Muscle development of vertebrates has been a paradigm of cell
differentiation for many years. Three types of muscle are found in the
vertebrate body: skele- tal, heart and smooth muscle, and there has been
a gradient of concern about these different muscle types in the sequence
they are mentioned here. Skeletal muscle has received much attention
because it can be induced to differentiate in vitro and because of the
clinical relevance of myopathies. The discovery of the muscle-specific
members of the bHLH and MADS families of transcription factors must be
regarded as a breakthrough not only in muscle research and have opened
new insights into the genetic control of differentiation. Conse-
quently, the effects of gene-targeting of the MyoD-related (myfs) and
MEF transcription factors soon became objects of investigation. Along
with the genetic control of skeletal and heart muscle development, the
temporal-spatial appearance of cells fated to become myocytes has been
of foremost interest. The source of all skeletal muscle of the trunk is
the paraxial mesoderm, which gives rise to metameric entities, the
somites. The somite can be regarded as a turntable of mesodermal cell
fates, chondrocytes, fibroblasts, angioblasts of these deriva- and
skeletal muscle precursors. The coordinated development tives is tightly
controlled by local tissue interactions between embryonic struc- tures
such as the neural tube, the notochord, the lateral plate and the
ectoderm.