Fig. 2. The Wnt7b^lacZ allele recapitulates endogenous Wnt7b expression. lacZ staining of E12.5 (A-J,L,N,O) and E14.5 (K,M) embryos reveals that the Wnt7b^lacZ allele drives expression of the lacZ gene in a pattern identical to the endogenous mouse Wnt7b gene. ß-galactosidase expression is observed in the future cerebral cortex (B, yellow arrowhead), in a narrow band across the roof of the midbrain (B, black arrowhead) and the medulla oblongata (C, arrowheads). Histological sections of E12.5 embryos reveals expression in the ependymal (D,L, arrow) and the outer marginal layers (D,L, arrowhead) of the neural tube and the corpus striatum (cs), pons (pons) and the medulla oblongata (mo) (H,I). ß-galactosidase expression is observed in the interdigital mesenchyme of the forming limb bud (E, arrowhead) but is excluded from the apical ridge (F, arrowhead). High levels of ß-galactosidase expression are observed in the developing lung (G, lu) and trachea, and are restricted to the airway epithelium (J, arrowheads indicate lung epithelium, arrow indicates trachea; K, arrowheads). By E14.5, expression in the airway epithelium is restricted to the distal regions (K, compare white arrowheads with black arrowhead). ß-Galactosidase expression is observed in the developing skin at E14.5 (M), in the metanephric tubules of the developing kidney (N, arrowheads), and in the epithelium of the bile duct (O, arrowhead). Scale bars: 1.5 mm in G; 750 µm in H; 500 µm in I; 350 µm in J; 250 µm in K,L,O; 125 µm in N; 75 µm in M.