A second insulin gene in fish genomes.

The recent characterization of diverse vertebrate genomes has revealed the importance of gene duplication in vertebrate evolution. Evidence suggests that a genome duplication event occurred on the lineage leading to teleost fish-species that are often used to understand human biology. The existence of a genome duplication event complicates the use of fish as a model for human diseases as there are often two fish homologues for a single copy human gene. Often the second homologue has not been recognized. Our searches of the near complete zebrafish and fugu fish genomes indicate that both species have two insulin genes. Phylogenetic analysis indicates that the two genes are likely the product of the fish-specific genome duplication. The maintenance of two insulin genes within the fish suggests that the two genes have different functions. Thus the well-characterized insulin genes in some fish species may not be complete homologues of the human insulin gene.