Fig. 1. The expression patterns of Wnt5a and Wnt3a are spatially and temporally distinct. (A,B) Whole-mount in situ hybridization at E7. No pulmonary expression is detected for Wnt5a (A, positive expression in esophagus, white arrow), whereas expression is detected for Wnt3a (white arrows, B). (C) Wnt5a expression is observed in the mesenchyme adjacent to the distal epithelium (black arrowheads) and weakly within the distal epithelium (arrow) at E11. (E) By E15, Wnt5a is expressed strongly in the epithelium (both luminal and budding, arrows). (G) At E20, Wnt5a is expressed in the epithelium surrounding the parabronchial lumen (black arrow), and in the proximal-most epithelium (red arrow). Interstitial vascular expression for Wnt5a is weakly present from E11 (red arrowhead, C); this expression is slightly stronger at E15 (red arrowhead, E; data not shown) but is not detectable at E20 (red arrowhead, G). (D) Wnt3a is strongly expressed in the interstitial vasculature (red arrowhead) and the distal epithelium (arrow) at E12. (F,H) Expression of Wnt3a is restricted to the budding epithelium (arrows, F) by E15, and is not detected after E16 (E20 section shown in H); red arrowheads in G and H highlight large interstitial vessels. P, parabronchi (distal airway); SB, secondary bronchi.