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10 years of CRISPR/CAS genomic engineering in Yarrowia lipolytica.
Yarrowia lipolytica is a versatile cell factory widely used in bioprocesses for producing lipids, organic acids, and other high-value compounds. Historically, its genetic engineering was constrained by low homologous recombination (HR) efficiency and the predominance of non-homologous end joining (NHEJ), limiting strain development and metabolic pathway optimization. The advent of CRISPR-Cas technologies has revolutionized genome editing in Y. lipolytica, enabling precise, efficient, and multiplexed modifications. Innovations such as pCAS1yl and pCRISPRyl plasmids, along with genomic Cas9 integration, have enhanced targeted editing efficiency. CRISPR applications now extend to metabolic engineering for lipids, itaconic acid, erythritol, and other compounds. Beyond canonical Cas9, alternative systems, including CRISPRa, Cas12a, base editors, and sgRNA libraries, provide increased flexibility and functional diversity. Central to these approaches is the rational design of guide RNAs (gRNAs), supported by bioinformatics platforms such as CHOPCHOP v3, CRISPOR, CCTop, and Cas-OFFinder, which assist in target site selection, off-target prediction, and editing optimization. This review summarizes the main CRISPR/Cas9 applications in Y. lipolytica, highlighting key engineered strains and emphasizing the critical role of bioinformatics in improving editing strategies. We also propose a pipeline for systematic gRNA design based on published evidence and discuss future perspectives, including the integration of machine learning, artificial intelligence, and emerging CRISPR variants to further advance yeast metabolic engineering.
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Precise, predictable genome integrations by deep-learning-assisted design of microhomology-based templates.
Precise CRISPR-based DNA integration and editing remain challenging, largely because of insufficient control of the repair process. We find that repair at the genome-cargo interface is predictable by deep learning models and adheres to sequence-context-specific rules. On the basis of in silico predictions, we devised a strategy of base-pair tandem repeat repair arms matching microhomologies at double-strand breaks. These repeat homology arms promote frame-retentive cassette integration and reduce deletions both at the target site and within the transgene. We demonstrate precise integrations at 32 loci in HEK293T cells. Germline-transmissible transgene integration and endogenous protein tagging in Xenopus and adult mouse brains demonstrated precise integration during early embryonic cleavage and in nondividing, differentiated cells. Optimized repair arms also facilitated small edits for scarless single-nucleotide or double-nucleotide changes using oligonucleotide templates in vitro and in vivo. We provide the design tool Pythia to facilitate precise genomic integration and editing for experimental and therapeutic purposes for a wide range of target cell types and applications.
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Chromosome Transplantation: Correction of the Chronic Granulomatous Disease Defect in Mouse Induced Pluripotent Stem Cells.
In spite of the progress in gene editing achieved in recent years, a subset of genetic diseases involving structural chromosome abnormalities, including aneuploidies, large deletions and complex rearrangements, cannot be treated with conventional gene therapy approaches. We have previously devised a strategy, dubbed chromosome transplantation (CT), to replace an endogenous mutated chromosome with an exogenous normal one. To establish a proof of principle for our approach, we chose as disease model the chronic granulomatous disease (CGD), an X-linked severe immunodeficiency due to abnormalities in CYBB (GP91) gene, including large genomic deletions. We corrected the gene defect by CT in induced pluripotent stem cells (iPSCs) from a CGD male mouse model. The Hprt gene of the endogenous X chromosome was inactivated by CRISPR/Cas9 technology thus allowing the exploitation of the hypoxanthine-aminopterin-thymidine selection system to introduce a normal donor X chromosome by microcell-mediated chromosome transfer. X-transplanted clones were obtained, and diploid XY clones which spontaneously lost the endogenous X chromosome were isolated. These cells were differentiated toward the myeloid lineage, and functional granulocytes producing GP91 protein were obtained. We propose the CT approach to correct iPSCs from patients affected by other X-linked diseases with large deletions, whose treatment is still unsatisfactory. Stem Cells 2019;37:876-887.
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Structure and engineering of the minimal type VI CRISPR-Cas13bt3.
