Smad1 enhances hemangioblast development. The blast-forming potential of iSmad1 EBs was examined. The iSmad1 EBs were left untreated (no dox) or treated with doxycycline from day 2 to 2.25 (d2 wo) and replated at day 3.75 for blast colony formation. In other samples, the EB-derived cells were replated with the addition of doxycycline in the methylcellulose (mec dox). Blast colonies (▪) and secondary EBs (⊡) were scored on day 4 after plating. For each sample, n = 3. Error bars indicate the SEM and the asterisks indicate a P < .01 compared to the no dox samples.