[Cloning of goldfish hAT transposon Tgf2 and its structure]

The hAT transposon family, including hobo of Drosophila, Ac of maize (Zea mays L.) and Tam3 of snapdragon (Ceratophyllum demersum L.), is proposed to be involved in transposition between genomic DNAs in "cut and paste" patterns. In 1996, a transposon of Tol2, the first autonomous transposon in vertebrate, was identified from the genome of albino medaka fish (Oryzias latipes). Since then, a new transgenic and gene trap system based on Tol2 has been developed and widely used in zebrafish. In this study, we designed gene-specific primers based on the conserved regions of amino acid sequences between medaka Tol2 and maize Ac. Meanwhile, PCR was carried out in 19 fish species or strains including goldfish. Finally, another similar hAT transposon, termed as Tgf2, was identified in the genomes from different strains of goldfish. Goldfish Tgf2 is 4720 bp in length including 4 exons and shares an identity of 97% with medaka Tol2. Distinct differences were observed in the terminal inverted repeat (TIR) and subterminal repeat (STR) regions between Tgf2 and Tol2. In addition, the internal inverted repeat (IIR) region of Tgf2 (1453 bp-2091 bp) tended to form a "+" crossing structure, rather than a stem-loop structure in medaka Tol2. The regions, including TIR, STR, and IIR, were supposed to be closely related to the transposing activities of hAT transposon family members. From these sequence differences, we may expect a probably high activity of goldfish Tgf2 in transposition and it could be further used as a tool for transgenesis and gene trap in aquaculture fish in future.