Genome editing by miniature CRISPR/Cas12f1 enzyme in Escherichia coli

Efficient CRISPR-Cas12f1-Mediated Multiplex Bacterial Genome Editing via Low-Temperature Recovery

CRISPR-Cas system is being used as a powerful genome editing tool with developments focused on enhancing its efficiency and accuracy. Recently, the miniature CRISPR-Cas12f1 system, which is small enough to be easily loaded onto various vectors for cellular delivery, has gained attention. In this study, we explored the influence of temperature conditions on multiplex genome editing using CRISPR-Cas12f1 in an Escherichia coli model. It was revealed that when two distinct targets in the genome are edited simultaneously, the editing efficiency can be enhanced by allowing cells to recover at a reduced temperature during the editing process. Additionally, employing 3'-end truncated sgRNAs facilitated the simultaneous single-nucleotide level editing of three targets. Our results underscore the potential of optimizing recovery temperature and sgRNA design protocols in developing more effective and precise strategies for multiplex genome editing across various organisms.

Innovative Delivery System Combining CRISPR-Cas12f for Combatting Antimicrobial Resistance in Gram-Negative Bacteria

Antimicrobial resistance poses a significant global challenge, demanding innovative approaches, such as the CRISPR-Cas-mediated resistance plasmid or gene-curing system, to effectively combat this urgent crisis. To enable successful curing of antimicrobial genes or plasmids through CRISPR-Cas technology, the development of an efficient broad-host-range delivery system is paramount. In this study, we have successfully designed and constructed a novel functional gene delivery plasmid, pQ-mini, utilizing the backbone of a broad-host-range Inc.Q plasmid. Moreover, we have integrated the CRISPR-Cas12f system into the pQ-mini plasmid to enable gene-curing in broad-host of bacteria. Our findings demonstrate that pQ-mini facilitates the highly efficient transfer of genetic elements to diverse bacteria, particularly in various species in the order of Enterobacterales, exhibiting a broader host range and superior conjugation efficiency compared to the commonly used pMB1-like plasmid. Notably, pQ-mini effectively delivers the CRISPR-Cas12f system to antimicrobial-resistant strains, resulting in remarkable curing efficiencies for plasmid-borne mcr-1 or blaKPC genes that are comparable to those achieved by the previously reported pCasCure system. In conclusion, our study successfully establishes and optimizes pQ-mini as a broad-host-range functional gene delivery vector. Furthermore, in combination with the CRISPR-Cas system, pQ-mini demonstrates its potential for broad-host delivery, highlighting its promising role as a novel antimicrobial tool against the growing threat of antimicrobial resistance.

Advances in miniature CRISPR-Cas proteins and their applications in gene editing

The CRISPR-Cas system consists of Cas proteins and single-stranded RNAs that recruit Cas proteins and specifically target the nucleic acid. Some Cas proteins can accurately cleave the target nucleic acid under the guidance of the single-stranded RNAs. Due to its exceptionally high specificity, the CRISPR-Cas system is now widely used in various fields such as gene editing, transcription regulation, and molecular diagnosis. However, the huge size of the most frequently utilized Cas proteins (Cas9, Cas12a, and Cas13, which contain 950-1,400 amino acids) can limit their applicability, especially in eukaryotic gene editing, where larger Cas proteins are difficult to deliver into the target cells. Recently discovered miniature CRISPR-Cas proteins, consisting of only 400 to 800 amino acids, offer the possibility of overcoming this limitation. This article systematically reviews the latest research progress of several miniature CRISPR-Cas proteins (Cas12f, Cas12j, Cas12k, and Cas12m) and their practical applications in the field of gene editing.

Low-Toxicity and High-Efficiency Streptomyces Genome Editing Tool Based on the Miniature Type V-F CRISPR/Cas Nuclease AsCas12f1

Genome editing tools based on SpCas9 and FnCpf1 have facilitated strain improvements for natural product production and novel drug discovery in Streptomyces. However, due to high toxicity, their editing requires high DNA transformation efficiency, which is unavailable in most streptomycetes. The transformation efficiency of an all-in-one editing tool based on miniature Cas nuclease AsCas12f1 was significantly higher than those of SpCas9 and FnCpf1 in tested streptomycetes, which is due to its small size and weak DNA cleavage activity. Using this tool, in Streptomyces coelicolor, we achieved 100% efficiency for single gene or gene cluster deletion and 46.7 and 40% efficiency for simultaneous deletion of two genes and two gene clusters, respectively. AsCas12f1 was successfully extended to Streptomyces hygroscopicus SIPI-054 for efficient genome editing, in which SpCas9/FnCpf1 does not work well. Collectively, this work offers a low-toxicity, high-efficiency genome editing tool for streptomycetes, particularly those with low DNA transformation efficiency.

