A group of researchers from the University of Illinois at Urbana-Champaign have discovered the gene-editing tool TALEN outperforms CRISPR-Cas9 when applied to tightly-packed DNA molecules.

Their experiments revealed that TALEN is up to five times more efficient than CRISPR-Cas9 in parts of these genome, called heterochromatin.

Defects in this particular area of human DNA can cause a range of diseases, including Fragile X syndrome, sickle cell anaemia and beta-thalassemia.

University of Illinois at Urbana-Champaign chemical and biomolecular engineering professor Huimin Zhao said: “CRISPR is a very powerful tool that led to a revolution in genetic engineering, but it still has some limitations.

“We found that CRISPR works better in the less-tightly wound regions of the genome, but TALEN can access those genes in the heterochromatin region better than CRISPR.

“We also saw that TALEN can have higher editing efficiency than CRISPR. It can cut the DNA and then make changes more efficiently than CRISPR.”

Zhao and his colleagues used single-molecule fluorescence microscopy to directly observe how the two genome-editing tools performed in living mammalian cells.

Fluorescent-labelled tags enabled the researchers to measure how long it took CRISPR and TALEN to move along the DNA and to detect and cut target sites.

The results of the study showed that TALEN was as much as five times more efficient than CRISPR in multiple experiments.


Comparison study shows that TALEN gene-editing tool could be better for certain applications

CRISPR is a bacterial molecule that detects invading viruses and can carry one of several enzymes, such as Cas-9, that allow it to cut viral genomes at specific sites.

TALEN also scans DNA to find and target specific genes. Both CRISPR and TALEN can be engineered to target specific genes to fight disease, improve crop plant characteristics or for other applications.

The ability of CRISPR-Cas9 to act like a pair of molecular scissors to cut out strands of human DNA was proven in 2013, and has since been looked upon as a potential tool for the future of disease prevention and treatment.

But the key relevance of this new research, according to Zhao and his colleagues, is that a broader selection of gene-editing tools is needed to target all parts of the genome.

The findings will lead to improved approaches for targeting various parts of the genome, Zhao said.

“Either we can use TALEN for certain applications, or we could try to make CRISPR work better in the heterochromatin,” he added.