Fig. S1

Characterization of pax7a:GFP transgene expression within the adult zebrafish myotome. (A-A'') pax7a:GFP transgenic expression overlaps with Pax7 antibody in a majority of cells within the skeletal muscle. pax7a:GFP-positive cells are also present in the skin (outer edge on left side of image). The dotted blue line represents the boundary between fast and slow muscle domains and the brown line indicates the horizontal myoseptum. pax7a:GFP is also expressed in the skin (outer edge of section). (B-B'') Higher magnification view of boxed region in A. pax7a-driven cytoplasmic GFP and anti-Pax7 labeling largely overlap (mustard arrowheads); thin cytoplasmic protrusions are also observed in cross-section. Some pax7a:GFP-positive cells are Pax7-negative (28% of total pax7a:GFP-positive population; purple arrowheads), which may represent cells with GFP-positive cytoplasm for which the nucleus is on an adjacent section. (C) pax7a:GFP-positive cells represent a subset of nuclei within the myotome. (D-D''') A majority (70%) of pax7a:GFP-positive; DAPI-positive cells are also Pax7-positive (aqua arrowheads). pax7a:GFP expression is also observed in areas lacking a corresponding nucleus (DAPI-negative; Pax7-negative) and therefore represent cytoplasmic protrusions of cells that cannot be scored for Pax7 expression (mustard arrowheads). (E-E'') pax7a:GFP-positive cells are found within the fast muscle domain, but are sparse compared to the slow muscle domain (as observed with anti-Pax7 labeling). Cells expressing both pax7a:GFP and Pax7 are indicated by mustard arrowheads. (F-F'') pax7a:GFP transgenic expression is also detected in the spinal cord. Scale bar in A”, E'', and F'' is 75 μm, in B” is 30 μm, in C is 100 μm, and in D''' is 50 μm.