Fig. 2

Mesp-b knockdown recapitulates and Mesp-ba^Myc expression rescues dermomyotome phenotype in tbx6 mutants. (A-F) Control and Mesp-b ATG MO-injected embryos at the 12-somite (A-C) and 24-h (D-F) stage. (A) ripply1, (B) meox1 and (C) myoD mRNA expression. Red asterisks indicate most recently formed somites; SI is outlined; red arrowheads indicate downregulation of all three genes in maturing somites. (D-F) Immunolabeling showing dermomyotome (Pax7, green) and corresponding myotome (MF20, blue; Mef2, red). Mesp-b morphants phenocopy tbx6 mutant dermomyotome but form somites similar to wild type; Mesp-b knockdown has no effect in tbx6 mutants. Dashed lines indicate central dermomyotome domain (top) and somite boundaries (bottom). (G-J,L-N) Non-transgenic and Tg(hsp70l:mesp-ba^myc) tbx6 mutants heat-shocked at the 12-somite stage. (G-J) Transgenic embryos show increase in Pax7⁺ dermomyotome cells (G,H) and rescued patterning of slow muscle fibers (F59, gray) within the myotome (MF20, blue) (I,J). (K) Schematic illustrating rescue of tbx6 mutant phenotypes by transient Mesp-ba^Myc expression. (L-N) Transgenics develop larger myotomes (brackets), and show partially rescued myotome boundaries, similar to wild type. Scale bars: 100µm in C; 50µm in F,J,N.