Pathophysiological implications of IgH locus accessibility to chromatin remodelling and to AID activity. – IgH-AID-Access

Here we propose to address these issues by making use of state-of-the-art technology (chromatin conformation capture coupled (3C), chromatin immunoprecipitation-sequencing (ChIP-Seq), 3-Dimensional-Fluorescence in situ hybridization (3D-FISH)).

The project allowed to definitely identify the IgH 3’ regulatory region as the master control element of somatic hypermutation and class switch recombination, and to show that it is in addition a target for AID along newly described types of Ig gene recombination that kill BCR expression (locus suicide recombination). Regarding the trans-acting factors facilitating AID recruitment, the project has provided identification of two new important factors for AID-initiated CSR, cohesin and mediator.

Identification of Locus suicide recombination (LSR) (Péron et al, Science 2012).
Future prospect: identifying the key elements governing the recruitment of AID on Ig loci.

Marquet M, Garot A, Denizot Y, Cogné M, Pinaud E. The Eµ enhancer region influences H chain expression and B cell fate without impacting IgVH repertoire and immune response in vivo.
J Immunol. 2014 193:1171
Laffleur B, Denis-Lagache N, Péron S, Sirac C, Moreau J, Cogné M. AID-induced remodeling of Ig genes and B cell fate. Oncotarget. 2014 15;5:1118.
Laffleur B, Bardet SM, Garot A, Brousse M, Cogné M. Immunoglobulin genes undergo legitimate repair in human B cells not only after cis- but also frequent trans-CSR.
Genes Immun. 2014 Jul-Aug;15(5):341-6.
Rouaud P, Saintamand A, Saad F, Carrion C, Lecardeur S, Cogné M, Denizot Y. Elucidation of the enigmatic IgD CSR via germline deletion of the IgH 3' regulatory region.
J Exp Med. 2014 5;211:975.
Medvedovic J, et al . Immunity. 2013 39):229.
Rouaud P, Vincent C, Saintamand A, Fiancette R, Marquet M, Robert I, Reina-San-Martin B, Pinaud E, Cogné M, Denizot Y. The IgH 3' regulatory region controls SHM.
J Exp Med. 2013 ;210:1501.
Lechouane F, Bonaud A, Delpy L, Casola S, Oruc Z, Chemin G, Cogné M, Sirac C. B-cell receptor signal strength influences terminal differentiation. Eur J Immunol. 2013 ;43:619-28.
Péron S, Laffleur B, Denis-Lagache N, Cook-Moreau J, Tinguely A, Delpy L, Denizot Y, Pinaud E, Cogné M. AID-driven deletion causes IgH locus suicide recombination in B cells.
Science. 2012 18;336
Rouaud P, Vincent C, Fiancette R, Cogné M, Pinaud E, Denizot Y. Enhancers located in heavy chain regulatory region are dispensable for diversity of VDJ recombination. J Biol Chem. 2012 ;287:8356.
Thomas-Claudepierre, A.S.*, Schiavo, E.*, Heyer, V., Fournier, M., Page, A., Robert, I., and Reina-San-Martin, B. (2013). The cohesin complex regulates immunoglobulin class switch recombination.
J Exp Med 210, 2495

B lymphocytes are unique in that they diversify their antigen receptors through somatic hypermutation (SHM) and class switch recombination (CSR). These transcription-dependent reactions are initiated by DNA damage inflicted by the Activation Induced Cytidine Deaminase (AID) enzyme. Restricting access of these processes to immunoglobulin (Ig) loci and notably to the IgH locus, is crucial for mounting effective immune responses and for avoiding alterations in non-Ig loci. This restriction is mediated by mechanisms controlling AID activity and by key transcriptional regulatory elements, including the IgH 3’ regulatory region (3’RR). Despite great progress, the molecular basis of 3’RR function, the mechanisms controlling AID targeting, and the relationship between these, remain largely unknown. Here we propose to address these issues by making use of state-of-the-art technology (chromatin conformation capture coupled (3C), chromatin immunoprecipitation-sequencing (ChIP-Seq), 3Dimensional-Fluorescence in situ hybridization (3D-FISH)). This will allow appreciate in parallel B cell differentiation, locus activity and chromatin state in a collection of mouse mutants where the 3’RR function is impaired. We will also explore the functional role in genome-wide AID targeting, and antibody diversification of cohesin and mediator, two complexes with an essential role in transcriptional regulation, which we have found to associate with AID. Finally, we will explore the pathophysiological effect of 3’RR polymorphisms in infectious and auto-immune or allergic settings.