Human dermal fibroblasts were cultured in ITS medium in the presence of 0 (DMSO carrier control, 0.02%), 1, 10, 100, and 1000 nM vitamin D3 for 14 days to determine the dose-dependent effect of vitamin D3 on alkaline phosphatase activity (A) and osteocalcin (C) gene expression. F-actin was stained with phalloidin in order to visualize changes in cell morphology in ITS (B) and ITS+vitD (100 nM, D) medium. Nuclei are counterstained with DAPI. Scale bar = 100 μm. *: p<0.05 compared to all other groups; #: p<0.05 compared to 0, 1, 10 nM