piggyBac: A vehicle for integrative DNA transformation of parasitic nematodes

In addition to their natural role in eukaryotic genome evolution, transposons can be powerful tools for functional genomics in diverse taxa. The piggyBac transposon has been applied as such in eukaryotic parasites, both protozoa and helminths, and in several important vector mosquitoes. piggyBac is advantageous for functional genomics because of its ability to transduce a wide range of taxa, its capacity to integrate large DNA ‘cargoes’ relative to other mobile genetic elements, its propensity to target transcriptional units and its ability to re-mobilize without leaving a pattern of non-excised sequences or ‘footprint’ in the genome. We recently demonstrated that piggyBac can integrate transgenes into the genome of the parasitic nematode Strongyloides ratti, an important model for parasitic nematode biology and a close relative of the significant human pathogen S. stercoralis. Unlike transgenes encoded in conventional plasmid vectors, which we assume are assembled into multi-copy episomal arrays as they are in Caenorhabditis elegans, transgenes integrated via piggyBac are not only stably inherited in S. ratti, they are also continuously expressed. This has allowed derivation of the first stable transgene expressing lines in any parasitic nematode, a significant advance in the development of functional genomic tools for these important pathogens.