Clustered Regularly Interspaced Short Palindromic Repeats Editing Research Articles

Software-based screening for efficient sgRNAs in Lactococcus lactis.

The two essential editing elements in the clustered regularly interspaced short palindromic repeats (CRISPR) editing system are promoter and single-guide RNA (sgRNA), the latter of which determines whether Cas protein can precisely target a specific location to edit the targeted gene. Therefore, the selection of sgRNA is crucial to the efficiency of the CRISPR editing system. Various online prediction tools for sgRNA are currently available. These tools can predict all possible sgRNAs of the targeted gene and rank sgRNAs according to certain scoring criteria in obedience to the demands of the user. We designed sgRNAs for Lactococcus lactis NZ9000 LLNZ_RS02020 (ldh) and LLNZ_RS10925 (upp) individually using online prediction software - CRISPOR and successfully constructed a series of knockout strains to allow comparison of the knockout efficiency of each sgRNA and analyze the differences between software predictions and actual experimental results. Our experimental results showed that the actual editing efficiency of the screened sgRNAs did not match the predicted results, a phenomenon that suggests that established findings from eukaryotic studies are not universally applicable to prokaryotes. software prediction can still be used as a tool for the initial screening of sgRNAs before further selection of suitable sgRNAs through experimental experience. This article is protected by copyright. All rights reserved.

LRRK2 Knockout Confers Resistance in HEK-293 Cells to Rotenone-Induced Oxidative Stress, Mitochondrial Damage, and Apoptosis

Leucine-rich repeat kinase 2 (LRRK2) has been linked to dopaminergic neuronal vulnerability to oxidative stress (OS), mitochondrial impairment, and increased cell death in idiopathic and familial Parkinson’s disease (PD). However, how exactly this kinase participates in the OS-mitochondria-apoptosis connection is still unknown. We used clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 LRRK2 knockout (KO) in the human embryonic kidney cell line 293 (HEK-293) to evaluate the cellular response to the mitochondrial inhibitor complex I rotenone (ROT), a well-known OS and cell death inducer. We report successful knockout of the LRRK2 gene in HEK-293 cells using CRISPR editing (ICE, approximately 60%) and flow cytometry (81%) analyses. We found that HEK-293 LRRK2 WT cells exposed to rotenone (ROT, 50 μM) resulted in a significant increase in intracellular reactive oxygen species (ROS, +7400%); oxidized DJ-1-Cys106-SO3 (+52%); phosphorylation of LRRK2 (+70%) and c-JUN (+171%); enhanced expression of tumor protein (TP53, +2000%), p53 upregulated modulator of apoptosis (PUMA, +1950%), and Parkin (PRKN, +22%); activation of caspase 3 (CASP3, +8000%), DNA fragmentation (+35%) and decreased mitochondrial membrane potential (ΔΨm, −58%) and PTEN induced putative kinase 1 (PINK1, −49%) when compared to untreated cells. The translocation of the cytoplasmic fission protein dynamin-related Protein 1 (DRP1) to mitochondria was also observed by colocalization with translocase of the outer membrane 20 (TOM20). Outstandingly, HEK-293 LRRK2 KO cells treated with ROT showed unaltered OS and apoptosis markers. We conclude that loss of LRRK2 causes HEK-293 to be resistant to ROT-induced OS, mitochondrial damage, and apoptosis in vitro. Our data support the hypothesis that LRRK2 acts as a proapoptotic kinase by regulating mitochondrial proteins (e.g., PRKN, PINK1, DRP1, and PUMA), transcription factors (e.g., c-JUN and TP53), and CASP3 in cells under stress conditions. Taken together, these observations suggest that LRRK2 is an important kinase in the pathogenesis of PD.

CRISPR Correction of the GBA Mutation in Human-Induced Pluripotent Stem Cells Restores Normal Function to Gaucher Macrophages and Increases Their Susceptibility to Mycobacterium tuberculosis.

