High-purity lineage selection of embryonic stem cell-derived neurons

Isolation and Enrichment of Defined Neural Cell Populations from Heterogeneous Neural Stem Cell Progeny

The renewable source of neural stem cells (NSCs) with multi-lineage differentiation capability toward neurons, astrocytes, and oligodendrocytes represents an ideal supply for cell therapy of central nervous system (CNS) diseases. In spite of this, the clinical use of NSCs is hampered by heterogeneity, poor neuronal cell yield, predominant astrocytic differentiation of NSC progeny, and possible uncontrolled proliferation and tumor formation upon transplantation. The ability to generate highly enriched and defined neural cell populations from the renewable source of NSCs might overcome many of these impediments and pave the way toward their successful clinical applications.Here, we describe a simple method for NSC differentiation and subsequent purification of neuronal progenitor cells, taking advantage of size and granularity differences between neuronal cells and other NSC progeny. This highly enriched neuronal cell population provides an invaluable source of cells for both in vitro and in vivo studies.

A single-cell Raman-based platform to identify developmental stages of human pluripotent stem cell-derived neurons

We developed a label-free and noninvasive single-cell Raman microspectroscopy (SCRM)-based platform to identify neural cell lineages derived from clinically relevant human induced pluripotent stem cells (hiPSCs). Through large-scale Raman spectral analysis, we can distinguish hiPSCs and hiPSC-derived neural cells using their intrinsic biochemical profile. We identified glycogen as a Raman biomarker for neuronal differentiation and validated the results using conventional glycogen detection assays. The parameters obtained from SCRM were processed by a novel machine learning method based on t-distributed stochastic neighbor embedding (t-SNE)-enhanced ensemble stacking, enabling highly accurate and robust cell classification. The platform and the proposed biomarker should also be applicable to other cell types and can shed light on developmental biology and glycogen metabolism disorders.

Stem cells with the capability to self-renew and differentiate into multiple cell derivatives provide platforms for drug screening and promising treatment options for a wide variety of neural diseases. Nevertheless, clinical applications of stem cells have been hindered partly owing to a lack of standardized techniques to characterize cell molecular profiles noninvasively and comprehensively. Here, we demonstrate that a label-free and noninvasive single-cell Raman microspectroscopy (SCRM) platform was able to identify neural cell lineages derived from clinically relevant human induced pluripotent stem cells (hiPSCs). By analyzing the intrinsic biochemical profiles of single cells at a large scale (8,774 Raman spectra in total), iPSCs and iPSC-derived neural cells can be distinguished by their intrinsic phenotypic Raman spectra. We identified a Raman biomarker from glycogen to distinguish iPSCs from their neural derivatives, and the result was verified by the conventional glycogen detection assays. Further analysis with a machine learning classification model, utilizing t-distributed stochastic neighbor embedding (t-SNE)-enhanced ensemble stacking, clearly categorized hiPSCs in different developmental stages with 97.5% accuracy. The present study demonstrates the capability of the SCRM-based platform to monitor cell development using high content screening with a noninvasive and label-free approach. This platform as well as our identified biomarker could be extensible to other cell types and can potentially have a high impact on neural stem cell therapy.

Cytosine-5 RNA Methylation Regulates Neural Stem Cell Differentiation and Motility

Loss-of-function mutations in the cytosine-5 RNA methylase NSUN2 cause neurodevelopmental disorders in humans, yet the underlying cellular processes leading to the symptoms that include microcephaly remain unclear. Here, we show that NSUN2 is expressed in early neuroepithelial progenitors of the developing human brain, and its expression is gradually reduced during differentiation of human neuroepithelial stem (NES) cells in vitro. In the developing Nsun2-/- mouse cerebral cortex, intermediate progenitors accumulate and upper-layer neurons decrease. Loss of NSUN2-mediated methylation of tRNA increases their endonucleolytic cleavage by angiogenin, and 5' tRNA fragments accumulate in Nsun2-/- brains. Neural differentiation of NES cells is impaired by both NSUN2 depletion and the presence of angiogenin. Since repression of NSUN2 also inhibited neural cell migration toward the chemoattractant fibroblast growth factor 2, we conclude that the impaired differentiation capacity in the absence of NSUN2 may be driven by the inability to efficiently respond to growth factors.

