Fig. 3. (A-D) Foxa2 whole-mount in situ hybridization of E11.5 (A,B) and E12.5 (C,D) Foxf1^+/- (A,C) and wild-type (B,D) lungs. Primary epithelial branches of the right lung are formed normally at E11.5 in the mutant, although with a tendency of the buds to be wider proximally and less well defined (A). At E12.5, growth of the lungs and epithelial branching are retarded in mutant embryos (C) compared with wild type (D). The mesenchyme surrounding the accessory lobe epithelial bud of the mutant right lung remains fused with that of the caudal lobe (C; arrowhead), while a separate accessory lobe has already formed in wild-type embryos (D). Ac, accessory lobe; Ca, caudal lobe; Cr, cranial lobe; LL, left lung; Me, medial lobe.