Gaucher disease (GD) is an autosomal recessive lysosomal storage disorder caused by mutations in the β-glucocerebrosidase (GCase) GBA gene, which result in macrophage dysfunction. CRISPR (clustered regularly interspaced short palindromic repeats) editing of the homozygous L444P (1448T→C) GBA mutation in type 2 GD (GBA-/-) human-induced pluripotent stem cells (hiPSCs) yielded both heterozygous (GBA+/-) and homozygous (GBA+/+) isogenic lines. Macrophages derived from GBA-/-, GBA+/- and GBA+/+ hiPSCs showed that GBA mutation correction restores normal macrophage functions: GCase activity, motility, and phagocytosis. Furthermore, infection of GBA-/-, GBA+/- and GBA+/+ macrophages with the Mycobacterium tuberculosis H37Rv strain showed that impaired mobility and phagocytic activity were correlated with reduced levels of bacterial engulfment and replication suggesting that GD may be protective against tuberculosis.

CRISPR editing demonstrates rs10490924 raised oxidative stress in iPSC-derived retinal cells from patients with ARMS2/HTRA1-related AMD

Genome-wide association studies (GWAS) have identified genetic risk loci for age-related macular degeneration (AMD) on the chromosome 10q26 (Chr10) locus and are tightly linked: the A69S (G>T) rs10490924 single-nucleotide variant (SNV) and the AATAA-rich insertion-deletion (indel, del443/ins54), which are found in the age-related maculopathy susceptibility 2 (ARMS2) gene, and the G512A (G>A) rs11200638 SNV, which is found in thehigh-temperature requirement A serine peptidase 1(HTRA1) promoter. The fourth variant is Y402H complement factor H (CFH), which directs CFHsignaling. CRISPR manipulation of retinal pigment epithelium (RPE) cells may allow one to isolate the effects of the individual SNV and thus identify SNV-specific effects on cell phenotype. Clustered regularly interspaced short palindromic repeats (CRISPR) editing demonstrates that rs10490924 raised oxidative stress in induced pluripotent stem cell (iPSC)-derived retinal cells from patients with AMD. Sodium phenylbutyrate preferentially reverses the cell death caused by ARMS2 rs10490924 but not HTRA1 rs11200638. This study serves as a proof of concept for the use of patient-specific iPSCs for functional annotation of tightly linked GWAS to study the etiology of a late-onset disease phenotype. More importantly, we demonstrate that antioxidant administration may be useful for reducing reactive oxidative stress in AMD, a prevalent late-onset neurodegenerative disorder.

CRISPR and gene editing in HIV therapy: A scoping review

Human immunodeficiency virus (HIV) is nowadays one of the major health problems worldwide. Several strategies have been explored for the eradication of latent HIV-1 reservoirs, current antiretroviral therapy stops the progression of HIV disease, however, as new therapies are being developed, CRISPR (clustered regularly interspaced short palindromic repeats) systems have recently been used as a genome editing technique. CRISPR is becoming progressively one of the possible cures, although it remains experimental, for HIV in medical research. This systematic review summarizes literature evidence of CRISPR gene editing in HIV/AIDS therapy. This study also identifies the research gaps in the current literature, helping to guide future research.

A streamlined CRISPR workflow to introduce mutations and generate isogenic iPSCs for modeling amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) represents a complex neurodegenerative disorder with significant genetic heterogeneity. To date, both the genetic etiology and the underlying molecular mechanisms driving this disease remain poorly understood, although in recent years several studies have highlighted a number of genetic mutations causative for ALS. With these mutations pointing to potential pathways that may be affected within individuals with ALS, having the ability to generate human neurons and other disease relevant cells containing these mutations becomes even more critical if new therapies are to emerge. Recent developments with the advent of induced pluripotent stem cells (iPSCs) and clustered regularly interspaced short palindromic repeats (CRISPR) gene editing fields gave us the tools to introduce or correct a specific mutation at any site within the genome of an iPSC, and thus model the specific contribution of risk mutations. In this study we describe a rapid and efficient way to either introduce a mutation into a control line, or to correct an allele-specific mutation, generating an isogenic control line from patient-derived iPSCs with a given mutation. The mutations introduced were the G94A (also known as G93A) mutation into SOD1 or H517Q into FUS, and the mutation corrected was a patient iPSC line with I114T mutation in SOD1. A combination of small molecules and growth factors were used to guide a stepwise differentiation of the edited cells into motor neurons in order to demonstrate that disease-relevant cells could be generated for downstream applications. Through a combination of iPSCs and CRISPR editing, the cells generated here will provide fundamental insights into the molecular mechanisms underlying neuron degeneration in ALS.

New Frontiers: Precise Editing of Allergen Genes Using CRISPR.

