Mutation of the Hedgehog receptor Smoothened blocks the ability of bone marrow cells to generate new BMP4^R cells in the spleen. (A) RT-PCR analysis of Smo expression in Smo^Δ/+ and Smo^Δ/Δ after poly(I)poly(C) treatment to delete the conditional allele. Hypoxanthine-guanine phosphoribosyl transferase expression is used as a loading control. (B) Smo^Δ/+, Smo^Δ/Δ, and control bone marrow cells were transplanted into WBB6F1 Kit^W/Wv recipient mice. Fourteen days after transplantation, cells were plated in methylcellulose media containing Epo or Epo + BMP4, and BFU-E were scored. Significant differences are indicated in the figure. At least 3 recipient mice were analyzed for each donor cell genotype. (C) Smo^Δ/+, Smo^Δ/Δ, and control mice were treated with PHZ to induce acute anemia and allowed to recover for 7 days. The mice were challenged with PHZ a second time on the indicated days after the initial treatment. At 36 hours after the second treatment, spleen cells were isolated and plated in methylcellulose media containing Epo alone, and BFU-E were scored. Significant differences are indicated in the figure. At least 3 mice per genotype were analyzed at each time point.