Comparative Analysis and Phylogenetic Insights of Cas14-Homology Proteins in Bacteria and Archaea

Type-V-F Cas12f proteins, also known as Cas14, have drawn significant interest within the diverse CRISPR-Cas nucleases due to their compact size. This study involves analyzing and comparing Cas14-homology proteins in prokaryotic genomes through mining, sequence comparisons, a phylogenetic analysis, and an array/repeat analysis. In our analysis, we identified and mined a total of 93 Cas14-homology proteins that ranged in size from 344 aa to 843 aa. The majority of the Cas14-homology proteins discovered in this analysis were found within the Firmicutes group, which contained 37 species, representing 42% of all the Cas14-homology proteins identified. In archaea, the DPANN group had the highest number of species containing Cas14-homology proteins, a total of three species. The phylogenetic analysis results demonstrate the division of Cas14-homology proteins into three clades: Cas14-A, Cas14-B, and Cas14-U. Extensive similarity was observed at the C-terminal end (CTD) through a domain comparison of the three clades, suggesting a potentially shared mechanism of action due to the presence of cutting domains in that region. Additionally, a sequence similarity analysis of all the identified Cas14 sequences indicated a low level of similarity (18%) between the protein variants. The analysis of repeats/arrays in the extended nucleotide sequences of the identified Cas14-homology proteins highlighted that 44 out of the total mined proteins possessed CRISPR-associated repeats, with 20 of them being specific to Cas14. Our study contributes to the increased understanding of Cas14 proteins across prokaryotic genomes. These homologous proteins have the potential for future applications in the mining and engineering of Cas14 proteins.

Leverage of nuclease-deficient CasX for preventing pathological angiogenesis

Gene editing with a CRISPR/Cas system is a novel potential strategy for treating human diseases. Pharmacological inhibition of phosphoinositide 3-kinase (PI3K) δ suppresses retinal angiogenesis in a mouse model of oxygen-induced retinopathy. Here we show that an innovative system of adeno-associated virus (AAV)-mediated CRISPR/nuclease-deficient (d)CasX fused with the Krueppel-associated box (KRAB) domain is leveraged to block (81.2% ± 6.5%) in vitro expression of p110δ, the catalytic subunit of PI3Kδ, encoded by Pik3cd. This CRISPR/dCasX-KRAB (4, 269 bp) system is small enough to be fit into a single AAV vector. We then document that recombinant AAV serotype (rAAV)1 efficiently transduces vascular endothelial cells from pathologic retinal vessels, which show high expression of p110δ; furthermore, we demonstrate that blockade of retinal p110δ expression by intravitreally injected rAAV1-CRISPR/dCasX-KRAB targeting the Pik3cd promoter prevents (32.1% ± 5.3%) retinal p110δ expression as well as pathological retinal angiogenesis in a mouse model of oxygen-induced retinopathy. These data establish a strong foundation for treating pathological angiogenesis by AAV-mediated CRISPR interference with p110δ expression.

Miniature CRISPR-Cas12f1-Mediated Single-Nucleotide Microbial Genome Editing Using 3'-Truncated sgRNA

The CRISPR-Cas system has been used as a convenient tool for genome editing because the nuclease that cuts the target DNA and the guide RNA that recognizes the target are separated into modules. Cas12f1, which has a smaller size than that of other Cas nucleases, is easily loaded into vectors and is emerging as a new genome editing tool. In this study, AsCas12f1 was used to negatively select only Escherichia coli cells obtained by oligonucleotide-directed genome editing. Although double-, triple-, and quadruple-base substitutions were accurately and efficiently performed in the genome, the performance of single-base editing was poor. To resolve this limitation, we serially truncated the 3'-end of sgRNAs and determined the maximal truncation required to maintain the target DNA cleavage activity of Cas12f1. Negative selection of single-nucleotide-edited cells was efficiently performed with the maximally 3'-truncated sgRNA-Cas12f1 complex in vivo. Moreover, Sanger sequencing showed that the accuracy of single-nucleotide substitution, insertion, and deletion in the microbial genome was improved. These results demonstrated that a truncated sgRNA approach could be widely used for accurate CRISPR-mediated genome editing.

Recent Advances in CRISPR-Cas Technologies for Synthetic Biology

With developments in synthetic biology, "engineering biology" has emerged through standardization and platformization based on hierarchical, orthogonal, and modularized biological systems. Genome engineering is necessary to manufacture and design synthetic cells with desired functions by using bioparts obtained from sequence databases. Among various tools, the CRISPR-Cas system is modularly composed of guide RNA and Cas nuclease; therefore, it is convenient for editing the genome freely. Recently, various strategies have been developed to accurately edit the genome at a single nucleotide level. Furthermore, CRISPR-Cas technology has been extended to molecular diagnostics for nucleic acids and detection of pathogens, including disease-causing viruses. Moreover, CRISPR technology, which can precisely control the expression of specific genes in cells, is evolving to find the target of metabolic biotechnology. In this review, we summarize the status of various CRISPR technologies that can be applied to synthetic biology and discuss the development of synthetic biology combined with CRISPR technology in microbiology.

