CRISPR-Cas9 Enzymes Research Articles

In vivo Treatment of a Severe Vascular Disease via a Bespoke CRISPR-Cas9 Base Editor.

Genetic vascular disorders are prevalent diseases that have diverse etiologies and few treatment options. Pathogenic missense mutations in the alpha actin isotype 2 gene ( ACTA2 ) primarily affect smooth muscle cell (SMC) function and cause multisystemic smooth muscle dysfunction syndrome (MSMDS), a genetic vasculopathy that is associated with stroke, aortic dissection, and death in childhood. Here, we explored genome editing to correct the most common MSMDS-causative mutation ACTA2 R179H. In a first-in-kind approach, we performed mutation-specific protein engineering to develop a bespoke CRISPR-Cas9 enzyme with enhanced on-target activity against the R179H sequence. To directly correct the R179H mutation, we screened dozens of configurations of base editors (comprised of Cas9 enzymes, deaminases, and gRNAs) to develop a highly precise corrective A-to-G edit with minimal deleterious bystander editing that is otherwise prevalent when using wild-type SpCas9 base editors. We then created a murine model of MSMDS that exhibits phenotypes consistent with human patients, including vasculopathy and premature death, to explore the in vivo therapeutic potential of this base editing strategy. Delivery of the customized base editor via an engineered SMC-tropic adeno-associated virus (AAV-PR) vector substantially prolonged survival and rescued systemic phenotypes across the lifespan of MSMDS mice, including in the vasculature, aorta, and brain. Together, our optimization of a customized base editor highlights how bespoke CRISPR-Cas enzymes can enhance on-target correction while minimizing bystander edits, culminating in a precise editing approach that may enable a long-lasting treatment for patients with MSMDS.

Secreted Particle Information Transfer (SPIT) - A Cellular Platform for In Vivo Genetic Engineering.

A multitude of tools now exist that allow us to precisely manipulate the human genome in a myriad of different ways. However, successful delivery of these tools to the cells of human patients remains a major barrier to their clinical implementation. Here we introduce a new cellular approach for in vivo genetic engineering, Secreted Particle Information Transfer (SPIT) that utilizes human cells as delivery vectors for in vivo genetic engineering. We demonstrate the application of SPIT for cell-cell delivery of Cre recombinase and CRISPR-Cas9 enzymes, we show that genetic logic can be incorporated into SPIT and present the first demonstration of human cells as a delivery platform for in vivo genetic engineering in immunocompetent mice. We successfully applied SPIT to genetically modify multiple organs and tissue stem cells in vivo including the liver, spleen, intestines, peripheral blood, and bone marrow. We anticipate that by harnessing the large packaging capacity of a human cell's nucleus, the ability of human cells to engraft into patients' long term and the capacity of human cells for complex genetic programming, that SPIT will become a paradigm shifting approach for in vivo genetic engineering.

The Technologist's Dilemma

The Technologist's Dilemma

Genome editing in animals with minimal PAM CRISPR-Cas9 enzymes

The requirement for Cas nucleases to recognize a specific PAM is a major restriction for genome editing. SpCas9 variants SpG and SpRY, recognizing NGN and NRN PAMs, respectively, have contributed to increase the number of editable genomic sites in cell cultures and plants. However, their use has not been demonstrated in animals. Here we study the nuclease activity of SpG and SpRY by targeting 40 sites in zebrafish and C. elegans. Delivered as mRNA-gRNA or ribonucleoprotein (RNP) complexes, SpG and SpRY were able to induce mutations in vivo, albeit at a lower rate than SpCas9 in equivalent formulations. This lower activity was overcome by optimizing mRNA-gRNA or RNP concentration, leading to mutagenesis at regions inaccessible to SpCas9. We also found that the CRISPRscan algorithm could help to predict SpG and SpRY targets with high activity in vivo. Finally, we applied SpG and SpRY to generate knock-ins by homology-directed repair. Altogether, our results expand the CRISPR-Cas targeting genomic landscape in animals.

Scalable characterization of the PAM requirements of CRISPR-Cas enzymes using HT-PAMDA.

The continued expansion of the genome-editing toolbox necessitates methods to characterize important properties of CRISPR-Cas enzymes. One such property is the requirement for Cas proteins to recognize a protospacer-adjacent motif (PAM) in DNA target sites. The high-throughput PAM determination assay (HT-PAMDA) is a method that enables scalable characterization of the PAM preferences of different Cas proteins. Here, we provide a step-by-step protocol for the method, discuss experimental design considerations, and highlight how the method can be used to profile naturally occurring CRISPR-Cas9 enzymes, engineered derivatives with improved properties, orthologs of different classes (e.g., Cas12a), and even different platforms (e.g., base editors). A distinguishing feature of HT-PAMDA is that the enzymes are expressed in a cell type or organism of interest (e.g., mammalian cells), permitting scalable characterization and comparison of hundreds of enzymes in a relevant setting. HT-PAMDA does not require specialized equipment or expertise and is cost effective for multiplexed characterization of many enzymes. The protocol enables comprehensive PAM characterization of dozens or hundreds of Cas enzymes in parallel in <2 weeks.

