Impact of DNA ligase IV on nonhomologous end joining pathways during class switch recombination in human cells - PubMed (original) (raw)

Impact of DNA ligase IV on nonhomologous end joining pathways during class switch recombination in human cells

Qiang Pan-Hammarström et al. J Exp Med. 2005.

Abstract

Class switch recombination (CSR) is a region-specific, transcriptionally regulated, nonhomologous recombinational process that is initiated by activation-induced cytidine deaminase (AID). The initial lesions in the switch (S) regions are subsequently processed and resolved, leading to recombination of the two targeted S regions. The mechanisms by which repair and ligation of the broken DNA ends occurs is still elusive. Recently, a small number of patients lacking DNA ligase IV, a critical component of the nonhomologous end joining (NHEJ) machinery, have been identified. We show that these patients display a considerably increased donor/acceptor homology at Smu-Salpha junctions compared with healthy controls. In contrast, Smu-Sgamma junctions show an increased frequency of insertions but no increase in junctional homology. These altered patterns of junctional resolution may be related to differences in the homology between the Smu and the downstream isotype S regions, and could reflect different modes of switch junction resolution when NHEJ is impaired. These findings link DNA ligase IV, and thus NHEJ, to CSR.

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Figures

Figure 1.

PCR amplification of Sμ–Sα fragments in Lig4D patients and controls. The numbers of Sμ–Sα switch fragments were determined from 10 PCR reactions run in parallel (lanes 1–10) using DNA from each individual. M, molecular weight marker.

Figure 2.

Sequences of Sμ–Sα junctions. The Sμ and Sα1 or Sα2 sequences are aligned above and below the recombined switch junctional sequences. Microhomology was determined by identifying the longest region at the switch junction of perfect uninterrupted donor/acceptor identity (boxed with solid lines). Imperfect repeat was determined by identifying the longest overlap region at the switch junction by allowing one mismatch on either side of the breakpoint (the extra nucleotide identity beyond the perfect-matched sequence identity is boxed by dotted lines). The Sμ and Sα breakpoints for each switch fragment are indicated by ▾ and ▴, respectively, and their positions in the germline sequences are indicated on the top or below the arrowheads. The number of base pairs involved in microhomology and imperfect repeat (numbers indicated in parentheses) for each junction is shown at the bottom right of each switch junction.

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Impact of DNA ligase IV on nonhomologous end joining pathways during class switch recombination in human cells - PubMed (original) (raw)