Genome engineering with clustered regularly interspaced short palindromic repeats (CRISPR) technology offers the unique potential for unequivocally deleting allergen genes at the source. Compared to prior gene editing approaches, CRISPR boasts substantial improvements in editing efficiency, throughput, and precision. CRISPR has demonstrated success in several clinical applications such as sickle cell disease and β-thalassemia, and preliminary knockout studies of allergenic proteins using CRISPR editing show promise. Given the advantages of CRISPR, as well as specific DNA targets in the allergen genes, CRISPR gene editing is a viable approach for tackling allergy, which may lead to significant disease improvement. This review will highlight recent applications of CRISPR editing of allergens, particularly cat allergen Fel d 1, and will discuss the advantages and limitations of this approach compared to existing treatment options.

Early onset epilepsy and sudden unexpected death in epilepsy with cardiac arrhythmia in mice carrying the early infantile epileptic encephalopathy 47 gain-of-function FHF1(FGF12) missense mutation.

Fibroblast growth factor homologous factors (FHFs) are brain and cardiac sodium channel-binding proteins that modulate channel density and inactivation gating. A recurrent de novo gain-of-function missense mutation in the FHF1(FGF12) gene (p.Arg52His) is associated with early infantile epileptic encephalopathy 47 (EIEE47; Online Mendelian Inheritance in Man database 617166). To determine whether the FHF1 missense mutation is sufficient to cause EIEE and to establish an animal model for EIEE47, we sought to engineer this mutation into mice. The Arg52His mutation was introduced into fertilized eggs by CRISPR (clustered regularly interspaced short palindromic repeats) editing to generate Fhf1R52H/F+ mice. Spontaneous epileptiform events in Fhf1R52H/+ mice were assessed by cortical electroencephalography (EEG) and video monitoring. Basal heart rhythm and seizure-induced arrhythmia were recorded by electrocardiography. Modulation of cardiac sodium channel inactivation by FHF1BR52H protein was assayed by voltage-clamp recordings of FHF-deficient mouse cardiomyocytes infected with adenoviruses expressing wild-type FHF1B or FHF1BR52H protein. All Fhf1R52H/+ mice experienced seizure or seizurelike episodes with lethal ending between 12 and 26days of age. EEG recordings in 19-20-day-old mice confirmed sudden unexpected death in epilepsy (SUDEP) as severe tonic seizures immediately preceding loss of brain activity and death. Within 2-53s after lethal seizure onset, heart rate abruptly declined from 572±16bpm to 108±15bpm, suggesting a parasympathetic surge accompanying seizures that may have contributed to SUDEP. Although ectopic overexpression of FHF1BR52H in cardiomyocytes induced a 15-mV depolarizing shift in voltage of steady-state sodium channel inactivation and slowed the rate of channel inactivation, heart rhythm was normal in Fhf1R52H/+ mice prior to seizure. The Fhf1 missense mutation p.Arg52His induces epileptic encephalopathy with full penetrance in mice. Both Fhf1 (p.Arg52His) and Scn8a (p.Asn1768Asp) missense mutations enhance sodium channel Nav 1.6 currents and induce SUDEP with bradycardia in mice, suggesting an FHF1/Nav 1.6 functional axis underlying altered brain sodium channel gating in epileptic encephalopathy.

Genetically Engineering the Nervous System with CRISPR-Cas.

The multitude of neuronal subtypes and extensive interconnectivity of the mammalian brain presents a substantial challenge to those seeking to decipher its functions. While the molecular mechanisms of several neuronal functions remain poorly characterized, advances in next-generation sequencing (NGS) and gene-editing technology have begun to close this gap. The clustered regularly interspaced short palindromic repeats (CRISPR)-associated protein (CRISPR-Cas) system has emerged as a powerful genetic tool capable of manipulating the genome of essentially any organism and cell type. This technology has advanced our understanding of complex neurologic diseases by enabling the rapid generation of novel, disease-relevant in vitro and transgenic animal models. In this review, we discuss recent developments in the rapidly accelerating field of CRISPR-mediated genome engineering. We begin with an overview of the canonical function of the CRISPR platform, followed by a functional review of its many adaptations, with an emphasis on its applications for genetic interrogation of the normal and diseased nervous system. Additionally, we discuss limitations of the CRISPR editing system and suggest how future modifications to existing platforms may advance our understanding of the brain.

