Fig. 5. SM UNC-45 mRNA expression begins when skeletal myogenic cells fuse to form myotubes while expression of GC UNC-45 mRNA decreases in differentiating cultures. (A) Phase-contrast images of C2C12 cultures at different stages of myogenesis; P shows proliferating myoblasts, F shows fusing myocytes, Y mt shows young myotubes, and O mt shows older myotubes. Bar, 20 µm. Total RNA was prepared from these cultures. (B) Differential expression of GC and SM UNC-45 mRNA at the proliferative stage and during the stages of myotube formation, detected in duplicate northern blots. GAPDH mRNA levels show that approximately equal amounts of RNA were loaded per lane. (C) Quantification of the expression levels of GC (gray bars) and SM (black bars) UNC-45 mRNAs at different stages of in vitro muscle differentiation, shown as pixels per band normalized to the levels of GAPDH mRNA per sample (mt, myotube cultures).