Analysis of the ability of BMP4 to induce the formation of stress BFU-Es in spleen cells from untreated mice. (A) Bone marrow (top) and spleen (bottom) cells from untreated f/f (▪) and control mice (▦) were plated in methylcellulose media containing Epo (3 U/mL) and the indicated concentration of BMP4. (B) Spleen cells from C57BL/6-+/+ mice were preincubated without (▪) or with BMP4 (15 ng/mL; ▦) for 24 hours, washed, and then plated in the methylcellulose media containing either Epo (3 U/mL) alone or Epo plus BMP4 (15 ng/mL). Error bars indicate standard deviation.