BMP-4 requirement for hemangioblast development. (A) Blast colony potential of day 4-EBs induced in the presence and absence of BMP-4 and soluble BMP-4 receptor (sBMP4R-lA, sBMP4R-lB, 250 ng/mL). The presence and absence of factor and receptor are indicated below the graph. (B) Flow cytometric analysis showing KDR and CD117 expression of the 4 different EB populations. (C) RT–PCR expression analyses of the same EB populations analyzed in panel A.