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Repair of CRISPR-guided RNA breaks enables site-specific RNA excision in human cells.
Genome editing with CRISPR RNA-guided endonucleases generates DNA breaks that are resolved by cellular DNA repair machinery. However, analogous methods to manipulate RNA remain unavailable. We show that site-specific RNA breaks generated with type-III CRISPR complexes are repaired in human cells and that this repair can be used for programmable deletions in human transcripts to restore gene function. Collectively, this work establishes a technology for precise RNA manipulation with potential therapeutic applications.
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Efficient homology-directed gene editing by CRISPR/Cas9 in human stem and primary cells using tube electroporation.
CRISPR/Cas9 efficiently generates gene knock-out via nonhomologous end joining (NHEJ), but the efficiency of precise homology-directed repair (HDR) is substantially lower, especially in the hard-to-transfect human stem cells and primary cells. Herein we report a tube electroporation method that can effectively transfect human stem cells and primary cells with minimal cytotoxicity. When applied to genome editing using CRISPR/Cas9 along with single stranded DNA oligonucleotide (ssODN) template in human induced pluripotent stem cells (iPSCs), up to 42.1% HDR rate was achieved, drastically higher than many reported before. We demonstrated that the high HDR efficiency can be utilized to increase the gene ablation rate in cells relevant to clinical applications, by knocking-out β2-microglobulin (B2M) in primary human mesenchymal stem cells (MSCs, 37.3% to 80.2%), and programmed death-1 (PD-1) in primary human T cells (42.6% to 58.6%). Given the generality and efficiency, we expect that the method will have immediate impacts in cell research as well as immuno- and transplantation therapies.
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Utilization of the CRISPR/Cas9 system for the efficient production of mutant mice using crRNA/tracrRNA with Cas9 nickase and FokI-dCas9.
The CRISPR/Cas9 system is a powerful genome editing tool for the production of genetically modified animals. To produce mutant mice, chimeric single-guide RNA (sgRNA) is cloned in a plasmid vector and a mixture of sgRNA and Cas9 are microinjected into the fertilized eggs. An issue associated with gene manipulation using the CRISPR/Cas9 system is that there can be off-target effects. To simplify the production of mutant mice with low risks of off-target effects caused by the CRISPR/Cas9 system, we demonstrated that genetically modified mice can be efficiently obtained using chemically synthesized CRISPR RNA (crRNA), trans-activating crRNA (tracrRNA), and modified Cas9s, such as the nickase version and FokI-fused catalytically inactive Cas9, by microinjection into fertilized eggs. Using this method, it is no longer necessary to clone sgRNA into a plasmid vector, and this enables high-throughput production of mutant mice.
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Linking CRISPR-Cas9 double-strand break profiles to gene editing precision with BreakTag.
Cas9 can cleave DNA in both blunt and staggered configurations, resulting in distinct editing outcomes, but what dictates the type of Cas9 incisions is largely unknown. In this study, we developed BreakTag, a versatile method for profiling Cas9-induced DNA double-strand breaks (DSBs) and identifying the determinants of Cas9 incisions. Overall, we assessed cleavage by SpCas9 at more than 150,000 endogenous on-target and off-target sites targeted by approximately 3,500 single guide RNAs. We found that approximately 35% of SpCas9 DSBs are staggered, and the type of incision is influenced by DNA:gRNA complementarity and the use of engineered Cas9 variants. A machine learning model shows that Cas9 incision is dependent on the protospacer sequence and that human genetic variation impacts the configuration of Cas9 cuts and the DSB repair outcome. Matched datasets of Cas9 and engineered variant incisions with repair outcomes show that Cas9-mediated staggered breaks are linked with precise, templated and predictable single-nucleotide insertions, demonstrating that a scission-based gRNA design can be used to correct clinically relevant pathogenic single-nucleotide deletions.
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[Construction of a stable TrxR1 knockout HCT-116 cell line using CRISPR/Cas9 gene editing system].
To investigate the cellular target selectivity of small molecules targeting thioredoxin reductase 1, we reported the construction and functional research of a stable TrxR1 gene (encode thioredoxin reductase 1) knockout HCT-116 cell line. We designed and selected TrxR1 knockout sites according to the TrxR1 gene sequence and CRISPR/Cas9 target designing principles. SgRNA oligos based on the selected TrxR1 knockout sites were obtained. Next, we constructed knockout plasmid by cloning the sgRNA into the pCasCMV-Puro-U6 vector. After transfection of the plasmid into HCT-116 cells, TrxR1 knockout HCT-116 cells were selected using puromycin resistance. The TrxR1 knockout efficiency was identified and verified by DNA sequencing, immunoblotting, TRFS-green fluorescent probe, and cellular TrxR1 enzyme activity detection. Finally, the correlation between TrxR1 expression and cellular effects of drugs specifically targeting TrxR1 was investigated by CCK-8 assay. The results demonstrated that the knockout plasmid expressing the sgRNA effectively knocked-out TrxR1 gene within HCT-116 cells, and no expression of TrxR1 protein could be observed in stable TrxR1 knockout HCT-116 (HCT116-TrxR1-KO) cells. The TrxR1-targeting inhibitor auranofin did not show any inhibitory activity against either cellular TrxR1 enzyme activity or cell proliferation. Based on these results, we conclude that a stable TrxR1 gene knockout HCT-116 cell line was obtained through CRISPR/Cas9 techniques, which may facilitate investigating the role of TrxR1 in various diseases.
