboratory of DNA Repair and Maintenance of Genome Stability, The Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin 13125, Germany
| | - Lisa Keller
- Laboratory of DNA Repair and Maintenance of Genome Stability, The Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin 13125, Germany
| | | | | | - Seolkyoung Jung
- Lymphocyte Nuclear Biology, NIAMS, NCI, NIH, Bethesda, MD 20892, USA
| | - Madlen Driesner
- Laboratory of DNA Repair and Maintenance of Genome Stability, The Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin 13125, Germany
| | - Roman I Subbotin
- Laboratory of Mass Spectrometry and Gaseous Ion Chemistry, The Rockefeller University, New York, NY 10065, USA
| | - Rafael Casellas
- Lymphocyte Nuclear Biology, NIAMS, NCI, NIH, Bethesda, MD 20892, USA
| | - Brian T Chait
- Laboratory of Mass Spectrometry and Gaseous Ion Chemistry, The Rockefeller University, New York, NY 10065, USA
| | - Michel C Nussenzweig
- Laboratory of Molecular Immunology, The Rockefeller University, New York, NY 10065, USA; Howard Hughes Medical Institute, The Rockefeller University, 1230 York Avenue, New York, NY 10065, USA
| | - Michela Di Virgilio
- Laboratory of DNA Repair and Maintenance of Genome Stability, The Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin 13125, Germany.
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5
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Duplication of a germline promoter downstream of the IgH 3' regulatory region impairs class switch recombination. Sci Rep 2018; 8:9164. [PMID: 29907762 PMCID: PMC6003904 DOI: 10.1038/s41598-018-27448-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2018] [Accepted: 06/01/2018] [Indexed: 01/13/2023] Open
Abstract
During an adaptive immune response, B cells can change their surface immunoglobulins from IgM to IgG, IgE or IgA through a process called class switch recombination (CSR). Switching is preceded by inducible non-coding germline transcription (GLT) of the selected constant gene(s), which is largely controlled by a super-enhancer called the 3' regulatory region (3'RR). Despite intense efforts, the precise mechanisms that regulate GLT are still elusive. In order to gain additional insights into these mechanisms, we analyzed GLT and CSR in mutant B cells carrying a duplication of the promoter of the α constant gene (Iα) downstream of 3'RR. Duplication of the Iα promoter affected differently GLT and CSR. While for most isotypes a drop in GLT was accompanied by a decrease in CSR, that was not the case for switching to IgA, which diminished despite unchanged GLT. Unexpectedly, there was no obvious effect on GLT and CSR to IgG3. Remarkably, specific stimuli that normally induce switching to IgG2b had contrasting effects in mutant B cells; Iγ2b was now preferentially responsive to the stimulus that induced Iα promoter. We propose that one mechanism underlying the induced 3'RR-mediated activation of GL promoters involves, at least in part, specific transcription factories.
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Inducible CTCF insulator delays the IgH 3' regulatory region-mediated activation of germline promoters and alters class switching. Proc Natl Acad Sci U S A 2017; 114:6092-6097. [PMID: 28533409 DOI: 10.1073/pnas.1701631114] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Class switch recombination (CSR) plays an important role in adaptive immune response by enabling mature B cells to switch from IgM expression to the expression of downstream isotypes. CSR is preceded by inducible germline (GL) transcription of the constant genes and is controlled by the 3' regulatory region (3'RR) in a stimulus-dependent manner. Why the 3'RR-mediated up-regulation of GL transcription is delayed to the mature B-cell stage is presently unknown. Here we show that mice devoid of an inducible CTCF binding element, located in the α constant gene, display a marked isotype-specific increase of GL transcription in developing and resting splenic B cells and altered CSR in activated B cells. Moreover, insertion of a GL promoter downstream of the CTCF insulator led to premature activation of the ectopic promoter. This study provides functional evidence that the 3'RR has a developmentally controlled potential to constitutively activate GL promoters but that this activity is delayed, at least in part, by the CTCF insulator, which borders a transcriptionally active domain established by the 3'RR in developing B cells.