Characterization and isolation of immature neurons of the adult mouse piriform cortex

Physiological studies indicate that the piriform or primary olfactory cortex of adult mammals exhibits a high degree of synaptic plasticity. Interestingly, a subpopulation of cells in the layer II of the adult piriform cortex expresses neurodevelopmental markers, such as the polysialylated form of neural cell adhesion molecule (PSA-NCAM) or doublecortin (DCX). This study analyzes the nature, origin, and potential function of these poorly understood cells in mice. As previously described in rats, most of the PSA-NCAM expressing cells in layer II could be morphologically classified as tangled cells and only a small proportion of larger cells could be considered semilunar-pyramidal transitional neurons. Most were also immunoreactive for DCX, confirming their immature nature. In agreement with this, detection of PSA-NCAM combined with that of different cell lineage-specific antigens revealed that most PSA-NCAM positive cells did not co-express markers of glial cells or mature neurons. Their time of origin was evaluated by birthdating experiments with halogenated nucleosides performed at different developmental stages and in adulthood. We found that virtually all cells in this paleocortical region, including PSA-NCAM-positive cells, are born during fetal development. In addition, proliferation analyses in adult mice revealed that very few cells were cycling in layer II of the piriform cortex and that none of them was PSA-NCAM-positive. Moreover, we have established conditions to isolate and culture these immature neurons in the adult piriform cortex layer II. We find that although they can survive under certain conditions, they do not proliferate in vitro either. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 748-763, 2016.

Directed midbrain and spinal cord neurogenesis from pluripotent stem cells to model development and disease in a dish

Induction of specific neuronal fates is restricted in time and space in the developing CNS through integration of extrinsic morphogen signals and intrinsic determinants. Morphogens impose regional characteristics on neural progenitors and establish distinct progenitor domains. Such domains are defined by unique expression patterns of fate determining transcription factors. These processes of neuronal fate specification can be recapitulated in vitro using pluripotent stem cells. In this review, we focus on the generation of dopamine neurons and motor neurons, which are induced at ventral positions of the neural tube through Sonic hedgehog (Shh) signaling, and defined at anteroposterior positions by fibroblast growth factor (Fgf) 8, Wnt1, and retinoic acid (RA). In vitro utilization of these morphogenic signals typically results in the generation of multiple neuronal cell types, which are defined at the intersection of these signals. If the purpose of in vitro neurogenesis is to generate one cell type only, further lineage restriction can be accomplished by forced expression of specific transcription factors in a permissive environment. Alternatively, cell-sorting strategies allow for selection of neuronal progenitors or mature neurons. However, modeling development, disease and prospective therapies in a dish could benefit from structured heterogeneity, where desired neurons are appropriately synaptically connected and thus better reflect the three-dimensional structure of that region. By modulating the extrinsic environment to direct sequential generation of neural progenitors within a domain, followed by self-organization and synaptic establishment, a reductionist model of that brain region could be created. Here we review recent advances in neuronal fate induction in vitro, with a focus on the interplay between cell intrinsic and extrinsic factors, and discuss the implications for studying development and disease in a dish.

Isolation and enrichment of defined neural cell populations from heterogeneous neural stem cell progeny

The renewable source of neural stem cells (NSCs) with multi-lineage differentiation capability towards neurons, astrocytes, and oligodendrocytes represent an ideal supply for cell therapy of central nervous system (CNS) diseases. In spite of this, the clinical use of NSCs is hampered by heterogeneity, poor neuronal cell yield, predominant astrocytic differentiation of NSC progeny and possible uncontrolled proliferation, and tumor formation upon transplantation. The ability to generate highly enriched and defined neural cell populations from the renewable source of NSCs might overcome many of these impediments and pave the way towards their successful clinical applications. Here, we describe a simple method for NSC differentiation and subsequent purification of neuronal progenitor cells, taking advantage of size and granularity differences between neuronal cells and other NSC progeny. This highly enriched neuronal cell population provides an invaluable source of cells for both in vitro and in vivo studies.