A Mini Review on CRISPR -Cas: The Cutting Edge Of DNA Editing

The ability to control and modify DNA—the code of life, has long been cherished by the scientists. They want to use genome editing to investigate different diseases that affect humans. With this easier access to DNA sequences, scientists are on the verge of a third revolution that will deeply impact our lives, to the extent that computers have changed society: we are entering the era of “gene editing”, following the era of “gene reading”. Gene editing is the rational and precise modification of DNA sequences program in living cells and organisms. Nuclease-based gene editing is already widely used in research as a cost-effective, fast, and easy way to conduct genetic experiments. Other recent approaches to targeted genome modification – zinc-finger nucleases [ZFNs] and transcription-activator like effector nucleases [TALENs]– enable researchers to generate permanent mutations by introducing double-stranded breaks to activate repair pathways. These approaches are costly and time-consuming to engineer, limiting their widespread use, particularly for large scale, high-throughput studies. A new gene editing technology known as CRISPR-Cas9 offers the potential for substantial improvement over previous technologies in that it is simple to use and inexpensive and has a relatively high degree of precision and efficiency. These characteristics have led many in the scientific and business communities to assert that CRISPR-Cas9 will lead to groundbreaking advances in many fields, including agriculture, energy, ecosystem conservation, and in the investigation, prevention, and treatment of diseases. The advent of facile genome engineering using the bacterial RNA-guided CRISPR-Cas9 system in animals and plants is transforming biology. This article is an aim to understand CRISPR (CLUSTERED REGULARLY INTERSPACED PALINDROMIC REPEAT) biology from its initial discovery through the elucidation of the CRISPR-Cas9 enzyme mechanism, which has set the stage for remarkable developments using this technology to modify, regulate, or mark genomic loci in a wide variety of cells and organisms from all three domains of life. CRISPR-Cas9 has triggered a revolution in which laboratories around the world are using the technology for innovative applications in biology. The power of this technology to systematically analyze gene functions in mammalian cells, study genomic rearrangements and the progression of cancers or other diseases, and potentially correct genetic mutations responsible for inherited disorders. CRISPR-Cas9 is having a major impact on functional genomics conducted in experimental systems. Its application in genome-wide studies will enable large-scale screening for drug targets and other phenotypes and will facilitate the generation of engineered animal models that will benefit pharmacological studies and the understanding of human diseases. CRISPR- Cas9 applications in plants and fungi also promise to change the pace and course of agricultural research. Future research directions to improve the technology will include engineering or identifying smaller Cas9 variants with distinct specificity that may be more amenable to delivery in human cells. Understanding the homology- directed repair mechanisms that follow Cas9-mediated DNA cleavage will enhance.

Abstract 6059: Targeting the anthracycline metabolizing enzyme AKR1C3 in adipocytes to improve cytotoxicity

Abstract Introduction: We have reported that mouse and human adipocytes take up and metabolize the anthracycline, daunorubicin (DNR), reducing its concentration in the adipocyte microenvironments. This may contribute to anthracycline resistance for cancers, which reside in adipocyte rich environments such as omentum and bone marrow. Adipocytes express several carbonyl- and aldo-keto reductases (CBRs and AKRs) which metabolize and inactivate anthracyclines, and it is unclear which of these might be important targets to improve treatment outcome. Experimental Procedures: We knocked out AKR1C3 in the human preadipocyte cell line Chub S7 using CRISPR/Cas9 gene editing technology. We chose AKR1C3 first as it is one of the overexpressed enzymes in adipocytes with the highest anthracycline-metabolizing activity. We delivered ribonucleoprotein complexes of CRISPR-Cas9 enzyme plus guide RNAs by nucleofection. Then we established single-cell derived clones and tested for successful KO by Western blot. Finally, we quantified adipocyte lysate AKR activity using a colorimetric assay based on NADPH-dependent reduction of phenanthrenequinone. Data Summary: We chose three Chub S7 preadipocyte clones that demonstrated successful AKR1C3 knockout based on almost undetectable protein expression by western blot. AKR activity was significantly reduced in all three clones; control preadipocytes had 44±4.7, while clones had activity of 28±7.3, 33±3.4, and 35±5.7 pmol/min/µg (p&amp;lt;0.05 for all comparisons, n=3 for each assay). Conclusions: These findings demonstrate that AKR1C3 knockout can be successfully done in human preadipocytes using a CRISPR-Cas9 system. Knockout of AKR1C3 significantly reduces overall aldoketoreductase activity in preadipocyte cells. This implies that a substantial portion of preadipocyte AKR activity is dependent on the isoenzyme, AKR1C3. Future testing is needed to determine whether AKR1C3 KO will reduce the clearance of anthracyclines from the cancer microenvironment, and may represent a treatment target to enhance anthracycline cytotoxicity. Citation Format: Vladislava Paharkova, Etan Orgel, Michael Neely, Stan. Louie, Steven Mittelman. Targeting the anthracycline metabolizing enzyme AKR1C3 in adipocytes to improve cytotoxicity [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6059.