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Complete cis Exclusion upon Duplication of the Eμ Enhancer at the Immunoglobulin Heavy Chain Locus. Mol Cell Biol 2015; 35:2231-41. [PMID: 25896912 DOI: 10.1128/mcb.00294-15] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Developing lymphocytes somatically diversify their antigen-receptor loci through V(D)J recombination. The process is associated with allelic exclusion, which results in monoallelic expression of an antigen receptor locus. Various cis-regulatory elements control V(D)J recombination in a developmentally regulated manner, but their role in allelic exclusion is still unclear. At the immunoglobulin heavy chain locus (IgH), the Eμ enhancer plays a critical role in V(D)J recombination. We generated a mouse line with a replacement mutation in the constant region of the locus that duplicates the Eμ enhancer and allows premature expression of the γ3 heavy chain. Strikingly, IgM expression was completely and specifically excluded in cis from the mutant allele. This cis exclusion recapitulated the main features of allelic exclusion, including differential exclusion of variable genes. Notably, sense and antisense transcription within the distal variable domain and distal V(H)-DJ(H) recombination were inhibited. cis exclusion was established and stably maintained despite an active endogenous Eμ enhancer. The data reveal the importance of the dynamic, developmental stage-dependent interplay between IgH locus enhancers and signaling in the induction and maintenance of allelic exclusion.
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Delgado-García M, Matesanz F, Alcina A, Fedetz M, García-Sánchez MI, Ruiz-Peña JL, Fernández Ó, Pinto Medel MJ, Leyva L, Arnal C, Delgado C, López Guerrero JA, González-Pérez A, Sáez ME, Villar LM, Álvarez-Cermeño JC, Picón C, Arroyo R, Varadé J, Urcelay E, Izquierdo G, Lucas M. A new risk variant for multiple sclerosis at the immunoglobulin heavy chain locus associates with intrathecal IgG, IgM index and oligoclonal bands. Mult Scler 2014; 21:1104-11. [DOI: 10.1177/1352458514556302] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2014] [Accepted: 09/28/2014] [Indexed: 11/16/2022]
Abstract
Background: Recent findings have shown a correlation between the intrathecal IgG index and variants at the immunoglobulin heavy chain (IGHC) locus in patients with multiple sclerosis (MS). Objectives: The objective of this paper is to analyse the association of the locus with MS susceptibility and its relationship with intrathecal immunoglobulin (Ig) parameters. Methods: We genotyped the rs11621145 variant, located at the IGHC locus, in 2726 patients with MS and 2133 healthy controls. Associations of intrathecal IgG and IgM indexes with rs11621145 were analysed by linear regression analysis in 538 MS patients. Results: We found that rs11621145 showed statistically significant evidence for association with susceptibility to MS (odds ratio = 0.69, p = 1.053E-09), though validation of this result in additional cohorts would be desirable. We confirmed the association between the IgG index and the rs11621145 ( p = 6.85E-07, Beta = 0.207). Furthermore, rs11621145 was inversely correlated with IgM index ( p = 7.24E-04, Beta = -0.277), and therefore marks a decreased likelihood of presenting IgM oligoclonal bands (odds ratio = 0.38, p = 2.35E-06). Conclusions: Our results suggest that the polymorphism of the IGHC locus could be altering the switching of the Ig isotype in B cells and it may be interfering with T-dependent and T-independent antibody responses.
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Affiliation(s)
- Mercedes Delgado-García
- Unidad de Esclerosis Múltiple, Hospital Universitario Virgen Macarena, Sevilla, Spain/These authors contributed equally to this work
| | - Fuencisla Matesanz
- Departamento de Biología Celular e Inmunología, Instituto de Parasitología y Biomedicina López Neyra (IPBLN), Consejo Superior de Investigaciones Científicas CSIC, 18016 Granada, Spain/These authors contributed equally to this work
| | - Antonio Alcina
- Departamento de Biología Celular e Inmunología, Instituto de Parasitología y Biomedicina López Neyra (IPBLN), Consejo Superior de Investigaciones Científicas CSIC, 18016 Granada, Spain
| | - María Fedetz
- Departamento de Biología Celular e Inmunología, Instituto de Parasitología y Biomedicina López Neyra (IPBLN), Consejo Superior de Investigaciones Científicas CSIC, 18016 Granada, Spain
| | | | - Juan Luis Ruiz-Peña
- Unidad de Esclerosis Múltiple, Hospital Universitario Virgen Macarena, Sevilla, Spain
| | - Óscar Fernández
- Unidad de Gestión Clínica de Neurociencias, Instituto de Biomedicina de Málaga (IBIMA), Hospital Regional Universitario de Málaga, Málaga, Spain
| | - María Jesús Pinto Medel
- Unidad de Gestión Clínica de Neurociencias, Instituto de Biomedicina de Málaga (IBIMA), Hospital Regional Universitario de Málaga, Málaga, Spain
