'Prime Editing' Crispr Tool

Nature reports: [edited]

For all the ease with which the wildly popular CRISPR–Cas9 gene-editing tool alters genomes, it’s still somewhat clunky and prone to errors and unintended effects. Now, a recently developed alternative offers greater control over genome edits.

The alternative method, called prime editing, improves the chances that researchers will end up with only the edits they want, instead of a mix of changes that they can’t predict.

CRISPR–Cas9 and prime editing both work by cutting DNA at a specific point in the genome. CRISPR–Cas9 breaks both strands of the DNA double helix and then relies on the cell’s own repair system to patch the damage and make the edits. This can lead to an uncontrollable mixture of edits that vary between cells.

In addition, the DNA repair system in most cells is far more likely to make those small, random insertions or deletions than to add a specific DNA sequence to the genome. That makes it difficult for researchers to use CRISPR–Cas9 to overwrite one piece of DNA with a sequence of their choosing.

Prime editing bypasses these problems. Although it also uses Cas9 to recognize specific DNA sequences — just like CRISPR–Cas9 does — the Cas9 enzyme in the prime editing tool is modified to nick only one DNA strand. Then, a second enzyme called reverse transcriptase and guided by a strand of RNA, makes the edits at the site of the cut.

The prime editing enzymes don’t have to break both strands of DNA to make changes, freeing researchers from relying on the cell’s DNA repair system — which they can’t control — to make the edits that they want. This means that prime editing could enable the development of treatments for genetic diseases caused by mutations that aren’t easily addressed by existing gene-editing tools.

But Liu’s team and others will now need to carefully evaluate how well the system works in a variety of cells and organisms. “This first study is just the beginning — rather than the end — of a long-standing aspiration in the life sciences to be able to make any DNA change at any position in an organism,” says Liu.

Image courtesy of  David Clode
------------