Functional expression and germline transmission of a human chromosome fragment in chimaeric mice

Rapid human genomic DNA cloning into mouse artificial chromosome via direct chromosome transfer from human iPSC and CRISPR/Cas9-mediated translocation

A 'genomically' humanized animal stably maintains and functionally expresses the genes on human chromosome fragment (hCF; <24 Mb) loaded onto mouse artificial chromosome (MAC); however, cloning of hCF onto the MAC (hCF-MAC) requires a complex process that involves multiple steps of chromosome engineering through various cells via chromosome transfer and Cre-loxP chromosome translocation. Here, we aimed to develop a strategy to rapidly construct the hCF-MAC by employing three alternative techniques: (i) application of human induced pluripotent stem cells (hiPSCs) as chromosome donors for microcell-mediated chromosome transfer (MMCT), (ii) combination of paclitaxel (PTX) and reversine (Rev) as micronucleation inducers and (iii) CRISPR/Cas9 genome editing for site-specific translocations. We achieved a direct transfer of human chromosome 6 or 21 as a model from hiPSCs as alternative human chromosome donors into CHO cells containing MAC. MMCT was performed with less toxicity through induction of micronucleation by PTX and Rev. Furthermore, chromosome translocation was induced by simultaneous cleavage between human chromosome and MAC by using CRISPR/Cas9, resulting in the generation of hCF-MAC containing CHO clones without Cre-loxP recombination and drug selection. Our strategy facilitates rapid chromosome cloning and also contributes to the functional genomic analyses of human chromosomes.

Actively transcribed rDNA and distal junction (DJ) sequence are involved in association of NORs with nucleoli

Although they are organelles without a limiting membrane, nucleoli have an exclusive structure, built upon the rDNA-rich acrocentric short arms of five human chromosomes (nucleolar organizer regions or NORs). This has raised the question: what are the structural features of a chromosome required for its inclusion in a nucleolus? Previous work has suggested that sequences adjacent to the tandemly repeated rDNA repeat units (DJ, distal junction sequence) may be involved, and we have extended such studies by addressing several issues related to the requirements for the association of NORs with nucleoli. We exploited both a set of somatic cell hybrids containing individual human acrocentric chromosomes and a set of Human Artificial Chromosomes (HACs) carrying different parts of a NOR, including an rDNA unit or DJ or PJ (proximal junction) sequence. Association of NORs with nucleoli was increased when constituent rDNA was transcribed and may be also affected by the status of heterochromatin blocks formed next to the rDNA arrays. Furthermore, our data suggest that a relatively small size DJ region, highly conserved in evolution, is also involved, along with the rDNA repeats, in the localization of p-arms of acrocentric chromosomes in nucleoli. Thus, we infer a cooperative action of rDNA sequence-stimulated by its activity-and sequences distal to rDNA contributing to incorporation into nucleoli. Analysis of NOR sequences also identified LncRNA_038958 in the DJ, a candidate transcript with the region of the suggested promoter that is located close to the DJ/rDNA boundary and contains CTCF binding sites. This LncRNA may affect RNA Polymerase I and/or nucleolar activity. Our findings provide the basis for future studies to determine which RNAs and proteins interact critically with NOR sequences to organize the higher-order structure of nucleoli and their function in normal cells and pathological states.

Full-length human dystrophin on human artificial chromosome compensates for mouse dystrophin deficiency in a Duchenne muscular dystrophy mouse model

Dystrophin maintains membrane integrity as a sarcolemmal protein. Dystrophin mutations lead to Duchenne muscular dystrophy, an X-linked recessive disorder. Since dystrophin is one of the largest genes consisting of 79 exons in the human genome, delivering a full-length dystrophin using virus vectors is challenging for gene therapy. Human artificial chromosome is a vector that can load megabase-sized genome without any interference from the host chromosome. Chimeric mice carrying a 2.4-Mb human dystrophin gene-loaded human artificial chromosome (DYS-HAC) was previously generated, and dystrophin expression from DYS-HAC was confirmed in skeletal muscles. Here we investigated whether human dystrophin expression from DYS-HAC rescues the muscle phenotypes seen in dystrophin-deficient mice. Human dystrophin was normally expressed in the sarcolemma of skeletal muscle and heart at expected molecular weights, and it ameliorated histological and functional alterations in dystrophin-deficient mice. These results indicate that the 2.4-Mb gene is enough for dystrophin to be correctly transcribed and translated, improving muscular dystrophy. Therefore, this technique using HAC gives insight into developing new treatments and novel humanized Duchenne muscular dystrophy mouse models with human dystrophin gene mutations.

Characterization of human anti-EpCAM antibodies for developing an antibody-drug conjugate

We previously generated fully human antibody-producing TC-mAb mice for obtaining potential therapeutic monoclonal antibodies (mAbs). In this study, we investigated 377 clones of fully human mAbs against a tumor antigen, epithelial cell adhesion molecule (EpCAM), to determine their antigen binding properties. We revealed that a wide variety of mAbs against EpCAM can be obtained from TC-mAb mice by the combination of epitope mapping analysis of mAbs to EpCAM and native conformational recognition analysis. Analysis of 72 mAbs reacting with the native form of EpCAM indicated that the EpCL region (amino acids 24-80) is more antigenic than the EpRE region (81-265), consistent with numerous previous studies. To evaluate the potential of mAbs against antibody-drug conjugates, mAbs were directly labeled with DM1, a maytansine derivative, using an affinity peptide-based chemical conjugation (CCAP) method. The cytotoxicity of the conjugates against a human colon cancer cell line could be clearly detected with high-affinity as well as low-affinity mAbs by the CCAP method, suggesting the advantage of this method. Thus, this study demonstrated that TC-mAb mice can provide a wide variety of antibodies and revealed an effective way of identifying candidates for fully human ADC therapeutics.

Metabolic Disposition of Triazolam and Clobazam in Humanized CYP3A Mice with a Double-Knockout Background of Mouse Cyp2c and Cyp3a Genes

