Cell cycle arrest and p53 prevent ON-target megabase-scale rearrangements induced by CRISPR-Cas9

ON-target genotoxicity in gene editing is generally underestimated. Here the authors report Fluorescence-Assisted Megabase-scale Rearrangements Detection (FAMReD) systems to detect and characterize rare large loss of heterozygosity: they show that ON-target genotoxicity can be prevented by p53 and cell cycle arrest. The CRISPR-Cas9 system has revolutionized our ability to precisely modify the genome and has led to gene editing in clinical applications. Comprehensive analysis of gene editing products at the targeted cut-site has revealed a complex spectrum of outcomes. ON-target genotoxicity is underestimated with standard PCR-based methods and necessitates appropriate and more sensitive detection methods. Here, we present two complementary Fluorescence-Assisted Megabase-scale Rearrangements Detection (FAMReD) systems that enable the detection, quantification, and cell sorting of edited cells with megabase-scale loss of heterozygosity (LOH). These tools reveal rare complex chromosomal rearrangements caused by Cas9-nuclease and show that LOH frequency depends on cell division rate during editing and p53 status. Cell cycle arrest during editing suppresses the occurrence of LOH without compromising editing. These data are confirmed in human stem/progenitor cells, suggesting that clinical trials should consider p53 status and cell proliferation rate during editing to limit this risk by designing safer protocols.

Automated summary

The authors developed a Fluorescence-Assisted Megabase-scale Rearrangements Detection (FAMReD) system to detect rare large loss of heterozygosity. They demonstrated that ON-target genotoxicity can be prevented by p53 and cell cycle arrest. Comprehensive analysis of gene editing products using this system revealed complex outcomes and highlighted the underestimation of ON-target genotoxicity.