Identification and change of collagen types in differentiating myoblasts and developing chick muscle

Abstract

COLLAGEN is the major structural protein in the supporting and connective tissues. In addition to its mechanical properties it has been considered to be involved in developmental processes^1–3. Previous studies on muscle development have concentrated on the contractile components but more recently there has been a realisation of the significance of connective tissue in this process. For example, in vitro studies have demonstrated the importance of a collagen substrate in promoting myoblast differentiation⁴, and more recently it was shown that all types of collagen were equally effective⁵: Mayne et al.⁶ demonstrated that clones of chick muscle cells were capable of synthesising type I collagen. Ketley et al.⁵ confirmed the synthesis of type I collagen and also reported that the collagen in intact chick muscle was solely of this type. On the other hand, Duance et al.⁷ and Bailey and Sims⁸ investigated the distribution of the genetically different collagen types within bovine muscle connective tissue and showed by biochemical and immunofluorescent techniques a specific distribution of the isomorphic forms of collagen in this tissue. Here we report our studies on the development of chick skeletal muscle which were designed to investigate some pertinent points: (1) the distribution of collagen types in chick muscle; (2) the role of collagen in the development of muscle as a functional tissue; (3) the cellular derivation of these different collagens. Chick muscle was chosen, first, because much is known about its development and differentiation in vitro, and second, because it is possible to manipulate its early development in the embryo in vivo^9,10. We have isolated three isomorphic forms of collagen from chick muscle, and using immunofluorescent techniques demonstrate a specific distribution of these collagen types within this tissue. Finally we have used in vitro muscle cell culture to examine how this distribution is achieved by temporal transitions in synthesis. These results suggest that collagen has a subtle role in the development of muscle.