Related Articles

We have devised a reproducible protocol by which human embryonic stem cells (hESCs) or inducible pluripotent stem cells (iPSCs) are efficiently differentiated to functional spinal motor neurons. This protocol comprises four major steps. Pluripotent stem cells are induced to form neuroepithelial (NE) cells that form neural tube-like rosettes in the absence of morphogens in the first 2 weeks. The NE cells are then specified to OLIG2-expressing motoneuron progenitors in the presence of retinoic acid (RA) and sonic hedgehog (SHH) or purmorphamine in the next 2 weeks. These progenitor cells further generate post- mitotic, HB9-expressing motoneurons at the 5th week and mature to functional motor neurons thereafter. It typically takes 5 weeks to generate the post-mitotic motoneurons and 8–10 weeks for the production of functional mature motoneurons. In comparison with other methods, our protocol does not use feeder cells, has a minimum dependence on proteins (purmorphamine replacing SHH), has controllable adherent selection and is adaptable for scalable suspension culture.

Background

The use of induced pluripotent stem cells (iPSCs) for the functional replacement of damaged neurons and in vitro disease modeling is of great clinical relevance. Unfortunately, the capacity of iPSC lines to differentiate into neurons is highly variable, prompting the need for a reliable means of assessing the differentiation capacity of newly derived iPSC cell lines. Extended passaging is emerging as a method of ensuring faithful reprogramming. We adapted an established and efficient embryonic stem cell (ESC) neural induction protocol to test whether iPSCs (1) have the competence to give rise to functional neurons with similar efficiency as ESCs and (2) whether the extent of neural differentiation could be altered or enhanced by increased passaging.

Results

Our gene expression and morphological analyses revealed that neural conversion was temporally delayed in iPSC lines and some iPSC lines did not properly form embryoid bodies during the first stage of differentiation. Notably, these deficits were corrected by continual passaging in an iPSC clone. iPSCs with greater than 20 passages (late-passage iPSCs) expressed higher expression levels of pluripotency markers and formed larger embryoid bodies than iPSCs with fewer than 10 passages (early-passage iPSCs). Moreover, late-passage iPSCs started to express neural marker genes sooner than early-passage iPSCs after the initiation of neural induction. Furthermore, late-passage iPSC-derived neurons exhibited notably greater excitability and larger voltage-gated currents than early-passage iPSC-derived neurons, although these cells were morphologically indistinguishable.

Conclusions

These findings strongly suggest that the efficiency neuronal conversion depends on the complete reprogramming of iPSCs via extensive passaging.

Specification of distinct cell types from human embryonic stem cells (hESCs) is key to the potential application of these naïve pluripotent cells in regenerative medicine. Determination of the nontarget differentiated populations, which is lacking in the field, is also crucial. Here, we show an efficient differentiation of motor neurons (~50%) by a simple sequential application of retinoid acid and sonic hedgehog (SHH) in a chemically defined suspension culture. We also discovered that purmorphamine, a small molecule that activates the SHH pathway, could replace SHH for the generation of motor neurons. Immunocytochemical characterization indicated that cells differentiated from hESCs were nearly completely restricted to the ventral spinal progenitor fate (NKX2.2+, Irx3+, and Pax7−), with the exception of motor neurons (HB9+) and their progenitors (Olig2+). Thus, the directed neural differentiation system with small molecules, even without further purification, will facilitate basic and translational studies using human motoneurons at a minimal cost.

We describe a chemically defined protocol for efficient differentiation of human embryonic stem cells (hESCs) to neural epithelial cells and then to functional spinal motor neurons. This protocol comprises four major steps. Human ESCs are differentiated without morphogens into neuroepithelial cells that form neural tube-like rosettes in the first two weeks. The neuroepithelial cells are then specified to Olig2-expressing motoneuorn progenitors in the presence of retinoic acid (RA) and sonic hedgehog (SHH) in the following 2 weeks. These OLIG2 progenitors generate post-mitotic, HB9 expressing motoneurons at the 5th week and mature to functional motor neurons thereafter. The protein factor SHH can be replaced by a small molecule purmorphamine in the entire process, which may facilitate potential clinical applications. This protocol has been shown equally effective in generating motor neurons from human induced pluropotent stem (iPS) cells.

