Fig. 2

Adult zebrafish satellite-like cells are concentrated predominantly in slow muscle. (A) Schematic of cross-section through adult zebrafish trunk musculature, depicting fast-twitch (red) and slow-twitch (green) muscle fiber domains and a concentration of SLCs (black dots) within the slow muscle domain. The horizontal myoseptum is indicated by a brown line; the gray circle at the dorsal midline depicts the spinal cord. (B) The number of Pax7-positive cells, normalized to total myofiber number, is significantly higher in slow versus fast muscle; Student's t-test (p**<0.01). (C-C'') Pax7-positive cells (in red) are more common within slow muscle. Slow muscle fibers are marked with smyhc1-driven GFP (left of the dotted blue line). The boundary between slow and fast muscle fiber domains is marked by a dotted white line. The area between dotted blue and dotted white lines may represent muscle fibers with an intermediate identity. The horizontal myoseptum is indicated by a brown line. (D-D'') Higher magnification view of slow muscle. For quantification shown in B, Pax7-positive cells (D''; examples depicted by blue arrowheads) within the smyhc1:GFP-positive domain (left of the dotted blue line) were counted and normalized to the number of smyhc1:GFP-positive myofibers in the same area. (E-E'') Pax7-positive cells (in green) are rare within ventral fast muscle. Fast (ventral) muscle fibers are marked with mylpfa-driven mCherry (right of the dotted brown line). The area between dotted brown and white lines (weakly expressing mylpfa:mCherry) may represent intermediate muscle fiber identity. A dotted white line separates fast and slow muscle domains. (F-F'') Higher magnification image of fast muscle. For quantification shown in B, Pax7-positive cells (F''; blue arrowheads) within the mylpfa:mCherry-positive domain were counted and normalized to the number of mylpfa:mCherry-positive myofibers in the same area. Scale bar in C” and E” is 150 µm and in D” and F” is 75 µm.