Embryonic Stem Cells for Neural Replacement Therapy: Prospects and Challenges

Hydrogels for central nervous system therapeutic strategies

The central nervous system shows a limited regenerative capacity, and injuries or diseases, such as those in the spinal, brain and retina, are a great problem since current therapies seem to be unable to achieve good results in terms of significant functional recovery. Different promising therapies have been suggested, the aim being to restore at least some of the lost functions. The current review deals with the use of hydrogels in developing advanced devices for central nervous system therapeutic strategies. Several approaches, involving cell-based therapy, delivery of bioactive molecules and nanoparticle-based drug delivery, will be first reviewed. Finally, some examples of injectable hydrogels for the delivery of bioactive molecules in central nervous system will be reported, and the key features as well as the basic principles in designing multifunctional devices will be described.

Engineered N-cadherin and L1 biomimetic substrates concertedly promote neuronal differentiation, neurite extension and neuroprotection of human neural stem cells

We investigated the design of neurotrophic biomaterial constructs for human neural stem cells, guided by neural developmental cues of N-cadherin and L1 adhesion molecules. Polymer substrates fabricated either as two-dimensional (2-D) films or three-dimensional (3-D) microfibrous scaffolds were functionalized with fusion chimeras of N-cadherin-Fc alone and in combination with L1-Fc, and the effects on differentiation, neurite extension and survival of H9 human-embryonic-stem-cell-derived neural stem cells (H9-NSCs) were quantified. Combinations of N-cadherin and L1-Fc co-operatively enhanced neuronal differentiation profiles, indicating the critical nature of the two complementary developmental cues. Notably, substrates presenting low levels of N-cadherin-Fc concentrations, combined with proportionately higher L1-Fc concentration, most enhanced neurite outgrowth and the degree of MAP2+ and neurofilament-M+ H9-NSCs. Low N-cadherin-Fc alone promoted improved cell survival following oxidative stress, compared to higher concentrations of N-cadherin-Fc alone or combinations with L1-Fc. Pharmacological and antibody blockage studies revealed that substrates presenting low levels of N-cadherin are functionally competent so long as they elicit a threshold signal mediated by homophilic N-cadherin and fibroblast growth factor signaling. Overall, these studies highlight the ability of optimal combinations of N-cadherin and L1 to recapitulate a "neurotrophic" microenvironment that enhances human neural stem cell differentiation and neurite outgrowth. Additionally, 3-D fibrous scaffolds presenting low N-cadherin-Fc further enhanced the survival of H9-NSCs compared to equivalent 2-D films. This indicates that similar biofunctionalization approaches based on N-cadherin and L1 can be translated to 3-D "transplantable" scaffolds with enhanced neurotrophic behaviors. Thus, the insights from this study have fundamental and translational impacts for neural-stem-cell-based regenerative medicine.

Noggin versus basic fibroblast growth factor on the differentiation of human embryonic stem cells

The difference between Noggin and basic fibroblast growth factor for the neural precursor differentiation from human embryonic stem cells has not been studied. In this study, 100 μg/L Noggin or 20 μg/L basic fibroblast growth factor in serum-free neural induction medium was used to differentiate human embryonic stem cells H14 into neural precursors using monolayer differentiation. Two weeks after induction, significantly higher numbers of neural rosettes formed in the Noggin-induced group than the basic fibroblast growth factor-induced group, as detected by phase contrast microscope. Immunofluorescence staining revealed expression levels of Nestin, β-III Tubulin and Sox-1 were higher in the induced cells and reverse-transcription PCR showed induced cells expressed Nestin, Sox-1 and Neurofilament mRNA. Protein and mRNA expression in the Noggin-induced group was increased compared with the basic fibroblast growth factor-induced group. Noggin has a greater effect than basic fibroblast growth factor on the induction of human embryonic stem cell differentiation into neural precursors by monolayer differentiation, as Noggin accelerates and increases the differentiation of neural precursors.

Optical control of muscle function by transplantation of stem cell-derived motor neurons in mice

Damage to the central nervous system caused by traumatic injury or neurological disorders can lead to permanent loss of voluntary motor function and muscle paralysis. Here, we describe an approach that circumvents central motor circuit pathology to restore specific skeletal muscle function. We generated murine embryonic stem cell-derived motor neurons that express the light-sensitive ion channel channelrhodopsin-2, which we then engrafted into partially denervated branches of the sciatic nerve of adult mice. These engrafted motor neurons not only reinnervated lower hind-limb muscles but also enabled their function to be restored in a controllable manner using optogenetic stimulation. This synthesis of regenerative medicine and optogenetics may be a successful strategy to restore muscle function after traumatic injury or disease.

