Fig. 5. Bone marrow-derived cells can form de novo myofibers. (A) Examples of GFP+ myofibers in WBM- and SP-transplanted mice at 5 and 14 days following CTX are shown. Three different myofiber types were visible in each condition: `red' GFP–/β-Gal+ (asterisk), `yellow' GFP+/β-Gal+ (arrowhead) and `green' GFP+/β-Gal– (arrow). (B) Serial sectioning was used to track certain `green' fibers throughout the length of the muscle. This particular fiber (found in an SP-transplanted mouse 5 days post-CTX) stayed `green' for its entire length (>290 µm) and contained at least four distinct nuclei. As the bottom panel illustrates, in the following section (slide 14), the surrounding `red' fibers were observed, but the `green' fiber in question was gone (arrow). The last section in which this `green' fiber was visible (slide 13) showed many GFP+ mononuclear cells in the immediate vicinity of the `green' fiber (arrowhead). (A) Scale bars: 65 µm in the first and second rows, 20 µm in the third row and 31 µm in the fourth row. (B) Scale bars, 20 µm.