title: Mediator facilitates transcriptional activation and dynamic long-range contacts at the IgH locus during class switch recombination.
abstract: Immunoglobulin (Ig) class switch recombination (CSR) is initiated by the transcription-coupled recruitment of activation-induced cytidine deaminase (AID) to Ig switch regions (S regions). During CSR, the IgH locus undergoes dynamic three-dimensional structural changes in which promoters, enhancers, and S regions are brought to close proximity. Nevertheless, little is known about the underlying mechanisms. In this study, we show that Med1 and Med12, two subunits of the mediator complex implicated in transcription initiation and long-range enhancer/promoter loop formation, are dynamically recruited to the IgH locus enhancers and the acceptor regions during CSR and that their knockdown in CH12 cells results in impaired CSR. Furthermore, we show that conditional inactivation of Med1 in B cells results in defective CSR and reduced acceptor S region transcription. Finally, we show that in B cells undergoing CSR, the dynamic long-range contacts between the IgH enhancers and the acceptor regions correlate with Med1 and Med12 binding and that they happen at a reduced frequency in Med1-deficient B cells. Our results implicate the mediator complex in the mechanism of CSR and are consistent with a model in which mediator facilitates the long-range contacts between S regions and the IgH locus enhancers during CSR and their transcriptional activation.
authors.affiliation: Institut de Génétique et de Biologie Moléculaire et Cellulaire, 67400 Illkirch, France Institut National de la Santé et de la Recherche Médicale, Unité 964, 67404 Illkirch, France Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7104, 67404 Illkirch, France Université de Strasbourg, 67400 Illkirch, France.
authors.forename: Anne-Sophie
authors.initials: AS
authors.lastname: Thomas-Claudepierre
authors.affiliation: Institut de Génétique et de Biologie Moléculaire et Cellulaire, 67400 Illkirch, France Institut National de la Santé et de la Recherche Médicale, Unité 964, 67404 Illkirch, France Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7104, 67404 Illkirch, France Université de Strasbourg, 67400 Illkirch, France.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Robert
authors.affiliation: Department of Pathology, School of Medicine, New York University, New York, NY 10003.
authors.forename: Pedro P
authors.initials: PP
authors.lastname: Rocha
authors.affiliation: Department of Pathology, School of Medicine, New York University, New York, NY 10003 Department of Biology, New York University, New York, NY 10003.
authors.forename: Ramya
authors.initials: R
authors.lastname: Raviram
authors.affiliation: Institut de Génétique et de Biologie Moléculaire et Cellulaire, 67400 Illkirch, France Institut National de la Santé et de la Recherche Médicale, Unité 964, 67404 Illkirch, France Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7104, 67404 Illkirch, France Université de Strasbourg, 67400 Illkirch, France.
authors.forename: Ebe
authors.initials: E
authors.lastname: Schiavo
authors.affiliation: Institut de Génétique et de Biologie Moléculaire et Cellulaire, 67400 Illkirch, France Institut National de la Santé et de la Recherche Médicale, Unité 964, 67404 Illkirch, France Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7104, 67404 Illkirch, France Université de Strasbourg, 67400 Illkirch, France.
authors.forename: Vincent
authors.initials: V
authors.lastname: Heyer
authors.affiliation: Department of Biology, New York University, New York, NY 10003 Department of Computer Science, Courant Institute of Mathematical Sciences, New York, NY 10003 Simons Center for Data Analysis, New York, NY 10010.
authors.forename: Richard
authors.initials: R
authors.lastname: Bonneau
authors.affiliation: Department of Pathology, School of Medicine, New York University, New York, NY 10003 Department of Biology, New York University, New York, NY 10003.
authors.forename: Vincent M
authors.initials: VM
authors.lastname: Luo
authors.affiliation: Department of Pathology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60208.
authors.forename: Janardan K
authors.initials: JK
authors.lastname: Reddy
authors.affiliation: Justus Liebig Universität Giessen, 35390 Giessen, Germany.
authors.forename: Tilman
authors.initials: T
authors.lastname: Borggrefe
authors.affiliation: Department of Pathology, School of Medicine, New York University, New York, NY 10003 New York University Cancer Institute, New York University, New York, NY 10003.
authors.forename: Jane A
authors.initials: JA
authors.lastname: Skok
authors.affiliation: Institut de Génétique et de Biologie Moléculaire et Cellulaire, 67400 Illkirch, France Institut National de la Santé et de la Recherche Médicale, Unité 964, 67404 Illkirch, France Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7104, 67404 Illkirch, France Université de Strasbourg, 67400 Illkirch, France reinab@igbmc.fr.
authors.forename: Bernardo
authors.initials: B
authors.lastname: Reina-San-Martin
mesh_terms: D000818:Animals; D001402:B-Lymphocytes / Q000378:metabolism; D002478:Cells, Cultured; D055785:Gene Knockdown Techniques; D056426:Genetic Loci; D017578:Immunoglobulin Class Switching / Q000235:genetics*; D007143:Immunoglobulin Heavy Chains / Q000235:genetics*; D056892:Mediator Complex / Q000378:metabolism*; D056913:Mediator Complex Subunit 1 / Q000378:metabolism*; D051379:Mice; D011485:Protein Binding; D011995:Recombination, Genetic / Q000235:genetics*; D014158:Transcription, Genetic; D015533:Transcriptional Activation / Q000235:genetics*
chemical_list: D007143:Immunoglobulin Heavy Chains; C538856:Med1 protein, mouse; C539582:Med12 protein, mouse; D056892:Mediator Complex; D056913:Mediator Complex Subunit 1