Age-related changes and location of type I, III and IV collagens during skeletal muscle development of double-muscled and normal bovine foetuses

The aim of this study was to investigate age-related changes in collagen content in muscles of normal and double-muscled (DM) bovine foetuses. Psoas major (PM) and triceps brachii (TB) muscles were collected from foetuses at 110 to 260 days post-conception (p.c.), frozen and powdered. Cyanogen bromide (CNBr) digestion and hydroxyproline measure ments were carried out on the powder. CNBr peptides underwent SDS-polyacrylamide gel electrophoresis, and type I and III collagen relative variations were measured by densitometric analysis. Type I and III procollagen mRNA were located by in situ hybridization and types I, III and IV collagen located by indirect immunofluorescence. Although there was no significant difference between normal and DM animals in the amounts of collagen (except in PM muscle at 180 and 230 days p.c.), there was nevertheless a tendency to lower collagen content in muscles of DM animals. Amounts of hydroxyproline in PM and TB muscles from 110 to 230 days p.c. increased two- and threefold to 8.5 μg per mg of dry matter (d.m.) and 12 μg per mg d.m., repectively, and then decreased up to 260 days p.c., when they were twice as high in TB muscle (9.1 μg per mg d.m.) as in PM (4.5 μg per mg d.m.). The same difference in hydroxyproline levels was observed between normal adult PM and TB muscles. These variations were explained, mainly, by those of type I. In foetal muscle, in both genotypes and as in adult muscle, perimysium was types I and III, and endomysium type I, III and IV. Procollagen type I and III mRNA were located in perimysium. In conclusion, this study emphasizes that at the end of foetal life, collagen content is representative of what it will be in adult in muscle of both normal and DM animals.