C-myc is expressed in mouse skeletal muscle nuclei during post-natal maturation

Previous data have indicated the presence of c-myc mRNA and protein in mature skeletal muscle, but whether the protein is present as a Myc/Max heterodimer capable of influencing transcription in that tissue or its potential role in pathological muscle tissue has not been examined. The expression of c-myc in normal and mdx dystrophic mouse skeletal muscle was therefore investigated. C-myc mRNA was detected by Northern hybridisation in normal and dystrophic mouse muscle from mice up to 40 days of age and immunohistochemical staining confirmed that c-myc protein was expressed in muscle fibre nuclei in the muscles of mice up to 40 days of age. The presence of Myc-containing complexes that are able to bind to the concensus Myc/Max binding site was demonstrated in these muscles using the electrophoretic mobility shift assay. These results show that c-myc protein is expressed in functional complexes in both normal and dystrophic mouse skeletal muscle during post-natal maturation. They also show that expression of c-myc in mouse skeletal muscle decreases to undetectable levels by about 40 days of age. Although no differences were detected between the expression of c-myc in mdx and control mouse muscle, these data show that muscle contains Myc protein which has previously been demonstrated to be capable of initiating programmed cell death in other tissues.