scholarly journals Exploring C-To-G Base Editing in Rice, Tomato, and Poplar

2021 ◽  
Vol 3 ◽  
Author(s):  
Simon Sretenovic ◽  
Shishi Liu ◽  
Gen Li ◽  
Yanhao Cheng ◽  
Tingting Fan ◽  
...  
Keyword(s):  
Dna Repair ◽  
Genome Editing ◽  
Target Sequence ◽  
Sequence Context ◽  
Cell Cycles ◽  
Base Editing ◽  
Target Sites ◽  
Base Transition ◽  
Repair Pathways ◽  
Adenine Base

As a precise genome editing technology, base editing is broadly used in both basic and applied plant research. Cytosine base editors (CBEs) and adenine base editors (ABEs) represent the two commonly used base editor types that mediate C-to-T and A-to-G base transition changes at the target sites, respectively. To date, no transversion base editors have been described in plants. Here, we assessed three C-to-G base editors (CGBEs) for targeting sequences with SpCas9’s canonical NGG protospacer adjacent motifs (PAMs) as well as three PAM-less SpRY-based CGBEs for targeting sequences with relaxed PAM requirements. The analyses in rice and tomato protoplasts showed that these CGBEs could make C-to-G conversions at the target sites, and they preferentially edited the C6 position in the 20-nucleotide target sequence. C-to-T edits, insertions and deletions (indels) were major byproducts induced by these CGBEs in the protoplast systems. Further assessment of these CGBEs in stably transformed rice and poplar plants revealed the preference for editing of non-GC sites, and C-to-T edits are major byproducts. Successful C-to-G editing in stably transgenic rice plants was achieved by rXRCC1-based CGBEs with monoallelic editing efficiencies up to 38% in T0 lines. The UNG-rAPOBEC1 (R33A)-based CGBE resulted in successful C-to-G editing in polar, with monoallelic editing efficiencies up to 6.25% in T0 lines. Overall, this study revealed that different CGBEs have different preference on preferred editing sequence context, which could be influenced by cell cycles, DNA repair pathways, and plant species.

scholarly journals Improving the Precision of Base Editing by Bubble Hairpin Single Guide RNA

mBio ◽  
2021 ◽  
Vol 12 (2) ◽  
Author(s):  
Zhiwei Hu ◽  
Yannan Wang ◽  
Qian Liu ◽  
Yan Qiu ◽  
Zhiyu Zhong ◽  
...  
Keyword(s):  
Genome Editing ◽  
Dna Breaks ◽  
Single Nucleotide ◽  
Base Editing ◽  
Guide Rna ◽  
Guide Rnas ◽  
Double Stranded Dna ◽  
Target Sites ◽  
Guide Sequence ◽  
Sgrna Design

ABSTRACT Base editing is a powerful genome editing approach that enables single-nucleotide changes without double-stranded DNA breaks (DSBs). However, off-target effects as well as other undesired editings at on-target sites remain obstacles for its application. Here, we report that bubble hairpin single guide RNAs (BH-sgRNAs), which contain a hairpin structure with a bubble region on the 5′ end of the guide sequence, can be efficiently applied to both cytosine base editor (CBE) and adenine base editor (ABE) and significantly decrease off-target editing without sacrificing on-target editing efficiency. Meanwhile, such a design also improves the purity of C-to-T conversions induced by base editor 3 (BE3) at on-target sites. Our results present a distinctive and effective strategy to improve the specificity of base editing. IMPORTANCE Base editors are DSB-free genome editing tools and have been widely used in diverse living systems. However, it is reported that these tools can cause substantial off-target editings. To meet this challenge, we developed a new approach to improve the specificity of base editors by using hairpin sgRNAs with a bubble. Furthermore, our sgRNA design also dramatically reduced indels and unwanted base substitutions at on-target sites. We believe that the BH-sgRNA design is a significant improvement over existing sgRNAs of base editors, and our design promises to be adaptable to various base editors. We expect that it will make contributions to improving the safety of gene therapy.

scholarly journals CRISPR-Cas9 genome editing in human cells works via the Fanconi Anemia pathway

