UNORTHODOX MYOGENESIS - POSSIBLE DEVELOPMENTAL SIGNIFICANCE AND IMPLICATIONS FOR TISSUE HISTOGENESIS AND REGENERATION

During the last few years several reports have described the occurrenc e of skeletal myogenesis in cells derived from embryonic, fetal and pe rinatal tissues that usually do not contribute to skeletal muscle in t he adult vertebrate body. After a brief description of current ideas o n myogenic determination in higher vertebrates, three examples of this unorthodox myogenesis will be described: 1) the occurrence of myogene sis in chick epiblast cells, cultured in isolation in serum-free mediu m; 2) the presence of cells endowed with myogenic potential in the emb ryonic mouse neural tube; and 3) the occurrence of spontaneous or indu ced myogenesis in mesenchymal cells during fetal and postnatal life. A possible embryological basis for unorthodox myogenesis, in relation t o gastrulation and morphogenetic fields, is then presented. It is also proposed that unorthodox myogenesis may represent a compensatory mech anism for higher vertebrates that have lost much of the regeneration p otential of lower vertebrates.