Human induced pluripotent stem cells (iPSCs) reprogrammed from somatic cells represent a promising unlimited cell source for generating patient-specific cells for biomedical research and personalized medicine. As a first step, critical to clinical applications, we attempted to develop defined culture conditions to expand and differentiate human iPSCs into functional progeny such as dopaminergic neurons for treating or modeling Parkinson's disease (PD). We used a completely defined (xeno-free) system that we previously developed for efficient generation of authentic dopaminergic neurons from human embryonic stem cells (hESCs), and applied it to iPSCs. First, we adapted two human iPSC lines derived from different somatic cell types for the defined expansion medium and showed that the iPSCs grew similarly as hESCs in the same medium regarding pluripotency and genomic stability. Second, by using these two independent adapted iPSC lines, we showed that the process of differentiation into committed neural stem cells (NSCs) and subsequently into dopaminergic neurons was also similar to hESCs. Importantly, iPSC-derived dopaminergic neurons were functional as they survived and improved behavioral deficits in 6-hydroxydopamine-leasioned rats after transplantation. In addition, iPSC-derived NSCs and neurons could be efficiently transduced by a baculoviral vector delivering episomal DNA for future gene function study and disease modeling using iPSCs. We also performed genome-wide microarray comparisons between iPSCs and hESCs, and we derived NSC and dopaminergic neurons. Our data revealed overall similarity and visible differences at a molecular level. Efficient generation of functional dopaminergic neurons under defined conditions will facilitate research and applications using PD patient-specific iPSCs. Stem Cells 2010;28:1893–1904

SUMMARY

Induced pluripotent stem cells (iPSCs) derived from somatic cells of patients represent a powerful tool for biomedical research and may provide a source for replacement therapies. However, the use of viruses encoding the reprogramming factors represents a major limitation of the current technology since even low vector expression may alter the differentiation potential of the iPSCs or induce malignant transformation. Here, we show that fibroblasts from five patients with idiopathic Parkinson’s disease can be efficiently reprogrammed and subsequently differentiated into dopaminergic neurons. Moreover, we derived hiPSCs free of reprogramming factors using Cre-recombinase excisable viruses. Factor-free hiPSCs maintain a pluripotent state and show a global gene expression profile, more closely related to hESCs than to hiPSCs carrying the transgenes. Our results indicate that residual transgene expression in virus-carrying hiPSCs can affect their molecular characteristics and that factor-free hiPSCs therefore represent a more suitable source of cells for modeling of human disease.

Human embryonic stem cells (hESC) and induced pluripotent stem cells (iPSC) provide new prospects for studying human neurodevelopment and modeling neurological disease. In particular, iPSC-derived neural cells permit a direct comparison of disease-relevant molecular pathways in neurons and glia derived from patients and healthy individuals. A prerequisite for such comparative studies are robust protocols that efficiently yield standardized populations of neural cell types. Here we show that long-term self-renewing neuroepithelial-like stem cells (lt-NES cells) derived from 3 hESC and 6 iPSC lines in two independent laboratories exhibit consistent characteristics including i) continuous expandability in the presence of FGF2 and EGF; ii) stable neuronal and glial differentiation competence; iii) characteristic transcription factor profile; iv) hindbrain specification amenable to regional patterning; v) capacity to generate functionally mature human neurons. We further show that lt-NES cells are developmentally distinct from fetal tissue-derived radial glia-like stem cells. We propose that lt-NES cells provide an interesting tool for studying human neurodevelopment and may serve as a standard system to facilitate comparative analyses of hESC and hiPSC-derived neural cells from control and diseased genetic backgrounds.

Chemical compounds have emerged as powerful tools for modulating embryonic stem cell (ESC) functions and deriving induced pluripotent stem cells (iPSCs), but documentation of compound-induced efficient directed differentiation in human ESC (hESCs) and human iPSC (hiPSCs) is limited. By screening a collection of chemical compounds, we identified compound C (also denoted as dorsomorphin), a protein kinase inhibitor, as a potent regulator of hESC and hiPSC fate decisions. Compound C suppresses mesoderm, endoderm and trophoectoderm differentiation and induces rapid and high-efficiency neural conversion in both hESCs and hiPSCs (88.7% and 70.4%, respectively). Interestingly, compound C is ineffective in inducing neural conversion in mouse ESCs (mESCs). Largescale kinase assay revealed that compound C targets at least seven TGF-β superfamily receptors, including both type I and type II receptors, and thereby blocks both the Activin and BMP signaling pathways in hESCs. Dual inhibition of Activin and BMP signaling accounts for the effects of compound C on hESC differentiation and neural conversion. We also identified muscle segment homeobox gene 2 (MSX2) as a downstream target gene of compound C and a key signaling intermediate of the BMP pathway in hESCs. Our findings provide a single-step cost-effective method for efficient derivation of neural progenitor cells in adherent culture from human pluripotent stem cells. Therefore, it will be uniquely suitable for the production of neural progenitor cells in large scale and should facilitate the use of stem cells in drug screening and regenerative medicine and study of early human neural development.

