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. 0.2 μg/ml follistatin was added to the medium for the last 2 day of differentiation. Follistatin was able to rescue the myotube maturation. This image is the control of different treatments in Figure 9A from JCB 189: 1157-1169, 2010. See also CIL: 13589, 13590.