| Alveoli are formed by the subdivision (septation) of the gas exchange saccules of the immature lung and other unidentified means. In rats, septation occurs between postnatal days 4 and 14; the unidentified mechanism continues until around day 40. Neither spontaneous compensatory alveolar formation of impaired septation nor regeneration of alveoli following destruction by disease occurs. However, all trans retinoic acid (ATRA) induces alveolar regeneration in adult rats with elastase-induced pulmonary emphysema (Nature Medicine 1997, 3:675). In our search to understand the molecular mechanism of alveolar formation the following hypothesis was established: septation always occurs via the same mechanism and same set of genes. Using animal models of septation, the following experimental approach was designed: (1) differential display to identify transcripts differentially expressed during septation; (2) confirmation of differential expression; (3) determination of expression in other models of septation; (4) cloning of the full-length cDNA; and (5) establishing ATRA as a regulator of the gene(s). Differential display of emphysematous rats ATRA-treated identified a 161 by cDNA, C1, whose upregulation was confirmed by RNase protection assay. The increase of C1 RNA by ATRA was lung-specific. During postnatal development, C1 RNA expression peaked twice: at gestational day 22 and again at postnatal day 8 before decreasing by day 14 to a level also found >50. In the neonate, ATRA upregulated C1 RNA expression, and dexamethasone, an inhibitor of septation, blunted the expression of C1. The concomitant administration of ATRA and dexamethasone resulted in rescue; C1 RNA levels were returned to the level of control diluent-treated animals. The cDNA was extended an additional 1973 by 5′ using SMART RACE (Rapid Amplification of cDNA Ends) and a nucleotide database search suggested C1 was a novel gene. Computer-generated translation of the nucleotide sequence indicated C1 would encode a polypeptide of 58 amino acids. In summary, the experiments performed in this thesis led to the identification of a novel gene, C1, whose RNA is upregulated at times when spontaneous or induced septation occur and downregulated during inhibition of septation. C1 may represent a molecule important in the formation of alveoli. |
