Model for the role of C/EBPα induction of PU.1 during hematopoiesis. PU.1 achieves sufficient levels in the absence of C/EBPα to help specify the CMPs. C/EBPα increases PU.1 to allow commitment of the CMP to the GMP stage. C/EBPα helps maintain PU.1 expression in the granulocyte lineage but further induces PU.1 in cooperation with cytokine signals and additional transcription factors to allow monocyte lineage specification.