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CRISPR/Cas9 Quality Control

Joffrey Mianné and colleagues at the MRC Harwell Institute have published new research in Elsevier Methods outlining their proposed protocols for effectively screening the results of CRISPR/Cas9 gene editing technology. 

CRISPR/Cas9 is a new gene editing technology that has revolutionised research in the field. The technology allows for faster, cheaper, and more precise gene editing than was previously possible. It is increasingly used in the field of mouse genetics to help study the relationship between genes and human disease. It is now the chosen method for the International Mouse Phenotyping Consortium (IMPC), a global project to identify the function of every gene in the mouse genome.

Despite the acceleration of the technology – the results obtained with CRISPR/Cas9 can often be unpredictable. Frequently the genetic change made is not present uniformly throughout the organism (known as mosaicism) and other unwanted changes can be found at the site where the gene has been altered. It is essential that mice taken forwards carry only the desired change so that any physiological changes seen are because of that and not something else on the genome. The ability to correctly select mice with the desired mutation requires robust and accurate methods.

The technology allows many types of genetic changes to be made, including deletions and even swapping the individual molecules making up the code of the DNA. Here the researchers have proposed a framework to analyse the results of CRISPR/Cas9 activity according to the type of genetic alteration intended. They have ascertained that due to the high level of unpredictability in the first generation it is better to definitively characterise the following generation and establish the mutant mouse line from there.

This research will contribute to the current debate on best practice for the use of CRISPR/Cas9 in biomedical research.

How CRISPR/Cas9 works

The CRISPR-Cas9 system is made up of two key molecules – the enzyme Cas9 and a piece of guide RNA. In brief, the guide RNA locates and binds to the target DNA where the change is going to be made. Its sequence is complementary to that of the target DNA. The Cas9 then acts as molecular scissors and makes a cut across both strands of DNA in the double helix. The cell then recognises that the DNA is damaged and attempts to repair it. Scientists have been able to harness the cell’s own DNA repair machinery to introduce changes into the genome.