Building Endogenous Gene Connections through RNA Self-Assembly Controlled CRISPR/Cas9 Function

High-resolution and programmable RNA-IN and RNA-OUT genetic circuit in living mammalian cells

RNAs and their encoded proteins intricately regulate diverse cell types and states within the human body. Dysregulated RNA expressions or mutations can lead to various diseased cell states, including tumorigenesis. Detecting and manipulating these endogenous RNAs offers significant promise for restoring healthy cell states and targeting tumors both in research and clinical contexts. This study presents an RNA-IN and RNA-OUT genetic circuit capable dynamically sensing and manipulating any RNA target in a programmable manner. The RNA-IN module employes a programmable CRISPR-associated protease (CASP) complex for RNA detection, while the RNA-OUT module utilizes an engineered protease-responsive dCas9-VPR activator. Additionally, the CASP module can detect point mutations by harnessing an uncovered dual-nucleotide synergistic switching effect within the CASP complex, resulting in the amplification of point-mutation signals from initially undetectable levels (1.5-fold) to a remarkable 94-fold. We successfully showcase the circuit's ability to rewire endogenous RNA-IN signals to activate endogenous progesterone biosynthesis pathway, dynamically monitor adipogenic differentiation of mesenchymal stem cells (MSCs) and the epithelial-to-mesenchmal trans-differentiation, as well as selective killing of tumor cells. The programmable RNA-IN and RNA-OUT circuit exhibits tremendous potential for applications in gene therapy, biosensing and design of synthetic regulatory networks.

High-content tailoring strategy to improve the multifunctionality of functional nucleic acids

Functional nucleic acids (FNAs) have attracted increasing attention in recent years due to their diverse physiological functions. The understanding of their conformational recognition mechanisms has advanced through nucleic acid tailoring strategies and sequence optimization. With the development of the FNA tailoring techniques, they have become a methodological guide for nucleic acid repurposing. Therefore, it is necessary to systematize the relationship between FNA tailoring strategies and the development of nucleic acid multifunctionality. This review systematically categorizes eight types of FNA multifunctionality, and introduces the traditional FNA tailoring strategy from five aspects, including deletion, substitution, splitting, fusion and elongation. Based on the current state of FNA modification, a new generation of FNA tailoring strategy, called the high-content tailoring strategy, was unprecedentedly proposed to improve FNA multifunctionality. In addition, the multiple applications of rational tailoring-driven FNA performance enhancement in various fields were comprehensively summarized. The limitations and potential of FNA tailoring and repurposing in the future are also explored in this review. In summary, this review introduces a novel tailoring theory, systematically summarizes eight FNA performance enhancements, and provides a systematic overview of tailoring applications across all categories of FNAs. The high-content tailoring strategy is expected to expand the application scenarios of FNAs in biosensing, biomedicine and materials science, thus promoting the synergistic development of various fields.

