Microcell-mediated Chromosome Transfer Research Articles

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.

The impact of an additional copy of chromosome 21 in B-cell precursor acute lymphoblastic leukemia.

A common finding in pediatric B-cell precursor acute lymphoblastic leukemia (BCPALL) is that chromosome 21 is never lost and an extra chromosome 21 is often gained. This implies an important role for chromosome 21 in the pathobiology of BCPALL, emphasized by the increased risk of BCPALL in children with Down syndrome. However, model systems of chromosome 21 gain are lacking. We therefore developed a BCPALL cell line (Nalm-6, DUX4-rearranged) with an additional chromosome 21 by means of microcell-mediated chromosome transfer. FISH, PCR, multiplex ligation-dependent probe amplification, and whole exome sequencing showed that an additional chromosome 21 was successfully transferred to the recipient cells. Transcription of some but not all genes on chromosome 21 was increased, indicating tight transcriptional regulation. Nalm-6 cells with an additional chromosome 21 proliferated slightly slower compared with parental Nalm-6 and sensitivity to induction chemotherapeutics was mildly increased. The extra copy of chromosome 21 did not confer sensitivity to targeted signaling inhibitors. In conclusion, a BCPALL cell line with an additional human chromosome 21 was developed, validated, and subjected to functional studies, which showed a minor but potentially relevant effect in vitro. This cell line offers the possibility to study further the role of chromosome 21 in ALL.

Treatment of CHO cells with Taxol and reversine improves micronucleation and microcell-mediated chromosome transfer efficiency

Microcell-mediated chromosome transfer is an attractive technique for transferring chromosomes from donor cells to recipient cells and has enabled the generation of cell lines and humanized animal models that contain megabase-sized gene(s). However, improvements in chromosomal transfer efficiency are still needed to accelerate the production of these cells and animals. The chromosomal transfer protocol consists of micronucleation, microcell formation, and fusion of donor cells with recipient cells. We found that the combination of Taxol (paclitaxel) and reversine rather than the conventional reagent colcemid resulted in highly efficient micronucleation and substantially improved chromosomal transfer efficiency from Chinese hamster ovary donor cells to HT1080 and NIH3T3 recipient cells by up to 18.3- and 4.9-fold, respectively. Furthermore, chromosome transfer efficiency to human induced pluripotent stem cells, which rarely occurred with colcemid, was also clearly improved after Taxol and reversine treatment. These results might be related to Taxol increasing the number of spindle poles, leading to multinucleation and delaying mitosis, and reversine inducing mitotic slippage and decreasing the duration of mitosis. Here, we demonstrated that an alternative optimized protocol improved chromosome transfer efficiency into various cell lines. These data advance chromosomal engineering technology and the use of human artificial chromosomes in genetic and regenerative medical research.

Panel of human cell lines with human/mouse artificial chromosomes

Human artificial chromosomes (HACs) and mouse artificial chromosomes (MACs) are non-integrating chromosomal gene delivery vectors for molecular biology research. Recently, microcell-mediated chromosome transfer (MMCT) of HACs/MACs has been achieved in various human cells that include human immortalised mesenchymal stem cells (hiMSCs) and human induced pluripotent stem cells (hiPSCs). However, the conventional strategy of gene introduction with HACs/MACs requires laborious and time-consuming stepwise isolation of clones for gene loading into HACs/MACs in donor cell lines (CHO and A9) and then transferring the HAC/MAC into cells via MMCT. To overcome these limitations and accelerate chromosome vector-based functional assays in human cells, we established various human cell lines (HEK293, HT1080, hiMSCs, and hiPSCs) with HACs/MACs that harbour a gene-loading site via MMCT. Model genes, such as tdTomato, TagBFP2, and ELuc, were introduced into these preprepared HAC/MAC-introduced cell lines via the Cre-loxP system or simultaneous insertion of multiple gene-loading vectors. The model genes on the HACs/MACs were stably expressed and the HACs/MACs were stably maintained in the cell lines. Thus, our strategy using this HAC/MAC-containing cell line panel has dramatically simplified and accelerated gene introduction via HACs/MACs.

Activation of PPARγ in bladder cancer via introduction of the long arm of human chromosome 9.

