Fig. 4.

Elevated ROS levels contribute to the severe genomic instability in H2ax/Atm double-deficient ES cells. (A) Intracellular ROS levels from WT, H2ax^−/−, Atm^−/−, HA^−/− ES cells, and cells treated with NAC (1 mM for 96 h) measured by DFC-mediated fluorescence. (B) H₂O₂ sensitivity of WT and H2ax^−/− ES cells. The percentages of surviving colonies after 7-day culture were plotted as the function of H₂O₂ concentration. Each data point represents the average of three independent experiments performed on at least two independent ES lines of each genotype. (C) Percentage of abnormal metaphases (Left) and average cytogenetic abnormalities per metaphase (Right) for WT and H2ax^−/− ES cells treated with 100 μM H₂O₂ for 24 h. (D) Percentage of abnormal metaphases (Left) and cytogenetic abnormalities per metaphase (Right) for H2ax^−/−, Atm^−/−, and HA^−/− ES cells treated with 1 mM NAC for at least 96 h.