Genome Of Mammalian Cells Research Articles

Genome Editing of Mammalian Cells Through RNA Transcript-Mediated Homologous Recombination Repair.

Double-stranded break (DSB) repair of eukaryotic DNA is mainly accomplished by nonhomologous end joining and homologous recombination (HR). Providing exogenous templates during HR repair can result in the editing of target genes, which is the central mechanism of the well-established clustered regularly interspaced short palindromic repeats (CRISPR) gene editing system. Currently, exogenous templates are mainly DNA molecules, which can provoke a cellular immune response within the cell. In order to verify the feasibility of RNA molecules as repair templates for HR in mammalian cell genome editing, we fused RNA template molecules to the 3'-end of single guide RNA (sgRNA), so that the sgRNA and the homologous template RNA form a single RNA molecule. The results show this construct can be used as a repair template to achieve target gene editing in mammalian cells. In addition, the factors influencing HR mediated by RNA template molecules were investigated, and it was found that increasing the length of homologous arms and inducing an R-loop near the DSBcan effectively promote HR repair. Furthermore, intracellular homologous chromosomes may compete with exogenous RNA templates. The findings in this article provide a reference for the utilization of RNA template molecules to mediate target gene editing in eukaryotic cells, as well as a basis for the study of the mechanism by which RNA molecules mediate the repair of DSBs.

Micronutrient regulation of the DNA methylome

The formation, inheritance, and removal of DNA methylation in the genome of mammalian cells is directly regulated by two families of enzymes–DNA methyltransferases (DNMTs) and Ten-Eleven Translocation proteins (TETs). DNMTs generate and maintain the inheritance of 5-methylcytosine (5mC), which is the substrate targeted by the TET enzymes for conversion to 5-hydroxymethylcytosine (5hmC) and its downstream oxidized derivatives. The activity of DNMT and TET is dependent on the availability of micronutrients and metabolite co-factors, including essential vitamins, amino acids, and trace metals, highlighting how DNA methylation levels can be directly enhanced, suppressed, or remodeled via metabolic and nutritional perturbations. Dynamic changes in DNA methylation are required during embryonic development, lineage specification, and maintenance of somatic cell function that can be fine-tuned based on the influence of essential micronutrients. As we age, DNA methylation and hydroxymethylation levels drift in patterning, leading to epigenetic dysregulation and genomic instability that underlies the formation and progression of multiple diseases including cancer. Understanding how DNA methylation can be regulated by micronutrients will have important implications for the maintenance of normal tissue function upon aging, and in the prevention and treatment of diseases for improved health and lifespan.

Efficient selection of knocked-in pluripotent stem cells using a dual cassette cellular elimination system

Although recent advances in genome editing technology with homology-directed repair have enabled the insertion of various reporter genes into the genome of mammalian cells, the efficiency is still low due to the random insertion of donor vectors into the host genome. To efficiently select knocked-in cells without random insertion, we developed the "double-tk donor vector system," in which the expression units of the thymidine kinase of herpes simplex virus (HSV-tk) are placed on both outer sides of homology arms. This system is superior in enriching knocked-in human induced pluripotent stem cells (hiPSCs) than conventional donor vector systems with a single or no HSV-tk cassette. Using this system, we efficiently generated fluorescent reporter knockin hiPSCs targeting POU5F1 (OCT3/4), EEF1A1, H2BC21 (H2B clustered histone 21), ISL1, and MYH7 genes. These results indicate that the double-tk donor vector system enables efficient selection of knocked-in hiPSCs carrying reporter proteins.

Tetracycline-Inducible and Reversible Stable Gene Expression in Human iPSC-Derived Neural Progenitors and in the Postnatal Mouse Brain.

