Researchers find way to boost CRISPR-Cas9 efficiency

SAN FRANCISCO, Aug. 28 -- Researchers at the University of California, Berkeley, have found a way to boost the efficiency of a gene-editing tool, known as clustered regularly interspaced short palindromic repeats associated protein 9 (CRISPR-Cas9), so that it cuts and disables genes up to fivefold in most types of human cells. While the key to figuring out the role of genes or the proteins they code for in the human body or in disease is disabling the gene to see what happens when it is removed, CRISPR-Cas9 is the go-to technique for knocking out genes in human cell lines to discover what the genes do and holds the promise of accelerating the process of making knockout cell lines. However, researchers must sometimes make and screen many variations of the genetic scissors to find one that works well. In the new study, published in a the journal Nature Communications, the UC Berkeley researchers found that this process can be made more efficient by introducing into the cell, along with the CRISPR-Cas9 protein, short pieces of deoxyribonucleic acid (DNA) that do not match any DNA sequences in the human genome. The short pieces of DNA, called oligonucleotides, seem to interfere with the DNA repair mechanisms in the cell to boost the editing performance of even mediocre CRISPR-Cas9s between 2½ and 5 times. "It turns out that if you do something really simple - just feed cells inexpensive synthetic oligonucleotides that have no homology anywhere in the human genome - the rates of editing go up as much as five times," said lead researcher Jacob Corn, the scientific director of UC Bekeley's Innovative Genomics Initiative and an assistant adjunct professor of molecular and cell biology. The technique boosts the efficiency of all CRISPR-Cas9s, even those that initially failed to work at all. Corn portrays CRISPR-Cas9 gene editing as a competition between cutting and DNA repair: once Cas9 cuts, the cell exactly replaces the cut DNA, which Cas9 cuts again, in an endless cycle of cut and repair until the repair enzymes make a mistake and the gene ends up disfunctional. Perhaps, he said, the oligonucleotides decrease the fidelity of the repair process, or make the cell switch to a more error-prone repair that allows Cas9 to more readily break the gene. The next frontier, he was quoted as saying in a UC Berkeley news release, is trying to take advantage of the peculiarities of DNA repair to improve sequence insertion, in order to replace a defective gene with a normal gene and possibly cure a genetic disease.