Erythroid Vegf modulates yolk sac erythropoiesis. (A) Primitive erythroid (EryP) colonies from whole E8.5 control (▭), +VEGF164^Eryth () and VEGF^ΔEpoR-iCre () embryos measured by methylcellulose assay. Results are given as percentage of control absolute number of colonies (100%). (B) Definitive erythroid colonies (BFU-E and CFU-E) from E10.5 control (▭+ - - -), +VEGF164^Eryth () and VEGF^ΔEpoR-iCre () yolk sac measured by methylcellulose assays. Cells (1 × 10⁵) were plated and results are given as percentage of control absolute number of colonies (100%). (C-D) Gata1 (C) and Gata2 (D) relative mRNA levels measured by qRT-PCR in E10.5 yolk sac. (E) Expression of Epor mRNA in E10.5 yolk sac from control, VEGF^ΔEpoRiCre, +VEGF164^Eryth, and +VEGF164/hGata2^Eryth embryos. Relative Epor mRNA levels were measured by qRT-PCR. (F) Definitive erythroid colonies (BFU-E and CFU-E) from E10.5 control (▭) and +VEGF164^Eryth () yolk sac measured by methylcellulose assays in 2 concentrations of Epo (3 and 100 U/mL). Cells (2 × 10⁵) were plated and results are given as percentage of control absolute number of colonies (100%). (G-H) Relative E10.5 yolk sac mRNA levels measured by qRT-PCR of (G) Gata1 target genes Alas2, Epb4.9, Hba and Hbb and (H) transcription factors Lmo2, PU.1, Runx1, Tal1 and Fog1. Bars in panels A through H represent mean ± SEM; *P < .05, **P < .01, ***P < .001.