Human embryonic (ESC) and induced pluripotent stem cells (iPSC) present exciting opportunities for studying development and in vitro disease modeling. However, reported variability in iPSC behavior has called their utility into question. We therefore constituted a test set of 16 iPSCs lines from 7 individuals of varying gender and health status, characterized them extensively for pluripotency, and evaluated their ability to terminally differentiate. Using standardized procedures in two independent laboratories, 13 of the iPSC lines gave rise to functional motor neurons with a range of efficiencies similar to ESCs. Although three iPSC lines were resistant to neural differentiation, early neuralization rescued their performance. Therefore, all lines in the test set passed a stringent test of differentiation capacity despite variations in expression of early pluripotency markers, transgenes and karyotype. This novel iPSC/ESC test set is a robust resource for those interested in the basic biology of stem cells and their applications.

Abstract

Induced pluripotent Huntington's disease monkey stem cells (rHD-iPSCs) were established by the overexpression of rhesus macaque transcription factors (Oct4, Sox2, and Klf4) in transgenic Huntington's monkey skin fibroblasts. The rHD-iPSCs were pluripotent and capable of differentiating into neuronal cell types in vitro and developed teratoma in immune compromised mice. We also demonstrated the upregulation of endogenous Oct4 and Sox2 after successful reprogramming to pluripotency in rHD-iPSCs, which was not expressed in skin fibroblasts. rHD-iPSCs also developed cellular features comparable to Huntington's disease (HD), including the accumulation of mutant huntingtin (htt) aggregate and the formation of intranuclear inclusions (NIs) paralleling neural differentiation in vitro. Induced pluripotent stem cells from transgenic HD monkeys open a new era of nonhuman primate modeling of human diseases. rHD-iPSCs that develop key HD cellular features and parallel neural differentiation can be a powerful platform for investigating the developmental impact on HD pathogenesis and developing new therapies, which can be evaluated in HD monkeys from whom the rHD-iPSCs were derived.

Abstract

Human embryonic stem cells (hESC) and induced pluripotent stem cells (iPSC) offer great hope for in vitro modeling of Parkinson's disease (PD), as well as for designing cell-replacement therapies. To realize these opportunities, there is an urgent need to develop efficient protocols for the directed differentiation of hESC/iPSC into dopamine (DA) neurons with the specific characteristics of the cell population lost to PD, i.e., A9-subtype ventral midbrain DA neurons. Here we use lentiviral vectors to drive the expression of LMX1A, which encodes a transcription factor critical for ventral midbrain identity, specifically in neural progenitor cells. We show that clonal lines of hESC engineered to contain one or two copies of this lentiviral vector retain long-term self-renewing ability and pluripotent differentiation capacity. Greater than 60% of all neurons generated from LMX1A-engineered hESC were ventral midbrain DA neurons of the A9 subtype, compared with ∼10% in green fluorescent protein–engineered controls, as judged by specific marker expression and functional analyses. Moreover, DA neuron precursors differentiated from LMX1A-engineered hESC were able to survive and differentiate when grafted into the brain of adult mice. Finally, we provide evidence that LMX1A overexpression similarly increases the yield of DA neuron differentiation from human iPSC. Taken together, our data show that stable genetic engineering of hESC/iPSC with lentiviral vectors driving controlled expression of LMX1A is an efficient way to generate enriched populations of human A9-subtype ventral midbrain DA neurons, which should prove useful for modeling PD and may be helpful for designing future cell-replacement strategies.

Sánchez-Danés and colleagues describe a system wherein they use lentiviral vectors to drive the expression of LMX1A, a transcription factor critical for neural progenitor cells, human embryonic stem cells, and induced pluripotent stem cells. They show that this approach can result in the generation of human A9-subtype ventral midbrain dopaminergic neurons, which should prove useful for modeling Parkinson's disease and may be helpful for designing future cell-replacement strategies.

