Researchers have developed a method to create induced pluripotent stem cells (iPSCs) with an unmodified genome. The technique, published online in Nature Methods, creates cells with the potential to differentiate into almost any cell in the body without introducing unwanted viruses into the cell's genetic makeup.
iPSCs are generated by 'reprogramming' body cells to become pluripotent. However, the viruses typically used to deliver the reprogramming factors integrate into the cell's genome, and can cause unwanted changes. This presents problems, in particular for clinical applications.
Allan Bradley and colleagues show that fully pluripotent iPSCs with an unmodified genome can be generated in the mouse. As in recently published work from two other groups, they use the piggyBac transposon as a vehicle to deliver the reprogramming factors to the cells. piggyBac is a piece of DNA that can integrate into the genome, but can later be removed without a trace. Notably, Bradley and colleagues show for the first time that the reprogrammed cells from which piggyBac has been seamlessly removed are fully pluripotent, as they contribute to multiple tissues in chimeric mice.
In addition, the authors incorporated a selectable gene into their reprogramming piggyBac construct. The gene renders cells that harbour the construct unable to grow in FIAU, a toxic agent. This strategy allows easy identification of iPSCs with an unmodified genome since upon removal of the piggyBac, these cells can grow in the presence of FIAU. This strategy will be useful in the future for isolating patient-specific human iPS cells with unmodified genomes.
Allan Bradley (Wellcome Trust Sanger Institute, Hinxton, UK)
Abstract available online.
(C) Nature Methods press release.
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