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Fig. 2. (A) Normal skeletal muscle in transverse section showing muscle fibres
separated by endomysial connective tissue and small profiles of vascular
supply. Part of a muscle spindle is visible toward the bottom left of the
micrograph. Satellite cells are impossible to identify at this magnification.
(Original micrograph x140; Toluidine Blue staining.) (B) Normal muscle
in longitudinal section, some 10 min following traumatic injury. Fibres are
broken and show hypercontracted myofibrils. There is extravasation of red
blood cells from a damaged vessel into the interstitial space. (Original
micrograph x140; Toluidine Blue staining.) (C) Micrograph of a section
of skeletal muscle from a muscle of a patient with Duchenne muscular
dystrophy. While there are some fibres of muscle present (to the left of the
field), much of the field is filled with dense collections of collagen bundles
and adipocytes (central and right of the field). (Original micrograph
x140; Toluidine Blue staining.) Much of the pathology literature on DMD
refers to muscle being replaced over time by adipose and connective tissues as
muscle fibres are damaged and the disease progresses. However, there is a
distinct possibility that the adipocytes and fibroblasts may have
differentiated from stem cells in the satellite cell position on fibres, since
this alternate differentiation can be observed in tissue culture and in aging
muscle (Jozsi et al., 2001;
Shefer et al., 2004;
Taylor-Jones et al., 2002).
Other descriptions of `transdifferentiation' are reported between vascular
smooth muscle and skeletal muscle and may relate to the apparent pool of stem
cells in the mesangioblast compartment in development
(Cossu and Bianco, 2003;
Galli et al., 2005;
Graves and Yablonka-Reuveni,
2000; Sampaolesi et al.,
2003).
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