Bladder cancer is divided into two molecular subtypes, luminal and basal, which form papillary and nodular tumors, respectively, and are identifiable by gene expression profiling. Although loss of heterozygosity (LOH) of the long arm of human chromosome 9 (9q) has been observed in the early development of both types of bladder cancer, the functional significance of LOH remains to be clarified. The present study introduced human chromosome 9q into basal bladder cancer cell line, SCaBER, using microcell-mediated chromosome transfer to investigate the effect of LOH of 9q on molecular bladder cancer subtypes. These cells demonstrated decreased proliferation and migration capacity compared with parental and control cells. Conversely, transfer of human chromosome 4 did not change the cell phenotype. Expression level of peroxisome proliferator-activated receptor (PPAR)γ, a marker of luminal type, increased 3.0-4.4 fold in SCaBER cells altered with 9q compared with parental SCaBER cells. Furthermore, the expression levels of tumor suppressor PTEN, which regulates PPARγ, also increased in 9q-altered cells. These results suggested that human chromosome 9q may carry regulatory genes for PPARγ that are involved in the progression of neoplastic transformation of bladder cancer.

Assembly of Multiple Full-Size Genes or Genomic DNA Fragments on Human Artificial Chromosomes Using the Iterative Integration System.

Human artificial chromosomes (HACs) are gene delivery vectors that have been used for decades for gene functional studies. HACs have several advantages over viral‐based gene transfer systems, including stable episomal maintenance in a single copy in the cell and the ability to carry up to megabase‐sized genomic DNA segments. We have previously developed the alphoidtetO‐HAC, which has a single gene acceptor loxP site that allows insertion of an individual gene of interest using Chinese hamster ovary (CHO) hybrid cells. The HAC, along with a DNA segment of interest, can then be transferred from donor CHO cells to various recipient cells of interest via microcell‐mediated chromosome transfer (MMCT). Here, we detail a protocol for loading multiple genomic DNA segments or genes into the alphoidtetO‐HAC vector using an iterative integration system (IIS) that utilizes recombinases Cre, ΦC31, and ΦBT. This IIS‐alphoidtetO‐HAC can be used for either serially assembling genomic loci or fragments of a large gene, or for inserting multiple genes into the same artificial chromosome. The insertions are executed iteratively, whereby each round results in the insertion of a new DNA segment of interest. This is accompanied by changes of expression of marker fluorescent proteins, which simplifies screening of correct clones, and changes of selection and counterselection markers, which constitutes an error‐proofing mechanism that removes mis‐incorporated DNA segments. In addition, the IIS‐alphoidtetO‐HAC carrying the genes can be eliminated from the cells, offering the possibility to compare the phenotypes of human cells with and without functional copies of the genes of interest. The resulting HAC molecules may be used to investigate biomedically relevant pathways or the regulation of multiple genes, and to potentially engineer synthetic chromosomes with a specific set of genes of interest. The IIS‐alphoidtetO‐HAC system is expected to be beneficial in creating multiple‐gene humanized models with the purpose of understanding complex multi‐gene genetic disorders. Published 2021. This article is a U.S. Government work and is in the public domain in the USA. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Integration of the first DNA segment of interest into the IIS‐alphoidteto‐HAC Basic Protocol 2: Integration of a second DNA segment of interest into the IIS‐alphoidteto‐HAC Basic Protocol 3: Integration of a third DNA segment of interest into the IIS‐alphoidteto‐HAC Support Protocol: Fluorescence in situ hybridization analysis for the circular IIS‐alphoidtetO‐HAC

Highly Efficient Microcell-Mediated Transfer of HACs Containing a Genomic Region of Interest into Mammalian Cells.

