Researchers Discover Mechanism Disrupting CRISPR-Cas9

CRISPR-Cas9 has made gene editing very easy. However, the tool has been found to be less precise than previously assumed as it leads to unwanted mutations in a cell's DNA. Researchers at Delft University of Technology (TUDelft) have now identified a mechanism that causes such mutations when CRISPR-Cas9 is used incorrectly. This can cause dormant genes to become expressed, which is potentially very dangerous. The researchers created a checklist based on their findings, and this checklist will prevent the harmful mechanism from being activated and makes gene editing using CRISPR-Cas9 safer.

Gene editing experts using CRISPR-Cas9 can change part of the genome by introducing a new DNA sequence. The Cas protein cuts open the DNA at a targeted spot, after which the cell is expected to repair its DNA using this new string of genetic material. Thus, new genes can be introduced. "When the repair mechanism uses the other chromosome as a template instead of the newly introduced string of DNA, the editing will not be successful", said researcher Dr. Jean-Marc Daran. Since repair using the other chromosome is far more efficient, repair using the intended DNA fragment almost never occurs. Worse than that, loss of heterozygosity can occur, which can have serious consequences.

The discovery of the repair mechanism that blocks gene editing was made through the research of Arthur Gorter de Vries, a PhD candidate at Delft University of Technology who was working on brewer's yeast. He tried to determine how domestication of brewer's yeast ultimately led to the modern strains of yeast that beer producers now use. As he was trying to remove a certain gene to determine its function, he could not confirm that the gene was removed successfully and noticed that the cells were behaving erratically. Gorter de Vries was targeting only one of the chromosomes in yeast, and further experiments showed that the yeast cells were using the other copy of the targeted chromosome as a template to repair the DNA that he had been trying to remove.

For more details, read the news release from TUDelft.