Mapping of microhomologies at CRISPR/Cas9 deletions
Ontology highlight
ABSTRACT: The CRISPR system is widely used in genome editing for biomedical research. Here, using either dual paired Cas9D10A nickases or paired Cas9 nuclease we characterise unintended larger deletions at on-target sites that frequently evade common genotyping practices. We found that unintended larger deletions are prevalent at multiple distinct loci on different chromosomes, in cultured cells and mouse embryos alike. We observed a high frequency of microhomologies at larger deletion breakpoint junctions, suggesting the involvement of microhomology-mediated end joining in their generation. In populations of edited cells, the distribution of larger deletion sizes is dependent on proximity to sgRNAs and cannot be predicted by microhomology sequences alone.
Project description:The use of whole genome microarrays for monitoring mutagenised or otherwise engineered genetic derivatives is a potentially powerful tool for checking genomic integrity. Using comparative genomic hybridization of a number of unrelated, directed deletion mutants in Escherichia coli K-12 MG1655 we identified unintended secondary genomic deletions in the flhDC region in deltafnr, deltacrp, and deltacreB mutants. These deletions were confirmed by PCR and phenotypic tests. Our findings show that non-motile progeny are found in some populations of MG1655 directed deletion mutants, and studies on the effects of gene knock-outs should be viewed with caution when the mutants have not been screened for the presence of secondary deletions, or confirmed by other methods. Keywords: comparative genomic hybridisation
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.
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.
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.
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.
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.
Project description:The use of whole genome microarrays for monitoring mutagenised or otherwise engineered genetic derivatives is a potentially powerful tool for checking genomic integrity. Using comparative genomic hybridization of a number of unrelated, directed deletion mutants in Escherichia coli K-12 MG1655 we identified unintended secondary genomic deletions in the flhDC region in fnr, crp, and creB mutants. These deletions were confirmed by PCR and phenotypic tests. Our findings show that non-motile progeny are found in some populations of MG1655 directed deletion mutants, and studies on the effects of gene knock-outs should be viewed with caution when the mutants have not been screened for the presence of secondary deletions, or confirmed by other methods. We used the CGH method to genetically characterize a series of regulatory gene deletion mutants we had made in MG1655 using the lamda-Red method of Datsenko and Wanner. A number of strains were tested using CGH, and each strain was tested only once. Genomic DNA isolated from wt MG1655 was used as a reference in all hybridisations.