Transposon-based gene vectors have become indispensable tools in vertebrate genetics for applications ranging from insertional mutagenesis and transgenesis in model species to gene therapy in humans. The transposon toolkit is expanding, but a careful, side-by-side characterization of the diverse transposon systems has been lacking. Here we compared the Sleeping Beauty (SB), piggyBac (PB), and Tol2 transposons with respect to overall activity, overproduction inhibition (OPI), target site selection, transgene copy number as well as long-term expression in human cells. SB was the most efficient system under conditions where the availability of the transposon DNA is limiting the transposition reaction including hard-to-transfect hematopoietic stem/progenitor cells (HSCs), and the most sensitive to OPI, underpinning the need for careful optimization of the transposon components. SB and PB were about equally active, and both more efficient than Tol2, under nonrestrictive conditions. All three systems provided long-term transgene expression in human cells with minimal signs of silencing. Indeed, mapping of Tol2 insertion sites revealed significant underrepresentation within chromosomal regions with H3K27me3 histone marks typically associated with transcriptionally repressed heterochromatin. SB, Tol2, and PB constitute complementary research tools for gene transfer in mammalian cells with important implications for fundamental and translational research
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