The Perpetual Vector Mosquito Threat and Its Eco-Friendly Nemeses

Mosquitoes are the most notorious arthropod vectors of viral and parasitic diseases for which approximately half the world's population, ~4,000,000,000, is at risk. Integrated pest management programs (IPMPs) have achieved some success in mitigating the regional transmission and persistence of these diseases. However, as many vector-borne diseases remain pervasive, it is obvious that IPMP successes have not been absolute in eradicating the threat imposed by mosquitoes. Moreover, the expanding mosquito geographic ranges caused by factors related to climate change and globalization (travel, trade, and migration), and the evolution of resistance to synthetic pesticides, present ongoing challenges to reducing or eliminating the local and global burden of these diseases, especially in economically and medically disadvantaged societies. Abatement strategies include the control of vector populations with synthetic pesticides and eco-friendly technologies. These "green" technologies include SIT, IIT, RIDL, CRISPR/Cas9 gene drive, and biological control that specifically targets the aquatic larval stages of mosquitoes. Regarding the latter, the most effective continues to be the widespread use of Lysinibacillus sphaericus (Ls) and Bacillus thuringiensis subsp. israelensis (Bti). Here, we present a review of the health issues elicited by vector mosquitoes, control strategies, and lastly, focus on the biology of Ls and Bti, with an emphasis on the latter, to which no resistance has been observed in the field.

CRISPR/Cas Genome Editing Technologies for Plant Improvement against Biotic and Abiotic Stresses: Advances, Limitations, and Future Perspectives

Crossbreeding, mutation breeding, and traditional transgenic breeding take much time to improve desirable characters/traits. CRISPR/Cas-mediated genome editing (GE) is a game-changing tool that can create variation in desired traits, such as biotic and abiotic resistance, increase quality and yield in less time with easy applications, high efficiency, and low cost in producing the targeted edits for rapid improvement of crop plants. Plant pathogens and the severe environment cause considerable crop losses worldwide. GE approaches have emerged and opened new doors for breeding multiple-resistance crop varieties. Here, we have summarized recent advances in CRISPR/Cas-mediated GE for resistance against biotic and abiotic stresses in a crop molecular breeding program that includes the modification and improvement of genes response to biotic stresses induced by fungus, virus, and bacterial pathogens. We also discussed in depth the application of CRISPR/Cas for abiotic stresses (herbicide, drought, heat, and cold) in plants. In addition, we discussed the limitations and future challenges faced by breeders using GE tools for crop improvement and suggested directions for future improvements in GE for agricultural applications, providing novel ideas to create super cultivars with broad resistance to biotic and abiotic stress.

Insights Gained from RNA Editing Targeted by the CRISPR-Cas13 Family

Clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated protein (Cas) systems, especially type II (Cas9) systems, have been widely developed for DNA targeting and formed a set of mature precision gene-editing systems. However, the basic research and application of the CRISPR-Cas system in RNA is still in its early stages. Recently, the discovery of the CRISPR-Cas13 type VI system has provided the possibility for the expansion of RNA targeting technology, which has broad application prospects. Most type VI Cas13 effectors have dinuclease activity that catalyzes pre-crRNA into mature crRNA and produces strong RNA cleavage activity. Cas13 can specifically recognize targeted RNA fragments to activate the Cas13/crRNA complex for collateral cleavage activity. To date, the Cas13X protein is the smallest effector of the Cas13 family, with 775 amino acids, which is a promising platform for RNA targeting due to its lack of protospacer flanking sequence (PFS) restrictions, ease of packaging, and absence of permanent damage. This study highlighted the latest progress in RNA editing targeted by the CRISPR-Cas13 family, and discussed the application of Cas13 in basic research, nucleic acid diagnosis, nucleic acid tracking, and genetic disease treatment. Furthermore, we clarified the structure of the Cas13 protein family and their molecular mechanism, and proposed a future vision of RNA editing targeted by the CRISPR-Cas13 family.

