Module 8: Figure chick myogenesis
Sites of myogenesis in the chick embryo.
a. Apart from the muscles in the head, all skeletal muscles arise from the somites. Panels b–e represent stages in the development of the muscle progenitors within these somites. b. A newly formed somite receives signals from the notochord (ntc), neural tube (nt) and lateral plate ectoderm (lpm), which are responsible for switching on the myogenic factors (e.g. MyoD, Myf-5) that begin to define the myogenic cell line. The dorsal cells (marked in blue) are destined to become the dermomyotome. c. A later stage somite, where a region of the dermomyotome (dm) has begun to differentiate into a dorsomedial lip (red), which expresses high levels of both MyoD and Myf-5. The ventral region of the somite forms the sclerotome that will begin to form vertebrae and ribs. d. Further on in development, cells at either end of the dermomyotome migrate out to form the epaxial and hypaxial myotome. The lateral region of the myotome continues to grow outwards, where it will form the muscles of the ventral body wall. e. In the region where the limb buds begin to form, muscle progenitor cells (MPCs) slough off from the hypaxial myotome and migrate into the ventral body and the limb bud, where they will begin to differentiate into skeletal muscle cells. Reproduced from Curr. Opin. Cell Biol., Vol. 13, Bailey, P., Holowacz, T. and Lassar, A.B., The origin of skeletal muscle stem cells in the embryo and the adult, pp. 679–689. Copyright (2001), with permission from Elsevier; see Bailey et al. 2001.