Human artificial chromosomes (HACs) are considered promising tools for gene delivery, functional analyses, and gene therapy. HACs have the potential to overcome many of the problems caused by the use of viral-based gene transfer systems, such as limited cloning capacity, lack of copy number control, and insertional mutagenesis during integration into host chromosomes. The recently developed alphoidtetO -HAC has an advantage over other HAC vectors because it can be easily eliminated from dividing cells by inactivation of its conditional kinetochore. This provides a unique control mechanism to study phenotypes induced by a gene or genes carried on the HAC. The alphoidtetO -HAC has a single gene acceptor loxP site that allows insertion of an individual gene of interest or a cluster of genes of up to several Mb in size in Chinese hamster ovary (CHO) hybrid cells. The HACs carrying chromosomal copies of genes can then be transferred from these donor CHO cells to different recipient cells of interest via microcell-mediated chromosome transfer (MMCT). Here, we describe a detailed protocol for loading a gene of interest into the alphoidtetO -HAC vector and for the subsequent transfer of the HAC to recipient cells using an improved MMCT protocol. The original MMCT protocol includes treatment of donor cells with colcemid to induce micronucleation, wherein the HAC becomes surrounded with a nuclear membrane. That step is followed by disarrangement of the actin cytoskeleton using cytochalasin B to help induce microcell formation. The updated MMCT protocol, described here, features the replacement of colcemid and cytochalasin B with TN16 + griseofulvin and latrunculin B, respectively, and the use of collagen/laminin surface coating to promote attachment of metaphase cells to plates during micronuclei induction. These modifications increase the efficiency of HAC transfer to recipient cells ten fold. The improved MMCT protocol has been successfully tested on several recipient cell lines, including human mesenchymal stem cells and mouse embryonic stem cells. © 2021 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Insertion of a BAC containing a gene of interest into a single loxP loading site of alphoidtetO -HAC in hamster CHO cells Basic Protocol 2: Microcell-mediated chromosome transfer from donor hamster CHO cells to mammalian cells.

Human chromosome 3p21.3 carries TERT transcriptional regulators in pancreatic cancer

Frequent loss of heterozygosity (LOH) on the short arm of human chromosome 3 (3p) region has been found in pancreatic cancer (PC), which suggests the likely presence of tumor suppressor genes in this region. However, the functional significance of LOH in this region in the development of PC has not been clearly defined. The human telomerase reverse transcriptase gene (hTERT) contributes to unlimited proliferative and tumorigenicity of malignant tumors. We previously demonstrated that hTERT expression was suppressed by the introduction of human chromosome 3 in several cancer cell lines. To examine the functional role of putative TERT suppressor genes on chromosome 3 in PC, we introduced an intact human chromosome 3 into the human PK9 and murine LTPA PC cell lines using microcell-mediated chromosome transfer. PK9 microcell hybrids with an introduced human chromosome 3 showed significant morphological changes and rapid growth arrest. Intriguingly, microcell hybrid clones of LTPA cells with an introduced human chromosome 3 (LTPA#3) showed suppression of mTert transcription, cell proliferation, and invasion compared with LTPA#4 cells containing human chromosome 4 and parental LTPA cells. Additionally, the promoter activity of mTert was downregulated in LTPA#3. Furthermore, we confirmed that TERT regulatory gene(s) are present in the 3p21.3 region by transfer of truncated chromosomes at arbitrary regions. These results provide important information on the functional significance of the LOH at 3p for development and progression of PC.

Abstract 1837: A human artificial chromosome (HAC)-based system as a powerful tool for stable co-expression of multiple proteins and therapeutic IgGs in mammalian cells