Functional maturation of hPSC-derived forebrain interneurons requires an extended timeline and mimics human neural development

Directed differentiation from human pluripotent stem cells (hPSCs) has seen significant progress in recent years. However, most differentiated populations exhibit immature properties of an early embryonic stage, raising concerns about their ability to model and treat disease. Here, we report the directed differentiation of hPSCs into medial ganglionic eminence (MGE)-like progenitors and their maturation into forebrain type interneurons. We find that early-stage progenitors progress via a radial glial-like stem cell enriched in the human fetal brain. Both in vitro and posttransplantation into the rodent cortex, the MGE-like cells develop into GABAergic interneuron subtypes with mature physiological properties along a prolonged intrinsic timeline of up to 7 months, mimicking endogenous human neural development. MGE-derived cortical interneuron deficiencies are implicated in a broad range of neurodevelopmental and degenerative disorders, highlighting the importance of these results for modeling human neural development and disease.

Differentiation of human neural progenitor cells in functionalized hydrogel matrices

Hydrogel-based three-dimensional (3D) scaffolds are widely used in the field of regenerative medicine, translational medicine, and tissue engineering. Recently, we reported the effect of scaffold formation on the differentiation and survival of human neural progenitor cells (hNPCs) using PuraMatrix™ (RADA-16) scaffolds. Here, we were interested in the impact of PuraMatrix modified by the addition of short peptide sequences, based on a bone marrow homing factor and laminin. The culture and differentiation of the hNPCs in the modified matrices resulted in an approximately fivefold increase in neuronal cells. The examination of apoptotic and necrotic cells, as well as the level of the anti-apoptotic protein Bcl-2, indicates benefits for cells hosted in the modified formulations. In addition, we found a trend to lower proportions of apoptotic or necrotic neuronal cells in the modified matrices. Interestingly, the neural progenitor cell pool was increased in all the tested matrices in comparison to the standard 2D culture system, while no difference was found between the modified matrices. We conclude that a combination of elevated neuronal differentiation and a protective effect of the modified matrices underlies the increased proportion of neuronal cells.

Highly pure and expandable PSA-NCAM-positive neural precursors from human ESC and iPSC-derived neural rosettes

Homogeneous culture of neural precursor cells (NPCs) derived from human pluripotent stem cells (hPSCs) would provide a powerful tool for biomedical applications. However, previous efforts to expand mechanically dissected neural rosettes for cultivation of NPCs remain concerns regarding non-neural cell contamination. In addition, several attempts to purify NPCs using cell surface markers have not demonstrated the expansion capability of the sorted cells. In the present study, we show that polysialic acid-neural cell adhesion molecule (PSA-NCAM) is detected in neural rosette cells derived from hPSCs, and employ PSA-NCAM as a marker for purifying expandable primitive NPCs from the neural rosettes. PSA-NCAM-positive NPCs (termed hNPC^PSA-NCAM+) were isolated from the heterogeneous cell population of mechanically harvested neural rosettes using magnetic-based cell sorting. The hNPC^PSA-NCAM+ extensively expressed neural markers such as Sox1, Sox2, Nestin, and Musashi-1 (80∼98% of the total cells) and were propagated for multiple passages while retaining their primitive characteristics in our culture condition. Interestingly, PSA-NCAM-negative cells largely exhibited characteristics of neural crest cells. The hNPC^PSA-NCAM+ showed multipotency and responsiveness to instructive cues towards region-specific neuronal subtypes in vitro. When transplanted into the rat striatum, hNPC^PSA-NCAM+ differentiated into neurons, astrocytes, and oligodendrocytes without particular signs of tumorigenesis. Furthermore, Ki67-positive proliferating cells and non-neural lineage cells were rarely detected in the grafts of hNPC^PSA-NCAM+ compared to those of neural rosette cells. Our results suggest that PSA-NCAM-mediated cell isolation provides a highly expandable population of pure primitive NPCs from hPSCs that will lend themselves as a promising strategy for drug screening and cell therapy for neurodegenerative disorders.

Purification of immature neuronal cells from neural stem cell progeny

Large-scale proliferation and multi-lineage differentiation capabilities make neural stem cells (NSCs) a promising renewable source of cells for therapeutic applications. However, the practical application for neuronal cell replacement is limited by heterogeneity of NSC progeny, relatively low yield of neurons, predominance of astrocytes, poor survival of donor cells following transplantation and the potential for uncontrolled proliferation of precursor cells. To address these impediments, we have developed a method for the generation of highly enriched immature neurons from murine NSC progeny. Adaptation of the standard differentiation procedure in concert with flow cytometry selection, using scattered light and positive fluorescent light selection based on cell surface antibody binding, provided a near pure (97%) immature neuron population. Using the purified neurons, we screened a panel of growth factors and found that bone morphogenetic protein-4 (BMP-4) demonstrated a strong survival effect on the cells in vitro, and enhanced their functional maturity. This effect was maintained following transplantation into the adult mouse striatum where we observed a 2-fold increase in the survival of the implanted cells and a 3-fold increase in NeuN expression. Additionally, based on the neural-colony forming cell assay (N-CFCA), we noted a 64 fold reduction of the bona fide NSC frequency in neuronal cell population and that implanted donor cells showed no signs of excessive or uncontrolled proliferation. The ability to provide defined neural cell populations from renewable sources such as NSC may find application for cell replacement therapies in the central nervous system.

