Generating and manipulating transgenic animals using transposable elements

Abstract

Transposable elements, or transposons, have played a significant role in the history of biological research. They have had a major influence on the structure of genomes during evolution, they can cause mutations, and their study led to the concept of so-called "selfish DNA". In addition, transposons have been manipulated as useful gene transfer vectors. While primarily restricted to use in invertebrates, prokaryotes, and plants, it is now clear that transposon technology and biology are just as relevant to the study of vertebrate species. Multiple transposons now have been shown to be active in vertebrates and they can be used for germline transgenesis, somatic cell transgenesis/gene therapy, and random germline insertional mutagenesis. The sophistication of these applications and the number of active elements are likely to increase over the next several years. This review covers the vertebrate-active retrotransposons and transposons that have been well studied and adapted for use as gene transfer agents. General considerations and predictions about the future utility of transposon technology are discussed.

Figure 1

"Copy-and-paste" and "cut-and-paste" transposons have been adapted for use as gene transfer vectors. In the top half of the figure, transposition of naturally occurring transposons is depicted. In the lower half of the figure, the general methods used to adapt these transposons for use as gene transfer agents is shown. Direct terminal repeats (TR) flank some retrotransposons. Inverted terminal repeats (IR) flank cut and paste transposons. Retrotransposons, such as the L1 element, encode open reading frames (ORF) of unknown function as well as integrases (IN) and reverse transcriptases (RT). Both kinds of elements can be manipulated so that special vector sequences are inserted. In the case of retrotransposons, the vector sequences are inserted into the 3' untranslated region. In the case of the "cut and paste", DNA transposons, the vector sequences replace the transposase gene, which is expressed from a heterologous promoter in trans.

Figure 2

General uses for transposon vectors in the generation and manipulation of transgenic animals. Many uses can be imagined for transposon systems that are active in vertebrates. Three of the main uses are shown here.