NGUYEN, L*; LECLAIR, E.E.: Ontogenetic expression of plunc, a mouse marker for selected derivatives of the pharyngeal epithelium.

In mammalian development the lung and thymus both form from local expansions of the embryonic gut tube. The thymus arises from ventral elongations of the third pharyngeal pouch, while the lung tree starts as a ventral outpouching of the foregut. Although the respiratory passages function in breathing and the thymus in the maturation of T-cells, both these organs express plunc, a novel secreted protein, in an unusual pattern of epithelial cells. In situ studies show that plunc is expressed discontinuously in mouse nasal epithelium starting at embryonic day 14 and continuing into adulthood. Plunc expression in the lungs begins between day 18 and birth and is present in the entire lining of the trachea and the large bronchial passages. plunc also appears in the embryonic mouse thymus on day 14, with segmental staining of the cells surrounding the larger medullary venules. Although no function has been proposed for plunc, similar sequences have recently been cloned from humans, rats and cows, suggesting an evolutionary conserved ontogenetic expression at least within mammals. In support of this we show that human tracheobronchial tissue expresses the human homolog hplunc in a manner similar to that observed in mice. No sequences homologous to plunc are present in the genomes of Saccharomyces, C. elegans, or Drosophila, indicating that this gene may play a role in the immune and/or respiratory maturation of “higher” animals. We are now assessing this role by colocalizing plunc with lung surfactant proteins and markers of the thymic epithelium, and by evaluating the behavior of overexpressed plunc in primary tracheobronchial cells in vitro. (Supported by the DePaul University Research Council)