EPO induction of Irs2, Trb3, S3G, Pim1, and PIm3 depends upon EPOR-H PY343 signals, while EPO inhibition of Foxo3a, Trb2, and Bim is EPOR-PY independent. Erythroid progenitor cells were expanded (in SP34-EX medium) from bone marrow preparations for wt-EPOR, EPOR-H, and EPOR-HM mice (n = 3 independent mice per group). For wt-EPOR, EPOR-HM, and EPOR-H EPO receptor alleles, schematics are provided. KitposCD71highTer119neg erythroblasts then were isolated, cultured for 5.5 hours in the absence of hematopoietic cytokines, and exposed to EPO (± 2.5 U/mL). At 90 minutes, RNA was isolated. cDNA was then prepared, and levels of Irs2, Trb3 Trb2, Foxo3a, Bim, Pim1, Pim3, and S3G transcripts were determined by quantitative PCR. Values are mean-fold modulation plus or minus SD.