Fig. 7. Analysis of pulmonary vein morphology in Pitx2 c^-/- embryos and fate mapping with Pitx2 abc^creneo allele. (A-D) Scanning electron microscopy of corrosion casts of wild type (A,C) and the Pitx2 c^-/- (B,D) embryos. In wild-type embryos, the LSCV drains into the coronary sinus, guarded by the valve of the coronary sinus. The RSCV and ICV are connected to right atrium by thin strips at the valves. The left and right pulmonary veins join to a common pulmonary vein that drains into left atrium. White stars indicate left atrium, just superior to entry of common pulmonary vein (A,C). By contrast, in Pitx2 c^-/- embryos, all these veins converge into a common, medial venous sinus (B,D). Stars indicate inferior caval vein, just inferior to entry of pulmonary vein and the left superior caval vein. This embryo also has bilateral inferior caval veins. (E-H) Fate mapping with Pitx2 abc^creneo allele. Transverse sections through lungs of 16.5 wild-type (E) and Pitx2 mutant (F). lacZ positive cells marking Pitx2 daughter cells are present in wild type but are severely reduced in mutant (arrows). (G,H) Whole mounts of 16.5 dpc lungs from wild type (G) and Pitx2 mutants (H), showing lacZ-positive cells in pulmonary veins of wild type and reduced staining in mutant (arrows).