CRISPR RNA Array-Guided Multisite Cleavage for Gene Disruption by Cas9 and Cpf1

Dibenzocyclooctyne-Branched Primer Assembled Gene Nanovector and Its Potential Applications in Genome Editing

The CRISPR/Cas9 system has been widely used as an efficient genome editing toolkit for gene therapy. The delivery of vectors encoding the full CRISPR/Cas9 components including Cas9 gene and gRNA expression element into cells is the crucial step to effective genome editing. However, the cargo gene sequence for genome editing is usually large, which reduces the cargo encapsulation efficiency and affects the vector size. To obtain a nanovector with high cargo gene loading capacity and biocompatible size, we report the construction of a gene nanovector from branch-PCR with a dibenzocyclooctyne (DBCO)-branched primer and establish the correlation mapping between gene length and nanovector size. The results show that the size of nanovectors can be tuned according to the gene length. According to the findings, we constructed nanovectors carrying the full CRISPR/Cas9 components in 100-200 nm and validated their application in genome editing. The results show that this kind of nanovector exhibits higher serum stability than plasmids and can reach comparable genome editing efficiency with plasmids. Hence, this type of gene nanovector obtained through branch-PCR can carry large gene cargos and maintain a biocompatible nanoscale size, which we envisage will expand its medical applications in gene therapy.

Target DNA mutagenesis-based fluorescence assessment of off-target activity of the CRISPR-Cas9 system

The RNA-guided CRISPR/Cas9 system could cleave double-stranded DNA at the on-target sites but also induce off-target mutations in unexpected genomic regions. The base-pairing interaction of sgRNA with off-target DNA was still not well understood and also lacked a direct cell-based assay. Herein we developed a fast target DNA mutagenesis-based fluorescence assay to directly detect the Cas9 activity at different off-target sites in living cells. The results showed that Cas9 nuclease had low tolerance to the nucleotide mismatches in the binding region adjacent to PAM sites, and a tradeoff between Cas9 activity and specificity was also observed compared with the high-fidelity Cas9 variant. The combination of computer-based predictions and this target DNA mutagenesis-based fluorescence assay could further provide accurate off-target prediction guidance to minimize off-target effects to enable safer genome engineering.