Researchers have created a significantly smaller version of the CRISPR gene editing system they call CasMINI. CRISPR has been used for gene editing for a long time and works like molecular scissors. Traditional CRISPR has multiple functions and can be used as a cutter or, in more advanced techniques, can be used to edit, label, or as an imager. While there are many different CRISPR systems in use today, Stanford researchers say they’re all too large to deliver easily directly into living organisms, cells, and tissues.
Instead, researchers have created a new and smaller gene editing system that they call CasMINI. It’s significantly smaller than other CRISPR systems, such as Cas9 that uses 1000 amino acids, and Cas12a using 1500 amino acids. By comparison, CasMINI has only 529 amino acids. However, despite being significantly smaller, CasMINI was shown in experiments to be able to edit genetic code just as the other larger CRISPR systems can.
Its significantly smaller size enables it to be more easily delivered directly into human cells. As a result, researchers believe it can be a tool for treating a wide range of conditions, including those that cause organ degeneration and genetic diseases. To create their significantly more compact system, project researchers began with the CRISPR protein Cas12f, also known as Cas14. That protein was chosen because it contains between 400 and 700 amino acids, making it smaller than the other systems from the start.
One challenge of using Cas12f is that since it originates from a single-celled organism, it isn’t well-suited to use in human cells. To make it function inside the human body, Xiaoshu Xu used about 40 mutations in the protein, allowing it to bypass a limitation that made it difficult for the protein to find its target inside the cells. The team spent a year performing various iterations using bioengineering, and eventually, some of the engineered proteins began to turn on.
Over the many iterations, researchers improved the protein’s performance by looking for a working variant that would turn human cells green by activating a green fluorescent protein in its genome. In the beginning, the team saw only one or two cells glowing green, but eventually, most cells were green when viewed under a microscope.
The researchers found that CasMINI worked with almost any gene the researchers tested it with. Currently, the team is working on collaborations with other scientists to use CasMINI for gene therapy.