Chapter 2 —— 24 —— toolbox for ‘soft’ genome editing involving HDR and prime editing, respectively. Contrary to HDR, prime editing does not require the transfer of donor DNA substrates and allows for genomic insertion of up to ∼44-bp of Figure2. Gene correction via interhomolog recombination between heterozygous allelic sequences. Interhomolog recombination (IHR) characteristic of meiosis in germ cells can be fostered in somatic cells subjected to allele-specific double-stranded DNA breaks (DSB), yet the major products are on-target mutagenesis in the form of NHEJderived small insertions and deletions (indels). In contrast, allele-specific single-stranded DNA breaks (SSB) can equally foster IHR in somatic cells especially when using multiplexing CRISPR-Cas9 nickases for in trans multiple nicking IHR (MN-IHR). In somatic cells with heterozygous mutations or compound heterozygous mutations (not shown) underlying genetic disorders, CRISPR-Cas9 nickase-induced IHR offers the prospect for new genetic therapy interventions via wild-type allele-templated gene repair.
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