Fig. 4.

Impaired alveolar epithelial cell differentiation/maturation in Fstl1^−/− lungs. (A) Expression of differentiation marker genes for lung epithelial cells in E18.5 embryos. (Scale bars, 50 μm.) (B) The relative expression levels of differentiation marker genes in E18.5 Fstl1^−/− lungs as determined by qRT-PCR. Data represent the mean ± SEM in triplicates. (C) Transmission EM of the lung septa of E18.5 embryos shown at low magnification (LM) and high magnification (HM). Squamous AEC-I cell in WT was closely opposite to densely stained capillary endothelial cell creating thin blood–air barrier (Upper Left). Cuboidal AEC-II cells in WT lungs contained many lamellar bodies (arrows) and apical microvilli (Lower Left). Surfactants (asterisk) were visible in the saccular spaces (Upper Left). The blood–air barrier was significantly thicker with increased numbers of undifferentiated cuboidal epithelial cells in Fstl1^−/− (Upper Right). These cells were immature with dispersed cytoplasmic glycogen and some small lamellar bodies (arrows; Lower Right). (Scale bars: Upper, 10 μm; Lower, 2 μm.) (D) Western blotting of pro–SP-C and pro–SP-B, mature SP-C, and mature SP-B proteins in extracts of whole lungs taken from WT and Fstl1^−/− embryos at E18.5.