The clustered regularly interspaced palindromic repeats (CRISPR)/CRISPR-associated (Cas) 9 nuclease system has provided a powerful tool for genome engineering. Double strand breaks may trigger nonhomologous end joining repair, leading to frameshift mutations, or homology-directed repair using an extrachromosomal template. Alternatively, genomic deletions may be produced by a pair of double strand breaks. The efficiency of CRISPR/Cas9-mediated genomic deletions has not been systematically explored. Here, Authors present a methodology for the production of deletions in mammalian cells, ranging from 1.3 kb to greater than 1 Mb. They observed a high frequency of intended genomic deletions. Nondeleted alleles are nonetheless often edited with inversions or small insertion/deletions produced at CRISPR recognition sites. Deleted alleles also typically include small insertion/deletions at predicted deletion junctions. Authors retrieved cells with biallelic deletion at a frequency exceeding that of probabilistic expectation.
Reference:Ran, F., et al. "Double nicking by RNA-guided CRISPR Cas9 for enhanced genome editing specificity." Cell 154.6 (2013): 1380-1389.
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