Fig. 6. Fate mapping of cardiac NCCs in Alk2/Wnt1-Cre mutants. Embryos carrying the R26 Cre reporter were stained for the ß-galactosidase activity at E10.5 (A-C) and at E11.5 (D-F) to identify cells derived from the NC (A,D, controls; B,C and E,F, Alk2 mutants). Arrows indicate the OFT. In the control, blue staining is more proximal than in the mutant. Frontal sections through the conotruncal region of control (G-I) and Alk2 mutant (J-L) at E11.5. Level and orientation of each section has been indicated in D and E. In control sections, arrows indicate positively staining NC-derived cells that contribute to formation of conotruncal cushions. In mutants, arrows highlight near-complete absence of NC-derived cells in the more proximal region (level a) and significant reduction of positively staining cells in more distal regions (levels b and c). M-O, the whole-mount staining of the control (M) and Alk2 mutant (N,O) hearts at E13. Both the aorta and pulmonary trunk stain positive for cells derived from NCCs (blue staining) in the control (M). In Alk2 mutants, the persistent truncus arteriosus shows positively staining cells, albeit with variable intensity (N,O). Scale bars: 200 µm in G-L.