Building RNA-Mediated Artificial Signaling Pathways between Endogenous Genes

ConspectusSophisticated genetic networks play a pivotal role in orchestrating cellular responses through intricate signaling pathways across diverse environmental conditions. Beyond the inherent complexity of natural cellular signaling networks, the construction of artificial signaling pathways (ASPs) introduces a vast array of possibilities for reshaping cellular responses, enabling programmable control of living organisms. ASPs can be integrated with existing cellular networks and redirect output responses as desired, allowing seamless communication and coordination with other cellular processes, thereby achieving designable transduction within cells. Among diversified ASPs, establishing connections between originally independent endogenous genes is of particular significance in modifying the genetic networks, so that cells can be endowed with new capabilities to sense and deal with abnormal factors related to differentiated gene expression (i.e., solve the issues of the aberrant gene expression induced by either external or internal stimuli). In a typical scenario, the two genes X and Y in the cell are originally expressed independently. After the introduction of an ASP, changes in the expression of gene X may exert a designed impact on gene Y, subsequently inducing the cellular response related to gene Y. If X represents a disease signal and Y serves as a therapeutic module, the introduction of the ASP empowers cells with a new spontaneous defense system to handle potential risks, which holds great potential for both fundamental and translational studies.In this Account, we primarily review our endeavors in the construction of RNA-mediated ASPs between endogenous genes that can respond to differentiated RNA expression. In contrast to other molecules that may be restricted to specific pathways, synthetic RNA circuits can be easily utilized and expanded as a general platform for constructing ASPs with a high degree of programmability and tunability for diversified functionalities through predictable Watson-Crick base pairing. We first provide an overview of recent advancements in RNA-based genetic circuits, encompassing but not limited to utilization of RNA toehold switches, siRNA and CRISPR systems. Despite notable progress, most reported RNA circuits have to contain at least one exogenous RNA X as input or one engineered RNA Y as a target, which is not suitable for establishing endogenous gene connections. While exogenous RNAs can be engineered and controlled as desired, constructing a general and efficient platform for manipulation of naturally occurring RNAs poses a formidable challenge, especially for the mammalian system. With a focus on this goal, we are devoted to developing efficient strategies to manipulate cell responses by establishing RNA-mediated ASPs between endogenous genes, particularly in mammalian cells. Our step-by-step progress in engineering customized cell signaling circuits, from bacterial cells to mammalian cells, from gene expression regulation to phenotype control, and from small RNA to long mRNA of low abundance and more complex secondary structures, is systematically described. Finally, future perspectives and potential applications of these RNA-mediated ASPs between endogenous genes are also discussed.

Developing a multi-modular assembled prime editing (mPE) system improved precise multi-base insertion efficiency in dicots

INTRODUCTION

The Prime Editing (PE) system is a precise and versatile genome editing tool with great potential in plant breeding and plant synthetic biology. However, low PE efficiency severely restricts its application, especially in dicots. PE can introduce small tags to trace target protein or cis-element to regulate gene transcription which is an expertise superior to other gene editing tools. Owing to low efficiency, PE adaption in stably transformed Arabidopsis is lacking.

OBJECTIVES

This study aimed to investigate the issue of low PE efficiency in dicots and develop systematic solutions to improve it. Currently, PE in dicots is undetectable and inconsistent, and this study seeks to address it. Split PE into several parts showed better performance in some target sites in mammal cells. We plan to discover the optimal split PE combination in dicot.

METHODS

We conducted large-scale transformation experiments in dicot model plants Arabidopsis thaliana (At) and Nicotiana benthamiana (Nb) by Agrobacterium-mediated transformation with deep amplicon sequencing (0.2-0.5 million clean total reads).

RESULTS

The editing efficiency decreased upon using a fused reverse transcriptase (RT) or an extended pegRNA separately and further decreased dramatically when these were used together. With the help of the pol II strategy to express PE gRNA (pegRNA), we named the most effective split PE combination as a multi-modular assembled prime editing system (mPE). mPE exhibited improved precise editing efficiency on most gene sites with various editing types, ranging from 1.3-fold to 1288.5-fold and achieved PE on some sites that could not be edited by original PE2. Especially, mPE showed superiority for multi-base insertion with an average improvement of 197.9-fold.

CONCLUSION

The original PE architecture strongly inhibited the cleavage activity of Cas9. Split PE improved PE efficiency extensively and was in favor of introducing small insertions in dicot plants, indicating that different PE variants might have their own expertise.

CRISPR-powered RNA sensing in vivo

RNA sensing in vivo evaluates past or ongoing endogenous RNA disturbances, which is crucial for identifying cell types and states and diagnosing diseases. Recently, the CRISPR-driven genetic circuits have offered promising solutions to burgeoning challenges in RNA sensing. This review delves into the cutting-edge developments of CRISPR-powered RNA sensors in vivo, reclassifying these RNA sensors into four categories based on their working mechanisms, including programmable reassembly of split single-guide RNA (sgRNA), RNA-triggered RNA processing and protein cleavage, miRNA-triggered RNA interference (RNAi), and strand displacement reactions. Then, we discuss the advantages and challenges of existing methodologies in diverse application scenarios and anticipate and analyze obstacles and opportunities in forthcoming practical implementations.

