Conserved Keratin Gene Clusters In Ancient Fish: An Evolutionary Seed For Terrestrial Adaptation
Type I and type II keratins are subgroups of intermediate filament proteins that provide toughness to the epidermis and protect it from water loss. In terrestrial vertebrates, the keratin genes form two major clusters, clusters 1 and 2, each of which is dominated by type I and II keratin genes. By contrast, such clusters are not observed in teleost fish. Although the diversification of keratins is believed to have made a substantial contribution to terrestrial adaptation, its evolutionary process has not been clarified. Here, we performed a comprehensive genomic survey of the keratin genes of a broad range of vertebrates. As a result, we found that ancient fish lineages such as elephant shark, reedfish, spotted gar, and coelacanth share both keratin gene clusters. We also discovered an expansion of keratin genes that form a novel subcluster in reedfish. Syntenic and phylogenetic analyses revealed that two pairs of
Two major keratin clusters are conserved from sharks to terrestrial vertebrates.
Adult epidermis-specific keratins in amphibians stem from the two major clusters.
A novel keratin gene subcluster was found in reedfish.
Functional diversification signatures were found in reedfish and amphibian keratins.