Potential sources of stem cells as a regenerative therapy for Parkinson's disease

Stem cells are believed to hold enormous promise as potential replacement therapy in the treatment of neurodegenerative diseases such as Parkinson's disease (PD). Stem cells were investigated to be the alternative therapeutic source capable of differentiating into dopamine (DA) neurons. Multiple important signaling factors were recorded for the induction of DA neuronal traits from mouse embryonic stem cells (ESCs) such as fibroblast growth factor 8, sonic hedgehog, and Wnt 1. Recent protocols were described for the differentiation of human ESCs into DA neurons, achieving high efficiency of DA neuronal derivation. Despite that, the use of human ESCs is still ethically controversial. The transcription factors necessary for DA neuron development from adult neural stem cells (NSCs), such as Pitx3, Nurr1, En-1, En-2, Lmx1a, Lmx1b, Msx1, and Ngn2, were investigated. In addition to replacement of lost DA neurons, adult NSCs were recorded to provide neuroprotective and neurogenic factors for the mesencephalon. In addition, induced pluripotent stem cells and bone marrow-derived mesenchymal stem cells represent reliable stem cell sources of DA neurons. Future studies are recommended to provide further insight into the regenerative capacity of stem cells needed for the treatment of PD.

Human ES and iPS cells as cell sources for the treatment of Parkinson's disease: current state and problems

Cell therapy using human embryonic stem cells (hESCs) is a promising therapeutic option for Parkinson's disease (PD), an incurable neurodegenerative disease. A prerequisite for clinical application of hESCs for PD is an efficient and strict differentiation of hESCs into midbrain dopamine (mDA) neuron-like cells, which would be directly translated into high effectiveness of the therapy with minimum risk of undesirable side effects. Due to fruitful efforts from many laboratories, a variety of strategies for improving efficiency of dopaminergic differentiation from hESCs have been developed, mostly by optimizing culture conditions, genetic modification, and modulating intracellular signaling pathways. The rapid advances in the fields of dopaminergic differentiation of hESCs, prevention of tumor formation, and establishment of safe human induced pluripotent stem cells (hiPSCs) would open the door to highly effective, tumor-free, and immune rejection-free cell therapy for PD in the near future.

CD15, CD24, and CD29 define a surface biomarker code for neural lineage differentiation of stem cells

Identification and use of cell surface cluster of differentiation (CD) biomarkers have enabled much scientific and clinical progress. We identify a CD surface antigen code for the neural lineage based on combinatorial flow cytometric analysis of three distinct populations derived from human embryonic stem cells: (1) CD15(+)/CD29(HI)/CD24(LO) surface antigen expression defined neural stem cells; (2) CD15(-)/CD29(HI)/CD24(LO) revealed neural crest-like and mesenchymal phenotypes; and (3) CD15(-)/CD29(LO)/CD24(HI) selected neuroblasts and neurons. Fluorescence-activated cell sorting (FACS) for the CD15(-)/CD29(LO)/CD24(HI) profile reduced proliferative cell types in human embryonic stem cell differentiation. This eliminated tumor formation in vivo, resulting in pure neuronal grafts. In conclusion, combinatorial CD15/CD24/CD29 marker profiles define neural lineage development of neural stem cell, neural crest, and neuronal populations from human stem cells. We believe this set of biomarkers enables analysis and selection of neural cell types for developmental studies and pharmacological and therapeutic applications.

