Factors controlling lineage specification in the neural crest

Induced pluripotent stem cells for disease modeling, cell therapy and drug discovery in genetic autonomic disorders: a review

The autonomic nervous system (ANS) regulates all organs in the body independent of consciousness, and is thus essential for maintaining homeostasis of the entire organism. Diseases of the ANS can arise due to environmental insults such as injury, toxins/drugs and infections or due to genetic lesions. Human studies and animal models have been instrumental to understanding connectivity and regulation of the ANS and its disorders. However, research into cellular pathologies and molecular mechanisms of ANS disorders has been hampered by the difficulties in accessing human patient-derived ANS cells in large numbers to conduct meaningful research, mainly because patient neurons cannot be easily biopsied and primary human neuronal cultures cannot be expanded.Human-induced pluripotent stem cell (hiPSC) technology can elegantly bridge these issues, allowing unlimited access of patient-derived ANS cell types for cellular, molecular and biochemical analysis, facilitating the discovery of novel therapeutic targets, and eventually leading to drug discovery. Additionally, such cells may provide a source for cell replacement therapy to replenish lost or injured ANS tissue in patients.Here, we first review the anatomy and embryonic development of the ANS, as this knowledge is crucial for understanding disease modeling approaches. We then review the current advances in human stem cell technology for modeling diseases of the ANS, recent strides toward cell replacement therapy and drug discovery initiatives.

P2X and P2Y receptors—role in the pathophysiology of the nervous system

Purinergic signalling plays a crucial role in proper functioning of the nervous system. Mechanisms depending on extracellular nucleotides and their P2 receptors also underlie a number of nervous system dysfunctions. This review aims to present the role of purinergic signalling, with particular focus devoted to role of P2 family receptors, in epilepsy, depression, neuropathic pain, nervous system neoplasms, such as glioma and neuroblastoma, neurodegenerative diseases like Parkinson’s disease, Alzheimer’s disease and multiple sclerosis. The above-mentioned conditions are associated with changes in expression of extracellular ectonucleotidases, P2X and P2Y receptors in neurons and glial cells, as well as releasing considerable amounts of nucleotides from activated or damaged nervous tissue cells into the extracellular space, which contributes to disturbance in purinergic signalling. The numerous studies indicate a potential possibility of using synthetic agonists/antagonists of P2 receptors in treatment of selected nervous system diseases. This is of particular significance, since numerous available agents reveal a low effectiveness and often produce side effects.

Generation of multipotent induced neural crest by direct reprogramming of human postnatal fibroblasts with a single transcription factor

Neural crest (NC) generates diverse lineages including peripheral neurons, glia, melanocytes, and mesenchymal derivatives. Isolating multipotent human NC has proven challenging, limiting our ability to understand NC development and model NC-associated disorders. Here, we report direct reprogramming of human fibroblasts into induced neural crest (iNC) cells by overexpression of a single transcription factor, SOX10, in combination with environmental cues including WNT activation. iNC cells possess extensive capacity for migration in vivo, and single iNC clones can differentiate into the four main NC lineages. We further identified a cell surface marker for prospective isolation of iNCs, which was used to generate and purify iNCs from familial dysautonomia (FD) patient fibroblasts. FD-iNC cells displayed defects in cellular migration and alternative mRNA splicing, providing insights into FD pathogenesis. Thus, this study provides an accessible platform for studying NC biology and disease through rapid and efficient reprogramming of human postnatal fibroblasts.

