The C2C12 cell line, a mouse myoblast line, was used here to study the regulatory factors in myogenic differentiation. After cultured in differentiation medium for 3 days, these cells differentiated into myotubes (Green) containing multiple nuclei (Blue). The myoblasts in this image were treated with 300ng/ml insulin-like growth factor II (IGF-II) and 50nM rapamycin (Rap) during differentiation. In the presence of both IGF-II and rapamycin, C2C12 cells differentiated into myotubes but arrested at a small myotube size with fewer myonuclei than mature myotubes. This image is one of different treatments in Figure 9A from JCB 189: 1157-1169, 2010. See also CIL: 13589, 13591.