Fig. 3

Cell cycle re-entry in C2C12 myotube cultures. Myotube cultures were treated with AraC to eliminate cycling myoblasts, and then treated with various concentrations of 1° or 2° newt extract in the culture medium. a Arrow in treated culture identifies MHC-positive myotube that was also positive for BrdU. Scale bar = 100 μm. b Following extract treatment in GM, the percentage of MHC-positive cells was determined (number of myotubes divided by total number of cells for left panel and number of myocytes divided by total number of cells for middle panel). Extract treatment led to significant reductions in myotubes and small increases in myocytes. In cultures treated with 0.3 mg/ml of secondary (2 °) extract, 23 % of MHC-positive myocytes incorporated BrdU. c Similar to (b), extract treatment in DM not only led to a reduction in myotubes but also led to a significantly increased number of MHC-positive mononucleated myocytes. *p < 0.0001