In a recent study, a team of researchers used a CRISPR/Cas9 system to evaluate the use of tRNA by deleting two tRNA genes from the genomes of hyperhepatocellular carcinoma and human chronic myeloid quasi-haploid leukaemia cells. The authors discovered numerous unexpected genomic changes at the target region using an improved droplet-based target enrichment approach followed by Oxford Nanopore Technology long-read sequencing. The method used in this study demonstrates that CRISPR/Cas9 can lead to the integration of endogenous and exogenous DNA fragments and also produce local inversions, duplications and insertions of functional target-derived fragments. This research presents evidence that a combination of duplication and inversion, as well as integration of exogenous DNA fragments and clustered interchromosomal rearrangements, can occur simultaneously. Furthermore, it was shown for the first time that the target-derived fragments were nevertheless functional despite these modifications, which may complicate mechanistic explanations. These results reveal a new example of unintended CRISPR/Cas9 editing events that can go unnoticed and have a significant impact on the conclusions drawn from experimental reads.
