FIG. 1.

Protein expression of Ckis during muscle differentiation. C2C12 myoblasts were cultured in high-mitogen medium (20% FCS-containing GM (A, lane 1) or in low-mitogen medium (2% FCS DM) for 48 h (A, lane 2) or for increasing various times as indicated (B, lanes 2 to 6). For each stage, total-cell extracts corresponding to 150 μg of proteins were resolved by SDS-PAGE on a 10% gel, and MyoD, troponin T, p16^Ink4a, p21^Cip1, p27^Kip1, and p57^Kip2 were detected by Western blot analysis using specific antibodies as described in Materials and Methods. Exposure times were 5 min for the Cip/Kip protein family, 1 min for MyoD, 1 min for troponin T, and 60 min for p16^Ink4a.