Microcarrier bead clusters after 15 days of culture, imaged at 10x magnification. Nuclei are stained blue with Hoechst 33342. Mitochondria are stained red with MitoTracker CMX-Ros. Normal gravity (a, b) and simulated microgravity (c, d) bead clusters both have differentiated, multinucleated myotubes spanning across bead gaps (white arrows). Scale bar = 100 μm.