The CRISPR-Cas9 gene editing system, which has revolutionized genetic engineering over the past decade, involves cutting DNA strands, a process that is quite difficult to control and can result in unwanted genetic changes. Now, thanks to researchers at the Massachusetts Institute of Technology and the University of California, San Francisco (UCSF), a new gene editing technology called CRISPRoff could change that, according to a press release.
The technique, described in a paper published in Cell on April 9, is reversible in contrast to traditional CRISPY, and the introduced changes can even be passed on to future rows of cells. This non-destructive gene editing protein acts as a simple gene switch-off, mimicking the benefits of the widely used CRISPR-Cas9 system without damaging the genetic material of cells.
“Fast forward four years [from the initial grant], and CRISPRoff is finally working as it is presented in science fiction fashion, “said co-senior author Luke Gilbert.” It’s exciting to see it work so well in practice. “
“The big story here is that we now have a simple tool that can silence the vast majority of genes,” said Jonathan Weissman, who is also a professor of biology at MIT and a researcher at the Howard Hughes Medical Institute. “We can do this for multiple genes simultaneously without any DNA damage, with a lot of homogeneity and in a way that can be reversed. It’s a great tool to control gene expression.”
Genetic engineering 2.0
In the classic CRISPR-Cas9 system, the outcome is difficult to limit, and there the researchers saw an opportunity for a different kind of gene editor.
The researchers created a small protein machine to build an epigenetic editor that could mimic natural DNA methylation, an epigenetic mechanism created by the addition of a methyl group (CH3) to DNA. The machine, guided by small RNAs, can spin methyl groups at specific locations on the strand. The methylated genes are then “silenced” or turned off, which is where the machine’s name comes from.
This does not change the sequence of the DNA strand, allowing the researchers to reverse the silencing effect using enzymes that remove methyl groups. The researchers called this method CRISPRon.
The researchers found that they could use this on / off switch to attack most genes in the human genome. In addition, it worked for the genes themselves as well as the other parts of the DNA that control gene expression without coding for proteins.
In addition, large methylated regions called CpG islands, something thought to be necessary for the DNA methylation mechanism, were also silenced by CRISPRoff.
CRISPRoff for practical applications
The method has been tested in induced pluripotent stem cells, which are cells that can change into other cell types in the body. When the researchers silenced a gene in the stem cells and prompted them to turn into neurons, it was found that the gene was silenced in 90 percent of the cells. This reveals that cells retain a memory of epigenetic modifications made by the CRISPRoff system.
In another study, the researchers used the technology to silence Tau protein, which can form clumps in the brain that cause memory loss and is implicated in Alzheimer’s disease, in neurons. It was seen that, while not quite clear, CRISPRoff could be used to reject Tau’s expression. “What we have shown is that this is a viable strategy to silence Tau and prevent that protein from being expressed,” Weissman said. “The question then is, how do you deliver this to an adult? And would it really be enough to affect Alzheimer’s? Those are big open questions, especially the latter.”
The researchers are now looking for new ways to apply gene editing technology. “This new CRISPRoff technology makes it possible [express a protein briefly] to write a program that the cell will remember and run indefinitely, ”says Gilbert. It changes the game, so now you’re basically writing a change that’s passed on through cell divisions – in some ways we can learn to have a version 2.0 of CRISPR-Cas9 that’s safer and just as effective and can do all these other things too. “