Fig. 1. Two distinct subpopulations appear in satellite cell-derived clones. (A-D) Single myofibers were isolated from EDL (A,B) or soleus (C,D) muscle and cultured for 4 (A,C) or 6 days (B,D). Two distinct subpopulations, including cells designated round cells (white arrowheads) with a rounded shape and more flattened cells designated thick cells (black arrowheads), appeared in either EDL- or soleus-fiber culture. Images were obtained by phase-contrast microscopy. Scale bars: 50 µm. (E) The ability to undergo myogenic differentiation of satellite cell clones derived from EDL (white column) and soleus muscles (black column). Single myofiber cultures were fixed on day 4 or 8, and then subjected to immunofluorescence for MHC. Expression of MHC was determined in 45-80 colonies. (F) Ultra-microscopic view of round cells. Round cells derived from gastrocnemius muscle were observed under a scanning electron microscope. The arrow indicates a filopodium. Scale bar: 10 µm.