Fusion of -like transposons and herpesviruses occurs frequently in teleosts.

BACKGROUND

Endogenous viral elements play important roles in eukaryotic evolution by giving rise to genetic novelties. Herpesviruses are a large family of DNA viruses, most of which do not have the ability to endogenize into host genomes. Recently, we identified a novel type of endogenous herpesvirus, which we named "", from the medaka () genome, in which the herpesvirus is fused with a -like DNA transposon, forming a novel mobile element. is a unique herpesvirus that retains its viral genes intact and has acquired the endogenized lifestyle by hijacking the transposon system. However, it is unclear how this novel element evolved in the teleost lineage and whether fusion of two mobile elements is a general phenomenon in vertebrates.

RESULTS

Here we performed a comprehensive genomic survey searching for -like viruses in publicly available genome data and found that they are widely distributed in teleosts, forming a clade within . Importantly, at least half of the identified -like viruses contain -like transposase genes, suggesting the generality of the transposon-herpesvirus fusion in teleosts. Phylogenetic tree topologies between the -like transposase gene and herpesvirus-like genes are nearly identical, supporting the idea of a long-term evolutionary relationship between them.

CONCLUSION

We propose that -like elements and -like viruses have co-existed for a long time, and that fusion of the two mobile genetic elements occurred frequently in teleosts.