Neural Crest Stem and Progenitor Cells

Antidepressant responsiveness in adulthood is permanently impaired after neonatal destruction of the neurogenic pool

The dynamic turnover of hippocampal neurons is implicated in the regulation of cognitive and affective behavior. Extending our previous demonstration that administration of dexamethasone (ND) to neonatal rats depletes the resident population of neural precursor cells (NPC) and restrains the size of the neurogenic regions, we now show that the adverse effects of ND persist into adulthood. Specifically, ND impairs repletion of the neurogenic pool and neurogenesis; ND also compromises cognitive performance, the ability to actively adapt to an acute stressor and, the efficacy of glucocorticoid (GC) negative feedback. Interestingly, although ND depletes the neurogenic pool, it does not permanently abolish the proliferative machinery of the residual NPC population; however, ND increases the susceptibility of hippocampal granule neurons to apoptosis. Although the antidepressant fluoxetine (FLX) reverses the latter phenomenon, it does not replenish the NPC pool. Treatment of ND-treated adult rats with FLX also improves GC negative feedback, albeit without rescuing the deleterious effects of ND on behavior. In summary, ND leads to protracted disruption of mental functions, some of which are resistant to antidepressant interventions. We conclude that manipulation of the NPC pool during early life may jeopardize the therapeutic potential of antidepressants in adulthood.

Inhibition of FGF signaling accelerates neural crest cell differentiation of human pluripotent stem cells

Neural crest (NC) is a transient population, arising during embryonic development and capable of differentiating into various somatic cells. The defects of neural crest development leads to neurocristopathy. Several signaling pathways were revealed their significance in NC cell specification. Fibroblast growth factor (FGF) is recognized as an important signaling during NC development, for instance Xenopus and avian; however, its contributions in human species are remained elusive. Here we used human pluripotent stem cells (hPSCs) to investigate the consequences of FGF inhibition during NC cell differentiation. The specific-FGF receptor inhibitor, SU5402, was used in this investigation. The inhibition of FGF did not found to affect the proliferation or death of hPSC-derived NC cells, but promoted hPSCs to commit NC cell fate. NC-specific genes, including PAX3, SLUG, and TWIST1, were highly upregulated, while hPSC genes, such as OCT4, and E-CAD, rapidly reduced upon FGF signaling blockage. Noteworthy, TFAP-2α, a marker of migratory NC cells, abundantly presented in SU5402-induced cells. This accelerated NC cell differentiation could be due to the activation of Notch signaling upon the blockage of ERK1/2 phosphorylation, since NICD was increased by SU5402. Altogether, this study proposed the contributions of FGF signaling in controlling human NC cell differentiation from hPSCs, the crosstalk between FGF and Notch, and might imply to the influences of FGF signaling in neurocristophatic diseases.

Existence of Neural Crest-Derived Progenitor Cells in Normal and Fuchs Endothelial Dystrophy Corneal Endothelium

Human corneal endothelial cells are derived from neural crest and because of postmitotic arrest lack competence to repair cell loss from trauma, aging, and degenerative disorders such as Fuchs endothelial corneal dystrophy (FECD). Herein, we identified a rapidly proliferating subpopulation of cells from the corneal endothelium of adult normal and FECD donors that exhibited features of neural crest-derived progenitor (NCDP) cells by showing absence of senescence with passaging, propensity to form spheres, and increased colony forming efficacy compared with the primary cells. The collective expression of stem cell-related genes SOX2, OCT4, LGR5, TP63 (p63), as well as neural crest marker genes PSIP1 (p75(NTR)), PAX3, SOX9, AP2B1 (AP-2β), and NES, generated a phenotypic footprint of endothelial NCDPs. NCDPs displayed multipotency by differentiating into microtubule-associated protein 2, β-III tubulin, and glial fibrillary acidic protein positive neurons and into p75(NTR)-positive human corneal endothelial cells that exhibited transendothelial resistance of functional endothelium. In conclusion, we found that mitotically incompetent ocular tissue cells contain adult NCDPs that exhibit a profile of transcription factors regulating multipotency and neural crest progenitor characteristics. Identification of normal NCDPs in FECD-affected endothelium holds promise for potential autologous cell therapies.

Face off against ROS: Tcof1/Treacle safeguards neuroepithelial cells and progenitor neural crest cells from oxidative stress during craniofacial development

One-third of all congenital birth defects affect the head and face, and most craniofacial anomalies are considered to arise through defects in the development of cranial neural crest cells. Cranial neural crest cells give rise to the majority of craniofacial bones, cartilages and connective tissues. Therefore, understanding the events that control normal cranial neural crest and subsequent craniofacial development is important for elucidating the pathogenetic mechanisms of craniofacial anomalies and for the exploring potential therapeutic avenues for their prevention. Treacher Collins syndrome (TCS) is a congenital disorder characterized by severe craniofacial anomalies. An animal model of TCS, generated through mutation of Tcof1, the mouse (Mus musculus) homologue of the gene primarily mutated in association with TCS in humans, has recently revealed significant insights into the pathogenesis of TCS. Apoptotic elimination of neuroepithelial cells including neural crest cells is the primary cause of craniofacial defects in Tcof1 mutant embryos. However, our understanding of the mechanisms that induce tissue-specific apoptosis remains incomplete. In this review, we describe recent advances in our understanding of the pathogenesis TCS. Furthermore, we discuss the role of Tcof1 in normal embryonic development, the correlation between genetic and environmental factors on the severity of craniofacial abnormalities, and the prospect for prenatal prevention of craniofacial anomalies.

