Erythroid-specific Vegf expression modulation. (A) Strategy used to conditionally express the Vegf₁₆₄ isoform from the ROSA26 locus or to delete all vascular endothelial growth factor (Vegf) isoforms specifically in the erythroid lineage. (B) ROSA26-LacZ reporter analysis of whole-mount X-gal stained embryonic day E8.5 embryo and sections from X-Gal stained blood island of E10.5 yolk sac (magnification: top right panel, 200×; bottom right panel, 400×) showing X-gal staining limited to circulating erythroid-lineage cells. (C) Relative Vegf mRNA levels measured by quantitative reverse-transcription–polymerase chain reaction (qRT-PCR) in E10.5 yolk sacs. (D) Vegf protein levels measured by enzyme-linked immunosorbent assay (ELISA) in E10.5 yolk sac. Bars represent mean ± SEM; *P < .05, ***P < .001. (E) Constitutive erythroid Vegf overexpression in +Vegf164^Eryth mice leads to heart edema (arrow) at E10.5. (F) Embryonic phenotypes of erythroid-specific VEGF164 expression modulation. Control embryo (left), Vegf^ΔEpoR-iCre embryo (middle), +VEGF164^Eryth embryo (right). Erythroid Vegf overexpression leads to red blood cell (RBC) deficiency in yolk sacs by E10.5 compared with control and VEGF^ΔEpoR-iCre embryos (black arrows). Sections of E10.5 yolk sac are represented and black arrows show circulating cells (magnification, 200×).