Abstract Background: Currently, there is increasing demand for recombinant therapeutic proteins produced in mammalian cell lines, especially therapeutic antibodies. MUC16-directed IgG and bispecific diabodies are one such example that represents a promising strategy for treatment of ovarian cancer. HEK293 and CHO cells are mostly used for large-scale stable expression of therapeutic proteins, however low protein yield, transgene silencing, cell line instability, and the time-consuming process of cell line development represent serious challenges. Here, we are presenting an alternative system for stable, high yield expression of multiple genes including complex therapeutic antibodies (HC and LC genes) and other proteins within single HAC. HAC vector propagate independently in cells without integration in the host chromosomes and has unlimited cloning capacity. Furthermore, this particular HAC can be targeted by transcriptional transactivators like tetR-VP16, eliminating transgene silencing, thereby providing stable long-term high yield protein production in mammalian cells. Methods: The targeting vector containing single or multiple genes is loaded at the unique LoxP site of tetO-HAC propagated in HPRT-deficient CHO cells by Cre-LoxP mediated recombination. As a result of recombination, functional HPRT gene will be reconstituted and HPRT-positive colonies are selected after 3 weeks growth in HAT medium. In the next step, HAC with therapeutic transgene(s) is transferred to the different high productive cell lines via MMCT technique following by high yield protein(s) expression in spinner flask. The alphoid tetO-HAC carries Bsr gene, so Blasticidin is used to select for the recipient cells that have taken up the HAC after Microcell-mediated chromosome transfer (MMCT). Results: Targeting vector with His-tagged MUC16 BiTEs gene (or iBAC caring HC and LC of anti-MUC16 IgG) was inserted into the HAC propagated in CHO cells. HPRT gene reconstitution was confirmed by PCR using a set of specific primers. Expression of His-tagged MUC16 BiTEs or anti-MUC16 IgG in CHO cells was confirmed by western blot and SDS-PAGE analysis. The yield of Ni- purified MUC16 BiTEs was up to 6 mg/l in original CHO cells. Our data from cellular models confirmed high efficacy of Ni- purified MUC16 BiTEs against OVCAR3 tumor cells, - up to 80% of the tumor cells were killed by T-cells in the presence of MUC16 BiTEs protein. After that, HAC/MUC16 BiTEs was successfully transferred to high productive ExpiHEK293F cells by MMCT. Therapeutic HAC transferring was confirmed by expression DsRed transgene linked with MUC16BiTEs through IRES and FISH analysis. FISH reveals the HAC propagated independently in ExpiHEK293F cells. Conclusions: Our data shows that the HAC is the new promising system for stable, high yield production of multiple therapeutic proteins. Citation Format: Artem Kononenko, Ian Laster, Oladapo Yeku, David Spriggs. A human artificial chromosome (HAC)-based system as a powerful tool for stable co-expression of multiple proteins and therapeutic IgGs in mammalian cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1837.

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.

Establishment of FXS-A9 panel with a single human X chromosome from fragile X syndrome-associated individual

Fragile X syndrome (FXS) is the most common inheritable form of intellectual disability. FMR1, the gene responsible for FXS, is located on human chromosome Xq27.3 and contains a stretch of CGG trinucleotide repeats in its 5′ untranslated region. FXS is caused by CGG repeats that expand beyond 200, resulting in FMR1 silencing via promoter hypermethylation. The molecular mechanism underlying CGG repeat expansion, a fundamental cause of FXS, remains poorly understood, partly due to a lack of experimental systems. Accumulated evidence indicates that the large chromosomal region flanking a CGG repeat is critical for repeat dynamics. In the present study, we isolated and introduced whole human X chromosomes from healthy, FXS premutation carriers, or FXS patients who carried disease condition-associated CGG repeat lengths, into mouse A9 cells via microcell-mediated chromosome transfer. The CGG repeat length-associated methylation status and human FMR1 expression in these monochromosomal hybrid cells mimicked those in humans. Thus, this set of A9 cells containing CGG repeats from three different origins (FXS-A9 panel) may provide a valuable resource for investigating a series of genetic and epigenetic CGG repeat dynamics during FXS pathogenesis.

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.

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

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. 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. 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.

Micronuclei-based model system reveals functional consequences of chromothripsis in human cells.

Cancer cells often harbor chromosomes in abnormal numbers and with aberrant structure. The consequences of these chromosomal aberrations are difficult to study in cancer, and therefore several model systems have been developed in recent years. We show that human cells with extra chromosome engineered via microcell-mediated chromosome transfer often gain massive chromosomal rearrangements. The rearrangements arose by chromosome shattering and rejoining as well as by replication-dependent mechanisms. We show that the isolated micronuclei lack functional lamin B1 and become prone to envelope rupture, which leads to DNA damage and aberrant replication. The presence of functional lamin B1 partly correlates with micronuclei size, suggesting that the proper assembly of nuclear envelope might be sensitive to membrane curvature. The chromosomal rearrangements in trisomic cells provide growth advantage compared to cells without rearrangements. Our model system enables to study mechanisms of massive chromosomal rearrangements of any chromosome and their consequences in human cells.

Functional characterization of a candidate tumor suppressor gene, Mirror Image Polydactyly 1, in nasopharyngeal carcinoma.

