Fig. 2

Histological examination of Col4a1 ^+/Δex41. a, b Hematoxylin and eosin staining of normal and Col4a1 mutant lungs at E16.5 shows typical pseudoglandular structures. c At E18.5, normal lungs are composed of dilated distal tubules surrounded by relatively thin mesenchyme with arising primary septa, which are characteristic of the saccular stage. d Col4a1 ^+/Δex41 lungs have fewer dilated tubules, thick interstitium, and fewer and shorter primary septa. e Normal alveolar and development at P6, showing secondary septa. f P6 Col4a1 ^+/Δex41 have fewer fully developed alveoli. g At P30, normal lungs show thin secondary septa and interstitium. h Col4a1 ^+/Δex41 mutant lungs in surviving mice display much fewer secondary septa and a thicker interstitium. i Toluidine blue staining of Col4a1 ^+/+ semi-thin lung sections show capillaries (arrowheads). j In Col4a1 ^+/Δex41, the septa have an increase of interstitial blood capillaries (arrowhead) and cells with lipid content (arrows). k–n Electron microscopy of normal and Col4a1 ^+/Δex41 lung septa at P30. m Col4a1 ^+/Δex41 septum showing capillaries (arrowheads), type II pneumocytes (arrows) and elastin fibers (red arrows). Scale bars = 200 μm in a–d, 35 μm in i, j, and 6 μm in k, l