Ian Slaymaker/Broad Institute of MIT and Harvard
Enhanced Humans

CRISPR Breakthrough: Scientists Overcome Off-Target Gene Editing Errors

Miguel SantosDecember 4th 2015
News
Ian Slaymaker/Broad Institute of MIT and Harvard
Enhanced Cas9

A newly engineered enzyme, called the “enhanced S. pyogenes Cas9” or eSpCas9, has shown to significantly reduce “off-target” editing errors, which is a major technical issue for the revolutionary CRISPR-Cas9 genome editing system.

MIT explains the problem with CRISPR, noting that cutting extra genes causes major problems for scientists working with CRISPR: “The CRISPR-Cas9 system works by making a precisely targeted modification in a cell’s DNA. The protein Cas9 alters the DNA at a location that is specified by a short RNA whose sequence matches that of the target site. While Cas9 is known to be highly efficient at cutting its target site, a major drawback of the system has been that, once inside a cell, it can bind to and cut additional sites that are not targeted.”

Ultimately, this breakthrough is an invaluable development for a number of high-precision genome editing applications because it solves this problem.

The enzyme was engineered by Feng Zhang and his colleagues from the Broad Institute of MIT and Harvard, and MIT’s McGovern Institute for Brain Research.

Precision Genome Editing

Using knowledge of the Cas9 protein structure, Zhang and his colleagues pinpointed three of the 1,400 amino acids making up the Cas9 enzyme that, when changed, led to a dramatic reduction to “off-target editing.” Essentially, by tweaking these three amino acids, the researchers are able to create a more precise Cas9 enzyme.

The Zhang Lab believes the same charge-changing technique will also apply for other RNA-guided DNA targeting enzymes like Cpf1, C2C1, and C2C3.

Genome editing (specifically, the quick and easy methods utilized by CRISPR) comes with many ethical and societal concerns. Hopefully, this development will alleviate some of these concerns, as errors will be significantly reduced.

In the press release, Zhang asserts  “Many of the safety concerns are related to off-target effects. We hope the development of eSpCas9 will help address some of those concerns. ” However, he notes that it certainly won’t fix all of the issues. “We certainly don’t see this as a magic bullet,” said Zhang. “The field is advancing at a rapid pace, and there is still a lot to learn before we can consider applying this technology for clinical use.”

That said, currently, the team is working to make the eSpCas9 enzyme available to researchers worldwide.

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