Our group has developed several approaches for stable, non-viral integration of inducible transgenic elements into the genome of mammalian cells. Specifically, a piggyBac tetracycline-inducible genetic element of interest (pB-tet-GOI) plasmid system allows for stable piggyBac transposition-mediated integration into cells, identification of cells that have been transfected using a fluorescent nuclear reporter, and robust transgene activation or suppression upon the addition of doxycycline (dox) to the cell culture or the diet of the animal. Furthermore, the addition of luciferase downstream of the target gene allows for quantitative assessment of gene activity in a non-invasive manner. More recently, we have developed a transgenic system as an alternative to piggyBac called mosaic analysis by dual recombinase-mediated cassette exchange (MADR), as well as additional in vitro transfection techniques and in vivo dox chow applications. The protocols herein provide instructions for the use of this system in cell lines and in the neonatal mouse brain. © 2023 Wiley Periodicals LLC. Basic Protocol 1: Cloning of respective genetic element of interest (GOI) into response plasmid Basic Protocol 2: In vitro nucleofection of iPSC-derived human/mouse neural progenitor cells and subsequent derivation of stable inducible cell lines Alternate Protocol: In vitro electroporation of iPSC-derived human/mouse neural progenitor cells Support Protocol: Recovery stage after in vitro transfection Basic Protocol 3: Adding doxycycline to cells to induce/reverse GOI Basic Protocol 4: Assessing gene expression in vitro by non-invasive bioluminescence imaging of luciferase activity.

Abstract LB059: DNA damage and somatic mutations in mammalian cells after irradiation with a nail polish dryer

Abstract Ultraviolet A (UVA) rays are long wavelengths that can penetrate the deeper layer of the skin and are responsible for the immediate tanning effect. A multitude of natural and artificial sources of UV exposure exist, including UV-emitting lamps that are commonly used in dentistry, cosmetics, and medical laboratories. Recently, several reports suggested that long-term use of UV-nail polish dryers, used for curating nail polish formulas, known as gel, may increase the risk for developing skin cancer. However, no experimental evaluation has been conducted to reveal the effect of radiation released by UV-nail polish dryers on mammalian cells. Here, we address the continuous exposure of clients and employees to UVA light by employing both murine and human primary cell models for irradiation, in an acute and chronic manner, using a UV-dryer machine. We, then, subject the cells to DNA sequencing either by bulk whole-genome sequencing after clonal expansion or by single-molecule duplex sequencing without clonal expansion. Our findings show that UVA-exposed samples manifest an increase of C:G>A:T transversions compared to control cells. The patterns of mutations found in these cells can be recapitulated by mutational signatures previously attributed to reactive oxygen species (ROS), namely COSMIC signatures SBS18/36. These results are further corroborated by the presence of high levels of ROS in irradiated samples, consistent with 8-oxo-7,8-dihydroguanine damage and mitochondrial dysfunction. Importantly, we show that in contrast to UVB exposure, UVA does not induce an increase of C:G>T:A transitions, indicating that different types of ultraviolet light radiation affect DNA through distinctive molecular mechanisms. Finally, re-examination of somatic mutations from skin cancers reported by the International Cancer Genome Consortium (ICGC) reveals that SBS18/36 are ubiquitously present in melanoma and account for 12% of the previously annotated driver mutations. In summary, this study demonstrates that radiation emitted by UV-nail polish dryers can both damage DNA and permanently engrave mutations on the genomes of mammalian cells. Citation Format: Maria Zhivagui, Areebah Hoda, Noelia Valenzuela, Yi-yu Yeh, Jason Dai, Yudou He, Shuvro P. Nandi, Burcak Otlu, Bennett Van Houten, Ludmil Alexandrov. DNA damage and somatic mutations in mammalian cells after irradiation with a nail polish dryer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB059.

A GC-centered view of 3D genome organization

In the past two decades, our understanding of how the genome of mammalian cells is spatially organized in the three-dimensional (3D) space of the nucleus and how key nuclear processes are orchestrated in this space has drastically expanded. While genome organization has been extensively studied at the nanoscale, the higher-order arrangement of individual portions of the genome with respect to their intranuclear as well as reciprocal placement is less thoroughly characterized. Emerging evidence points to the existence of a complex radial arrangement of chromatin in the nucleus. However, what shapes this radial organization and whether it has any functional implications remain elusive. In this mini review, we first summarize our current knowledge on this rather overlooked aspect of mammalian genome organization. We then present a theoretical framework for explaining how the genome might be radially organized, focusing on the role of the guanine and cytosine density along the linear genome. Last, we discuss outstanding questions, hoping to inspire future experiments and spark interest in this topic within the 3D genome community.

