Fig. 1. EKLF expression is initiated prior to erythroid commitment in the mouse fetal liver. (A) Schematic of the Peklf-GFP transgene after site-specific, uni-directional integration into the Ainv18 homing site, yielding the Peklf-GFP ES cell clone. (B-D) Flow cytometric analysis of GFP (B) and CD71/Ter119 expression (C) in fetal liver cells derived from E13.5 Peklf-GFP embryos, as quantified in Table 1. GFP⁺/Ter119^- cells selected for colony assays are marked in D. (E-H) Erythroid (CFU-E and BFU-E), megakaryocyte, granulocyte and macrophage progenitor-derived colonies from GFP⁺/Ter119^- cells were quantified and compared with those derived from GFP^-/Ter119^- cells. Cells were morphologically assessed by cytospin and May-Grünwald/Giemsa staining. (E) Erythroid cells; (F) megakaryocyte; (G) granulocytes; (H) macrophages. Scale bars: 5 µm. (I) Enrichment is defined as a colony number greater than 10% of total colonies (red vertical line) because 10% of Ter119^- sorted fetal liver cells at E13.5 are GFP⁺. The arithmetic mean of three independent experiments ±s.d. is shown.