GFP expression in Flk1⁺/GFP embryo. (A) Schematic representation of GFP knock-in allele. (B) The effect of deletion of the PGK-neo cassette in Flk1⁺/GFP neo-in and Flk1⁺/GFP neo-out embryos at E8.5. (C) GFP expression during LS-OB stage. (D) GFP expression at the late bud (LB) stage. (E) GFP expression at 8.5 dpc. (F) GFP expression at 10.5 dpc; ex indicates extraembryonic region; em, embryonic region; BI, blood island; and DA, dorsal aorta.