Hhex induces self-renewal of promyelocytes. (A) Wild-type LSK cells were retrovirally transduced with empty (MIG) or Hhex-encoding retroviruses, cultured in methylcellulose in the presence of IL-3, SCF, and EPO, and colony counts determined weekly. (B) Cumulative cell counts of methylcellulose cultures as in panel A. (C) Representative fields from week 4 cultures of MIG and MIG-Hhex–transduced LSK cells (original magnification ×400). (D) Cells harvested from methylcellulose cultures at the indicated round of plating were cytocentrifuged, stained with May-Grünwald-Giemsa, and the proportion of each cell type was determined by morphological examination. Data are representative of 3 separate experiments. (E) May-Grünwald-Giemsa–stained cytocentrifuge preparation of week 4 Hhex-transformed promyelocytes (original magnification ×400). (F) Fluorescence-activated cell sorter (FACS) plots of phenotypic markers (Mac-1, Kit, and Gr-1) and GFP expression in a representative Hhex-induced promyelocyte cell line. E, erythroblast; G, neutrophilic granulocyte; M, monocyte/macrophage; pro, promyelocyte.