Knockout (KO) of mouse Cyp3a genes increases the expression of hepatic CYP2C enzymes, which can metabolize triazolam, a typical substrate of human CYP3A. There is still marked formation of 1'-hydroxytriazolam in Cyp3a-KO (3aKO) mice after triazolam dosing. Here, we generated a new model of humanized CYP3A (hCYP3A) mice with a double-KO background of Cyp3a and Cyp2c genes (2c3aKO), and we examined the metabolic profiles of triazolam in wild-type (WT), 2c3aKO, and hCYP3A/2c3aKO mice in vitro and in vivo In vitro studies using liver microsomes showed that the formation of 1'-hydroxytriazolam in 2c3aKO mice was less than 8% of that in WT mice. The formation rate of 1'-hydroxytriazolam in hCYP3A/2c3aKO mice was eightfold higher than that in 2c3aKO mice. In vivo studies showed that area under the curve (AUC) of 1'-hydroxytriazolam in 2c3aKO mice was less than 3% of that in WT mice. The AUC of 1'-hydroxytriazolam in hCYP3A/2c3aKO mice was sixfold higher than that in 2c3aKO mice. These results showed that formation of 1'-hydroxytriazolam was significantly decreased in 2c3aKO mice. Metabolic functions of human CYP3A enzymes were distinctly found in hCYP3A mice with the 2c3aKO background. Moreover, hCYP3A/2c3aKO mice treated with clobazam showed human CYP3A-mediated formation of desmethylclobazam and prolonged elimination of desmethylclobazam, which is found in poor metabolizers of CYP2C19. The novel hCYP3A mouse model without mouse Cyp2c and Cyp3a genes (hCYP3A/2c3aKO) is expected to be useful to evaluate human CYP3A-mediated metabolism in vivo SIGNIFICANT STATEMENT: Humanized CYP3A (hCYP3A/2c3aKO) mice with a background of double knockout (KO) for mouse Cyp2c and Cyp3a genes were generated. Although CYP2C enzymes played a compensatory role in the metabolism of triazolam to 1'-hydroxytriazolam in the previous hCYP3A/3aKO mice with Cyp2c genes, the novel hCYP3A/2c3aKO mice clearly showed functions of human CYP3A enzymes introduced by chromosome engineering technology.

Pathological Comparison of TDP-43 Between Motor Neurons and Interneurons Expressed by a Tetracycline Repressor System on the Mouse Artificial Chromosome

Background

Cytoplasmic mislocalization of TAR-DNA binding protein of 43 kDa (TDP-43) is a major hallmark of amyotrophic lateral sclerosis (ALS). TDP-43 aggregation is detected in the cortical and spinal motor neurons in most ALS cases; however, pathological mechanism of this mislocalized TDP-43 remains unknown.

Methods

We generated a tetracycline-inducible TDP-43 A315T system on a mouse artificial chromosome (MAC) vector to avoid transgene-insertional mutagenesis, established a mouse embryonic stem (ES) cell line holding this MAC vector system, and investigated whether overexpressed exogenous TDP-43 A315T was mislocalized in the cytoplasm of the ES cell-derived neurons and triggered the neurotoxic effects on these cells.

Results

Inducible TDP-43 A315T system was successfully loaded onto the MAC and introduced into the mouse ES cells. These ES cells could differentiate into motor neurons and interneurons. Overexpression of TDP-43 A315T by addition of doxycycline in both neurons resulted in mislocalization to cytoplasm. Mislocalized TDP-43 caused cell death of motor neurons, but not interneurons.

Conclusion

Vulnerability to cytoplasmic mislocalized TDP-43 is selective on neuronal types, whereas mislocalization of overexpressed TDP-43 occurs in even insusceptible neurons. This inducible gene expression system using MAC remains useful for providing critical insights into appearance of TDP-43 pathology.

Simultaneous loading of PCR-based multiple fragments on mouse artificial chromosome vectors in DT40 cell for gene delivery

Homology-directed repair-mediated knock-in (HDR-KI) in combination with CRISPR-Cas9-mediated double strand break (DSB) leads to high frequency of site-specific HDR-KI. While this characteristic is advantageous for generating genetically modified cellular and animal models, HDR-KI efficiency in mammalian cells remains low. Since avian DT40 cells offer distinct advantage of high HDR-KI efficiency, we expanded this practicality to adapt to mammalian research through sequential insertion of target sequences into mouse/human artificial chromosome vector (MAC/HAC). Here, we developed the simultaneous insertion of multiple fragments by HDR method termed the simHDR wherein a target sequence and selection markers could be loaded onto MAC simultaneously. Additionally, preparing each HDR donor containing homology arm by PCR could bypass the cloning steps of target sequence and selection markers. To confirm the functionality of the loaded HDR donors, we constructed a MAC with human leukocyte antigen A (HLA-A) gene in the DT40 cells, and verified the expression of this genomic region by reverse transcription PCR (RT-PCR) and western blotting. Collectively, the simHDR offers a rapid and convenient approach to generate genetically modified models for investigating gene functions, as well as understanding disease mechanisms and therapeutic interventions.

Analysis of in vitro and in vivo metabolism of zidovudine and gemfibrozil in trans-chromosomic mouse line expressing human UGT2 enzymes

UDP-glucuronosyltransferases (UGTs) catalyze the conjugation of various substrates with sugars. Since the UGT2 family forms a large cluster spanning 1.5 Mb, transgenic mouse lines carrying the entire human UGT2 family have not been constructed because of limitations in conventional cloning techniques. Therefore, we made a humanized mouse model for UGT2 by chromosome engineering technologies. The results showed that six UGT2 isoforms examined were expressed in the liver of adult humanized UGT2 (hUGT2) mice. Thus, the functions of human UGT2B7 in the liver of hUGT2 mice were evaluated. Glucuronide of azidothymidine (AZT, zidovudine), a typical UGT2B7 substrate, was formed in the liver microsomes of hUGT2 mice but not in the liver microsomes of wild-type and Ugt2-knockout mice. When AZT was intravenously administered, AZT glucuronide was detected in the bile and urine of hUGT2 mice, but it was not detected in the bile and urine of wild-type and Ugt2-knockout mice. These results indicated that the hUGT2 mice express functional human UGT2B7 in the liver. This finding was also confirmed by using gemfibrozil as an alternative UGT2B7 substrate. Gemfibrozil glucuronide was formed in the liver microsomes of hUGT2 mice and was mainly excreted in the bile of hUGT2 mice after intravenous dosing of gemfibrozil. This hUGT2 mouse model will enable improved predictions of pharmacokinetics, urinary and biliary excretion and drug-drug interactions mediated by human UGT2, at least UGT2B7, in drug development research and basic research.

Efficient human-like antibody repertoire and hybridoma production in trans-chromosomic mice carrying megabase-sized human immunoglobulin loci

Trans-chromosomic (Tc) mice carrying mini-chromosomes with megabase-sized human immunoglobulin (Ig) loci have contributed to the development of fully human therapeutic monoclonal antibodies, but mitotic instability of human mini-chromosomes in mice may limit the efficiency of hybridoma production. Here, we establish human antibody-producing Tc mice (TC-mAb mice) that stably maintain a mouse-derived, engineered chromosome containing the entire human Ig heavy and kappa chain loci in a mouse Ig-knockout background. Comprehensive, high-throughput DNA sequencing shows that the human Ig repertoire, including variable gene usage, is well recapitulated in TC-mAb mice. Despite slightly altered B cell development and a delayed immune response, TC-mAb mice have more subsets of antigen-specific plasmablast and plasma cells than wild-type mice, leading to efficient hybridoma production. Our results thus suggest that TC-mAb mice offer a valuable platform for obtaining fully human therapeutic antibodies, and a useful model for elucidating the regulation of human Ig repertoire formation.

