In vitro characterization of human satellite cells. Representative images of in vitro characterization of cultured myoblasts using immunofluorescence with an antibody against desmin (A and B), BrdU (C) and MF20 (D). Specific antibody labeling was revealed using Alexa fluor 488 green fluorochrome. Nuclei were visualized with Hoechst (blue). Myogenic purity was determined after explantation (A) and increased after CD56 selection (B). To determine the proliferation index, cells were cultured for 48 hours in culture medium supplemented with 10 μg/ml BrdU (C). To determine the fusion index, cells were cultured in differentiation medium for 120 hours (D). Original magnification 100 × (A, B and C) and 100 × (D).