The widespread IS200/IS605 transposon family encodes diverse programmable RNA-guided endonucleases

Assessment of Miniature AsCas12f1 Variants for Gene Editing and Activation

Miniature CRISPR/Cas systems possess delivery advantages for gene therapy. The type V-F Cas12f1 from Acidibacillus sulfuroxidans is exceptionally compact (422 amino acids) and has been engineered by several studies as compact genome editing tools through protein and single guide RNA (sgRNA) engineering. However, a comparative evaluation of gene editing and activation efficiencies mediated by different AsCas12f1 variants and sgRNA scaffolds is lacking. This study tested combinations of four AsCas12f1 protein variants and six sgRNA scaffolds for their gene editing and transcription activation efficiencies. The protein variant AsCas12f1-HKRA performed the best in gene editing and activation when paired with sgRNA-en_v2.1 scaffold. Furthermore, we validated a super miniature gene activator by fusing a small activation domain to AsCas12f1-HKRA. Our findings recommend using AsCas12f1-HKRA and sgRNA-en_v2.1 for gene editing and activation applications.

Evolution-guided protein design of IscB for persistent epigenome editing in vivo

Naturally existing enzymes have been adapted for a variety of molecular technologies, with enhancements or modifications to the enzymes introduced to improve the desired function; however, it is difficult to engineer variants with enhanced activity while maintaining specificity. Here we engineer the compact Obligate Mobile Element Guided Activity (OMEGA) RNA-guided endonuclease IscB and its guiding RNA (ωRNA) by combining ortholog screening, structure-guided protein domain design and RNA engineering, and deep learning-based structure prediction to generate an improved variant, NovaIscB. We show that the compact NovaIscB achieves up to 40% indel activity (~100-fold improvement over wild-type OgeuIscB) on the human genome with improved specificity relative to existing IscBs. We further show that NovaIscB can be fused with a methyltransferase to create a programmable transcriptional repressor, OMEGAoff, that is compact enough to be packaged in a single adeno-associated virus vector for persistent in vivo gene repression. This study highlights the power of combining natural diversity with protein engineering to design enhanced enzymes for molecular biology applications.

TIGR on the loose: A dual-guide RNA system for DNA targeting

A recent study1 unveils tandem interspaced guide RNAs (TIGRs) that simultaneously engage both strands of target DNA and direct Tas protein activity. It offers insights into the evolution of RNA-guided proteins and introduces a promising tool for genome editing.

TIGR-Tas: A family of modular RNA-guided DNA-targeting systems in prokaryotes and their viruses

RNA-guided systems provide remarkable versatility, enabling diverse biological functions. Through iterative structural and sequence homology-based mining starting with a guide RNA-interaction domain of Cas9, we identified a family of RNA-guided DNA-targeting proteins in phage and parasitic bacteria. Each system consists of a tandem interspaced guide RNA (TIGR) array and a TIGR-associated (Tas) protein containing a nucleolar protein (Nop) domain, sometimes fused to HNH (TasH)- or RuvC (TasR)-nuclease domains. We show that TIGR arrays are processed into 36-nucleotide RNAs (tigRNAs) that direct sequence-specific DNA binding through a tandem-spacer targeting mechanism. TasR can be reprogrammed for precise DNA cleavage, including in human cells. The structure of TasR reveals striking similarities to box C/D small nucleolar ribonucleoproteins and IS110 RNA-guided transposases, providing insights into the evolution of diverse RNA-guided systems.

Directed Evolution of OgeuIscB With Enhanced Activity in Human Cells

The miniature RNA-guided endonuclease IscB, as the evolutionary progenitor of Cas9, is attracting increased attention for genome editing due to its compact size and suitability for in vivo delivery. However, the poor editing efficiency of IscB in eukaryotic cells presents a significant challenge to its widespread application in precise site-specific human genome editing. In this study, we employed structure-guided rational design and protein engineering to optimize OgeuIscB, resulting in the identification of enIscB-F138R, which further enhanced editing activity up to 3.49-fold in mammalian cells compared to the high-activity OgeuIscB variant enIscB. Furthermore, we engineered an enIscB-F138R nickase-based adenine base editor, termed miABE-F138R, exhibiting enhanced base editing efficiency relative to miABE. To illustrate the practical applications of miABE-F138R, we applied it to rectify the prevalent R560C mutation in Pde6β associated with autosomal recessive retinitis pigmentosa, resulting in a significant improvement in activity compared to miABE. In conclusion, enIscB-F138R and miABE-F138R offer adaptable platforms for genome editing with potential significance in future biomedical applications.

Research progress of gene editing technology in neurological diseases

Gene editing (GE) technology is a genetic manipulation technique based on artificial nucleases that enables the precise modification of DNA or RNA. With the development of technology, GE in disease treatment is becoming increasingly widespread, playing an essential role in haematology, cancer, and neurological disorders (ND). This review describes the principles, advantages, and limitations of four GE technologies, focusing on the fourth generation of GE (next-generation GE). The next-generation GE technology breaks the limitations of traditional GE technology, makes GE more precise and stable, and broadens the scope of gene technology applications. Additionally, this review explores the latest gene therapy strategies for ND, focusing on the application of next-generation GE technologies to examine the prospects for the application of GE technologies. This study discusses and analyses the great advantages and potential of GE technology for treating ND and elucidates the shortcomings of GE in this field.

Viral delivery of an RNA-guided genome editor for transgene-free germline editing in Arabidopsis

Genome editing is transforming plant biology by enabling precise DNA modifications. However, delivery of editing systems into plants remains challenging, often requiring slow, genotype-specific methods such as tissue culture or transformation1. Plant viruses, which naturally infect and spread to most tissues, present a promising delivery system for editing reagents. However, many viruses have limited cargo capacities, restricting their ability to carry large CRISPR-Cas systems. Here we engineered tobacco rattle virus (TRV) to carry the compact RNA-guided TnpB enzyme ISYmu1 and its guide RNA. This innovation allowed transgene-free editing of Arabidopsis thaliana in a single step, with edits inherited in the subsequent generation. By overcoming traditional reagent delivery barriers, this approach offers a novel platform for genome editing, which can greatly accelerate plant biotechnology and basic research.

