Effects of MYB-GATA1 on differentiation, proliferation and survival. (A) Counting of CFUs at day 12. Each graph represents one type of CFU, as indicated. (B) Identification of various types of cells by staining with MGG. Immature granulocytic cells correspond to undifferentiated blasts, myeloblasts, and promyelocytes; mature granulocytic cells correspond to myelocytes, metamyelocytes, and neutrophils. (C) MGG staining of lin⁻ cells expressing MYB-GATA1 in platings 2-5 shows immature cells with discordant morphologic characteristics (basophilic cytoplasm and lobated nuclei with condensed chromatin). Magnification ×630. (D) FACS analysis of cells transduced with MYB-GATA1 and collected from methylcellulose at each plating. Cells remained CD11b⁺/GR-1⁺ throughout. Each graph represents the mean values ± SEM of 4 independent assays. (E) Number of colonies counted after 12 days of differentiation in methylcellulose in MYB-GATA1–transduced lin⁻ cells compared with controls. (F) Image of large and dense colonies of CFU-G when cells were transduced with MYB-GATA1. Magnification ×40. (G) In vitro immortalization assay of transduced lin⁻ cells. At each plating, colonies were counted. Cells transduced with MYB-GATA1 continued to form colonies throughout the 5 platings. Statistical analyses were made using paired t test, for counting of CFU, cells and colonies and 2-way ANOVA for in vitro immortalization assay, *P < .05, **P < .005, and ***P < .001.