| | - Laura Leyva
- Unidad de Gestión Clínica de Neurociencias, Instituto de Biomedicina de Málaga (IBIMA), Hospital Regional Universitario de Málaga, Málaga, Spain
| | - Carmen Arnal
- Servicio de Neurología, Hospital Virgen de las Nieves, Granada, Spain
| | | | | | | | - María E Sáez
- Centro Andaluz de Estudios Bioinformáticos (CAEBi), Sevilla, Spain
| | - Luisa María Villar
- Hospital Ramon y Cajal, Departments of Immunology and Neurology, MS Unit, (IRYCIS), Madrid, Spain
| | | | - Carmen Picón
- Hospital Ramon y Cajal, Departments of Immunology and Neurology, MS Unit, (IRYCIS), Madrid, Spain
| | - Rafael Arroyo
- Multiple Sclerosis Unit, Hospital Clínico San Carlos, Instituto de Investigación Sanitaria del Hospital Clínico San Carlos (IdISSC), Madrid, Spain
| | - Jezabel Varadé
- ImmunologyDepartment, Hospital Clínico San Carlos, Instituto de Investigación Sanitaria del Hospital Clínico S. Carlos (IdISSC), Madrid, Spain
| | - Elena Urcelay
- ImmunologyDepartment, Hospital Clínico San Carlos, Instituto de Investigación Sanitaria del Hospital Clínico S. Carlos (IdISSC), Madrid, Spain
| | - Guillermo Izquierdo
- Unidad de Esclerosis Múltiple, Hospital Universitario Virgen Macarena, Sevilla, Spain/These authors contributed equally to this work
| | - Miguel Lucas
- Servicio de Biología Molecular, Hospital Universitario Virgen Macarena, Facultad de Medicina, Sevilla, Spain/These authors contributed equally to this work
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Begum NA, Honjo T. Evolutionary comparison of the mechanism of DNA cleavage with respect to immune diversity and genomic instability. Biochemistry 2012; 51:5243-56. [PMID: 22712724 DOI: 10.1021/bi3005895] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
It is generally assumed that the genetic mechanism for immune diversity is unique and distinct from that for general genome diversity, in part because of the high efficiency and strict regulation of immune diversity. This expectation was partially met by the discovery of RAG1 and -2, which catalyze V(D)J recombination to generate the immune repertoire of B and T lymphocyte receptors. RAG1 and -2 were later shown to be derived from a transposon. On the other hand, activation-induced cytidine deaminase (AID), which mediates both somatic hypermutation (SHM) and the class-switch recombination (CSR) of the immunoglobulin genes, evolved earlier than RAG1 and -2 in jawless vertebrates. This review compares immune diversity and general genome diversity from an evolutionary perspective, shedding light on the roles of DNA-cleaving enzymes and target recognition markers. This comparison revealed that AID-mediated SHM and CSR share the cleaving enzyme topoisomerase 1 with transcription-associated mutation (TAM) and triplet contraction, which is involved in many genetic diseases. These genome-altering events appear to target DNA with non-B structure, which is induced by the inefficient correction of the excessive supercoiling that is caused by active transcription. Furthermore, an epigenetic modification on chromatin (histone H3K4 trimethylation) is used as a mark for DNA cleavage sites in meiotic recombination, V(D)J recombination, CSR, and SHM. We conclude that acquired immune diversity evolved via the appearance of an AID orthologue that utilized a preexisting mechanism for genomic instability, such as TAM.
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Affiliation(s)
- Nasim A Begum
- Department of Immunology and Genomic Medicine, Graduate School of Medicine, Kyoto University, Kyoto 606-8501, Japan
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Haddad D, Oruc Z, Puget N, Laviolette-Malirat N, Philippe M, Carrion C, Le Bert M, Khamlichi AA. Sense transcription through the S region is essential for immunoglobulin class switch recombination. EMBO J 2011; 30:1608-20. [PMID: 21378751 DOI: 10.1038/emboj.2011.56] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2010] [Accepted: 02/07/2011] [Indexed: 11/10/2022] Open
Abstract
Class switch recombination (CSR) occurs between highly repetitive sequences called switch (S) regions and is initiated by activation-induced cytidine deaminase (AID). CSR is preceded by a bidirectional transcription of S regions but the relative importance of sense and antisense transcription for CSR in vivo is unknown. We generated three mouse lines in which we attempted a premature termination of transcriptional elongation by inserting bidirectional transcription terminators upstream of Sμ, upstream of Sγ3 or downstream of Sγ3 sequences. The data show, at least for Sγ3, that sense transcriptional elongation across S region is absolutely required for CSR whereas its antisense counterpart is largely dispensable, strongly suggesting that sense transcription is sufficient for AID targeting to both DNA strands.