Discovery of diverse and high-quality mRNA capping enzymes through a language model-enabled platform

Mining and expanding high-quality genetic parts for synthetic biology and bioengineering are urgent needs in the research and development of next-generation biotechnology. However, gene mining has relied on sequence homology or ample expert knowledge, which fundamentally limits the establishment of a comprehensive genetic part catalog. In this work, we propose SYMPLEX (synthetic biological part mining platform by large language model-enabled knowledge extraction), a universal gene-mining platform based on large language models. We applied SYMPLEX to mine enzymes responsible for messenger RNA (mRNA) capping, a key process in eukaryotic posttranscriptional modification, and obtained thousands of diverse candidates with traceable evidence from biomedical literature and databases. Of the 46 experimentally tested integral capping enzyme candidates, 14 demonstrated in vivo cross-species capping activity, and 2 displayed superior in vitro activity over the commercial vaccinia capping enzymes currently used in mRNA vaccine production. SYMPLEX provides a distinct paradigm for functional gene mining and offers powerful tools to facilitate knowledge discovery in fundamental research.

Reprogrammable RNA-targeting CRISPR systems evolved from RNA toxin-antitoxins

Despite ongoing efforts to study CRISPR systems, the evolutionary origins giving rise to reprogrammable RNA-guided mechanisms remain poorly understood. Here, we describe an integrated sequence/structure evolutionary tracing approach to identify the ancestors of the RNA-targeting CRISPR-Cas13 system. We find that Cas13 likely evolved from AbiF, which is encoded by an abortive infection-linked gene that is stably associated with a conserved non-coding RNA (ncRNA). We further characterize a miniature Cas13, classified here as Cas13e, which serves as an evolutionary intermediate between AbiF and other known Cas13s. Despite this relationship, we show that their functions substantially differ. Whereas Cas13e is an RNA-guided RNA-targeting system, AbiF is a toxin-antitoxin (TA) system with an RNA antitoxin. We solve the structure of AbiF using cryoelectron microscopy (cryo-EM), revealing basic structural alterations that set Cas13s apart from AbiF. Finally, we map the key structural changes that enabled a non-guided TA system to evolve into an RNA-guided CRISPR system.

Engineering an optimized hypercompact CRISPR/Cas12j-8 system for efficient genome editing in plants

The Cas12j-8 nuclease, derived from the type V CRISPR system, is approximately half the size of Cas9 and recognizes a 5'-TTN-3' protospacer adjacent motif sequence, thus potentially having broad application in genome editing for crop improvement. However, its editing efficiency remains low in plants. In this study, we rationally engineered both the crRNA and the Cas12j-8 nuclease. The engineered crRNA and Cas12j-8 markedly improved genome editing efficiency in plants. When combined, they exhibited robust editing activity in soybean and rice, enabling the editing of target sites that were previously uneditable. Notably, for certain target sequences, the editing activity was comparable to that of SpCas9 when targeting identical sequences, and it outperformed the Cas12j-2 variant, nCas12j-2, across all tested targets. Additionally, we developed cytosine base editors based on the engineered crRNA and Cas12j-8, demonstrating an average increase of 5.36- to 6.85-fold in base-editing efficiency (C to T) compared with the unengineered system in plants, with no insertions or deletions (indels) observed. Collectively, these findings indicate that the engineered hypercompact CRISPR/Cas12j-8 system serves as an efficient tool for genome editing mediated by both nuclease cleavage and base editing in plants.

Fanzors, a family of eukaryotic RNA-guided DNA endonucleases

Fanzor proteins represent the first confirmed family of RNA-guided DNA endonucleases in eukaryotes. Originally identified in 2013 as TnpB homologs, Fanzors remained functionally uncharacterized until 2023, when three independent research groups demonstrated their activity as programmable nucleases. Comprehensive bioinformatic analysis revealed over 3000 unique Fanzor sequences across diverse eukaryotic phyla and viruses. Fanzors share core mechanisms with their prokaryotic counterparts, utilizing a RuvC domain for DNA cleavage and requiring a Fanzor RNA (ωRNA) for targeting. However, they exhibit distinctive features, including diverse target adjacent motif preferences, extended ωRNA structure, and RuvC domain rearrangements. The eukaryotic origins of Fanzors make them promising tools for mammalian genome editing, with initial studies demonstrating successful editing in human cells without extensive engineering.

Engineering a New Generation of Gene Editors: Integrating Synthetic Biology and AI Innovations

CRISPR-Cas technology has revolutionized biology by enabling precise DNA and RNA edits with ease. However, significant challenges remain for translating this technology into clinical applications. Traditional protein engineering methods, such as rational design, mutagenesis screens, and directed evolution, have been used to address issues like low efficacy, specificity, and high immunogenicity. These methods are labor-intensive, time-consuming, and resource-intensive and often require detailed structural knowledge. Recently, computational strategies have emerged as powerful solutions to these limitations. Using artificial intelligence (AI) and machine learning (ML), the discovery and design of novel gene-editing enzymes can be streamlined. AI/ML models predict activity, specificity, and immunogenicity while also enhancing mutagenesis screens and directed evolution. These approaches not only accelerate rational design but also create new opportunities for developing safer and more efficient genome-editing tools, which could eventually be translated into the clinic.

Unlocking the potential of 'Egusi' melon (Colocynthis citrullus L.) as a crop for biotechnological improvement

'Egusi' melon (Colocynthis citrullus L.) plays a critical role in food security and potential biofuel production in West Africa. Its seeds are valued for both their nutritional and potential industrial applications, especially in biodiesel production. However, the crop faces significant challenges, including the impacts of climate change, water scarcity, declining arable land, and increased pressure from pests and diseases. These challenges threaten the stability of 'Egusi' production and may hinder its ability to meet future demand. To address these issues, there is a growing need to complement conventional breeding methods with biotechnological approaches. Molecular approaches; including genomics, transcriptomics, proteomics, and metabolomics; have been utilized for the improvement of several cucurbit species. However, information on molecular breeding of 'Egusi' is very limited. The current review focuses on 'Egusi' melon, its biology, uses, and factors affecting its improvement, and highlights critical knowledge gaps in the molecular breeding of 'Egusi'. The review also examines the potential of omics technologies and outlines the importance of genetic transformation and genome editing methods such as CRISPR that could drive the development of more resilient and high-yielding 'Egusi'varieties that will contribute to sustainability and profitability of 'Egusi' farming.

