Ontogeny of Mia1 expression in the developing lung. Whole mount in situ hybridization (ISH) shows that Mia1 is expressed in lung distal epithelium on days E10.5 (A), E11.5 (B), and E12.5 (C), but is not detected in the tracheal epithelium. Epithelial expression continues on day E13.5 (D), but signal is also present in incipient tracheal cartilage (arrowheads). Panels A–D are at the same magnification; bar = 590 μm. Tissue section ISH shows that Mia1 is expressed in the distal but not proximal (arrows) epithelium on days E14.5 (E, F) and E15.5 (G, H). On day E16.5 the expression pattern changes, and only the most distal epithelium is positive for Mia1 (I,J). On day E18.5 signal for Mia1 is seen in the proximal epithelium (K,L), a pattern that continues on postnatal day 1 (M,N). Mia1 is essentially undetectable in the adult lung (O,P). Panels E–P are at the same magnification; bar = 100 μm.