A. B. 
Developmental regulation of cTnC gene expression in vitro. A: Differentiation of C2C12 myo- 
blasts into myotubes induced by serum deprivation. Cultures of C2C12 myoblasts are shown on 
the left. After 48 h of serum deprivation, more than 95 percent of the myoblasts have differen- 
tiated into myotubes (right panel). Magnification, X 54. 
B: Northern blot analysis ofRNA samples isolated from murine BALB/c cardiac tissue (marked 
HeartJ, undifferentiated C2C12 myoblasts (C2C12 Myoblast), and differentiated C2C12 myo- 
tubes (C2C12 Myotube) hybridized to the murine cTnC cDNA probe. The bottom panel shows the 
same filters hybridized to a glyceraldehyde- 3-phosphate dehydrogenase (GPD) probe. 
From Parmacek, M.S., and Leiden, J. M. 1989. J Biol Chem 264:13217-13225. 
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