Accumulation of the c-mos protein is correlated with post-natal development of skeletal muscle.

Previously we reported that c-mos proto-oncogene RNA was developmentally up-regulated during post-natal maturation of the rat skeletal muscle. Using two different site-directed affinity-purified antipeptide antibodies we can observe that c-mos product (p43 c-mos) accumulates increasingly during post-natal development of the skeletal muscle and exhibits protein kinase activity. We find that in adult rat p43 c-mos is 10-fold higher in skeletal muscle than in ovaries, and 20- to 40-fold higher than in heart, lung, testis and liver, and may represent about 0.005% of the total soluble proteins. In addition adult skeletal muscle from Xenopus, mouse and man was found to contain p43 c-mos. These data argue in favour of a novel muscle-specific function of c-mos.