Trans-chromosomic (Tc) mice have helped the development of therapeutic antibodies, but chromosome instability limits its application. Here the authors develop a new line of Tc mice with full human Ig heavy and kappa loci integrated into the mouse artificial chromosome for stable passage, and confirm efficient generation of B cell responses and specific antibodies.

A transchromosomic rat model with human chromosome 21 shows robust Down syndrome features

Progress in earlier detection and clinical management has increased life expectancy and quality of life in people with Down syndrome (DS). However, no drug has been approved to help individuals with DS live independently and fully. Although rat models could support more robust physiological, behavioral, and toxicology analysis than mouse models during preclinical validation, no DS rat model is available as a result of technical challenges. We developed a transchromosomic rat model of DS, TcHSA21rat, which contains a freely segregating, EGFP-inserted, human chromosome 21 (HSA21) with >93% of its protein-coding genes. RNA-seq of neonatal forebrains demonstrates that TcHSA21rat expresses HSA21 genes and has an imbalance in global gene expression. Using EGFP as a marker for trisomic cells, flow cytometry analyses of peripheral blood cells from 361 adult TcHSA21rat animals show that 81% of animals retain HSA21 in >80% of cells, the criterion for a "Down syndrome karyotype" in people. TcHSA21rat exhibits learning and memory deficits and shows increased anxiety and hyperactivity. TcHSA21rat recapitulates well-characterized DS brain morphology, including smaller brain volume and reduced cerebellar size. In addition, the rat model shows reduced cerebellar foliation, which is not observed in DS mouse models. Moreover, TcHSA21rat exhibits anomalies in craniofacial morphology, heart development, husbandry, and stature. TcHSA21rat is a robust DS animal model that can facilitate DS basic research and provide a unique tool for preclinical validation to accelerate DS drug development.

Mouse models of aneuploidy to understand chromosome disorders

An organism or cell carrying a number of chromosomes that is not a multiple of the haploid count is in a state of aneuploidy. This condition results in significant changes in the level of expression of genes that are gained or lost from the aneuploid chromosome(s) and most cases in humans are not compatible with life. However, a few aneuploidies can lead to live births, typically associated with deleterious phenotypes. We do not understand why phenotypes arise from aneuploid syndromes in humans. Animal models have the potential to provide great insight, but less than a handful of mouse models of aneuploidy have been made, and no ideal system exists in which to study the effects of aneuploidy per se versus those of raised gene dosage. Here, we give an overview of human aneuploid syndromes, the effects on physiology of having an altered number of chromosomes and we present the currently available mouse models of aneuploidy, focusing on models of trisomy 21 (which causes Down syndrome) because this is the most common, and therefore, the most studied autosomal aneuploidy. Finally, we discuss the potential role of carrying an extra chromosome on aneuploid phenotypes, independent of changes in gene dosage, and methods by which this could be investigated further.

Construction of stable mouse artificial chromosome from native mouse chromosome 10 for generation of transchromosomic mice

Mammalian artificial chromosomes derived from native chromosomes have been applied to biomedical research and development by generating cell sources and transchromosomic (Tc) animals. Human artificial chromosome (HAC) is a precedent chromosomal vector which achieved generation of valuable humanized animal models for fully human antibody production and human pharmacokinetics. While humanized Tc animals created by HAC vector have attained significant contributions, there was a potential issue to be addressed regarding stability in mouse tissues, especially highly proliferating hematopoietic cells. Mouse artificial chromosome (MAC) vectors derived from native mouse chromosome 11 demonstrated improved stability, and they were utilized for humanized Tc mouse production as a standard vector. In mouse, however, stability of MAC vector derived from native mouse chromosome other than mouse chromosome 11 remains to be evaluated. To clarify the potential of mouse centromeres in the additional chromosomes, we constructed a new MAC vector from native mouse chromosome 10 to evaluate the stability in Tc mice. The new MAC vector was transmitted through germline and stably maintained in the mouse tissues without any apparent abnormalities. Through this study, the potential of additional mouse centromere was demonstrated for Tc mouse production, and new MAC is expected to be used for various applications.

Molecular organization of recombinant human-Arabidopsis chromosomes in hybrid cell lines

Although plants and animals are evolutionarily distant, the structure and function of their chromosomes are largely conserved. This allowed the establishment of a human-Arabidopsis hybrid cell line in which a neo-chromosome was formed by insertion of segments of Arabidopsis chromosomes into human chromosome 15. We used this unique system to investigate how the introgressed part of a plant genome was maintained in human genetic background. The analysis of the neo-chromosome in 60- and 300-day-old cell cultures by next-generation sequencing and molecular cytogenetics suggested its origin by fusion of DNA fragments of different sizes from Arabidopsis chromosomes 2, 3, 4, and 5, which were randomly intermingled rather than joined end-to-end. The neo-chromosome harbored Arabidopsis centromeric repeats and terminal human telomeres. Arabidopsis centromere wasn’t found to be functional. Most of the introgressed Arabidopsis DNA was eliminated during the culture, and the Arabidopsis genome in 300-day-old culture showed significant variation in copy number as compared with the copy number variation in the 60-day-old culture. Amplified Arabidopsis centromere DNA and satellite repeats were localized at particular loci and some fragments were inserted into various positions of human chromosome. Neo-chromosome reorganization and behavior in somatic cell hybrids between the plant and animal kingdoms are discussed.

Engineering of human induced pluripotent stem cells via human artificial chromosome vectors for cell therapy and disease modeling

Genetic engineering of induced pluripotent stem cells (iPSCs) holds great promise for gene and cell therapy as well as drug discovery. However, there are potential concerns regarding the safety and control of gene expression using conventional vectors such as viruses and plasmids. Although human artificial chromosome (HAC) vectors have several advantages as a gene delivery vector, including stable episomal maintenance and the ability to carry large gene inserts, the full potential of HAC transfer into iPSCs still needs to be explored. Here, we provide evidence of a HAC transfer into human iPSCs by microcell-mediated chromosome transfer via measles virus envelope proteins for various applications, including gene and cell therapy, establishment of versatile human iPSCs capable of gene loading and differentiation into T cells, and disease modeling for aneuploidy syndrome. Thus, engineering of human iPSCs via desired HAC vectors is expected to be widely applied in biomedical research.

Blastocyst complementation using Prdm14-deficient rats enables efficient germline transmission and generation of functional mouse spermatids in rats

Murine animal models from genetically modified pluripotent stem cells (PSCs) are essential for functional genomics and biomedical research, which require germline transmission for the establishment of colonies. However, the quality of PSCs, and donor-host cell competition in chimeras often present strong barriers for germline transmission. Here, we report efficient germline transmission of recalcitrant PSCs via blastocyst complementation, a method to compensate for missing tissues or organs in genetically modified animals via blastocyst injection of PSCs. We show that blastocysts from germline-deficient Prdm14 knockout rats provide a niche for the development of gametes originating entirely from the donor PSCs without any detriment to somatic development. We demonstrate the potential of this approach by creating PSC-derived Pax2/Pax8 double mutant anephric rats, and rescuing germline transmission of a PSC carrying a mouse artificial chromosome. Furthermore, we generate mouse PSC-derived functional spermatids in rats, which provides a proof-of-principle for the generation of xenogenic gametes in vivo. We believe this approach will become a useful system for generating PSC-derived germ cells in the future.