Stem cell therapy for neonatal brain injury: perspectives and challenges

Cerebral palsy is a major health problem caused by brain damage during pregnancy, delivery, or the immediate postnatal period. Perinatal stroke, intraventricular hemorrhage, and asphyxia are the most common causes of neonatal brain damage. Periventricular white matter damage (periventricular leukomalacia) is the predominant form in premature infants and the most common antecedent of cerebral palsy. Stem cell treatment has proven effective in restoring injured organs and tissues in animal models. The potential of stem cells for self-renewal and differentiation translates into substantial neuroprotection and neuroregeneration in the animal brain, with minimal risks of rejection and side effects. Stem cell treatments described to date have used neural stem cells, embryonic stem cells, mesenchymal stem cells, umbilical cord stem cells, and induced pluripotent stem cells. Most of these treatments are still experimental. In this review, we focus on the efficacy of stem cell therapy in animal models of cerebral palsy, and discuss potential implications for current and future clinical trials.

Similarly derived and cultured hESC lines show variation in their developmental potential towards neuronal cells in long-term culture

BACKGROUND

Human embryonic stem cells (hESCs) can differentiate into any human cell type, including CNS cells, and thus have high potential in regenerative medicine. Several protocols exist for neuronal differentiation of hESCs, which do not necessarily work for all hESC lines.

MATERIALS & METHODS

We tested the differentiation capacity of four similarly derived and cultured hESC lines (HS181, HS360, HS362 and HS401) in suspension culture in relatively simple neural differentiation medium for up to 20 weeks.

RESULTS

All the hESC lines differentiated into neuronal cells, but in a line-dependent manner. Using our method, the HS181- and HS360-derived neurospheres differentiated in vitro into pure neuronal cell populations within 6 weeks, whereas HS362 and HS401 reached their peak of differentiation in 12 weeks, but never produced pure neuronal cell populations using the present method. The withdrawal of FGF from suspension culture increased the in vitro differentiation potential. The hESC-derived neurospheres formed functional neuronal networks when replated on a microelectrode array and responded as expected to pharmacologic modulation.

CONCLUSION

Simple neurosphere culture is a suitable method for producing hESC-derived neuronal cells that can form functional neuronal networks from a number of hESC lines. The variation in the differentiation potential of hESC lines into neuronal cells must be carefully considered by those comparing various differentiation methods and designing transplantation therapies for neuronal disorders.

The pregnancy hormones human chorionic gonadotropin and progesterone induce human embryonic stem cell proliferation and differentiation into neuroectodermal rosettes

INTRODUCTION

The physiological signals that direct the division and differentiation of the zygote to form a blastocyst, and subsequent embryonic stem cell division and differentiation during early embryogenesis, are unknown. Although a number of growth factors, including the pregnancy-associated hormone human chorionic gonadotropin (hCG) are secreted by trophoblasts that lie adjacent to the embryoblast in the blastocyst, it is not known whether these growth factors directly signal human embryonic stem cells (hESCs).

METHODS

Here we used hESCs as a model of inner cell mass differentiation to examine the hormonal requirements for the formation of embryoid bodies (EB's; akin to blastulation) and neuroectodermal rosettes (akin to neurulation).

RESULTS

We found that hCG promotes the division of hESCs and their differentiation into EB's and neuroectodermal rosettes. Inhibition of luteinizing hormone/chorionic gonadotropin receptor (LHCGR) signaling suppresses hESC proliferation, an effect that is reversed by treatment with hCG. hCG treatment rapidly upregulates steroidogenic acute regulatory protein (StAR)-mediated cholesterol transport and the synthesis of progesterone (P4). hESCs express P4 receptor A, and treatment of hESC colonies with P4 induces neurulation, as demonstrated by the expression of nestin and the formation of columnar neuroectodermal cells that organize into neural tubelike rosettes. Suppression of P4 signaling by withdrawing P4 or treating with the P4-receptor antagonist RU-486 inhibits the differentiation of hESC colonies into EB's and rosettes.

CONCLUSIONS

Our findings indicate that hCG signaling via LHCGR on hESC promotes proliferation and differentiation during blastulation and neurulation. These findings suggest that trophoblastic hCG secretion and signaling to the adjacent embryoblast could be the commencement of trophic support by placental tissues in the growth and development of the human embryo.