Adult periodontal-derived neural progenitor and stem cells. Institut fur Molekulare Diagnostik und Innovative Therapie: WO2008031451

The application is in the field of neural stem cells (NSCs) and cellular therapy. It aims to identify and characterize neural progenitor and stem cells from adult periodontal tissue. Neural progenitor and stem cells were isolated and characterized from periodontal tissue originating from biopsies of adult patients. Adult human periodontal-derived neural progenitor and stem cells can be induced to differentiate into neuronal and glial cells, osteoblasts and cells of the periodontium. They survive and integrate when transplanted into organotypic hippocampal slice cultures. The application claims the use of periodontal neural progenitor and stem cells for cellular therapy, particularly for the treatment of the periodontal diseases and neurodegenerative diseases and neurological injuries. Periodontal tissue can be harvested with minimal invasive procedures from the patient himself, providing a promising source of tissue for NSC-based therapy and autologous transplantation.

Efficient production of mesencephalic dopamine neurons by Lmx1a expression in embryonic stem cells

Signaling factors involved in CNS development have been used to control the differentiation of embryonic stem cells (ESCs) into mesencephalic dopamine (mesDA) neurons, but tend to generate a limited yield of desired cell type. Here we show that forced expression of Lmx1a, a transcription factor functioning as a determinant of mesDA neurons during embryogenesis, effectively can promote the generation of mesDA neurons from mouse and human ESCs. Under permissive culture conditions, 75%-95% of mouse ESC-derived neurons express molecular and physiological properties characteristic of bona fide mesDA neurons. Similar to primary mesDA neurons, these cells integrate and innervate the striatum of 6-hydroxy dopamine lesioned neonatal rats. Thus, the enriched generation of functional mesDA neurons by forced expression of Lmx1a may be of future importance in cell replacement therapy of Parkinson disease.

Derivation of homogeneous GABAergic neurons from mouse embryonic stem cells

Embryonic stem cells (ESCs) promise an unlimited source of defined cells for cell transplantation therapy, while protocols for derivation of homogeneous populations of desirable cell types are yet to be developed and/or refined. Gamma aminobutyric acid (GABA) is a major inhibitory neurotransmitter in the central nervous system, and disturbed GABAergic signaling is associated with a host of neurological conditions. We developed a simple ES cell differentiation protocol which led to the production of uniform GABAergic neurons in approximately 2 weeks. The differentiation protocol involved treatment of embryoid bodies (EBs) with high concentrations (10(-5)-10(-)(4) M) of all-trans-retinoic acid (RA) for 3 days. After plating these EBs on attached dishes in neural supportive medium, 93-96% of the cells became GABA-positive neurons in 7-11 days. These cells also expressed immature neuronal markers with voltage-gated delayed rectifier potassium currents, suggesting that they were immature GABAergic neurons. The technology may have implications for modeling and treatment of GABAergic signaling-related diseases and injuries.

Neural stem cells: mechanisms of fate specification and nuclear reprogramming in regenerative medicine

Recently, intense interest in the potential use of neural stem cells (NSC) in the clinical therapy of brain disease and injury has resulted in rapid progress in research on the properties of NSC, their innate and directed differentiation potential and the induced reprogramming of differentiated somatic cells to revert to a pluripotent NSC-like state. The aim of this review is to give an overview of our current operational definitions of the NSC lineage, the growing understanding of extrinsic and intrinsic mechanisms, including heritable but reversible epigenetic chromatin modifications that regulate the maintenance and differentiation of NSC in vivo, and to emphasize ground-breaking efforts of cellular reprogramming with the view to generating patient-specific stem cells for cell replacement therapy. This is set against a summary of current practical procedures for the isolation, research and application of NSC, and of the state of the art in NSC-based regenerative medicine of the nervous system. Both provide the backdrop for the translation of recent findings into innovative clinical applications, with the hope of increasing the safety, efficiency and ethical acceptability of NSC-based therapies in the near future.

Stem cell sources for regenerative medicine

Tissue-resident stem cells or primitive progenitors play an integral role in homeostasis of most organ systems. Recent developments in methodologies to isolate and culture embryonic and somatic stem cells have many new applications poised for clinical and preclinical trials, which will enable the potential of regenerative medicine to be realized. Here, we overview the current progress in therapeutic applications of various stem cells and discuss technical and social hurdles that must be overcome for their potential to be realized.

