Developmental changes in tropoelastin mRNA levels in rat lung: evaluation by in situ hybridization

Alveolarization of the immature lung is thought to be influenced by the presence of elastic fibers that could provide structural support for developing septa. Although morphometric studies have established that alveolar septal development occurs from days 4 to 13 in the neonatal rat, the precise time period over which elastin synthesis occurs has proved difficult to determine. We have evaluated the usefulness of in situ hybridization techniques to follow tropoelastin message expression in parenchymal tissue, small vessels, and bronchioles in the developing rat lung from days 4 through 18. This method proved to be sufficiently sensitive to detect differences in rates of tropoelastin message expression from days 4 through 18 (P less than 0.0001). Peak tropoelastin message expression was observed in the small vessels on day 4 and in parenchymal tissue on days 9 through 11. Because the time course of tropoelastin message expression in small vessels differs from that in parenchymal tissue, the use of lung extracts to analyze rates of tropoelastin synthesis in the developing lung may be in error.