Genome profiling of mouse pulmonary epithelial type II cells

Pulmonary alveoli contain two distinct populations of epithelial cells. Type II cells produce pulmonary surfactant lipids and surfactant-associated proteins (SP) required for maintaining alveolar surface tension at the air-liquid interface and host defense against respiratory pathogens. Type II cells are also progenitors for epithelial type I cells, a terminally differentiated elongated cell that covers microvascular endothelial cells and participates in gas exchange. Despite some indirect evidence, it is unknown whether subpopulations of type II cells exist. We created a line of transgenic mice expressing enhanced green fluorescent protein (EGFP) under control of the human SP-C promoter. Expression of EGFP may define a subpopulation of type II cells because it is 1) expressed in approximately 10% of type II cells, 2) appears much later in embryonic development than SP-C, and 3) selectively proliferates in mice infected with influenza A virus. To determine whether EGFP defines a unique subpopulation of type II cells, RNA was isolated from EGFP-positive and negative type II cells and hybridized to affymetrix arrays. Of the genes detected in EGFP-positive cells, most were equally detected in EGFP-negative cells. However, approximately 350 genes were selectively elevated 5-fold in EGFP-positive cells and 1500 genes selectively expressed by EGFP-negative cells. These findings suggest EGFP defines a subpopulation of type II epithelial cells in this line of transgenic mice.

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