Target Site Selection Research Articles

CRISPR-Cas9 as a gene editing tool using cardiac glycoside reductase operon for digoxin metabolism

Gene editing technology has gained popularity over the past two decades with the scientific advancements being made in genetics and computational biology. CRISPR-Cas9 technique allows us to target genetic material and perform accurate manipulation of targeted gene function. Cgr operon, commonly found in the gut microbiome bacteria of E. lenta has several attributes which can be modified using the CRISPR-Cas9 methodology. Here, we briefly describe how the Cas9 nuclease can be used to prevent Digoxin from being suppressed by the cgr gene, directly correlating to improved cardiac function. The editing tool is described to assist in mutating the genetic material of cgr gene discussing the inhibition of Na+/K+ ATPase in cardiac myocytes and CG-content. The principle of operation behind CRISPR-Cas9 is described using non-homologous end joining or homology-directed repair cellular mechanisms. Target site selection, designing sgRNAs and introducing various mutations are discussed with limitations of current technology and possible applications in the field of point of care diagnostics and biosensing developing therapeutic interventions using cgr operon.

CRISPR therapy: A revolutionary breakthrough in genetic medicine

Gene editing with CRISPR-Cas9 technology revolutionizes modern medicine by enabling precise DNA modifications. Initially discovered as a bacterial defense mechanism, the Cas9 enzyme, guided by RNA, can target and cut specific DNA sites, allowing for gene editing. Applications include genetic engineering, functional studies, and potential treatments for genetic diseases like cancer. Notably, in 2023, CRISPR-Cas9 was approved for treating sickle cell anaemia with significant results, despite challenges like long-term security and high costs. CRISPR-Cas9 technology allows for correcting genetic defects, treating diseases, and improving agricultural crops. It can regulate gene transcription through the CRISPRi system, using an inactive Cas9 to interfere with gene expression without permanently altering DNA. This gene-editing tool shows promise in gene therapy, potentially curing diseases like HIV-1, sickle cell disease, and haemophilia B. However, challenges include off-target mutations and efficient delivery of CRISPR/Cas9. Precise target site selection and dosage control are crucial, with tools like CasOT helping identify and prevent unwanted mutations. CRISPR-Cas9 requires a PAM sequence to function, narrowing its targets in the genome but increasing specificity. Production of gRNA faces challenges due to mRNA processing, with alternatives like the artificial gene RGR showing promise. Efficient delivery methods are still needed, with current techniques involving DNA and RNA injection. Future applications include treating genetic diseases and agricultural improvements, with ongoing research essential for overcoming challenges and ensuring safety and accuracy. Global collaboration is vital for the ethical use of this technology. Contribution to evidence-based healthcare: CRISPR therapy represents an exciting frontier in genetic medicine, allowing for precise gene editing and opening up new possibilities for treating incurable diseases.

Integrative Transcriptomic and Target Metabolite Analysis as a New Tool for Designing Metabolic Engineering in Yeast.

Precision fermentation processes, especially when using edited microorganisms, demand accuracy in the bioengineering process to maximize the desired outcome and to avoid adverse effects. The selection of target sites to edit using CRISPR/Cas9 can be complex, resulting in non-controlled consequences. Therefore, the use of multi-omics strategies can help in the design, selection and efficiency of genetic editing. In this study, we present a multi-omics approach based on targeted metabolite analysis and transcriptomics for the designing of CRISPR/Cas9 in baker's yeast as a more efficient strategy to select editing regions. Multi-omics shows potential to reveal new metabolic bottlenecks and to elucidate new metabolic fluxes, which could be a key factor in minimizing the metabolic burden in edited microorganisms. In our model, we focus our attention on the isoprenoid synthesis due to their industrial interest. Targeted metabolite detection combined with a transcriptomic analysis revealed hydroxymethylglutaryl-CoA reductases (HMGs) as the best target gene to induce an increase in isoprenoid synthesis. Thus, an extra copy of HMG1 was introduced using, for the first time, the synthetic UADH1 promoter. The multi-omics analysis of the recombinant strain results in an accurate assessment of yeast behavior during the most important growth phases, highlighting the metabolic burden, Crabtree effect or the diauxic shift during culture.

Transposition with Tn3-family elements occurs through interaction with the host β-sliding clamp processivity factor.

