Fig. 1.

Localized DNA damage in mutant cells. MEFs were seeded on coverslips, labeled with anti-γH2A.X antibody (red), and studied by fluorescence microscopy. DNA was DAPI stained (blue). Quantitation (A) showed an increased proportion of γH2A.X-positive micronuclei in Dido mutant MEFs. Error bars indicate standard deviation. (B–E) Representative images of WT (B) cells and Dido (C), Ku80 (D), and ATM (E) mutants are shown. Micronuclei are indicated with arrowheads. Strong γH2A.X labeling was found in micronuclei (C), although Dido mutant MEFs show no further DNA damage. The weaker signals correspond to constitutive foci not related to DSBs. (Scale bar, 5 μm.)