Insights into the compact CRISPR-Cas9d system

Cas9d, the smallest known member of the Cas9 family, employs a compact domain architecture for effective target cleavage. However, the underlying mechanism remains unclear. Here, we present the cryo-EM structures of the Cas9d-sgRNA complex in both target-free and target-bound states. Biochemical assays elucidated the PAM recognition and DNA cleavage mechanisms of Cas9d. Structural comparisons revealed that at least 17 base pairs in the guide-target heteroduplex is required for nuclease activity. Beyond its typical role as an adaptor between Cas9 enzymes and targets, the sgRNA also provides structural support and functional regulation for Cas9d. A segment of the sgRNA scaffold interacts with the REC domain to form a functional target recognition module. Upon target binding, this module undergoes a coordinated conformational rearrangement, enabling heteroduplex propagation and facilitating nuclease activity. This hybrid functional module precisely monitors heteroduplex complementarity, resulting in a lower mismatch tolerance compared to SpyCas9. Moreover, structure-guided engineering in both the sgRNA and Cas9d protein led to a more compact Cas9 system with well-maintained nuclease activity. Altogether, our findings provide insights into the target recognition and cleavage mechanisms of Cas9d and shed light on the development of high-fidelity mini-CRISPR tools.

OMEGA-guided DNA polymerases enable random mutagenesis in a tunable window

Targeted random mutagenesis is crucial for breeding, directed evolution, and gene function studies, yet efficient tools remain scarce. Here, we present obligate mobile element guided activity (OMEGA)-R, an innovative targeted random mutagenesis system that integrates SpyCatcher-enIscB and PolI3M-TBD-SpyTag, outperforming existing state-of-the-art technologies in key metrics, such as protein size, mutagenesis efficiency, window length, and continuity. OMEGA-R achieves a dramatic enhancement of on-target mutagenesis, reaching a rate of 1.4 × 10-5 base pairs (bp) per generation (bpg), with minimal off-target effects, in both Escherichia coli and Bacillus subtilis. The system also demonstrates exceptional compatibility with high-throughput screening (HTS) technologies, including fluorescence-activated droplet sorting (FADS) and phage-assisted continuous evolution (PACE). Utilizing OMEGA-R, we successfully identified a series of effective mutations within the T7 promoter (pT7), ribosome-binding site (RBS), superfolder GFP (sfGFP), and autocyclizing ribozyme (AR), which are invaluable for the development of high-performance biotechnology tools. These findings underscore the high efficiency and broad application potential of OMEGA-R.

Emerging applications of gene editing technologies for the development of climate-resilient crops

Climate change threatens global crop yield and food security due to rising temperatures, erratic rainfall, and increased abiotic stresses like drought, heat, and salinity. Gene editing technologies, including CRISPR/Cas9, base editors, and prime editors, offer precise tools for enhancing crop resilience. This review explores the mechanisms of these technologies and their applications in developing climate-resilient crops to address future challenges. While CRISPR/enables targeted modifications of plant DNA, the base editors allow for direct base conversion without inducing double-stranded breaks, and the prime editors enable precise insertions, deletions, and substitutions. By understanding and manipulating key regulator genes involved in stress responses, such as DREB, HSP, SOS, ERECTA, HsfA1, and NHX; crop tolerance can be enhanced against drought, heat, and salt stress. Gene editing can improve traits related to root development, water use efficiency, stress response pathways, heat shock response, photosynthesis, membrane stability, ion homeostasis, osmotic adjustment, and oxidative stress response. Advancements in gene editing technologies, integration with genomics, phenomics, artificial intelligence (AI)/machine learning (ML) hold great promise. However, challenges such as off-target effects, delivery methods, and regulatory barriers must be addressed. This review highlights the potential of gene editing to develop climate-resilient crops, contributing to food security and sustainable agriculture.

Efforts to Downsize Base Editors for Clinical Applications

Since the advent of the clustered regularly interspaced short palindromic repeats (CRISPR) system in the gene editing field, diverse CRISPR-based gene editing tools have been developed for treating genetic diseases. Of these, base editors (BEs) are promising because they can carry out precise gene editing at single-nucleotide resolution without inducing DNA double-strand breaks (DSBs), which pose significant risks of genomic instability. Despite their outstanding advantages, the clinical application of BEs remains challenging due to their large size, which limits their efficient delivery, particularly in adeno-associated virus (AAV)-based systems. To address this issue, various strategies have been explored to reduce the size of BEs. These approaches include truncating the nonessential domains and replacing the bulky components with smaller substitutes without compromising the editing efficiency. In this review, we highlight the importance of downsizing BEs for therapeutic applications and introduce recent advances in size-reduction strategies. Additionally, we introduce the ongoing efforts to overcome other limitations of BEs, providing insights into their potential for improving in vivo gene editing.

Experimental strategy for characterization of novel TnpB orthologs

TnpB proteins encoded in IS200/IS605 and IS607 mobile genetic elements are among the most widespread proteins in the microbial world. They function as RNA-guided DNA nucleases that play a critical role in transposon proliferation and are the predecessors of CRISPR-Cas12 effector proteins of the type V CRISPR-Cas family. Small size of TnpB nucleases makes them an attractive alternative for larger Cas9 and Cas12 proteins in genome editing applications. However, only a small fraction of TnpB nucleases characterized to date are active in human cells, highlighting the need to identify new TnpB variants that can function as genome editors. Here, we present an experimental pipeline for the characterization of TnpB proteins by combining in silico analysis with in vitro assays. To validate it we determined guide RNA and identified TAM for a set of TnpB orthologs. The proposed workflow can be employed for rapid screening and characterization of the huge TnpB protein family to identify novel TnpB variants that might expand the genome editing toolbox.

