Increased oncogene expression and resistance to apoptosis in IgH-hEBI2 mice. (A) qPCR analysis of c-Myc transcript levels in splenic B220⁺ cell populations from IgH-hEBI2 and WT mice relative to the expression of the control gene GAPDH. The results are mean ± SEM of data from 5 mice. **P < .01 by the nonparametric Mann-Whitney test. (B) Quantification of expression of c-Myc protein in spleen B220⁺ cells from IgH-hEBI2 and WT mice as determined by western blot. The results are mean ± SEM of data from 2 to 3 mice. *P < .05 by Student t test. (C) FISH analysis of IgH and c-Myc localization in IgH-hEBI2 mice. The IgH allele is labeled with biotin and detected with streptavidin–AlexaFluor 568 (red). c-Myc is labeled with digoxygenin and detected with anti-Dig-FITC (green). The nuclei are stained with DAPI (blue). Image taken with a ×100 oil immersion objective magnification. (D) Heatmap of 93 anti- and proapoptotic genes and their expression in B220⁺ cells in young (12-15 weeks) IgH-hEBI2 in relation to the corresponding transcription in age-matched WT mice. Data shown from 3 IgH-hEBI2 mice. *P < .05 by Student t test. (E) Quantification of expression of BCL-2 protein in spleen B220⁺ cells from IgH-hEBI2 and WT mice as determined by western blot. The results are mean ± SEM of data from 2 to 3 mice. *P < .05 by Student t test. (F) Kaplan-Meier plot of IgH-hEBI2 and BCL-2xIgH-hEBI2 mice. The curves show data from 66 (IgH-hEBI2) and 9 (BCL-2xIgH-hEBI2) mice. (G) Etoposide (topoisomerase II inhibitor) induced apoptosis in spleen B220⁺ cells from IgH-hEBI2 and WT mice as determined by FACS with the late apoptotic marker propidium iodide. The results are given as fold increase in apoptotic cells compared with untreated cells and shown as mean ± SEM of data from 5 mice. **P < .01 by Student t test.