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Affiliation(s)
- Dania Haddad
- CNRS UMR 5089-IPBS (Institut de Pharmacologie et de Biologie Structurale) and Université Paul Sabatier III, Equipe 'Instabilité génétique et régulation transcriptionnelle', Toulouse Cedex, France
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11
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Leduc C, Haddad D, Laviolette-Malirat N, Nguyen Huu NS, Khamlichi AA. Combined deficiency of MSH2 and Sμ region abolishes class switch recombination. Eur J Immunol 2010; 40:2925-31. [PMID: 20812239 DOI: 10.1002/eji.201040605] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Class switch recombination (CSR) is mediated by G-rich tandem repeated sequences termed switch regions. Transcription of switch regions generates single-stranded R loops that provide substrates for activation-induced cytidine deaminase. Mice deficient in MSH2 have a mild defect in CSR and analysis of their switch junctions has led to a model in which MSH2 is more critical for switch recombination events outside than within the tandem repeats. It is also known that deletion of the whole Sμ region severely impairs but does not abrogate CSR despite the lack of detectable R loops. Here, we demonstrate that deficiency of both MSH2 and the Sμ region completely abolishes CSR and that the abrogation occurs at the genomic level. This finding further supports the crucial role of MSH2 outside the tandem repeats. It also indicates that during CSR, MSH2 has access to activation-induced cytidine deaminase targets in R-loop-deficient Iμ-Cμ sequences rarely used in CSR, suggesting an MSH2-dependent DNA processing activity at the Iμ exon that may decrease with transcription elongation across the Sμ region.
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Affiliation(s)
- Claire Leduc
- CNRS UMR5089, Institut de Pharmacologie et de Biologie Structurale, Equipe Instabilité génétique et régulation transcriptionnelle, Toulouse, France
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12
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Haddad D, Dougier HL, Laviolette N, Puget N, Khamlichi AA. Replacement of Imu-Cmu intron by NeoR gene alters Imu germ-line expression but has no effect on V(D)J recombination. Mol Immunol 2009; 47:961-71. [PMID: 20036775 DOI: 10.1016/j.molimm.2009.11.024] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2009] [Accepted: 11/13/2009] [Indexed: 01/23/2023]
Abstract
The NeoR gene has often been used to unravel the mechanisms underlying long-range interactions between promoters and enhancers during V(D)J assembly and class switch recombination (CSR) in the immunoglobulin heavy chain (IgH) locus. This approach led to the notion that CSR is regulated through competition of germ-line (GL) promoters for activities displayed by the 3' regulatory region (3'RR). This polarized long-range effect of the 3'RR is disturbed upon insertion of NeoR gene in the IgH constant (C(H)) region, where only GL transcription derived from upstream GL promoters is impaired. In the context of V(D)J recombination, replacement of Emu enhancer or Emu core enhancer (cEmu) by NeoR gene fully blocked V(D)J recombination and mu0 GL transcription which originates 5' of DQ52 and severely diminished Imu GL transcription derived from Emu/Imu promoter, suggesting a critical role for cEmu in the regulation of V(D)J recombination and of mu0 and Imu expression. Here we focus on the effect of NeoR gene on mu0 and Imu GL transcription in a mouse line in which the Imu-Cmu intron was replaced by a NeoR gene in the sense-orientation. B cell development was characterized by a marked but incomplete block at the pro-B cell stage. However, V(D)J recombination was unaffected in sorted pro-B and pre-B cells excluding an interference with the accessibility control function of Emu. mu0 GL transcription initiation was relatively normal but the maturation step seemed to be affected most likely through premature termination at NeoR polyadenylation sites. In contrast, Imu transcription initiation was impaired suggesting an interference of NeoR gene with the IgH enhancers that control Imu expression. Surprisingly, in stark contrast with the NeoR effect in the C(H) region, LPS-induced NeoR expression restored Imu transcript levels to normal. The data suggest that Emu enhancer may be the master control element that counteracts the down-regulatory "Neo effect" on Imu expression upon LPS stimulation. More importantly, they reveal a complex and developmentally regulated interplay between IgH enhancers in the control of Imu expression.
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Affiliation(s)
- Dania Haddad
- CNRS UMR 5089, Institut de Pharmacologie et de Biologie Structurale, Equipe Instabilité génétique et régulation transcriptionnelle, 205 route de Narbonne, 31077 Toulouse, France
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