Figure 1. Signaling pathway reporter activity identified distinct mesenchymal cells in the adult mouse lung.

(A–D) Axin2^CreERT2:tdT reporter mice express tdTomato throughout the lung mesenchyme. (E–H) Axin2-lineage traced cells shows that Axin2+ positive cells surrounding the airways rarely express Pdgfrα (E, black arrowhead) whereas they do express Pdgfrβ+ (F, white arrowhead). In contrast, Axin2+ cells in the alveolar region are predominantly Pdgfrα positive (E and G, white arrowheads) and generally do not express Pdgfrβ (H, black arrowhead). (I) Wnt2-expressing mesenchymal cells are only present in the alveolar compartment. (J and K) Immunostaining shows that Wnt2-derived cells are Pdgfrα+ (white arrowhead) and not Pdgfrβ+ (black arrowhead). (L) Wnt2^creERT2:R26R^tdTomato:Pdgfrα^EGFP mice reveal that the majority of Wnt2+ cells are Pdgfrα^EGFP positive. (M) Axin2^CreERT2:tdT:Pdgfrα^EGFP mice reveal Axin2-Pα double positive and Axin2-tdT single positive cells, with the Axin2-Pα cells found primarily in the alveolar region (inset). (N) Quantification of the spatial distribution of Axin2 and Pdgfrα^EGFP positive cells (left graph) and quantification of the alveolar distribution of Wnt2 mesenchymal cells (right graph). (O) Schematic showing the mesenchymal populations and their general spatial distributions. Data in N are means ± SEM. Scale bars A–K low magnification are 50 µm, high magnification are 10 µm. aw=airway, v=blood vessel, asm= airway smooth muscle, pbm= peri-bronchial mesenchyme and epi=epithelium.