Specification of region-specific neurons including forebrain glutamatergic neurons from human induced pluripotent stem cells

Background

Directed differentiation of human induced pluripotent stem cells (hiPSC) into functional, region-specific neural cells is a key step to realizing their therapeutic promise to treat various neural disorders, which awaits detailed elucidation.

Methodology/Principal Findings

We analyzed neural differentiation from various hiPSC lines generated by others and ourselves. Although heterogeneity in efficiency of neuroepithelial (NE) cell differentiation was observed among different hiPSC lines, the NE differentiation process resembles that from human embryonic stem cells (hESC) in morphology, timing, transcriptional profile, and requirement for FGF signaling. NE cells differentiated from hiPSC, like those from hESC, can also form rostral phenotypes by default, and form the midbrain or spinal progenitors upon caudalization by morphogens. The rostrocaudal neural progenitors can further mature to develop forebrain glutamatergic projection neurons, midbrain dopaminergic neurons, and spinal motor neurons, respectively. Typical ion channels and action potentials were recorded in the hiPSC-derived neurons.

Conclusions/Significance

Our results demonstrate that hiPSC, regardless of how they were derived, can differentiate into a spectrum of rostrocaudal neurons with functionality, which supports the considerable value of hiPSC for study and treatment of patient-specific neural disorders.

Stromal cell-secreted factors promote the survival of embryonic stem cell-derived early neural stem/progenitor cells via the activation of MAPK and PI3K-Akt pathways

Neural stem/progenitor cells (NS/PCs) have been studied extensively with the hope of using them clinically to repair the damaged central nervous system. However, little is known about the signals that regulate the proliferation, survival, and differentiation of NS/PCs in early development. To clarify the underlying mechanisms, we took advantage of an in vitro ES cell differentiation system from which we can obtain neurospheres containing NS/PCs with characteristics of the early caudal neural tube, by treating embryoid bodies (EBs) with a low concentration of retinoic acid (RA). We found that conditioned medium from the PA6 stromal cell line (PA6CM) increased the efficiency of neurosphere formation by suppressing apoptosis and promoting the survival of the NS/PCs. PA6CM also induced the phosphorylation of Erk1/2 and Akt1 in cells derived from the EBs. Furthermore, inhibitors of the MAPK and PI3K-Akt signaling pathways, U0126 and LY294002, attenuated the effects of PA6CM, significantly increasing the number of apoptotic cells and decreasing the number of viable cells among the ES cell-derived NS/PCs. Thus, PA6CM appears to contain soluble factors that promote the survival of ES cell-derived early NS/PCs through the activation of the MAPK and PI3K-Akt pathways.

Differential processing of amyloid-beta precursor protein directs human embryonic stem cell proliferation and differentiation into neuronal precursor cells

The amyloid-beta precursor protein (AbetaPP) is a ubiquitously expressed transmembrane protein whose cleavage product, the amyloid-beta (Abeta) protein, is deposited in amyloid plaques in neurodegenerative conditions such as Alzheimer disease, Down syndrome, and head injury. We recently reported that this protein, normally associated with neurodegenerative conditions, is expressed by human embryonic stem cells (hESCs). We now report that the differential processing of AbetaPP via secretase enzymes regulates the proliferation and differentiation of hESCs. hESCs endogenously produce amyloid-beta, which when added exogenously in soluble and fibrillar forms but not oligomeric forms markedly increased hESC proliferation. The inhibition of AbetaPP cleavage by beta-secretase inhibitors significantly suppressed hESC proliferation and promoted nestin expression, an early marker of neural precursor cell (NPC) formation. The induction of NPC differentiation via the non-amyloidogenic pathway was confirmed by the addition of secreted AbetaPPalpha, which suppressed hESC proliferation and promoted the formation of NPCs. Together these data suggest that differential processing of AbetaPP is normally required for embryonic neurogenesis.