In Vitro Reconstitutive Base Excision Repair (BER) Assay.

The mammalian cell genome is continuously exposed to endogenous and exogenous insults that modify its DNA. These modifications can be single-base lesions, bulky DNA adducts, base dimers, base alkylation, cytosine deamination, nitrosation, or other types of base alteration which interfere with DNA replication. Mammalian cells have evolved with a robust defense mechanism to repair these base modifications (damages) to preserve genomic stability. Base excision repair (BER) is the major defense mechanism for cells to remove these oxidative or alkylated single-base modifications. The base excision repair process involves replacement of a single-nucleotide residue by two sub-pathways, the single-nucleotide (SN) and the multi-nucleotide or long-patch (LP) base excision repair pathways. These reactions have been reproduced in vitro using cell free extracts or purified recombinant proteins involved in the base excision repair pathway. In the present chapter, we describe the detailed methodology to reconstitute base excision repair assay systems. These reconstitutive BER assay systems use artificially synthesized and modified DNA. These reconstitutive assay system will be a true representation of biologically occurring damages and their repair.

Transgenic mice harboring direct repeat substrates reveal key underlying causes of homologous recombination in vivo

Homology directed repair is a critical process for maintaining the genome of mammalian cells. While considered to be relatively error free, homologous recombination (HR) can lead to insertions, deletions, translocations, and loss of heterozygosity. Furthermore, it is known that conditions that cause HR events are often carcinogenic, and that HR modulates susceptibility to cancer chemotherapeutics, making HR relevant to both cancer etiology and treatment. To learn about HR in vivo, several laboratories have developed mouse models that harbor direct repeat substrates for which HR yields a phenotype that can be visualized by either a change in pigmentation or by expression of a fluorescent protein. An exciting aspect of this work is that it is possible to detect recombinant cells within intact tissues and thus learn about how physiological changes, genes, and exposures modulate HR susceptibility in vivo, as well as which cell types are most susceptible to HR, and the extent to which recombinant cells have undergone clonal expansion. Here, we review progress in studying HR in vivo for four different mouse strains that harbor direct repeat substrates for HR detection, namely the pun mice, the fluorescent yellow direct repeat (FYDR) mice, the EGFP-DR mice, and the ROSA26 direct repeat (RaDR) mice. Key advances in our understanding of fundamental processes that modulate HR susceptibility in vivo are the focus of this review.

Differentiation Capacity of Bone Marrow-Derived Rat Mesenchymal Stem Cells from DsRed and Cre Transgenic Cre/loxP Models

Cre/loxP recombination is a well-established technique increasingly used for modifying DNA both in vitro and in vivo. Nucleotide alterations can be edited in the genomes of mammalian cells, and genetic switches can be designed to target the expression or excision of a gene in any tissue at any time in animal models. In this study, we propose a system which worked via the Cre/loxP switch gene and DsRed/emGFP dual-color fluorescence imaging. Mesenchymal stem cells (MSCs) can be used to regenerate damaged tissue because of their differentiation capacity. Although previous studies have presented evidence of fusion of transplanted MSCs with recipient cells, the possibility of fusion in such cases remains debated. Moreover, the effects and biological implications of the fusion of MSCs at the tissue and organ level have not yet been elucidated. Thus, the method for determining this issue is significant and the models we proposed can illustrate the question. However, the transgenic rats exhibited growth slower than that of wild-type rats over several weeks. The effects on the stemness, proliferation, cell cycle, and differentiation ability of bone marrow–derived rat MSCs (BM-rMSCs) from the models were examined to ensure our design was appropriate for the in vivo application. We demonstrated that MSC surface markers were maintained in DsRed and Cre transgenic rMSCs (DsRed-rMSCs and Cre-rMSCs, respectively). A WST-8 assay revealed decreased proliferative activity in these DsRed-rMSCs and Cre-rMSCs; this result was validated through cell counting. Furthermore, cell cycle analysis indicated a decrease in the proportion of G1-phase cells and a concomitant increase in the proportion of S-phase cells. The levels of cell cycle–related proteins also decreased in the DsRed-rMSCs and Cre-rMSCs, implying decelerated phase transition. However, the BM-rMSCs collected from the transgenic rats did not exhibit altered adipogenesis, osteogenesis, or chondrogenesis. The specific markers of these types of differentiation were upregulated after induction. Therefore, BM-rMSCs from DsRed and Cre transgenic models can be used to investigate the behavior of MSCs and related mechanisms. Such application may further the development of stem cell therapy for tissue damage and other diseases.

