Figure 1. Depletion of p53 or Ku80 increases the rate of spontaneous micronuclei formation in WI38 human fibroblasts. WI38 fibroblasts were infected with p53, Ku80, or both shRNA constructs and selected as described previously in Materials and Methods. Seven days after the infection, cells were fixed and stained with DAPI to visualize nuclear structure. (A) Representative Western blot showing p53 and Ku80 protein levels following shRNA infection. Ku80 knockdown is 30% and Ku80-depleted WI38 cells display a 3.9-fold increase in p53 by densitometric analysis. β-actin is shown as a protein loading control. NT=non-transfected cells. (B) Representative DAPI images for each cell type. Examples of micronuclei are marked with white arrows, enlarged and displayed as insets with white borders. (C) Quantitation of micronuclei, represented by the percent of cells containing at least one micronucleus. Data are pooled from two independent experiments, where at least 400 cells from each condition were counted per experiment, and standard deviation is included. Statistics determined using Student's T test are indicated by: *P<0.05; **P<0.01; ***P<0.001.