Human induced pluripotent stem cells (iPSCs) are reprogrammed by transient expression of transcription factors in somatic cells. Approximately 1% of somatic cells can be reprogrammed into iPSCs, while the remaining somatic cells are differentially reprogrammed. Here, we established induced pluripotent cancer stem-like cells (iCSCs) as self-renewing pluripotent cell clones. Stable iCSC lines were established from unstable induced epithelial stem cell (iESC) lines through re-plating followed by embryoid body formation and serial transplantation. iCSCs shared the expression of pluripotent marker genes with iPSCs, except for REX1 and LIN28, while exhibited the expression of somatic marker genes EMP1 and PPARγ. iESCs and iCSCs could generate teratomas with high efficiency by implantation into immunodeficient mice. The second iCSCs isolated from dissociated cells of teratoma from the first iCSCs were stably maintained, showing a gene expression profile similar to the first iCSCs. In the first and second iCSCs, transgene-derived Oct4, Sox2, Klf4, and c-Myc were expressed. Comparative global gene expression analyses demonstrated that the first iCSCs were similar to iESCs, and clearly different from human iPSCs and somatic cells. In iCSCs, gene expression kinetics of the core pluripotency factor and the Myc-related factor were pluripotent type, whereas the polycomb complex factor was somatic type. These findings indicate that pluripotent tumorigenicity can be conferred on somatic cells through up-regulation of the core pluripotency and Myc-related factors, prior to establishment of the iPSC molecular network by full reprogramming through down-regulation of the polycomb complex factor.

By sequentially applying sonic hedgehog (C25II) and CHIR99021 (GSK3β inhibitor) to induce the midbrain floor plate progenitors and fibroblast growth factor 8 (FGF8) to promote dopaminergic differentiation in a chemically defined medium, we have established a robust system for generation of midbrain dopamine (DA) neurons from human and rhesus monkey embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs). We found that CHIR99021 specifies diencephalon to hindbrain fates in a concentration-dependent manner and only a narrow concentration range of CHIR99021 at a particular window is necessary to induce the midbrain floor plate progenitors, expressing Corin, En1, FoxA2 and Lmx1a. FGF8 enhances the dopaminergic fate of the progenitors, thus generating DA neurons with midbrain characteristics, including expression of TH, Lmx1a/b, FoxA2, FoxP1, Nurr1 and En1 as well as typical electrophysiological properties. More than half of these DA neurons expressed A9 DA neuron markers Girk2 and ALDH1a1. The new strategy will allow generation of enriched populations of functional midbrain DA neurons from both human and monkey PSCs for disease modeling, drug testing, and potential cell therapy.

Current neural induction protocols in human ES cells (hESCs) rely on embryoid body formation, stromal feeder co-culture, or selective survival conditions; each strategy displaying significant drawbacks such as poorly defined culture conditions, protracted differentiation and low yield.

Here we report that the synergistic action of two inhibitors of SMAD signaling, Noggin and SB431542, is sufficient for inducing rapid and complete neural conversion of hESCs under adherent culture conditions. Temporal fate analysis reveals a transient FGF5+ epiblast-like stage followed by PAX6+ neural cells competent of rosette formation. Initial cell density determines the ratio of CNS versus neural crest progeny. Directed differentiation of human iPSCs into midbrain dopamine and spinal motoneurons confirm robustness and general applicability of the novel induction protocol.

Noggin/SB431542 based neural induction should greatly facilitate the use of hESC and hiPSCs in regenerative medicine and disease modeling and obviate the need for stromal feeder or embryoid body based protocols.

The production of induced pluripotent stem cells (iPSCs) from somatic cells provides a means to create valuable tools for basic research and may also produce a source of patient-matched cells for regenerative therapies. iPSCs may be generated using multiple protocols and derived from multiple cell sources. Once generated, iPSCs are tested using a variety of assays including immunostaining for pluripotency markers, generation of three germ layers in embryoid bodies and teratomas, comparisons of gene expression with embryonic stem cells (ESCs) and production of chimeric mice with or without germline contribution2. Importantly, iPSC lines that pass these tests still vary in their capacity to produce different differentiated cell types2. This has made it difficult to establish which iPSC derivation protocols, donor cell sources or selection methods are most useful for different applications.

