‘Softer' Form of CRISPR Edits Genes More Accurately

A research group at the University of California, San Diego, led by Ethan Bier and Annabel Guichard, has developed a new form of CRISPR that can more efficiently insert correct DNA sequences at the site of a mutation, with fewer off-target effects.

The method uses a variant of the Cas9 enzyme called a nickase, which only cuts one strand of the DNA double helix. “We found that ‘softly' nicking, or cutting, one strand of the DNA is even more efficient than making a clean double-stranded break,” says Bier.

The research team tested the nickase approach in fruit flies that had a mutation that turned their eyes white instead of red. They found that the nickase system corrected the eye color mutation in up to 65 percent of cells, giving the flies red eyes. Standard CRISPR-Cas9 corrected the mutation in up to 30 percent of cells, causing each eye to have a small patch of red.

The team did not introduce any extra pieces of DNA as a template for the cell to correct the mutation on the chromosome, so the molecular machinery must have used the other chromosome that was inherited from the other parent as a template. The team confirmed later that this was the case.

For more details, read the article in NewScientist.