Type I and II pneumocyte differentiation in the developing fetal chicken lung: conservation of pivotal proteins from birds to human in the struggle for life at birth.

BACKGROUND: Antenatal corticosteroids and surfactant replacement therapy have dramatically reduced mortality caused by lung disease in premature babies. Knowledge about mechanisms regulating epithelial differentiation of the respiratory membrane is limited, as are effects of pharmacological interventions. The chicken fetus is a valuable model for exploring pharmacological actions on developing organs. However, more precise information about the timing of developmental events in the chicken lung is needed for human correlation.
OBJECTIVES: Characterization of morphological development and protein expression in the respiratory membrane of the developing chicken lung to create a platform for pharmacological testing in a human context.
METHODS: Fetal chicken lungs, embryonic days (E) 7-20, were characterized by morphology and protein expression of epithelial differentiation markers. This was compared with publications on the same processes during human lung development.
RESULTS: The respiratory membranes of developing chicken and human lungs show basic similarities. In chicken, surfactant protein B is expressed in cuboidal type II epithelial cells from E17. Aquaporin 5 is expressed in the epithelium from E7 and selectively in type I pneumocytes from E17. The type I pneumocyte and endothelial marker, caveolin 1, is expressed in the endothelium from E7 to E20.
CONCLUSION: Despite phylogenetic distance, central aspects of cellular development in the chicken and human lung are similar. The fetal chicken model has important additional advantages to mammalian models, including fetal independence and short incubation, and is thus well suited for in vivo studies of lung maturation relevant to human development.