Harnessing Catalytic RNA Circuits for Construction of Artificial Signaling Pathways in Mammalian Cells

Engineering of genetic networks with artificial signaling pathways (ASPs) can reprogram cellular responses and phenotypes under different circumstances for a variety of diagnostic and therapeutic purposes. However, construction of ASPs between originally independent endogenous genes in mammalian cells is highly challenging. Here we report an amplifiable RNA circuit that can theoretically build regulatory connections between any endogenous genes in mammalian cells. We harness the system of catalytic hairpin assembly with combination of controllable CRISPR-Cas9 function to transduce the signals from distinct messenger RNA expression of trigger genes into manipulation of target genes. Through introduction of these RNA-based genetic circuits, mammalian cells are endowed with autonomous capabilities to sense the changes of RNA expression either induced by ligand stimuli or from various cell types and control the cellular responses and fates via apoptosis-related ASPs. Our design provides a generalized platform for construction of ASPs inside the genetic networks of mammalian cells based on differentiated RNA expression.

Photoactivatable Engineering of CRISPR/Cas9-Inducible DNAzyme Probe for In Situ Imaging of Nuclear Zinc Ions

DNAzyme-based fluorescent probes for imaging metal ions in living cells have received much attention recently. However, employing in situ metal ions imaging within subcellular organelles, such as nucleus, remains a significant challenge. We developed a three-stranded DNAzyme probe (TSDP) that contained a 20-base-pair (20-bp) recognition site of a CRISPR/Cas9, which blocks the DNAzyme activity. When Cas9, with its specialized nuclear localization function, forms an active complex with sgRNA within the cell nucleus, it cleaves the TSDP at the recognition site, resulting in the in situ formation of catalytic DNAzyme structure. With this design, the CRISPR/Cas9-inducible imaging of nuclear Zn2+ is demonstrated in living cells. Moreover, the superiority of CRISPR-DNAzyme for spatiotemporal control imaging was demonstrated by integrating it with photoactivation strategy and Boolean logic gate for dynamic monitoring nuclear Zn2+ in both HeLa cells and mice. Collectively, this conceptual design expands the DNAzyme toolbox for visualizing nuclear metal ions and thus provides new analytical methods for nuclear metal-associated biology.

Plant Functional Genomics Based on High-Throughput CRISPR Library Knockout Screening: A Perspective

Plant biology studies in the post-genome era have been focused on annotating genome sequences' functions. The established plant mutant collections have greatly accelerated functional genomics research in the past few decades. However, most plant genome sequences' roles and the underlying regulatory networks remain substantially unknown. Clustered, regularly interspaced short palindromic repeat (CRISPR)-associated systems are robust, versatile tools for manipulating plant genomes with various targeted DNA perturbations, providing an excellent opportunity for high-throughput interrogation of DNA elements' roles. This study compares methods frequently used for plant functional genomics and then discusses different DNA multi-targeted strategies to overcome gene redundancy using the CRISPR-Cas9 system. Next, this work summarizes recent reports using CRISPR libraries for high-throughput gene knockout and function discoveries in plants. Finally, this work envisions the future perspective of optimizing and leveraging CRISPR library screening in plant genomes' other uncharacterized DNA sequences.

Engineering CRISPR guide RNAs for programmable RNA sensors

As the most valuable feature of the CRISPR system, the programmability based on Watson-Crick base pairing has been widely exploited in engineering RNA sensors. The base pairing in these systems offers a connection between the RNA of interest and the CRISPR effector, providing a highly specific mechanism for RNA detection both in vivo and in vitro. In the last decade, despite the many successful RNA sensing approaches developed during the era of CRISPR explosion, a deeper understanding of the characteristics of CRISPR systems and the continuous expansion of the CRISPR family members indicates that the CRISPR-based RNA sensor remains a promising area from which a variety of new functions and applications can be engineered. Here, we present a systematic overview of the various strategies of engineering CRISPR gRNA for programmable RNA detection with an aim to clarify the role of gRNA's programmability among the present limitations and future development of CRISPR-enabled RNA sensors.

