Nickases Show Promise in Better Results for CRISPR Gene Editing

The power and the promise of CRISPR/Cas9 genome editing for clinical  application with gene therapy - ScienceDirect

New research shows that the use of nickases provides better results when using CRISPR gene editing techniques.

A study published in Science Advances shows that the nickase method may the safer, more reliable option when used to product genetic mutations to fight diseases.

CRISPR a Game-Changer for Gene Therapy

Gene editing has been a revolutionary tool for scientists in recent years. CRISPR gene editing has been used for a decade to correct gene mutations, leading to a range of applications in health care and the food industry. CRISPR has been a game-changer when it comes to addressing therapies to fight genetic diseases.

However, there has been a major downside to the most commonly used technique for CRISPR gene editing. The process at times is imprecise and leads to off-target results, which can have unwanted effects to the process.

CRISPR gene editing uses a nuclease derived from bacteria and guide RNA (gRNA). The combination allows scientists to knock out, knock in, repress, activate or modify genes. The gRNA and nuclease form a ribonucleoprotein (RNP) that pinpoints and cuts specific sequences of DNA.

The most commonly used nuclease is Cas9, derived from Streptococcus pyogenes. This approach, however, results in double-stranded breaks in the DNA.

New Study Shows Nickases Boost Accuracy

A team of researchers from the University of California, San Diego used a Cas9 variant called a nickase to address the errors that sometimes arise with Cas9. The new approach is considered a safer approach to gene therapy.

The technique uses a nickase, which uses DNA repair machinery. It targets a single strand of a mutated DNA sequence on a chromosome, as opposed to the double strands with Cas9. The single-strand approach allows the body to naturally copy a counterpart functional non-mutated element on the same chromosome, allowing the defect to be repaired.

When using two nickases, scientists can produce not blunt ends as with Cas9, but cohesive ends. The cohesive ends provide more control for gene mutation and integration.

The biologists used fruit flies with mutations that gave them white eyes instead of red. The results were dramatic.

Using nickases, the researches found that they were able to restore the red eye color to a high level in 50 percent to 70 percent of cases. Traditional Cas9 dual strand-cutting created a patchy result and only 20 percent to 30 percent restoration of the red eye color.

The traditional editing technique is less successful in this test but also frequently results in off-target mutations. The team noted that their research found that the nickase technique causes fewer on- and off-target mutations.

The impact of the findings could be significant. If the positive events can be increased using these techniques, there are more opportunities for transformational therapies. The scientists concluded that the nickase approaches “may enable the development of alternative gene therapies for correcting dominant or trans-heterozygous disease-causing DNA alterations.”

Simplicity is a distinct advantage, the scientists noted. The nickase approach uses few components. In addition, while Cas9 creates full DNA breaks and related mutations, the DNA nicks are softer.

 

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