Transcription factors in skeletal myogenesis of vertebrates.

Abstract

All skeletal muscles of the vertebrate body and some head muscles are derived from the somites. Somites are transient metameric structures that are laid down in a rostral to caudal direction on each side of the neural tube and notochord during embryogenesis. Initially, somites bud off from the unsegmented paraxial mesoderm and form epithelial, ball-shaped structures with a centrally located somitocoel. During further development the somites differentiate and eventually will give rise to the sclerotome and the dermomyotome (Christ and Ordahl 1995; Brand-Saberi and Christ 2000). Because of inductive and repressive instructions from surrounding tissues, the somite acquires a dorsal-ventral, anterior-posterior and medial-lateral polarity. Cells in the ventral part of the somite de-epithelialise and become mesenchymal cells of the sclerotome forming the axial skeleton. Cells in the dorsal portion of the somite retain their epithelial character and form the dermomyotome, which will give rise to the dermis of the skin and most of the skeletal muscle of the body. The dermomyotome is further separated in a medial and a lateral population of cells, giving rise to the epaxial muscles (deep muscles of the back) and the hypaxial muscles (appendicular musculature, abdominal muscles, diaphragm, hypoglossal chord), respectively (Ordahl and Le Douarin 1992; Christ and Ordahl 1995).