Fetal lung development: airway pressure enhances the expression of developmental genes

The mechanisms by which static airway pressures in the developing lung affect development are unknown. The in vitro murine fetal lung model with airway ligation reproduces the phenomenon of intraluminal airway pressure in developing lungs. We have applied the technique of differential display of mRNAs to fetal murine lungs that were maintained in organ culture with and without tracheal ligation. The goal of this investigation was to identify genes that are induced or enhanced by airway pressure during lung development.

Fetuses were harvested from CD-1 mice on gestational day (Gd) 14. The lungs were removed and trachea either transected or ligated and organ cultured for 7 days. Total RNA was extracted from cultured unligated controls and ligated lungs. Reverse transcription (RT) of the purified total RNA from each pooled sample was performed with anchor primer H-T11G or C and one of 24 arbitrary primers followed by polymerase chain reaction (PCR) of the RT mixtures. PCR products were electrophoresed on a DNA sequencing gel. Differentially expressed cDNA bands of interest were cut from the dried gel. Each cDNA was then reamplified. Reamplified cDNAs were extracted, PCR amplified, cloned, and sequenced for homology to existing sequences in the GenBank database.

Sequencing identified 4 differentially expressed genes enhanced by tracheal ligation: hepatoma-derived growth factor (HDGF), ribosomal protein S24, stathmin, and parathyroid hormone (PTH).

Genes enhanced by airway pressure or tracheal ligation are mitogenic for fibroblasts, correlate with cell proliferation, regulate cell proliferation and differentiation, and may play a role in growth in distal lung and type II cell differentiation. Further work is necessary to identify the mechanisms by which these genes influence lung maturational processes.