Project description:Endogenous Uridine-rich small nuclear RNAs (U snRNAs) form RNA-protein complexes to process eukaryotic pre-mRNA into mRNA. Previous studies have demonstrated programmable U snRNA guide-targeted exon inclusion and exclusion. We investigated whether snRNAs can also enhance RNA base editing over state-of-the-art RNA-targeting technologies in human cells. Compared to adenosine deaminase acting on RNA (ADAR)-recruiting circular RNAs, we find that guided A>I snRNAs consistently increase adenosine-to-inosine editing for higher exon count genes, perturb substantially fewer off-target genes, and localize more persistently to the nucleus where ADAR is expressed. A>I snRNAs also more efficiently edit lncRNAs and pre-mRNA 3′ splice sites to promote splicing changes. Finally, snRNA-H/ACA box snoRNA fusions (U>Ψ snRNAs) increase targeted RNA pseudouridylation without DKC1 overexpression, facilitating improved CFTR rescue from nonsense-mediated mRNA decay in a Cystic fibrosis human bronchial epithelial cell model. Our results advance the endogenous protein-mediated RNA base editing toolbox and RNA-targeting technologies to treat genetic diseases.
Project description:C-to-T base editing mediated by CRISPR/Cas9 base editors (BEs) needs a G/C-rich PAM and the editing fidelity is compromised by unwanted indels and non-C-to-T substitutions. We developed CRISPR/Cpf1-based BEs to recognize a T-rich PAM and induce efficient C-to-T editing with few indels and/or non-C-to-T substitutions. The requirement of editing fidelity in therapeutic-related trials necessitates the development of CRISPR/Cpf1-based BEs, which also facilitates base editing in A/T-rich regions.
Project description:Even the latest generation of base editor (BE3) causes unwanted indels and non-C-to-T substitutions, compromising the fidelity of base editing outcome. Here we report a enhanced base editing system. The enhanced base edting system decreased the formation of unintended indels and C-to-A/C-to-G substitutions, and increased the frequency of desired C-to-T substitution, thereby improving both the accuracy and efficiency of base editing.
Project description:Adenine and cytosine base editors (ABEs and CBEs) represent a new genome editing technology that allows the programmable installation of A-to-G or C-to-T alterations on DNA. We engineered Streptococcus pyogenes Cas9-based adenine and cytosine base editor (SpACE) that enables efficient simultaneous introduction of A-to-G and C-to-T substitutions in the same base editing window on DNA.
Project description:Programmable base editing of RNA enables rewriting the genetic codes on specific sites. Current tools for specific RNA editing dependent on the assembly or recruitment of the guide RNA into an RNA/protein complex, which may cause delivery barrier and low editing efficiency. Here we report a new set of tools, RNA editing with individual RNA-binding enzyme (REWIRE), to perform precise base editing with a single engineered protein. The REWIRE system contains a human-originated programmable RNA-binding domain (PUF domain) to specifically recognize target sequence and different deaminase domains to achieve A-to-I or C-to-U editing. By utilizing this system, we have achieved editing efficiencies up to 80% in A-to-I editing and 65% in C-to-U editing, with a few non-specific editing sites in the targeted region and a low level off-target effect globally. We applied the REWIREs to correct disease-associated mutations and modify mitochondrial RNAs, and further optimized the REWIREs to improve the editing efficiency and minimize off-target effects. As a single-component base editing system originated from human proteins, REWIRE presents a precise and efficient RNA-editing platform with broad applicability in basic research and gene therapy.
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.