A team of researchers have now for the first time succeeded in converting skin cells into pluripotent stem cells by activating the cell's own genes. This was achieved by using gene editing technology - called CRISPRa - that can be directed to activate genes. The method utilizes a blunted version of the Cas9 'gene scissors' that does not cut DNA and can therefore be used to activate gene expression without mutating the genome.
"CRISPR/Cas9 can be used to activate genes. This is an attractive possibility for cellular reprogramming because multiple genes can be targeted at the same time. Reprogramming based on activation of endogenous genes rather than overexpression of transgenes is also theoretically a more physiological way of controlling cell fate and may result in more normal cells. In this study, authors show that it is possible to engineer a CRISPR activator system that allows robust reprogramming of iPSC", according to the senior author.
An important key for the success was also activating a critical genetic element that was earlier found to regulate the earliest steps of human embryo development after fertilization. "Using this technology, pluripotent stem cells were obtained that resembled very closely typical early embryonal cells", another author says.
Authors reprogrammed primary human skin fibroblasts into induced pluripotent stem cells (iPSCs) using CRISPRa, targeting endogenous OCT4, SOX2, KLF4, MYC, and LIN28A promoters. The low basal reprogramming efficiency was improved by an order of magnitude by additionally targeting a conserved Alu-motif enriched near genes involved in embryo genome activation (EEA-motif). This effect is mediated in part by more efficient activation of NANOG and REX1.
The discovery also suggests that it might be possible to improve many other reprogramming tasks by addressing genetic elements typical of the intended target cell type.
Generating induced pluripotent stem cells (iPSC) using CRISPR
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