Myogenic regulation of mammalian skeletal muscle fibres.

Motor nerves can only modify the phenotype of muscle fibres within a myogenically determined range. The particular range of a given fibre is an intrinsic property of that fibre, depending on the type of muscle (limb or jaw) and the specific tag imprinted upon it during development.

Identification of two ryanodine receptor transcripts in neonatal, slow-, and fast-twitch rabbit skeletal muscles.

Analysis of the primary structure of the rabbit skeletal muscle ryanodine receptor led to the identification of two molecules of 5032 and 5037 residues, respectively. Such a sequence discrepancy is likely to be due to the alternative splicing of a 15 bp exon (1) encoding a 5 amino acid insertion (Ala-Gly-Asp-Ala-Gln) after residue 3479. By using PCR on first strand cDNA, we searched for the 15 base pair insertion in the ryanodine receptor mRNA from adult slow- and fast-twitch skeletal muscle, as well as from fast-muscles, at various stages of post-natal development. All rabbit skeletal muscle mRNAs, regardless of their developmental stage and twitch properties, contain two RYR transcripts, suggesting the coexistence of two RYR isoforms in mammalian skeletal muscle.