Figure 2.

A multipotent epithelial progenitor cell population is localized within the distal epithelial buds throughout lung development. (A) Confocal image of Embryonic Day 14.5 (E14.5) FoxJ1-GFP lung. E-cadherin (blue) labels the epithelium. Progenitor cells (Sox9⁺, red) are located at the budding tips of the epithelium. As the lung branches and cells exit the distal tips, they turn off Sox9 and other distal epithelium-specific genes, become committed to a specific lineage, and begin to differentiate. Differentiating cells (in this example, green fluorescent protein [GFP⁺] ciliated cells; green) are located proximally to the tips. Bar = 50 μm. (B, C) The conducting airways are laid down between E10 and E16 and the alveoli between E17 and E18. A multipotent progenitor population is located at the distal epithelial tips throughout lung development and therefore must transition from generating conducting airway cells to generating alveolar cells. There are several possible mechanisms by which this may occur. (B) Progenitors are multipotent throughout lung development and the fate of their progeny is completely dependent on extrinsic signaling. (C) There is only one population of progenitor cells, but its competence to give rise to different cell types changes over the course of development.