Fig. 8. Double ablation of Fgfr1/Fgfr2 disrupts OFT cushion formation. (A) H&E staining of sagittal sections of E10.5 mouse OFTs. High-magnification views of the boxed areas in a,b representing proximal (p) and distal (d) OFT are shown in a1,a2,b1,b2. Note the reduced cellularity in both distal and proximal parts of mutant OFT cushions. (B) Compromised EMT in the Fgfr1/Fgfr2 double ablation (Fgfr1/r2^cn/Nkx) OFT endocardium. Immunostaining reveals sustained PECAM expression in mutant OFT cushion cells (a,b) and increased VEGFA expression in the mutant OFT myocardium (c,d). Insets are high-magnification views of the same section. (C) Reduced proliferation of cardiac NCCs upon Fgfr1/Fgfr2 double ablation. (a-d) Proliferating cells were labeled with anti-phosphorylated histone 3 (pH3, red), NCCs with anti-AP2⁺ antibody (green), and nuclei with To-Pro3 (blue). Triple-positive cells are indicated by arrows. (e,f) The number of AP2⁺ and triple-positive cells from four individuals (mean ±s.d.). (D) (a-f) Embryos at the 4 ss stained with the indicated antibodies and To-Pro3 demonstrate that total and proliferating ISL1⁺ cells in the SHF are reduced in the mutants. Note that only MAP kinase, but not AKT, phosphorylation is compromised in the mutants. Yellow arrows indicate proliferating ISL1⁺ cells. (g,h) Total ISL1⁺ and proliferating ISL1⁺ cell numbers in the OFT and SM (mean ±s.d.). F/F, Fgfr1/Fgfr2 double-floxed embryos; CN, Fgfr1/Fgfr2 double conditional-null mutants.