Murine myoblasts, C₂C₁₂ cells, were cultured in low serum differentiation medium for 3 days then fixed and tripled labeled for actin (red) with rhodamine-phalloidin; muscle-specific myosin heavy chain (green) by immuonfluorescence with Alexafluor 488 secondary antibody; and nuclei (blue) with To-Pro-3. As myoblasts differentiate, they upregulate myosin and other muscle-specific proteins, and fuse to form multinucleate myotubes, which mature into muscle fibers.