Thyroid transcription factor-1, hepatocyte nuclear factor-3beta and surfactant protein A and B in the developing chick lung.

Expression of surfactant proteins SP-A, SP-B and the transcription factors TTF-1 and HNF-3beta was identified by immunohistochemistry in the developing chicken. SP-B, a small hydrophobic peptide critical for lung function and surfactant homeostasis in mammals, was detected in the epithelial cells of parabronchi in embryonic chicken lung from the 15th day of incubation, prior to the onset of the breathing movements and was expressed at high levels in the posthatching chicken lung. SP-A, an abundant surfactant protein involved in innate defence of the mammalian lung, was detected in the chick embryo in subsets of epithelial cells in the mesobronchus, starting from d 15 and was detected in the posthatching chicken lung. The transcription factors hepatocyte nuclear factor 3beta (HNF-3beta) and thyroid transcription factor-1 (TTF-1), both regulators epithelial cell differentiation and gene expression in mammalian species, were detected at the onset of lung bud formation (d 4 of incubation) and throughout lung development. Abundant nuclear expression was detected in nuclei of respiratory epithelial cells of developing bronchial tubules for both transcription factors. In contrast to the surfactant proteins, expression of both TTF-1 and HNF-3beta decreased markedly in posthatching chicken lung. The expression of SP-A and SP-B in chick lung demonstrates the conservation of surfactant proteins in vertebrates. The temporospatial pattern of TTF-1 and HNF-3beta overlaps with that of SP-A and SP-B, supporting their potential roles in chick lung development and demonstrating the conservation of regulatory mechanisms contributing to gene expression in respiratory epithelial cells in vertebrates.