These methylated genes are then “silenced,” or turned off, hence the name CRISPRoff.īecause the method does not alter the sequence of the DNA strand, the researchers can reverse the silencing effect using enzymes that remove methyl groups, a method they called CRISPRon.Īs they tested CRISPRoff in different conditions, the researchers discovered a few interesting features of the new system. To build an epigenetic editor that could mimic natural DNA methylation, the researchers created a tiny protein machine that, guided by small RNAs, can tack methyl groups onto specific spots on the strand. “It changes the game so now you're basically writing a change that is passed down through cell divisions - in some ways we can learn to create a version 2.0 of CRISPR-Cas9 that is safer and just as effective, and can do all these other things as well.” “With this new CRISPRoff technology, you can to write a program that's remembered and carried out indefinitely by the cell,” says Gilbert. In order for them to work in cells, the cells had to be continually expressing artificial proteins to maintain the changes. Weissman and collaborators had previously created two other epigenetic editors called CRISPRi and CRISPRa - but both of these came with a caveat. Problems with a cell’s epigenetics are responsible for many human diseases such as Fragile X syndrome and various cancers, and can be passed down through generations.Įpigenetic gene silencing often works through methylation - the addition of chemical tags to to certain places in the DNA strand - which causes the DNA to become inaccessible to RNA polymerase, the enzyme which reads the genetic information in the DNA sequence into messenger RNA transcripts, which can ultimately be the blueprints for proteins. This sort of modification is what scientists call “epigenetic” - genes may be silenced or activated based on chemical changes to the DNA strand. That’s where the researchers saw an opportunity for a different kind of gene editor - one that didn’t alter the DNA sequences themselves, but changed the way they were read in the cell. “It's very hard to control the outcomes.” “As beautiful as CRISPR-Cas9 is, it hands off the repair to natural cellular processes, which are complex and multifaceted,” Weissman says. Plus, their reliance on “in-house” cellular repair mechanisms means it is hard to limit the outcome to a single desired change. Then the cell’s existing repair machinery patches up the holes.īecause these methods alter the underlying DNA sequence, they are permanent. The system can be targeted to specific genes in human cells using a single guide RNA, where the Cas9 proteins create tiny breaks in the DNA strand. The classic CRISPR-Cas9 system uses a DNA-cutting protein called Cas9 found in bacterial immune systems. “It's exciting to see it work so well in practice.” “Fast forward four years, and CRISPRoff finally works as envisioned in a science fiction way,” says co-senior author Gilbert. The project was partially funded by a 2017 grant from the Defense Advanced Research Projects Agency to create a reversible gene editor. It's a great tool for controlling gene expression.”

“We can do this for multiple genes at the same time without any DNA damage, with great deal of homogeneity, and in a way that can be reversed. “The big story here is we now have a simple tool that can silence the vast majority of genes,” says Weissman, who is also a professor of biology at MIT and an investigator with the Howard Hughes Medical Institute. Designed by Whitehead Institute Member Jonathan Weissman, University of California San Francisco Assistant Professor Luke Gilbert, Weissman lab postdoc James Nuñez, and collaborators, the method is stable enough to be inherited through hundreds of cell divisions, and is also fully reversible.

Now, in a paper published online in Cell on April 9, researchers describe a new gene editing technology called CRISPRoff that allows researchers to control gene expression with high specificity while leaving the sequence of the DNA unchanged. While the system could potentially be useful in treating a variety of diseases, CRISPR-Cas9 editing involves cutting DNA strands, leading to permanent changes to the cell’s genetic material. Over the past decade, the CRISPR-Cas9 gene editing system has revolutionized genetic engineering, allowing scientists to make targeted changes to organisms’ DNA.

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