Project description:The advent of base editors (BEs) holds a promising potential in correcting pathogenic-related point mutations to treat relevant diseases. Unexpectedly, Cas9 nickase (nCas9) derived BEs lead to DNA double-strand breaks, which can trigger unwanted cellular responses including a p53-mediated DNA damage response (DDR). Here, we showed that catalytically-dead-Cas12a (dCas12a) conjugated BEs induced no DNA break and minimally activated DDR proteins including H2AX, ATM, ATR and p53. We further developed a BEACON (Base Editing induced by human APOBEC3A and Cas12a without DNA break) system that fuses dCas12a to the engineered APOBEC3A with enhanced deamination efficiency and editing specificity. By using BEACON, efficient C-to-T editing was achieved at levels comparable to AncBE4max and only low levels of DDR and RNA off-target (OT) effects were triggered in mammalian cells. BEACON also induced in vivo base editing in mouse embryos and targeted C-to-T conversions were detected in F0 mice.
Project description:The advent of base editors (BEs) holds a promising potential in correcting pathogenic-related point mutations to treat relevant diseases. Unexpectedly, Cas9 nickase (nCas9) derived BEs lead to DNA double-strand breaks, which can trigger unwanted cellular responses including a p53-mediated DNA damage response (DDR). Here, we showed that catalytically-dead-Cas12a (dCas12a) conjugated BEs induced no DNA break and minimally activated DDR proteins including H2AX, ATM, ATR and p53. We further developed a BEACON (Base Editing induced by human APOBEC3A and Cas12a without DNA break) system that fuses dCas12a to the engineered APOBEC3A with enhanced deamination efficiency and editing specificity. By using BEACON, efficient C-to-T editing was achieved at levels comparable to AncBE4max and only low levels of DDR and RNA off-target (OT) effects were triggered in mammalian cells. BEACON also induced in vivo base editing in mouse embryos and targeted C-to-T conversions were detected in F0 mice.
2020-05-05 | GSE145550 | GEO
Project description:Engineering CjCas9 for Efficient Base Editing and Prime Editing
Project description:Base Editing has been touted the most intelligent and precise application of the CRISPR platform so far, merging the simplicity of RNA-guided nucleases with deaminases that allow for the programmable generation of single base substitutions - without introduction of double-strand breaks. Even though the two-component system has been expected to cause off-target substitutions, studies involving cytosine base editors (CBEs) showed that in most cases, relatively few single base off-targets could be detected on DNA. We introduce the concept of multi-dimensional off-targeting, presenting an extensive amount of RNA cytidines being edited by DNA base editors. Epitranscriptomic off-target effects affected different cell lines and were independent of the guide RNAs used, suggesting Cas9-independent activity of the cytidine deaminase rAPOBEC1 on single-stranded RNA. With the help of protein engineering, we developed CBE variants with massively reduced inadvertent mutation of RNA that preserve and enhance DNA base editing capabilities.
Project description:Base Editing has been touted the most intelligent and precise application of the CRISPR platform so far, merging the simplicity of RNA-guided nucleases with deaminases that allow for the programmable generation of single base substitutions - without introduction of double-strand breaks. Even though the two-component system has been expected to cause off-target substitutions, studies involving cytosine base editors (CBEs) showed that in most cases, relatively few single base off-targets could be detected on DNA. We introduce the concept of multi-dimensional off-targeting, presenting an extensive amount of RNA cytidines being edited by DNA base editors. Epitranscriptomic off-target effects affected different cell lines and were independent of the guide RNAs used, suggesting Cas9-independent activity of the cytidine deaminase rAPOBEC1 on single-stranded RNA. With the help of protein engineering, we developed CBE variants with massively reduced inadvertent mutation of RNA that preserve and enhance DNA base editing capabilities.