The mouse F3/contactin glycoprotein: structural features, functional properties and developmental significance of its regulated expression

F3/Contactin is an immunoglobulin superfamily component expressed in the nervous tissue of several species. Here we focus on the structural and functional properties of its mouse relative, on the mechanisms driving its regulated expression and on its developmental role. F3/Contactin is differentially expressed in distinct populations of central and peripheral neurons and in some non-neuronal cells. Accordingly, the regulatory region of the underlying gene includes promoter elements undergoing differential activation, associated with an intricate splicing profile, indicating that transcriptional and posttranscriptional mechanisms contribute to its expression. Transgenic models allowed to follow F3/Contactin promoter activation in vivo and to modify F3/Contactin gene expression under a heterologous promoter, which resulted in morphological and functional phenotypes. Besides axonal growth and pathfinding, these concerned earlier events, including precursor proliferation and commitment. This wide role in neural ontogenesis is consistent with the recognized interaction of F3/Contactin with developmental control genes belonging to the Notch pathway.

Neural commitment of embryonic stem cells: molecules, pathways and potential for cell therapy

The study of neuronal differentiation of embryonic stem cells has raised major interest over recent years. It allows a better understanding of fundamental aspects of neurogenesis and, at the same time, the generation of neurons as tools for various applications ranging from drug testing to cell therapy and regenerative medicine. Since the first report of human embryonic stem (ES) cells derivation, many studies have shown the possibility of directing their differentiation towards neurons. However, there are still many challenges ahead, including gaining a better understanding of the mechanisms involved and developing techniques to allow the generation of homogeneous neuronal and glial subtypes. We review the current state of knowledge of embryonic neurogenesis which has been acquired from animal models and discuss its translation into in vitro strategies of neuronal differentiation of ES cells. We also highlight several aspects of current protocols which need to be optimized to generate high-quality embryonic stem cell-derived neuronal precursors suitable for clinical applications. Finally, we discuss the potential of embryonic stem cell-derived neurons for cell replacement therapy in several central nervous system diseases.

Klf5 is involved in self-renewal of mouse embryonic stem cells

Self-renewal of embryonic stem cells (ESCs) is maintained by a complex regulatory mechanism involving transcription factors Oct3/4 (Pou5f1), Nanog and Sox2. Here, we report that Klf5, a Zn-finger transcription factor of the Kruppel-like family, is involved in ESC self-renewal. Klf5 is expressed in mouse ESCs, blastocysts and primordial germ cells, and its knockdown by RNA interference alters the molecular phenotype of ESCs, thereby preventing their correct differentiation. The ability of Klf5 to maintain ESCs in the undifferentiated state is supported by the finding that differentiation of ESCs is prevented when Klf5 is constitutively expressed. Maintenance of the undifferentiated state by Klf5 is, at least in part, due to the control of Nanog and Oct3/4 transcription, because Klf5 directly binds to the promoters of these genes and regulates their transcription.

Nucleofection of human embryonic stem cells

Human embryonic stem cells (HESCs) are widely used as a model system for human cell type specification. Genetic modification forms a valuable tool for HESC technology, as it provides the basis for lineage selection, i.e., the purification of a specific cell type after differentiation. Electroporation is an efficient way to transfect HESCs. Nucleofection is an electroporation-based transfection technique which utilizes cell-type-specific buffer solutions and specific electric settings. Customization of these two parameters has been proven to result in highly efficient gene transfer even in hard-to-transfect cells. We can show that nucleofection surpasses conventional electroporation in efficiency and decreases the experimental effort for transfection of HESCs.

Lineage selection of functional and cryopreservable human embryonic stem cell-derived neurons

A major prerequisite for the biomedical application of human embryonic stem cells (hESC) is the derivation of defined and homogeneous somatic cell types. Here we present a human doublecortin (DCX) promoter-based lineage-selection strategy for the generation of purified hESC-derived immature neurons. After transfection of hESC-derived neural precursors with a DCX-enhanced green fluorescent protein construct, fluorescence-activated cell sorting enables the enrichment of immature human neurons at purities of up to 95%. Selected neurons undergo functional maturation and are able to establish synaptic connections. Considering that the applicability of purified hESC-derived neurons would largely benefit from an efficient cryopreservation technique, we set out to devise defined freezing conditions involving caspase inhibition, which yield post-thaw recovery rates of up to 83%. Combined with our lineage-selection procedure this cryopreservation technique enables the generation of human neurons in a ready-to-use format for a large variety of biomedical applications.

