On the stability of the myogenic cell line in avian limb bud development.

Number of experiments of our group (Chevallier et al., 1976, 1977; Kieny et al., 1979; Kieny and Chevallier, 1980; Mauger and Kieny, 1980 a, b) have led to the idea that the somite-derived cells which invade the somatopleural limb mesoderm constitute a distinct myogenic cell lineage. An idea opposite to the lineage view, namely that of the multipotency of the limb bud cells, has been put forward. In an attempt to clarify this controversy, we raised the question whether somite-derived myogenic cells are able to change their phenotypic differentiation when placed in abnormal environmental conditions after randomization of the relative position of the limb mesenchymal cells. In order to ascertain the possibility for a presumptive myogenic cell to differentiate into a chondrocyte or a fibroblast, it was essential to be able to distinguish between cells of myogenic origin and others. Therefore, firstly, we created a bispecific wing bud, in which the cells of the myogenic line were quail cells and the other limb cells were chick cells. Secondly, we constructed a recombinant wing bud with a chick wing ectodermal hull stuffed with a piece of dissociated and reaggregated mesoderm of 4-day bispecific wing buds. The recombinant wing bud was grown as a graft on a chick host. The histological observations show that most cells derived from the quail myogenic line congregate into muscle masses where they differentiate into myocytes. Nonetheless, a few of them are able to participate in the cartilaginous element, where they never express their myogenic phenotype but are morphologically integrated in the chick cartilaginous environment.