Differentiation of neural precursors and dopaminergic neurons from human embryonic stem cells

Directed differentiation of human embryonic stem cells (hESCs) to a functional cell type, including neurons, is the foundation for application of hESCs. We describe here a reproducible, chemically defined protocol that allows directed differentiation of hESCs to nearly pure neuroectodermal cells and neurons. First, hESC colonies are detached from mouse fibroblast feeder layers and form aggregates to initiate the differentiation procedure. Second, after 4 days of suspension culture, the ESC growth medium is replaced with neural induction medium to guide neuroectodermal specification. Third, the differentiating hESC aggregates are attached onto the culture surface at day 6-7, where columnar neural epithelial cells appear and organize into rosettes. Fourth, the neural rosettes are enriched by detaching rosettes and leaving the peripheral flat cells attached and expanded as neuroepithelial aggregates in the same medium. Finally, the neuroepithelial aggregates are dissociated and differentiated to nearly pure neurons. This stepwise differentiation protocol results in the generation of primitive neuroepithelia at day 8-10, neural progenitors at the second and third week, and postmitotic neurons at the fourth week, which mirrors the early phase of neural development in a human embryo. Identification of the primitive neuroepithelial cells permits efficient patterning of region-specific progenitors and neuronal subtypes such as midbrain dopaminergic neurons.

Human embryonic stem cells: a potential source of transplantable neural progenitor cells

The primary therapeutic goal of embryonic stem cell (ESC) research is cell replacement therapy. During the last decade, great strides have been made in developing in vitro protocols for differentiating human ESCs into neuroepithelial progenitors. More recent progress has been made in further directing them into becoming cells with specialized regional and neurotransmitter identities, such as midbrain dopaminergic and spinal motor neurons. Along with directed differentiation, other current efforts are aimed at efficient enrichment, avoidance of immune rejection, demonstration of functional integration, genetic modification to regulate neurotransmitter and factor release, directed axon growth, in vivo cell tracking, and measures to ensure safety. This review will focus on the potential of ESCs as a source of transplantable cells for use in cell replacement therapy.

Temporal and epigenetic regulation of neurodevelopmental plasticity

The anticipated therapeutic uses of neural stem cells depend on their ability to retain a certain level of developmental plasticity. In particular, cells must respond to developmental manipulations designed to specify precise neural fates. Studies in vivo and in vitro have shown that the developmental potential of neural progenitor cells changes and becomes progressively restricted with time. For in vitro cultured neural progenitors, it is those derived from embryonic stem cells that exhibit the greatest developmental potential. It is clear that both extrinsic and intrinsic mechanisms determine the developmental potential of neural progenitors and that epigenetic, or chromatin structural, changes regulate and coordinate hierarchical changes in fate-determining gene expression. Here, we review the temporal changes in developmental plasticity of neural progenitor cells and discuss the epigenetic mechanisms that underpin these changes. We propose that understanding the processes of epigenetic programming within the neural lineage is likely to lead to the development of more rationale strategies for cell reprogramming that may be used to expand the developmental potential of otherwise restricted progenitor populations.

Human embryonic stem cells for brain repair?

Cell therapy has been perceived as the main or ultimate goal of human embryonic stem (ES) cell research. Where are we now and how are we going to get there? There has been rapid success in devising in vitro protocols for differentiating human ES cells to neuroepithelial cells. Progress has also been made to guide these neural precursors further to more specialized neural cells such as spinal motor neurons and dopamine-producing neurons. However, some of the in vitro produced neuronal types such as dopamine neurons do not possess all the phenotypes of their in vivo counterparts, which may contribute to the limited success of these cells in repairing injured or diseased brain and spinal cord in animal models. Hence, efficient generation of neural subtypes with correct phenotypes remains a challenge, although major hurdles still lie ahead in applying the human ES cell-derived neural cells clinically. We propose that careful studies on neural differentiation from human ES cells may provide more immediate answers to clinically relevant problems, such as drug discovery, mechanisms of disease and stimulation of endogenous stem cells.

Cellular therapy for childhood neurodegenerative disease. Part I: rationale and preclinical studies

✓ Successful cellular replacement in the diseased human central nervous system (CNS) faces numerous hurdles. In this first installment of a 2-part review, the authors report on the preclinical challenges involved in preparing for a major Phase I trial investigating the safety of human neural stem cell transplantation in a lysosomal storage disorder. Specifically, they discuss choice of the ideal disease for treatment, best donor cell type and source for implantation, the in vitro and in vivo methods used to estimate safety and efficacy, the challenges to noninvasive tracking of cells after transplantation, and the unique issues related to the immunology of CNS cellular transplantation.

