Conservation of surfactant protein A: evidence for a single origin for vertebrate pulmonary surfactant

• Published in: Journal of molecular evolution 1998-02, Vol.46 (2), p.131-138
• Main Authors: Sullivan, L C, Daniels, C B, Phillips, I D, Orgeig, S, Whitsett, J A
• Format: Article
• Language: English
• Subjects: Animals; Blotting, Northern; Blotting, Western; Evolution, Molecular; Humans; Immunohistochemistry; Lung - metabolism; Proteolipids - physiology; Pulmonary Surfactant-Associated Protein A; Pulmonary Surfactant-Associated Proteins; Pulmonary Surfactants - physiology; Vertebrates
• ISSN: 0022-2844
• DOI: 10.1007/PL00006287

Surface tension is reduced at the air-liquid interface in the lung by a mixture of lipids and proteins termed pulmonary surfactant. This study is the first to provide evidence for the presence of a surfactant-specific protein (Surfactant Protein A-SP-A) in the gas-holding structures of representatives of all the major vertebrate groups. Western blot analysis demonstrated cross-reactivity between an antihuman SP-A antibody and material lavaged from lungs or swimbladders of members from all vertebrate groups. Immunocytochemistry localized this SP-A-like protein to the air spaces of lungs from the actinopterygiian fish and lungfish. Northern blot analysis indicated that regions of the mouse SP-A cDNA sequence are complementary to lung mRNA from all species examined. The presence of an SP-A-like protein and SP-A mRNA in members of all the major vertebrate groups implies that the surfactant system had a single evolutionary origin in the vertebrates. Moreover, the evolution of the surfactant system must have been a prerequisite for the evolution of airbreathing. The presence of SP-A in the goldfish swimbladder demonstrates a role for the surfactant system in an organ that is no longer used for airbreathing.