Control of Muscle Development in Vertebrates

The precursor cells of the epaxial skeletal muscles (body and trunk muscles) arise from the somites, repetitive epithelial structures that during gastrulation are transiently formed immediately adjacent to the neural tube from the paraxial mesoderm [1, 2]. The ventromedial region of the somites further differentiates into the sclerotome, whereas the dorsolateral domain forms the dermomyotome, that, most likely in a multistep process [2], gives rise to a second layer, the myotome. Within specific portions of the dermomyotome and the myotome, muscle precursor cells develop which during later stages of embryogenesis produce skeletal muscle in well defined regions of the body. Cells from the medial part of the dermomyotome migrate to the medial part of the myotome and differentiate into epaxial muscle that will yield back muscles. Similarly, cells from the lateral dermomyotome translocate to the lateral myotome and give rise to hypaxial muscle that will produce the ventral body wall muscles from the thorax and the abdomen. The hypaxial muscles from the limbs, however, are also derived from precursor cells from the dermomyotome, but in contrast to the body wall musculature, these cells do not use the myotomes as an intermediate location. These cells are often translocated over considerable distances through the body before they proliferate further and differentiate into the muscle of the limbs, the diaphragm, and typically, the tip of the tongue. The rest of the tongue and the other muscles of the head are not only derived from migratory cells from (rostral) somites, but also from paraxial head mesoderm and prechordal mesoderm.

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