a, c, d, Representative micrographs of anti-γH2AX (a), anti-pATR (c) and anti-p53 immunofluorescence signal (d) in vehicle- or HU-treated MDCK-II cells (c), and in vehicle-, HU- or Nutlin3-treated MDCK-II cells (a, d). DNA is stained with Hoechst. Scale bars, 20 μm. b, Quantification of extrusions per hour after the indicated treatments. n = 13, 6, 5, 5 and 5 (biological replicates) each for control, PFT, zVAD-FMK, SB 218078 and PF477736 treatments, respectively. Each data point represents a separate experiment. These data were collected and analysed for statistical significance with the data in Fig. 4g. P values are indicated; n.s., not significant. e, Quantification of anti-p53 immunofluorescence signal in MDCK-II cells treated with vehicle, HU, or Nutlin-3. n = 9, 7 and 5 (biological replicates) for vehicle, HU and Nutlin3, respectively. Each data point represents mean fluorescence intensity signal from one image of hundreds of cells. Kruskal–Wallis one-way ANOVA followed by Dunn’s correction was performed. P values are indicated. Data in b, e are represented as mean ± s.d.