Frequency of MHC-positive myocytes and myotubes in double-labeled cultures from the PM of E14, E18, 1-day posthatched, and 3-week posthatched chickens. (A) E14, (B) E18, (C) 1-day posthatch, and (D) 3-week posthatch cultures. Duplicate cultures were double-labeled at each time point with mAbs against embryonic fast MHC (EB165 indirectly labeled with GAM-TRITC) and ventricular MHC (HV11 directly labeled with fluorescein). Nuclei were counterstained with DAPI and the number of nuclei within MHC-positive cells versus total nuclei was determined. At least 500 nuclei in 10 or more fields were counted per plate. Error bars represent standard deviation and are smaller than the symbols if not seen. Values decrease due to continued proliferation of nonmyogenic cells. emb/vent, coexpression of embryonic and ventricular MHC; vent, expression of ventricular MHC.