Generalizable sgRNA design for improved CRISPR/Cas9 editing efficiency.

The development of clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated protein 9 (Cas9) technology has provided a simple yet powerful system for targeted genome editing. In recent years, this system has been widely used for various gene editing applications. The CRISPR editing efficacy is mainly dependent on the single guide RNA (sgRNA), which guides Cas9 for genome cleavage. While there have been multiple attempts at improving sgRNA design, there is a pressing need for greater sgRNA potency and generalizability across various experimental conditions. We employed a unique plasmid library expressed in human cells to quantify the potency of thousands of CRISPR/Cas9 sgRNAs. Differential sequence and structural features among the most and least potent sgRNAs were then used to train a machine learning algorithm for assay design. Comparative analysis indicates that our new algorithm outperforms existing CRISPR/Cas9 sgRNA design tools. The new sgRNA design tool is freely accessible as a web application, http://crispr.wustl.edu. Supplementary data are available at Bioinformatics online.

Development of both type I–B and type II CRISPR/Cas genome editing systems in the cellulolytic bacterium Clostridium thermocellum

The robust lignocellulose-solubilizing activity of C. thermocellum makes it a top candidate for consolidated bioprocessing for biofuel production. Genetic techniques for C. thermocellum have lagged behind model organisms thus limiting attempts to improve biofuel production. To improve our ability to engineer C. thermocellum, we characterized a native Type I–B and heterologous Type II Clustered Regularly-Interspaced Short Palindromic Repeat (CRISPR)/cas (CRISPR associated) systems. We repurposed the native Type I–B system for genome editing. We tested three thermophilic Cas9 variants (Type II) and found that GeoCas9, isolated from Geobacillus stearothermophilus, is active in C. thermocellum. We employed CRISPR-mediated homology directed repair to introduce a nonsense mutation into pyrF. For both editing systems, homologous recombination between the repair template and the genome appeared to be the limiting step. To overcome this limitation, we tested three novel thermophilic recombinases and demonstrated that exo/beta homologs, isolated from Acidithiobacillus caldus, are functional in C. thermocellum. For the Type I–B system an engineered strain, termed LL1586, yielded 40% genome editing efficiency at the pyrF locus and when recombineering machinery was expressed this increased to 71%. For the Type II GeoCas9 system, 12.5% genome editing efficiency was observed and when recombineering machinery was expressed, this increased to 94%. By combining the thermophilic CRISPR system (either Type I–B or Type II) with the recombinases, we developed a new tool that allows for efficient CRISPR editing. We are now poised to enable CRISPR technologies to better engineer C. thermocellum for both increased lignocellulose degradation and biofuel production.

Questions Answered and Unanswered by the First CRISPR Editing Study in a Canine Model of Duchenne Muscular Dystrophy.

Clustered regularly interspaced short palindromic repeats (CRISPR) editing is being considered as a potential gene repair therapy to treat Duchenne muscular dystrophy, a dystrophin-deficient lethal muscle disease affecting all muscles in the body. A recent preliminary study from the Olson laboratory (Amoasii et al. Science 2018;362:89-91) showed robust dystrophin restoration in a canine Duchenne muscular dystrophy model following intramuscular or intravenous delivery of the CRISPR editing machinery by adeno-associated virus serotype 9. Despite the limitation of the small sample size, short study duration, and the lack of muscle function data, the Olson lab findings have provided important proof of principle for scaling up CRISPR therapy from rodents to large mammals. Future large-scale, long-term, and comprehensive studies are warranted to establish the safety and efficacy of CRISPR editing therapy in large mammals.

Gene editing in plants: progress and challenges.

The clustered regularly interspaced short palindromic repeat (CRISPR)-associated protein 9 (Cas9) genome editing system is a powerful tool for targeted gene modifications in a wide range of species, including plants. Over the last few years, this system has revolutionized the way scientists perform genetic studies and crop breeding, due to its simplicity, flexibility, consistency and high efficiency. Considerable progress has been made in optimizing CRISPR/Cas9 systems in plants, particularly for targeted gene mutagenesis. However, there are still a number of important challenges ahead, including methods for the efficient delivery of CRISPR and other editing tools to most plants, and more effective strategies for sequence knock-ins and replacements. We provide our viewpoint on the goals, potential concerns and future challenges for the development and application of plant genome editing tools.

