U2OS cells on glass coverslips were either untreated (NT, A) or treated with irradiation (IR, 10Gy, B,C). Cells were fixed with 4% formaldehyde at indicated time points. P53, p21 antibodies were detected using an Alexa-488 conjugated goat anti rabbit IgG. PML antibody were detected using a rhodamine-x conjugated goat anti mouse IgG. Cell nuclei were counterstained with DAPI (blue). Images were captured at 100× magnification. Representative images were shown. Representative foci with p53/PML colocalization were pointed with white arrows. Representative confocal images were shown in C.