Embryonic stem cells and prospects for their use in regenerative medicine approaches to motor neurone disease

Human embryonic stem cells are pluripotent cells with the potential to differentiate into any cell type in the presence of appropriate stimulatory factors and environmental cues. Their broad developmental potential has led to valuable insights into the principles of developmental and cell biology and to the proposed use of human embryonic stem cells or their differentiated progeny in regenerative medicine. This review focuses on the prospects for the use of embryonic stem cells in cell-based therapy for motor neurone disease or amyotrophic lateral sclerosis, a progressive neurodegenerative disease that specifically affects upper and lower motor neurones and leads ultimately to death from respiratory failure. Stem cell-derived motor neurones could conceivably be used to replace the degenerated cells, to provide authentic substrates for drug development and screening and for furthering our understanding of disease mechanisms. However, to reliably and accurately culture motor neurones, the complex pathways by which differentiation occurs in vivo must be understood and reiterated in vitro by embryonic stem cells. Here we discuss the need for new therapeutic strategies in the treatment of motor neurone disease, the developmental processes that result in motor neurone formation in vivo, a number of experimental approaches to motor neurone production in vitro and recent progress in the application of stem cells to the treatment and understanding of motor neurone disease.

Use of stem cells for the treatment of multiple sclerosis

The reported evidence of neurodegeneration in multiple sclerosis (MS) may explain the lack of efficacy of the currently used immunomodulating modalities and the irreversible axonal damage, which results in accumulating disability. To date, efforts for neuroprotective treatments have not been successful in clinical studies in other CNS diseases. Therefore, for MS, the use of stem cells may provide a logical solution, since these cells can migrate locally into the areas of white-matter lesions (plaques) and have the potential to support local neurogenesis and rebuilding of the affected myelin. This is achieved both by support of the resident CNS stem cell repertoire and by differentiation of the transplanted cells into neurons and myelin-producing cells (oligodendrocytes). Stem cells were also shown to possess immunomodulating properties, inducing systemic and local suppression of the myelin-targeting autoimmune lymphocytes. Several types of stem cells (embryonic and adult) have been described and extensively studied in animal models of CNS diseases and the various models of MS (experimental autoimmune encephalomyelitis [EAE]). In this review, we summarize the experience with the use of different types of stem cells in CNS disease models, focusing on the models of EAE and describe the advantages and disadvantages of each stem cell type for future clinical applications in MS.

Human adult olfactory neural progenitors promote axotomized rubrospinal tract axonal reinnervation and locomotor recovery

We investigated the effects of engrafted human adult olfactory neuroepithelial neurosphere forming cells (NSFCs) on regeneration and reinnervation of rubrospinal tract (RST) axons and locomotor recovery following partial cervical hemisection that completely ablated the RST. Weekly behavioral testing showed greater functional recovery of forelimb use during the 12 weeks after NSFCs engraftment than in the control rats. Anterograde tracing with biotinylated dextran amine (BDA) confirmed the presence of RST axons within the white matter 4-8 segments caudal to the grafts. Both immunofluorescence and immunoelectron microscopy revealed the BDA-labeled RST axonal terminals reestablished synaptic connections with motoneurons in the ventral horn of the distal cervical spinal cord. Further study of forelimb functional recovery in NSFCs-engrafted subgroups considered the effects of a second dorsolateral funiculotomy, irreversibly destroying the recovery, and the injection of muscimol, blocking RST neuronal activity reversibly. These results highlight the unique potential of human olfactory neuroepithelial-derived progenitors as an autologous cell source for spinal cord repair.

Embryonic stem cell bank: a work proposal

Human embryonic stem cells (hESCs) have an unlimited capacity to proliferate by a self-renewal process and can be differentiated in the three germ layers, opening doors to new clinical therapies to replace missing or damaged cells. The number of research groups and projects using human stem cells has increased largely in the last 5 yr. The creation of stem cell banks is another important step to support the advance of research in this field. Banks must be operated within the strict regulatory famework of good manufacturing practices and good laboratory practices that assure the highest quality standards and must implement a quality system that complies with international quality systems standards. It may also be appropriate to aim at an accreditation in order to assure correct laboratory practices at all times. Stem cell banks should receive the lines previously derived by other groups and hESCs should be provided for groups that justify their use in a research project previously approved by an ethical committee. The assays generally accepted as typical of hESCs together with the microbiological analysis should be performed in order to assure a consistent, reliable, and safe line for the researchers. In this article, the Andalusian Stem Cell Bank proposes a model of a stem cell banking process in order to create a flow diagram of hESC lines and, following the international initiatives in stem cells research, to achieve the full characterization of cells and a standardization of protocols that would simplify the hESCs culture.