Embryonic stem cell-derived Pitx3-enhanced green fluorescent protein midbrain dopamine neurons survive enrichment by fluorescence-activated cell sorting and function in an animal model of Parkinson's disease

Both fetal ventral mesencephalic (VM) and embryonic stem (ES) cell-derived dopamine neurons have been used successfully to correct behavioral responses in animal models of Parkinson's disease. However, grafts derived from fetal VM cells or from ES cells contain multiple cell types, and the majority of these cells are not dopamine neurons. Isolation of ES cell-derived dopamine neurons and subsequent transplantation would both elucidate the capacity of these neurons to provide functional input and also further explore an efficient and safer use of ES cells for the treatment of Parkinson's disease. Toward this goal, we used a Pitx3-enhanced green fluorescent protein (Pitx3-eGFP) knock-in mouse blastocyst-derived embryonic stem (mES) cell line and fluorescence-activated cell sorting (FACS) to select and purify midbrain dopamine neurons. Initially, the dopaminergic marker profile of intact Pitx3-eGFP mES cultures was evaluated after differentiation in vitro. eGFP expression overlapped closely with that of Pitx3, Nurr1, Engrailed-1, Lmx1a, tyrosine hydroxylase (TH), l-aromatic amino acid decarboxylase (AADC), and vesicular monoamine transporter 2 (VMAT2), demonstrating that these cells were of a midbrain dopamine neuron character. Furthermore, postmitotic Pitx3-eGFP(+) dopamine neurons, which constituted 2%-5% of all live cells in the culture after dissociation, could be highly enriched to >90% purity by FACS, and these isolated neurons were viable, extended neurites, and maintained a dopaminergic profile in vitro. Transplantation to 6-hydroxydopamine-lesioned rats showed that an enriched dopaminergic population could survive and restore both amphetamine- and apomorphine-induced functions, and the grafts contained large numbers of midbrain dopamine neurons, which innervated the host striatum. Disclosure of potential conflicts of interest is found at the end of this article.

Electrophysiological evaluation of engrafted stem cell-derived neurons

Recent advances in the neural stem cell field have provided a wealth of methods for generating large amounts of purified neuronal precursor cells. It has become a question of paramount importance to determine whether these cells integrate and interact with established neural circuitry after engraftment. In principle, neurons have to fulfill three basic functions: receive incoming signals via synapses, compute and forward processed information to other neurons or effector cells. It is anticipated that functionally integrating stem cell-derived donor neurons perform accordingly. Here we provide protocols for the efficient electrophysiological evaluation of engrafted cells and highlight current limitations thereof.

High-throughput identification of genes promoting neuron formation and lineage choice in mouse embryonic stem cells

The potential of embryonic stem cells to differentiate to all cell types makes them an attractive model for development and a potential source of cells for transplantation therapies. Candidate approaches have identified individual genes and proteins that promote the differentiation of embryonic stem cells to desired fates. Here, we describe a rapid large-scale screening strategy for the identification of genes that influence the pluripotency and differentiation of embryonic stem cells to specific fates, and we use this approach to identify genes that induce neuron formation. The power of the strategy is validated by the fact that, of the 15 genes that resulted in the largest increase in neuron number, 8 have previously been implicated in neuronal differentiation or survival, whereas 7 represent novel genes or known genes not previously implicated in neuronal development. This is a simple, fast, and generally applicable strategy for the identification of genes promoting the formation of any specific cell type from embryonic stem cells. Disclosure of potential conflicts of interest is found at the end of this article.

Bone morphogenetic protein-mediated modulation of lineage diversification during neural differentiation of embryonic stem cells

Embryonic stem cells (ES cells) can give rise to a broad spectrum of neural cell types. The biomedical application of ES cells will require detailed knowledge on the role of individual factors modulating fate specification during in vitro differentiation. Bone morphogenetic proteins (BMPs) are known to exert a multitude of diverse differentiation effects during embryonic development. Here, we show that exposure to BMP2 at distinct stages of neural ES cell differentiation can be used to promote specific cell lineages. During early ES cell differentiation, BMP2-mediated inhibition of neuroectodermal differentiation is associated with an increase in mesoderm and smooth muscle differentiation. In fibroblast growth factor 2-expanded ES cell-derived neural precursors, BMP2 supports the generation of neural crest phenotypes, and, within the neuronal lineage, promotes distinct subtypes of peripheral neurons, including cholinergic and autonomic phenotypes. BMP2 also exerts a density-dependent promotion of astrocyte differentiation at the expense of oligodendrocyte formation. Experiments involving inhibition of the serine threonine kinase FRAP support the notion that these effects are mediated via the JAK/STAT pathway. The preservation of diverse developmental BMP2 effects in differentiating ES cell cultures provides interesting prospects for the enrichment of distinct neural phenotypes in vitro.