Implementation of RAGATH RNA-associated DNA Endonucleases as Genome Editing Tool in Escherichia coli

The preferred method for Escherichia coli genome editing relies on Cas9 from Streptococcus pyogenes (SpCas9) and λ-Red recombinase. Although SpCas9 is currently the most active RNA-guided DNA endonuclease, a significant number of escapers are often observed, making it inefficient across different sites, particularly when inserting large fragments. In this study, we identified two RAGATH RNA-associated DNA endonucleases (RADs) derived from IS607 transposons. Both of them exhibited high cleavage activity in E. coli. When combined with λ-Red recombinase, they achieved editing efficiencies approaching 100%. Even at target sites where SpCas9 exhibited low editing efficiency, RADs maintained efficiencies ranging from 57% to 94%. Moreover, RADs exhibited higher efficiencies in inserting large fragments in certain cases compared to SpCas9. Taken together, these RAD-based genome editing tools provide viable alternatives to SpCas9, particularly for challenging targets and/or large fragment insertions.

Improving adenine base editing precision by enlarging the recognition domain of CRISPR-Cas9

Domain expansion contributes to diversification of RNA-guided-endonucleases including Cas9. However, it remains unclear how REC domain expansion could benefit Cas9. In this study, we identify an insertion spot that is compatible with large REC insertion and succeeds in enlarging the non-catalytic REC domain of Streptococcus pyogenes Cas9. The natural-evolution-like giant SpCas9 (GS-Cas9) is created and shows substantially improved editing precision. We further discover that enlarging the REC domain could enable regulation of the N-terminal adenine deaminase TadA8e tethered to the Cas9 scaffold, which contributes to substantially reducing unexpected editing and improving the precision of the adenine base editor ABE8e. We provide proof of concept for evolution-inspired expansion of Cas9 and offer an alternative solution for optimizing gene editors. Our study also indicates a vast potential for engineering the topological malleability of RNA-guided endonucleases and base editors.

Characterization of the genome editing with miniature DNA nucleases TnpB and IscB in Escherichia coli strains

DNA endonucleases TnpB and IscB are emerging candidates for combating drug-resistant bacteria, particularly Escherichia coli, due to their specificity in targeting DNA and smaller size. However, the genome-editing of TnpB/IscB in E. coli remains unclear. This study characterized the genome editing of TnpB/IscB in different E. coli strains. First, the toxicity and cleavage results indicated TnpB was effective only in MG1655, whereas IscB and enIscB demonstrated functionality in ATCC9637/BL21(DE3). Subsequently, a genome-editing tool was established in MG1655 by using TnpB (as a thermophilic programmable endonuclease), achieving up to 100% editing efficiency, while IscB/enIscB achieved editing in ATCC9637/BL21(DE3). Additionally, the editing plasmids were successfully cured. Finally, the mechanism underlying the escape of E. coli during TnpB/IscB editing was elucidated. Overall, this study successfully applied TnpB/IscB/enIscB to genome editing in E. coli, which will expand the genetic manipulation toolbox in E. coli and facilitate the development of the antimicrobial drugs.

Latent activity in TnpB revealed by mutational scanning

TnpB is an evolutionarily diverse family of RNA-guided endonucleases associated with prokaryotic transposons. Due to their small size and putative evolutionary relationship to Cas12s, TnpB holds significant potential for genome editing and mechanistic exploration. However, most TnpBs lack robust gene-editing activity, and unbiased profiling of mutational effects on editing activity has not been experimentally explored. Here, we mapped comprehensive sequence-function landscapes of a TnpB ribonucleoprotein and discovered many activating mutations in both the protein and RNA. Single-position changes in the RNA outperform existing variants, highlighting the utility of systematic RNA scaffold mutagenesis. Leveraging the mutational landscape of the TnpB protein, we identified enhanced protein variants from a combinatorial library of activating mutations. These variants increased editing in human cells and N. benthamiana by over two-fold and fifty-fold relative to wild-type TnpB, respectively. In total, this study highlights unknown elements critical for regulation of endonuclease activity in both the TnpB protein and the RNA, and reveals a surprising amount of latent activity accessible through mutation.

Unlocking crops' genetic potential: Advances in genome and epigenome editing of regulatory regions

Genome editing tools could precisely and efficiently target plant genomes leading to the development of improved crops. Besides editing the coding regions, researchers can employ editing technologies to target specific gene regulatory elements or modify epigenetic marks associated with distal regulatory regions, thereby regulating gene expression in crops. This review outlines several prominent genome editing technologies, including CRISPR-Cas9, TALENs, and ZFNs and recent advancements. The applications for genome and epigenome editing especially of regulatory regions in crop plants is also discussed, including efforts to enhance abiotic stress tolerance, yield, disease resistance and plant phenotype. Additionally, the review addresses the potential of epigenetic modifications, such as DNA methylation and histone modifications, to alter gene expression for crop improvement. Finally, the limitations and future scope of utilizing various genome editing tools to manipulate regulatory elements for gene regulation to unlock the full potential of these tools in plant breeding has been discussed.

Structure of Fanzor2 reveals insights into the evolution of the TnpB superfamily

RNA-guided endonucleases, once thought to be exclusive to prokaryotes, have been recently identified in eukaryotes and are called Fanzors. They are classified into two clades, Fanzor1 and Fanzor2. Here we present the cryo-electron microscopy structure of Acanthamoeba polyphaga mimivirus Fanzor2, revealing its ωRNA architecture, active site and features involved in transposon-adjacent motif recognition. A comparison to Fanzor1 and TnpB structures highlights divergent evolutionary paths, advancing our understanding of RNA-guided endonucleases.

CRISPR-Cas12a bends DNA to destabilize base pairs during target interrogation

RNA-guided endonucleases are involved in processes ranging from adaptive immunity to site-specific transposition and have revolutionized genome editing. CRISPR-Cas9, -Cas12 and related proteins use guide RNAs to recognize ∼20-nucleotide target sites within genomic DNA by mechanisms that are not yet fully understood. We used structural and biochemical methods to assess early steps in DNA recognition by Cas12a protein-guide RNA complexes. We show here that Cas12a initiates DNA target recognition by bending DNA to induce transient nucleotide flipping that exposes nucleobases for DNA-RNA hybridization. Cryo-EM structural analysis of a trapped Cas12a-RNA-DNA surveillance complex and fluorescence-based conformational probing show that Cas12a-induced DNA helix destabilization enables target discovery and engagement. This mechanism of initial DNA interrogation resembles that of CRISPR-Cas9 despite distinct evolutionary origins and different RNA-DNA hybridization directionality of these enzyme families. Our findings support a model in which RNA-mediated DNA interference begins with local helix distortion by transient CRISPR-Cas protein binding.