Lineage relationship of direct-developing melanocytes and melanocyte stem cells in the zebrafish

Previous research in zebrafish has demonstrated that embryonic and larval regeneration melanocytes are derived from separate lineages. The embryonic melanocytes that establish the larval pigment pattern do not require regulative melanocyte stem cell (MSC) precursors, and are termed direct-developing melanocytes. In contrast, the larval regeneration melanocytes that restore the pigment pattern after ablation develop from MSC precursors. Here, we explore whether embryonic melanocytes and MSCs share bipotent progenitors. Furthermore, we explore when fate segregation of embryonic melanocytes and MSCs occurs in zebrafish development. In order to achieve this, we develop and apply a novel lineage tracing method. We first demonstrate that Tol2-mediated genomic integration of reporter constructs from plasmids injected at the 1-2 cell stage occurs most frequently after the midblastula transition but prior to shield stage, between 3 and 6 hours post-fertilization. This previously uncharacterized timing of Tol2-mediated genomic integration establishes Tol2-mediated transposition as a means for conducting lineage tracing in zebrafish. Combining the Tol2-mediated lineage tracing strategy with a melanocyte regeneration assay previously developed in our lab, we find that embryonic melanocytes and larval regeneration melanocytes are derived from progenitors that contribute to both lineages. We estimate 50-60 such bipotent melanogenic progenitors to be present in the shield-stage embryo. Furthermore, our examination of direct-developing and MSC-restricted lineages suggests that these are segregated from bipotent precursors after the shield stage, but prior to the end of convergence and extension. Following this early fate segregation, we estimate approximately 100 embryonic melanocyte and 90 MSC-restricted lineages are generated to establish or regenerate the zebrafish larval pigment pattern, respectively. Thus, the dual strategies of direct-development and MSC-derived development are established in the early gastrula, via fate segregation of the two lineages.

Production of chick embryo extract for the cultivation of murine neural crest stem cells

The neural crest arises from the neuro-ectoderm during embryogenesis and persists only temporarily. Early experiments already proofed pluripotent progenitor cells to be an integral part of the neural crest(1). Phenotypically, neural crest stem cells (NCSC) are defined by simultaneously expressing p75 (low-affine nerve growth factor receptor, LNGFR) and SOX10 during their migration from the neural crest(2,3,4,5). These progenitor cells can differentiate into smooth muscle cells, chromaffin cells, neurons and glial cells, as well as melanocytes, cartilage and bone(6,7,8,9). To cultivate NCSC in vitro, a special neural crest stem cell medium (NCSCM) is required(10). The most complex part of the NCSCM is the preparation of chick embryo extract (CEE) representing an essential source of growth factors for the NCSC as well as for other types of neural explants. Other NCSCM ingredients beside CEE are commercially available. Producing CCE using laboratory standard equipment it is of high importance to know about the challenging details as the isolation, maceration, centrifugation, and filtration processes. In this protocol we describe accurate techniques to produce a maximized amount of pure and high quality CEE.

Functional neurons and melanocytes induced from immortal lines of postnatal neural crest-like stem cells

Stem cells, that is, cells that can both reproduce themselves and differentiate into functional cell types, attract much interest as potential aids to healing and disease therapy. Embryonic neural crest is pluripotent and generates the peripheral nervous system, melanocytes, and some connective tissues. Neural-crest-related stem cells have been reported previously in postnatal skin: committed melanocytic stem cells in the hair follicle, and pluripotent cell types from the hair follicle and papilla that can produce various sets of lineages. Here we describe novel pluripotent neural crest-like stem cells from neonatal mouse epidermis, with different potencies, isolated as 3 independent immortal lines. Using alternative regulatory factors, they could be converted to large numbers of either Schwann precursor cells, pigmented melanocytes, chondrocytes, or functional sensory neurons showing voltage-gated sodium channels. Some of the neurons displayed abundant active TRPV1 and TRPA1 receptors. Such functional neurons have previously been obtained in culture only with difficulty, by explantation. The system was also used to generate comparative gene expression data for the stem cells, melanocytes, and melanoblasts that sufficiently explain the lack of pigment in melanoblasts and provide a rationale for some genes expressed apparently ectopically in melanomas, such as ephrin receptors.