Centromere identity and function put to use: construction and transfer of mammalian artificial chromosomes to animal models

Mammalian artificial chromosomes (MACs) are widely used as gene expression vectors and have various advantages over conventional expression vectors. We review and discuss breakthroughs in MAC construction, initiation of functional centromeres allowing their faithful inheritance, and transfer from cell culture to animal model systems. These advances have contributed to advancements in synthetic biology, biomedical research, and applications in industry and in the clinic.

The genomic structure of a human chromosome 22 nucleolar organizer region determined by TAR cloning

The rDNA clusters and flanking sequences on human chromosomes 13, 14, 15, 21 and 22 represent large gaps in the current genomic assembly. The organization and the degree of divergence of the human rDNA units within an individual nucleolar organizer region (NOR) are only partially known. To address this lacuna, we previously applied transformation-associated recombination (TAR) cloning to isolate individual rDNA units from chromosome 21. That approach revealed an unexpectedly high level of heterogeneity in human rDNA, raising the possibility of corresponding variations in ribosome dynamics. We have now applied the same strategy to analyze an entire rDNA array end-to-end from a copy of chromosome 22. Sequencing of TAR isolates provided the entire NOR sequence, including proximal and distal junctions that may be involved in nucleolar function. Comparison of the newly sequenced rDNAs to reference sequence for chromosomes 22 and 21 revealed variants that are shared in human rDNA in individuals from different ethnic groups, many of them at high frequency. Analysis infers comparable intra- and inter-individual divergence of rDNA units on the same and different chromosomes, supporting the concerted evolution of rDNA units. The results provide a route to investigate further the role of rDNA variation in nucleolar formation and in the empirical associations of nucleoli with pathology.

Development of Caco-2 cells expressing four CYPs via a mammalian artificial chromosome

Background

Oral administration is the most common way to deliver drugs to the systemic circulation or target organs. Orally administered drugs are absorbed in the intestine and metabolized in the intestine and liver. In the early stages of drug development, it is important to predict first-pass metabolism accurately to select candidate drugs with high bioavailability. The Caco-2 cell line derived from colorectal cancer is widely used as an intestinal model to assess drug membrane permeability. However, because the expression of major drug-metabolizing enzymes, such as cytochrome P450 (CYP), is extremely low in Caco-2 cells, it is difficult to predict intestinal metabolism, which is a significant factor in predicting oral drug bioavailability. Previously, we constructed a mouse artificial chromosome vector carrying the CYP (CYP2C9, CYP2C19, CYP2D6, and CYP3A4) and P450 oxidoreductase (POR) (4CYPs-MAC) genes and increased CYP expression and metabolic activity in HepG2 cells via transfer of this vector.

Results

In the current study, to improve the Caco-2 cell assay model by taking metabolism into account, we attempted to increase CYP expression by transferring the 4CYPs-MAC into Caco-2 cells. The Caco-2 cells carrying the 4CYPs-MAC showed higher CYP mRNA expression and activity. In addition, high metabolic activity, availability for permeation test, and the potential to assess drug–drug interactions were confirmed.

Conclusions

The established Caco-2 cells with the 4CYPs-MAC are expected to enable more accurate prediction of the absorption and metabolism in the human intestine than parental Caco-2 cells. The mammalian artificial chromosome vector system would provide useful models for drug development.

A non-mosaic transchromosomic mouse model of down syndrome carrying the long arm of human chromosome 21

Animal models of Down syndrome (DS), trisomic for human chromosome 21 (HSA21) genes or orthologs, provide insights into better understanding and treatment options. The only existing transchromosomic (Tc) mouse DS model, Tc1, carries a HSA21 with over 50 protein coding genes (PCGs) disrupted. Tc1 is mosaic, compromising interpretation of results. Here, we “clone” the 34 MB long arm of HSA21 (HSA21q) as a mouse artificial chromosome (MAC). Through multiple steps of microcell-mediated chromosome transfer, we created a new Tc DS mouse model, Tc(HSA21q;MAC)1Yakaz (“TcMAC21”). TcMAC21 is not mosaic and contains 93% of HSA21q PCGs that are expressed and regulatable. TcMAC21 recapitulates many DS phenotypes including anomalies in heart, craniofacial skeleton and brain, molecular/cellular pathologies, and impairments in learning, memory and synaptic plasticity. TcMAC21 is the most complete genetic mouse model of DS extant and has potential for supporting a wide range of basic and preclinical research.

Applications of bottom-up human artificial chromosomes in cell research and cell engineering

Chromosome manipulation is a useful technique in biological science. We have constructed human artificial chromosomes (HACs) based on the transfection of centromeric alphoid DNA precursors into cultured human cells. Moreover, HAC-based technology has been developed into a novel gene expression vector tool for introducing large-size genomic DNA. This technique provides natural expression, as well as stable expression without the gene silencing that often occurs with conventional vectors in mammalian cells. Here we review the properties of HACs, and issues regarding the use of HAC technology for basic and applied research.

Transchromosomic technology for genomically humanized animals

"Genomically" humanized animals are invaluable tools for generating human disease models and for biomedical research. Humanized animal models have generally been developed via conventional transgenic technologies; however, conventional gene delivery vectors such as viruses, plasmids, bacterial artificial chromosomes, P1 phase-derived artificial chromosomes, and yeast artificial chromosomes have limitations for transgenic animal creation as their loading gene capacity is restricted, and the expression of transgenes is unstable. Transchromosomic (Tc) techniques using mammalian artificial chromosomes, including human chromosome fragments, human artificial chromosomes, and mouse artificial chromosomes, have overcome these limitations. These tools can carry multiple genes or Mb-sized genomic loci and their associated regulatory elements, which has facilitated the creation of more useful and complex transgenic models for human disease, drug development, and humanized animal research. This review describes the history of Tc animal development, the applications of Tc animals, and future prospects.

Current advances in microcell-mediated chromosome transfer technology and its applications

Chromosomes and chromosomal gene delivery vectors, human/mouse artificial chromosomes (HACs/MACs), can introduce megabase-order DNA sequences into target cells and are used for applications including gene mapping, gene expression control, gene/cell therapy, and the development of humanized animals and animal models of human disease. Microcell-mediated chromosome transfer (MMCT), which enables chromosome transfer from donor cells to target cells, is a key technology for these applications. In this review, we summarize the principles of gene transfer with HACs/MACs; their engineering, characteristics, and utility; and recent advances in the chromosome transfer technology.

