Evidence for horizontal transfer of the LTR retrotransposon mdg3, which lacks an env gene.

Horizontal (interspecific) transfer is regarded as a possible strategy for the propagation of transposable elements through evolutionary time. To date, however, conclusive evidence that transposable elements are capable of horizontal transfer from one species to another has been limited to class II or DNA-type elements. We tested the possibility of such transfer for several Drosophila melanogaster LTR retrotransposons of the gypsy group in an experiment in which D. melanogaster and D. virilis somatic cell lines were used as donor and recipient cells, respectively. This approach was chosen in light of the high levels of LTR retrotransposon amplification and expression observed in cultured D. melanogaster cells. In the course of the experiment, parallel analysis for mdg1, mdg3, 17.6, 297, 412 and B104/roo retrotransposons was performed to detect their presence in the genome of recipient cells. Only the mdg3 retrotransposon, which lacks an env gene, was found to be transmitted into recipient cells. This model, based on the use of cultured cells, is a promising system for further investigating the mechanisms of LTR retrotransposon transfer.