Art modulates cell cycle response following IR. (a) Representative micrographs of WT and ArtΔ/Δ MSC metaphase spreads. (b) The mitotic indices of WT (filled bars) and ArtΔ/Δ (open bars) MSCs following exposure to IR at indicated doses were determined by quantification of metaphase cells. Mitotic index is expressed as the percentage of mitotic figures per total nuclei. Significance was determined by t-testing (**P < 0.01; ***P < 0.005). (c-g) The mitotic indices of WT and ArtΔ/Δ MSCs or control fibroblast 6, 12 and 24 hours following 1 Gy ionizing irradiation were determined by immunostaining for the mitotic marker pH3. (c) Shown are representative merged micrographs of pH3+ (green) and DAPI DNA counterstained (blue) WT or ArtΔ/Δ MEFs and MSCs at each time point after IR. Scale bars, 10 μm. The fraction of phospho-H3-positive cells for WT (filled bar) and ArtΔ/Δ (open bar) MSCs (d) or MEFs (f) were determined for each time point after IR. Data from (d and f) were also normalized to the 0 Gy controls. Normalized data are shown for MSC (e) and MEF (g). Error bars indicate standard error.