The Eng +7 and Eng +9 regions target blood progenitors in developing embryos. (A) Schematic diagram of the human ENG locus. The exons and enhancer fragments are drawn to scale and are represented as black and green rectangles, respectively. (B) F₀ transgenic embryos generated using various ENG fragments subcloned into ENG (P) promoter lacZ constructs. (i-vi) representative X-Gal stained whole-mount E11.5 embryos. (vii-xii) Sections (magnified ×20) through the hearts of corresponding embryos; (vii) no endocardial staining; (viii-xii) variable degrees of endocardial staining. (xiii-xviii) Sections (magnified ×20; insets ×100) through the livers of corresponding embryos; (xiii) no staining in FL cells; (xiv) staining of flat endothelial cells (); (xv-xviii) staining of round hematopoietic cells (). A table summarizing the number of X-Gal stained F₀ transgenic embryos that showed staining in the heart and/or liver out of the number of transgenic embryos generated with each construct is also shown. (C) Analyses of E11.5 embryos from a litter of −8/P/lacZ/+7/+9 (L1091) x WT crosses. (i) Tissue sections from X-Gal stained embryos showing reporter activity in yolk sac and dorsal aorta endothelium and blood cells in the placenta and fetal liver (magnified ×20, ×40, ×100, respectively). (ii) A table summarizing results from in vitro colony-forming assays using sorted cell fractions from FDG treated E11.5 FLs. (iii-v) Flow cytometry of FDG treated nontransgenic and transgenic E11.5 FLs from a litter of −8/P/lacZ/+7/+9 (L1091) x WT crosses. The transgene targets 3% to 4% of FL cells; the majority of which are (iii) endoglin positive, (iv) c-Kit positive, (v) endoglin and c-Kit dual positive. BFU-E, burst-forming unit-erythroid; CFU-G, colony-forming unit-granulocyte; CFU-GEMM, colony-forming unit granulocyte/erythroid/macrophage/megakaryocyte.