Since the discovery of the CRISPR-Cas9 system, targeting DNA more precisely for gene editing has become much easier. However, deleting part of the genetic code may not be necessary in all cases, especially if there is a way to turn off a gene of interest instead. Fortunately, scientists have discovered that CRISPR/Cas9 can also be used to do just that: turn off genes without altering the underlying DNA sequence.
When we refer to a cell’s DNA, we are actually talking about the same genetic code that exists in every cell of the body, from hair follicles to all organs, skin…. all. But DNA alone does not determine what a specific cell is or how it functions. There is another layer of information that is needed to give cells their unique identity: the epigenome. This layer is made up of various chemical compounds attached to certain areas along the genetic code that determine which genes are turned on, in other words, on or off.
The epigenome is also sensitive to environmental influences. Where DNA is static, epigenetic factors can change. If an abnormal epigenetic change were to occur, it is likely that the cell would not function properly. Many diseases, such as cancer and diabetes, are associated with unusual epigenetic changes. And, because these changes are reversible, it is believed that therapies could be developed to counteract the abnormal changes, restoring a cell to proper functioning.
Different types of epigenetic mechanisms affect gene expression, including DNA methylation, histone modifications and non-coding RNA. The most studied and abundant of these is DNA methylation, which involves adding a chemical group to DNA.
Previous studies have shown that genes with more DNA methylation tend to be turned off, and those with less are turned on. Unfortunately, controlling the amount of DNA methylation at a specific gene is problematic. What’s more, researchers still don’t know exactly what this epigenetic mechanism does to cell function and how its dysregulation ultimately leads to disease development.
To better understand how a particular state of DNA methylation contributes to disease, scientists at McGill University decided to block DNA methylation at specific targets. To do this, they used CRISPR Cas9 genome-editing technology to precisely target methylation activity and “demethylate” DNA. The process they developed proved that a gene can be modified – or rather gene activity can be tuned – anywhere on DNA without altering the genetic code and without off-target activity at others. places on the DNA.
Their work, published as an open-access article in Nature Communication, explains the procedures needed to remove DNA methylation marks on any gene of interest. They hope other scientists will use this new technique to determine whether DNA methylation incorrectly turns off an important gene that should be turned on. Knowing this could help determine the role of DNA methylation, not just as a marker, but as a contributor to a particular disease.
For example, researchers could assess whether DNA methylation prevents the insulin gene from regulating blood sugar in diabetics. Additionally, further studies using the CRISPR/Cas9 epigenome editing technique could also lead to the development of new disease treatments or therapies.
Source: Daniel M. Sapozhnikov, Moshe Szyf. (2021). Unraveling the functional role of DNA demethylation at specific promoters by targeted steric blocking of DNA methyltransferase with CRISPR/dCas9. Nature Communication.
Reference: How to turn specific genes on and off. McGill University. November 9, 2021.