Altered myosin heavy chain phenotype in locomotor and non‐locomotor muscles of mini‐muscle mice bred for high running capacity

Abstract

Replicated selective breeding of mice for high voluntary wheel running for over 50 generations resulted in four lines of mice that display a high‐running phenotype. Individuals in two of the four lines display a smaller hindlimb muscle mass (mini‐muscle mice), inherited as a Mendelian recessive. In one line (lab designation line 3), all mice now have the mini‐muscle phenotype. Previous studies suggested that mini‐muscle mice also have differences in myosin heavy chain (MyHC) isoform content in hindlimb muscles. This study evaluated whether the changes in MyHC content were restricted to locomotor muscles. Electrophoretic analyses revealed that both locomotor (vastus lateralis, trapezius) and non‐locomotor (lingual) muscles of mini‐muscle mice had greatly reduced 2b MyHC isoform content compared to control mice. The loss in 2b MyHC isoform content in the mini‐muscle mice was compensated by a corresponding increase in 2a and 2x MyHC isoforms. The data suggest that alterations in the MyHC isoform profile in mini‐muscle mice are not restricted to locomotor muscles. Thus, the underlying gene appears to have a general influence on specifying muscle phenotype. NSF IOB‐0543429 to T.G.