Dual guide RNA-mediated concurrent C&G-to-T&A and A&T-to-G&C conversions using CRISPR base editors.

Base editing tools enable precise genome modifications, disease modeling, and promising gene therapy. However, many human genetic diseases are elicited by multi-nucleotide variants (MNVs) with heterogeneous substitutions at the same genomic locus. Based on the adenine and cytosine base editors, dual base editors that can catalyze concurrent C-to-T and A-to-G editing have been developed, while simultaneous C&G-to-T&A and A&T-to-G&C conversions on the same allele have not been achieved at the desirable site. Here we propose a strategy of combining base editors with dual guide RNAs (gRNAs) that target two overlapped neighboring loci on the opposite strands, which can induce simultaneous C&G-to-T&A and A&T-to-G&C conversions within their overlapping targeting windows. Moreover, one of the paired gRNAs is mutated to perfectly match another gRNA-edited sequence, efficiently facilitating concurrent base conversions on the same allele. To further expand the targeting scopes, PAMless SpRY Cas9-mediated base editors are combined with our optimized dual gRNAs system to induce expected concurrent base editing and to install neighboring pathogenic MNVs in TP53 in cancer cells. In addition, more complex mutation types can be achieved by integrating dual base editors and our dual gRNAs strategy. Thus, we establish a general strategy to efficiently induce MNVs in human genome, helping to dissect the functions of pathogenic MNVs with multifarious types.