Fig. 4. Ablation of Hh signaling within CNCCs results in a single OFT due to a reduced number of CNCCs. (A,B) Wnt1-Cre-mediated ablation of Smo results in a single OFT and abnormal arch-artery patterning at E18.5 (B, arrows) compared with controls (A). (C-D') NCC-lineage trace using the R26R reporter demonstrates a reduction in the total number, as well as abnormal localization, of CNCCs within the developing OFT at E10.5 (D,D', arrows) compared with controls (C,C'). (C'',D'') Section analysis of C and D in the frontal plane reveals reduced cushion size (D'') compared with controls (C''). (E-F') Reduction of Hh signaling is detected by the Ptch1^lacZ activity shown in whole-mount (F) and sagittal (F') sections compared with controls (E,E'). In Wnt1-Cre; Smo^flox/- mutants, there is decreased activity within the pharyngeal arches (bracket, F) and dorsal to the aortic sac (arrow in F). (G,H) Constitutive activation of the Hh pathway within NCCs using Smo^OEX also results in a single OFT (H versus G). (I-L') Proximal/distal section analysis of Wnt1-Cre; Smo^OEX embryos at E10.5 (J,J') and E11.5 (L,L') reveals abnormal localization and the compaction of cells within the OFT (J,J'), and that, despite the presence of cushions, septation is not taking place (L,L') when compared with controls at E10.5 (I,I') and E11.5 (K,K'). In all panels, arrows and arrowheads mark abnormal and normal findings, respectively, in mutants as compared with control embryos. Ao, aorta; Pa, pulmonary artery; AS, aortic sac; AHF, anterior heart field; A, atrium; V, ventricle.