Tn3 family transposons are a widespread group of replicative transposons, notorious for contributing to the dissemination of antibiotic resistance, particularly the global prevalence of carbapenem resistance. The transposase (TnpA) of these elements catalyzes DNA breakage and rejoining reactions required for transposition. However, the molecular mechanism for target site selection with these elements remains unclear. Here, we identify a QLxxLR motif in N-terminal of Tn3 TnpAs and demonstrate that this motif allows interaction between TnpA of Tn3 family transposon Tn1721 and the host β-sliding clamp (DnaN), the major processivity factor of the DNA replication machinery. The TnpA-DnaN interaction is essential for Tn1721 transposition. Our work unveils a mechanism whereby Tn3 family transposons can bias transposition into certain replisomes through an interaction with the host replication machinery. This study further expands the diversity of mobile elements that use interaction with the host replication machinery to bias integration.

Natural and Engineered Guide RNA-Directed Transposition with CRISPR-Associated Tn7-Like Transposons.

CRISPR-Cas (clustered regularly interspaced short palindromic repeats-CRISPR-associated nuclease) defense systems have been naturally coopted for guide RNA-directed transposition on multiple occasions. In all cases, cooption occurred with diverse elements related to the bacterial transposon Tn7. Tn7 tightly controls transposition; the transposase is activated only when special targets are recognized by dedicated target-site selection proteins. Tn7 and the Tn7-like elements that coopted CRISPR-Cas systems evolved complementary targeting pathways: one that recognizes a highly conserved site in the chromosome and a second pathway that targets mobile plasmids capable of cell-to-cell transfer. Tn7 and Tn7-like elements deliver a single integration into the site they recognize and also control the orientation of the integration event, providing future potential for use as programmable gene-integration tools. Early work has shown that guide RNA-directed transposition systems can be adapted to diverse hosts, even within microbial communities, suggesting great potential for engineering these systems as powerful gene-editing tools.

AB067. New drug development for the use of PARP1-E2F1 transcriptional inhibitors in the treatment of glioblastoma.

Glioblastoma (GBM) is the most malignant brain tumor and ranks among the most lethal of all human cancers, without improvements in survival over the last 30 years. Data obtained in our group suggest that PARP1, a well-known DNA-repairing protein, could also play a key role in the regulation of cell cycle through its interaction with the transcription factor E2F1. Therefore, considering that most oncogenic processes are associated with cell cycle deregulation, we hypothesized that disruption of PARP1-E2F1 interaction would provide a novel therapeutic approach to different types of cancer. The identification of novel compounds disrupting PARP1-E2F1 interaction was carried out by combining in silico and in vitro screening, using a rational drug design. The virtual screen was performed using a molecular library of several million compounds at the selected target site, using AtomNet® (Atomwise, San Francisco, CA, USA), the first deep learning neural network for structure-based drug design and discovery. Since there is no complete structural information of the PARP1-E2F1 protein-protein interaction, a homologous structure of the BRCT domain of BRCA1 complex with the phospho-peptide (PDBID: 1T2V) was used to identify the potential binding interface of BRCT domain of PARP-1 (PDBID: 2COK) and the E2F1 protein. Top scoring compounds were clustered and filtered to obtain a final subset of 83 compounds that were incorporated to our in vitro screening, which included both transcriptional E2F1 activity and survival studies. Complete culture medium supplemented with the compounds selected in the in silico screening (10 μM) were added and incubated for 24 hours. E2F1 activity was observed by measuring luminescence. For the viability assay, the fluorescence reading was performed (excitation 544 nm and emission 590 nm). The in silico and in vitro screening resulted in 12 compounds that inhibited E2F1 transcriptional activity and significantly reduced cell number. The highest inhibition of both E2F1 transcriptional activity and cell growth was observed with compound 3797, which was selected for further studies. Both in silico and in vitro results indicate that inhibition of PARP1-E2F1 transcriptional activity may provide a new rationale for designing novel therapeutic approaches for the treatment of GBM.

A programmable seekRNA guides target selection by IS1111 and IS110 type insertion sequences

IS1111 and IS110 insertion sequence (IS) family members encode an unusual DEDD transposase type and exhibit specific target site selection. The IS1111 group include identifiable subterminal inverted repeats (sTIR) not found in the IS110 type1. IS in both families include a noncoding region (NCR) of significant length and, as each individual IS or group of closely related IS selects a different site, we had previously proposed that an NCR-derived RNA was involved in target selection2. Here, we find that the NCR is usually downstream of the transposase gene in IS1111 family IS and upstream in the IS110 type. Four IS1111 and one IS110 family members that target different sequences are used to demonstrate that the NCR determines a short seeker RNA (seekRNA) that co-purified with the transposase. The seekRNA is essential for transposition of the IS or a cargo flanked by IS ends from and to the preferred target. Short sequences matching both top and bottom strands of the target are present in the seekRNA but their order in IS1111 and IS110 family IS is reversed. Reprogramming the seekRNA and donor flank to target a different site is demonstrated, indicating future biotechnological potential for these systems.

