Myosin components of the latissimus dorsi and the pectoralis major muscles in the dystrophic chicken.

The myosin composition of the anterior latissimus dorsi, the posterior latissimus dorsi, and the pectoralis major muscles was examined in the inbred White Leghorn dystrophic chicken and its isogenic normal line at different ages during development and maturation. Using the biochemical methods of native gel electrophoresis, one- and two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS PAGE), and peptide mapping, it was found that myosin isozyme changes occurred normally in the anterior latissimus dorsi muscle. However, in the posterior latissimus dorsi muscle, slow myosin components which were not present in the adult normal muscle were present in the adult dystrophic muscle. In addition, the pectoralis major muscle of the dystrophic chicken failed to undergo the neonatal to adult fast myosin isozyme transition. Our data also showed that muscle cell cultures derived from the pectoralis major muscle of dystrophic chickens expressed identical myosin components to cultures derived from normal embryos. However, since these cultures only produced embryonic myosins even after 1 month in culture, it implied that cells in tissue culture were phenotypically normal because present cell culture conditions were insufficient to induce the fetal to adult isozyme changes.