The most stringent test of whether a stem cell line has sufficient developmental potential to generate all tissues required for survival of an organism (termed full pluripotency) is tetraploid embryo complementation (TEC)3-5. Technically, TEC involves electrofusion of two-cell embryos to generate tetraploid (4n) one-cell embryos that can be cultured in vitro to the blastocyst stage6. Diploid (2n) pluripotent stem cells (e.g. ESCs or iPSCs) are then injected into the blastocoel cavity of the tetraploid blastocyst and transferred to a recipient female for gestation (see Figure 1). The tetraploid component of the complemented embryo contributes almost exclusively to the extraembryonic tissues (placenta, yolk sac), whereas the diploid cells constitute the embryo proper, resulting in a fetus derived entirely from the injected stem cell line.

Recently, we reported the derivation of iPSC lines that reproducibly generate adult mice via TEC1. These iPSC lines give rise to viable pups with efficiencies of 5-13%, which is comparable to ESCs3,4,7 and higher than that reported for most other iPSC lines8-12. These reports show that direct reprogramming can produce fully pluripotent iPSCs that match ESCs in their developmental potential and efficiency of generating pups in TEC tests. At present, it is not clear what distinguishes between fully pluripotent iPSCs and less potent lines13-15. Nor is it clear which reprogramming methods will produce these lines with the highest efficiency. Here we describe one method that produces fully pluripotent iPSCs and "all- iPSC" mice, which may be helpful for investigators wishing to compare the pluripotency of iPSC lines or establish the equivalence of different reprogramming methods.

Background

For regenerative therapy using induced pluripotent stem cell (iPSC) technology, cell type of origin to be reprogrammed should be chosen based on accessibility and reprogramming efficiency. Some studies report that iPSCs exhibited a preference for differentiation into their original cell lineages, while others did not. Therefore, the type of cell which is most appropriate as a source for iPSCs needs to be clarified.

Methodology/Principal Findings

Genetically matched human iPSCs from different origins were generated using bone marrow stromal cells (BMSCs) and dermal fibroblasts (DFs) of the same donor, and global gene expression profile, DNA methylation status, and differentiation properties into the chondrogenic and osteogenic lineage of each clone were analyzed. Although genome-wide profiling of DNA methylation suggested tissue memory in iPSCs, genes expressed differentially in BMSCs and DFs were equally silenced in our bona fide iPSCs. After cell-autonomous and induced differentiation, each iPSC clone exhibited various differentiation properties, which did not correlate with cell-of-origin.

Conclusions/Significance

The reprogramming process may remove the difference between DFs and BMSCs at least for chondrogenic and osteogenic differentiation. Qualified and genetically matched human iPSC clone sets established in this study are valuable resources for further basic study of clonal differences.

Stem cells have provided great hope for the treatment of a variety of human diseases. However, the molecular mechanisms underlying stem cell pluripotency, self-renewal, and differentiation remain to be unveiled. Epigenetic regulators, including histone deacetylases (HDACs), have been shown to coordinate with cell-intrinsic transcription factors and various signaling pathways to regulate stem cell pluripotency, self-renewal, and fate determination. This paper focuses on the role of HDACs in the proliferation and neuronal differentiation of neural stem cells and the application of HDAC inhibitors in reprogramming somatic cells to induced pluripotent stem cells (iPSCs). It promises to be an active area of future research.

The advent of induced pluripotent stem cells (iPSCs) has brought the goal of using patient-derived cells for tissue repair closer to reality. However, the mechanisms involved in reprogramming to a pluripotent state are still not clear. It is understood that reprogramming to pluripotency involves epigenetic remodeling and the reactivation of “core” pluripotency factors. However, little is known about the mechanisms involved in overcoming senescence while avoiding oncogenesis, the maintenance of self-renewal, and the regulation of the balance between pluripotency and differentiation. Here, we review recent advances in reprogramming technology and what is currently known about the mechanism of reprogramming to pluripotency. Work with patient-derived iPSCs is already providing new insights into the cellular and molecular mechanisms involved in human disease. Further advances in reprogramming technology should result in efficient methods to reprogram patient-derived cells into iPSCs for use in regenerative medicine.

