Bioengineers have repurposed a ‘non-working’ CRISPR system to make a smaller version of the genome engineering tool. Its diminutive size should make it easier to deliver into human cells, tissues and the body for gene therapy.

«CRISPR can be as simple as a cutter, or more advanced as a regulator, an editor, a labeler or imager. Many applications are emerging from this exciting field,» said Qi, who is also an assistant professor of chemical and systems biology in the Stanford School of Medicine and a Stanford ChEM-H institute scholar.

The many different CRISPR systems in use or being clinically tested for gene therapy of diseases in the eye, liver and brain, however, remain limited in their scope because they all suffer from the same flaw: they’re too large and, therefore, too hard to deliver into cells, tissues or living organisms.

In a paper published Sept. 3 in Molecular Cell, Qi and his collaborators announce what they believe is a major step forward for CRISPR: An efficient, multi-purpose, mini CRISPR system. Whereas the commonly used CRISPR systems — with names like Cas9 and Cas12a denoting various versions of CRISPR-associated (Cas) proteins — are made of about 1000 to 1500 amino acids, their «CasMINI» has 529.

The researchers confirmed in experiments that CasMINI could delete, activate and edit genetic code just like its beefier counterparts. Its smaller size means it should be easier to deliver into human cells and the human body, making it a potential tool for treating diverse ailments, including eye disease, organ degeneration and genetic diseases generally.

Persistent effort

To make the system as small as possible, the researchers decided to start with the CRISPR protein Cas12f (also known as Cas14), because it contains only about 400 to 700 amino acids. However, like other CRISPR proteins, Cas12f naturally originates from Archaea — single-celled organisms — which means it is not well-suited to mammalian cells, let alone human cells or bodies. Only a few CRISPR proteins are known to work in mammalian cells without modification. Unfortunately, CAS12f is not one of them. This makes it an enticing challenge for bioengineers like Qi.

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Materials provided by Stanford University. Original written by Taylor Kubota. Note: Content may be edited for style and length.