CRISPR/Cas9-Mediated Genome Editing in Epstein-Barr Virus-Transformed Lymphoblastoid B-Cell Lines.

Epstein-Barr virus (EBV) efficiently transforms primary human B cells into immortalized lymphoblastoid cell lines (LCLs), which are extensively used in human genetic, immunological and virological studies. LCLs provide unlimited sources of DNA for genetic investigation, but can be difficult to manipulate, for instance because low retroviral or lentiviral transduction frequencies hinder experiments that require co-expression of multiple components. This unit details Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas9 engineering for robust LCL genome editing. We describe the generation and delivery of single-guide RNAs (sgRNAs), or dual-targeting sgRNAs, via lentiviral transduction of LCLs that stably express Cas9 protein. CRISPR/Cas9 editing allows LCL loss-of-function studies, including knock-out of protein-coding genes or deletion of DNA regulatory elements, and can be adapted for large-scale screening approaches. Low transfection efficiencies are a second barrier to performing CRISPR editing in LCLs, which are not typically lipid-transfectable. To circumvent this barrier, we provide an optimized protocol for LCL nucleofection of Cas9/sgRNA ribonucleoprotein complexes (RNPs) as an alternative route to achieve genome editing in LCLs. These editing approaches can also be employed in other B-cell lines, including Burkitt lymphoma and diffuse large B-cell lymphoma cells, and are highly reproducible. © 2018 by John Wiley & Sons, Inc.

CRISPR editing in biological and biomedical investigation

Recently, clustered regularly interspaced short palindromic repeats (CRISPR) based genomic editing technologies have armed researchers with powerful new tools to biological and biomedical investigations. To further improve and expand its functionality, natural, and engineered CRISPR associated nine proteins (Cas9s) have been investigated, various CRISPR delivery strategies have been tested and optimized, and multiple schemes have been developed to ensure precise mammalian genome editing. Benefiting from those in-depth understanding and further development of CRISPR, versatile CRISPR-based platforms for genome editing have been rapidly developed to advance investigations in biology and biomedicine. In biological research area, CRISPR has been widely adopted in both fundamental and applied research fields, such as accurate base editing, transcriptional regulation, and genome-wide screening. In biomedical research area, CRISPR has also shown its extensive applicability in the establishment of animal models for genetic disorders especially those large animals and non-human primates models, and gene therapy to combat virus infectious diseases, to correct monogenic disorders in vivo or in pluripotent cells. In this prospect article, after highlighting recent developments of CRISPR systems, we outline different applications and current limitations of CRISPR use in biological and biomedical investigation. Finally, we provide a perspective for future development and potential risks of this multifunctional technology.

CRISPR Editing in Biological and Biomedical Investigation.

The CRISPR (clustered regularly interspaced short palindromic repeat)-Cas (CRISPR-associated protein) system, a prokaryotic RNA-based adaptive immune system against viral infection, is emerging as a powerful genome editing tool in broad research areas. To further improve and expand its functionality, various CRISPR delivery strategies have been tested and optimized, and key CRISPR system components such as Cas protein have been engineered with different purposes. Benefiting from more in-depth understanding and further development of CRISPR, versatile CRISPR-based platforms for genome editing have been rapidly developed to advance investigations in biology and biomedicine. In biological research area, CRISPR has been widely adopted in both fundamental and applied research fields, such as genomic and epigenomic modification, genome-wide screening, cell and animal research, agriculture transforming, livestock breeding, food manufacture, industrial biotechnology, and gene drives in disease agents control. In biomedical research area, CRISPR has also shown its extensive applicability in the establishment of animal models for genetic disorders, generation of tissue donors, implementation of antimicrobial and antiviral studies, identification and assessment of new drugs, and even treatment for clinical diseases. However, there are still several problems to consider, and the biggest concerns are the off-target effects and ethical issues of this technology. In this prospect article, after highlighting recent development of CRISPR systems, we outline different applications and current limitations of CRISPR in biological and biomedical investigation. Finally, we provide a perspective on future development and potential risks of this multifunctional technology. J. Cell. Biochem. 119: 52-61, 2018. © 2017 Wiley Periodicals, Inc.

CRISPR Editing in Biological and Biomedical Investigation.