A Toolkit for Effective and Successive Genome Engineering of Escherichia coli

The bacterium Escherichia coli has been well-justified as an effective workhorse for industrial applications. In this study, we developed a toolkit for flexible genome engineering of this microorganism, including site-specific insertion of heterologous genes and inactivation of endogenous genes, such that bacterial hosts can be effectively engineered for biomanufacturing. We first constructed a base strain by genomic implementation of the cas9 and λRed recombineering genes. Then, we constructed plasmids for expressing gRNA, DNA cargo, and the Vibrio cholerae Tn6677 transposon and type I-F CRISPR-Cas machinery. Genomic insertion of a DNA cargo up to 5.5 kb was conducted using a transposon-associated CRISPR-Cas system, whereas gene inactivation was mediated by a classic CRISPR-Cas9 system coupled with λRed recombineering. With this toolkit, we can exploit the synergistic functions of CRISPR-Cas, λRed recombineering, and Tn6677 transposon for successive genomic manipulations. As a demonstration, we used the developed toolkit to derive a plasmid-free strain for heterologous production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) by genomic knock-in and knockout of several key genes with high editing efficiencies.

Guide RNA engineering enables efficient CRISPR editing with a miniature Syntrophomonas palmitatica Cas12f1 nuclease

Gene therapy is limited by inefficient delivery of large clustered regularly interspaced short palindromic repeat (CRISPR) effectors, such as Cas9 and Cas12a nucleases. Cas12f nucleases are currently one of the most compact CRISPR genome editors. However, the available toolkit of efficient Cas12f editors is limited. Here, we report the characterization and engineering of a miniature CRISPR-Cas12f system from Syntrophomonas palmitatica (SpaCas12f1, 497 amino acids). We show that CRISPR-SpaCas12f1 cleaves double-stranded DNA (dsDNA) with 5' T-rich PAM specificity and is naturally active for genome editing in bacteria. We identify that CRISPR-SpaCas12f1 trans-activating CRISPR RNA (tracrRNA) harbors a unique head-to-toe hairpin structure, and the natural hairpin structure is a key factor in restricting genome editing by SpaCas12f1 in human cells. Systematical engineering of SpaCas12f1 guide RNA transforms CRISPR-SpaCas12f1 into an efficient genome editor comparable to Francisella novicida CRISPR-Cas12a. Our findings expand the mini CRISPR toolbox, paving the way for therapeutic applications of CRISPR-SpaCas12f1 and engineering compact genome manipulation technologies.

CRISPR based therapeutics: a new paradigm in cancer precision medicine

Background

Clustered regularly interspaced short palindromic repeat (CRISPR)-CRISPR-associated protein (Cas) systems are the latest addition to the plethora of gene-editing tools. These systems have been repurposed from their natural counterparts by means of both guide RNA and Cas nuclease engineering. These RNA-guided systems offer greater programmability and multiplexing capacity than previous generation gene editing tools based on zinc finger nucleases and transcription activator like effector nucleases. CRISPR-Cas systems show great promise for individualization of cancer precision medicine.

Main body

The biology of Cas nucleases and dead Cas based systems relevant for in vivo gene therapy applications has been discussed. The CRISPR knockout, CRISPR activation and CRISPR interference based genetic screens which offer opportunity to assess functions of thousands of genes in massively parallel assays have been also highlighted. Single and combinatorial gene knockout screens lead to identification of drug targets and synthetic lethal genetic interactions across different cancer phenotypes. There are different viral and non-viral (nanoformulation based) modalities that can carry CRISPR-Cas components to different target organs in vivo.

Conclusion

The latest developments in the field in terms of optimization of performance of the CRISPR-Cas elements should fuel greater application of the latter in the realm of precision medicine. Lastly, how the already available knowledge can help in furtherance of use of CRISPR based tools in personalized medicine has been discussed.

Efficient Genome Editing by a Miniature CRISPR-AsCas12f1 Nuclease in Bacillus anthracis

A miniature CRISPR-Cas12f has been demonstrated to serve as an effective genome editing tool in gram negative bacteria as well as human cells. Here, we developed an alternative method to edit the genome of Bacillus anthracis based on the AsCas12f1 nuclease from Acidibacillus sulfuroxidans. When the htrA gene on the chromosome and the lef gene on the plasmid pXO1 were selected as targets, the CRISPR-AsCas12f1 system showed very high efficiency (100%). At the same time, a high efficiency was observed for large-fragment deletion. Our results also indicated that the length of the homologous arms of the donor DNA had a close relationship with the editing efficiency. Furthermore, a two-plasmid CRISPR-AsCas12f1 system was also constructed and combined with the endonuclease I-SceI for potential multi-gene modification. This represents a novel tool for mutant strain construction and gene function analyses in B. anthracis and other Bacillus cereus group bacteria.