A revised model for concentration-dependent function of PU.1 in hematopoiesis. The model of hematopoiesis shown is based on a revised model of hematopoiesis proposed by Adolfsson et al. [31]. PU.1 concentration is indicated by a gradient from red (high) to blue (low) in the top to bottom direction. The position of each cell type within this gradient indicates the relative concentration of PU.1. Mature megakaryocytes, erythrocytes, and T cells do not express PU.1. Abbreviations are as follows: HSC, hematopoietic stem cell; MPP, multipotential progenitor; LMPP, lymphoid-primed multipotential progenitor; CLP, common lymphoid progenitor; pro-B, progenitor B cell; B, mature B cell; pro-NK, progenitor natural killer cell; NK, mature natural killer cell; pro-T, progenitor T cell; T, mature T cell; MEP, megakaryocyte-erythroid progenitor; Meg, megakaryocyte; E, erythrocyte; GMP, granulocyte-macrophage progenitor; Mac, macrophage; Neut, neutrophil.