Tandem Cas13a/crRNA-Mediated CRISPR-FET Biosensor: A One-for-All Check Station for Virus without Amplification

The path toward field-effect transistor (FET) application from laboratory to clinic has delivered a compelling push in the biomedical domain, yet ultrasensitive and timely pathogen identification without PCR remains a long-lasting challenge. Herein, we create a generic check station termed "CRISPR-FET", first incorporating the CRISPR/Cas13a system within the FET modality, for accelerated and unamplified detection of viral RNA. Unlike conventional FETs bearing target-specific receptors, this sensor holds three unique advancements: (i) an ingenious sensing mechanism is used, which converts the signal of a large-sized analyte into an on-chip cleavage response of an immobilized CRISPR reporter, enabling signal generation events to occur all within the Debye length; (ii) the multipurpose inspection of the CoV ORF1ab, CoV N gene, and HCV RNA unveils the potential for "one-for-all" scalable FET-based molecular diagnostics; and (iii) it is shown that Cas13a-crRNAs targeting different sites of the viral genome can be deployed in tandem to amplify the FET response, empowering the detection limit down to 1.56 aM, which is a world-record level of sensitivity in the FET for direct viral gene sensing. Notably, a brilliant clinical applicability was made in distinguishing HCV-infected patients from normal controls. Overall, this study sheds new insights into FET-based nucleic acid sensing technology and invokes a vision for its possible future roles in diagnosis of various viral diseases.

CRISPR/Cas13-assisted hepatitis B virus covalently closed circular DNA detection

Background and aims

The formation of an intranuclear pool of covalently closed circular DNA (cccDNA) in the liver is the main cause of persistent hepatitis B virus (HBV) infection. Here, we established highly sensitive and specific methods to detect cccDNA based on CRISPR-Cas13a technology.

Methods

We used plasmid-safe ATP-dependent DNase (PSAD) enzymes and HindIII to digest loose circle rcDNA and double-stranded linear DNA, amplify specific HBV cccDNA fragments by rolling circle amplification (RCA) and PCR, and detect the target gene using CRISPR-Cas13a technology. The CRISPR-Cas13a-based assay for the detection of cccDNA was further clinically validated using HBV-related liver tissues, plasma, whole blood and peripheral blood mononuclear cells (PBMCs).

Results

Based on the sample pretreatment step, the amplification step and the detection step, we established a new CRISPR-Cas13a-based assay for the detection of cccDNA. After the amplification of RCA and PCR, 1 copy/μl HBV cccDNA could be detected by CRISPR/Cas13-assisted fluorescence readout. We used ddPCR, qPCR, RCA-qPCR, PCR-CRISPR and RCA-PCR-CRISPR methods to detect 20, 4, 18, 14 and 29 positive samples in liver tissue samples from 40 HBV-related patients, respectively. HBV cccDNA was almost completely undetected in the 20 blood samples of HBV patients (including plasma, whole blood and PBMCs) by the above 5 methods.

Conclusions

We developed a novel CRISPR-based assay for the highly sensitive and specific detection of HBV cccDNA, presenting a promising alternative for accurate detection of HBV infection, antiviral therapy evaluation and treatment guidance.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12072-022-10311-0.

CASowary: CRISPR-Cas13 guide RNA predictor for transcript depletion

BACKGROUND

Recent discovery of the gene editing system - CRISPR (Clustered Regularly Interspersed Short Palindromic Repeats) associated proteins (Cas), has resulted in its widespread use for improved understanding of a variety of biological systems. Cas13, a lesser studied Cas protein, has been repurposed to allow for efficient and precise editing of RNA molecules. The Cas13 system utilizes base complementarity between a crRNA/sgRNA (crispr RNA or single guide RNA) and a target RNA transcript, to preferentially bind to only the target transcript. Unlike targeting the upstream regulatory regions of protein coding genes on the genome, the transcriptome is significantly more redundant, leading to many transcripts having wide stretches of identical nucleotide sequences. Transcripts also exhibit complex three-dimensional structures and interact with an array of RBPs (RNA Binding Proteins), both of which may impact the effectiveness of transcript depletion of target sequences. However, our understanding of the features and corresponding methods which can predict whether a specific sgRNA will effectively knockdown a transcript is very limited.

