Figure 6. Exo1 deletion impairs DNA damage signal induction and confers resistance to DNA damaging agents.

A) Representative photographs of BrdU-positive cells or TUNNEL positive cells in the intestinal basal crypts of 4 month old mice of the indicated genotypes: 24 hours after 4Gy γ-irradiation (IR). Magnification bars: 200 μm. B,C) Histogram showing the number of BrdU-positive cells per crypt (B) or TUNNEL positive cells per crypt (C) in the small intestine of 4 month old irradiated (IR) mice of the indicated genotypes (n=5 mice/group). D) Histogram showing the relative reduction of BrdU positive cells in 15Gy irradiated (24 hours after IR) compared to non- irradiated cells of the indicated genotypes. E) Histogram showing the relative increase in cells in G1 stage of cell cycle in 15Gy irradiated (24 hours after IR) compared to non- irradiated cells of the indicated genotypes. F) Survival curve of mouse embryonic stem cells of the indicated genotypes at 3–4 days after 6TG treatment at indicated doses. Survival curves for Exo1^−/− (complete gene knockout) and Exo1^{exonΔ−/−} (knockout of the nuclease domain, which was used throughout this study) were generated in two separate experiments. The survival curves for Msh2^−/− and WT are the averaged survival curves from two separate experiments. G) Histogram showing the number γH2AX foci per nuclei in the small intestine of 4 month old mice (n=5 per group) of the indicated genotypes: 24 hours after 4Gy γ-irradiation (IR). H) Histogram showing the number of 53BP1 foci per crypt in the small intestine of 4 month old mice (n=5 per group) of the indicated genotypes: 24 hours after 4Gy γ-irradiation (IR). I) Western blots showing expression of phosphorylated ATR (Ser345), phosphorylated Chk2 (T68), and phosphorylated p53 (Ser15) along with β-actin as a loading control in mouse ear fibroblasts of the indicated genotypes at 24hrs after 15Gy irradiation and in non-irradiated controls.