2017 ◽  
Author(s):  
Chris D Richardson ◽  
Katelynn R Kazane ◽  
Sharon J Feng ◽  
Nicholas L Bray ◽  
Axel J Schäfer ◽  
...  
Keyword(s):  
Dna Repair ◽  
Genome Editing ◽  
Fanconi Anemia ◽  
High Efficiency ◽  
Genetic Diseases ◽  
Dermal Fibroblasts ◽  
Human Cells ◽  
Individual Gene ◽  
Break Site ◽  
Repair Pathways

AbstractCRISPR-Cas9 genome editing creates targeted double strand breaks (DSBs) in eukaryotic cells that are processed by cellular DNA repair pathways. Co-administration of single stranded oligonucleotide donor DNA (ssODN) during editing can result in high-efficiency (>20%) incorporation of ssODN sequences into the break site. This process is commonly referred to as homology directed repair (HDR) and here referred to as single stranded template repair (SSTR) to distinguish it from repair using a double stranded DNA donor (dsDonor). The high efficacy of SSTR makes it a promising avenue for the treatment of genetic diseases1,2, but the genetic basis of SSTR editing is still unclear, leaving its use a mostly empiric process. To determine the pathways underlying SSTR in human cells, we developed a coupled knockdown-editing screening system capable of interrogating multiple editing outcomes in the context of thousands of individual gene knockdowns. Unexpectedly, we found that SSTR requires multiple components of the Fanconi Anemia (FA) repair pathway, but does not require Rad51-mediated homologous recombination, distinguishing SSTR from repair using dsDonors. Knockdown of FA genes impacts SSTR without altering break repair by non-homologous end joining (NHEJ) in multiple human cell lines and in neonatal dermal fibroblasts. Our results establish an unanticipated and central role for the FA pathway in templated repair from single stranded DNA by human cells. Therapeutic genome editing has been proposed to treat genetic disorders caused by deficiencies in DNA repair, including Fanconi Anemia. Our data imply that patient genotype and/or transcriptome profoundly impact the effectiveness of gene editing treatments and that adjuvant treatments to bias cells towards FA repair pathways could have considerable therapeutic value.

scholarly journals Base editing in Streptomyces with Cas9-deaminase fusions

2019 ◽  
Author(s):  
Zhiyu Zhong ◽  
Junhong Guo ◽  
Liang Deng ◽  
Li Chen ◽  
Jian Wang ◽  
...  
Keyword(s):  
Genome Editing ◽  
Target Genes ◽  
Genetic Manipulation ◽  
Strand Break ◽  
High Fidelity ◽  
Nucleotide Substitutions ◽  
Base Editing ◽  
Dna Double Strand Break ◽  
Repair Template ◽  
Adenine Base

AbstractConventional CRISPR/Cas genetic manipulation has been profitably applied to the genus Streptomyces, the most prolific bacterial producers of antibiotics. However, its reliance on DNA double-strand break (DSB) formation leads to unacceptably low yields of desired recombinants. We have adapted for Streptomyces recently-introduced cytidine base editors (CBEs) and adenine base editors (ABEs) which enable targeted C-to-T or A-to-G nucleotide substitutions, respectively, bypassing DSB and the need for a repair template. We report successful genome editing in Streptomyces at frequencies of around 50% using defective Cas9-guided base editors and up to 100% by using nicked Cas9-guided base editors. Furthermore, we demonstrate the multiplex genome editing potential of the nicked Cas9-guided base editor BE3 by programmed mutation of nine target genes simultaneously. Use of the high-fidelity version of BE3 (HF-BE3) essentially improved editing specificity. Collectively, this work provides a powerful new tool for genome editing in Streptomyces.

scholarly journals Base editing and prime editing in laboratory animals

2021 ◽  
pp. 002367722199389
Author(s):  
Federico Caso ◽  
Benjamin Davies
Keyword(s):  
Genome Editing ◽  
Laboratory Animal ◽  
Genome Engineering ◽  
Point Mutations ◽  
Animal Research ◽  
Ease Of Use ◽  
Laboratory Animals ◽  
Genomic Change ◽  
Base Editing ◽  
Adenine Base