Building a carbon dioxide storage portfolio for the Barrow-Dampier sub-basins through regional screening – an integrated geoscience approach

Safe geological carbon dioxide (CO2) storage (GCS) requires rocks with suitable injectivity, capacity and sealing properties to ensure secure long-term containment of injected CO2. A regional understanding of the subsurface is essential to determine the potential for GCS of a basin and to select target sites. This is best addressed by integrating the basin’s tectono-stratigraphic evolution, its gross depositional environment, and its hydrodynamic, thermal and stress regimes. A basin-scale GCS assessment for the Barrow-Dampier sub-basins was conducted by Geoscience Australia and SLB. The objective of the study is to high-grade geological intervals and sites for potential GCS and to understand potential storage capacity and key risk factors. Stratigraphic and structural mapping of key storage intervals was performed using the reprocessed seismic volume and well database associated with the project. Analysis of critically stressed faults was used to estimate the likelihood of reactivation based on the far-field regional stress field and fault mechanical properties. Pressure, temperature, porosity, permeability, and water geochemistry data have been screened for >500 wells for assessing the storage unit intervals and predicting the hydrodynamic regime. Calibrated 2D basin models provide information on the regional pressure-temperature regime, porosity/permeability distribution, and sealing effectiveness. Potentiometric surface maps for the aquifer systems inform the distribution of potential CO2 plume migration. Results of this integrated regional basin study are used to quantify the risk of identified storage containers and to map the chance of success for GCS at a regional scale. The project results are publicly available via NOPIMS.

Effects of PNA Sequence and Target Site Selection on Function of a 4.5S Non-Coding RNA.

Peptide nucleic acid (PNA) based antisense strategy is a promising therapeutic approach to specifically inhibit target gene expression. However, unlike protein coding genes, identification of an ideal PNA binding site for non-coding RNA is not straightforward. Here, we compare the inhibitory activities of PNA molecules that bind a non-coding 4.5S RNA called SRP RNA, a key component of the bacterial signal recognition particle (SRP). A 9-mer PNA (PNA9) complementary to the tetraloop region of the RNA was more potent in inhibiting its interaction with the SRP protein, compared to an 8-mer PNA (PNA8) targeting a stem-loop. PNA9, which contained a homo-pyrimidine sequence could form a triplex with the complementary stretch of RNA in vitro as confirmed using a fluorescent derivative of PNA9 (F-PNA13). The RNA-PNA complex formation resulted in inhibition of SRP function with PNA9 and F-PNA13, but not PNA8 highlighting the importance of target site selection. Surprisingly, F-PNA13 which was more potent in inhibiting SRP function in vitro, showed weaker antibacterial activity compared to PNA9 likely due to poor cell penetration of the longer PNA. Our results underscore the importance of suitable target site selection and optimum PNA length to develop better antisense molecules against non-coding RNA.

How to use CRISPR/Cas9 in plants: from target site selection to DNA repair.

A tool for precise, target-specific, efficient, and affordable genome editing is a dream for many researchers, from those who conduct basic research to those who use it for applied research. Since 2012, we have tool that almost fulfils such requirements; it is based on clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein (Cas) systems. However, even CRISPR/Cas has limitations and obstacles that might surprise its users. In this review, we focus on the most frequently used variant, CRISPR/Cas9 from Streptococcus pyogenes, and highlight key factors affecting its mutagenesis outcomes: (i) factors affecting the CRISPR/Cas9 activity, such as the effect of the target sequence, chromatin state, or Cas9 variant, and how long it remains in place after cleavage; and (ii) factors affecting the follow-up DNA repair mechanisms including mostly the cell type and cell cycle phase, but also, for example, the type of DNA ends produced by Cas9 cleavage (blunt/staggered). Moreover, we note some differences between using CRISPR/Cas9 in plants, yeasts, and animals, as knowledge from individual kingdoms is not fully transferable. Awareness of these factors can increase the likelihood of achieving the expected results of plant genome editing, for which we provide detailed guidelines.