DNA targeting by compact Cas9d and its resurrected ancestor

Type II CRISPR endonucleases are widely used programmable genome editing tools. Recently, CRISPR-Cas systems with highly compact nucleases have been discovered, including Cas9d (a type II-D nuclease). Here, we report the cryo-EM structures of a Cas9d nuclease (747 amino acids in length) in multiple functional states, revealing a stepwise process of DNA targeting involving a conformational switch in a REC2 domain insertion. Our structures provide insights into the intricately folded guide RNA which acts as a structural scaffold to anchor small, flexible protein domains for DNA recognition. The sgRNA can be truncated by up to ~25% yet still retain activity in vivo. Using ancestral sequence reconstruction, we generated compact nucleases capable of efficient genome editing in mammalian cells. Collectively, our results provide mechanistic insights into the evolution and DNA targeting of diverse type II CRISPR-Cas systems, providing a blueprint for future re-engineering of minimal RNA-guided DNA endonucleases.

Extended pegRNAs enhance the editing capability of Prime editing

Genome editing is highly valuable in biomedical research. Despite their versatility, current Prime editing (PE) techniques are limited to short sequence alterations [up to ~44 base pairs (bp)], and exhibit inconsistent or low efficiency across genomic loci, particularly when faced with poly-T sequences. To address these challenges, we developed an extended PE (exPE) technique that can potentially execute any precise genome editing. By harnessing RNA polymerase II (Pol II) promoters to transcribe extended PE guide RNAs (expegRNAs), exPE substantially improves editing efficiency and overcomes the challenges posed by poly-T sequences. Compared with conventional PE, exPE achieves up to a 14-fold increase in the efficiency of base conversions and short insertions, and, remarkably, up to a 259-fold improvement in regions with poly-T sequences. Uniquely, exPE enables seamless insertion of gene-sized DNA fragments into genomes, potentially correcting nearly 90% of human genetic variants, thereby broadening its applications in genetic research and therapy.

Engineered IscB-ωRNA system with expanded target range for base editing

As the evolutionary ancestor of Cas9 nuclease, IscB proteins serve as compact RNA-guided DNA endonucleases and nickases, making them strong candidates for base editing. Nevertheless, the narrow targeting scope limits the application of IscB systems; thus, it is necessary to find more IscBs that recognize different target-adjacent motifs (TAMs). Here, we identified 10 of 19 uncharacterized IscB proteins from uncultured microbes with activity in mammalian cells. Through protein and ωRNA engineering, we further enhanced the activity of IscB ortholog IscB.m16 and expanded its TAM scope from MRNRAA to NNNGNA, resulting in a variant named IscB.m16*. By fusing the deaminase domains with IscB.m16* nickase, we generated IscB.m16*-derived base editors that exhibited robust base-editing efficiency in mammalian cells and effectively restored Duchenne muscular dystrophy proteins in diseased mice through single adeno-associated virus delivery. Thus, this study establishes a set of compact base-editing tools for basic research and therapeutic applications.

Evolutionary origins of archaeal and eukaryotic RNA-guided RNA modification in bacterial IS110 transposons

Transposase genes are ubiquitous in all domains of life and provide a rich reservoir for the evolution of novel protein functions. Here we report deep evolutionary links between bacterial IS110-family transposases, which catalyse RNA-guided DNA recombination using bridge RNAs, and archaeal/eukaryotic Nop5-family proteins, which promote RNA-guided RNA 2'-O-methylation using C/D-box snoRNAs. On the basis of conservation of protein sequence, domain architecture, three-dimensional structure and non-coding RNA features, alongside phylogenetic analyses, we propose that programmable RNA modification emerged through the exaptation of components derived from IS110-like transposons. These findings underscore how recurrent domestication events of transposable elements have driven the evolution of RNA-guided mechanisms.

From bench to bedside: cutting-edge applications of base editing and prime editing in precision medicine

CRISPR-based gene editing technology theoretically allows for precise manipulation of any genetic target within living cells, achieving the desired sequence modifications. This revolutionary advancement has fundamentally transformed the field of biomedicine, offering immense clinical potential for treating and correcting genetic disorders. In the treatment of most genetic diseases, precise genome editing that avoids the generation of mixed editing byproducts is considered the ideal approach. This article reviews the current progress of base editors and prime editors, elaborating on specific examples of their applications in the therapeutic field, and highlights opportunities for improvement. Furthermore, we discuss the specific performance of these technologies in terms of safety and efficacy in clinical applications, and analyze the latest advancements and potential directions that could influence the future development of genome editing technologies. Our goal is to outline the clinical relevance of this rapidly evolving scientific field and preview a roadmap for successful DNA base editing therapies for the treatment of hereditary or idiopathic diseases.

All-in-one AAV-mediated Nrl gene inactivation rescues retinal degeneration in Pde6a mice

Retinitis pigmentosa (RP) is a complex group of inherited retinal diseases characterized by progressive death of photoreceptor cells and eventual blindness. Pde6a, which encodes a cGMP-specific phosphodiesterase, is a crucial pathogenic gene for autosomal recessive RP (RP43); there is no effective therapy for this form of RP. The compact CRISPR/Staphylococcus aureus Cas9 (CRISPR/SaCas9) system, which can be packaged into a single adeno-associated virus (AAV), holds promise for simplifying effective gene therapy. Here, we demonstrated that all-in-one AAV-SaCas9-mediated Nrl gene inactivation can efficiently prevent retinal degeneration in a RP mouse model with Pde6anmf363/nmf363 mutation. We screened single-guide RNAs capable of efficiently editing the mouse Nrl gene in N2a cells and then achieved effective gene editing by using a single AAV to codeliver SaCas9 and an optimal Nrl-sg2 into the mouse retina. Excitingly, in vivo inactivation of Nrl improved photoreceptor cell survival and rescued retinal function in treated Pde6a-deficient mice. Thus, we showed that a practical, gene-independent method, AAV-SaCas9-mediated Nrl inactivation, holds promise for future therapeutic applications in patients with RP.

