Identification of TEKTIN1-expressing multiciliated cells during spontaneous differentiation of non-human primate embryonic stem cells.

Tektins are a group of microtubule-stabilizing proteins necessary for cilia and flagella assembly. TEKTIN1 (TEKT1) is used as a sperm marker for monitoring germ cell differentiation in embryonic stem (ES) and induced pluripotent stem (iPS) cells. Although upregulation of TEKT1 has been reported during spontaneous differentiation of ES and iPS cells, it is unclear which cells express TEKT1. To identify TEKT1-expressing cells, we established an ES cell line derived from cynomolgus monkeys (Macaca fascicularis), which expresses Venus controlled by the TEKT1 promoter. Venus expression was detected at 5 weeks of differentiation on the surface of the embryoid body (EB), and it gradually increased with the concomitant formation of a leash-like structure at the EB periphery. Motile cilia were observed on the surface of the Venus-positive leash-like structure after 8 weeks of differentiation. The expression of cilia markers as well as TEKT1-5 and 9 + 2 microtubule structures, which are characteristic of motile cilia, were detected in Venus-positive cells. These results demonstrated that TEKT1-expressing cells are multiciliated epithelial-like cells that form a leash-like structure during the spontaneous differentiation of ES and iPS cells. These findings will provide a new research strategy for studying cilia biology, including ciliogenesis and ciliopathies.

The SMAD2/3 corepressor SNON maintains pluripotency through selective repression of mesendodermal genes in human ES cells.

Activin/Nodal signaling via SMAD2/3 maintains human embryonic stem cell (hESC) pluripotency by direct transcriptional regulation of NANOG or, alternatively, induces mesoderm and definitive endoderm (DE) formation. In search of an explanation for these contrasting effects, we focused on SNON (SKIL), a potent SMAD2/3 corepressor that is expressed in hESCs but rapidly down-regulated upon differentiation. We show that SNON predominantly associates with SMAD2 at the promoters of primitive streak (PS) and early DE marker genes. Knockdown of SNON results in premature activation of PS and DE genes and loss of hESC morphology. In contrast, enforced SNON expression inhibits DE formation and diverts hESCs toward an extraembryonic fate. Thus, our findings provide novel mechanistic insight into how a single signaling pathway both regulates pluripotency and directs lineage commitment.

Laser-assisted cell removing (LACR) technology contributes to the purification process of the undifferentiated cell fraction during pluripotent stem cell culture.

Purification of undifferentiated cells by removing differentiated parts is an essential step in pluripotent stem cell culture. This process has been traditionally performed manually using a fine glass capillary or plastic tip under a microscope, or by culturing in a selective medium supplemented with anti-differentiation inhibitors. However, there are several inevitable problems associated with these methods, such as contamination or biological side-effects. Here, we developed a laser-assisted cell removing (LACR) technology that enables precise, fast, and contact-less cell removal. Using LACR combined with computational image recognition/identification-discriminating technology, we achieved automatic cell purification (A-LACR). Practicability of A-LACR was evaluated by two demonstrations: selective removal of trophoblast stem (TS) cells from human iPS and TS cell co-cultures, and purification of undifferentiated iPS cells by targeting differentiated cells that spontaneously developed. Our results suggested that LACR technology is a novel approach for stem cell processing in regenerative medicine.

Isolation and characterization of ventricular-like cells derived from NKX2-5eGFP/w and MLC2vmCherry/w double knock-in human pluripotent stem cells.

Human pluripotent stem cell (hPSC)-derived cardiomyocytes (CMs) are a promising source for cell transplantation into the damaged heart, which has limited regenerative ability. Many methods have been developed to obtain large amounts of functional CMs from hPSCs for therapeutic applications. However, during the differentiation process, a mixed population of various cardiac cells, including ventricular, atrial, and pacemaker cells, is generated, which hampers the proper functional analysis and evaluation of cell properties. Here, we established NKX2-5eGFP/w and MLC2vmCherry/w hPSC double knock-ins that allow for labeling, tracing, purification, and analysis of the development of ventricular cells from early to late stages. As with the endogenous transcriptional activities of these genes, MLC2v-mCherry expression following NKX2-5-eGFP expression was observed under previously established culture conditions, which mimic the in vivo cardiac developmental process. Patch-clamp and microelectrode array electrophysiological analyses showed that the NKX2-5 and MLC2v double-positive cells possess ventricular-like properties. The results demonstrate that the NKX2-5eGFP/w and MLC2vmCherry/w hPSCs provide a powerful model system to capture region-specific cardiac differentiation from early to late stages. Our study would facilitate subtype-specific cardiac development and functional analysis using the hPSC-derived sources.

