Duplication and Divergence of Elastin in Jawed Fishes, Including Tetraploid Rainbow Trout (<em>Oncorhynchus mykiss</em>)

Background/objectives: Elastin is a highly hydrophobic extracellular matrix protein responsible for the extensibility and elastic recoil of various organs. The Windkessel effect in blood vessels dampens pressure variations during the cardiac cycle to provide continuous perfusion of tissues. Duplication of the elastin gene in teleost fish led to the neofunctionalization of the ElnB paralog, which confers the uniquely low stiffness of the bulbus arteriosus to protect the fragile gill capillaries from large pressure variations. Methods: We have examined the diversity of elastins in all major fish clades by searching for eln genes in the sequenced genomes. Results: Tetraploid salmonids have two elna genes but a single elnb, except for the tandem duplicated elnb genes in sockeye salmon and lake whitefish, while the tetraploid common carp possesses four elna and elnb genes on separate chromosomes. Rainbow trout showed strong elastin staining in the larval bulbus and ventral aorta, and elnb was highly expressed in the bulbus of juvenile and adult fish. Teleost ElnB differs from the ElnA paralog by containing considerably longer hydrophobic domains. The single elastin in cartilaginous and lobe-finned fish showed high overall hydrophobicity, and no relationship was found between the hydrophobicity levels of fish elastin and the ventral aortic blood pressure. Conclusion: The differential gene expression of teleost elna and elnb during cardiac development probably evolved together with the divergence in the genetic structure that resulted in larger hydrophobic domains of the ElnB paralog and decreases stiffness of bulbus arteriosus.