Fig. 2. (A) Myogenic specification factors are suppressed in G0 and activated in
G1. Western blot analysis of total protein shows that both MyoD and Myf5 are
present in asynchronous adherent cultures of C2C12 myoblasts (Mb) but not in
C3H fibroblasts (Fb) as expected. 72 hour myotube cultures (Mt) strongly
express MyoD but not Myf5. Neither MRF is expressed after 12 or 48 hours of
suspension culture (S12, S48). Replating for 2 to 30 hours (R2-R30) causes
induction of MyoD earlier (at R6) than Myf5 (at R18). Data are representative
of three independent experiments. (B) Synchronization in G0 does not induce
differentiation. Northern blot analysis of RNA isolated from asynchronous,
arrested, reactivated or differentiated C2C12 cells. The differentiation
marker MCK is only detected in myotubes (Mt), but not in asynchronous
myoblasts (Mb), at 12 or 48 hours in suspension (S12, S48) or at 2-30 hours
after replating (R2-R30). Histone mRNA indicates the extent of DNA synthesis.
MyoD and Myf5 mRNAs correlate with the protein data in Fig. 2A. Data are
representative of three independent experiments.
