Munostaining of BrdU and Pecam1. The staining revealed that while the numbers of the BrdU-positive endocardial cells were comparable Homatropine (methylbromide) between the control and CKO hearts (Fig. 3A vs. 3B), the endothelial cells of the immature vessels derived from the Vegfr1-null endocardial cells were mostly BrdU-positive, forming highly proliferative coronary plexuses (Fig. 3B, 3C). In contrast, quantitative analysis also showed a 23 decrease in the number of BrdU-positive cardiomyocytes in the R1 CKO hearts (Fig. 3D). We also coimmunostained the embryonic hearts with Caspase3 and Pecam1 antibodies. The results showed that a significant portion of plexus endothelial cells in the E11.5 R1 CKO hearts was positive for Caspase3 (Fig. 3F, 3H, 3J, 3K). These observations suggest that the increased coronary plexuses in theE11.5 R1 CKO hearts are formed by overproliferation, yet these plexuses are not stable and undergo apoptosis. We next examined E14.5 hearts by Pecam1 wholemount and sectional staining and found that the coronary networks at this later stage were comparable between the control (Fig. 4A, 4C, 4E, 4G) and R1 CKO hearts (Fig. 3B, 3D, 3F, 3H). Quantitative analysis confirmed that the numbers of endothelial cells were similar between the two groups (Fig. 4I). Despite the recovery of the coronary vascular development from its early defect, the ventricular wall thickness of the R1 CKO hearts was significantly reduced (Fig. 4E, 4F, 4J). To determine whether the precocious plexuses were derived from the R1 CKO ventricular endocardial cells, we performed the cell fate-mapping analysis in the triple transgenic Nfatc1Cre ;R26fsEGFP;Vegfr1f/f embryos. The result showed that the precocious plexuses in the E11.5 R1 CKO hearts were formed by the EGFP-tagged and Pecam1-positive cells (Fig. 5A-F), thus confirmed that these immature coronary plexuses were originated from the R1 CKO endocardial cells. The fate-mapping analysis also revealed comparable coronary vasculatures formed between the control and R1 CKO hearts at E14.5 (Fig. 5G, 5H). Together, the results from these cell fate studies suggest that the endocardially-produced Vegfr1 may play two independent roles in the coronary angiogenesis and ventricular morphogenesis. In addition, the early-formed coronary plexuses in the R1 CKO hearts are likely self-eliminated through apoptosis in the later coronary development. This may explain why the early precocious coronary formation does not result in persistent coronary vascular defects.Vegfr1 Regulates Coronary AngiogenesisFigure 6. R1 CKO endocardial cells form excessive coronary plexuses by augmented coronary angiogenesis. A, Schematic diagram and EGFP/Pecam1 Z-360 site 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, 23977191 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 i.Munostaining of BrdU and Pecam1. The staining revealed that while the numbers of the BrdU-positive endocardial cells were comparable between the control and CKO hearts (Fig. 3A vs. 3B), the endothelial cells of the immature vessels derived from the Vegfr1-null endocardial cells were mostly BrdU-positive, forming highly proliferative coronary plexuses (Fig. 3B, 3C). In contrast, quantitative analysis also showed a 23 decrease in the number of BrdU-positive cardiomyocytes in the R1 CKO hearts (Fig. 3D). We also coimmunostained the embryonic hearts with Caspase3 and Pecam1 antibodies. The results showed that a significant portion of plexus endothelial cells in the E11.5 R1 CKO hearts was positive for Caspase3 (Fig. 3F, 3H, 3J, 3K). These observations suggest that the increased coronary plexuses in theE11.5 R1 CKO hearts are formed by overproliferation, yet these plexuses are not stable and undergo apoptosis. We next examined E14.5 hearts by Pecam1 wholemount and sectional staining and found that the coronary networks at this later stage were comparable between the control (Fig. 4A, 4C, 4E, 4G) and R1 CKO hearts (Fig. 3B, 3D, 3F, 3H). Quantitative analysis confirmed that the numbers of endothelial cells were similar between the two groups (Fig. 4I). Despite the recovery of the coronary vascular development from its early defect, the ventricular wall thickness of the R1 CKO hearts was significantly reduced (Fig. 4E, 4F, 4J). To determine whether the precocious plexuses were derived from the R1 CKO ventricular endocardial cells, we performed the cell fate-mapping analysis in the triple transgenic Nfatc1Cre ;R26fsEGFP;Vegfr1f/f embryos. The result showed that the precocious plexuses in the E11.5 R1 CKO hearts were formed by the EGFP-tagged and Pecam1-positive cells (Fig. 5A-F), thus confirmed that these immature coronary plexuses were originated from the R1 CKO endocardial cells. The fate-mapping analysis also revealed comparable coronary vasculatures formed between the control and R1 CKO hearts at E14.5 (Fig. 5G, 5H). Together, the results from these cell fate studies suggest that the endocardially-produced Vegfr1 may play two independent roles in the coronary angiogenesis and ventricular morphogenesis. In addition, the early-formed coronary plexuses in the R1 CKO hearts are likely self-eliminated through apoptosis in the later coronary development. This may explain why the early precocious coronary formation does not result in persistent coronary vascular defects.Vegfr1 Regulates Coronary AngiogenesisFigure 6. 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, 23977191 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 i.
