The hAT transposon-like sequence homologous to Japanese medaka Tol2 was found in the European lamprey genome.

Here we report novel hAT transposon-like sequences from the European lampreys, Lampetra fluviatilis and L. planeri, which are highly homologous to the Japanese medaka Tol2 element and were termed Tel2 (transposable element in European lampreys, Tol2-related). The copy number was estimated to be approximately 20-30 per genome, although almost all copies are disrupted. Synteny analysis suggested that the Tel2 element emerged in the genome of the common ancestor of L. fluviatilis and L. planeri; subsequently, its copy number increased and most copies became disrupted. Three representative copies that include both terminal inverted repeats and an internal region without long indel mutations were identified in the two species. None of the copies include an internal inverted repeat, which is a characteristic of Tol2 element. The possibility of current transposition activity could not be assessed because the complete coding sequence for an active transposase was not isolated. The mutation rate of the Tel2 sequence in the presumed pseudogene for the transposase, compared to Tol2 element, was lower than that in the conserved orthologous gene between medaka and the lampreys. These findings suggest that Tel2 elements were recently introduced into the lamprey genomes, derived from an origin other than that of the teleost element. Previously, the distribution of Tol2-homologous hAT transposons was limited to Asian ray-finned fishes. In this study, we identified the novel element Tel2 in European jawless fish, which supports our hypothesis that this transposon family has influenced vertebrate evolution across various taxonomic groups.