Skeletal muscle translocation in vertebrates.

It is now over 30 years since Bodo Christ first demonstrated that the musculature of the limb originated from the somites and overturned the then prevailing view that limb muscle develops from a local source. Subsequently, using electron microscopy and histological procedures, Bodo Christ identified that cells of the somites undergo an epithelial to mesenchymal transition which enabled them to move from their paraxial point of origin to distal locations. These studies defined this translocation as one of the major mechanisms allowing myogenic cells to translocate around the body. The other means used to translocate muscle involves the movement of cells as a sheet. The deployment of one of these two mechanisms has been postulated to be involved in the formation of all the hypaxial musculature of the vertebrate body. In this paper we describe the formation of muscles both in the head and in the body, which use a translocatory mechanism during their development. We highlight recent data showing that muscle translocation is a far more complex process than first thought but which in itself can be used as a valuable tool to address questions regarding tissue patterning and development.