Conditional recombination reveals distinct subsets of epithelial cells in trachea, bronchi, and alveoli.

To identify relationships amongst tracheal and alveolar epithelial cells during lung development, we used conditional systems controlled by the rat CCSP and human SFTPC gene promoters to express Cre-recombinase in the developing mouse lung, thereby permanently labeling cells by expression of alkaline phosphatase or green fluorescent protein. When controlled by the rat CCSP promoter, continuous exposure of the fetus to doxycycline caused widespread recombination in conducting airway epithelial cells, including cells of the trachea, bronchi, and bronchioles before birth, and in both conducting and peripheral airways after birth. Neuroepithelial cells, identified by CGRP staining, were never labeled.

Increased expression of thyroid transcription factor-1 (TTF-1) in respiratory epithelial cells inhibits alveolarization and causes pulmonary inflammation.

Thyroid transcription factor-1 (TTF-1), a member of the Nkx2 family of homeodomain-containing transcription factors, is expressed in the epithelium of the lung. TTF-1 is a critical regulator of transcription for the surfactant proteins (SP) A, B, and C and is essential for lung morphogenesis. Sites and levels of TTF-1 expression vary during lung morphogenesis and following injury.