title: Spt5 accumulation at variable genes distinguishes somatic hypermutation in germinal center B cells from ex vivo-activated cells.
abstract: Variable (V) genes of immunoglobulins undergo somatic hypermutation by activation-induced deaminase (AID) to generate amino acid substitutions that encode antibodies with increased affinity for antigen. Hypermutation is restricted to germinal center B cells and cannot be recapitulated in ex vivo-activated splenic cells, even though the latter express high levels of AID. This suggests that there is a specific feature of antigen activation in germinal centers that recruits AID to V genes which is absent in mitogen-activated cultured cells. Using two Igh knock-in mouse models, we found that RNA polymerase II accumulates in V regions in B cells after both types of stimulation for an extended distance of 1.2 kb from the TATA box. The paused polymerases generate abundant single-strand DNA targets for AID. However, there is a distinct accumulation of the initiating form of polymerase, along with the transcription cofactor Spt5 and AID, in the V region from germinal center cells, which is totally absent in cultured cells. These data support a model where mutations are prevalent in germinal center cells, but not in ex vivo cells, because the initiating form of polymerase is retained, which affects Spt5 and AID recruitment.
authors.affiliation: Laboratory of Molecular Biology and Immunology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224.
authors.forename: Robert W
authors.initials: RW
authors.lastname: Maul
authors.affiliation: Laboratory of Molecular Biology and Immunology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224.
authors.forename: Zheng
authors.initials: Z
authors.lastname: Cao
authors.affiliation: Department of Biology, Brandeis University, Waltham, MA 02454.
authors.forename: Lakshmi
authors.initials: L
authors.lastname: Venkataraman
authors.affiliation: Department of Biology, Brandeis University, Waltham, MA 02454.
authors.forename: Carol A
authors.initials: CA
authors.lastname: Giorgetti
authors.affiliation: Department of Biology, Brandeis University, Waltham, MA 02454.
authors.forename: Joan L
authors.initials: JL
authors.lastname: Press
authors.affiliation: Centre National de la Recherche Scientifique UMR 7276, Université de Limoges, 87025 Limoges, France.
authors.forename: Yves
authors.initials: Y
authors.lastname: Denizot
authors.affiliation: Laboratory of Molecular Biology and Immunology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224.
authors.forename: Hansen
authors.initials: H
authors.lastname: Du
authors.affiliation: Laboratory of Molecular Biology and Immunology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224.
authors.forename: Ranjan
authors.initials: R
authors.lastname: Sen
authors.affiliation: Laboratory of Molecular Biology and Immunology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224 gearhartp@mail.nih.gov.
authors.forename: Patricia J
authors.initials: PJ
authors.lastname: Gearhart
mesh_terms: D020413:3' Untranslated Regions; D000818:Animals; D001402:B-Lymphocytes / Q000276:immunology* / Q000378:metabolism*; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism*; D003564:Cytidine Deaminase / Q000235:genetics; D004257:DNA Polymerase II / Q000378:metabolism; D004277:DNA, Single-Stranded / Q000378:metabolism; D005260:Female; D023061:Gene Order; D056426:Genetic Loci; D018858:Germinal Center / Q000276:immunology* / Q000378:metabolism*; D007135:Immunoglobulin Variable Region; D008213:Lymphocyte Activation / Q000235:genetics / Q000276:immunology; D008297:Male; D051379:Mice; D008954:Models, Biological; D017384:Sequence Deletion; D027041:Somatic Hypermutation, Immunoglobulin; D035602:Transcriptional Elongation Factors / Q000378:metabolism*; D000098830:AICDA (Activation-Induced Cytidine Deaminase)
chemical_list: D020413:3' Untranslated Regions; D002868:Chromosomal Proteins, Non-Histone; D004277:DNA, Single-Stranded; D007135:Immunoglobulin Variable Region; D035602:Transcriptional Elongation Factors; C069940:SPT5 transcriptional elongation factor; D004257:DNA Polymerase II; D000098830:AICDA (Activation-Induced Cytidine Deaminase); D003564:Cytidine Deaminase