Biology of the adult enteric neural stem cell

An increasing body of evidence has accumulated in recent years supporting the existence of neural stem cells in the adult gut. There are at least three groups that have obtained them using different methodologies and have described them in vitro. There is a growing amount of knowledge on their biology, but many questions are yet unanswered. Among these questions is whether these cells are part of a permanent undifferentiated pool or are recruited in a regular basis; in addition, the factors and genes involved in their survival, proliferation, migration, and differentiation are largely unknown. Finally, with between 10 and 20% of adults suffering from diseases involving the enteric nervous system, most notably irritable bowel syndrome and gastroesophageal reflux, what is the possible role of enteric nervous stem cells in health and disease?

Establishment and controlled differentiation of neural crest stem cell lines using conditional transgenesis

Murine neural crest stem cells (NCSCs) are a multipotent transient population of stem cells. After being formed during early embryogenesis as a consequence of neurulation at the apical neural fold, the cells rapidly disperse throughout the embryo, migrating along specific pathways and differentiating into a wide variety of cell types. In vitro the multipotency is lost rapidly, making it difficult to study differentiation potential as well as cell fate decisions. Using a transgenic mouse line, allowing for spatio-temporal control of the transforming c-myc oncogene, we derived a cell line (JoMa1), which expressed NCSC markers in a transgene-activity dependent manner. JoMa1 cells express early NCSC markers and can be instructed to differentiate into neurons, glia, smooth muscle cells, melanocytes, and also chondrocytes. A cell-line, clonally derived from JoMa1 culture, termed JoMa1.3 showed identical behavior and was studied in more detail. This system therefore represents a powerful tool to study NCSC biology and signaling pathways. We observed that when proliferative and differentiation stimuli were given, enhanced cell death could be detected, suggesting that the two signals are incompatible in the cellular context. However, the cells regain their differentiation potential after inactivation of c-MycER(T). In summary, we have established a system, which allows for the biochemical analysis of the molecular pathways governing NCSC biology. In addition, we should be able to obtain NCSC lines from crossing the c-MycER(T) mice with mice harboring mutations affecting neural crest development enabling further insight into genetic pathways controlling neural crest differentiation.

The expression and functions of glycoconjugates in neural stem cells

The mammalian central nervous system is organized by a variety of cells such as neurons and glial cells. These cells are generated from a common progenitor, the neural stem cell (NSC). NSCs are defined as undifferentiated neural cells that are characterized by their high proliferative potential while retaining the capacity for self-renewal and multipotency. Glycoconjugates carrying carbohydrate antigens, including glycoproteins, glycolipids, and proteoglycans, are primarily localized on the plasma-membrane surface of cells and serve as excellent biomarkers at various stages of cellular differentiation. Moreover, they also play important functional roles in determining cell fate such as self-renewal, proliferation, and differentiation. In the present review, we discuss the expression pattern and possible functions of glycoconjugates and carbohydrate antigens in NSCs, with an emphasis on stage-specific embryonic antigen-1, human natural killer antigen-1, polysialic acid-neural cell-adhesion molecule, prominin-1, gp130, chondroitin sulfate proteoglycans, heparan sulfate proteoglycans, cystatin C, galectin-1, glycolipids, and Notch.

NT-3 and CNTF exert dose-dependent, pleiotropic effects on cells in the immature dorsal root ganglion: Neuregulin-mediated proliferation of progenitor cells and neuronal differentiation

Neurons in the nascent dorsal root ganglia are born and differentiate in a complex cellular milieu composed of postmitotic neurons, and mitotically active glial and neural progenitor cells. Neurotrophic factors such as NT-3 are critically important for promoting the survival of postmitotic neurons in the DRG. However, the factors that regulate earlier events in the development of the DRG such as the mitogenesis of DRG progenitor cells and the differentiation of neurons are less defined. Here we demonstrate that both NT-3 and CNTF induce distinct dose-dependent responses on cells in the immature DRG: at low concentrations, they induce the proliferation of progenitor cells while at higher concentrations they promote neuronal differentiation. Furthermore, the mitogenic response is indirect; that is, NT-3 and CNTF first bind to nascent neurons in the DRG--which then stimulates those neurons to release mitogenic factors including neuregulin. Blockade of this endogenous neuregulin activity completely blocks the CNTF-induced proliferation and reduces about half of the NT-3-mediated proliferation. Thus, the genesis and differentiation of neurons and glia in the DRG are dependent upon reciprocal interactions among nascent neurons, glia, and mitotically active progenitor cells.

