Figure 2. CEBPA promotes AT2 and suppresses progenitor programs in neonatal AT2 cells.

(A) Confocal images of immunostained wild type lungs showing little CEBPA expression at E14.5 and E16.5 when branch tips are dominated by SOX9 progenitors but CEBPA expression in cuboidal cells outlined with E-Cadherin (ECAD) at E18.5. (B) Confocal images of immunostained neonatal AT2-specific Cebpa mutant and littermate control lungs showing loss of CEBPA in GFP+ recombined cells (asterisk: escaper), without affecting its expression in alveolar macrophages in the airspace (AM), and reduced LAMP3. Tam, 250 ug tamoxifen. Images are representative for at least three lungs (same for subsequent immunostainings). (C) Transmission electron microscopy (TEM) images showing reduction in lamellar bodies in mutant AT2 cells without affecting their apical microvilli. Tam, 250 ug tamoxifen. See Fig. S2B for more examples and quantification. (D) Confocal images showing lineage labeled mutant AT2 cells expressing an AT1 marker HOPX and no longer cuboidal (ECAD outline) (arrowhead). (E) Confocal images showing lineage labeled mutant AT2 cells ectopically expressing a progenitor marker SOX9 and a proliferation marker KI67. (F) Quantification of (D) and (E). Each symbol represents one mouse from littermate pairs (Student’s t-test). Scale: 10 um for all except for (C) 1 um. See Table S2 for raw data.