RESULTS

Here we present a novel machine learning and computational tool, CASowary, to predict the efficacy of a sgRNA. We used publicly available RNA knockdown data from Cas13 characterization experiments for 555 sgRNAs targeting the transcriptome in HEK293 cells, in conjunction with transcriptome-wide protein occupancy information. Our model utilizes a Decision Tree architecture with a set of 112 sequence and target availability features, to classify sgRNA efficacy into one of four classes, based upon expected level of target transcript knockdown. After accounting for noise in the training data set, the noise-normalized accuracy exceeds 70%. Additionally, highly effective sgRNA predictions have been experimentally validated using an independent RNA targeting Cas system - CIRTS, confirming the robustness and reproducibility of our model's sgRNA predictions. Utilizing transcriptome wide protein occupancy map generated using POP-seq in HeLa cells against publicly available protein-RNA interaction map in Hek293 cells, we show that CASowary can predict high quality guides for numerous transcripts in a cell line specific manner.

CONCLUSIONS

Application of CASowary to whole transcriptomes should enable rapid deployment of CRISPR/Cas13 systems, facilitating the development of therapeutic interventions linked with aberrations in RNA regulatory processes.

A one-step platform for screening high-efficient and minimal off-target CRISPR/Cas13 crRNAs to eradicate SARS-CoV-2 virus for treatment of COVID-19 patients

Coronavirus disease 2019 (COVID-19) is a new respiratory illness caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and now spreads globally. Currently, therapeutics and effective treatment options remain scarce and there is no proven drug to treat COVID-19. Targeting the positive-sense RNA genome and viral mRNAs of SARS-CoV-2 to simultaneously degrade viral genome templates for replication and viral mRNAs for essential gene expression would be a strategy to completely realize virus elimination. Type VI CRISPR enzymes Cas13 have recently been identified as programmable RNA-guided, RNA-targeting Cas proteins with nuclease activity that allows for RNA cleavage and degradation. The precise viral RNA detection and antiviral application of the CRISPR/Cas13 system depend on high-efficient and minimal off-target crRNAs. Although a computer-based algorithm has been applied for the design of crRNAs targeting SRAS-CoV-2, the experimental screening system to identify optimal crRNA is not available. We develop a one-step experimental screening system to identify high-efficient crRNAs with minimal off-target effects for CRISPR/Cas13-based SARS-CoV-2 elimination. This platform provides the foundation for CRISPR/Cas13-based diagnostics and therapeutics for COVID-19. This platform is versatile and could also be applied for crRNAs screening for other RNA viruses.

Potential of CRISPR/Cas system in the diagnosis of COVID-19 infection

INTRODUCTION

Emerging novel infectious diseases and persistent pandemics with potential to destabilize normal life remain a public health concern for the whole world. The recent outbreak of pneumonia caused by Coronavirus infectious disease-2019 (COVID-19) resulted in high mortality due to a lack of effective drugs or vaccines. With a constantly increasing number of infections with mutated strains and deaths across the globe, rapid, affordable and specific detections with more accurate diagnosis and improved health treatments are needed to combat the spread of this novel pathogen COVID-19.

AREAS COVERED

Researchers have started to utilize the recently invented clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated proteins (CRISPR/Cas)-based tools for the rapid detection of novel COVID-19. In this review, we summarize the potential of CRISPR/Cas system for the diagnosis and enablement of efficient control of COVID-19.

EXPERT OPINION

Multiple groups have demonstrated the potential of utilizing CRISPR-based diagnosis tools for the detection of SARS-CoV-2. In coming months, we expect more novel and rapid CRISPR-based kits for mass detection of COVID-19-infected persons within a fraction of a second. Therefore, we believe science will conquer COVID-19 in the near future.