Genome editing by programmable RNA-dependent Cas endonucleases has revolutionised the field of genome engineering, achieving targeted genomic change at unprecedented efficiencies with considerable application in laboratory animal research. Despite its ease of use and wide application, there remain concerns about the precision of this technology and a number of unpredictable consequences have been reported, mostly resulting from the DNA double-strand break (DSB) that conventional CRISPR editing induces. In order to improve editing precision, several iterations of the technology been developed over the years. Base editing is one of most successful developments, allowing for single base conversions but without the need for a DSB. Cytosine and adenine base editing are now established as reliable methods to achieve precise genome editing in animal research studies. Both cytosine and adenine base editors have been applied successfully to the editing of zygotes, resulting in the generation of animal models. Similarly, both base editors have achieved precise editing of point mutations in somatic cells, facilitating the development of gene therapy approaches. Despite rapid progress in optimising these tools, base editing can address only a subset of possible base conversions within a relatively narrow window and larger genomic manipulations are not possible. The recent development of prime editing, originally defined as a simple ‘search and replace’ editing tool, may help address these limitations and could widen the range of genome manipulations possible. Preliminary reports of prime editing in animals are being published, and this new technology may allow significant advancements for laboratory animal research.

scholarly journals Disintegration promotes proto-spacer integration by the Cas1-Cas2 complex

2020 ◽  
Author(s):  
Chien-Hui Ma ◽  
Kamyab Javanmardi ◽  
Ilya J. Finkelstein ◽  
Makkuni Jayaram
Keyword(s):  
Dna Repair ◽  
Streptococcus Pyogenes ◽  
Target Site ◽  
Dna Transposition ◽  
Insertion Event ◽  
Dna Integration ◽  
Biochemical Investigation ◽  
Target Sites ◽  
Repair Pathways ◽  
Integration Event

Abstract‘Disintegration’—the reversal of transposon DNA integration at a target site—is regarded as an abortive off-pathway reaction. Here we challenge this view with a biochemical investigation of the mechanism of protospacer insertion by the Streptococcus pyogenes Cas1-Cas2 complex, which is mechanistically analogous to DNA transposition. In supercoiled target sites, the predominant outcome is the disintegration of one-ended insertions that fail to complete the second integration event. In linear target sites, one-ended insertions far outnumber complete proto-spacer insertions. The second insertion event is most often accompanied by disintegration of the first, mediated either by the 3’-hydroxyl exposed during integration or by water. One-ended integration intermediates may mature into complete spacer insertions via DNA repair pathways that are also involved in transposon mobility. We propose that disintegration-promoted integration is functionally important in the adaptive phase of CRISPR-mediated bacterial immunity, and perhaps in other analogous transposition reactions.

A Simple Heat Treatment Increases SpCas9-Mediated Mutation Efficiency in Arabidopsis

2021 ◽  
Author(s):  
Shuta Kurokawa ◽  
Hafizur Rhaman ◽  
Naoshi Yamanaka ◽  
Chisato Ishizaki ◽  
Shaikhul Islam ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Genome Editing ◽  
Target Sequence ◽  
Simple Method ◽  
Guide Rna ◽  
Highly Active ◽  
Seed Population ◽  
Target Sites ◽  
Mutation Efficiency ◽  
Rna Genes

Abstract The CRISPR/Cas9 system is now commonly employed for genome editing in various plants such as Arabidopsis, rice, and tobacco. In general, in genome editing of the Arabidopsis genome, the SpCas9 and guide RNA genes are introduced into the genome by the floral dip method. Mutations induced in the target sequence by SpCas9 are confirmed after selecting transformants by screening the T1 seed population. The advantage of this method is that genome-edited plants can be isolated easily. However, mutation efficiency in Arabidopsis using SpCas9 is not as high as that achieved in rice and tobacco, which are subjected to a tissue culture step. In this study, we compared four promoters and found that the parsley UBIQITIN promoter is highly active in Arabidopsis meristem tissue. Furthermore, we examined whether a simple heat treatment could improve mutation efficiency in Arabidopsis. Just one heat treatment at 37 °C for 24 hours increased the mutation efficiency at all four target sites from 3% to 42%, 43% to 62%, 54% to 75%, and 89 to 91%, respectively, without detectable off-target mutations. We recommend heat treatment of plate-grown plants at 37 °C for 24 hours as a simple method to increase the efficiency of CRISPR/Cas9-mediated mutagenesis in Arabidopsis.

