W/W^v mice exhibit a delayed expansion of stress BFU-Es in the spleen during the recovery from acute anemia. W/W^v, W^v/⁺, and control mice were treated with phenylhydrazine to induce acute anemia. (A) Spleen cells and (B) bone marrow cells were plated in methylcellulose media containing Epo (3 U/mL) at the indicated times after PHZ treatment, and the number of stress BFU-Es were measured. (A-B) *P < .05, **P < .01, ***P < .005 when one value was compared with the previous time point. Each time point represents the average of 3 mice each done in triplicate. (C) Reverse transcription–polymerase chain reaction (RT-PCR) analysis of BMP4 expression in the spleen of W/W^v and control mice. Error bars indicate standard deviation (SD).