Fig. 3. Deletion of Wnt7b results in proportionate decreases in replication of epithelial and mesenchymal tip cells. (A,A') Schematic depiction (A') of BrdU staining (brown) of E14.5 lung bud tip (A). Replication is highest in tip epithelium (A', dark yellow) and tip mesenchyme (A', dark purple) as compared with proximal epithelium (A', light yellow) and mesenchyme (A', light purple). (B,C) TUNEL staining of E14.5 wild-type (B) and Wnt7b mutant (C) mouse lungs shows no increase in apoptosis in the mutant. Dotted lines encircle epithelium. (D,E) BrdU staining of E14.5 wild-type (D) and mutant (E) lungs demonstrates decreased replication in mesenchymal and epithelial cells of the mutant. Arrowheads point to the tips. Dotted lines encircle epithelium. (F) A comparison of the percentage of BrdU-labeled cells in wild-type (gray) and mutant (white) tips demonstrates proportionate drops in epithelial and mesenchymal replication (P<0.001).