Leptin integrates vertebrate evolution: From oxygen to the blood–gas barrier

The following are the proceedings of a symposium held at the Second International Congress for Respiratory Science in Bad Honnef, Germany. The goals of the symposium were to delineate the blood–gas barrier phenotype across vertebrate species; to delineate the interrelationship between the evolution of the blood–gas barrier, locomotion and metabolism; to introduce the selection pressures for the evolution of the surfactant system as a key to understanding the physiology of the blood–gas barrier; to introduce the lung lipofibroblast and its product, leptin, which coordinately regulates pulmonary surfactant, type IV collagen in the basement membrane and host defense, as the cell-molecular site of selection pressure for the blood–gas barrier; to drill down to the gene regulatory network(s) involved in leptin signaling and the blood–gas barrier phenotype; to extend the relationship between leptin and the blood–gas barrier to diving mammals.