Fig. 7. Rspo2^Tg/Tg lungs exhibit reduced Wnt signaling. The Rspo2^Tg allele was crossed into the Wnt signaling reporter TOPGAL line and β-galactosidase activity examined in whole-mount lung specimens at E11.5: Rspo2^+/+ (A), Rspo2^Tg/Tg (B,C,E). A, B and E are littermates. White arrows indicate high levels of Wnt signaling activity in the distal tips of wild-type lungs compared with the lower level in the distal tips of mutants (arrowheads). (D) Quantitation of β-galactosidase activity in E11.5 lung buds. (F) Semi-quantitative real-time RT-PCR of E11.5 cDNA samples, indicating that Irx3 is reduced threefold. (G,H) Sox9 is expressed in a normal proximal distal pattern in Rspo2^+/+ (G) and Rspo2^Tg/Tg (H) lungs.