CRISPR Gene Editing Used in New Technique That Takes Advantage of Good Chromosome

Many people who suffer from a genetic condition have two distinct mutations within the affected gene(s). Researchers have used CRISPR gene editing technology to develop a new technique that takes advantage of this.

The two mutations of an affected gene are almost always different, and one of the mutations is often relatively normal. Researchers hypothesized that a section of a person’s normal chromosome could be used to repair the same section of a person’s abnormal chromosome. 

If successful, the new technique could reduce cost and time of treatment. It also may improve patient outcomes, as people’s biological material is being used to perform the repair. 

Specifically, the technique uses a nickase to complete homologous chromosome-templated repair (HTR). Because gene editing is homologous, it shouldn’t be plagued by the errors that are common when joining non-homologous ends of DNA. The technique is viable for both single-strand breaks (SSBs) and double-strand breaks (DSBs).

In the method, CRISPR gene editing is used to cut the mutated gene so that the abnormal chromosome can be repaired. Only a small cut is needed, giving the method its name “nickase” because the DNA is nicked.

The researchers first tried this new method out on flies’ eye color chromosomes. They used the homologous chromosome-templated repair (HTR) to nick DSBs. The flies then had eyes that were white with large red patches, giving a strong visualization of the method’s effectiveness.

The next step was to use the same technique but only nick a single strand of DNA. This too proved to be an effective and successful test case.

The researchers found that Cas9-derived nickases H841A or D10A were most effective for SSBs. Fully active Cas9 CRISPR gene editing technology was most effective for DSBs.

Researchers were pleasantly surprised at just how effective the nickases were. Although they hypothesized that the technique might work, this was not one of their strongest conjectures. If it did work, it wasn’t expected to work as well as it did. Because gene editing is homologous, it shouldn’t be plagued by the errors that are common when joining non-homologous ends of DNA.

Implications for the treatment of genetic conditions in people aren’t determined at this point in time, as researchers have just established the technique does indeed work. They weren’t even necessarily considering potential human clinical applications, as the result itself was “completely unexpected” according to Sitara Roy, PhD.

The technique is highly flexible, though, which could allow it to be used in multiple clinical applications. Once alterations for human-specific genetic conditions are made, this could serve as one of the most widely used HTR gene editing models for people. Of course, it relies on the most widely used CRISPR gene editing technology.

Within CRISPR gene editing methods and techniques, this new method also helps improve the technology itself. It took Cas9-based CRISPR edits in a slightly new direction, and showed improvement in effectiveness. Compared to traditional Cas9-based edits, the nickase technique has fewer on- and off-target mutations.

This research was published in the journal Science Advances. The article title was  “Cas9/Nickase-induced allelic conversion by homologous chromosome-templated repair in Drosophila somatic cells.”