Art is dispensable for MSC resistance to ionizing irradiation. (a) Three independent biological replicates of WT or ArtΔ/Δ MSCs or control fibroblasts were plated at 5 × 104 cells per dish each and cultured for 10 days. Viable cell counts, measured by exclusion of the vital dye trypan blue, were determined every 2 days. Error bars indicate standard error. (b) Clonogenicity assay for sensitivity to ionizing irradiation. A total of 1 × 105 WT or ArtΔ/Δ MEFs or 5 × 105 WT or ArtΔ/Δ MSCs were irradiated at the indicated doses, plated to 100-mm dishes and cultured until colonies were visibly evident for the unirradiated WT controls of each cell type. Cells on all plates were then fixed and stained with crystal violet histological stain. (c) Quantification of clonogenicity (from (b)) following IR. Colonies were counted and normalized to the unirradiated control for MEFs or MSCs, respectively. Error bars indicate standard error. (d) WT and ArtΔ/Δ MSCs or control fibroblasts were exposed to ionizing radiation (IR) at indicated doses, plated at equivalent densities in triplicate and harvested for analysis after 7 days. Viable cell counts were determined for single-cell suspensions by trypan blue exclusion. Relative resistance to IR is expressed as the viable cell count at each dose normalized to the unirradiated control for each sample. Error bars denote standard error.