Mirror Image Polydactyly 1 (MIPOL1) is generally associated with congenital anomalies. However, its role in cancer development is poorly understood. Previously, by utilizing the functional complementation approach, microcell-mediated chromosome transfer (MMCT), a tumor suppressor gene, MIPOL1, was identified. MIPOL1 was confirmed to be downregulated in nasopharyngeal carcinoma (NPC) cells and tumor tissues, and re-expression of MIPOL1 induced tumor suppression. The aim of the current study is to further elucidate the functional tumor suppressive role of MIPOL1. In our study, with an expanded sample size of different clinical stages of NPC tumor tissues, we further confirmed the downregulation of MIPOL1 in different cancer stages. MIPOL1 re-expression down-regulated angiogenic factors and reduced phosphorylation of metastasis-associated proteins including AKT, p65, and FAK. In addition, MIPOL1 was confirmed to interact with a tumor suppressor, RhoB, and re-expression of MIPOL1 enhanced RhoB activity. The functional role of MIPOL1 was further validated by utilizing a panel of wild-type (WT) and truncated MIPOL1 expression constructs. The MIPOL1 tumor-suppressive effect can only be observed in the WT MIPOL1-expressing cells. In vitro and nude mice in vivo functional studies further confirmed the critical role of WT MIPOL1 in inhibiting migration, invasion and metastasis in NPC. Overall, our study provides strong evidence about the tumor-suppressive role of MIPOL1 in inhibiting angiogenesis and metastasis in NPC.

Induced Chromosomal Aneuploidy Results in Global and Consistent Deregulation of the Transcriptome of Cancer Cells

Chromosomal aneuploidy is a defining feature of epithelial cancers. The pattern of aneuploidies is cancer-type specific. For instance, the gain of chromosome 13 occurs almost exclusively in colorectal cancer. We used microcell-mediated chromosome transfer to generate gains of chromosome 13 in the diploid human colorectal cancer cell line DLD-1. Extra copies of chromosome 13 resulted in a significant and reproducible up-regulation of transcript levels of genes on chromosome 13 (P = .0004, FDR = 0.01) and a genome-wide transcriptional deregulation in all 8 independent clones generated. Genes contained in two clusters were particularly affected: the first cluster on cytoband 13q13 contained 7 highly up-regulated genes (NBEA, MAB21L1, DCLK1, SOHLH2, CCDC169, SPG20 and CCNA1, P = .0003) in all clones. A second cluster was located on 13q32.1 and contained five upregulated genes (ABCC4, CLDN10, DZIP1, DNAJC3 and UGGT2, P = .003). One gene, RASL11A, localized on chromosome band 13q12.2, escaped the copy number-induced overexpression and was reproducibly and significantly down-regulated on the mRNA and protein level (P = .0001, FDR = 0.002). RASL11A expression levels were also lower in primary colorectal tumors as compared to matched normal mucosa (P = .0001, FDR = 0.0001. Overexpression of RASL11A increases cell proliferation and anchorage independent growth while decreasing cell migration in +13 clones. In summary, we observed a strict correlation of genomic copy number and resident gene expression levels, and aneuploidy dependent consistent genome-wide transcriptional deregulation.

Chromosome Transplantation: Correction of the Chronic Granulomatous Disease Defect in Mouse Induced Pluripotent Stem Cells.

In spite of the progress in gene editing achieved in recent years, a subset of genetic diseases involving structural chromosome abnormalities, including aneuploidies, large deletions and complex rearrangements, cannot be treated with conventional gene therapy approaches. We have previously devised a strategy, dubbed chromosome transplantation (CT), to replace an endogenous mutated chromosome with an exogenous normal one. To establish a proof of principle for our approach, we chose as disease model the chronic granulomatous disease (CGD), an X-linked severe immunodeficiency due to abnormalities in CYBB (GP91) gene, including large genomic deletions. We corrected the gene defect by CT in induced pluripotent stem cells (iPSCs) from a CGD male mouse model. The Hprt gene of the endogenous X chromosome was inactivated by CRISPR/Cas9 technology thus allowing the exploitation of the hypoxanthine-aminopterin-thymidine selection system to introduce a normal donor X chromosome by microcell-mediated chromosome transfer. X-transplanted clones were obtained, and diploid XY clones which spontaneously lost the endogenous X chromosome were isolated. These cells were differentiated toward the myeloid lineage, and functional granulocytes producing GP91 protein were obtained. We propose the CT approach to correct iPSCs from patients affected by other X-linked diseases with large deletions, whose treatment is still unsatisfactory. Stem Cells 2019;37:876-887.