OpenTein: a database of digital whole-slide images of stem cell-derived teratomas.

Human stem cells are promising sources for regenerative therapy. To ensure safety of future therapeutic applications, the differentiation potency of stem cells has to be tested and be widely opened to the public. The potency is generally assessed by teratoma formation comprising differentiated cells from all three germ layers, and the teratomas can be inspected through high-quality digital images. The teratoma assay, however, lacks consistency in transplantation protocols and even in interpretation, which needs community-based efforts for improving the assay quality. Here, we have developed a novel database OpenTein (Open Teratoma Investigation, http://opentein.hgc.jp/) to archive and freely distribute high-resolution whole-slide images and relevant records. OpenTein has been designed as a searchable, zoomable and annotatable web-based repository system. We have deposited 468 images of teratomas derived by our transplantation of human stem cells, and users can freely access and process such digital teratoma images. Approximately, the current version of OpenTein responds within 11.2 min for processing 2.03 gigapixel teratoma images. Our system offers valuable tools and resources in the new era of stem cell biology.

Magnesium chloride and polyamine can differentiate mouse embryonic stem cells into trophectoderm or endoderm.

Magnesium chloride and polyamines stabilize DNA and chromatin. Furthermore, they can induce nucleosome aggregation and chromatin condensation in vitro. To determine the effects of elevating the cation concentrations in the nucleus of a living cell, we microinjected various concentrations of mono-, di- and polyvalent cation solutions into the nuclei of mouse embryonic stem (ES) cells and traced their fates. Here, we show that an elevation of either MgCl2, spermidine or spermine concentration in the nucleus exerts a significant effect on mouse ES cells, and can differentiate a certain population of the cells into trophectoderm, a lineage that mouse ES cells do not normally generate, or endoderm. It is hypothesized that the cell differentiation was most probably caused by the condensation of chromatin including the Oct3/4 locus, which was induced by the elevated concentrations of these cations.

Slow Cooling Cryopreservation Optimized to Human Pluripotent Stem Cells.

Human pluripotent stem cells (hPSCs) have the potential for unlimited expansion and differentiation into cells that form all three germ layers. Cryopreservation is one of the key processes for successful applications of hPSCs, because it allows semi-permanent preservation of cells and their easy transportation. Most animal cell lines, including mouse embryonic stem cells, are standardly cryopreserved by slow cooling; however, hPSCs have been difficult to preserve and their cell viability has been extremely low whenever cryopreservation has been attempted.Here, we investigate the reasons for failure of slow cooling in hPSC cryopreservation. Cryopreservation involves a series of steps and is not a straightforward process. Cells may die due to various reasons during cryopreservation. Indeed, hPSCs preserved by traditional methods often suffer necrosis during the freeze-thawing stages, and the colony state of hPSCs prior to cryopreservation is a major factor contributing to cell death.It has now become possible to cryopreserve hPSCs using conventional cryopreservation methods without any specific equipment. This review summarizes the advances in this area and discusses the optimization of slow cooling cryopreservation for hPSC storage.

Optimization of slow cooling cryopreservation for human pluripotent stem cells.

Human pluripotent stem cells (hPSCs) have the potential for unlimited expansion and differentiation into cell types of all three germ layers. Cryopreservation is a key process for successful application of hPSCs. However, the current conventional method leads to poor recovery of hPSCs after thawing. Here, we demonstrate a highly efficient recovery method for hPSC cryopreservation by slow freezing and single-cell dissociation. After confirming hPSC survivability after freeze-thawing, we found that hPSCs that were freeze-thawed as colonies showed markedly decreased survival, whereas freeze-thawed single hPSCs retained the majority of their viability. These observations indicated that hPSCs should be cryopreserved as single cells. Freeze-thawed single hPSCs efficiently adhered and survived in the absence of a ROCK inhibitor by optimization of the seeding density. The high recovery rate enabled conventional colony passaging for subculture within 3 days post-thawing. The improved method was also adapted to a xeno-free culture system. Moreover, the cell recovery postcryopreservation was highly supported by coating culture surfaces with human laminin-521 that promotes adhesion of dissociated single hPSCs. This simplified but highly efficient cryopreservation method allows easy handling of cells and bulk storage of high-quality hPSCs.

Secondary Publication: Proposal for Points of Consideration for Pluripotent Stem Cell Culture.

