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APOBEC3s induce mutations during the repair of CRISPR-Cas9-generated DNA breaks.

ABSTRACT: APOBEC-AID family of cytidine deaminase prefers single-stranded nucleic acids for cytidine to uracil deamination. Single-stranded nucleic acids are commonly involved in the DNA repair system for breaks generated by CRISPR-Cas9. Here, we show in human cells that APOBEC3s can trigger the cytidine deamination of single-stranded oligodeoxynucleotides, which ultimately results in base substitution mutations in genomic DNA through the homology-directed repair (HDR) of Cas9-generated double-strand breaks . In addition, the APOBEC3-catalyzed deamination in genomic single-stranded DNA formed during the repair of Cas9 nickase-generated single-strand breaks can be further processed to yield mutations mainly involving insertions or deletions (indels). Mechanistically, both APOBEC3-mediated deamination and DNA repair proteins play important roles in the generation of these indels. Correspondingly, optimizing conditions for the repair of CRISPR-Cas9-generated DNA breaks, such as using double-stranded donors in HDR or temporarily suppressing endogenous APOBEC3s, can substantially repress these unwanted mutations in genomic DNA.

ORGANISM(S): Homo sapiens

PROVIDER: GSE105146 | GEO | 2017/11/10

SECONDARY ACCESSION(S): PRJNA414960

REPOSITORIES: GEO

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Project description:The gain-of-function mutation of c.G6055A (p.G2019S) in Leucine-rich repeat kinase 2 (LRRK2) gene is the most prevalent genetic cause of Parkinson’s disease (PD). Although clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9-based genome editing has been used to generate isogenic control lines, there are risks of creating indels and genomic instability together with a lower efficiency in non-dividing cells. The recent advance of adenine base editors (ABEs) could convert targeted A•T base pairs to G•C base pairs without double-strand DNA breaks or donor DNA templates and function in post-mitotic cells. Here, we demonstrate a complete correction of an induced pluripotent stem cell (iPSC) line derived from a PD patient having LRRK2 p.G2019S mutation using variable genome editing methods, including CRISPR/Cas9-based homology-directed repair (HDR) and ABEs. The corrected isogenic iPSCs derived dopaminergic neurons showed a down-regulated LRRK2 kinase activity, decreased phospho-a-synuclein accumulations, reduced apoptosis and restored neurite shrinkage phenotypes. The mutation correction efficacy, off-target and indels rates between CRISPR/Cas9-HDR and ABE were compared. Among the 47 clones generated by HDR, 3 clones (6.4%) were on-targeted corrected, while ABE showed a much higher correction rate (13 of 53 clones, 24.5%). Whole genome sequencing analysis revealed that there are 27 clones of HDR (57.4%) having deletions but none in clones of ABE, albeit ABE created 14 clones (26.4%) having off-target missense mutations. RNA sequencing and proteomic analysis of the mutant line identified 2220 differentially expressed genes compared with its isogenic control. Enrichment analysis demonstrated an over-representation of PD relevant pathways, including calcium ion dependent exocytosis, synaptic transports well as potential novel targets relevant to PD pathophysiology. These results envision that ABE could directly correct the pathogenic PD mutation in iPSCs for exploring the earliest events in PD pathophysiology and providing dopaminergic neurons for future cell therapies.

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APOBEC3s induce mutations during the repair of CRISPR-Cas9-generated DNA breaks.

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