The CRISPR/Cas9 System as a Tool to Engineer Chromosomal Translocation In Vivo

Engineered model of t(7;12)(q36;p13) AML recapitulates patient-specific features and gene expression profiles

Acute myeloid leukaemia carrying the translocation t(7;12)(q36;p13) is an adverse-risk leukaemia uniquely observed in infants. Despite constituting up to 30% of cases in under 2-year-olds, it remains poorly understood. Known molecular features are ectopic overexpression of the MNX1 gene and generation of a fusion transcript in 50% of patients. Lack of research models has hindered understanding of t(7;12) biology, which has historically focused on MNX1 overexpression rather than the cytogenetic entity itself. Here, we employed CRISPR/Cas9 to generate t(7;12) in the human K562 cell line, and in healthy CD34+ haematopoietic progenitors where the translocation was not sustained in long-term cultures or through serial replating. In contrast, in K562 cells, t(7;12) was propagated in self-renewing clonogenic assays, with sustained myeloid bias in colony formation and baseline depletion of erythroid signatures. Nuclear localisation analysis revealed repositioning of the translocated MNX1 locus to the interior of t(7;12)-harbouring K562 nuclei — a known phenomenon in t(7;12) patients which associates with ectopic overexpression of MNX1. Crucially, the K562-t(7;12) model successfully recapitulated the transcriptional landscape of t(7;12) patient leukaemia. In summary, we engineered a clinically-relevant model of t(7;12) acute myeloid leukaemia with the potential to unravel targetable molecular mechanisms of disease.

Multiplex Genome-Editing Technologies for Revolutionizing Plant Biology and Crop Improvement

Multiplex genome-editing (MGE) technologies are recently developed versatile bioengineering tools for modifying two or more specific DNA loci in a genome with high precision. These genome-editing tools have greatly increased the feasibility of introducing desired changes at multiple nucleotide levels into a target genome. In particular, clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein (Cas) [CRISPR/Cas] system-based MGE tools allow the simultaneous generation of direct mutations precisely at multiple loci in a gene or multiple genes. MGE is enhancing the field of plant molecular biology and providing capabilities for revolutionizing modern crop-breeding methods as it was virtually impossible to edit genomes so precisely at the single base-pair level with prior genome-editing tools, such as zinc-finger nucleases (ZFNs) and transcription activator-like effector nucleases (TALENs). Recently, researchers have not only started using MGE tools to advance genome-editing applications in certain plant science fields but also have attempted to decipher and answer basic questions related to plant biology. In this review, we discuss the current progress that has been made toward the development and utilization of MGE tools with an emphasis on the improvements in plant biology after the discovery of CRISPR/Cas9. Furthermore, the most recent advancements involving CRISPR/Cas applications for editing multiple loci or genes are described. Finally, insights into the strengths and importance of MGE technology in advancing crop-improvement programs are presented.

Multiplex Site-Directed Gene Editing Using Polyethylene Glycol-Mediated Delivery of CRISPR gRNA:Cas9 Ribonucleoprotein (RNP) Complexes to Carrot Protoplasts

The aim of this work was to show an efficient, recombinant DNA-free, multiplex gene-editing method using gRNA:Cas9 ribonucleoprotein (RNP) complexes delivered directly to plant protoplasts. For this purpose, three RNPs were formed in the tube, their activity was confirmed by DNA cleavage in vitro, and then they were delivered to carrot protoplasts incubated with polyethylene glycol (PEG). After 48 h of incubation, single nucleotide deletions and insertions and small deletions at target DNA sites were identified by using fluorescent-PCR capillary electrophoresis and sequencing. When two or three RNPs were delivered simultaneously, long deletions of 33-152 nt between the gRNA target sites were generated. Such mutations occurred with an efficiency of up to 12%, while the overall editing effectiveness was very high, reaching 71%. This highly efficient multiplex gene-editing method, without the need for recombinant DNA technology, can be adapted to other plants for which protoplast culture methods have been established.

