Scientists from the University of Sheffield, in collaboration with the MRC Laboratory of Medical Sciences and Imperial College London, have made a breakthrough in understanding why CRISPR-Cas9 gene-editing technology sometimes makes unintended cuts in DNA. This discovery could lead to more accurate and safer gene therapies for genetic diseases.
Understanding the CRISPR-Cas9 Challenge
CRISPR-Cas9 has revolutionized medicine by providing a programmable way to cut and edit DNA sequences. It has enabled groundbreaking therapies for conditions like sickle cell anemia and is increasingly used in personalized cancer treatments and rapid diagnostics. However, the technology isn’t perfect—it can sometimes cut DNA sequences that weren’t intended targets, leading to off-target effects that compromise both safety and efficacy.
These misplaced DNA edits can be costly, with billions spent annually during the search for new therapies. Understanding why these errors occur has been a mystery for nearly a decade.
The Role of DNA Shape in Gene Editing Errors
The research team discovered that the physical twisting of DNA plays a crucial role in these mistakes. When DNA is supercoiled—twisted under strain as it naturally occurs inside cells—it becomes more susceptible to unintentional cutting by the CRISPR-Cas9 system.
Using state-of-the-art imaging techniques, including cryo-electron microscopy and atomic force microscopy, the researchers visualized how CRISPR-Cas9 interacts with supercoiled DNA at near-atomic resolution. They found that as DNA twists and buckles under stress, it reduces the energy required for the Cas9 protein to bind and cut, facilitating off-target activity.
Advanced Imaging Techniques Reveal New Insights
The study utilized DNA minicircles—tiny loops of DNA that mimic the torsional stress experienced by DNA inside cells. These minicircles were small enough to visualize using advanced microscopy techniques while maintaining their supercoiled state.
Professor Alice Pyne from the University of Sheffield explained: “We were able to image DNA minicircles in solution, observing their helical structure as they buckled under stress in their supercoiled state. These minicircles are smaller than anything we’ve been able to previously create, pushing the limits of our microscopy technologies.”
Implications for Future Gene Therapies
This discovery opens the door to developing new CRISPR-Cas9 variants that are less error-prone. Current high-fidelity variants were designed using linear DNA structures, but in actual cells, DNA is supercoiled to different degrees. This means that the reduction in off-target activity seen in laboratory settings might not translate directly to the body.
Dr. Quentin Smith, lead author of the study, noted: “This study definitely paves the way to generate Cas9 variants that are sensitive to topology. Most high-fidelity variants were designed using linear DNA structures. But in cells, the DNA is supercoiled to different degrees, so you might not get the same reduction in off-target activity in the body that you see in the lab.”
Advancing Precision Medicine
The findings could significantly improve the design of high-fidelity, low-error CRISPR gene-editing technologies. More accurate gene-editing tools would minimize costly errors in medicine development and potentially accelerate the development of new gene therapies for genetic diseases.
Sylvia Whittle, a PhD student involved in the research, emphasized the impact: “By visualizing and quantifying changes in the DNA helical structure, we were able to gain fresh insight into how effective different Cas9 interactions can be. This study lays the foundation for generating Cas9 variants that are less error-prone. Achieving that step would have a huge impact on healthcare development.”
Collaborative Research Excellence
This groundbreaking research was made possible through collaboration between multiple institutions and was funded by the Medical Research Council, the Engineering and Physical Sciences Research Council, and a UKRI Future Leaders Fellowship. The study demonstrates the University of Sheffield’s commitment to advancing cutting-edge research in biotechnology and medicine.
The research team’s work represents a significant step forward in understanding the fundamental mechanisms of gene editing, bringing us closer to developing more precise and reliable gene therapies that could transform treatment options for patients with genetic diseases.
Learn More About Gene Therapy Research
For those interested in pursuing research in this field, the University of Sheffield offers programs in Chemical, Materials, and Biological Engineering. The university’s cross-faculty research centers harness interdisciplinary expertise to solve pressing global challenges in biotechnology and medicine.
Explore the University of Sheffield’s research centers and discover how you can contribute to advancing gene therapy technologies that could change lives.
