Mapping of microhomologies at CRISPR/Cas9 deletions
Ontology highlight
ABSTRACT:
ORGANISM(S): Mus musculus
PROVIDER: GSE130621 | GEO | 2019/05/13
REPOSITORIES: GEO
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Project description:Mapping of microhomologies at CRISPR/Cas9 deletions
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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
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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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Project description:Paired Nickases TREX2 related Raw sequence reads
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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.
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Project description:Inactivation of Pten occurs by multiple mechanisms including epigenetic silencing, point mutations, insertion, and deletion, which are tissue dependent. Although frequent loss of heterozygosity around Pten locus and plausible involvement of epigenetic silencing have been reported in radiation-induced thymic lymphomas, the frequency of Pten inactivation and the spectrum of causal aberrations have not yet been extensively characterized. Here, we assessed the principal mode of inactivation by comprehensively analyzing expression and alterations of Pten gene in 23 radiation-induced thymic lymphomas developed in B6C3F1 mice. We found no evidence for methylation-associated silencing of Pten gene. Instead, we found complex structural abnormalities in 8 lymphomas (35%) that included missense and nonsense mutations, 1- and 3-bp insertions, and focal deletions. Sequencing of deletion breakpoints suggested that illegitimate V(D)J recombination and microhomology-mediated rearrangement were responsible for the focal deletions. Seven out of these 8 lymphomas had biallelic alterations, and 4 of them did not express any Pten protein. These aberrations of Pten were well coincided with downstream Akt phosphorylation on Ser473. In conclusion, Pten inactivation, which is frequently biallelic and is caused by a variety of structural abnormalities but not by epigenetic silencing, is involved in radiation-induced lymphomagenesis. Three thymic lymphomas were analyzed by array-CGH method.
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