Fig. 6

Transplanted PreMel produce melanin and express TYR in vivo. a Schematic representation of PreMel differentiation and the in vivo setup. 1 × 10⁶ cells (ADSC, PreMel, or HEM) were injected intradermally into the back skin of NSG mice, and melanin production was evaluated after 14 days. b Melanin determination in NSG mouse skin shows that PreMel synthetize melanin in vivo to a lesser extent than HEM. Fontana-Masson staining for melanin in the human skin as a positive control (c). Black arrows show HEM in situ in the basal membrane of the epidermis. d Mice treated with ADSC are negative for melanin staining. e PreMel are positive for the Fontana-Masson staining (indicated by black arrows). f HEM injected in the mouse skin are positive for melanin, (scale bar = 100 μm). The presence of injected cells was also determined by TYR immunofluorescence in the human skin (g) and in mouse skin slides. h TYR-negative ADSC were stained with anti-human CD90 to demonstrate their presence. i Similar to in vitro samples, PreMel are positive for TYR in the mouse skin, demonstrating that the melanin synthesis machinery is active in differentiated cells in vivo. j Injected HEM are also positive for TYR in this in vivo setting (scale bar = 10 μm)