Targeted Delivery of CRISPR/Cas13 as a Promising Therapeutic Approach to Treat SARS-CoV-2

On a worldwide scale, the outbreak of the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) has led to extensive damage to the health system as well as the global economy. Hitherto, there has been no approved drug or vaccine for this disease. Therefore, the use of general antiviral drugs is at the first line of treatment, though complicated with limited effectiveness and systemic side effects. Given the pathophysiology of the disease, researchers have proposed various strategies not only to find a more specific therapeutic way but also to reduce the side effects. One strategy to accomplish these goals is to use CRISPR/Cas13 system. Recently, a group of scientists has used the CRISPR/Cas13 system, which is highly effective in eliminating the genome of RNA viruses. Due to the RNA nature of the coronavirus genome, it seems that this system can be effective against the disease. The main challenge regarding the application of this system is to deliver it to the target cells efficiently. To solve this challenge, it seems that using virosomes with protein S on their membrane surface can be helpful. Studies have shown that protein S interacts with its specific receptor in target cells named Angiotensin-Converting Enzyme 2 (ACE2). Here, we propose if CRISPR/Cas13 gene constructs reach the infected cells efficiently using a virosomal delivery system, the virus genome will be cleaved and inactivated. Considering the pathophysiology of the disease, an important step to implement this hypothesis is to embed protein S on the membrane surface of virosomes to facilitate the delivery of gene constructs to the target cells.

Very long intergenic non-coding (vlinc) RNAs directly regulate multiple genes in cis and trans

BACKGROUND

The majority of the human genome is transcribed in the form of long non-coding (lnc) RNAs. While these transcripts have attracted considerable interest, their molecular mechanisms of function and biological significance remain controversial. One of the main reasons behind this lies in the significant challenges posed by lncRNAs requiring the development of novel methods and concepts to unravel their functionality. Existing methods often lack cross-validation and independent confirmation by different methodologies and therefore leave significant ambiguity as to the authenticity of the outcomes. Nonetheless, despite all the caveats, it appears that lncRNAs may function, at least in part, by regulating other genes via chromatin interactions. Therefore, the function of a lncRNA could be inferred from the function of genes it regulates. In this work, we present a genome-wide functional annotation strategy for lncRNAs based on identification of their regulatory networks via the integration of three distinct types of approaches: co-expression analysis, mapping of lncRNA-chromatin interactions, and assaying molecular effects of lncRNA knockdowns obtained using an inducible and highly specific CRISPR/Cas13 system.

RESULTS

We applied the strategy to annotate 407 very long intergenic non-coding (vlinc) RNAs belonging to a novel widespread subclass of lncRNAs. We show that vlincRNAs indeed appear to regulate multiple genes encoding proteins predominantly involved in RNA- and development-related functions, cell cycle, and cellular adhesion via a mechanism involving proximity between vlincRNAs and their targets in the nucleus. A typical vlincRNAs can be both a positive and negative regulator and regulate multiple genes both in trans and cis. Finally, we show vlincRNAs and their regulatory networks potentially represent novel components of DNA damage response and are functionally important for the ability of cancer cells to survive genotoxic stress.

CONCLUSIONS

This study provides strong evidence for the regulatory role of the vlincRNA class of lncRNAs and a potentially important role played by these transcripts in the hidden layer of RNA-based regulation in complex biological systems.

Programmable technologies to manipulate gene expression at the RNA level

RNA has long been an enticing therapeutic target, but is now garnering increased attention, largely driven by clinical successes of RNA interference-based drugs. While gene knockdown by well-established RNA interference- and other oligonucleotide-based strategies continues to advance in the clinic, the repertoire of targetable effectors capable of altering gene expression at the RNA level is also rapidly expanding. In this review, we focus on several recently developed bifunctional molecular technologies that both interact with and act upon a target RNA. These new approaches for programmable RNA knockdown, editing, splicing, translation, and chemical modifications stand to provide impactful new modalities for therapeutic development in the coming decades.

