Art -deficient MSCs differentiate normally. (a) ArtΔ/Δ and WT MSCs were grown in adipogenic culture medium for 7 days, fixed and stained with the fluorescent lipid-binding dye LipidTOX (Invitrogen). Shown are bright field, fluorescent and merged images for each. (b) ArtΔ/Δ and WT MSCs were grown in osteogenic culture medium for 14 days, fixed and stained with Alizarin red to detect mineralization indicative of osteocytic development. (c) ArtΔ/Δ and WT MSCs were grown in adipogenic or unsupplemented culture medium for 14 days, fixed and stained with LipidTOX and DAPI counterstain. The fraction of LipidTOX-positive cells was determined for each sample and culture condition at days 0, 7 and 14. Error bars indicate standard error. (d-f) Mitotic indices for undifferentiated, adipogenic or osteogenic cultures of ArtΔ/Δ and WT MSCs were determined by immunostaining for M-phase marker phosphorylated histone H3 (phospho-H3). (d) Representative fluorescence micrographs of phospho-H3-positive cells (green), DAPI DNA counterstain (blue), and merged are shown for ArtΔ/Δ and WT MSCs. Scale bars, 10 μm. Fractions of positive phospho-H3 staining were determined at days 0, 3, 7 and 14 of (e) undifferentiated control, (f) adipogenic or (g) osteogenic culture conditions. Error bars indicate standard error.