Figure 1. Antigen-receptor-associated aberrations in 53BP1^−/− lymphocytes.

a, Upper panel: schematic of the TCRα-TCRδ locus with positions of the BACs used for generation of DNA-FISH probes indicated. Middle panel: Representative examples of projections of confocal sections, analyzed by three-dimensional FISH on freshly isolated thymocytes. Bottom panel: frequency at which TCRcα or (TCRvα+ TCRcα) signal is lost from one allele in WT, 53BP1^−/−, p53^−/−, 53BP1^−/−p53^−/−, 53BP1^−/−Nbs1^tr735 and Atm^−/− thymocytes (>200 cells analyzed per genotype in each of two experiments;error bars, s.d.). b, TCRα associated chromosomal aberrations in lymph node T cells determined by FISH using a TCRα locus spanning BAC (red signal, right panel), a chromosome 14 paint (green signal, right panel) and a telomere repeat specific probe (white signal, right panel). T cells were stimulated with anti-TCR/CD28 antibodies for 48 hours. (error bars, s.d., n≥3).c, Frequency of IgH-associated abnormalities in metaphase spreads from bone marrow and splenic B cells from WT, 53BP1^−/−, 53BP1^−/−p53^−/− and 53BP1^−/−Nbs1^tr735 mice (error bars, s.d., n≥3). B220⁺ bone marrow cells were cultured on irradiated S17 stromal cells in the presence of IL7 for 5 days. Splenic CD43-negative B cells were cultured for 1 day with RP105, which induces proliferation but not CSR⁸. FISH was performed using probes specific for the IgHcα locus (red signal, right panel), chromosome 12 (green signal, right panel) and telomeric repeats (white signal, right panel).