Characterization of glycoconjugate antigens in mouse embryonic neural precursor cells

Neuronal and glial cells organizing the central nervous system (CNS) are generated from common neural precursor cells (NPCs) during neural development. However, the expression of cell-surface glycoconjugates that are crucial for determining the properties and biological function of these cells at different stages of development has not been clearly defined. In this study, we investigated the expression of several stage-specific glycoconjugate antigens, including several b-series gangliosides GD3, 9-O-acetyl GD3, GT1b and GQ1b, stage-specific embryonic antigen-1 (SSEA-1) and HNK-1, in mouse embryonic NPCs employing immunocytochemistry and flow cytometry. In addition, several of these antigens were positively identified by chemical means for the first time. We further showed that the SSEA-1 immunoreactivity was contributed by both glycoprotein and glycolipid antigens, and that of HNK-1 was contributed only by glycoproteins. Functionally, SSEA-1 may participate in migration of the cells from neurospheres in an NPC cell culture system, and the effect could be repressed by anti-SSEA-1 antibody. Based on this observation, we identified beta1 integrin as one of the SSEA-1 carrier glycoproteins. Our data thus provide insights into the functional role of certain glycoconjugate antigens in NPCs during neural development.

The metabotropic P2Y4 receptor participates in the commitment to differentiation and cell death of human neuroblastoma SH-SY5Y cells

Extracellular nucleotides exert a variety of biological actions through different subtypes of P2 receptors. Here we characterized in the human neuroblastoma SH-SY5Y cells the simultaneous presence of various P2 receptors, belonging to the P2X ionotropic and P2Y metabotropic families. Western blot analysis detected the P2X1,2,4,5,6,7 and P2Y1,2,4,6, but not the P2X3 and P2Y12 receptors. We then investigated which biological effects were mediated by the P2Y4 subtype and its physiological pyrimidine agonist UTP. We found that neuronal differentiation of the SH-SY5Y cells with dibutiryl-cAMP increased the expression of the P2Y4 protein and that UTP itself was able to positively interfere with neuritogenesis. Moreover, transient transfection and activation of P2Y4 also facilitated neuritogenesis in SH-SY5Y cells, as detected by morphological phase contrast analysis and confocal examination of neurofilament proteins NFL. This was concurrent with increased transcription of immediate-early genes linked to differentiation such as cdk-5 and NeuroD6, and activity of AP-1 transcription family members such as c-fos, fos-B, and jun-D. Nevertheless, a prolonged activation of the P2Y4 receptor by UTP also induced cell death, both in naive, differentiated, and P2Y4-transfected SH-SY5Y cells, as measured by direct count of intact nuclei and cytofluorimetric analysis of damaged DNA. Taken together, our data indicate that the high expression and activation of the P2Y4 receptor participates in the neuronal differentiation and commitment to death of SH-SY5Y cells.

Coexpression of Brn-3a POU protein with p53 in a population of neuronal progenitor cells is associated with differentiation and protection against apoptosis

The Brn-3a transcription factor is critical for survival and differentiation of sensory neurons derived from neural crest cells (NCC). Interaction of Brn-3a with p53 results in differential effects on target gene expression, which profoundly affects fate of neuronal cells. Here we demonstrate colocalization of p53 in a subset of Brn-3a-positive NCC-derived cells fated for the sensory neuronal lineage. The distinct morphology of Brn-3a/p53-coexpressing cells suggested a differentiated neuronal cell type, and this was confirmed by colocalization of p53 with differentiation marker NF-160. Functional effects of Brn-3a/p53 coexpression were analyzed in NCC cultured from Brn-3a -/- embryos, which showed significantly increased apoptosis upon induction of p53 compared with wild-type NCC, suggesting that Brn-3a modulates the p53-mediated fate of NCC that coexpress both factors. Thus, p53 is expressed in neuronal cells undergoing differentiation as well as apoptosis. Interaction with Brn-3a in sensory neurons may be critical for modulating p53-mediated gene expression and hence cell fate.