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

AlphoidtetO-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 alphoidtetO-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 alphoidtetO-HAC vector into human iPSCs (hiPSCs) remains a challenging task. In this study, we performed the microcell-mediated chromosome transfer (MMCT) of alphoidtetO-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, alphoidtetO-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 alphoidtetO-HAC as a gene therapy tool in future biomedical applications.

206 Towards the generation of transchromosomic goats for the production of fully human immunoglobulin

We have previously reported that inactivation of endogenous immunoglobulin (Ig) genes can enhance the production of human polyclonal antibodies (hpAb) in transchromosomic (Tc) cattle containing a human artificial chromosome (HAC) comprising the entire human Ig gene repertoire. Goats offer the advantages of having a shorter gestation period and growing to adult size much faster than larger ungulates. Therefore, based upon our previously established Tc cattle platform, in this study, we aimed to generate immunoglobulin lambda light chain knockout (IGLλ −/− )/HAC Tc goats expressing hpAb using CRISPR/Cas9 and somatic cell nuclear transfer (SCNT) techniques. First, we designed multiple specific single-guide RNAs (sgRNA) targeting the coding sequences of constant regions of goat IGLλ1, IGLλ2 (both in NC_030824.1), and IGLλ3 (NW_017189530.1) and constructed corresponding gene targeting vectors. Gene targeting efficiency analysis in goat fibroblasts showed that the sgRNA were efficient in directing Cas9 to generate targeted indels in corresponding IGLλ genes with efficiencies ranging between 20 and 30%. We then targeted the IGLλ genes and generated a cloned IGLλ −/− fetus by SCNT (first round of cloning; G1) using single cell-derived IGLλ −/− fibroblast colonies as nuclear donors and established IGLλ −/− fetal fibroblast cell lines. Second, we established IGLλ −/− /HAC fibroblast colonies by transferring the isKcHACΔ, a HAC containing the entire unrearranged human immunoglobulin heavy-chain and kappa-chain sequences, into the IGLλ −/− fetal fibroblast cells via microcell-mediated chromosome transfer (MMCT; Matsushita et al. 2014 PLoS One 9, e90383). The resulting IGLλ −/− /HAC fibroblasts were used as nuclear donors for the production of IGLλ −/− /HAC goats by SCNT (second round of cloning; G2). A total of 311 one-cell stage G2 embryos were generated using 4 IGLλ −/− /HAC fetal fibroblast colonies and surgically transferred into 19 oestrus-synchronized recipients. Seven pregnancies were confirmed (7/19; 36.8%) with ultrasonography at Day 60±3 of gestation, and 1 pregnancy (1/7; 14.3%) developed to term, leading to the birth of a live and healthy kid. Genetic and serological characterisation of this Tc goat produced by the second round of SCNT is in progress.

Generation of a novel isogenic trisomy panel in human embryonic stem cells via microcell-mediated chromosome transfer

Aneuploidy is the gain or loss of a chromosome. Down syndrome or trisomy (Ts) 21 is the most frequent live-born aneuploidy syndrome in humans and extensively studied using model mice. However, there is no available model mouse for other congenital Ts syndromes, possibly because of the lethality of Ts in vivo, resulting in the lack of studies to identify the responsible gene(s) for aneuploid syndromes. Although induced pluripotent stem cells derived from patients are useful to analyse aneuploidy syndromes, there are concerns about differences in the genetic background for comparative studies and clonal variations. Therefore, a model cell line panel with the same genetic background has been strongly desired for sophisticated comparative analyses. In this study, we established isogenic human embryonic stem (hES) cells of Ts8, Ts13, and Ts18 in addition to previously established Ts21 by transferring each single chromosome into parental hES cells via microcell-mediated chromosome transfer. Genes on each trisomic chromosome were globally overexpressed in each established cell line, and all Ts cell lines differentiated into all three embryonic germ layers. This cell line panel is expected to be a useful resource to elucidate molecular and epigenetic mechanisms of genetic imbalance and determine how aneuploidy is involved in various abnormal phenotypes including tumourigenesis and impaired neurogenesis.