Differential expression of C-protein isoforms in developing and degenerating mouse striated muscles

With the aim of clarifying the roles of C‐protein isoforms in developing mammalian skeletal muscle, we cloned the complementary DNA (cDNAs) encoding mouse fast (F) and slow (S) skeletal muscle C‐proteins and determined their entire sequences. Northern blotting with these cDNAs together with mouse cardiac (C) C‐protein cDNA was performed. It revealed that in adult mice, C, F, and S isoforms are expressed in a tissue‐specific fashion, although the messages for both F and S isoforms are transcribed in extensor digitorum longus muscle, which has been categorized as a fast muscle. In addition, although C isoform is expressed first and transiently during development of chicken skeletal muscles, C isoform is not expressed in mouse skeletal muscles at all through the developmental stages; S isoform is first expressed, followed by the appearance of F isoform. Finally, in dystrophic mouse skeletal muscles, the expression of S isoform is increased as it is in dystrophic chicken muscle. These observations suggest that mutations in C isoform (MyBP‐C) do not lead to any disturbance in skeletal muscle, although they may lead to familial hypertrophic cardiomyopathy. We also suggest that the expression of S isoform may be stimulated in degenerating human dystrophic muscles. © 1999 John Wiley & Sons, Inc. Muscle Nerve 22: 196–207, 1999