Characterization of human urine-derived stem cells. (a) Phase-contrast microscopy of USCs in primary culture. (b) Alizarin Red S staining showing the osteogenic differentiation of USCs. (c) Oil red O staining showing the adipogenic differentiation of USCs. (d). Flow cytometry analysis of the expression of USCs surface markers. Scale bars = 100 μm. USCs, urine-derived stem cells.