Figure 5: Ectopic expression of H2A.X enables efficient DNA repair and protects cells from genotoxic stress.

(a,b) Alkaline comet assay of HCT116 parental cells (WT), H2A.X knockout cells (KO) and revertant cells (KO+H2A.X) 3 h after exposure to 30 Gy of ionizing radiation. (a) Representative images, scale bars, 100 μm; (b) Quantification of comet tail moments. Brackets indicate significance of differences. Error bars represent the s.e.m. (n=50). Statistical significance was determined by a two-tailed, unpaired Student’s t-test.(c,d) HCT116 cell cultures (WT, KO and KO+H2A.X) were exposed to 1 Gy of ionizing radiation. DNA damage levels were analysed by counting γ-H2A.X foci (green) in nuclei counterstained for DNA (red). Scale bars, 20 μm. Statistical significance was determined by a two-tailed, unpaired Student’s t-test. The experiments were repeated three times. (c) Representative images, × 40 magnification (d) Quantification of γ-H2A.X foci per cell. Data are means±s.d.; n=3. Fpc is foci per cell. Statistical significance was determined by a two-tailed, unpaired Student’s t-test. (e,f) HCT116 cell cultures (WT, KO and KO+H2A.X) were exposed to increasing doses of ionizing radiation, and incubated at 37 °C for 15 days. Colonies stained with Coomassie blue were counted for survival estimation. (e) Representative images. (f) Colony survival. Data are means±s.d.; n=3. Statistical significance was determined by a two-tailed, unpaired Student’s t-test.