Fluorescence-activated single cell sorting of human embryonic stem cells

Human embryonic stem cells (hESC) are the subject of intense investigation for use in regenerative medicine, in toxicity testing, and as models for the study of human development. Automated cell sorting will enhance the isolation of homogenous pools of differentiated hESCs both for basic studies and for therapeutic applications. Sorting could also be used to deplete undifferentiated, potentially tumourigenic cells. However, hESCs are sensitive to single cell disaggregation and recover poorly when plated at clonal density. Here we report a method for successful semi-automated single cell sorting of hESCs. This method utilizes an ES-specific promoter-transgene construct and automated FACS-based single cell sorting and plating. Clonal recovery in physiologic oxygen (2%) was increased fourfold over room oxygen (21%; p < 0.01). This automated protocol will help to realize proposed hESC strategies that are hampered by low throughput and poor yields.

Merging fields: stem cells in neurogenesis, transplantation, and disease modeling

Traditionally, applied stem cell research has been segregating into strategies aiming at endogenous repair and cell transplantation. Recent advances in both fields have unraveled unexpected potential for synergy between these disparate fields. The increasing dissection of the step-wise integration of adult-born neurons into an established brain circuitry provides a highly informative blueprint for the functional incorporation of grafted neurons into a host brain. On the other hand, in vitro recapitulation of developmental differentiation cascades permits the de novo generation of various neural cell types from pluripotent embryonic stem (ES) cells. Advanced tools in stem cell engineering enable not only genetic selection and instruction of disease-specific donor cells for neural replacement but also the exploitation of stem cells as transgenic cellular model systems for human diseases. In a comparative approach we here illuminate the functional integration of neurons derived from endogenous and transplanted stem cells, the evolving technologies for advanced stem cell engineering and the impact of cloned and mutated stem cells on disease modeling.

Stage-specific conditional mutagenesis in mouse embryonic stem cell-derived neural cells and postmitotic neurons by direct delivery of biologically active Cre recombinase

Conditional mutagenesis using Cre/loxP recombination is a powerful tool to investigate genes involved in neural development and function. However, the efficient delivery of biologically active Cre recombinase to neural cells, particularly to postmitotic neurons, represents a limiting factor. In this study, we devised a protocol enabling highly efficient conditional mutagenesis in ESC-derived neural progeny. Using a stepwise in vitro differentiation paradigm, we demonstrate that recombinant cell-permeable Cre protein can be used to efficiently induce recombination at defined stages of neural differentiation. Recombination rates of more than 90% were achieved in multipotent pan-neural and glial precursors derived from the Z/EG reporter mouse ESC line, in which Cre recombination activates enhanced green fluorescent proteinexpression. Recombined precursor cells displayed a normal phenotype and were able to differentiate into neurons and/or glial cells, indicating that Cre treatment has no overt side effects on proliferation and neural differentiation. Our data further demonstrate that recombination via Cre protein transduction is not restricted to dividing cells but can even be applied to postmitotic neurons. The ability to conduct Cre/loxP recombination at defined stages of stem cell differentiation in an expression-independent manner provides new prospects for studying the role of individual genes under stringent temporal control.

Neural stem cell systems: diversities and properties after transplantation in animal models of diseases

Currently available effective treatments of the diseased or damaged central nervous system (CNS) are restricted to a limited pharmacological relief of symptoms or those given to avoid further damage. Therefore the search is on for treatments that can restore function in the CNS. During recent years replacement of damaged neurons by cell transplantation is being enthusiastically explored as a potential treatment for many neurodegenerative diseases, stroke and traumatic brain injury. Several references in both scientific journals and popular newspapers concerning different types of cultured stem cells, potentially exploitable to treat pathological conditions of the brain, raise important questions pertinent to the fundamental and realistic differences between grafts of primary neural cells and the transplantation of in vitro expanded neural stem cells (NSCs). Our aim is to review the available information on the grafting of different NSC types into the adult rodent brain, focusing on critical aspects for the development of clinical therapies to replace damaged neurons.