E2F-2 is a Retinoblastoma (Rb)-regulated transcription factor induced during terminal erythroid maturation. Cyclin E-mediated Rb hyper-phosphorylation induces E2F transcriptional activator functions. E2F-2-loss causes reduced peripheral red blood cell (RBC) counts, without altering relative abundances of erythroblast subpopulations. To determine how E2F-2 regulates RBC production, we comprehensively studied erythropoiesis using knockout...