A novel Xist RNA-mediated chromosome inactivation model using a mouse artificial chromosome

OBJECTIVE

To develop a mouse artificial chromosome (MAC) carrying the mouse Xist gene (X-inactive specific transcript; Xist-MAC) as a systematic in vitro approach for investigating Xist RNA-mediated chromosome inactivation.

RESULTS

Ectopic expression of the Xist gene in CHO cells led to the accumulation of Xist RNA in cis on the MAC. In addition, the introduction of Xist-MAC to embryonic stem cells from male mice via microcell-mediated chromosome transfer resulted in the accumulation of Xist RNA in cis on the MAC. Chromosomal inactivation was observed in the differentiated state. Moreover, this phenomenon was accompanied by the epigenetic modification of H3K27 trimethylation.

CONCLUSIONS

We successfully generated a novel chromosome inactivation model, Xist-MAC, which will provide a valuable tool for the screening and functional analysis of X chromosome inactivation-related genes and proteins.

Technology used to build and transfer mammalian chromosomes

In the near twenty-year existence of the human and mammalian artificial chromosome field, the technologies for artificial chromosome construction and installation into desired cell types or organisms have evolved with the rest of modern molecular and synthetic biology. Medical, industrial, pharmaceutical, agricultural, and basic research scientists seek the as yet unrealized promise of human and mammalian artificial chromosomes. Existing technologies for both top-down and bottom-up approaches to construct these artificial chromosomes for use in higher eukaryotes are very different but aspire to achieve similar results. New capacity for production of chromosome sized synthetic DNA will likely shift the field towards more bottom-up approaches, but not completely. Similarly, new approaches to install human and mammalian artificial chromosomes in target cells will compete with the microcell mediated cell transfer methods that currently dominate the field.

Humanising the mouse genome piece by piece

To better understand human health and disease, researchers create a wide variety of mouse models that carry human DNA. With recent advances in genome engineering, the targeted replacement of mouse genomic regions with orthologous human sequences has become increasingly viable, ranging from finely tuned humanisation of individual nucleotides and amino acids to the incorporation of many megabases of human DNA. Here, we examine emerging technologies for targeted genomic humanisation, we review the spectrum of existing genomically humanised mouse models and the insights such models have provided, and consider the lessons learned for designing such models in the future.

Generation of transgenic mice has become routine in studying gene function and disease mechanisms, but often this is not enough to fully understand human biology. Here, the authors review the current state of the art of targeted genomic humanisation strategies and their advantages over classic approaches.

Humanized UGT2 and CYP3A transchromosomic rats for improved prediction of human drug metabolism

Genomically humanized animals overcoming species differences are invaluable for biomedical research. Although rats would be preferred over mice for several applications, generation of a humanized model is restricted to mice due to the difficulty of complex genetic manipulations in rats. In this study, we successfully generated humanized rats with megabase-sized gene clusters via combination of chromosome transfer using mouse artificial chromosome vector and genome editing technologies. In the humanized UGT2 and CYP3A transchromosomic rats described in this paper, the expression of the human genes, as well as the pharmacokinetics and metabolism of relevant probe substrates, accurately mimic the situation in humans. Thus, the advanced technologies can be used to generate fully humanized rats useful for biomedical research.

Although “genomically” humanized animals are invaluable tools for generating human disease models as well as for biomedical research, their development has been mainly restricted to mice via established transgenic-based and embryonic stem cell-based technologies. Since rats are widely used for studying human disease and for drug efficacy and toxicity testing, humanized rat models would be preferred over mice for several applications. However, the development of sophisticated humanized rat models has been hampered by the difficulty of complex genetic manipulations in rats. Additionally, several genes and gene clusters, which are megabase range in size, were difficult to introduce into rats with conventional technologies. As a proof of concept, we herein report the generation of genomically humanized rats expressing key human drug-metabolizing enzymes in the absence of their orthologous rat counterparts via the combination of chromosome transfer using mouse artificial chromosome (MAC) and genome editing technologies. About 1.5 Mb and 700 kb of the entire UDP glucuronosyltransferase family 2 and cytochrome P450 family 3 subfamily A genomic regions, respectively, were successfully introduced via the MACs into rats. The transchromosomic rats were combined with rats carrying deletions of the endogenous orthologous genes, achieved by genome editing. In the “transchromosomic humanized” rat strains, the gene expression, pharmacokinetics, and metabolism observed in humans were well reproduced. Thus, the combination of chromosome transfer and genome editing technologies can be used to generate fully humanized rats for improved prediction of the pharmacokinetics and drug–drug interactions in humans, and for basic research, drug discovery, and development.

Antigen-Specific Human Monoclonal Antibodies from Transgenic Mice

Due to the difficulties found when generating fully human monoclonal antibodies (mAbs) by the traditional method, several efforts have attempted to overcome these problems, with varying levels of success. One approach has been the development of transgenic mice carrying immunoglobulin (Ig) genes in germline configuration. The engineered mouse genome can undergo productive rearrangement in the B-cell population, with the generation of mouse B lymphocytes expressing human Ig (hIg) chains. To avoid the expression of mouse heavy or light chains, the endogenous mouse Ig (mIg) loci must be silenced by gene-targeting techniques. Subsequently, to obtain antigen-specific mAbs, conventional immunization protocols can be followed and the mAb technique used (fusion of activated B cells with mouse myeloma cells, screening, cloning, freezing, and testing) with these animThis chapter summarizes the most common chromatographic mAb andals expressing human Ig genes. This chapter describes the type of transgenic-knockout mice generated for various research groups, provides examples of human mAbs developed by research groups and companies, and includes protocols of immunization, generation, production, and purification of human mAbs from such mice. In addition, it also addresses the problems detected, and includes some of the methods that can be used to analyze functional activities with human mAbs.

Transfer of Synthetic Human Chromosome into Human Induced Pluripotent Stem Cells for Biomedical Applications

Alphoid^tetO-type human artificial chromosome (HAC) has been recently synthetized as a novel class of gene delivery vectors for induced pluripotent stem cell (iPSC)-based tissue replacement therapeutic approach. This HAC vector was designed to deliver copies of genes into patients with genetic diseases caused by the loss of a particular gene function. The alphoid^tetO-HAC vector has been successfully transferred into murine embryonic stem cells (ESCs) and maintained stably as an independent chromosome during the proliferation and differentiation of these cells. Human ESCs and iPSCs have significant differences in culturing conditions and pluripotency state in comparison with the murine naïve-type ESCs and iPSCs. To date, transferring alphoid^tetO-HAC vector into human iPSCs (hiPSCs) remains a challenging task. In this study, we performed the microcell-mediated chromosome transfer (MMCT) of alphoid^tetO-HAC expressing the green fluorescent protein into newly generated hiPSCs. We used a recently modified MMCT method that employs an envelope protein of amphotropic murine leukemia virus as a targeting cell fusion agent. Our data provide evidence that a totally artificial vector, alphoid^tetO-HAC, can be transferred and maintained in human iPSCs as an independent autonomous chromosome without affecting pluripotent properties of the cells. These data also open new perspectives for implementing alphoid^tetO-HAC as a gene therapy tool in future biomedical applications.

