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DNA Repair in Human Cells by Class 1 Crispr Gene Editing System

Researchers from Osaka University broaden understanding of Class 1 CRISPR gene editing system in human cells.

CRISPR – short for “clusters of regularly interspaced short palindromic repeats” – has been the cause for controversy since the Chinese biophysical researcher, He Jiankui, first claimed that he has used CRISPR-Cas gene editing technology to create the world’s first gene-edited babies in November 2018.

Despite the controversy researchers are still grappling to understand the intricate molecular mechanisms of the CRISPR gene editing system. A team of Japanese researchers led by Osaka University described in a study that was published in December 2019 on Nature Communications how the Class 1 CRISPR system uses Cas3 protein to edit human cell DNA in a unidirectional manner.

There are two main classes of CRISPR systems, Class 1 and Class 2, that are distinguished by the number of helper proteins needed to cut the DNA. While most gene editing approaches use single-component Class 2 CRISPR systems, very little is known about the utility of multi-component Class 1 systems in eukaryotic gene editing.

“Class 2 CRISPR systems, particularly those using the Cas9 or Cas12a enzymes, are widely used for eukaryotic genome editing,” says lead author of the study Hiroyuki Morisaka. “However, these systems aren’t perfect: as well as introducing unintended mutations, genome editing efficiencies using these methods can be somewhat variable.”

The researchers therefore decided to investigate whether Class 1 CRISPR systems could offer a more efficient and safer alternative.

Using a Cas3 protein-based Class 1 CRISPR system, the team successfully demonstrated both DNA deletions and insertions in human cells. Notably, the Cas3 protein induced unidirectional deletions of large sections of DNA, setting it apart from Class 2 enzymes which usually need help to achieve such large genome edits. Most importantly though, Cas3 achieved more efficient genome editing than Cas9, with no prominent off-target effects.

To confirm the therapeutic potential of the system, the researchers carried out Cas3-based repair of the DMD gene in induced pluripotent stem cells from a patient with Duchenne muscular dystrophy.

“Our results suggest that this Cas3-based method offers a superior alternative to Class 2 CRISPR gene editing systems,” says senior author Tomoji Mashimo. “As well as its obvious therapeutic uses, we envisage potential applications in drug discovery, disease prevention, and crop improvement. [APBN]