Class switch recombination junctions are not affected by the absence of the immunoglobulin heavy chain Eμ enhancer

Abstract

After encountering antigen, B-cells undergo class switch recombination (CSR) that substitutes the constant (C) μ gene with C γ , C ε , or C α , thereby generating IgG, IgE, and IgA antibodies with new effector functions but the same antigenic specificity. 1 The DNA-editing enzyme activation-induced deaminase (AID) is required for CSR by targeting specific DNA switch (S) regions preceding the C region, except C δ. 2 S μ is the donor region, while S γ,ε,α are the acceptor regions. CSR is controlled in cis by the immunoglobulin heavy chain (IgH) 3'regulatory region (3'RR). 3 The 3'RR is essential to poise AID on the S acceptor region. During CSR IgH, intrachromosomal interactions (schematized in Fig. 1a) are found between the 3'RR and the intronic E μ enhancer. 1,4 Looping allows transcriptional binding activators to enhancers to facilitate CSR. However, CSR is only modestly influenced by E μ deletion. 5-7 During CSR, two different DNA repair pathways take place: the classical nonhomologous end joining (c-NHEJ) and the alternative end joining (A-EJ) pathways. The c-NHEJ pathway (which uses components such as 53BP1, Ku70, ku80, XRCC4, and ligase 4) is preferentially implicated for blunt and microhomology structure junctions and the A-EJ pathway (which uses components such as CtIP, MRN, PARP1, DNA Pol θ) favors junctions with large homology. 8,9 Data have reported that when an element of the DNA damage response pathway is defective, the molecular signature of CSR junctions is affected, suggesting that junctions are repaired through a different DNA repair pathway. 10 We recently reported a new computational tool (CSReport) for the automatic analysis of CSR junctions sequenced by high-throughput sequencing, 11 and used it to analyze the rare S μ-S δ junctions during IgD CSR, 12,13 S μ-S γ,α junctions in wild-type (wt) mice 14 and UNG-deficient mice. 15 Even if E μ-deficient mice exhibited a modest defect in IgH CSR, it is conceivable that its participation in CSR 3D loop interactions would be important for the DNA repair process. We used the CSReport and high-throughput sequencing to analyze the molecular signature of S μ-S γ3, S μ-S γ1 , and S μ-S α junctions in E μ-deficient mice to perform a more in depth search for a putative difference in their DNA repair pathways compared to those in wt mice. The mice were housed and the procedures were conducted in agreement with European Directive 2010/63/EU on animals used for scientific purposes applied in France as the « Décret n°2012-118 du 1 er février 2013 relatif à la protection des animaux utilisés à des fins scientifiques ». Accordingly, the present project (APAFiS≠13855) was authorized by the « Ministère de l'Education Nationale, de l'Enseignement

Eμ and 3′RR transcriptional enhancers of the IgH locus cooperate to promote c-myc–induced mature B-cell lymphomas

“…13 Moreover, deletion of the E m enhancer did not affect CSR and DNA repair. 36 Are these E m -39RR IgH intrachromosomal interactions really relevant? We favor the hypothesis that they are only mechanical because of the IgH location of both E m and 39RR and to 3-dimensional folding bringing switch regions into contact with each other.…”

Mouse Models of c-myc Deregulation Driven by IgH Locus Enhancers as Models of B-Cell Lymphomagenesis

“…E μ -deficient mice revealed its role in controlling IgH locus access at immature B-cell stages and thus its key role for efficient VDJ recombination ( 7 , 8 ). In contrast, E μ is dispensable for late B-cell maturation events such as IgH locus transcription for Ig synthesis and CSR ( 9 , 10 ). In 1985, transgenic mice bearing c-myc coupled to the E μ enhancer were reported to consistently develop immature (pre-B) and sometimes mature B-cell lymphomas ( 11 ).…”