GREPore-seq: A Robust Workflow to Detect Changes After Gene Editing Through Long-range PCR and Nanopore Sequencing

To achieve the enormous potential of gene-editing technology in clinical therapies,one needs to evaluate both the on-target efficiency and unintended editing consequences comprehensively.However,there is a lack of a pipelined,large-scale,and economical workflow for detecting genome editing outcomes,in particular insertion or deletion of a large fragment.Here,we describe an approach for efficient and accurate detection of multiple genetic changes after CRISPR/Cas9 editing by pooled nanopore sequencing of barcoded long-range PCR products.Recognizing the high error rates of Oxford nanopore sequencing,we developed a novel pipeline to capture the barcoded sequences by grepping reads of nanopore amplicon sequencing(GREPore-seq).GREPore-seq can assess nonhomologous end-joining(NHEJ)-mediated double-stranded oligodeoxynucleotide(dsODN)insertions with comparable accuracy to Illumina next-generation sequencing(NGS).GREPore-seq also reveals a full spectrum of homology-directed repair(HDR)-mediated large gene knock-in,correlating well with the fluorescence-activated cell sorting(FACS)analysis results.Of note,we discovered low-level fragmented and full-length plasmid backbone insertion at the CRISPR cutting site.Therefore,we have established a practical workflow to evaluate various genetic changes,including quantifying insertions of short dsODNs,knock-ins of long pieces,plasmid insertions,and large fragment deletions after CRISPR/Cas9-mediated editing.GREPore-seq is freely available at GitHub(https://github.com/lisiang/GREPore-seq)and the National Genomics Data Center(NGDC)BioCode(https://ngdc.cncb.ac.cn/biocode/tools/BT007293).