Analyses of Homing Endonucleases and Mechanism of Action of CRISPR-Cas9 HNH Endonucleases

Aim: To analyze different HNH endonucleases from various sources including the HNH endonuclease regions of CRISPR-Cas9 proteins for their conserved motifs, metal-binding sites and catalytic amino acids and propose a plausible mechanism of action for HNH endonucleases, using CRISPR-Cas9 as the model enzyme.&#x0D; Study Design: Multiple sequence analysis (MSA) of homing endonucleases including the CRISPR-Cas9 using Clustal Omega was studied. Other biochemical, Site-directed mutagenesis (SDM) and X-ray crystallographic data were also analyzed.&#x0D; Place and Duration of Study: School of Biotechnology, Madurai Kamaraj University, Madurai, India, between 2007 and 2013.&#x0D; Methodology: Bioinformatics, Biochemical, SDM and X-ray crystallographic data of the HNH endonucleases from different organisms including CRISPR-Cas9 enzymes were analyzed. The advanced version of Clustal Omega was used for protein sequence analysis of different HNH endonucleases from various sources. The conserved motifs identified by the bioinformatics analysis were analyzed further with the data already available from biochemical and SDM and X-ray crystallographic analyses of this group of enzymes and to confirm the possible amino acids involved in the active sites and catalysis.&#x0D; Results: Different types of homing endonucleases from various sources including the HNH endonuclease regions of CRISPR-Cas9 enzymes exhibit different catalytic regions and metal-binding sites. However, the catalytic amino acid, i.e., the proton acceptor histidine (His), is completely conserved in all homing endonucleases analyzed. From these data, a plausible mechanism of action for HNH endonucleases, using CRISPR-Cas9 from Streptococcus pyogenes, as the model enzyme is proposed. Furthermore, multiple sequence alignment (MSA) of various homing endonucleases from different organisms showed many highly conserved motifs also among them. However, some of the HNH endonucleases showed consensus only around the active site regions. Possible catalytic amino acids identified among them belong to either -DH---N or -HH--N types. There are at least two types of metal-binding sites and bind Mg2+ or Zn2+ or both. The CRISPR-Cas9 enzyme from S. pyogenes belongs to the -DH- based HNH endonucleases and possesses –DxD- type metal-binding site where it possibly binds to a Mg2+ ion. The other HNH enzymes possess one or two invariant Zn binding CxxC/ CxxxC motifs.&#x0D; Conclusions: The CRISPR-Cas9 enzymes are found to be -DH- type where the first D is likely to involve in metal-binding and the second invariant H acts as the proton acceptor and the N in –HNH- Cas9 confers specificity by interacting with the nucleotide near the catalytic region. In this communication, a metal-bound water molecule is shown as the nucleophile initiating catalysis. Homing endonucleases may be used as novel DNA binding and cleaving reagents for a variety of genome editing applications and Zinc finger nucleases have already found applications in genome editing.

Versatile transcription control based on reversible dCas9 binding.

The ability to control transcription in a time-dependent manner in vitro promises numerous applications in molecular biology and nanotechnology. Here we demonstrate an approach that enables precise, independent control over the production of multiple RNA transcripts in vitro using single guide RNA (sgRNA)-directed transcription blockades by catalytically dead Streptococcus pyogenes CRISPR-Cas9 enzyme (dCas9). We show that when bound to a DNA template, the dCas9:sgRNA complex forms a robust blockade to transcription by RNA polymerases (RNAPs) from bacteriophages SP6, T3, and T7 (>99.5% efficiency), and a partial blockade to transcription by Escherichia coli RNAP (∼70% efficiency). We find that all three bacteriophage RNAPs dissociate from the DNA template upon encountering the dCas9 blockade, while E. coli RNAP stays bound for at least the 90-min duration of our experiments. The blockade maintains >95% efficiency when four mismatches are introduced into the 5′ end of the sgRNA target sequence. Notably, when using such a mismatched blockade, production of specific RNA species can be activated on demand by addition of a double-stranded competitor DNA perfectly matching the sgRNA. This strategy enables the independent production of multiple RNA species in a temporally controlled fashion from the same DNA template, demonstrating a new approach for transcription control.

