FIGURE 9.

Constitutively reduced H3K9 methylation reduced DSB repair. A, U2OS cells were pretreated with 800 nm concentrations of the G9a inhibitor (G9ai in DMSO) UNC0638 or DMSO alone (control) and plated onto glass coverslips. Three days after treatment initiation, the cells were exposed to 2 Gy of γ-irradiation. The cells were fixed at the time points indicated and stained for γH2AX and H3K9me2 by immunofluorescence. γH2AX foci and H3K9me2 levels were quantified by CellProfiler software. The mean foci number is denoted by the horizontal bar. Total numbers of nuclei assays are indicated on the graph. The number γH2AX foci were compared for each time point using analysis of variance with Bonferroni's correction for multiple comparisons. G9a inhibition resulted in a 63% reduction in H3K9me3 levels at the time of γ-irradiation (Fig. 2F). B, Suv39h1/h2 double null MEFs (DN) and isogenic wild type control MEFs (WT) were assayed for γH2AX foci numbers, as above. n.s., not significant.