Rescue of erythropoiesis by ROSA26-based hGata2 expression. (A) Phenotypes of +Vegf164/hGata2^Eryth embryos. White arrows show RBCs in E10.5 yolk sac blood vessels. Sections of E10.5 yolk sac are represented and black arrows show circulating RBCs cells in yolk sac vasculature (magnification, 200×). (B) Vegf relative protein levels measured by ELISA in E10.5 yolk sac. (C) Primitive erythroid colonies (EryP) from E8.5 whole control (- - -), +Vegf164^Eryth (), and +Vegf164/hGata2^Eryth () embryos measured by methylcellulose assays. Results are given as percentage of control absolute number of colonies (100%). (D) Definitive erythroid colonies (BFU-E and CFU-E) from E10.5 control (▭), +VEGF164^Eryth (), and +Vegf164/hGata2^Eryth () yolk sac measured by methylcellulose assay. Cells (1 × 10⁵) were plated and results are given as percentage of control absolute number of colonies (100%). (E-G) E10.5 yolk sac relative mRNA levels measured by qRT-PCR of (E) Gata1, (F) Gata1 target genes Alas2, Epb4.9, Hba and Hbb, and (G) transcription factors LMO2, PU.1, RUNX1, TAL1, and FOG1. Bars in panels B through H represent mean ± SEM; *P < .05, **P < .01, ***P < .001.