CRISPR-Cas-mediated chromosome engineering for crop improvement and synthetic biology

Plant breeding relies on the presence of genetic variation, as well as on the ability to break or stabilize genetic linkages between traits. The development of the genome-editing tool clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein (Cas) has allowed breeders to induce genetic variability in a controlled and site-specific manner, and to improve traits with high efficiency. However, the presence of genetic linkages is a major obstacle to the transfer of desirable traits from wild species to their cultivated relatives. One way to address this issue is to create mutants with deficiencies in the meiotic recombination machinery, thereby enhancing global crossover frequencies between homologous parental chromosomes. Although this seemed to be a promising approach at first, thus far, no crossover frequencies could be enhanced in recombination-cold regions of the genome. Additionally, this approach can lead to unintended genomic instabilities due to DNA repair defects. Therefore, efforts have been undertaken to obtain predefined crossovers between homologues by inducing site-specific double-strand breaks (DSBs) in meiotic, as well as in somatic plant cells using CRISPR-Cas tools. However, this strategy has not been able to produce a substantial number of heritable homologous recombination-based crossovers. Most recently, heritable chromosomal rearrangements, such as inversions and translocations, have been obtained in a controlled way using CRISPR-Cas in plants. This approach unlocks a completely new way of manipulating genetic linkages, one in which the DSBs are induced in somatic cells, enabling the formation of chromosomal rearrangements in the megabase range, by DSB repair via non-homologous end-joining. This technology might also enable the restructuring of genomes more globally, resulting in not only the obtainment of synthetic plant chromosome, but also of novel plant species.

Genome-editing approaches and applications: a brief review on CRISPR technology and its role in cancer

The development of genome-editing technologies in 1970s has discerned a new beginning in the field of science. Out of different genome-editing approaches such as Zing-finger nucleases, TALENs, and meganucleases, clustered regularly interspaced short palindromic repeats-CRISPR-associated protein 9 (CRISPR/Cas9) is a recent and versatile technology that has the ability of making changes to the genome of different organisms with high specificity. Cancer is a complex process that is characterized by multiple genetic and epigenetic changes resulting in abnormal cell growth and proliferation. As cancer is one of the leading causes of deaths worldwide, a large number of studies are done to understand the molecular mechanisms underlying the development of cancer. Because of its high efficiency and specificity, CRISPR/Cas9 has emerged as a novel and powerful tool in the field of cancer research. CRISPR/Cas9 has the potential to accelerate cancer research by dissecting tumorigenesis process, generating animal and cellular models, and identify drug targets for chemotherapeutic approaches. However, despite having tremendous potential, there are certain challenges associated with CRISPR/Cas9 such as safe delivery to the target, potential off-target effects and its efficacy which needs to be addressed prior to its clinical application. In this review, we give a gist of different genome-editing technologies with a special focus on CRISPR/Cas9 development, its mechanism of action and its applications, especially in different type of cancers. We also highlight the importance of CRISPR/Cas9 in generating animal models of different cancers. Finally, we present an overview of the clinical trials and discuss the challenges associated with translating CRISPR/Cas9 in clinical use.

Toward precise CRISPR DNA fragment editing and predictable 3D genome engineering

Ever since gene targeting or specific modification of genome sequences in mice was achieved in the early 1980s, the reverse genetic approach of precise editing of any genomic locus has greatly accelerated biomedical research and biotechnology development. In particular, the recent development of the CRISPR/Cas9 system has greatly expedited genetic dissection of 3D genomes. CRISPR gene-editing outcomes result from targeted genome cleavage by ectopic bacterial Cas9 nuclease followed by presumed random ligations via the host double-strand break repair machineries. Recent studies revealed, however, that the CRISPR genome-editing system is precise and predictable because of cohesive Cas9 cleavage of targeting DNA. Here, we synthesize the current understanding of CRISPR DNA fragment-editing mechanisms and recent progress in predictable outcomes from precise genetic engineering of 3D genomes. Specifically, we first briefly describe historical genetic studies leading to CRISPR and 3D genome engineering. We then summarize different types of chromosomal rearrangements by DNA fragment editing. Finally, we review significant progress from precise 1D gene editing toward predictable 3D genome engineering and synthetic biology. The exciting and rapid advances in this emerging field provide new opportunities and challenges to understand or digest 3D genomes.