CRISPR/Cas9 ribonucleoprotein-mediated genome and epigenome editing in mammalian cells.

The clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated protein (Cas) system has revolutionized the ability to edit the mammalian genome, providing a platform for the correction of pathogenic mutations and further investigation into gene function. CRISPR reagents can be delivered into the cell as DNA, RNA, or pre-formed ribonucleoproteins (RNPs). RNPs offer numerous advantages over other delivery approaches due to their ability to rapidly target genomic sites and quickly degrade thereafter. Here, we review the production steps and delivery methods for Cas9 RNPs. Additionally, we discuss how RNPs enhance genome and epigenome editing efficiencies, reduce off-target editing activity, and minimize cellular toxicity in clinically relevant mammalian cell types. We include details on a broad range of editing approaches, including novel base and prime editing techniques. Finally, we summarize key challenges for the use of RNPs, and propose future perspectives on the field.

A Novel Type V CRISPR System with Potential for Genome Editing in the Liver

RNA guided CRISPR genome editing systems can make specific changes to the genomes of mammalian cells and have the potential to treat a range of diseases including those that can be addressed by editing hepatocytes. Attempts to edit the liver in vivo have relied almost exclusively on the Cas9 nucleases derived from the bacteria S treptococcus pyogenes or Staphylococcus aureus to which humans are commonly exposed. Pre-existing immunity to both these proteins has been reported in humans which raises concerns about their in vivo application. In silico analysis of a large metagenomics database followed by testing in mammalian cells in culture identified MG29-1, a novel CRISPR system which is a member of the Type V family but exhibits only 41 % amino acid identity to Francisella tularensis Cas12a/cpf1. MG29-1 is a 1280 amino acid RNA programmable nuclease that utilizes a single guide RNA comprised of a 22 nucleotide (nt) constant region and a 20 to 25 nt spacer, recognizes the PAM KTTN (predicted frequency 1 in 16 bp) and generates staggered cuts. MG29-1 was derived from a sample taken from a hydrothermal vent and it is therefore unlikely that humans will have developed pre-existing immunity to this protein. A screen for sgRNA targeting serum albumin in the mouse liver cell line Hepa1-6 identified 6 guides that generated more than 80% INDELS. The MG29-1 system was optimized for in vivo delivery by screening chemical modifications to the guide that improve stability in mammalian cell lysates while retaining or improving editing activity. Two lead guide chemistries were evaluated in mice using MG29-1 mRNA and sgRNA packaged in lipid nanoparticles (LNP). Three days after a single IV administration on-target editing was evaluated in the liver by Sanger sequencing. The sgRNA that was the most stable in the in vitro assay generated INDELS that ranged from 20 to 25% while a sgRNA with lower in vitro stability failed to generate detectable INDELs. The short sgRNA and small protein size compared to spCas9 makes MG29-1 an attractive alternative to spCas9 for in vivo editing applications. Evaluation of the potential of MG29-1 to perform gene knockouts and gene additions via non-homologous end joining is ongoing. DisclosuresNo relevant conflicts of interest to declare.

CRISPR/Cas9-Mediated Genome Editing to Generate Clonal iPSC Lines.

The ability to reprogram somatic cells into induced pluripotent stem cells (iPSCs) was developed in 2006 and represented a major breakthrough in stem cell research. A more recent milestone in biomedical research was reached in 2013 when the CRISPR/Cas9 system was used to edit the genome of mammalian cells. The coupling of both human (h)iPSCs and CRISPR/Cas9 technology offers great promise for cell therapy and regenerative medicine. However, several limitations including time and labor consumption, efficiency and efficacy of the system, and the potential off-targets effects induced by the Cas9 nuclease still need to be addressed. Here, we describe a detailed method for easily engineering genetic changes in hiPSCs, using a nucleofection-mediated protocol to deliver the CRISPR/Cas9 components into the cells, and discuss key points to be considered when designing your experiment. The clonal, genome-edited hiPSC line generated via our method can be directly used for downstream applications.

