Unformatted text preview: e muscle fiber
(muscle cell) Myofibril
muscle fiber FIGURE 17.21 Muscle satellite cells (A) The stem cells of skeletal
muscle are the satellite cells, located beneath the basal lamina of muscle fibers. (B) Electron micrograph showing a satellite cell and the nucleus of a muscle fiber. (From S. Chargé and M. Rudnicki, 2003. Physiol.
Rev. 84: 209; courtesy of Sophie Chargé and Michael Rudnicki.) Satellite
Myofibril Clever and his colleagues in 2007. Signaling by the Wnt pathway (see Figure 15.44) plays a major role in controlling the proliferation of these stem
cells, and it is thought that Wnt polypeptides secreted by fibroblasts of the
underlying connective tissue are responsible for intestinal stem cell maintenance. Wnt signaling is also involved in regulation of several other types of
stem cells, including stem cells of the skin and hematopoietic system. In
addition, signaling by the TGF-b, Hedgehog, and Notch pathways (see Figures 15.41, 15.43, and 15.45) play important roles in stem cell regula...
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