SpliceMO-mediated Scl knockdown is highly specific. (A, B) Wholemount 10-somite (14 hpf) embryos (10.5 × magnification); posterior/anterior views as indicated; dorsal, top; numbers of embryos represented in gray. (A) Coinjection with correctly spliced scl mRNA but not myoD mRNA, together with the scl spliceMO, rescued early gata1 and pu.1 expression in the PLM and the PLM and ALM, respectively. Nkx2.5 in the heart (A) and Pax2.1 in the pronephric duct mesoderm (B) were unaffected by these injections. Ectopic anterior expression of des at 10 somites (14 hpf) confirms that myoD mRNA was active.