The lung cell type enriched transcriptome
The lung is a respiratory organ responsible for gaseous exchange between air and blood. The lung contains many branching airways, or bronchioles, which end in small cup shaped structures called alveoli, where gaseous exchange occurs. These many branching airways give the lung a massive surface area over which gaseous exchange can take place.
2422 genes were predicted to have cell type specificity in the lung.
Lung cell type enriched transcriptome: Summary
Genes with predicted cell type specificity within lung are detailed in Table 1. Identified genes are subdivided into 3 specificity categories, based on the difference between the enrichment score in the corresponding cell type, compared to the other cell types profiled in the tissue (see Methods Summary page for details):
Lung cell type enriched transcriptome: Illustrative examples
Respiratory ciliated cells
Ciliated cells are epithelial cells that line the bronchi and bronchioles. Their luminal surface is covered in motile cilia, which beat constantly and serve to move inhaled dust or microbes that are trapped in the sticky mucus coating of the lung towards the esophagus for digestion and disposal. Genes classified as having specificity in ciliated cells include Dynein axonemal intermediate chain 1 (DNAI1), which forms part of the dynein complex of the respiratory cilia, as well as the Armadillo Repeat Containing 3 (ARMC3) gene.
Mitotic cells are found in many tissues, and are responsible for cell renewal to replace aging, damaged or dying cells. In the bronchus, cells at the base of the ciliated epithelial layer divide to replace damaged cells from the epithelial surface, in lung tissue the cell renewal required to heal after injury is thought to involve reprogramming of alveolar type II cells. Genes classified as having specificity in mitotic cells include centromere protein F (CENPF), essential for chromosome segregation during mitosis, as well as the apoptotic inhibitor Survivin (BIRC5).
Alveolar type I cells
Alveolar type I cells are thin epithelial cells that line the walls of the alveoli and allow gaseous exchange between the air and the blood. Genes classified as having specificity in type I alveolar cells include Sciellin (SCEL), thought to regulate protein assembly in stratified epithelia, as well as LMO7, thought to be involved in protein-protein interactions.
Alveolar type II cells
Alveolar type II cells are smaller than type I cells, and are primarily responsible for the secretion of surfactant, a film of phospholipids and proteins that coat the inside of the alveoli, both assisting in gaseous exchange and lowering surface tension, preventing the alveoli from collapsing. Genes classified as having specificity in type II alveolar cells include surfactant protein C (SFTPC),a hydrophobic protein essential for surfactant function, as well as the RAP1 GTPase activating protein RAP1GAP.