ABSTRACTThe revolutionary technology for genome editing known as the clustered regularly interspaced short palindromic repeat (CRISPR)‐CRISPR‐associated protein 9 (Cas9) system has sparked advancements in biological and biomedical research. The scientific breakthrough of the development of CRISPR‐Cas9 technology has allowed us to recapitulate human diseases by generating animal models of interest ranging from zebrafish to non‐human primates. The CRISPR‐Cas9 system can also be used to delineate the mechanisms underlying the development of human disorders and to precisely correct disease‐causing mutations. Repurposing this technology enables wider applications in transcriptome and epigenome manipulation and holds promise to reach the clinic. In this review, we highlight the latest advances of the CRISPR‐Cas9 system in different platforms and discuss the hurdles and challenges this technology is facing. J. Cell. Biochem. 118: 4152–4162, 2017. © 2017 Wiley Periodicals, Inc.

Method for Multiplexing CRISPR/Cas9 in Saccharomyces cerevisiae Using Artificial Target DNA Sequences.

Genome manipulation has become more accessible given the advent of the CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) editing technology. The Cas9 endonuclease binds a single stranded (single guide) RNA (sgRNA) fragment that recruits the complex to a corresponding genomic target sequence where it induces a double stranded break. Eukaryotic repair systems allow for the introduction of exogenous DNA, repair of existing mutations, or deletion of endogenous gene products. Targeting of Cas9 to multiple genomic positions (termed 'multiplexing') is achieved by the expression of multiple sgRNAs within the same nucleus. However, an ongoing concern of the CRISPR field has been the accidental targeting of Cas9 to alternative ('off-target') DNA locations within a genome. We describe the use (dubbed Multiplexing of Cas9 at Artificial Loci) of installed artificial Cas9 target sequences into the yeast genome that allow for (i) multiplexing with a single sgRNA; (ii) a reduction/elimination in possible off-target effects, and (iii) precise control of the placement of the intended target sequence(s).

CRISPR: From Prokaryotic Immune Systems to Plant Genome Editing Tools.

The clustered regularly interspaced short palindromic repeats (CRISPR) system is a prokaryotic adaptive immune system that has the ability to identify specific locations on the bacteriophage (phage) genome to create breaks in it, and internalize the phage genome fragments in its own genome as CRISPR arrays for memory-dependent resistance. Although CRISPR has been used in the dairy industry for a long time, it recently gained importance in the field of genome editing because of its ability to precisely target locations in a genome. This system has further been modified to locate and target any region of a genome of choice due to modifications in the components of the system. By changing the nucleotide sequence of the 20-nucleotide target sequence in the guide RNA, targeting any location is possible. It has found an application in the modification of plant genomes with its ability to generate mutations and insertions, thus helping to create new varieties of plants. With the ability to introduce specific sequences into the plant genome after cleavage by the CRISPR system and subsequent DNA repair through homology-directed repair (HDR), CRISPR ensures that genome editing can be successfully applied in plants, thus generating stronger and more improved traits. Also, the use of the CRISPR editing system can generate plants that are transgene-free and have mutations that are stably inherited, thus helping to circumvent current GMO regulations.

A CRISPR Path to Engineering New Genetic Mouse Models for Cardiovascular Research.

Previous efforts to target the mouse genome for the addition, subtraction, or substitution of biologically informative sequences required complex vector design and a series of arduous steps only a handful of laboratories could master. The facile and inexpensive clustered regularly interspaced short palindromic repeats (CRISPR) method has now superseded traditional means of genome modification such that virtually any laboratory can quickly assemble reagents for developing new mouse models for cardiovascular research. Here, we briefly review the history of CRISPR in prokaryotes, highlighting major discoveries leading to its formulation for genome modification in the animal kingdom. Core components of CRISPR technology are reviewed and updated. Practical pointers for 2-component and 3-component CRISPR editing are summarized with many applications in mice including frameshift mutations, deletion of enhancers and noncoding genes, nucleotide substitution of protein-coding and gene regulatory sequences, incorporation of loxP sites for conditional gene inactivation, and epitope tag integration. Genotyping strategies are presented and topics of genetic mosaicism and inadvertent targeting discussed. Finally, clinical applications and ethical considerations are addressed as the biomedical community eagerly embraces this astonishing innovation in genome editing to tackle previously intractable questions.