Human pluripotent stem cells, such as human embryonic stem cells and human induced pluripotent stem cells, are used in basic research and various applied fields, including drug discovery and regenerative medicine. Stem cell technologies have developed rapidly in recent years, and the supply of culture materials has improved. This has facilitated the culture of human pluripotent stem cells and has enabled an increasing number of researchers and bioengineers to access this technology. At the same time, it is a challenge to share the basic concepts and techniques of this technology among researchers and technicians to ensure the reproducibility of research results. Human pluripotent stem cells differ from conventional somatic cells in many aspects, and many points need to be considered in their handling, even for those experienced in cell culture. Therefore, we have prepared this proposal, "Points of Consideration for Pluripotent Stem Cell Culture," to promote the effective use of human pluripotent stem cells. This proposal includes seven items to be considered and practices to be confirmed before using human pluripotent stem cells. These are laws/guidelines and consent/material transfer agreements, diversity of pluripotent stem cells, culture materials, thawing procedure, media exchange and cell passaging, freezing procedure, and culture management. We aim for the concept of these points of consideration to be shared by researchers and technicians involved in the cell culture of pluripotent stem cells. In this way, we hope the reliability of research using pluripotent stem cells can be improved, and cell culture technology will advance.

Tissue-specific demethylation in CpG-poor promoters during cellular differentiation.

Epigenetic regulation is essential in determining cellular phenotypes during differentiation. Although tissue-specific DNA methylation has been studied, the significance of methylation variance for tissue phenotypes remains unresolved, especially for CpG-poor promoters. Here, we comprehensively studied methylation levels of 27 578 CpG sites among 21 human normal tissues from 12 anatomically different regions using an epigenotyping beadarray system. Remarkable changes in tissue-specific DNA methylation were observed within CpG-poor promoters but not CpG-rich promoters. Of note, tissue-specific hypomethylation is accompanied by an increase in gene expression, which gives rise to specialized cellular functions. The hypomethylated regions were significantly enriched with recognition motifs for transcription factors that regulate cell-type-specific differentiation. To investigate the dynamics of hypomethylation events, we analyzed methylation levels of the entire APOA1 gene locus during in vitro differentiation of embryonic stem cells toward the hepatic lineage. A decrease in methylation was observed after day 13, coinciding with alpha-fetoprotein detection, in the vicinity of its transcription start sites (TSSs), and extends up to ∼200 bp region encompassing the TSS at day 21, equivalent to the hepatoblastic stage. This decrease is even more pronounced in the adult liver, where the entire APOA1 gene locus is hypomethylated. Furthermore, when we compared the methylation status of induced pluripotent stem (iPS) cells with their parental cell, IMR-90, we found that fibroblast-specific hypomethylation is restored to a fully methylated state in iPS cells after reprogramming. These results illuminate tissue-specific methylation dynamics in CpG-poor promoters and provide more comprehensive views on spatiotemporal gene regulation in terminal differentiation.

Identification of small molecules that promote human embryonic stem cell self-renewal.

Human embryonic stem cells (hESCs) and induced pluripotent cells have the potential to provide an unlimited source of tissues for regenerative medicine. For this purpose, development of defined/xeno-free culture systems under feeder-free conditions is essential for the expansion of hESCs. Most defined/xeno-free media for the culture of hESCs contain basic fibroblast growth factor (bFGF). Therefore, bFGF is thought to have an almost essential role for the expansion of hESCs in an undifferentiated state. Here, we report identification of small molecules, some of which were neurotransmitter antagonists (trimipramine and ethopropazine), which promote long-term hESC self-renewal without bFGF in the medium. The hESCs maintained high expression levels of pluripotency markers, had a normal karyotype after 20 passages, and could differentiate into all three germ layers.

Prolonged maturation culture favors a reduction in the tumorigenicity and the dopaminergic function of human ESC-derived neural cells in a primate model of Parkinson's disease.

For the safe clinical application of embryonic stem cells (ESCs) for neurological diseases, it is critical to evaluate the tumorigenicity and function of human ESC (hESC)-derived neural cells in primates. We have herein, for the first time, compared the growth and function of hESC-derived cells with different stages of neural differentiation implanted in the brains of primate models of Parkinson's disease. We herein show that residual undifferentiated cells expressing ESC markers present in the cell preparation can induce tumor formation in the monkey brain. In contrast, a cell preparation matured by 42-day culture with brain-derived neurotrophic factor/glial cell line-derived neurotrophic factor (BDNF/GDNF) treatment did not form tumors and survived as primarily dopaminergic (DA) neurons. In addition, the monkeys with such grafts showed behavioral improvement for at least 12 months. These results support the idea that hESCs, if appropriately matured, can serve as a source for DA neurons without forming any tumors in a primate brain.

