Extended Data Figure 7: Sustained meox1 activity promotes muscle progenitor formation and suppresses endothelial fate.

a–l, Injection of meox1 mRNA. a–h, meox1 mRNA injection induces expression of pax7a. At 10 somites, pax7a transcript localization is expanded from its wild-type expression in anterior border cells (a) to the entire AP extent of the somite (b) (38% n = 26). c, High magnification view of the region boxed in a. d, High magnification view of the region boxed in b. e, f, Lateral views, anterior to the left, of 15-somite stage embryos injected with meox1 mRNA show a dorsal-ventral expansion of pax7a expression (bracket, f) when compared to uninjected sibling (bracket, e). g, h, meox1 injection induces ectopic pax7a expression in 26 somite injected embryos (h) when compared to wild type (g) (26%, of injected embryos n = 31). i–l, Injection of meox1 mRNA into the Tg(fli1a–GFP) line specifically inhibits ISV sprouting (n = 37, j, l) when compared to uninjected siblings (i, k). k is a high magnification view of the region boxed in i. l is a high magnification view of the region boxed in j. m–v′, Ectopic expression of meox1 in the embryonic vasculature can cell autonomously induce Pax7 in a subset of cells and disrupt vasculature formation. m–q′, Expression of mCherry (red) from the fli1a promoter does not induce vascular malformations when injected in the fli1a–GFP line (m, n) and does not induce ectopic Pax7 (Green) o–q′. r–v′, By contrast expression of Meox1–mCherry fusion (red) but not mCherry alone from the fli1a promoter induced vascular malformations, specifically inhibiting ISV formation when injected in the Tg(fli1a–GFP) line (r–s) and induces ectopic Pax7 within vascular cells (arrows, n = 15, 18%). t–v′, Blue, DAPI nuclear counterstain, scale bars 50 μm.