The development of technologies that allow the stable delivery of large genomic 
DNA fragments in mammalian systems is important for genetic studies as well as 
for applications in gene therapy. DNA transposons have emerged as flexible and 
efficient molecular vehicles to mediate stable cargo transfer. However, the 
ability to carry DNA fragments >10 kb is limited in most DNA transposons. Here, 
we show that the DNA transposon piggyBac can mobilize 100-kb DNA fragments in 
mouse embryonic stem (ES) cells, making it the only known transposon with such a 
large cargo capacity. The integrity of the cargo is maintained during 
transposition, the copy number can be controlled and the inserted giant 
transposons express the genomic cargo. Furthermore, these 100-kb transposons can 
also be excised from the genome without leaving a footprint. The development of 
piggyBac as a large cargo vector will facilitate a wider range of genetic and 
genomic applications.