Customizing cellular signal processing by synthetic multi-level regulatory circuits

As synthetic biology permeates society, the signal processing circuits in engineered living systems must be customized to meet practical demands. Towards this mission, novel regulatory mechanisms and genetic circuits with unprecedented complexity have been implemented over the past decade. These regulatory mechanisms, such as transcription and translation control, could be integrated into hybrid circuits termed "multi-level circuits". The multi-level circuit design will tremendously benefit the current genetic circuit design paradigm, from modifying basic circuit dynamics to facilitating real-world applications, unleashing our capabilities to customize cellular signal processing and address global challenges through synthetic biology.

Target-dependent RNA polymerase as universal platform for gene expression control in response to intracellular molecules

Controlling gene expression in response to specific molecules is an essential technique for regulating cellular functions. However, current platforms with transcription and translation regulators have a limited number of detectable molecules to induce gene expression. Here to address these issues, we present a Target-dependent RNA polymerase (TdRNAP) that can induce RNA transcription in response to the intracellular target specifically recognized by single antibody. By substituting the fused antibody, we demonstrate that TdRNAPs respond to a wide variety of molecules, including peptides, proteins, RNA, and small molecules, and produce desired transcripts in human cells. Furthermore, we show that multiple TdRNAPs can construct orthogonal and multilayer genetic circuits. Finally, we apply TdRNAP to achieve cell-specific genome editing that is autonomously triggered by detecting the target gene product. TdRNAP can expand the molecular variety for controlling gene expression and provide the genetic toolbox for bioengineering and future therapeutic applications.

MiRNA-Responsive CRISPR-Cas System via a DNA Regulator

Clustered regularly interspaced short palindromic repeats (CRISPR)- CRISPR-associated protein 9 (Cas9) genome editing technology is widely used for gene editing because it provides versatility in genetic manipulation. Several methods for regulating CRISPR activity already exist for accurate editing, but these require complex engineering. Thus, a simple and convenient regulatory system is required. In this study, we devised a CRISPR activation system using a DNA regulator that can be activated by miRNAs. The designed regulator was divided into two parts. The inhibition component consisted of the protospacer-adjacent motif (PAM) and seed sequence, which are important for Cas9 target recognition and bind to the ribonucleoprotein (RNP) complex for inhibition. The miRNA recognition component has a single-stranded toehold DNA for target miRNA binding and a partial double-stranded DNA complementary to the remaining miRNA sequence. In the presence of target miRNAs, the structure of the regulator is disrupted by the miRNAs, leading to its dissociation from the RNP complex and subsequent restoration of CRISPR activity. This method is easy to design and can be applied to various miRNAs via simple sequence manipulation. Therefore, this strategy provides a general platform for controlled genome editing.

Establishing artificial gene connections through RNA displacement-assembly-controlled CRISPR/Cas9 function

Construction of synthetic circuits that can reprogram genetic networks and signal pathways is a long-term goal for manipulation of biosystems. However, it is still highly challenging to build artificial genetic communications among endogenous RNA species due to their sequence independence and structural diversities. Here we report an RNA-based synthetic circuit that can establish regulatory linkages between expression of endogenous genes in both Escherichiacoli and mammalian cells. This design employs a displacement-assembly approach to modulate the activity of guide RNA for function control of CRISPR/Cas9. Our experiments demonstrate the great effectiveness of this RNA circuit for building artificial connections between expression of originally unrelated genes. Both exogenous and naturally occurring RNAs, including small/microRNAs and long mRNAs, are capable of controlling expression of another endogenous gene through this approach. Moreover, an artificial signal pathway inside mammalian cells is also successfully established to control cell apoptosis through our designed synthetic circuit. This study provides a general strategy for constructing synthetic RNA circuits, which can introduce artificial connections into the genetic networks of mammalian cells and alter the cellular phenotypes.