Type VI CRISPR-Cas13 effector enzymes catalyze RNA-guided RNA cleavage and have been harnessed for various technologies, such as RNA detection, targeting, and editing. Recent studies identified Cas13bt3 (also known as Cas13X.1) as a miniature Cas13 enzyme, which can be used for knockdown and editing of target transcripts in mammalian cells. However, the action mechanism of the compact Cas13bt3 remains unknown. Here, we report the structures of the Cas13bt3-guide RNA complex and the Cas13bt3-guide RNA-target RNA complex. The structures revealed how Cas13bt3 recognizes the guide RNA and its target RNA and provided insights into the activation mechanism of Cas13bt3, which is distinct from those of the other Cas13a/d enzymes. Furthermore, we rationally engineered enhanced Cas13bt3 variants and ultracompact RNA base editors. Overall, this study improves our mechanistic understanding of the CRISPR-Cas13 enzymes and paves the way for the development of efficient Cas13-mediated transcriptome modulation technologies.
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Repair of the TGFBI gene in human corneal keratocytes derived from a granular corneal dystrophy patient via CRISPR/Cas9-induced homology-directed repair.
Granular corneal dystrophy (GCD) is an autosomal dominant hereditary disease in which multiple discrete and irregularly shaped granular opacities are deposited in the corneal stroma. GCD is caused by a point mutation in the transforming growth factor-β-induced (TGFBI) gene, located on chromosome 5q31. Here, we report the first successful application of CRISPR-Cas9-mediated genome editing for the correction of a TGFBI mutation in GCD patient-derived primary corneal keratocytes via homology-directed repair (HDR). To correct genetic defects in GCD patient cells, we designed a disease-specific guide RNA (gRNA) targeting the R124H mutation of TGFBI, which causes GCD type 2 (GCD2). An R124H mutation in primary human corneal keratocytes derived from a GCD2 patient was corrected by delivering a CRISPR plasmid expressing Cas9/gRNA and a single-stranded oligodeoxynucleotide HDR donor template in vitro. The gene correction efficiency was 20.6% in heterozygous cells and 41.3% in homozygous cells. No off-target effects were detected. These results reveal a new therapeutic strategy for GCD2; this method may also be applicable to other heredity corneal diseases.
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Advancements in genomic crop techniques and considerations for regulation and food safety.
Advancements in genomic crop techniques have led to the development of new genetic technologies, such as base- and prime editing, but improvements have been made to existing conventional techniques as well. Fields in which these advancements occur include targeted mutagenesis, conventional random mutagenesis, and developments with null segregants, e.g., crops from which transgenic elements have been crossed out. In this review, we describe the developments in these three fields and provide considerations concerning regulatory and safety aspects. Because of differences in legislation of modern biotechnology between countries or regions, regulatory challenges are to be expected given the ongoing developments in genomic crop techniques. Moreover, the nature of the mutations induced with these newly developed techniques is not different from those induced with conventional techniques, making the modified crop plants indistinguishable from non-modified counterparts of the same crop species. Thus, enforcement of regulations cannot solely rely on technical analytical methods. Also, potential off-target or unintended effects in the primary mutants remain underexplored. Yet, these do not raise safety concerns owing to the experience with the crop breeding practice of iterative cycles for desirable traits selection, as well as the segregation and discard of unwanted phenotypes. Given that regulation will always change after innovation and developments within the sector advance rapidly, we advocate that both authorities and the breeding sector pro-actively implement a food safety culture. Such a safety culture will help developers of genomic technologies in crops to identify potential food safety issues at an early stage of development of future products.
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The establishment of a novel high-throughput screening system using RNA-guided genome editing to identify chemicals that suppress aldosterone synthase expression.
