Schematic representation of four different approaches for delivery of components of the DNA transposon-based gene delivery systems. Panel a illustrates the conventional delivery of transposase and transposon by plasmid DNA transfection. This approach relies on nuclear uptake of both helper and donor plasmid DNA allowing transcription of transposase-encoding mRNA, mRNA export, production of transposase in the cytoplasm, and subsequent nuclear import of transposases. Transposases bind to the transposon donor plasmid and facilitates transposition. A variant of this approach is based on transfection of in vitro-transcribed mRNA encoding the transposase (not shown). Panel b represents an emerging approach based on virus-mediated delivery of DNA transposon systems. The example shown demonstrates the use of integrase-defective lentiviral vector (IDLVs) as carriers of the transposase gene (left) and the transposon (right), allowing transposition from reverse-transcribed (RT) lentiviral DNA intermediates (here represented by circular forms). Related approaches have been developed for vectors based on adenoviruses, adeno-associated viruses, and herpes simplex viruses. Panel c illustrates the use of reverse transcription-defective retroviral vectors as carriers of transposase-encoding mRNA. Modifications of the primer binding site, where reverse transcriptions is normally initiated by an annealed tRNA, inhibit reverse transcription and thus facilitating vector RNA delivery, and direct translation into protein. The transposon donor is in this example delivered by plasmid DNA transfection. Panel d demonstrates the possibility of delivering DNA transposon systems in engineered ‘all-in-one’ lentiviral particles that co-deliver both transposase protein and the donor for DNA transposition. Transposase subunits delivered by lentiviral protein transduction are delivered in the virus context and facilitate efficient transposition through mechanisms that may benefit from the close interaction between transposases and the reverse-trancribed donor within the viral pre-integration complex. Question marks indicate that it is currently unknown at which stage transposases bind to the donor to form the synaptic transposition complex.