Mutation of Ptc induces stress BFU-E formation in the bone marrow in vivo and in vitro. (A, top) Bone marrow or spleen cells as indicated were isolated from Ptc^Δ/+ and Ptc^Δ/Δ mice and plated in methylcellulose media containing Epo alone, and BFU-E were scored. (A, bottom) PCR analysis of Ptc deletion by 4-hydroxytamoxifen. (B) Bone marrow cells were isolated from Ptc^floxed/+ and Ptc^{floxed/floxed};CreER, and deletion of Ptc was induced in vitro by incubating the cells overnight with 4-hydroxytamoxifen. (Top) The cells were washed and plated in methylcellulose media containing Epo alone, and BFU-E were scored. (bottom) PCR analysis of Ptc deletion by 4-hydroxytamoxifen. (C) Real-time RT-PCR analysis of BMP4 expression by in vitro deleted Ptc^Δ/+ and Ptc^Δ/Δ bone marrow cells. Significant differences are indicated in the figure. All assays were done in triplicate and are representative of 2 independent experiments.