Neural crest cell plasticity and its limits

The neural crest (NC) yields pluripotent cells endowed with migratory properties. They give rise to neurons, glia, melanocytes and endocrine cells, and to diverse 'mesenchymal' derivatives. Experiments in avian embryos have revealed that the differentiation of the NC 'neural' precursors is strongly influenced by environmental cues. The reversibility of differentiated cells (such as melanocytes or glia) to a pluripotent precursor state can even be induced in vitro by a cytokine, endothelin 3. The fate of 'mesenchymal' NC precursors is strongly restricted by Hox gene expression. In this context, however, facial skeleton morphogenesis is under the control of a multistep crosstalk between the epithelia (endoderm and ectoderm) and NC cells.

Immunohistochemical Study of Intermediate Filaments and Neuroendocrine Marker Expression in Leydig Cells of Laboratory Rodents

The aims of this study were to detect the expression of intermediate filaments and to verify the existence of marker substances for neuronal and neuroendocrine cells within the interstitial Leydig cells of laboratory rodent's testes, such as it has been described in other species. Adult male rats, mice, gerbils, Syrian hamsters and guinea-pigs were used and the localization of the different markers was achieved by the streptoavidin-peroxidase immunohistochemical method. The present study demonstrates in all rodents studied a similar pattern of localization in Leydig cells of intermediate filaments (vimentin, cytokeratin, neurofilament 200 kD and glial fibrillary acidic protein) and other marker substances (S-100, CgA, substance P and neurone-specific enolase), which are typical of neuroendocrine (APUD cells or paraneurones) and glial cells. The expression of these substances, related to neurotransmitters or neurohomones and other proteins characteristic of neuroendocrine cells, could suggest that it is a neural crest derived cell. Although this study provides more evidences about the immunoexpression of neuronal and glial markers in Leydig cells, this fact cannot be related directly to their embryological origin, because the current data support the hypothesis of a mesenchymal origin of the Leydig cells.

PACAP promotes sensory neuron differentiation: blockade by neurotrophic factors

Developing neurons encounter a panoply of extracellular signals as they differentiate. A major goal is to identify these extrinsic cues and define the mechanisms by which neurons simultaneously integrate stimulation by multiple factors yet initiate one specific biological response. Factors that are known to exert potent activities in the developing nervous system include the NGF family of neurotrophic factors, ciliary neurotrophic factor (CNTF), and pituitary adenylate cyclase-activating peptide (PACAP). Here we demonstrate that PACAP promotes the differentiation of nascent dorsal root ganglion (DRG) neurons in that it increases both the number of neural-marker-positive cells and axonogenesis without affecting the proliferation of neural progenitor cells. This response is mediated through the PAC1 receptor and requires MAP kinase activation. Moreover, we find that, in the absence of exogenously added PACAP, blockade of the PAC1 receptor inhibits neuronal differentiation. These data coupled with our finding that both PACAP and the PAC1 receptor are expressed during the peak period of neuronal differentiation in the DRG suggest that PACAP functions in vivo to promote the differentiation of nascent sensory neurons. Interestingly, we also demonstrate that the neurotrophic factors NT-3 and CNTF completely block the PACAP-induced neuronal differentiation. This points to the intricate integration of cellular signals by nascent neurons and, to our knowledge, is the first evidence for neurotrophic factor abrogation of a pathway regulated by G-protein-coupled receptors (GPCRs).

Multipotentiality of the neural crest

Multiple neural and non-neural cell types arise from the neural crest (NC) in vertebrate embryos. Recent work has provided evidence for multipotent stem cells and intermediate precursors in the early NC cell population as well as in various NC derivatives in embryos and even in adult. Advances have been made towards understanding how cytokines, regulatory genes and cell-cell interactions cooperate to control commitment and differentiation to pigment cells, glia and neurone subtypes. In addition, NC cell fates appeared to be unstable, as differentiated NC cells can reverse to multipotent precursors and transdifferentiate in vitro.