Efficient and accurate homologous recombination in hESCs and hiPSCs using helper-dependent adenoviral vectors.

Low efficiencies of gene targeting via homologous recombination (HR) have limited basic research and applications using human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs). Here, we show highly and equally efficient gene knockout and knock-in at both transcriptionally active (HPRT1, KU80, LIG1, LIG3) and inactive (HB9) loci in these cells using high-capacity helper-dependent adenoviral vectors (HDAdVs). Without the necessity of introducing artificial DNA double-strand breaks, 7-81% of drug-resistant colonies were gene-targeted by accurate HR, which were not accompanied with additional ectopic integrations. Even at the motor neuron-specific HB9 locus, the enhanced green fluorescent protein (EGFP) gene was accurately knocked in in 23-57% of drug-resistant colonies. In these clones, induced differentiation into the HB9-positive motor neuron correlated with EGFP expression. Furthermore, HDAdV infection had no detectable adverse effects on the undifferentiated state and pluripotency of hESCs and hiPSCs. These results suggest that HDAdV is one of the best methods for efficient and accurate gene targeting in hESCs and hiPSCs and might be especially useful for therapeutic applications.

Efficient integration of transgenes into a defined locus in human embryonic stem cells.

Random integration is one of the more straightforward methods to introduce a transgene into human embryonic stem (ES) cells. However, random integration may result in transgene silencing and altered cell phenotype due to insertional mutagenesis in undefined gene regions. Moreover, reliability of data may be compromised by differences in transgene integration sites when comparing multiple transgenic cell lines. To address these issues, we developed a genetic manipulation strategy based on homologous recombination and Cre recombinase-mediated site-specific integration. First, we performed gene targeting of the hypoxanthine phosphoribosyltransferase 1 (HPRT) locus of the human ES cell line KhES-1. Next, a gene-replacement system was created so that a circular vector specifically integrates into the targeted HPRT locus via Cre recombinase activity. We demonstrate the application of this strategy through the creation of a tetracycline-inducible reporter system at the HPRT locus. We show that reporter gene expression was responsive to doxycycline and that the resulting transgenic human ES cells retain their self-renewal capacity and pluripotency.

Efficient derivation and banking of clinical-grade human embryonic stem cell lines in accordance with Japanese regulations.

Introduction: We recently established clinical-grade human embryonic stem cell (hESC) line KthES11 in accordance with current good manufacturing practice standards in Japan. Despite this success, the establishment efficiency was very low at 7.1% in the first period. Methods: To establish clinical-grade hESC lines, we used xeno-free chemically defined medium StemFit AK03N with the LM-E8 fragments instead of feeder cells. The protocol was then optimized, especially in the early culture phase. Results: We established five hESC lines (KthES12, KthES13, KthES14, KthES15, and KthES16) with 45.5% efficiency. All five hESC lines showed typical hESC-like morphology, a normal karyotype, pluripotent state, and differentiation potential for all three germ layers. Furthermore, we developed efficient procedures to prepare master cell stocks for clinical-grade hESC lines and an efficient strategy for quality control testing. Conclusions: Our master cell stocks of hESC lines may contribute to therapeutic applications using human pluripotent stem cells in Japan and other countries.

Neutrophil differentiation from human-induced pluripotent stem cells.

Induced pluripotent stem (iPS) cells are of potential value not only for regenerative medicine, but also for disease investigation. The present study describes the development of a neutrophil differentiation system from human iPS cells (hiPSCs) and the analysis of neutrophil function and differentiation. The culture system used consisted of the transfer of hiPSCs onto OP9 cells and their culture with vascular endothelial growth factor (VEGF). After 10 days, TRA 1-85(+) CD34(+) VEGF receptor-2 (VEGFR-2)(high) cells were sorted and co-cultured with OP9 cells in the presence of hematopoietic cytokines for 30 days. Floating cells were collected and subjected to morphological and functional analysis. These hiPSC-derived neutrophils were similar to peripheral blood mature neutrophils in morphology, contained functional neutrophil specific granules, and were equipped with the basic functions such as phagocytosis, superoxide production, and chemotaxis. In the process of differentiation, myeloid cells appeared sequentially from immature myeloblasts to mature segmented neutrophils. Expression patterns of surface antigen, transcription factors, and granule proteins during differentiation were also similar to those of granulopoiesis in normal bone marrow. In conclusion, differentiation of mature neutrophils from hiPSCs was successfully induced in a similar process to normal granulopoiesis using an OP9 co-culture system. This system may be applied to elucidate the pathogenesis of various hematological diseases that affect neutrophils.

