CRISPR Improvements

As a gene editing technique, CRISPR/Cas9 was already a major breakthrough compared to previous methods, but researchers know there’s a lot of room for further improvement. To date, CRISPR has proven to be less efficient when employing the cellular process of homology-directed DNA repair (HDR) versus non homologous end joining.

But scientists led by Jacob Corn, the scientific director of the Innovative Genomics Initiative at the University of California, Berkeley have now managed to raise the success rate to 60 percent of homology-directed repair with CRISPR/Cas9-induced breaks.

“We have found that Cas9-mediated HDR frequencies can be increased by rationally designing the orientation, polarity and length of the donor ssDNA [single-stranded DNA] to match the properties of the Cas9-DNA complex,” the researchers stated in the study, which was published in Nature Biotechnology.

They continue, “We also found that these donor designs, when paired with tiled catalytically inactive dCas9 molecules [which bind to DNA without cleaving it], can stimulate HDR to approximately 1%, almost 50-fold greater than donor alone.”

A view of the Cas9 protein (red and blue) bound to a double strand of DNA (purple and grey). Image Credit: Christopher Richardson/ UC Berkeley 
Different Molecular Level

This is a major improvement in CRISPR-Cas9 technology, especially given the unprecedented 60 percent success rate achieved when replacing a short stretch of DNA with another.

“The exciting thing about CRISPR-Cas9 is the promise of fixing genes in place in our genome, but the efficiency for that can be very low,” said Corn. “If you think of gene editing as a word processor, we know how to cut, but we need a more efficient way to paste and glue a new piece of DNA where we make the cut.”

This improved technique will prove to be useful when repairing genetic mutations that are the main cause for hereditary diseases; for example, sickle cell disease or severe combined immune deficiency.


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