miR-21 negatively regulates stemness-related properties of miR-21 knock-in neonatal dermal cells. Passage 2 microRNA (miR)-21 knock-in neonatal dermal cells were pretreated with miR-21 antagomir or control antagomir (50 nM) for 48 hours, and wild-type neonatal dermal cells were treated with control antagomir (50 nM) for 48 hours. (A) The proliferation ability of the three groups was detected every 2 days after seeding. Colony formation assay including (B) colony numbers, (C) colony sizes, and (D) colony size distribution of the three groups was also measured. (E) Representative photographs of migration of the three groups at indicated time points. (F) Relative migration rate of the three groups presented as mean ± standard deviation (n = 6 per time point for each group). (G) Adipogenic and (H) osteogenic differentiation of the three groups were measured by staining with Oil-Red O and Alizarin Red and quantifying them respectively. CFU, colony-forming units; d, days; h, hours; miR-21 cells, miR-21 knock-in neonatal dermal cells; wild-type, wild-type neonatal dermal cells; OD, optical density. *P < 0.05, **P < 0.01. Scale bar = 500 μm.