FIG. 4.

Multiple phenotypes of the Sim2 mutant may contribute to lung atelectasis. Panels A and B show two examples of 12-h BrdU-labeled E18.5 ribs. Proliferating cells (HRP-positive brown nuclei) were found in the rib protrusions. r, rib; s, sternum. Black lines outline the protrusions. Panels C and D show two examples of the PAS-stained rib protrusions (open arrowheads) and their connections to the intercostal muscle. A solid arrowhead marks the extension off of some protrusions. Panels E (+/+) and E′ (−/−) show Mallory's staining of the pleural mesothelium basement membrane in the mutant indicating it was disrupted after the mutant had shown severe dyspnea. Before severe dyspnea, however, the mutant mesothelium appeared normal (data not shown). Higher magnification of the mesothelium (arrowhead) is to the right of each figure in black frames. Panels F (+/+) and F′ (−/−) show 2H3 (antineurofilament) staining of the innervated nerves (arrowheads) in the diaphragm (black brackets). Panels G (+/+) and G′ (−/−) show MF20 (antimyosin) staining of muscle fibers in the diaphragm (white brackets). Table 2 provides a summary of the frequency and phenotype of rib protrusions and scoliosis.