Has collagen a role in muscle pattern formation in the developing chick wing? 1. An immunofluorescence study

We have used antibodies to three of the isomorphic forms of collagen, types I, III and V, in an immunofluorescence microscopy study of myogenesis in the embryonic chick wing, concentrating on the period between stages 27 and 30 (5 to 7.5 days incubation) which is when the dorsal and ventral muscle masses separate into discrete muscle. We have demonstrated the presence of all three collagen types at the ectoderm-mesenchyme junction from stage 27 onwards. Type I collagen and then type III collagen are found in progressively deeper layers of the dermis at the later stages. Both types I and V collagen are initially present in the cartilage elements, but type I collagen becomes restricted to the periphery of these structure at later stages. The developing muscle areas show a lack of staining at all stages and it is only at the latest stages that types I and III collagen first appear in the surrounding epimysium. We discuss possible mechanisms for the division of the muscle masses in the light of this information on the distribution of collagen types.