Progress in precise and predictable genome editing in plants with base editing

2021 ◽  
pp. 123-146
Author(s):  
Sabine Fräbel ◽  
◽  
Shai J. Lawit ◽  
Jingyi Nie ◽  
David G. Schwark ◽  
...  
Keyword(s):  
Nucleic Acid ◽  
Genome Editing ◽  
Gene Editing ◽  
In Planta ◽  
Reading Frame ◽  
Base Editing ◽  
Adenine Base

Base editors are gene editing tools that allow targeted nucleic acid conversions, most commonly C>T and A>G, through pairing of deamination domains with impaired nucleases. Multiple deaminase domains and architectures have been demonstrated in planta across a wide array of species, with both cytosine and adenine base editing frequencies being observed at over 80%. The ability of base editors to introduce nucleic acid diversity while maintaining the same reading frame should make them powerful tools for plant genetic editing moving forward.

scholarly journals Peptide fusion improves prime editing efficiency

2021 ◽  
Author(s):  
Minja Velimirovic ◽  
Larissa Zanetti ◽  
Max W Shen ◽  
James D Fife ◽  
Lin Lin ◽  
...  
Keyword(s):  
Dna Repair ◽  
Amino Acid ◽  
Genome Editing ◽  
Cell Lines ◽  
High Throughput ◽  
Editing Efficiency ◽  
Human Dna ◽  
Target Sites ◽  
Multiple Cell ◽  
Related Proteins

Prime editing enables search-and-replace genome editing but is limited by low editing efficiency. We present a high-throughput approach, PepSEq, to measure how fusion of 12,000 85-amino acid peptides derived from human DNA repair-related proteins influences prime editing efficiency. We show that peptide fusion can enhance prime editing, prime-enhancing peptides combine productively, and a top dual peptide-prime editor increases prime editing significantly in multiple cell lines across dozens of target sites.

scholarly journals Approaches to Enhance Precise CRISPR/Cas9-Mediated Genome Editing

2021 ◽  
Vol 22 (16) ◽  
pp. 8571
Author(s):  
Christopher E. Denes ◽  
Alexander J. Cole ◽  
Yagiz Alp Aksoy ◽  
Geng Li ◽  
G. Gregory Neely ◽  
...  
Keyword(s):  
Dna Repair ◽  
Genome Editing ◽  
Nuclear Dna ◽  
Great Promise ◽  
End Joining ◽  
Strand Breaks ◽  
Homology Directed Repair ◽  
Repair Pathways ◽  
Non Homologous End Joining ◽  
Small Molecule Modulators

Modification of the human genome has immense potential for preventing or treating disease. Modern genome editing techniques based on CRISPR/Cas9 show great promise for altering disease-relevant genes. The efficacy of precision editing at CRISPR/Cas9-induced double-strand breaks is dependent on the relative activities of nuclear DNA repair pathways, including the homology-directed repair and error-prone non-homologous end-joining pathways. The competition between multiple DNA repair pathways generates mosaic and/or therapeutically undesirable editing outcomes. Importantly, genetic models have validated key DNA repair pathways as druggable targets for increasing editing efficacy. In this review, we highlight approaches that can be used to achieve the desired genome modification, including the latest progress using small molecule modulators and engineered CRISPR/Cas proteins to enhance precision editing.

Advances in genome editing through control of DNA repair pathways

2019 ◽  
Vol 21 (12) ◽  
pp. 1468-1478 ◽  
Author(s):  
Charles D. Yeh ◽  
Christopher D. Richardson ◽  
Jacob E. Corn
Keyword(s):  
Dna Repair ◽  
Genome Editing ◽  
Repair Pathways
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