Differentiation potentialities of distinct myogenic cell precursors in avian embryos.

Interspecific grafting experiments between chick and quail embryos were carried out to investigate the differentiation capacities of myoblasts from different development stages. Grafts consisted of 3.5-day-old embryonic quail dermomyotomes isolated from the cranial level, 7- to 10-day-old and 16-day-old embryonic quail pectoralis muscles, 15-day-old postnatal quail pectoralis muscle, and 3- to 10-day-old embryonic quail cardiac and gut muscles. Grafts were implanted into 2-day-old chick embryos in place of the dorsal halves of somites from the prospective wing level. After implantation of dermomyotome fragments, we observed that quail cells participated in trunk and limb musculature. After implantation of 7- to 10-day-old embryonic muscle, quail cells were rarely found in the limb but systematically took part in the formation of trunk muscles. All these capacities were totally lost in 16-day-old embryonic and 15-day-old postnatal muscles. After implantation of nonsomitic derivatives such as embryonic cardiac and gut muscles, implanted cells never participated either in wing or trunk musculature. After dermomyotome, embryonic muscle, and gut implantation, quail cells were capable of invading the dermis and aggregating into feather germs. Our results extend those previously reported and indicate that somitic myogenic derivatives which do not migrate in the normal course of embryogenesis have migratory potentialities and are able to give rise to axial muscles. All these potentialities are lost as myogenesis proceeds in embryos.