Potential of CRISPR/Cas13 System in Treatment and Diagnosis of COVID-19

The novel coronavirus disease 2019 (COVID-19) belongs to coronaviridae families like sarbecovirus (SARS), and causes pyrexia, pertussis, and acute respiratory distress syndrome (ARDS) in major. Started from Wuhan, China, COVID-19 now forced the World Health Organization (WHO) call it a global pandemic. These dreadful figures elevate the need for rapid action for a rapid diagnostic tool, an efficacious therapy, or vaccine for such widespread disease. In this article, we reviewed all the latest research and trials including conventional antiviral medicines that have a narrow and finite effect on COVID-19. Recently, some advances were made by a nucleotide/nucleoside analogues (NUC) inhibitor (remdesivir), ivermectin (antiparasitic drug), and convalescent plasma; the later one has more recently been approved by the Food and Drug Administration (FDA). Additionally, a clinical-grade soluble human angiotensin-converting enzyme (ACE2), named hrsACE2, was able to inhibit the infection of human blood vessel organoids, as well as the human kidney organoids, by the virus. As of now, innovative therapeutics based on the CRISPR/Cas13d might overcome the challenge of COVID-19 either as a treatment option or precise and rapid diagnostic tool due to its rapid and precise nature. In this updated comprehensive rapid review, we tried to cover all recent findings in terms of genomics, diagnosis, prevention, and treatment.

CRISPR/Cas13: A potential therapeutic option of COVID-19

The novel coronavirus called severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can be considered as the most important current global issue, as it has caused the novel coronavirus disease (COVID-19) pandemic, which has resulted in high mortality and morbidity rates all around the world. Although scientists are trying to discover novel therapies and develop and evaluate various previous treatments, at the time of writing this paper, there was no definite therapy and vaccine for COVID-19. So, as COVID-19 has called ideas for treatment, controlling, and diagnosis, we discussed the application of Clustered Regularly Interspaced Short Palindromic Repeats/Cas13 (CRISPR/Cas13) as a treatment of COVID-19, which received less attention compared with other potential therapeutic options.

m6A Editing: New Tool to Improve Crop Quality?

N⁶-methyladenosine (m⁶A) is the most common type of eukaryotic mRNA modification. It plays an important role in regulating plant growth and development and stress resistance. m⁶A modification influences nearly all aspects of RNA metabolism and functionality and has great potential for improving crop quality. However, changing m⁶A modification levels as a whole may have unpredictable effects, making it impossible to accurately predict the effect of specific m⁶A modifications on RNA. In this opinion article, the main challenges and possible solutions for exploring m⁶A modification functions in plant systems are discussed. An m⁶A editing platform that uses new high-throughput methods to identify m⁶A modification at single-base resolution, and genome editing for selective editing of specific m⁶A sites for crop improvement is proposed.

[Knockdown the expression of ku70 and lig4 in HEK293T cells by CRISPR/Cas13 system]

Clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated proteins (Cas) system is a hotspot of gene editing and gene expression research, in which CRISPR/Cas13 system provides a new direction for RNA interference and editing. In this study, we designed and synthesized the corresponding gRNAs of CRISPR/Cas13a and CRISPR/Cas13b systems in non-homologous end joining (NHEJ) pathway, such as Ku70 and Lig4, and then detected the expression of ku70 and lig4 in HEK293T cells. The CRISPR/Cas13a system could efficiently knockdown the mRNA expression of ku70 and lig4 more than 50%, and CRISPR/Cas13b system also suppressed ku70 and lig4 about 92% and 76%, respectively. Also, CRISPR/Cas13a, b systems could down-regulate Ku70 and Lig4 proteins level to 68% and 53%, respectively. The study demonstrates that the CRISPR/Cas13 system could effectively knockdown the expression of RNA and protein in HEK293T cells, providing a new strategy for gene function and regulation research.

CRISPR/Cas13 as a Tool for RNA Interference

Almost all biological processes involve RNA, making it crucial to develop tools for manipulation of the transcriptome. The bacterial CRISPR/Cas13 system was recently rewired to facilitate RNA manipulation in eukaryotes, including plants. We discuss here the opportunities and limitations of using CRISPR/Cas13 in plants for various types of RNA manipulation.