Inflammation conditional genome editing mediated by the CRISPR-Cas9 system

The specificity of CRISPR-Cas9 in response to particular pathological stimuli remains largely unexplored. Hence, we designed an inflammation-inducible CRISPR-Cas9 system by grafting a sequence that binds with NF-κB to the CRISPR-Cas9 framework, termed NBS-CRISPR. The genetic scissor function of this developed genome-editing tool is activated on encountering an inflammatory attack and is inactivated or minimized in non-inflammation conditions. Furthermore, we employed this platform to reverse inflammatory conditions by targeting the MyD88 gene, a crucial player in the NF-κB signaling pathway, and achieved impressive therapeutic effects. Finally, during inflammation, P65 (RELA) can translocate to the nucleus from the cytoplasm. Herein, to avoid Cas9 leaky DNA cleavage activity i, we constructed an NBS-P65-CRISPR system expressing the Cas9-p65 fusion protein. Our inflammation inducible Cas9-mediated genome editing strategy provides new perspectives and avenues for pathological gene interrogation.

Genetic switches based on nucleic acid strand displacement

Toehold-mediated strand displacement (TMSD) is an isothermal switching process that enables the sequence-programmable and reversible conversion of DNA or RNA strands between single- and double-stranded conformations or other secondary structures. TMSD processes have already found widespread application in DNA nanotechnology, where they are used to drive DNA-based molecular devices or for the realization of synthetic biochemical computing circuits. Recently, researchers have started to employ TMSD also for the control of RNA-based gene regulatory processes in vivo, in particular in the context of synthetic riboregulators and conditional guide RNAs for CRISPR/Cas. Here, we provide a review over recent developments in this emerging field and discuss the opportunities and challenges for such systems in in vivo applications.

Orthogonal Chemical Activation of Enzyme-Inducible CRISPR/Cas9 for Cell-Selective Genome Editing

The precision and therapeutic potential of CRISPR/Cas9 genome editing are greatly challenged by the less control over Cas9-mediated DNA cleavage. Herein, we introduce a conditional and cell-selective genome editing system controlled by disease-associated enzymes, termed enzyme-inducible CRISPR (eiCRISPR). eiCRISPR comprises Cas9 protein, a self-blocked inactive single-guide RNA (bsgRNA), and a chemically caged deoxyribozyme (DNAzyme) that activates bsgRNA and eiCRISPR in a controllable manner. We design chemical modifications of DNAzyme to suppress its ability to cleave the blocking region of bsgRNA, while the decaging of DNAzyme triggered by the tumor cell-overexpressed enzyme, for instance, NAD(P)H:quinone oxidoreductase (NQO1), restores the activity of bsgRNA and switches on eiCRISPR selectively for genome editing in cancer cells. Moreover, using a biodegradable lipid nanoparticle to deliver eiCRISPR in a tumor-bearing xenograft, we show that the in vivo activation of eiCRISPR enables the editing of human papillomavirus 18 E6 for potential cancer therapy. The strategy of postsynthetic and site-specific modification of DNAzyme is compatible with endogenous chemistries for regulating eiCRISPR for cell-selective genome editing and targeted gene therapy.

RNA-Responsive gRNAs for Controlling CRISPR Activity: Current Advances, Future Directions, and Potential Applications

CRISPR-Cas9 has emerged as a major genome manipulation tool. As Cas9 can cause off-target effects, several methods for controlling the expression of CRISPR systems were developed. Recent studies have shown that CRISPR activity could be controlled by sensing expression levels of endogenous transcripts. This is particularly interesting, as endogenous RNAs could harbor important information about the cell type, disease state, and environmental challenges cells are facing. Single-guide RNA (sgRNA) engineering played a major role in the development of RNA-responsive CRISPR systems. Following further optimizations, RNA-responsive sgRNAs could enable the development of novel therapeutic and research applications. This review introduces engineering strategies that could be employed to modify Streptococcus pyogenes sgRNAs with a focus on recent advances made toward the development of RNA-responsive sgRNAs. Future directions and potential applications of these technologies are also discussed.