Comparative Analysis of Active LTR Retrotransposons in Sunflower (Helianthus annuus L.): From Extrachromosomal Circular DNA Detection to Protein Structure Prediction

Plant genomes possess numerous transposable element (TE) insertions that have occurred during evolution. Most TEs are silenced or diverged; therefore, they lose their ability to encode proteins and are transposed in the genome. Knowledge of active plant TEs and TE-encoded proteins essential for transposition and evasion of plant cell transposon silencing mechanisms remains limited. This study investigated active long terminal repeat (LTR) retrotransposons (RTEs) in sunflowers (Helianthus annuus), revealing heterogeneous and phylogenetically distinct RTEs triggered by epigenetic changes and heat stress. Many of these RTEs belong to three distinct groups within the Tekay clade, showing significant variations in chromosomal insertion distribution. Through protein analysis of these active RTEs, it was found that Athila RTEs and Tekay group 2 elements possess additional open reading frames (aORFs). The aORF-encoded proteins feature a transposase domain, a transmembrane domain, and nuclear localization signals. The aORF proteins of the Tekay subgroup exhibited remarkable conservation among over 500 Tekay members, suggesting their functional importance in RTE mobility. The predicted 3D structure of the sunflower Tekay aORF protein showed significant homology with Tekay proteins in rice, maize, and sorghum. Additionally, the structural features of aORF proteins resemble those of plant DRBM-containing proteins, suggesting their potential role in RNA-silencing modulation. These findings offer insights into the diversity and activity of sunflower RTEs, emphasizing the conservation and structural characteristics of aORF-encoded proteins.

CRISPR in mobile genetic elements: counter-defense, inter-element competition and RNA-guided transposition

CRISPR are adaptive immunity systems that protect bacteria and archaea from viruses and other mobile genetic elements (MGE) via an RNA-guided interference mechanism. However, in the course of the host-parasite co-evolution, CRISPR systems have been recruited by MGE themselves for counter-defense or other functions. Some bacteriophages encode fully functional CRISPR systems that target host defense systems, and many others recruited individual components of CRISPR systems, such as single repeat units that inhibit host CRISPR systems and CRISPR mini-arrays that target related viruses contributing to inter-virus competition. Many plasmids carry type IV or subtype V-M CRISPR systems that appear to be involved in inter-plasmid competition. Numerous Tn7-like and Mu-like transposons encode CRISPR-associated transposases (CASTs) in which interference-defective CRISPR systems of type I or type V mediate RNA-guided, site-specific transposition. The recruitment of CRISPR systems and their components by MGE is a manifestation of extensive gene shuttling between host immune systems and MGE, a major trend in the coevolution of MGE with their hosts.

AAV-mediated gene therapies by miniature gene editing tools

The advent of CRISPR-Cas has revolutionized precise gene editing. While pioneering CRISPR nucleases like Cas9 and Cas12 generate targeted DNA double-strand breaks (DSB) for knockout or homology-directed repair, next generation CRISPR technologies enable gene editing without DNA DSB. Base editors directly convert bases, prime editors make diverse alterations, and dead Cas-regulator fusions allow nuanced control of gene expression, avoiding potentially risks like translocations. Meanwhile, the discovery of diminutive Cas12 orthologs and Obligate Mobile Element-Guided Activity (OMEGA) nucleases has overcome cargo limitations of adeno-associated viral vectors, expanding prospects for in vivo therapeutic delivery. Here, we review the ever-evolving landscape of cutting-edge gene editing tools, focusing on miniature Cas12 orthologs and OMEGA effectors amenable to single AAV packaging. We also summarize CRISPR therapies delivered using AAV vectors, discuss challenges such as efficiency and specificity, and look to the future of this transformative field of in vivo gene editing enabled by AAV vectors delivery.

Biology and applications of CRISPR-Cas12 and transposon-associated homologs

CRISPR-associated Cas12 proteins are a highly variable collection of nucleic acid-targeting proteins. All Cas12 variants use RNA guides and a single nuclease domain to target complementary DNA or, in rare cases, RNA. The high variability of Cas12 effectors can be explained by a series of independent evolution events from different transposon-associated TnpB-like ancestors. Despite basic structural and functional similarities, this has resulted in unprecedented variation of the Cas12 effector proteins in terms of size, domain composition, guide structure, target identity and interference strategy. In this Review, we compare the unique molecular features of natural and engineered Cas12 and TnpB variants. Furthermore, we provide an overview of established genome editing and diagnostic applications and discuss potential future directions.

CRISPR beyond: harnessing compact RNA-guided endonucleases for enhanced genome editing

The CRISPR-Cas system, an adaptive immunity system in prokaryotes designed to combat phages and foreign nucleic acids, has evolved into a groundbreaking technology enabling gene knockout, large-scale gene insertion, base editing, and nucleic acid detection. Despite its transformative impact, the conventional CRISPR-Cas effectors face a significant hurdle-their size poses challenges in effective delivery into organisms and cells. Recognizing this limitation, the imperative arises for the development of compact and miniature gene editors to propel advancements in gene-editing-related therapies. Two strategies were accepted to develop compact genome editors: harnessing OMEGA (Obligate Mobile Element-guided Activity) systems, or engineering the existing CRISPR-Cas system. In this review, we focus on the advances in miniature genome editors based on both of these strategies. The objective is to unveil unprecedented opportunities in genome editing by embracing smaller, yet highly efficient genome editors, promising a future characterized by enhanced precision and adaptability in the genetic interventions.

Engineered IscB-ωRNA system with improved base editing efficiency for disease correction via single AAV delivery in mice

IscBs, as hypercompact ancestry proteins of Cas9 nuclease, are suitable for in vivo gene editing via single adeno-associated virus (AAV) delivery. Due to the low activity of natural IscBs in eukaryotic cells, recent studies have been focusing on improving OgeuIscB's gene editing efficiency via protein engineering. However, in vivo gene editing efficacy of IscBs for disease correction remained to be demonstrated. Here, we showed effective gene knockout and base editing in mouse embryos. To further improve IscB activity, we performed systematic engineering of IscB-associated ωRNA and identified a variant, ωRNA∗-v2, with enhanced gene editing efficiency. Furthermore, our study demonstrated the efficacy of an engineered IscB-ωRNA system for robust gene knockout and base editing in vivo. Single AAV delivery of IscB-derived cytosine and adenine base editors achieved disease correction in a mouse model of tyrosinemia. Therefore, our results indicated the great potential of miniature IscBs for developing single-AAV-based gene editing therapeutics.

