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

Yusuke Inoue, Masahiko Kumagai, Xianbo Zhang, Tomonori Saga, Deshou Wang, Akihiko Koga, Hiroyuki Takeda

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 "Teratorn", from the medaka (Oryzias latipes) genome, in which the herpesvirus is fused with apiggyBac-like DNA transposon, forming a novel mobile element.Teratornis 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. Here we performed a comprehensive genomic survey searching forTeratorn-like viruses in publicly available genome data and found that they are widely distributed in teleosts, forming a clade withinAlloherpesviridae. Importantly, at least half of the identifiedTeratorn-like viruses containpiggyBac-like transposase genes, suggesting the generality of the transposon-herpesvirus fusion in teleosts. Phylogenetic tree topologies between thepiggyBac-like transposase gene and herpesvirus-like genes are nearly identical, supporting the idea of a long-term evolutionary relationship between them. We propose thatpiggyBac-like elements andTeratorn-like viruses have co-existed for a long time, and that fusion of the two mobile genetic elements occurred frequently in teleosts.