ldb1 is required for definitive fetal erythropoiesis. (A) Giemsa-stained peripheral blood from E12.5 Tie2Cre ldb^+/fl and Tie2Cre ldb^fl/Δ embryos. Bars, 50 µm. Original magnification, 400×. One representative of three experiments is shown. (B) Number of total fetal liver cells, LSK cells, LK cells, CMPs + GMPs, MEPs, and Ter119⁺ cells in E12.5 Ldb1^fl/Δ Tie2Cre and control embryos (controls consisted of littermate ldb^+/fl ± Tie2Cre and ldb^fl/Δ embryos). NS, not significant; **, P < 0.01. MEP, CMP, and GMP populations were designated as shown in C. Ter119⁺ cell counts were obtained from 39 control embryos and 9 Tie2Cre ldb^fl/Δ embryos. LSK, LK, CMP+GMP, and MEP cell counts were obtained from 32 control embryos and 12 Tie2Cre ldb^fl/Δ embryos. Values are expressed as means ± SD. (C) Lin^lo/−Sca1⁻c-kit⁺FcγR^lo/−CD34^lo/− MEPs (left), total (Ter119⁺) erythroid cells (center), and CD71^hiTer119^lo proerythroblasts (right) in E12.5 Tie2Cre ldb^fl/Δ and Tie2Cre ldb^+/fl mice. Numbers are the percentage of cells in the indicated gate. (D) Numbers of erythroid (E), non-erythroid (non-E), and total colonies in day 8 methylcellulose cultures from E12.5 control and Tie2Cre ldb^fl/Δ fetal livers. NS, not significant; *, P < 0.05; **, P < 0.01. One representative of three experiments is shown. Values are expressed as means ± SD. (E) Representative primitive erythroid (EryP), definitive erythroid (BFU-E), and myeloid (CFU-GM) colonies from Tie2Cre ldb^+/fl and Tie2Cre ldb^fl/Δ fetal livers at day 8 of culture. Bars, 200 µm. Original magnification, 50×. Images are representative of duplicate cultures from three litters.