SIRT7 mediates release of NPM from nucleoli in response to genotoxic stress in vitro and in vivo. (A) Immunofluorescence (IF) staining for NPM of SIRT7-deficient primary MEFs 12 h after UVC irradiation (80 J/m2; UV) or without treatment (CTR) (n = 4). (Scale bars, 20 μm.) (B) IF staining of stable SIRT7 KD U2OS cells for NPM (green) and SIRT7 (red) 12 h after UVC irradiation (40 J/m2) or without treatment (n = 4). (Scale bars, 25 μm.) (C) IF staining of skin sections from age-matched WT and SIRT7 KO mice for NPM (red) and keratin (green), 12 h after exposure to 5,000 J/m2 UVA irradiation (n = 4). (Scale bars, 5 μm.) (D) IF staining of NPM in SIRT7 KO primary MEFs after exposure to 8 nM actinomycin D for 6 h (n = 3). (Scale bars, 10 μm.) Nuclei in A, B, and D were counterstained with DAPI. Scr., scrambled.