Intracellular Delivery by Membrane Disruption: Mechanisms, Strategies, and Concepts

Intracellular delivery is a key step in biological research and has enabled decades of biomedical discoveries. It is also becoming increasingly important in industrial and medical applications ranging from biomanufacture to cell-based therapies. Here, we review techniques for membrane disruption-based intracellular delivery from 1911 until the present. These methods achieve rapid, direct, and universal delivery of almost any cargo molecule or material that can be dispersed in solution. We start by covering the motivations for intracellular delivery and the challenges associated with the different cargo types-small molecules, proteins/peptides, nucleic acids, synthetic nanomaterials, and large cargo. The review then presents a broad comparison of delivery strategies followed by an analysis of membrane disruption mechanisms and the biology of the cell response. We cover mechanical, electrical, thermal, optical, and chemical strategies of membrane disruption with a particular emphasis on their applications and challenges to implementation. Throughout, we highlight specific mechanisms of membrane disruption and suggest areas in need of further experimentation. We hope the concepts discussed in our review inspire scientists and engineers with further ideas to improve intracellular delivery.

Production of a Human Cell Line with a Plant Chromosome

It is a major challenge in biology to know whether chromosome functions of replication, segregation, gene expression, inheritance, etc. are conserved among evolutionary distant organisms where common structural features are maintained. Establishment of hybrid cell lines between evolutionary distant organisms, such as humans and plants, would be one of the promising synthetic approaches to study the evolutionary conservation of chromosome functions. In this chapter, we describe the protocol for successful establishment of human cell lines with a functional plant chromosome. Systematic analyses of hybrid cells will facilitate the evolutionary study of organisms with respect to chromosome functions. It will also provide a basic platform for genome writing and construction of chromosomal shuttle vectors .

Development of a multiple-gene-loading method by combining multi-integration system-equipped mouse artificial chromosome vector and CRISPR-Cas9

Mouse artificial chromosome (MAC) vectors have several advantages as gene delivery vectors, such as stable and independent maintenance in host cells without integration, transferability from donor cells to recipient cells via microcell-mediated chromosome transfer (MMCT), and the potential for loading a megabase-sized DNA fragment. Previously, a MAC containing a multi-integrase platform (MI-MAC) was developed to facilitate the transfer of multiple genes into desired cells. Although the MI system can theoretically hold five gene-loading vectors (GLVs), there are a limited number of drugs available for the selection of multiple-GLV integration. To overcome this issue, we attempted to knock out and reuse drug resistance genes (DRGs) using the CRISPR-Cas9 system. In this study, we developed new methods for multiple-GLV integration. As a proof of concept, we introduced five GLVs in the MI-MAC by these methods, in which each GLV contained a gene encoding a fluorescent or luminescent protein (EGFP, mCherry, BFP, Eluc, and Cluc). Genes of interest (GOI) on the MI-MAC were expressed stably and functionally without silencing in the host cells. Furthermore, the MI-MAC carrying five GLVs was transferred to other cells by MMCT, and the resultant recipient cells exhibited all five fluorescence/luminescence signals. Thus, the MI-MAC was successfully used as a multiple-GLV integration vector using the CRISPR-Cas9 system. The MI-MAC employing these methods may resolve bottlenecks in developing multiple-gene humanized models, multiple-gene monitoring models, disease models, reprogramming, and inducible gene expression systems.

Combinations of chromosome transfer and genome editing for the development of cell/animal models of human disease and humanized animal models

Chromosome transfer technology, including chromosome modification, enables the introduction of Mb-sized or multiple genes to desired cells or animals. This technology has allowed innovative developments to be made for models of human disease and humanized animals, including Down syndrome model mice and humanized transchromosomic (Tc) immunoglobulin mice. Genome editing techniques are developing rapidly, and permit modifications such as gene knockout and knockin to be performed in various cell lines and animals. This review summarizes chromosome transfer-related technologies and the combined technologies of chromosome transfer and genome editing mainly for the production of cell/animal models of human disease and humanized animal models. Specifically, these include: (1) chromosome modification with genome editing in Chinese hamster ovary cells and mouse A9 cells for efficient transfer to desired cell types; (2) single-nucleotide polymorphism modification in humanized Tc mice with genome editing; and (3) generation of a disease model of Down syndrome-associated hematopoiesis abnormalities by the transfer of human chromosome 21 to normal human embryonic stem cells and the induction of mutation(s) in the endogenous gene(s) with genome editing. These combinations of chromosome transfer and genome editing open up new avenues for drug development and therapy as well as for basic research.

Faithful Artificial Chromosome Propagation Using Spermatogonial Stem Cells

Artificial chromosomes are useful in making functional vectors for very large genes, studying chromosome physiology, and modeling chromosomal disorders. Shinohara et al. have succeeded for the first time in creating transchromosomic mice by manipulating spermatogonial stem cells (SSCs), which exhibited superior chromosomal stability compared with embryonic stem cells (ESCs).

Transfer of a Mouse Artificial Chromosome into Spermatogonial Stem Cells Generates Transchromosomic Mice

The introduction of megabase-sized large DNA fragments into the germline has been a difficult task. Although microcell-mediated chromosome transfer into mouse embryonic stem cells (ESCs) allows the production of transchromosomic mice, ESCs have unstable karyotypes and germline transmission is unreliable by chimera formation. As spermatogonial stem cells (SSCs) are the only stem cells in the germline, they represent an attractive target for germline modification. Here, we report successful transfer of a mouse artificial chromosome (MAC) into mouse germline stem cells (GSCs), cultured spermatogonia enriched for SSCs. MAC-transferred GSCs maintained the host karyotype and MAC more stably than ESCs, which have significant variation in chromosome number. Moreover, MAC-transferred GSCs produced transchromosomic mice following microinjection into the seminiferous tubules of infertile recipients. Successful transfer of MACs to GSCs overcomes the problems associated with ESC-mediated germline transmission and provides new possibilities in germline modification.