Aldosterone is synthesized in the adrenal by the aldosterone synthase CYP11B2. Although the control of CYP11B2 expression is important to maintain the mineral homeostasis, its overexpression induced by the depolarization-induced calcium (Ca2+) signaling activation has been reported to increase the synthesis of aldosterone in primary aldosteronism (PA). The drug against PA focused on the suppression of CYP11B2 expression has not yet been developed, since the molecular mechanism of CYP11B2 transcriptional regulation activated via Ca2+ signaling remains unclear. To address the issue, we attempted to reveal the mechanism of the transcriptional regulation of CYP11B2 using chemical screening. We generated a cell line by inserting Nanoluc gene as a reporter into CYP11B2 locus in H295R adrenocortical cells using the CRSPR/Cas9 system, and established the high-throughput screening system using the cell line. We then identified 9 compounds that inhibited the CYP11B2 expression induced by potassium-mediated depolarization from the validated compound library (3399 compounds). Particularly, tacrolimus, an inhibitor of phosphatase calcineurin, strongly suppressed the CYP11B2 expression even at 10 nM. These results suggest that the system is effective in identifying drugs that suppress the depolarization-induced CYP11B2 expression. Our screening system may therefore be a useful tool for the development of novel medicines against PA.
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Developing mitochondrial base editors with diverse context compatibility and high fidelity via saturated spacer library.
DddA-derived cytosine base editors (DdCBEs) greatly facilitated the basic and therapeutic research of mitochondrial DNA mutation diseases. Here we devise a saturated spacer library and successfully identify seven DddA homologs by performing high-throughput sequencing based screen. DddAs of Streptomyces sp. BK438 and Lachnospiraceae bacterium sunii NSJ-8 display high deaminase activity with a strong GC context preference, and DddA of Ruminococcus sp. AF17-6 is highly compatible to AC context. We also find that different split sites result in wide divergence on off-target activity and context preference of DdCBEs derived from these DddA homologs. Additionally, we demonstrate the orthogonality between DddA and DddIA, and successfully minimize the nuclear off-target editing by co-expressing corresponding nuclear-localized DddIA. The current study presents a comprehensive and unbiased strategy for screening and characterizing dsDNA cytidine deaminases, and expands the toolbox for mtDNA editing, providing additional insights for optimizing dsDNA base editors.
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Analysis of Off-Target Mutations in CRISPR-Edited Rice Plants Using Whole-Genome Sequencing.
The CRISPR/Cas systems have become the most widely used tool for genome editing in plants and beyond. However, CRISPR/Cas systems may cause unexpected off-target mutations due to sgRNA recognizing highly homologous DNA sequence elsewhere in the genome. Whole-genome sequencing (WGS) can be used to identify on- and off-target mutation. Here, we describe a pipeline of analyzing WGS data using a series of open source software for analysis of off-target mutations in CRISPR-edited rice plants. In this pipeline, the adapter is trimmed using SKEWER. Then, the cleaned reads are mapped to reference genome by applying BWA. To avoid mapping bias, the GATK is used to realign reads near indels (insertions and deletions) and recalibrate base quality controls. Whole-genome single nucleotide variations (SNVs) and indels are detected by LoFreq*, Mutect2, VarScan2, and Pindel. Last, SNVs and indels are compared with in silico off-target sites using Cas-OFFinder.
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Data Mining by Pluralistic Approach on CRISPR Gene Editing in Plants.
Genome engineering by site-specific nucleases enables reverse genetics and targeted editing of genomes in an efficacious manner. Contemporary revolutionized progress in targeted-genome engineering technologies based on Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-related RNA-guided endonucleases facilitate coherent interrogation of crop genome function. Evolved as an innate component of the adaptive immune response in bacterial and archaeal systems, CRISPR/Cas system is now identified as a versatile molecular tool that ensures specific and targeted genome modification in plants. Applications of this genome redaction tool-kit include somatic genome editing, rectification of genetic disorders or gene therapy, treatment of infectious diseases, generation of animal models, and crop improvement. We review the utilization of these synthetic nucleases as precision, targeted-genome editing platforms with the inherent potential to accentuate basic science "strengths and shortcomings" of gene function, complement plant breeding techniques for crop improvement, and charter a knowledge base for effective use of editing technology for ever-increasing agricultural demands. Furthermore, the emerging importance of Cpf1, Cas9 nickase, C2c2, as well as other innovative candidates that may prove more effective in driving novel applications in crops are also discussed. The mined data has been prepared as a library and opened for public use at www.lipre.org.
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