Long-Standing Activity with Characteristic Genomic Insertion Signatures in Reptilian Bov-B LINEs and Associated Sauria SINEs.

Although long interspersed nuclear elements (LINEs) and short interspersed nuclear elements (SINEs) are typically passed down to descendants as part of the genome, the Bov-B LINE was likely horizontally transferred from a snake to the ancestor of ruminants. Plant RTE-clade LINEs and their associated SINEs possess a genomic insertion signature different from that of mammalian L1 LINEs. However, the reason for the increased frequency of horizontal transfer in RTE-clade LINEs such as Bov-B relative to that in L1-clade LINEs has not yet been clarified. In this study, we identified family members of the reptilian Bov-B LINE and associated Sauria SINE across various squamate species to determine the amplification timing of the LINE. The findings revealed that the LINE may be over 180 million years old. Moreover, profiling of target site duplications showed that a characteristic genomic insertion signature of the LINE and SINE closely resembled the signature of the plant RTE-clade LINEs. We conducted phylogenetic analyses of RTE-clade LINEs with characteristic genomic insertion signatures and estimated their divergence times. The findings suggest an ancient origin (over 411 MYA) of the retrotranspositional mechanism underlying this signature; however, a complex evolutionary trajectory of LINEs across species warrants further investigation.