CRISPR/Cas9 in Cancer Immunotherapy: Animal Models and Human Clinical Trials

Even though chemotherapy and immunotherapy emerged to limit continual and unregulated proliferation of cancer cells, currently available therapeutic agents are associated with high toxicity levels and low success rates. Additionally, ongoing multi-targeted therapies are limited only for few carcinogenesis pathways, due to continually emerging and evolving mutations of proto-oncogenes and tumor-suppressive genes. CRISPR/Cas9, as a specific gene-editing tool, is used to correct causative mutations with minimal toxicity, but is also employed as an adjuvant to immunotherapy to achieve a more robust immunological response. Some of the most critical limitations of the CRISPR/Cas9 technology include off-target mutations, resulting in nonspecific restrictions of DNA upstream of the Protospacer Adjacent Motifs (PAM), ethical agreements, and the lack of a scientific consensus aiming at risk evaluation. Currently, CRISPR/Cas9 is tested on animal models to enhance genome editing specificity and induce a stronger anti-tumor response. Moreover, ongoing clinical trials use the CRISPR/Cas9 system in immune cells to modify genomes in a target-specific manner. Recently, error-free in vitro systems have been engineered to overcome limitations of this gene-editing system. The aim of the article is to present the knowledge concerning the use of CRISPR Cas9 technique in targeting treatment-resistant cancers. Additionally, the use of CRISPR/Cas9 is aided as an emerging supplementation of immunotherapy, currently used in experimental oncology. Demonstrating further, applications and advances of the CRISPR/Cas9 technique are presented in animal models and human clinical trials. Concluding, an overview of the limitations of the gene-editing tool is proffered.

From gene editing to genome engineering: restructuring plant chromosomes via CRISPR/Cas

In the last years, tremendous progress has been achieved in the field of gene editing in plants. By the induction of single site-specific double-strand breaks (DSBs), the knockout of genes by non-homologous end joining has become routine in many plant species. Recently, the efficiency of inducing pre-planned mutations by homologous recombination has also been improved considerably. However, very little effort has been undertaken until now to achieve more complex changes in plant genomes by the simultaneous induction of several DSBs. Several reports have been published on the efficient induction of deletions. However, the induction of intrachromosomal inversions and interchromosomal recombination by the use of CRISPR/Cas has only recently been reported. In this review, we want to sum up these results and put them into context with regards to what is known about natural chromosome rearrangements in plants. Moreover, we review the recent progress in CRISPR/Cas-based mammalian chromosomal rearrangements, which might be inspiring for plant biologists. In the long run, the controlled restructuring of plant genomes should enable us to link or break linkage of traits at will, thus defining a new area of plant breeding.

Efficient induction of heritable inversions in plant genomes using the CRISPR/Cas system

During the evolution of plant genomes, sequence inversions occurred repeatedly making the respective regions inaccessible for meiotic recombination and thus for breeding. Therefore, it is important to develop technologies that allow the induction of inversions within chromosomes in a directed and efficient manner. Using the Cas9 nuclease from Staphylococcus aureus (SaCas9), we were able to obtain scarless heritable inversions with high efficiency in the model plant Arabidopsis thaliana. Via deep sequencing, we defined the patterns of junction formation in wild-type and in the non-homologous end-joining (NHEJ) mutant ku70-1. Surprisingly, in plants deficient of KU70, inversion induction is enhanced, indicating that KU70 is required for tethering the local broken ends together during repair. However, in contrast to wild-type, most junctions are formed by microhomology-mediated NHEJ and thus are imperfect with mainly deletions, making this approach unsuitable for practical applications. Using egg-cell-specific expression of Cas9, we were able to induce heritable inversions at different genomic loci and at intervals between 3 and 18 kb, in the percentage range, in the T1 generation. By screening individual lines, inversion frequencies of up to the 10% range were found in T2. Most of these inversions had scarless junctions and were without any sequence change within the inverted region, making the technology attractive for use in crop plants. Applying our approach, it should be possible to reverse natural inversions and induce artificial ones to break or fix linkages between traits at will.

The advances in CRISPR technology and 3D genome

The clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein (Cas) system is a prokaryotic immune system that used to resist foreign genetic factors. It rapidly becomes the hot technology in life sciences and is applies for genome editing to solve the problem of genome-derived diseases. Using CRISPR/Cas technique, the biological DNA sequence can be repaired, cut, replaced, or added. It can effectively change the human stem cells and is expected to achieve results in the treatment. Compared with ZFN and TALEN genome editing techniques, CRISPR is more effective, accurate, and convenient. The application of CRISPR technique in three dimensional (3D) genome structure makes us understand the relationship between linear DNA sequence and 3D chromatin structure. Utilizing CRISPR/Cas9 genome editing to reverse or delete CTCF binding sites, to recognize changes of topological isomerism of the genome and interactions between chromatin loops. The purpose of this review is to introduce the characteristics and classification of the current CRISPR/Cas system, multiple functions, and potential therapeutic uses, as well as to outline the effect of the technique on chromatin loops by changing CTCF sites in 3D genomes. We will also briefly describe the importance of ethical dilemmas to be faced in CRISPR applications and provide a perspective for potential CRISPR considerations.