Figure 7
Formation of spindle-like structures (SLS) by muscle cells during wound healing. (A) Double labeling of muscle tissue with rhodamine-labeled phalloidin (green) and Hoescht (red) shows the presence of SLS at the injury site. The lack of nuclei within or near the SLS shows the non-cellular nature of these structures. (B) Rhodamine-labeled phalloidin shows the circular muscle band at 6 dpi proximal to the injury site and the released SLS's (arrows) in the bodywall dermis. (C) Double labeling with rhodamine-labeled phalloidin (red) and an antibody against holothurian collagen (green) shows a magnification of the circular muscle and the SLS in the dermal connective tissue of the body wall. Cell extensions or linkers labeled with phalloidin can be observed (arrowhead). (D-G) Longitudinal muscle sections labeled with Rhodamine-labeled phalloidin. (D) At 6 dpi, proximal to the injury site, showing the loose arrangement of the muscle bundles and the presence of SLS's. (E) Magnification of D shows the large number of SLS's present around and within the muscle fibers at this stage. (F) At 28 dpi the muscle bundles are largely organized, and few SLS are observed. (G) Magnification of F showing the reduced number of SLS at the muscle terminals. (H) Quantification of SLS's shows an increase during the first week of regeneration, from 2–6 dpi. At later stages the number of SLSs decreases, although their numbers remain higher than in sham-operated controls or non-injured animals. Dotted line denotes the number of cells found within the bodywall of non-injured animals and of controls. CB-collagen band, CC-coelomic cavity, CM = circular muscle, lCT loose connective tissue, LM-longitudinal muscle, SLS's-spindle-like structure. Arrowhead indicates the SLS phalloidin-positive linker. Bar = (A&C) 10 um, (B) 25 μm, (D& F) 200 μm, (E & G) 50 μm. Each point represents the mean ± S.E. of at least three animals. **p < 0.01.