A genetic system for biasing the sex ratio in mice.

Biasing the sex ratio of populations of different organisms, including plants, insects, crustacean, and fish, has been demonstrated by genetic and non-genetic approaches. However, biasing the sex ratio of mammalian populations has not been demonstrated genetically. Here, we provide a first proof of concept for such a genetic system in mammals by crossing two genetically engineered mouse lines. The maternal line encodes a functional Cas9 protein on an autosomal chromosome, whereas the paternal line encodes guide RNAs on the Y chromosome targeting vital mouse genes. After fertilization, the presence of both the Y-encoded guide RNAs from the paternal sperm and the Cas9 protein from the maternal egg targets the vital genes in males. We show that these genes are specifically targeted in males and that this breeding consequently self-destructs solely males. Our results pave the way for a genetic system that allows biased sex production of livestock.

Temperature-Responsive Competitive Inhibition of CRISPR-Cas9

CRISPR-Cas immune systems utilize RNA-guided nucleases to protect bacteria from bacteriophage infection. Bacteriophages have in turn evolved inhibitory "anti-CRISPR" (Acr) proteins, including six inhibitors (AcrIIA1-AcrIIA6) that can block DNA cutting and genome editing by type II-A CRISPR-Cas9 enzymes. We show here that AcrIIA2 and its more potent homolog, AcrIIA2b, prevent Cas9 binding to DNA by occluding protein residues required for DNA binding. Cryo-EM-determined structures of AcrIIA2 or AcrIIA2b bound to S.pyogenes Cas9 reveal a mode of competitive inhibition of DNA binding that is distinct from other known Acrs. Differences in thetemperature dependence of Cas9 inhibition by AcrIIA2 and AcrIIA2b arise from differences in both inhibitor structure and the local inhibitor-binding environment on Cas9. These findings expand the natural toolbox for regulating CRISPR-Cas9 genome editing temporally, spatially, and conditionally.

Interference proceedings and innovation goals of the CRISPR-Cas9 patent

... The United States' Patent Trial and Appeal Board (PTAB), formerly US Patent and Trademark Office’s Board of Patent Appeals and Interferences (BPAI),1 decided a highly contested interference proceeding concerning the Type-II CRISPR-Cas9 gene editing technology in February 2017.2Clustered regularly interspaced short palindromic repeats (CRISPR) has been hailed as one of the most important innovations of bio-science in the 21st century.3 It allows scientists to edit gene sequences in an effective manner, akin to a word processor. This is a sharp improvement from pre-existing methods like Transcription Activator-Like Effector Nucleases (TALENs) and Zinc-Finger Nucleases (ZFNs) in biological research.4 CRISPR is an adaptive immune process first noticed in bacteria. Jennifer Doudna, of the University of California, and Emmanuelle Charpentier, now at the Max Planck Institute for Infection Biology, published an article in 2012 demonstrating the use of this process to edit genome sequences in vitro (‘Jinek 2012’).5 By delivering a synthetic RNA protein, the CRISPR-Cas9 enzyme could be guided to a specific gene site. The process enabled them to remove specific genes or add new ones and change the genetic sequencing. Doudna and Charpentier filed for a patent before the USPTO in March 2013.

Improved route to single-base genome editing

In a new approach to genome editing called “base editing,” researchers have engineered the CRISPR-Cas9 enzyme to modify individual DNA bases more efficiently and more accurately than with existing ...

What history tells us XL. The success story of the expression 'genome editing'.

The expression « genome editing » designates the possibilities opened by the CRISPR-Cas9 enzyme to cut and modify genemes at precise positions. This expression has been rapidly adopted by biologists, but also journalists and laymen. I descibe steps in the recent emergence of this expression, as well as the reasons of its success.

Genome editing. The new frontier of genome engineering with CRISPR-Cas9.

The advent of facile genome engineering using the bacterial RNA-guided CRISPR-Cas9 system in animals and plants is transforming biology. We review the history of CRISPR (clustered regularly interspaced palindromic repeat) biology from its initial discovery through the elucidation of the CRISPR-Cas9 enzyme mechanism, which has set the stage for remarkable developments using this technology to modify, regulate, or mark genomic loci in a wide variety of cells and organisms from all three domains of life. These results highlight a new era in which genomic manipulation is no longer a bottleneck to experiments, paving the way toward fundamental discoveries in biology, with applications in all branches of biotechnology, as well as strategies for human therapeutics.