Collateral nuclease activity of TnpB triggered by high temperature enables fast and sensitive nucleic acid detection

TnpB proteins encoded in the IS200/IS605 family are RNA-guided endonuclease which can be harnessed in genome editing. However, the collateral nuclease activity of TnpB remains poorly understood, which limits the development of TnpB-based diagnostic tools. Here we showed that TnpB from a thermophilic archaeon exhibits enhanced collateral ssDNA cleavage activity (trans-cleavage) activated by high temperature. Mutations either in the TAM or seed sequences of the target DNA impair the trans-cleavage activity, which indicates its potential to be employed in molecular diagnostic. Importantly, by optimizing the length and the sequences of the collateral substrates, we have developed a new nucleic acid detection method based on TnpB with a sensitivity of 29 cp μl-1 in 30 min, which we name it TESD (TnpB Enable fast and Sensitive Detection). In summary, our findings illustrate the collateral nuclease activity of a TnpB from thermophiles and provide a novel platform for molecular diagnostics.

Emerging Gene-editing nano-therapeutics for Cancer

Remarkable progress has been made in the field of genome engineering after the discovery of CRISPR/Cas9 in 2012 by Jennifer Doudna and Emmanuelle Charpentier. Compared to any other gene-editing tools, CRISPR/Cas9 attracted the attention of the scientific community because of its simplicity, specificity, and multiplex editing possibilities for which the inventors were awarded the Nobel prize for chemistry in 2020. CRISPR/Cas9 allows targeted alteration of the genomic sequence, gene regulation, and epigenetic modifications using an RNA-guided site-specific endonuclease. Though the impact of CRISPR/Cas9 was undisputed, some of its limitations led to key modifications including the use of miniature-Cas proteins, Cas9 Retron precise Parallel Editing via homologY (CRISPEY), Cas-Clover, or development of alternative methods including retron-recombineering, Obligate Mobile Element Guided Activity(OMEGA), Fanzor, and Argonaute proteins. As cancer is caused by genetic and epigenetic alterations, gene-editing was found to be highly useful for knocking out oncogenes, editing mutations to regain the normal functioning of tumor suppressor genes, knock-out immune checkpoint blockade in CAR-T cells, producing 'off-the-shelf' CAR-T cells, identify novel tumorigenic genes and functional analysis of multiple pathways in cancer, etc. Advancements in nanoparticle-based delivery of guide-RNA and Cas9 complex to the human body further enhanced the potential of CRISPR/Cas9 for clinical translation. Several studies are reported for developing novel delivery methods to enhance the tumor-specific application of CRISPR/Cas9 for anticancer therapy. In this review, we discuss new developments in novel gene editing techniques and recent progress in nanoparticle-based CRISPR/Cas9 delivery specific to cancer applications.

Sequence modeling and design from molecular to genome scale with Evo

The genome is a sequence that encodes the DNA, RNA, and proteins that orchestrate an organism's function. We present Evo, a long-context genomic foundation model with a frontier architecture trained on millions of prokaryotic and phage genomes, and report scaling laws on DNA to complement observations in language and vision. Evo generalizes across DNA, RNA, and proteins, enabling zero-shot function prediction competitive with domain-specific language models and the generation of functional CRISPR-Cas and transposon systems, representing the first examples of protein-RNA and protein-DNA codesign with a language model. Evo also learns how small mutations affect whole-organism fitness and generates megabase-scale sequences with plausible genomic architecture. These prediction and generation capabilities span molecular to genomic scales of complexity, advancing our understanding and control of biology.

Engineered PsCas9 enables therapeutic genome editing in mouse liver with lipid nanoparticles

Clinical implementation of therapeutic genome editing relies on efficient in vivo delivery and the safety of CRISPR-Cas tools. Previously, we identified PsCas9 as a Type II-B family enzyme capable of editing mouse liver genome upon adenoviral delivery without detectable off-targets and reduced chromosomal translocations. Yet, its efficacy remains insufficient with non-viral delivery, a common challenge for many Cas9 orthologues. Here, we sought to redesign PsCas9 for in vivo editing using lipid nanoparticles. We solve the PsCas9 ribonucleoprotein structure with cryo-EM and characterize it biochemically, providing a basis for its rational engineering. Screening over numerous guide RNA and protein variants lead us to develop engineered PsCas9 (ePsCas9) with up to 20-fold increased activity across various targets and preserved safety advantages. We apply the same design principles to boost the activity of FnCas9, an enzyme phylogenetically relevant to PsCas9. Remarkably, a single administration of mRNA encoding ePsCas9 and its guide formulated with lipid nanoparticles results in high levels of editing in the Pcsk9 gene in mouse liver, a clinically relevant target for hypercholesterolemia treatment. Collectively, our findings introduce ePsCas9 as a highly efficient, and precise tool for therapeutic genome editing, in addition to the engineering strategy applicable to other Cas9 orthologues.

Overview on Current Selectable Marker Systems and Novel Marker Free Approaches in Fruit Tree Genetic Engineering

Selectable marker genes are useful for recognizing which cells have integrated specific sequences in their genome after genetic transformation processes. They are especially important for fruit trees genetic transformation to individuate putatively genetically modified events, because most of the protocols used to genetic engineer these species are often unsuccessful or with low efficiency. Traditional selectable marker genes, mainly of bacterial origin, confer antibiotics/herbicides-resistance or metabolic advantages to transformed cells. Genes that allow the visual recognition of engineered tissues without using any selective agent, such as morphogenic regulators and reporter genes, are also used as selection tools to in vitro identify genetically modified regenerated lines. As final step, genetic engineered plants should be tested in field conditions, where selectable marker genes are no longer necessary, and strongly unpopular especially for the commercial development of the new products. Thus, different approaches, mainly based on the use of site-specific recombinases and/or editing nucleases, are being now used to recover marker-free fruit crops. This review describes and comments the most used and suitable selection tools of interest, particularly for fruit tree genetic engineering. Lastly, a spotlight highlights the biosafety aspects related to the use of selectable marker genes exploited for fruit species genetic engineering.

