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On- and off-target effects of paired CRISPR-Cas nickase in primary human cells - Illumina

ABSTRACT: Undesired on- and off-target effects of CRISPR-Cas nucleases remain a challenge in therapeutic genome editing. While the use of Cas9 nickases has been shown to minimize off-target mutagenesis, their use in therapeutic genome editing has been hampered by a lack of efficacy. To overcome this limitation, we and others have developed double nickase-based strategies to generate staggered DNA double breaks to mediate gene disruption or gene correction with high efficiency. However, the impact of paired single-strand nicks on genome integrity has remained largely unexplored. Here, we developed a novel CAST-Seq pipeline, D-CAST, to characterize chromosomal rearrangements induced by paired CRISPR-Cas9 nickases at three different loci in primary keratinocytes derived from epidermolysis bullosa patients. While targeting COL7A1, COL17A1, or LAMA3 with Cas9 nucleases caused previously undescribed chromosomal rearrangements, no chromosomal translocations were detected following single or paired Cas9-based nickase editing. Conversely, whereas single nickase applications did not result in gross genomic aberrations, the double nicking strategy induced large deletions/inversions within a 10 kb region surrounding the target sites at all three loci, similar to the nucleases. Taken together, our data indicate that double-nickase approaches combine efficient editing with greatly reduced off-target effects, but still leave substantial chromosomal rearrangements at on-target sites.

ORGANISM(S): Homo sapiens

PROVIDER: GSE241778 | GEO | 2024/03/15

REPOSITORIES: GEO

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On- and off-target effects of paired CRISPR-Cas nickase in primary human cells - long-read

Project description:Undesired on- and off-target effects of CRISPR-Cas nucleases remain a challenge in therapeutic genome editing. While the use of Cas9 nickases has been shown to minimize off-target mutagenesis, their use in therapeutic genome editing has been hampered by a lack of efficacy. To overcome this limitation, we and others have developed double nickase-based strategies to generate staggered DNA double breaks to mediate gene disruption or gene correction with high efficiency. However, the impact of paired single-strand nicks on genome integrity has remained largely unexplored. Here, we developed a novel CAST-Seq pipeline, D-CAST, to characterize chromosomal rearrangements induced by paired CRISPR-Cas9 nickases at three different loci in primary keratinocytes derived from epidermolysis bullosa patients. While targeting COL7A1, COL17A1, or LAMA3 with Cas9 nucleases caused previously undescribed chromosomal rearrangements, no chromosomal translocations were detected following single or paired Cas9-based nickase editing. Conversely, whereas single nickase applications did not result in gross genomic aberrations, the double nicking strategy induced large deletions/inversions within a 10 kb region surrounding the target sites at all three loci, similar to the nucleases. Taken together, our data indicate that double-nickase approaches combine efficient editing with greatly reduced off-target effects, but still leave substantial chromosomal rearrangements at on-target sites.

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Project description:Undesired on- and off-target effects of CRISPR-Cas nucleases remain a challenge in genome editing. While the use of Cas9 nickases has been shown to minimize off-target mutagenesis, their use in therapeutic genome editing has been hampered by a lack of efficacy. To overcome this limitation, we and others have developed double nickase-based strategies to generate staggered DNA double-strand breaks to mediate gene disruption or gene correction with high efficiency. However, the impact of paired single-strand nicks on genome integrity has remained largely unexplored. Here, we developed a novel CAST-Seq pipeline, D-CAST, to characterize chromosomal aberrations induced by paired CRISPR-Cas9 nickases at three different loci in primary keratinocytes derived from epidermolysis bullosa patients. While targeting COL7A1, COL17A1, or LAMA3 with Cas9 nucleases caused previously undescribed chromosomal rearrangements, no chromosomal translocations were detected following paired nickase editing. While the double nicking strategy induced large deletions/inversions within a 10 kb region surrounding the target sites at all three loci, similar to the nucleases, the chromosomal on-target aberrations were qualitatively different and included a high proportion of insertions. Taken together, our data indicate that double-nickase approaches combine efficient editing with greatly reduced off-target effects, but still leave substantial chromosomal aberrations at on-target sites.

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Expanding the editable genome and CRISPR-Cas9 versatility using DNA cutting-free gene targeting based on in trans paired nicking

Project description:Genome editing typically involves recombination between donor nucleic acids and genomic sequences subjected to double-stranded DNA breaks (DSBs) made by programmable nucleases (e.g. CRISPR-Cas9). Yet, amongst other deleterious by-products, DSBs yield translocations, off-target mutations and, most pervasively, unpredictable on-target allelic disruptions. Remarkably, hitherto, the untoward phenotypic consequences of on-target disruptions at allelic and non-allelic (e.g. pseudogene) sequences have received scant scrutiny and, crucially, remain to be addressed. Here, we demonstrate that gene-edited cells can lose fitness due to on-target DSBs and report that simultaneous single-stranded DNA break formation at donor and target DNA by CRISPR-Cas9 “nickases” overcomes, to a great extent, such genotype-phenotype disrupting events. Moreover, in trans paired nicking gene editing can efficiently and precisely add large DNA segments (i.e. live-cell reporter tags) into essential and multiple-copy genomic sequences while circumventing most of the allelic and non-allelic collateral mutations and chromosomal rearrangements characteristic of nuclease-dependent gene editing procedures.

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Project description:The goal of these experiments were to test the on-target and target-adjacent editing efficiencies of different single-nucleobase editing systems. Previous studies have shown that tethering DNA mutating enzymes to Cas9-nickase-UGI complexes results in editing of chromosomal DNA. However, these editing events encompass undesirable target-adjacent nucleobase edits. Here, we characterize a novel approach that reduces the frequency of target-adjacent editing while maintaining a high level of on-target editing.

2020-02-23 | E-MTAB-8742 | biostudies-arrayexpress

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