a–g, Mice were irradiated with 8 Gy or injected with AOM. a, b, Immunoblot analysis of the indicated proteins from primary colon epithelial cells 24 h after irradiation. Densitometric quantification of signal intensity (mean ± s.e.m.; n = 2). Phosphorylated (p)-p53 and actin, p-SMC and SMC, PUMA and actin, and p21 immunoblots were derived from one gel each. Band densities were normalized to loading (p-p53, PUMA) or sample-processing (p-SMC, SMC, p21) controls. c, d, Fold induction of p21 and Puma gene expression in colon epithelial cells 24 h after irradiation or AOM treatment was determined by qRT–PCR (AOM, n = 10; 8 Gy, n = 5; Stat3fl/fl, n = 4; Stat3fl/fl;Vil1-cre, n = 5; mean ± s.e.m.). e, Apoptosis (red, cCaspase-3) in LGR5+ (blue) colon stem cells (arrows). Representative immunofluorescence images 8 h after irradiation. f, g, Quantification of cCaspase-3+EpCam+ colonic epithelial cells 8 h after treatment with AOM or 8 Gy irradiation (f; n = 3; mean ± s.e.m.) and representative immunofluorescence images (g; cCaspase-3, red; EpCam, blue). Scale bars, 25 µm. Data are representative of two (d–g) or three (a–c) biologically independent experiments.