Skeletal muscle is postmitotic in adults; however, a population of pluripotent mononucleated cells, which are situated between the outer sarcolemma and the basal lamina of the myofibers,
12 are responsible for muscle repair and regeneration. In the unperturbed state, satellite cells are normally quiescent, becoming activated when the muscle suffers regeneration, development, or training.
13 However, in the unperturbed EOMs of adult humans there is a small percentage of activated satellite cells,
11 positive for a myogenic lineage-specific marker, MyoD. MyoD is expressed in both activated satellite cells and myoblasts,
14 15 but not in quiescent satellite cells,
16 myotubes, or mature myofibers. Furthermore, a continuous process of myonuclear addition to normal uninjured myofibers occurs in EOMs.
17 Myogenin is another myogenic regulatory factor that is observed in activated satellite cells from skeletal muscles
15 and EOMs.
11 In culture, it appears after MyoD1 expression and before developmental myosin.
18 c-Met, the receptor for hepatocyte growth factor (HGF), a multifunctional cytokine expressed on skeletal muscle that activates satellite cells through interaction with its receptor, is another effective molecular marker for quiescent, activated or proliferating satellite cells. Cornelison and Wold
16 detected it beneath the basal lamina of presumptive satellite cells in intact muscle and also observed in satellite cell cultures that c-Met m-RNA and protein are expressed by all myofiber-associated satellite cells. c-Met was not detected in fibroblasts or other mononucleated cells from healthy muscle explants. Barani et al.
19 described a significant increase in the expression of c-met in proliferating myoblasts. McLoon et al.
20 observed that 17% of the myofibers had associated c-Met-positive satellite cells in EOM from rabbits.