Figure 1.

Effect of continuous exposure of A549 cells to 20 μM EdU on the level of expression of γH2AX and ATM-Ser1981^P. Exponentially growing cells were untreated (Ctrl) or treated with EdU for 2, 4, or 6 h. The presence of γH2AX and ATM-Ser1981^P was detected immunocytochemically with phosphospecific Abs and intensity of cell fluorescence measured by laser scanning cytometry (LSC). The bivariate distributions illustrate expression of these phosphoproteins in relation to cellular DNA content (cell cycle phase). The skewed dashed lines show the upper threshold of nonspecific fluorescence of the cells treated with the secondary Ab only, respectively. The figures above the respective arrows indicate the percent increase in the mean values of S-phase cells of γH2AX and ATM-Ser1981^P fluorescence in the EdU-treated cells with respect to the untreated (Ctrl) cells.