Fanca deficiency reduces A/T transitions in somatic hypermutation and alters class switch recombination junctions in mouse B cells.
Bottom Line: Whereas SHM involves an error-prone repair process that introduces novel point mutations into the Ig gene, the mismatches generated during CSR are processed to create double-stranded breaks (DSBs) in DNA, which are then repaired by the NHEJ pathway.As several lines of evidence suggest a possible role for the FANC pathway in SHM and CSR, we analyzed both processes in B cells derived from Fanca(-/-) mice.Here we show that Fanca is required for the induction of transition mutations at A/T residues during SHM and that despite globally normal CSR function in splenic B cells, Fanca is required during CSR to stabilize duplexes between pairs of short microhomology regions, thereby impeding short-range recombination downstream of DSB formation.
Affiliation: Centre National de la Recherche Scientifique UMR 8200, Institut Gustave Roussy, 94805 Villejuif, France Université Paris Sud, 91400 Orsay, France Programme Equipe Labellisées, Ligue Contre le Cancer, 75013 Paris, France.Show MeSH
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Mentions: To address the role of Fanca in the repair of the DSBs created during CSR, we analyzed Sμ-Sγ1 junctions from Fanca−/− and WT splenic B cells after activation with αCD40 plus IL-4 for 4 d. Fanca−/− B cells displayed a slight decrease in the frequency of direct and short MH (up to 6 bp) junctions (Fig. 3 A) and an increase in the frequency of long MH (>7 bp) junctions, although the mean MH length was similar in the two groups of mice (2.45 ± 0.23 bp in Fanca−/− vs. 2.29 ± 0.19 bp in WT mice). Moreover, sequence analysis revealed that the probability of nucleotide insertions at junctions was significantly higher in Fanca−/− than in WT mice (Fig. 3, A and B). Finally, analysis of breakpoint distribution within the S regions showed a similar pattern between WT and Fanca−/− mice (not depicted), supporting a specific role for Fanca in broken DNA end processing during CSR.
Affiliation: Centre National de la Recherche Scientifique UMR 8200, Institut Gustave Roussy, 94805 Villejuif, France Université Paris Sud, 91400 Orsay, France Programme Equipe Labellisées, Ligue Contre le Cancer, 75013 Paris, France.