Growth factor inhibitor screen shows BMP signaling is necessary for erythroid development and inhibitory for EC specification. All embryos were treated with inhibitor starting at st13 and assayed by in situ hybridization at st32. Blood differentiation marker was hba1 and the EC differentiation marker was aplnr. Inhibitors are indicated at the top of each column. (A,G) Control embryo treated with dimethylsulfoxide carrier. (B,H) Inhibition of the FGF signaling pathway using the specific inhibitor SU5402. (C,I) Inhibition of the VEGF signaling pathway using the specific inhibitor Ki8751. (D,J) Inhibition of the BMP signaling pathway using the specific inhibitor LDN193189. (E,K) Inhibition of the WNT signaling pathway using the specific inhibitor XAV939. (F,L) Inhibition of the NOTCH signaling pathway using the specific inhibitor RO4929097. For each treatment and probe, the same embryo is shown in a lateral, ventral (′), and magnified ventral (″) view. Of the experimental treatments, inhibition of BMP signaling had the most dramatic effect on reducing blood differentiation while enabling EC differentiation. Numbers at lower right of the lateral view panel indicate the number of embryos displaying the illustrated phenotype.