Human embryonic stem cell-derived neural precursors develop into neurons and integrate into the host brain

Whether and how in-vitro-produced human neural precursors mature and integrate into the brain are crucial to the utility of human embryonic stem (hES) cells in treating neurological disorders. After transplantation into the ventricles of neonatal immune-deficient mice, hES-cell-derived neural precursors stopped expressing the cell division marker Ki67, except in neurogenic areas, and differentiated into neurons and then glia in a temporal course intrinsic to that of human cells regardless of location. The human cells located in the gray matter became neurons in the olfactory bulb and striatum, whereas those in the white matter produced exclusively glia. Importantly, the grafted human cells formed synapses. Thus, the in-vitro-produced human neural precursors follow their intrinsic temporal program to produce neurons and glia and, in response to environmental signals, generate cells appropriate to their target regions and integrate into the brain.

A Scaleable and Defined System for Generating Neural Stem Cells from Human Embryonic Stem Cells

The ability to differentiate human ESCs (hESCs) to defined lineages in a totally controlled manner is fundamental to developing cell-based therapies and studying human developmental mechanisms. We report a novel, scaleable, and widely applicable system for deriving and propagating neural stem cells from hESCs without the use of animal products, proprietary formulations, or genetic manipulation. This system provides a definitive platform for studying human neural development and has potential therapeutic implications.

Neural subtype specification from embryonic stem cells

One of the keys to using embryonic stem cells (ESCs) in brain research and potential application in neurological diseases is directed differentiation of neuronal and glial subtypes. This may be achieved by application of developmental principles in guiding cell lineage specification from naïve stem cells. Establishment of defined ESC differentiation models that recapitulate in vivo development, especially from human ESCs, will most likely provide a dynamic tool for dissecting molecular mechanisms underlying early embryonic development that is otherwise not readily obtainable. This is also a rational and realistic way of producing enriched populations of functional neurons and glia for pathological analyses as well as possible therapeutic applications.

Directed differentiation of dopaminergic neuronal subtypes from human embryonic stem cells

How dopamine (DA) neuronal subtypes are specified remains unknown. In this study we show a robust generation of functional DA neurons from human embryonic stem cells (hESCs) through a specific sequence of application of fibroblast growth factor 8 (FGF8) and sonic hedgehog (SHH). Treatment of hESC-derived Sox1+ neuroepithelial cells with FGF8 and SHH resulted in production of tyrosine hydroxylase (TH)-positive neurons that were mostly bipolar cells, coexpression with gamma-aminobutyric acid, and lack of midbrain marker engrailed 1 (En1) expression. However, FGF8 treatment of precursor cells before Sox1 expression led to the generation of a similar proportion of TH+ neurons characteristic of midbrain projection DA neurons with large cell bodies and complex processes and coexpression of En1. This suggests that one mechanism of generating neuronal subtypes is temporal availability of morphogens to a specific group of precursors. The in vitro-generated DA neurons were electrophysiologically active and released DA in an activity-dependent manner. They may thus provide a renewable source of functional human DA neurons for drug screening and development of sustainable therapeutics for disorders affecting the DA system.

Specification of motoneurons from human embryonic stem cells

An understanding of how mammalian stem cells produce specific neuronal subtypes remains elusive. Here we show that human embryonic stem cells generated early neuroectodermal cells, which organized into rosettes and expressed Pax6 but not Sox1, and then late neuroectodermal cells, which formed neural tube-like structures and expressed both Pax6 and Sox1. Only the early, but not the late, neuroectodermal cells were efficiently posteriorized by retinoic acid and, in the presence of sonic hedgehog, differentiated into spinal motoneurons. The in vitro-generated motoneurons expressed HB9, HoxC8, choline acetyltransferase and vesicular acetylcholine transporter, induced clustering of acetylcholine receptors in myotubes, and were electrophysiologically active. These findings indicate that retinoic acid action is required during neuroectoderm induction for motoneuron specification and suggest that stem cells have restricted capacity to generate region-specific projection neurons even at an early developmental stage.

Neural Differentiation from Embryonic Stem Cells: Which Way?

Embryonic stem (ES) cells can in theory produce all cell types of a living organism while renewing themselves with a stable genetic background. These unique features make ES cells a favorable tool for biomedical researches as well as a potential source for therapeutic application. A first step for approaching to ES cells is the directed differentiation to cells of interest, such as the neural cell lineage. Here, we summarize the up and down sides of each category of neural differentiation protocols that have so far been used in mouse and human ES cells, and introduce an efficient and plausible method used in our laboratory for derivation of neuroectodermal cells from human ES cells. This synthesis has led to our suggestions on issues for future design of neural differentiation protocols.