Abstract 4483: New drug development opportunities for PARP1

Abstract Personalized therapies allow, not only the increase of its therapeutic efficiency, but also the reduction of the secondary effects associated to the treatment of cancer. Data obtained in our group suggest that PARP1 could play a key role in the cell cycle regulation through its interaction with E2F1 transcription factor. Considering that most oncogenic processes is associated with cell cycle deregulation, the disruption of this interaction would provide a new therapeutic target of great interest and wide spectrum of indications. Therefore, our goal was to find molecules that interfere its role in cell-cycle regulation without affecting its function on DNA repair. The identification of novel compounds disrupting the PARP1/E2F1 interaction was carried out by combining in silico and in vitro screening, using a rational drug design. The virtual screen was performed using a molecular library of several million compounds at the selected target site, using AtomNet® (Atomwise), the first deep learning neural network for structure-based drug design and discovery. Since there is no complete structural information of the PARP-1/E2F1 protein-protein interaction, a homologous structure of BRCT domain of BRCA1 complex with the phospho-peptide (PDBID: 1T2V) was utilized to identify the potential binding interface of BRCT domain of PARP-1 (PDBID: 2COK) and the E2F1 protein. Top scoring compounds were clustered and filtered to arrive at a final subset of 83 compounds, library that were incorporated to our in vitro screening, which included both transcriptional (E2F1 activity) and survival studies. Twelve compounds were finally selected, based upon their higher capacity of inhibiting E2F1 activity.This work was supported by Agencia Estatal de Investigación (AEl/10.13039/501100011033), Xunta de Galicia (GPC GI-1862, ED431B 2020/26; ED431G 2019/02) and European Regional Development Fund-ERDF. AIMS Awards Program - Project A19-513, Atomwise Inc. Citation Format: Pablo Iglesias, David Moreiras, Laura Porres-Ventin, Lara Gonzalez-Rendo, Jose A. Zumalave, Victor M. Arce, Jose A. Costoya. New drug development opportunities for PARP1 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4483.

Combining CRISPR-Cas-mediated terminal resolution with a novel genetic workflow to achieve high-diversity adenoviral libraries

While recombinant adenoviruses (rAds) are widely used in both laboratory and medical gene transfer, library-based applications using this vector platform are not readily available. Recently, we developed a new method, the CRISPR-Cas9 mediated invivo terminal resolution aiding high-efficiency rescue of rAds from recombinant DNA. Here we report on a genetic workflow that allows construction of bacterial artificial chromosome-based rAd libraries reconstituted using highly efficient terminal resolution. We utilized frequent, pre-existing genomic sequences to allow the insertion of a selection marker, complementing two selected target sites into novel endonuclease recognition sites. In the second step, this selection marker is replaced with a transgene or mutation of interest via Gibson assembly. Our approach does not cause unwanted genomic off-target mutations while providing substantial flexibility for the site and nature of the genetic modification. This new genetic workflow, which we termed half site-directed fragment replacement (HFR) allows the introduction of more than 106 unique modifications into rAd encoding BACs using laboratory scale methodology. To demonstrate the power of HFR, we rescued barcoded viral vector libraries yielding a diversity of approximately 2.5×104 unique rAds per cm2 of transfected cell culture.

Streamlined Agrobacterium rhizogenes-mediated hairy root transformation for efficient CRISPR/Cas9-based gene editing evaluation in diverse Citrullus varieties

Streamlined Agrobacterium rhizogenes-mediated hairy root transformation for efficient CRISPR/Cas9-based gene editing evaluation in diverse Citrullus varieties

Target Site Selection and Storage Capacity Evaluation of CO2 Geological Storage in Yulin, China

Target Site Selection and Storage Capacity Evaluation of CO2 Geological Storage in Yulin, China

Application Of The CRISPR-Cas9 System to Drug Discovery in Breast Cancer

To elucidate the functioning of the CRISPR-Cas9 system in the realm of drug discovery, a series of experiments were undertaken. Firstly, CRISPR-Cas9 was employed to facilitate both positive and negative selection screening within human cells. Subsequently, an exploration of genes vital for pluripotent stem cell and cancer cell viability was conducted. Following this, in a melanoma model, a screen was performed to identify genes whose loss contributes to resistance against vemurafenib, a therapeutic agent targeting the mutant protein kinase BRAF. Notably, the top-ranking candidate genes included previously verified genes such as NF1 and MED12, alongside novel discoveries in the form of CUL3, NF2, TADA1, and TADA2B. This investigation revealed a remarkable consistency among distinct guide RNAs directed at the same gene, with an elevated rate of successful hit confirmation. These findings underscore the potential of genome-scale screening employing Cas9, thus substantiating CRISPR-Cas9 as a potent methodology for large-scale sequencing and the selection of target sites.

