Fig. 3. Wnt7b^lacZ–/– neonates die quickly after birth, because of respiratory distress, and display lung hypoplasia. Examination of neonates during birth revealed that a population of them did not turn pink but were cyanotic and gasped for air, quickly succumbing within minutes (A versus B). Examination of wild-type lungs showed that they were expanded by inhalation of air (C), which can be observed as air bubbles in the distal regions of the lung (D). The Wnt7b^lacZ–/– lungs were collapsed and hypoplastic, lacking visible air in the lung periphery (E). Histology of these lungs revealed the collapsed nature of the airways in Wnt7b^lacZ–/– mice and the overall smaller size of the lungs (F,G). Lungs from E12.5 Wnt7b^lacZ–/– and Wnt7b^lacZ+/– embryos were removed and stained for ß-galactosidase expression to reveal the extent of lung hypoplasia (H). Cross-sections from E14.5 wild-type and Wnt7b^lacZ–/– embryos further reveals the extent of lung hypoplasia (I,J).