An introduction to CRISPR-Cas systems for reprogramming the genome of mammalian cells.

In the past few decades, it has been possible to introduce unprecedented mutations in genes of the mammalian cells owing to the development of advanced technologies/methods/assays. Sometimes, these mutations occurring at the cellular level may even cost the life of organisms. A number of diseases in mammals have shown to leave some serious impact on their lives. There are no drugs or medicines available in market for the correction or repair of these mutated genes in order to reverse gene function. A pressing need therefore arises to develop a next generation technology that cannot just corrects gene mutations but also restores gene function. Recent advances in CRISPR-Cas9 technology play a key role for correction of defective genes in wide range of mammalian cells. This chapter highlights CRISPR-Cas systems for basic, biomedical, biotechnological and therapeutic applications.

Genome-Wide Mutagenesis in Mice: In Search for Genes Regulating Immune Responses and Inflammation

Genome-wide mutagenesis induced by N-ethyl-N-nitrosourea (ENU) results in efficient introduction of mutations into the genome of mammalian spermatogonial cells. This feature is being used to generate animals with phenotypes associated with defects in various functional systems. In particular, using this methodology, it was possible to identify molecular mechanisms of immune responses, identify genes that regulate the development of various organs, etc. This minireview covers genetic studies of immunological and inflammatory reactions in mice using ENU mutagenesis, which led to important findings concerning the regulation of critical signaling pathways of innate and adaptive immunity.

Chimeric DNA-RNA Guide RNA Designs.

CRISPR-associated nuclease (Cas) has been widely applied to modify the genomes of various cell types. As RNA-guided endonucleases, Cas enzymes can target different genomic sequences simply by changing the guide sequence of the CRISPR RNA (crRNA) or single guide RNA (sgRNA). Recent studies have demonstrated that DNA-RNA chimeric crRNA or sgRNA can efficiently guide the Cas9 protein for genome editing with reduced off-target effects. This chapter aims to describe a procedure for using chimeric RNA to modify the genomes of mammalian cells.

Abstract 4802: Functional analysis of cancer associated mitochondrial genome alterations

Abstract It is well documented that a variety of alterations can occur in the mitochondrial genome during human tumor development. These alterations often correlate with cancer phenotypes like treatment resistance and metastasis. Alterations to the mitochondrial genome may therefore be a biomarker for early detection, prognosis and/or predictor of therapeutic sensitivity. However, a method to easily and quickly create isogenic populations of human cells with mitochondrial genome specific alterations is not available. To combat this, we have developed a technology using transient expression of mitochondria targeted TAL domain nickases and TAL endonucleases (TALENs). This the first reliable method to introduce specific mutations into the mitochondrial genome of mammalian cells. We have efficiently induced mtDNA deletions in zebrafish embryos, human and mouse cell lines. In mouse NIH3T3 fibroblasts, we deleted a mitochondrial genome region corresponding to the same disease sequence seen in the human Kearns-Sayre Syndrome (KSS). The deletion resulted in a measurable phenotype including decreased mitochondria basal respiration, ATP production and maximal respiration. We are expanding this work by engineering targeted and precise mtDNA deletions in conjunction with known cancer initiating nuclear mutations in mammalian cells, as well as systemically in mice. These tools will allow us to determine the effect mitochondrial alterations have on the transformation of cancer cells harboring known cancer causing nuclear mutations. We are also developing an inducible system for expressing mitoTALENs, making it possible to create “conditional” loss of function mutations in mitochondrial genes in human cell lines, including induced pluripotent stem cells (iPSCs). This inducible model system will be highly useful in settings where the mitochondrial deletion may cause a selective disadvantage during early cellular differentiation. Citation Format: Neil Otto. Functional analysis of cancer associated mitochondrial genome alterations [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4802.

CRISPR-Cas9 Genome Editing Tool for the Production of Industrial Biopharmaceuticals.

