Identification of a functional transposase of the <i>Tol2</i> element, an <i>Ac</i> -like element from the Japanese medaka fish, and its transposition in the zebrafish germ lineage

<jats:p> The <jats:italic>Tol2</jats:italic> element of the medaka fish <jats:italic>Oryzias latipes</jats:italic> belongs to the hAT family of transposons ( <jats:italic>hobo</jats:italic> / <jats:italic>Ac</jats:italic> / <jats:italic>Tam3</jats:italic> ). We report here identification of a functional transposase of <jats:italic>Tol2</jats:italic> that is capable of catalyzing its transposition in the germ line of zebrafish <jats:italic>Danio rerio</jats:italic> . A transcript produced from <jats:italic>Tol2</jats:italic> encodes a putative transposase. Zebrafish fertilized eggs were coinjected with mRNA transcribed <jats:italic>in vitro</jats:italic> , using cDNA of the <jats:italic>Tol2</jats:italic> transcript as a template and a plasmid DNA harboring a mutant <jats:italic>Tol2</jats:italic> , which had a deletion in the putative transposase gene but retained necessary cis sequences. The injected fish were raised to adulthood and mated to noninjected fish, and genomic DNA of the progeny fish were analyzed by PCR and Southern hybridization. Half of F <jats:sub>1</jats:sub> fish obtained from one of eight injected fish contained the <jats:italic>Tol2</jats:italic> DNA in their genomes but not the vector portion. Among these F <jats:sub>1</jats:sub> fish, <jats:italic>Tol2</jats:italic> insertions at four different loci were identified, and some F <jats:sub>1</jats:sub> fish carried two or three different <jats:italic>Tol2</jats:italic> insertions, indicating that the germ line of the founder fish is highly mosaic. Sequencing analyses revealed that, in all cases, <jats:italic>Tol2</jats:italic> was surrounded by zebrafish genomic sequences, and an 8-bp duplication was created at the target site, indicating that <jats:italic>Tol2</jats:italic> was integrated in the zebrafish genome through transposition. This study identifies an autonomous member of a DNA-based transposable element from a vertebrate genome. The <jats:italic>Tol2</jats:italic> transposon system should thus be used to develop novel transgenesis and insertional mutagenesis methods in zebrafish and possibly in other fishes. </jats:p>