Development of induced pluripotent stem cells (iPSCs) using forced expression of specific sets of transcription factors has changed the field of stem cell research extensively. Two important limitations for research application of embryonic stem cells (ESCs), namely, ethical and immunological issues, can be circumvented using iPSCs. Since the development of first iPSCs, tremendous effort has been directed to the development of methods to increase the efficiency of the process and to reduce the extent of genomic modifications associated with the reprogramming procedure. The established lineage-specific differentiation protocols developed for ESCs are being applied to iPSCs, as they have great potential in regenerative medicine for cell therapy, disease modeling either for drug development or for fundamental science, and, last but not least, toxicity testing. This paper reviews efforts aimed at practical development of iPSC differentiation to neural/cardiac lineages and further the use of these iPSCs-derived cells for drug development and toxicity testing.

Human pluripotent stem cells (PSCs), including embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), provide a dynamic tool for revealing early embryonic development, modeling pathological processes, and developing therapeutics through drug discovery and potential cell replacement. The first step toward the utilities of human PSCs is directed differentiation to functionally specialized cell tissue types. Following developmental principles, human ESCs, and lately iPSCs, have been effectively differentiated to region-and/or transmitter-specific neuronal and glial types, including cerebral glutamatergic, striatal γ-aminobutyric acid (GABA)-ergic, forebrain cholinergic, midbrain dopaminergic, and spinal motor neurons, as well as astrocytes and oligodendrocytes. These studies also reveal unique aspects of human cell biology, including intrinsically programmed developmental course, differential uses of transcription factors for neuroectoderm specification, and distinct responses to extracellular signals in regulating cell fate. Such information will be instrumental for translating biological findings to therapeutic development.

Immune rejection and risk of tumor formation are perhaps the greatest hurdles in the field of stem cell transplantation. Here, we report the generation of several lines of induced pluripotent stem cells (iPSCs) from Cynomolgus macaque (CM) skin fibroblasts carrying specific major histocompatibility complex (MHC) haplotypes. In order to develop a collection of MHC-matched iPSCs, we genotyped the MHC locus of 25 CM by microsatellite PCR analysis. Using retroviral infection of dermal skin fibroblasts, we generated several CM-iPSC lines carrying different haplotypes. We characterized the immunological properties of CM-iPSCs and demonstrated that CM-iPSCs can be induced to differentiate in vitro along specific neuronal populations, such as midbrain dopaminergic (DA) neurons. Midbrain-like DA neurons generated from CM-iPSCs integrated into the striatum of a rodent model of Parkinson’s disease (PD) and promoted behavioral recovery. Importantly, neither tumor formation nor inflammatory reactions were observed in the transplanted animals up to six months after transplantation. We believe that the generation and characterization of such histocompatible iPSCs will allow the pre-clinical validation of safety and efficacy of iPSCs for neurodegenerative diseases and several other human conditions in the field of regenerative medicine.

Background

Understanding how lineage choices are made during embryonic stem (ES) cell differentiation is critical for harnessing strategies for controlled production of therapeutic somatic cell types for cell transplantation and pharmaceutical drug screens. The in vitro generation of dopaminergic neurons, the type of cells lost in Parkinson's disease patients' brains, requires the inductive molecules sonic hedgehog and FGF8, or an unknown stromal cell derived inducing activity (SDIA). However, the exact identity of the responding cells and the timing of inductive activity that specify a dopaminergic fate in neural stem/progenitors still remain elusive.

Results

Using ES cells carrying a neuroepithelial cell specific vital reporter (Sox1-GFP) and FACS purification of Sox1-GFP neural progenitors, we have investigated the temporal aspect of SDIA mediated dopaminergic neuron specification during ES cell differentiation. Our results establish that SDIA induces a dopaminergic neuron fate in nascent neural stem or progenitor cells at, or prior to, Sox1 expression and does not appear to have further instructive role or neurotrophic activity during late neuronal differentiation of neural precursors. Furthermore, we show that dopaminergic neurons could be produced efficiently in a monolayer differentiation paradigm independent of SDIA activity or exogenous signalling molecules. In this case, the competence for dopaminergic neuron differentiation is also established at the level of Sox1 expression.

Conclusion

Dopaminergic neurons are specified early during mouse ES cell differentiation. The subtype specification seems to be tightly linked with the acquisition of a pan neuroectoderm fate.