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Are we ready to genetically modify a human embryo? Or is it too late to ask?
After the announcement that a scientist genetically altered human embryos and implanted them for gestation last November, the increased discussion has revolved around the ethical lapses that occurred in the process. The scientist, He Jiankui, forged ethical approval documents, chose a disease target that is preventable and treatable, and did not replicate a naturally occurring mutation, creating a new mutation instead. Aside from these and other ethical concerns about his procedure and protocol, several fundamental questions remain: should scientists be altering the human germline at this time and, if so, under what circumstances? If not, under what circumstances might such research be permissible, if at all? And who should make these decisions? We believe that it is too early for this research to be conducted in embryos intended for gestation. Additional safety and efficacy research on animal and non-implanted embryos is needed. But more importantly, a broad societal conversation should inform decisions about the future of germline editing, including determining the scope of relevant ethical considerations, such as the conditions under which the research is ready for human application (if at all), and the oversight such research requires. Abbreviations: First-in-Human (FIH); National Academies of Science, Engineering, and Medicine (NASEM).
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Advances of genetic engineering in streptococci and enterococci.
In the post-genome era, reverse genetic engineering is an indispensable methodology for experimental molecular biology to provide a deeper understanding of the principal relationship between genomic features and biological phenotypes. Technically, genetic engineering is carried out through allele replacement of a target genomic locus with a designed nucleotide sequence, so called site-directed mutagenesis. To artificially manipulate allele replacement through homologous recombination, researchers have improved various methodologies that are optimized to the bacterial species of interest. Here, we review widely used genetic engineering technologies, particularly for streptococci and enterococci, and recent advances that enable more effective and flexible manipulation. The development of genetic engineering has been promoted by synthetic biology approaches based on basic biological knowledge of horizontal gene transfer systems, such as natural conjugative transfer, natural transformation, and the CRISPR/Cas system. Therefore, this review also describes basic insights into molecular biology that underlie improvements in genetic engineering technology.
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Regulation of the Homeostasis of Early Embryo Development in Dairy Cows by Targeted Editing of the PRLR Gene-Mediated Activation of the Anti-Heat Stress Pathway.
The intensification of global climate warming exacerbates the issue of heat stress in dairy cows, making the SLICK mutation in the prolactin receptor (PRLR) gene a critical target for enhancing heat tolerance in these animals. This study aims to investigate the effects of CRISPR/Cas9-mediated editing of the PRLR gene on the biological characteristics of bovine fibroblasts and early embryonic development following somatic cell nuclear transfer (SCNT). Using the CRISPR/Cas9 system, we targeted and edited a 20 bp-150 bp region within exon nine of the PRLR gene. After conducting off-target predictions and activity screenings, we identified optimal guide RNA (sgRNA) sequences and established stable transgenic cell lines. Transcriptome sequencing was performed on edited cells to identify key genes and validate their expression profiles. Edited cells were utilized as donor cells for SCNT, during which we assessed oocyte levels of reactive oxygen species (ROS), glutathione (GSH), and mitochondrial function to analyze embryonic developmental performance. We constructed a cellular stress resistance network aimed at mitigating damage transmission while maintaining embryonic developmental homeostasis. This research provides technical support and theoretical reference for genetic editing breeding programs aimed at improving heat tolerance in dairy cattle.
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Application of CRISPR-mediated genome engineering in cancer research.
Cancer is a multistep process that arises from a series of genetic and epigenetic events. With recent technological advances there has been a burst in genome sequencing and epigenetic studies revealing a plethora of alterations that may contribute to cancer. However, the great challenge for the cancer research community is the systematic functional characterization of these genetic and epigenetic events to assess their role in cancer initiation and progression. Recent advances in genome engineering using CRISPR/Cas9, an ancient bacterial immune-like system, have revolutionized cancer genetics. Here we highlight the breakthroughs in the effective use of these novel genome-editing techniques, and we discuss the challenges and potential applications of these tools for cancer biology.
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Genome engineering with Cas9 and AAV repair templates, successes and pitfalls.
Genome editing, in particular the CRISPR/Cas9 system, is widely used to generate new animal models. However, the generation of mutations, such as conditional knock-out or knock-in, can remain complex and inefficient, in particular because of the difficulty to deliver the donor DNA (single or double stranded) into the nucleus of fertilized oocytes. The use of recombinant adeno-associated viruses (rAAV) as donor DNA is a rapidly developing approach that promises to improve the efficiency of creation of animal models. In this mini-review, we explore the progress and challenges of using CRISPR/Cas9 in combination with rAAV for precise genome editing. We will summarise the current knowledge of rAAV transduction, data on its use in rodent embryos in combination with CRISPR/Cas9 to easily generate sequence replacements or insertions, the limitations of rAAV and the unexpected events observed to date, and the protocol optimisations already in place to facilitate its use in the generation of animal models.
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