Fig. 7
Abnormal alveolar tropoelastin and elastin fiber accumulation. a At E18.5, tropoelastin expression in the developing septa in normal lungs is detected at the tips (arrow) and throughout the interstitium (arrowhead). c By contrast, in Col4a1 +/Δex41 lungs, tropoelastin expression shows a patchy interstitial accumulation (arrowhead) with abnormal expression in the maldeveloped primary septa (arrow). b Hart’s staining marks the lung elastin fibers at E18.5. Control lungs show well-defined thin elastin fibers (black) in the saccule spaces (arrowhead) and at the tip of developing primary septa (arrow). d Saccule elastin fibers in Col4a1 +/Δex41 mutants are interstitial and tortuous or fragmented at E18.5 (arrows). e Real-time PCR for Tropoelastin. The expression of Tropoelastin is decreased in Col4a1 +/Δex41 (Wilcoxon rank-sum test P < 0.07). Gapdh was used as a normalizer. f, g At P6, tropoelastin is found at the tips of developing septa (arrow) and in elastin fibers (arrow). h, i Mutants show a decrease of tropoelastin (arrow) and abnormal accumulation of elastin fibers at the septa tips (arrow). j At P30, while tropoelastin expression is localized at the tip of secondary septa marking the myofibroblasts (arrow) and in the septal interstitium as a thin line (arrowhead). k In Col4a1 +/Δex41 mutants, tropoelastin is localized diffusely throughout the stumpy septal tips and in the interstitium of the secondary septa in a patchy pattern (arrow and arrowhead). l Tie2-Cre; Col4a1 +/Flex41 lungs show defined expression of tropoelastin at the tip of the lung septa as do normal lungs, but the septa are reduced in size (arrow). In addition, the less severe Tie2-Cre; Col4a1 +/Flex41 mutants show no tropoelastin localization in the interstitium (arrowhead). m After alveolarization, elastin fibers build up on the tip of secondary septa (arrow). n In Col4a1 +/Δex41, excessive accumulation of elongated elastin fibers is apparent (arrows). o In Tie2-Cre; Col4a1 +/Flex41 elastin fibers are not elongated or ectopic in the interstitium (arrow) when compared to the abnormal elongation apparent in Col4a1 +/Δex41 n. Scale bars = 100 μm in a–d and f–l