The CRISPR-Cas9 gene editing system, which has revolutionized genetic engineering over the past decade, involves cutting DNA strands, which is a process that is difficult to control and can result in unwanted genetic changes. Now, thanks to researchers from the Massachusetts Institute of Technology and the University of California, San Francisco (UCSF), a new gene-editing technology called CRISPRoff can change that, according to a press release.
The technique, described in an article published in Cell on April 9, is different from traditional CRISPY reversible, and the introduced changes can even be transferred to future cell lines. This non-destructive gene processing protein serves as a simple switch for genes, recreating the benefits of the widely used CRISPR-Cas9 system without damaging cells’ genetic material.
“Four years ahead [from the initial grant], and CRISPRoff ultimately works as suggested in a science fiction way, “says fellow 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,” says 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 several genes at the same time without any DNA damage, with a lot of homogeneity, and in a way that can be reversed. It’s an excellent tool to control gene expression.”
‘Genetic Engineering 2.0’
In the classic CRISPR-Cas9 system, it is difficult to limit the outcome, this is where the researchers saw the opportunity for a different kind of gene editor.
The researchers created a small protein machine to build an epigenetic editor that can mimic natural DNA methylation, which is an epigenetic mechanism that occurs by the addition of a methyl (CH3) group to DNA. The machine, led by small RNAs, can change methyl groups at specific spots on the wire. The methylated genes are then ‘silenced’ or switched off, this is where the machine’s name comes from.
It does not alter the sequence of the DNA strand, enabling the researchers to reverse the attenuation effect using enzymes that remove methyl groups. The researchers call this method CRISPRon.
The researchers discovered that they could use this on-off switch to target most genes in the human genome. Furthermore, it worked for the genes themselves as well as the other regions of DNA that control gene expression without encoding proteins.
In addition, large methylated regions called CpG islands, something considered essential for DNA methylation mechanisms, have also been silenced by CRISPRoff.
CRISPRoff for practical applications
The method has been tested in induced pluripotent stem cells, these are cells that can change into other cell types in the body. When the researchers silenced a gene in the stem cells and had them transformed into neurons, it was seen that the gene remained silent in 90 percent of the cells. It reveals that cells retain a memory of epigenetic adaptations made by the CRISPRoff system.
In another study, the researchers used technology to silence Tau proteins, which can form in the brain, which can cause memory loss and which are involved in Alzheimer’s disease, in neurons. It was seen that, although not completely eliminated, CRISPRoff could be used to reject Tau’s expression. “What we’ve shown is that it’s a viable strategy to silence Tau and prevent protein from being expressed,” says Weissman. “So the question is how can you deliver it to an adult. And would that really be enough to affect Alzheimer’s? These are big open questions, especially the latter.”
The researchers are now exploring new ways to apply the gene editing technology. “With this new CRISPRoff technology you can [express a protein briefly] to write a program that is remembered and executed indefinitely by the cell, “says Gilbert. This changes the game, so now you’re basically writing a change transmitted by 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 all these other things can too do. “