title: Pms2 and uracil-DNA glycosylases act jointly in the mismatch repair pathway to generate Ig gene mutations at A-T base pairs.
abstract: During somatic hypermutation (SHM) of immunoglobulin genes, uracils introduced by activation-induced cytidine deaminase are processed by uracil-DNA glycosylase (UNG) and mismatch repair (MMR) pathways to generate mutations at G-C and A-T base pairs, respectively. Paradoxically, the MMR-nicking complex Pms2/Mlh1 is apparently dispensable for A-T mutagenesis. Thus, how detection of U:G mismatches is translated into the single-strand nick required for error-prone synthesis is an open question. One model proposed that UNG could cooperate with MMR by excising a second uracil in the vicinity of the U:G mismatch, but it failed to explain the low impact of UNG inactivation on A-T mutagenesis. In this study, we show that uracils generated in the G1 phase in B cells can generate equal proportions of A-T and G-C mutations, which suggests that UNG and MMR can operate within the same time frame during SHM. Furthermore, we show thatUng-/-Pms2-/-mice display a 50% reduction in mutations at A-T base pairs and that most remaining mutations at A-T bases depend on two additional uracil glycosylases, thymine-DNA glycosylase and SMUG1. These results demonstrate that Pms2/Mlh1 and multiple uracil glycosylases act jointly, each one with a distinct strand bias, to enlarge the immunoglobulin gene mutation spectrum from G-C to A-T bases.
authors.affiliation: Institut Necker-Enfants Malades, Institut National de la Santé et de la Recherche Médicale U1151, Centre National de la Recherche Scientifique UMR 8253, Faculté de Médecine-Site Broussais, Université Paris Descartes, Sorbonne Paris Cité, 75014 Paris, France.
authors.forename: Giulia
authors.identifier: 0000-0002-3279-2941
authors.initials: G
authors.lastname: Girelli Zubani
authors.affiliation: Institut Necker-Enfants Malades, Institut National de la Santé et de la Recherche Médicale U1151, Centre National de la Recherche Scientifique UMR 8253, Faculté de Médecine-Site Broussais, Université Paris Descartes, Sorbonne Paris Cité, 75014 Paris, France.
authors.forename: Marija
authors.identifier: 0000-0002-0648-2050
authors.initials: M
authors.lastname: Zivojnovic
authors.affiliation: Institut Necker-Enfants Malades, Institut National de la Santé et de la Recherche Médicale U1151, Centre National de la Recherche Scientifique UMR 8253, Faculté de Médecine-Site Broussais, Université Paris Descartes, Sorbonne Paris Cité, 75014 Paris, France.
authors.forename: Annie
authors.initials: A
authors.lastname: De Smet
authors.affiliation: Institut Cochin, Institut National de la Santé et de la Recherche Médicale U1016, Centre National de la Recherche Scientifique UMR8104, Faculté de Médecine-Site Cochin, Université Paris Descartes, Sorbonne Paris Cité, 75006 Paris, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Albagli-Curiel
authors.affiliation: Institut Necker-Enfants Malades, Institut National de la Santé et de la Recherche Médicale U1151, Centre National de la Recherche Scientifique UMR 8253, Faculté de Médecine-Site Broussais, Université Paris Descartes, Sorbonne Paris Cité, 75014 Paris, France.|Département d'Immunologie, Institut Pasteur, 75015 Paris, France.
authors.forename: François
authors.initials: F
authors.lastname: Huetz
authors.affiliation: Institut Necker-Enfants Malades, Institut National de la Santé et de la Recherche Médicale U1151, Centre National de la Recherche Scientifique UMR 8253, Faculté de Médecine-Site Broussais, Université Paris Descartes, Sorbonne Paris Cité, 75014 Paris, France.
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Weill
authors.affiliation: Institut Necker-Enfants Malades, Institut National de la Santé et de la Recherche Médicale U1151, Centre National de la Recherche Scientifique UMR 8253, Faculté de Médecine-Site Broussais, Université Paris Descartes, Sorbonne Paris Cité, 75014 Paris, France.
authors.forename: Claude-Agnès
authors.identifier: 0000-0002-4519-4473
authors.initials: CA
authors.lastname: Reynaud
authors.affiliation: Institut Necker-Enfants Malades, Institut National de la Santé et de la Recherche Médicale U1151, Centre National de la Recherche Scientifique UMR 8253, Faculté de Médecine-Site Broussais, Université Paris Descartes, Sorbonne Paris Cité, 75014 Paris, France sebastien.storck@inserm.fr.
authors.forename: Sébastien
authors.identifier: 0000-0002-2682-5962
authors.initials: S
authors.lastname: Storck
mesh_terms: D000818:Animals; D020029:Base Pairing; D053843:DNA Mismatch Repair; D004706:Endodeoxyribonucleases / Q000502:physiology; D016193:G1 Phase; D005803:Genes, Immunoglobulin; D051379:Mice; D008810:Mice, Inbred C57BL; D000070976:Mismatch Repair Endonuclease PMS2 / Q000502:physiology*; D009154:Mutation; D051981:Uracil-DNA Glycosidase / Q000502:physiology*
chemical_list: D004706:Endodeoxyribonucleases; C492249:Mbd4 protein, mouse; D051981:Uracil-DNA Glycosidase; C499533:Pms2 protein, mouse; D000070976:Mismatch Repair Endonuclease PMS2