New tool turns CRISPR into "genetic Swiss Army Knife"
The CRISPR tool is fast developing into a powerful way to edit the genes of bacteria, mammals, plants, humans, and even reptiles. It’s often referred to as “genetic scissors,” but a new improvement turns it into a “genetic Swiss Army Knife.” Research led by Caltech has refined the formula to help the tool zoom in on specific organs, tissues or cell types, and give it greater control over what happens next.
CRISPR contains two main parts: guide RNA molecules that direct the tool to specific parts of the genome, and an enzyme that can then edit the genes at that specific location. The most commonly-used enzyme is Cas9, but other variations are emerging, such as Cas12a, Cas12b and CasX.
But as useful as CRISPR can be, it’s not perfect. Rather than focus on the enzyme, the Caltech team instead made improvements to the guide RNA. The problem they set out to solve is that these molecules are “always on,” meaning they will seek out their target no matter where they are in an organism. This could lead to off-target mutations.
So the researchers on the new study engineered conditional guide RNAs (cgRNAs) that are more precise, and more powerful once they get to their target. They work on the kind of IF/THEN statements normally seen in computing: the cgRNAs can react to the presence or the absence of an RNA trigger, and then either become active or inactive in response.
In practice, that means CRISPR can wait until it detects certain biomarkers in a cell – say, those that indicate disease – and then either activate or silence a gene to help treat that disease. And since healthy cells wouldn’t have that biomarker, the cgRNAs wouldn’t be triggered there, keeping the treatment targeted.
The team tested the technique in bacteria, and were able to demonstrate both ON/OFF and OFF/ON logic. RNA triggers successfully switched off cgRNAs that started on, while others switched on cgRNAs that started off.
"There is still a long way to go to realize the potential of dynamic RNA nanotechnology for engineering programmable conditional regulation in living organisms, but these results with CRISPR/Cas9 in bacterial and mammalian cells provide a proof of principle that we can build on in seeking to provide biologists and doctors with powerful new tools,” says Niles Pierce, lead author of the study.
The research was published in the journal ACS Central Science.