R1 CKO endocardial cells form excessive coronary plexuses by augmented coronary angiogenesis.

A, Schematic diagram and EGFP/Pecam1 double labeling illustrating that Vegf120 promotes angiogenesis by the genetically labeled ventricular endocardial cells in the Matrigel culture of E11.5 Nfatc1Cre;R26fsEGFP ventricle to form endothelial tubular networks. B, C, Images of endothelial networks developed from the cultured ventricles of the E11.5 Nfatc1Cre;R26fsEGFP (control) (B) or Nfatc1Cre;R26fsEGFP;Vegfr1f/f (R1 CKO) embryos (C) showing excessive endothelial tube formation (arrows) by the R1 CKO endocardial cells. D, E, Images of E12.5 ventricular explants showing that endothelial tube formation by the endocardial cells are greatly reduced in both control (D) and R1 CKO (E) hearts, although R1 CKO ventricles still form more endothelial tubes. F, Statistical analysis showing that angiogenic branching occurs mainly at E11.5 and the process is reduced significantly at E12.5. Of note, there is significantly increased endothelial branching by the R1 CKO endocardial cells at E11.5. n  = 5 ventricular explants per group, *p<0.01, error bars = SD.