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Retro-MMCT method allows transfer of a mouse artificial chromosome into GSCs

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GSCs maintained exogenous chromosomes more stably than ESCs

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Transchromosomic mice were born from GSCs following germ cell transplantation

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Unlike ESCs, transchromosomic mice were born directly in F1 generation

Small chromosomal regions position themselves autonomously according to their chromatin class

The spatial arrangement of chromatin is linked to the regulation of nuclear processes. One striking aspect of nuclear organization is the spatial segregation of heterochromatic and euchromatic domains. The mechanisms of this chromatin segregation are still poorly understood. In this work, we investigated the link between the primary genomic sequence and chromatin domains. We analyzed the spatial intranuclear arrangement of a human artificial chromosome (HAC) in a xenospecific mouse background in comparison to an orthologous region of native mouse chromosome. The two orthologous regions include segments that can be assigned to three major chromatin classes according to their gene abundance and repeat repertoire: (1) gene-rich and SINE-rich euchromatin; (2) gene-poor and LINE/LTR-rich heterochromatin; and (3) gene-depleted and satellite DNA-containing constitutive heterochromatin. We show, using fluorescence in situ hybridization (FISH) and 4C-seq technologies, that chromatin segments ranging from 0.6 to 3 Mb cluster with segments of the same chromatin class. As a consequence, the chromatin segments acquire corresponding positions in the nucleus irrespective of their chromosomal context, thereby strongly suggesting that this is their autonomous property. Interactions with the nuclear lamina, although largely retained in the HAC, reveal less autonomy. Taken together, our results suggest that building of a functional nucleus is largely a self-organizing process based on mutual recognition of chromosome segments belonging to the major chromatin classes.

Multiple expression cassette exchange via TP901-1, R4, and Bxb1 integrase systems on a mouse artificial chromosome

The site-specific excision of a target DNA sequence for genetic knockout or lineage tracing is a powerful tool for investigating biological systems. Currently, site-specific recombinases (SSRs), such as Cre or Flp recombination target cassettes, have been successfully excised or inverted by a single SSR to regulate transgene expression. However, the use of a single SSR might restrict the complex control of gene expression. This study investigated the potential for expanding the multiple regulation of transgenes using three different integrase systems (TP901-1, R4, and Bxb1). We designed three excision cassettes that expressed luciferase, where the luciferase expression could be exchanged to a fluorescent protein by site-specific recombination. Individual cassettes that could be regulated independently by a different integrase were connected in tandem and inserted into a mouse artificial chromosome (MAC) vector in Chinese hamster ovary cells. The transient expression of an integrase caused the targeted luciferase activity to be lost and fluorescence was activated. Additionally, the integrase system enabled the specific excision of targeted DNA sequences without cross-reaction with the other recombination targets. These results suggest that the combined use of these integrase systems in a defined locus on a MAC vector permits the multiple regulation of transgene expression and might contribute to genomic or cell engineering.

Maintenance and Function of a Plant Chromosome in Human Cells

Replication, segregation, gene expression, and inheritance are essential features of all eukaryotic chromosomes. To delineate the extent of conservation of chromosome functions between humans and plants during evolutionary history, we have generated the first human cell line containing an Arabidopsis chromosome. The Arabidopsis chromosome was mitotically stable in hybrid cells following cell division, and initially existed as a translocated chromosome. During culture, the translocated chromosomes then converted to two types of independent plant chromosomes without human DNA sequences, with reproducibility. One pair of localization signals of CENP-A, a marker of functional centromeres was detected in the Arabidopsis genomic region in independent plant chromosomes. These results suggest that the chromosome maintenance system was conserved between human and plants. Furthermore, the expression of plant endogenous genes was observed in the hybrid cells, implicating that the plant chromosomal region existed as euchromatin in a human cell background and the gene expression system is conserved between two organisms. The present study suggests that the essential chromosome functions are conserved between evolutionarily distinct organisms such as humans and plants. Systematic analyses of hybrid cells may lead to the production of a shuttle vector between animal and plant, and a platform for the genome writing.

Successful transmission and transcriptional deployment of a human chromosome via mouse male meiosis

Most human aneuploidies originate maternally, due in part to the presence of highly stringent checkpoints during male meiosis. Indeed, male sterility is common among aneuploid mice used to study chromosomal abnormalities, and male germline transmission of exogenous DNA has been rarely reported. Here we show that, despite aberrant testis architecture, males of the aneuploid Tc1 mouse strain produce viable sperm and transmit human chromosome 21 to create aneuploid offspring. In these offspring, we mapped transcription, transcriptional initiation, enhancer activity, non-methylated DNA, and transcription factor binding in adult tissues. Remarkably, when compared with mice derived from female passage of human chromosome 21, the chromatin condensation during spermatogenesis and the extensive epigenetic reprogramming specific to male germline transmission resulted in almost indistinguishable patterns of transcriptional deployment. Our results reveal an unexpected tolerance of aneuploidy during mammalian spermatogenesis, and the surprisingly robust ability of mouse developmental machinery to accurately deploy an exogenous chromosome, regardless of germline transmission.

Chromosome transplantation as a novel approach for correcting complex genomic disorders

Genomic disorders resulting from large rearrangements of the genome remain an important unsolved issue in gene therapy. Chromosome transplantation, defined as the perfect replacement of an endogenous chromosome with a homologous one, has the potential of curing this kind of disorders. Here we report the first successful case of chromosome transplantation by replacement of an endogenous X chromosome carrying a mutation in the Hprt gene with a normal one in mouse embryonic stem cells (ESCs), correcting the genetic defect. The defect was also corrected by replacing the Y chromosome with an X chromosome. Chromosome transplanted clones maintained in vitro and in vivo features of stemness and contributed to chimera formation. Genome integrity was confirmed by cytogenetic and molecular genome analysis. The approach here proposed, with some modifications, might be used to cure various disorders due to other X chromosome aberrations in induced pluripotent stem (iPS) cells derived from affected patients.

Effects of duration of electric pulse on in vitro development of cloned cat embryos with human artificial chromosome vector

The current applications for cat cloning include production of models for the study of human and animal diseases. This study was conducted to investigate the optimal fusion protocol on in vitro development of transgenic cloned cat embryos by comparing duration of electric pulse. Cat fibroblast cells containing a human artificial chromosome (HAC) vector were used as genetically modified nuclear donor cells. Couplets were fused and activated simultaneously with a single DC pulse of 3.0 kV/cm for either 30 or 60 μs. Low rates of fusion and embryo development to the blastocyst stage were observed in the reconstructed HAC-transchromosomic embryos, when the duration of fusion was prolonged to 60 μs. In contrast, the prolongation of electric pulse duration improved the embryo development and quality in the reconstructed control embryos without HAC vector. Our results suggested that the optimal parameters of electric pulses for fusion in cat somatic cell nuclear transfer vary among the types used for donor cells.