TldR: TnpB's evolutionary shift from transposon nucleases to RNA-guided transcriptional regulators

TnpB proteins are transposon-encoded nucleases involved in transposon DNA propagation. Wiegand et al. identified a new class of TnpB-derived proteins, called TnpB-like nuclease-dead repressors (TldRs), which function as RNA-guided transcriptional regulators targeting conserved promoter regions. In Enterobacteriaceae, bacteriophages use TldRs and an adjacent phage gene to modulate host flagellar assembly.

Gene therapy and gene editing strategies in inherited blood disorders

Gene therapy has shown significant potential in treating various diseases, particularly inherited blood disorders such as hemophilia, sickle cell disease, and thalassemia. Advances in understanding the regulatory network of disease-associated genes have led to the identification of additional therapeutic targets for treatment, especially for β-hemoglobinopathies. Erythroid regulatory factor BCL11A offers the most promising therapeutic target for β-hemoglobinopathies, and reduction of its expression using the commercialized gene therapy product Casgevy has been approved for use in the UK and USA in 2023. Notably, the emergence of innovative gene editing technologies has further broadened the gene therapy landscape, presenting possibilities for treatment. Intensive studies indicate that base editing and prime editing, built upon CRISPR technology, enable precise single-base modification in hematopoietic stem cells for addressing inherited blood disorders ex vivo and in vivo. In this review, we present an overview of the current landscape of gene therapies, focusing on clinical research and gene therapy products for inherited blood disorders, evaluation of potential gene targets, and the gene editing tools employed in current gene therapy practices, which provides an insight for the establishment of safer and more effective gene therapy methods for a wider range of diseases in the future.

Efficient Rescue of Retinal Degeneration in Pde6a Mice by Engineered Base Editing and Prime Editing

Retinitis pigmentosa (RP) is a complex spectrum of inherited retinal diseases marked by the gradual loss of photoreceptor cells, ultimately leading to blindness. Among these, mutations in PDE6A, responsible for encoding a cGMP-specific phosphodiesterase, stand out as pivotal in autosomal recessive RP (RP43). Unfortunately, no effective therapy currently exists for this specific form of RP. However, recent advancements in genome editing, such as base editing (BE) and prime editing (PE), offer a promising avenue for precise and efficient gene therapy. Here, it is illustrated that the engineered BE and PE systems, particularly PE, exhibit high efficiency in rescuing a target point mutation with minimal bystander effects in an RP mouse model carrying the Pde6a (c.2009A > G, p.D670G) mutation. The optimized BE and PE systems are first screened in N2a cells and subsequently assessed in electroporated mouse retinas. Notably, the optimal PE system, delivered via dual adeno-associated virus (AAV), precisely corrects the pathogenic mutation with average 9.4% efficiency, with no detectable bystander editing. This correction restores PDE6A protein expression, preserved photoreceptors, and rescued retinal function in Pde6a mice. Therefore, this study offers a proof-of-concept demonstration for the treatment of Pde6a-related retinal degeneration using BE and PE systems.

Effective genome editing with an enhanced ISDra2 TnpB system and deep learning-predicted ωRNAs

Transposon (IS200/IS605)-encoded TnpB proteins are predecessors of class 2 type V CRISPR effectors and have emerged as one of the most compact genome editors identified thus far. Here, we optimized the design of Deinococcus radiodurans (ISDra2) TnpB for application in mammalian cells (TnpBmax), leading to an average 4.4-fold improvement in editing. In addition, we developed variants mutated at position K76 that recognize alternative target-adjacent motifs (TAMs), expanding the targeting range of ISDra2 TnpB. We further generated an extensive dataset on TnpBmax editing efficiencies at 10,211 target sites. This enabled us to delineate rules for on-target and off-target editing and to devise a deep learning model, termed TnpB editing efficiency predictor (TEEP; https://www.tnpb.app ), capable of predicting ISDra2 TnpB guiding RNA (ωRNA) activity with high performance (r > 0.8). Employing TEEP, we achieved editing efficiencies up to 75.3% in the murine liver and 65.9% in the murine brain after adeno-associated virus (AAV) vector delivery of TnpBmax. Overall, the set of tools presented in this study facilitates the application of TnpB as an ultracompact programmable endonuclease in research and therapeutics.

CRISPR-Cas systems and applications for crop bioengineering

CRISPR-Cas technologies contribute to enhancing our understanding of plant gene functions, and to the precise breeding of crop traits. Here, we review the latest progress in plant genome editing, focusing on emerging CRISPR-Cas systems, DNA-free delivery methods, and advanced editing approaches. By illustrating CRISPR-Cas applications for improving crop performance and food quality, we highlight the potential of genome-edited crops to contribute to sustainable agriculture and food security.

De novo gene synthesis by an antiviral reverse transcriptase

Defense-associated reverse transcriptase (DRT) systems perform DNA synthesis to protect bacteria against viral infection, but the identities and functions of their DNA products remain largely unknown. We show that DRT2 systems encode an unprecedented immune pathway that involves de novo gene synthesis through rolling circle reverse transcription of a noncoding RNA (ncRNA). Programmed template jumping on the ncRNA generates a concatemeric cDNA, which becomes double-stranded upon viral infection. This DNA product constitutes a protein-coding, nearly endless open reading frame (neo) gene whose expression leads to potent cell growth arrest, restricting the viral infection. Our work highlights an elegant expansion of genome coding potential through RNA-templated gene creation and challenges conventional paradigms of genetic information encoded along the one-dimensional axis of genomic DNA.

Targeted mutagenesis in Arabidopsis and medicinal plants using transposon-associated TnpB

The programmable nuclease TnpB is significantly smaller than Cas9, can edit genes in medicinal plants, including Artemisia annua, Salvia miltiorrhiza, Scutellaria baicalensis, Isatis indigotica, and Codonopsis pilosula, and has potential uses in molecular breeding to enhance crop yield and quality.