Figure 1: Distinct morphologic lung abnormalities in infants with TBX4 mutations.

Lungs from Infant A (A-F) showing congenital alveolar dysplasia. H&E stained section (A) shows normally developed branching bronchi and bronchioles accompanied by arteries (arrows), veins appropriately located in the interlobular septa (arrowheads), and malformed lobules comprised of variable numbers of simplified saccular airspaces (*) with bronchioles focally abutting the pleura (inset). Epithelial cell immunostaining with cytokeratin 7 (B) highlights branching conducting airways (arrows) and variable numbers of simplified saccules comprising the malformed lobules (*). Confocal immunofluorescence low (C,E) and higher power images (D,F) show aberrant lack of co-expression of the alveolar type II cell (AT2) markers NKX2.1 and ABCA3 in the atypical epithelial cells lining distal saccular airspaces (C-D) and absence of nuclear staining for the alveolar type I cell marker (AT1), HOPX (E-F). Staining for smooth muscle actin (ACTA2) is also shown. Lungs from Infant B (G-L) showing alveolar growth abnormality. H&E stained section shows deficient alveolarization with variably enlarged and simplified alveoli (inset) and subpleural cystically dilated airspaces (*). Epithelial cell immunostaining with pancytokeratin (H) highlights the focally enlarged and simplified alveolar spaces that predominant in subpleural regions (*). In contrast to Infant A, confocal immunofluorescence low (I,K) and higher power images (J, L) of the lung biopsy from Infant B show co-expression of NKX2.1 and ABCA3 as seen in normal AT2 cell differentiation (I-J) and nuclear HOPX expression indicative of AT1 cell differentiation (K-L). Original magnification: 20x (A-B, G-H); 200x (A inset, G inset); 20X objective with pixel size of 0.63 μm (C, E, I, K); 60X objective with pixel size of 0.21 μm (D, F, J, L).