Myogenic Stem Cell-Dependent Regeneration in Fish Figure 8. Delayed regeneration of ventral muscle associated with fewer Pax7-positive cells. An adult S. macrurus and delineation of its ventral and dorsal muscle groups. Four images show the regeneration of the most distal portion (2 to 3 cm) of the ventral muscle over a 120-day period after its ampuation. Blue arrow points to the distal ventral muscle region removed including portions of the ventral fin. Serial longitudinal cryosections of a tail 10 days after ventral muscle excision were immunolabeled with anti-Pax7 (red) antibody to show the incidence of Pax7 immunolabeling at two different depths of the tail region adjacent to the muscle excision area. Dotted lines on the top two Pax7 images represent site of ventral muscle excision. The bottom panel shows longitidunal section from the same animal immunolabeled with anti-BrdU (red) and MyHC (MF20; green) antibodies. A dotted line has been added to the bottom image (BrdU/MyHC) to clearly discern the boundary between skeletal muscle and fin adjacent to the site of excision. MyHC is not expressed in the fin. Scale bar for Pax7/BrdU immunolabeled images: 200 mm. doi:10.1371/journal.pone.0036819.g008 Figure 9. No evidence of cell dedifferentiation. Portions of longitudinal cryosections (14-mm thick) from intact tails (A and D) and tails 4 (B) and 14 days (C) after amputation. Tissue sections were immunoreacted with anti-laminin (A and B) to study changes in basal lamina morphology that may indicate cellularization (arrows), anti-BrdU (C) to investigate myonuclei proliferation after tail cut (arrow), and anti-myosin heavy chain (D, red) to examine changes in muscle protein expression in intact mature electrocytes proximal to the tail transection site. Sections in D were co- immunolabeled with anti-Pax7 (green). Abbreviations: EC, electrocyte. Scale bars: 50 mm. doi:10.1371/journal.pone.0036819.g009 PLoS ONE | www.plosone.org 11 May 2012 | Volume 7 | Issue 5 | e36819