Relationship between land tenure and land use in unplanned settlements in Lusaka, Zambia

Relationship between land tenure and land use in unplanned settlements in Lusaka, Zambia

Mechanism of target site selection by type V-K CRISPR-associated transposases.

CRISPR-associated transposases (CASTs) repurpose nuclease-deficient CRISPR effectors to catalyze RNA-guided transposition of large genetic payloads. Type V-K CASTs offer potential technology advantages but lack accuracy, and the molecular basis for this drawback has remained elusive. Here, we reveal that type V-K CASTs maintain an RNA-independent, "untargeted" transposition pathway alongside RNA-dependent integration, driven by the local availability of TnsC filaments. Using cryo-electron microscopy, single-molecule experiments, and high-throughput sequencing, we found that a minimal, CRISPR-less transpososome preferentially directs untargeted integration at AT-rich sites, with additional local specificity imparted by TnsB. By exploiting this knowledge, we suppressed untargeted transposition and increased type V-K CAST specificity up to 98.1% in cells without compromising on-target integration efficiency. These findings will inform further engineering of CAST systems for accurate, kilobase-scale genome engineering applications.

Recent advances in structure-based enzyme engineering for functional reconstruction.

Structural information can help engineer enzymes. Usually, specific amino acids in particular regions are targeted for functional reconstruction to enhance the catalytic performance, including activity, stereoselectivity, and thermostability. Appropriate selection of target sites is the key to structure-based design, which requires elucidationof the structure-function relationships. Here, we summarize the mutations of residues in different specific regions, including active center, access tunnels, and flexible loops, on fine-tuning the catalytic performance of enzymes, and discuss the effects of altering the local structural environment on the functions. In addition, we keep up with the recent progress of structure-based approaches for enzyme engineering, aiming to provide some guidance on how to take advantage of the structural information.

The HIV-1 Capsid-Targeted Inhibitor GSK878 Alters Selection of Target Sites for HIV DNA Integration.

Decades of effort have yielded highly effective antiviral agents to treat HIV, but viral strains have evolved resistance to each inhibitor type, focusing attention on the importance of developing new inhibitor classes. A particularly promising new target is the HIV capsid, the function of which can be disrupted by highly potent inhibitors that persist long term in treated subjects. Studies with such inhibitors have contributed to an evolving picture of the role of capsid itself-the inhibitors, like certain capsid protein (CA) amino acid substitutions, can disrupt intracellular trafficking to alter the selection of target sites for HIV DNA integration in cellular chromosomes. In this study, we compare effects on HIV integration targeting for two potent inhibitors-a new molecule targeting CA, GSK878, and the previously studied lenacapavir (LEN, formerly known as GS-6207). We find that both inhibitors reduce integration in active transcription units and near epigenetic marks associated with active transcription. A careful study of integration near repeated sequences indicated frequencies were also altered for integration within multiple repeat classes. One notable finding was increased integration in centromeric satellite repeats in the presence of LEN and GSK878, which is of interest because proviruses integrated in centromeric repeats have been associated with transcriptional repression, inducibility, and latency. These data add to the picture that CA protein remains associated with preintegration complexes through the point in infection during which target sites for integration are selected, and specify new aspects of the consequences of disrupting this mechanism.

Modularity and diversity of target selectors in Tn7 transposons

To spread, transposons must integrate into target sites without disruption of essential genes while avoiding host defense systems. Tn7-like transposons employ multiple mechanisms for target-site selection, including protein-guided targeting and, in CRISPR-associated transposons (CASTs), RNA-guided targeting. Combining phylogenomic and structural analyses, we conducted a broad survey of target selectors, revealing diverse mechanisms used by Tn7 to recognize target sites, including previously uncharacterized target-selector proteins found in newly discovered transposable elements (TEs). We experimentally characterized a CAST I-D system and a Tn6022-like transposon that uses TnsF, which contains an inactivated tyrosine recombinase domain, to target the comM gene. Additionally, we identified a non-Tn7 transposon, Tsy, encoding a homolog of TnsF with an active tyrosine recombinase domain, whichwe show also inserts into comM. Our findings show that Tn7 transposons employ modular architecture and co-opt target selectors from various sources to optimize target selection and drive transposon spread.