Role of SOX2 in maintaining pluripotency of human embryonic stem cells.

Human embryonic stem cell (ESC) pluripotency is thought to be regulated by several key transcription factors including OCT4, NANOG, and SOX2. Although the functions of OCT4 and NANOG in human ESCs are well defined, that of SOX2 has not been fully characterized. To investigate the role of SOX2, we modulated the level of SOX2 expression in human ESCs. Reduction of SOX2 expression in human ESCs induced trophectodermal and partial endodermal differentiation. Interestingly, CDX2, a typical trophectoderm-associated gene, was not up-regulated. In contrast, using the Tet-on gene inducible system, SOX2 over-expression in human ESCs induced trophectoderm differentiation accompanied by increased CDX2 expression. Additionally, SOX2 over-expression resulted in an increase in CGalpha-positive cells, which marks later stage trophectoderm development, rather than placental lactogen-positive cells. Thus, over-expression as well as repression of SOX2 expression in human ESCs resulted in their differentiation into the trophectoderm lineage. Our data show that SOX2 plays an important role in the maintenance of pluripotency of human ESCs and possibly, trophoblast development.

Cardiomyocytes develop from anterior primitive streak cells induced by ß-catenin activation and the blockage of BMP signaling in hESCs.

Cardiomyocytes arise from cells that migrate to the mid-to-anterior region of the primitive streak (PS) during embryogenesis. We previously showed that canonical Wnt/ß-catenin pathway signaling leads to the development of nascent PS populations from human embryonic stem cells (hESCs) and that synergistic activation of the Wnt/ß-catenin pathway and inhibition of bone morphogenetic protein (BMP) signaling by Noggin induced the formation of anterior PS cells. We herein demonstrate that anterior PS cells induced by the activation of ß-catenin with Noggin differentiate into functional cardiomyocytes when cultured in suspension with BMP4 and fibroblast growth factor 2 (FGF2). All aggregates generated from the anterior PS cells developed into contracting cells demonstrating their cardiac potential. More than 30% of the cells in each aggregate were α-actinin-positive cardiomyocytes. In addition, these cardiomyocytes could be easily purified up to 80% by simple size fractionation. In contrast, the posterior PS cells induced by ß-catenin activation without Noggin showed poor cardiac potential. These results show that the commitment to a cardiac lineage in vitro occurs through similar cellular and molecular signaling pathways involved in cardiac development in vivo, thus providing a valuable culture model for studying early cardiac developmental events in hESCs.

Highly efficient transient gene expression and gene targeting in primate embryonic stem cells with helper-dependent adenoviral vectors.

Human embryonic stem (hES) cells are regarded as a potentially unlimited source of cellular materials for regenerative medicine. For biological studies and clinical applications using primate ES cells, the development of a general strategy to obtain efficient gene delivery and genetic manipulation, especially gene targeting via homologous recombination (HR), would be of paramount importance. However, unlike mouse ES (mES) cells, efficient strategies for transient gene delivery and HR in hES cells have not been established. Here, we report that helper-dependent adenoviral vectors (HDAdVs) were able to transfer genes in hES and cynomolgus monkey (Macaca fasicularis) ES (cES) cells efficiently. Without losing the undifferentiated state of the ES cells, transient gene transfer efficiency was approximately 100%. Using HDAdVs with homology arms, approximately one out of 10 chromosomal integrations of the vector was via HR, whereas the rate was only approximately 1% with other gene delivery methods. Furthermore, in combination with negative selection, approximately 45% of chromosomal integrations of the vector were targeted integrations, indicating that HDAdVs would be a powerful tool for genetic manipulation in hES cells and potentially in other types of human stem cells, such as induced pluripotent stem (iPS) cells.

Generation of clinical-grade human embryonic stem cell line KthES11 according to Japanese regulations.

The human embryonic stem cell line, KthES11, is derived from a normal healthy blastocyst donated for clinical research. The inner cell mass (ICM) was isolated using mechanical dissection and plated on laminin fragments. Cell line derivation, its propagation and storage were performed without feeders in an animal product-free environment according to current Good Manufacturing Practice (cGMP) standards. KthES11 shows a normal karyotype, pluripotent state and differentiation to the three germ layers. The cell line was further validated for sterility, mycoplasma-free, antibiotic residues and specific human pathogens.