Alterations in Ca2+-dependent and cAMP-dependent signaling pathways affect neurogenesis and melanogenesis of quail neural crest cells in vitro

Trunk neural crest cells primarily form neurons, nerve supportive cells of the peripheral nervous system and melanocytes. We are interested in signal transduction pathways that affect the production of peripheral neurons or melanocytes. Quail neural crest cell cultures were treated with a variety of drugs that affect components of protein kinase A- (PKA-), protein kinase C- (PKC-) and inositol-3-phosphate- (I3P-) dependent pathways. Forskolin, a drug that increases cAMP levels, augmented melanocyte populations and reduced neuronal populations in our cultures. H8 and H89, two drugs that inhibit PKA, reduced melanocyte populations well below control levels. Down regulation of PKC with a phorbol ester, PMA, or with calphostin C inhibited neurogenesis. PMA also enhanced melanogenesis. Increasing intracellular calcium levels (with A23187 or thapsigargin) resulted in cultures with few melanocytes but many neurons, compared to untreated controls. An antagonist of the I3P pathway, wortmannin, prevented the appearance of neurons but did not affect melanocyte populations. In summary, molecules that altered the PKA-dependent pathway affected melanogenesis. Manipulations of the I3P and/or PKC-dependent pathways influenced neurogenesis. Stimulation of one pathway often inhibited appearance of cells associated with the alternative pathway.

Neural crest stem cell and cardiac endothelium defects in the TrkC null mouse

TrkC null mice have multiple cardiac malformations. Since neural crest cells participate in cardiac outflow tract septation, the aim of this study was to determine at the cellular level the putative neural crest defect. We have identified three types of progenitor cells: stem cells that undergo self-renewal and can generate many cell types, cells that are restricted in their developmental potentials, and cells that are committed to the smooth muscle cell lineage. In TrkC null mice, there is a greater than 50% decrease in stem cell numbers and an equivalent increase in fate-restricted cells. The outflow tract wall is thickened and the endothelial tube is disorganized. We conclude that deletion of the TrkC gene causes precocious fate restrictions of the neural crest stem cell and a defect of the outflow tract endothelium, both of which may contribute to the outflow tract malformations that occur in TrkC null mice.

Differentiating adult hippocampal stem cells into neural crest derivatives

To investigate the degree of plasticity of hippocampal neural stem cells from adult mice (mHNSC), we have analyzed their differentiation in co-culture with quail neural crest cells. In mixed culture, mHNSC give rise to several non-neuronal neural crest derivatives, including melanocytes, chondrocytes and smooth muscle cells. The data suggest that neural crest cell-derived short-range cues that are recognized across species can instruct adult mHNSC to differentiate into neural crest phenotypes.

Neuroblastoma - a developmental perspective

Genetic investigation of neuroblastoma has provided few clues to account for the variability in clinical phenotype which is such a characteristic feature of this tumour. Indeed, efforts to identify the primary genetic event(s) responsible for tumour development have been overwhelmed by the number and range of different genetic abnormalities observed, particularly in the more aggressive neuroblastoma subtypes. Since neuroblastoma is a consequence of aberrant development of the sympathetic nervous system (SNS), investigation of the genetic components known to be involved in the control of SNS developmental, may provide the key to understanding tumour behaviour. The neurotrophins and the glial family ligands both play very significant roles in different stages of SNS development and merit more detailed investigation as to how they might influence neuroblastoma tumorigenesis.

The early steps of neural crest development

The neural crest is an intriguing cell population that gives rise to many derivatives which are all generated far from their final destinations. From its induction to the delamination of the cells, multiple signalling pathways converge to regulate the expression of effector genes, the products of which endow the cells with invasive and migratory properties reminiscent of those displayed by malignant cells in tumours. As such, the neural crest constitutes an excellent model to study cell migration.