Dermal fibroblasts from three healthy controls and three patients with PXE were cultured in DMEM medium containing 10% fetal bovine serum. Immunofluorescent staining (green fluorescence) was performed in cells cultured in normal medium and medium supplemented with 4 mM Pi with or without 3 μM minocycline for 4 days. The cellular localization of H2AX, PAR, PARP1, and TP53 in cells cultured in medium containing 4 mM Pi was provided in Supplementary Figure S1. Ctr, control; Mino, minocycline; Pi, inorganic phosphate; Bar = 200 μm.