Fig. 8

GFP perdurance in the pax7a:GFP transgenic line implicates satellite-like cells as a source of new muscle fibers during injury-induced repair. (A) Schematic diagram depicting Pax7 protein and pax7a:GFP transgene expression in satellite-like cells and myofibers. pax7a:GFP-positive; Pax7-positive cells represent satellite-like cells. Cells that show pax7a:GFP expression within the cytoplasm but are Pax7-negative are likely differentiating or differentiated cells in which pax7a-driven GFP perdures. (B-B'') At 5 dpi, pax7a:GFP and Pax7 double-positive satellite-like cells are present at the injury site (arrowheads); however, GFP expression is also detected in Pax7-negative presumptive newly-forming myofibers. (C-E) At 4 dpi, many cells expressing MyHC (A4.1025), a differentiation marker, also express pax7a:GFP. (C'-E') Magnified view of boxed region in C-E highlights the overlap of pax7a:GFP and MyHC expression. (F-F'') pax3a:GFP and myog:H2B-mRFP transgene expression overlap in presumptive newly-forming myofibers at 4 dpi (white arrowheads), but pax3a:GFP-positive, myog:H2B-mRFP-negative are also present (mustard arrowheads). A rare presumptive newly-forming myofiber with a centrally-located nucleus is indicated by a blue arrowhead. Scale bar in B-E is 75 µm, in C', D', E' and F-F” is 30 µm.