A broad range of cell lines with characteristic features are used as bio-factories to produce recombinant proteins for basic research and therapeutic purposes. Genetic engineering strategies have been used to manipulate the genome of mammalian cells, insects, and yeasts for heterologous expression. One reason is that the glycosylation pattern of the expression hosts differs somehow from mammalian cells, which may cause immunogenic reactions upon administration in humans. CRISPR-Cas9 is a simple, efficient, and versatile genome engineering tool that can be programmed to precisely make double-stranded breaks at the desired loci. Compared to the classical genome editing methods, a CRISPR-Cas9 system is an ideal tool, providing the opportunity to integrate or delete genes from the target organisms. Besides broadened applications, limited studies have used CRISPR-Cas9 for editing the endogenous pathways in expression systems for biopharmaceutical applications. In the present review, we discuss the use of CRISPR-Cas9 in expression systems to improve host cell lines, increase product yield, and humanize glycosylation pathways by targeting intrinsic genes.

Applications of CRISPR for musculoskeletal research.

The ability to edit DNA at the nucleotide level using clustered regularly interspaced short palindromic repeats (CRISPR) systems is a relatively new investigative tool that is revolutionizing the analysis of many aspects of human health and disease, including orthopaedic disease. CRISPR, adapted for mammalian cell genome editing from a bacterial defence system, has been shown to be a flexible, programmable, scalable, and easy-to-use gene editing tool. Recent improvements increase the functionality of CRISPR through the engineering of specific elements of CRISPR systems, the discovery of new, naturally occurring CRISPR molecules, and modifications that take CRISPR beyond gene editing to the regulation of gene transcription and the manipulation of RNA. Here, the basics of CRISPR genome editing will be reviewed, including a description of how it has transformed some aspects of molecular musculoskeletal research, and will conclude by speculating what the future holds for the use of CRISPR-related treatments and therapies in clinical orthopaedic practice.Cite this article: Bone Joint Res 2020;9(7):351–359.

Rapid Tagging of Human Proteins with Fluorescent Reporters by Genome Engineering using Double-Stranded DNA Donors.

Tagging proteins with fluorescent reporters such as green fluorescent protein (GFP) is a powerful method to determine protein localization, especially when proteins are tagged in the endogenous context to preserve native genomic regulation. However, insertion of fluorescent reporters into the genomes of mammalian cells has required the construction of plasmids containing selection markers and/or extended sequences homologous to the site of insertion (homology arms). Here we describe a streamlined protocol that eliminates all cloning steps by taking advantage of the high propensity of linear DNAs to engage in homology‐directed repair of DNA breaks induced by the Cas9 RNA‐guided endonuclease. The protocol uses PCR amplicons, or synthetic gene fragments, with short homology arms (30‐40 bp) to insert fluorescent reporters at specific genomic locations. The linear DNAs are introduced into cells with preassembled Cas9‐crRNA‐tracrRNA complexes using one of two transfection procedures, nucleofection or lipofection. The protocol can be completed under a week, with efficiencies ranging from 0.5% to 20% of transfected cells depending on the locus targeted. © 2019 The Authors.

Enhancing the Therapeutic Potential of Mesenchymal Stem Cells with the CRISPR-Cas System.

Mesenchymal stem cells (MSCs), also known as multipotent mesenchymal stromal stem cells, are found in the perivascular space of several tissues. These cells have been subject of intense research in the last decade due to their low teratogenicity, as well as their ability to differentiate into mature cells and to secrete immunomodulatory and trophic factors. However, they usually promote only a modest benefit when transplanted in experimental disease models, one of the limitations for their clinical application. The CRISPR-Cas system, in turn, is highlighted as a simple and effective tool for genetic engineering. This system was tested in clinical trials over a relatively short period of time after establishing its applicability to the edition of the mammalian cell genome. Similar to the research evolution in MSCs, the CRISPR-Cas system demonstrated inconsistencies that limited its clinical application. In this review, we outline the evolution of MSC research and its applicability, and the progress of the CRISPR-Cas system from its discovery to the most recent clinical trials. We also propose perspectives on how the CRISPR-Cas system may improve the therapeutic potential of MSCs, making it more beneficial and long lasting.