BMP4, SCF, and hypoxia preferentially expand Kit⁺CD71⁺TER119⁺ stress erythroid progenitors. (A) Flow cytometry analysis of Kit, CD71, and TER119 expression of spleen cells cultured in media containing Epo at 20% O₂ or Epo + BMP4 + SCF at 2% O₂. Top panel shows expression at day 0 and day 5 of culture. Bottom panel shows the total number of Kit⁺CD71⁺TER119⁺ cells on each day of the 5-day culture period. The flow diagrams for this analysis are presented in Figure S3. (B). The top panel shows the flow diagrams gated on Kit⁺ cells showing the expression of CD71 and Ter119. Bottom panel shows the total number of Kit⁺CD71⁺TER119⁺ cells at day 4 of culture in the indicated conditions. (C) Total number of Kit⁻CD71⁺TER119⁺ cells generated on each day when spleen cells were cultured in Epo at 20% O₂ or Epo + BMP4 + SCF at 2% O₂ for 5 days. The flow diagrams for these data are presented in Figure S4B. These data are representative of 3 independent experiments.