Lmo2 binding is required for early erythroid, myeloid, and endothelial gene expression. (A) Erythroid (gata1 and pu.1 in the PLM), myeloid (pu.1 in the ALM), and endothelial (flt4) gene expression defects in scl morphants can only be rescued by coinjection with an mRNA encoding a bHLH construct which includes the phenylalanine residue of the Scl second helix essential for the interaction between Scl and Lmo2. Whole-mount 15s embryos; views as indicated; numbers of embryos represented in gray. Arrow indicates rescued endothelial gene expression in the position of the dorsal aorta. (B) Western analysis shows that both HA-tagged constructs are expressed in injected whole-embryo extracts.