Moving toward a higher efficiency of microcell-mediated chromosome transfer

Microcell-mediated chromosome transfer (MMCT) technology enables individual mammalian chromosomes, megabase-sized chromosome fragments, or mammalian artificial chromosomes that include human artificial chromosomes (HACs) and mouse artificial chromosomes (MACs) to be transferred from donor to recipient cells. In the past few decades, MMCT has been applied to various studies, including mapping the genes, analysis of chromosome status such as aneuploidy and epigenetics. Recently, MMCT was applied to transfer MACs/HACs carrying entire chromosomal copies of genes for genes function studies and has potential for regenerative medicine. However, a safe and efficient MMCT technique remains an important challenge. The original MMCT protocol includes treatment of donor cells by Colcemid to induce micronucleation, where each chromosome becomes surrounded with a nuclear membrane, followed by disarrangement of the actin cytoskeleton using Cytochalasin B to help induce microcells formation. In this study, we modified the protocol and demonstrated that replacing Colcemid and Cytochalasin B with TN-16 + Griseofulvin and Latrunculin B in combination with a Collage/Laminin surface coating increases the efficiency of HAC transfer to recipient cells by almost sixfold and is possibly less damaging to HAC than the standard MMCT method. We tested the improved MMCT protocol on four recipient cell lines, including human mesenchymal stem cells and mouse embryonic stem cells that could facilitate the cell engineering by HACs.

Highly Efficient Transfer of Chromosomes to a Broad Range of Target Cells Using Chinese Hamster Ovary Cells Expressing Murine Leukemia Virus-Derived Envelope Proteins

Microcell-mediated chromosome transfer (MMCT) is an essential step for introducing chromosomes from donor cells to recipient cells. MMCT allows not only for genetic/epigenetic analysis of specific chromosomes, but also for utilization of human and mouse artificial chromosomes (HACs/MACs) as gene delivery vectors. Although the scientific demand for genome scale analyses is increasing, the poor transfer efficiency of the current method has hampered the application of chromosome engineering technology. Here, we developed a highly efficient chromosome transfer method, called retro-MMCT, which is based on Chinese hamster ovary cells expressing envelope proteins derived from ecotropic or amphotropic murine leukemia viruses. Using this method, we transferred MACs to NIH3T3 cells with 26.5 times greater efficiency than that obtained using the conventional MMCT method. Retro-MMCT was applicable to a variety of recipient cells, including embryonic stem cells. Moreover, retro-MMCT enabled efficient transfer of MAC to recipient cells derived from humans, monkeys, mice, rats, and rabbits. These results demonstrate the utility of retro-MMCT for the efficient transfer of chromosomes to various types of target cell.

Quantitative assessment of chromosome instability induced through chemical disruption of mitotic progression

Most solid tumors are aneuploid, carrying an abnormal number of chromosomes, and they frequently missegregate whole chromosomes in a phenomenon termed chromosome instability (CIN). While CIN can be provoked through disruption of numerous mitotic pathways, it is not clear which of these mechanisms are most critical, or whether alternative mechanisms could also contribute significantly in vivo. One difficulty in determining the relative importance of candidate CIN regulators has been the lack of a straightforward, quantitative assay for CIN in live human cells: While gross mitotic abnormalities can be detected visually, moderate levels of CIN may not be obvious, and are thus problematic to measure. To address this issue, we have developed the first Human Artificial Chromosome (HAC)-based quantitative live-cell assay for mitotic chromosome segregation in human cells. We have produced U2OS-Phoenix cells carrying the alphoid^tetO-HAC encoding copies of eGFP fused to the destruction box (DB) of anaphase promoting complex/cyclosome (APC/C) substrate hSecurin and sequences encoding the tetracycline repressor fused to mCherry (TetR-mCherry). Upon HAC missegregation, daughter cells that do not obtain a copy of the HAC are GFP negative in the subsequent interphase. The HAC can also be monitored live following the TetR-mCherry signal. U2OS-Phoenix cells show low inherent levels of CIN, which can be enhanced by agents that target mitotic progression through distinct mechanisms. This assay allows direct detection of CIN induced by clinically important agents without conspicuous mitotic defects, allowing us to score increased levels of CIN that fall below the threshold required for discernable morphological disruption.

Regulation of functional KCNQ1OT1 lncRNA by β-catenin

Long noncoding RNAs (lncRNAs) have been implicated in many biological processes through epigenetic mechanisms. We previously reported that KCNQ1OT1, an imprinted antisense lncRNA in the human KCNQ1 locus on chromosome 11p15.5, is involved in cis-limited silencing within an imprinted KCNQ1 cluster. Furthermore, aberration of KCNQ1OT1 transcription was observed with a high frequency in colorectal cancers. However, the molecular mechanism of the transcriptional regulation and the functional role of KCNQ1OT1 in colorectal cancer remain unclear. Here, we show that the KCNQ1OT1 transcriptional level was significantly increased in human colorectal cancer cells in which β-catenin was excessively accumulated in the nucleus. Additionally, overexpression of β-catenin resulted in an increase in KCNQ1OT1 lncRNA-coated territory. On the other hand, knockdown of β-catenin resulted in significant decrease of KCNQ1OT1 lncRNA-coated territory and an increase in the mRNA expression of the SLC22A18 and PHLDA2 genes that are regulated by KCNQ1OT1. We showed that β-catenin can promote KCNQ1OT1 transcription through direct binding to the KCNQ1OT1 promoter. Our evidence indicates that β-catenin signaling may contribute to development of colorectal cancer by functioning as a novel lncRNA regulatory factor via direct targeting of KCNQ1OT1.

Stable maintenance of de novo assembled human artificial chromosomes in embryonic stem cells and their differentiated progeny in mice

De novo assembled alphoid(tetO)-type human artificial chromosomes (HACs) represent a novel promising generation of high capacity episomal vectors. Their function and persistence, and any adverse effects, in various cell types in live animals, have not, however, been explored. In this study we transferred the alphoid(tetO)-HAC into mouse ES cells and assessed whether the presence of this extra chromosome affects their pluripotent properties. Alphoid(tetO)-HAC-bearing ES cells were indistinguishable from their wild-type counterparts: they retained self-renewal potential and full capacity for multilineage differentiation during mouse development, whereas the HAC itself was mitotically and transcriptionally stable during this process. Our data provide the first example of fully synthetic DNA behaving like a normal chromosome in cells of living animals. It also opens a new perspective into functional genetic studies in laboratory animals as well as stem cell-based regenerative medicine.

Engineering Stem Cells for Biomedical Applications

Stem cells are characterized by a number of useful properties, including their ability to migrate, differentiate, and secrete a variety of therapeutic molecules such as immunomodulatory factors. As such, numerous pre-clinical and clinical studies have utilized stem cell-based therapies and demonstrated their tremendous potential for the treatment of various human diseases and disorders. Recently, efforts have focused on engineering stem cells in order to further enhance their innate abilities as well as to confer them with new functionalities, which can then be used in various biomedical applications. These engineered stem cells can take on a number of forms. For instance, engineered stem cells encompass the genetic modification of stem cells as well as the use of stem cells for gene delivery, nanoparticle loading and delivery, and even small molecule drug delivery. The present Review gives an in-depth account of the current status of engineered stem cells, including potential cell sources, the most common methods used to engineer stem cells, and the utilization of engineered stem cells in various biomedical applications, with a particular focus on tissue regeneration, the treatment of immunodeficiency diseases, and cancer.