Journal Article

IgH class switching and translocations use a robust non-classical end-joining pathway

Geyer, Mark, Franco, Sonia, Gumaste, Sunil, Boboila, Cristian, Yan, Catherine T., Rajewsky, Klaus, Murphy, Michael, Manis, John P., Souza, Ellen Kris, Hickernell, Thomas R., Zarrin, Ali A., Alt, Frederick W.

2007

Overview

Programmed DNA breaks are made and repaired at two points during the development of antibody-producing B cells. While the breaks occurring during V(D)J recombination utilize factors that promote non-homologous end joining, this study finds that breaks that happen during class switch recombination require only a subset of these factors, suggesting that there are other as-yet-unrecognized proteins that function in this process. Immunoglobulin variable region exons are assembled in developing B cells by V(D)J recombination. Once mature, these cells undergo class-switch recombination (CSR) when activated by antigen. CSR changes the heavy chain constant region exons (C h ) expressed with a given variable region exon from Cμ to a downstream C h (for example, Cγ, Cε or Cα), thereby switching expression from IgM to IgG, IgE or IgA. Both V(D)J recombination and CSR involve the introduction of DNA double-strand breaks and their repair by means of end joining 1 , 2 . For CSR, double-strand breaks are introduced into switch regions that flank Cμ and a downstream C h , followed by fusion of the broken switch regions 1 . In mammalian cells, the ‘classical’ non-homologous end joining (C-NHEJ) pathway repairs both general DNA double-strand breaks and programmed double-strand breaks generated by V(D)J recombination 2 , 3 . C-NHEJ, as observed during V(D)J recombination, joins ends that lack homology to form ‘direct’ joins, and also joins ends with several base-pair homologies to form microhomology joins 3 , 4 . CSR joins also display direct and microhomology joins, and CSR has been suggested to use C-NHEJ 5 , 6 , 7 , 8 . Xrcc4 and DNA ligase IV (Lig4), which cooperatively catalyse the ligation step of C-NHEJ, are the most specific C-NHEJ factors; they are absolutely required for V(D)J recombination and have no known functions other than C-NHEJ 2 . Here we assess whether C-NHEJ is also critical for CSR by assaying CSR in Xrcc4- or Lig4-deficient mouse B cells. C-NHEJ indeed catalyses CSR joins, because C-NHEJ-deficient B cells had decreased CSR and substantial levels of IgH locus (immunoglobulin heavy chain, encoded by Igh ) chromosomal breaks. However, an alternative end-joining pathway, which is markedly biased towards microhomology joins, supports CSR at unexpectedly robust levels in C-NHEJ-deficient B cells. In the absence of C-NHEJ, this alternative end-joining pathway also frequently joins Igh locus breaks to other chromosomes to generate translocations.

• Publisher: Nature Publishing Group UK,Nature Publishing,Nature Publishing Group
• Subject: Animals / Antibody diversity / B-Lymphocytes - cytology / B-Lymphocytes - metabolism / B-Lymphocytes - radiation effects / Base Sequence / Biological and medical sciences / Cell Proliferation / Cells, Cultured / Cellular biology / Chemical properties / Chromosome aberrations / Chromosome Breakage / Chromosomes / Deoxyribonucleic acid / DNA / DNA-Binding Proteins - deficiency / DNA-Binding Proteins - genetics / Fundamental and applied biological sciences. Psychology / Genes, Immunoglobulin Heavy Chain - genetics / Genetic aspects / Genetic recombination / Genic rearrangement. Recombination. Transposable element / Humanities and Social Sciences / Immunoglobulin Class Switching - genetics / Immunoglobulin G - genetics / Immunoglobulin G - metabolism / Immunoglobulins / Immunology / In Situ Hybridization, Fluorescence / letter / Mammals / Medical genetics / Medical sciences / Mice / Molecular and cellular biology / Molecular biology / Molecular genetics / multidisciplinary / Radiation, Ionizing / Recombination, Genetic - genetics / Science / Science (multidisciplinary) / Telomere - genetics / Translocation, Genetic - genetics