Small-molecule–based inhibition of BMP signaling results in increased primitive myeloid potential. (A) Murine EBs were treated for 24 hours with 0.25 μM LDN, harvested on the indicated days of EB differentiation, and subjected to western blotting analysis of pathway-restricted R-SMAD phosphorylation. Phospho-SMAD levels were compared with total expression of SMAD1, and β-actin was used as a loading control. Embryoid bodies treated with LDN on day 2 or 4 of EB differentiation were cultured to day 6, harvested, and seeded on cytokine-supplemented methylcellulose medium to gauge primitive hematopoietic potential, including (B) erythroid progenitors and early myeloid lineages, (C) macrophage progenitors, and (D) megakaryocyte progenitors. Results of hematopoietic progenitor assays are reported as mean ± SEM from at least 3 experimental repeats, with values normalized to relevant controls. **P < .01. EryP, erythroid progenitor; MacP, macrophage progenitor; MegaP, megakaryocyte progenitor.