Opposing roles of PARP-1 and PARP-2 in c-Myc–driven B-cell lymphoma. (A) Kaplan-Meier curves comparing B-cell lymphoma–free survival of Eμ-Myc^T/+, Eμ-Myc^T/+Parp-1^−/−, and Eμ-Myc^T/+Parp-2^−/− mice. Survival was monitored for 500 days. (B) Representation of the median and 25th and 75th percentile survival periods of Eμ-Myc^T/+, Eμ-Myc^T/+Parp-1^−/−, and Eμ-Myc^T/+Parp-2^−/− mice. (C) Quantitative reverse transcription polymerase chain reaction analysis of c-Myc gene expression in BM pre-B cells. Samples were normalized according to β-actin expression levels. Results are expressed as log₂-fold expression compared with levels measured in wild-type (WT) cells. Values represent mean ± SEM obtained from 3 independent experiments. (D) Representative flow cytometric dot plots showing pre-B, immature, and mixed B-cell lymphomas. (E) Bar plot showing the percentage of pre-B, immature, and mixed B-cell lymphoma tumors in each genotype. (F-G) Representation of terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling–positive (TUNEL⁺) (F) and Ki67⁺ (G) cells in tumors from the indicated genotypes. Values represent mean ± SEM for 10 randomly selected fields. *P < .05, **P < .01, ***P < .001. Ig, immunoglobulin.