Scl DNA binding is not required for early erythroid, myeloid, or endothelial gene expression. Whole-mount 10s embryos; posterior/anterior views as indicated; dorsal, top; numbers of embryos represented in gray. Coinjection of scl expression constructs containing only the bHLH or HLH domains with the scl spliceMO was sufficient to rescue early gata1 and pu.1 expression in the PLM and the PLM and ALM, respectively. Expression of the endothelial gene flt4 in the PLM could also be restored to normal levels, and ectopic expression of full-length scl or either construct resulted in the expansion of flt4 expression into the presomitic mesoderm (arrowheads).^12,17  Structures of Scl constructs used in each case are illustrated.