Cell replacement therapy using embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) is a promising strategy for the treatment of neurologic diseases such as Parkinson's disease (PD). However, a limiting factor for effective cell transplantation is the low survival rate of grafted cells, especially neurons. In this study, we modified the host environment and investigated whether the simultaneous administration of soluble factors can improve the survival and differentiation of murine iPSC-derived dopaminergic (DA) neurons in host brains. With the goal of applying this technology in clinical settings in the near future, we selected drugs that were already approved for clinical use. The drugs included two commonly used anti-convulsants, valproic acid (VPA) and zonisamide (ZNS), and estradiol (E2), also known as biologically active estrogen. Following neural induction of murine iPSCs, we collected neural progenitor cells (NPCs) by sorting PSA-NCAM+ cells, then treated the PSA-NCAM+ cells with drugs for 4 days. An immunofluorescence study revealed that 0.01 mM and 0.1 mM of VPA and 10 nM of E2 increased the percentage of tyrosine hydroxylase+ (TH: a DA neuron marker) cells in vitro. Furthermore, 0.1 mM of VPA increased the percentage of TH+ cells that simultaneously express the midbrain markers FOXA2 and NURR1. Next, in order to determine the effects of the drugs in vivo, the iPSC-derived NPCs were transplanted into the striata of intact SD rats. The animals received intraperitoneal injections of one of the drugs for 4 weeks, then were subjected to an immunofluorescence study. VPA administration (150 mg/kg/daily) increased the number of NeuN+ post-mitotic neurons and TH+ DA neurons in the grafts. Furthermore, VPA (150 mg/kg/daily) and ZNS (30 mg/kg/daily) increased the number of TH+FOXA2+ midbrain DA neurons. These results suggest that the systemic administration of VPA and ZNS may improve the efficiency of cell replacement therapy using iPSCs to treat PD.

Recent breakthroughs in creating induced pluripotent stem cells (iPSCs) provide alternative means to obtain ES-like cells without destroying embryos by introducing four reprogramming factors (Oct3/4, Sox2, and Klf4/c-Myc or Nanog/ Lin28) into somatic cells. iPSCs are versatile tools for investigating early developmental processes and could become sources of tissues or cells for regenerative therapies. Here, for the first time, we describe a strategy to analyze genomics datasets of mouse embryonic fibroblasts (MEFs) and embryonic stem (ES) cells to identify genes constituting barriers to iPSC reprogramming. We further show that computational chemical biology combined with genomics analysis can be used to identify small molecules regulating reprogramming. Specific down-regulation by small interfering RNAs (siRNAs) of several key MEF-specific genes encoding proteins with catalytic or regulatory functions, including WISP1, PRRX1, HMGA2, NFIX, PRKG2, COX2, and TGFβ3, greatly increased reprogramming efficiency. Based on this rationale, we screened only 17 small molecules in reprogramming assays and discovered that the NSAID Nabumetone and the anti-cancer drug OHTM can generate iPS cells without Sox2. Nabumetone could also produce iPS cells in the absence of c-Myc or Sox2 without compromising self-renewal and pluripotency of derived iPS cells. In summary, we report a new concept of combining genomics and computational chemical biology to identify new drugs useful for iPSC generation. This hypothesis-driven approach provides an alternative to shot-gun screening and accelerates understanding of molecular mechanisms underlying iPS cell induction.

Oligodendrocytes are the myelinating cells of the central nervous system. For regenerative cell therapy in demyelinating diseases, there is significant interest in deriving a pure population of lineage-committed oligodendrocyte precursor cells (OPCs) for transplantation. OPCs are characterized by the activity of the transcription factor Olig2 and surface expression of a proteoglycan NG2. Using the GFP-Olig2 (G-Olig2) mouse embryonic stem cell (mESC) reporter line, we optimized conditions for the differentiation of mESCs into GFP+Olig2+NG2+ OPCs. In our protocol, we first describe the generation of embryoid bodies (EBs) from mESCs. Second, we describe treatment of mESC-derived EBs with small molecules: (1) retinoic acid (RA) and (2) a sonic hedgehog (Shh) agonist purmorphamine (Pur) under defined culture conditions to direct EB differentiation into the oligodendroglial lineage. By this approach, OPCs can be obtained with high efficiency (>80%) in a time period of 30 days. Cells derived from mESCs in this protocol are phenotypically similar to OPCs derived from primary tissue culture. The mESC-derived OPCs do not show the spiking property described for a subpopulation of brain OPCs in situ. To study this electrophysiological property, we describe the generation of spiking mESC-derived OPCs by ectopically expressing NaV1.2 subunit. The spiking and nonspiking cells obtained from this protocol will help advance functional studies on the two subpopulations of OPCs.