Lgr5 Marks Neural Crest Derived Multipotent Oral Stromal Stem Cells

It has been suggested that multipotent stem cells with neural crest (NC) origin persist into adulthood in oral mucosa. However their exact localization and role in normal homeostasis is unknown. In this study, we discovered that Lgr5 is expressed in NC cells during embryonic development, which give rise to the dormant stem cells in the adult tongue and oral mucosa. Those Lgr5 positive oral stromal stem cells display properties of NC stem cells including clonal growth and multipotent differentiation. RNA sequencing revealed that adult Lgr5+ oral stromal stem cells express high number of neural crest related markers like Sox9, Twist1, Snai1, Myc, Ets1, Crabp1, Epha2, and Itgb1. Using lineage-tracing experiments, we show that these cells persist more than a year in the ventral tongue and some areas of the oral mucosa and give rise to stromal progeny. In vivo transplantation demonstrated that these cells reconstitute the stroma. Our studies show for the first time that Lgr5 is expressed in the NC cells at embryonic day 9.5 (E9.5) and is maintained during embryonic development and postnataly in the stroma of the ventral tongue, and some areas of the oral mucosa and that Lgr5+ cells participate in the maintenance of the stroma.

Prevention of Treacher Collins syndrome craniofacial anomalies in mouse models via maternal antioxidant supplementation

Craniofacial anomalies account for approximately one-third of all birth defects and are a significant cause of infant mortality. Since the majority of the bones, cartilage and connective tissues that comprise the head and face are derived from a multipotent migratory progenitor cell population called the neural crest, craniofacial disorders are typically attributed to defects in neural crest cell development. Treacher Collins syndrome (TCS) is a disorder of craniofacial development and although TCS arises primarily through autosomal dominant mutations in TCOF1, no clear genotype-phenotype correlation has been documented. Here we show that Tcof1 haploinsufficiency results in oxidative stress-induced DNA damage and neuroepithelial cell death. Consistent with this discovery, maternal treatment with antioxidants minimizes cell death in the neuroepithelium and substantially ameliorates or prevents the pathogenesis of craniofacial anomalies in Tcof1(+/-) mice. Thus maternal antioxidant dietary supplementation may provide an avenue for protection against the pathogenesis of TCS and similar neurocristopathies.

Neural crest specification by inhibition of the ROCK/Myosin II pathway

Neural crest is a population of multipotent progenitor cells that form at the border of neural and non-neural ectoderm in vertebrate embryos, and undergo epithelial-mesenchymal transition and migration. According to the traditional view, the neural crest is specified in early embryos by signaling molecules including BMP, FGF, and Wnt proteins. Here, we identify a novel signaling pathway leading to neural crest specification, which involves Rho-associated kinase (ROCK) and its downstream target nonmuscle Myosin II. We show that ROCK inhibitors promote differentiation of human embryonic stem cells (hESCs) into neural crest-like progenitors (NCPs) that are characterized by specific molecular markers and ability to differentiate into multiple cell types, including neurons, chondrocytes, osteocytes, and smooth muscle cells. Moreover, inhibition of Myosin II was sufficient for generating NCPs at high efficiency. Whereas Myosin II has been previously implicated in the self-renewal and survival of hESCs, we demonstrate its role in neural crest development during ESC differentiation. Inhibition of this pathway in Xenopus embryos expanded neural crest in vivo, further indicating that neural crest specification is controlled by ROCK-dependent Myosin II activity. We propose that changes in cell morphology in response to ROCK and Myosin II inhibition initiate mechanical signaling leading to neural crest fates.

Neural crest cell-autonomous roles of fibronectin in cardiovascular development

The chemical and mechanical properties of extracellular matrices (ECMs) modulate diverse aspects of cellular fates; however, how regional heterogeneity in ECM composition regulates developmental programs is not well understood. We discovered that fibronectin 1 (Fn1) is expressed in strikingly non-uniform patterns during mouse development, suggesting that regionalized synthesis of the ECM plays cell-specific regulatory roles during embryogenesis. To test this hypothesis, we ablated Fn1 in the neural crest (NC), a population of multi-potent progenitors expressing high levels of Fn1. We found that Fn1 synthesized by the NC mediated morphogenesis of the aortic arch artery and differentiation of NC cells into vascular smooth muscle cells (VSMCs) by regulating Notch signaling. We show that NC Fn1 signals in an NC cell-autonomous manner through integrin α5β1 expressed by the NC, leading to activation of Notch and differentiation of VSMCs. Our data demonstrate an essential role of the localized synthesis of Fn1 in cardiovascular development and spatial regulation of Notch signaling.

Association Between Prediagnostic Serum 25-Hydroxyvitamin D Concentration and Glioma

There are no previous studies of the association between prediagnostic serum vitamin D concentration and glioma. Vitamin D has immunosuppressive properties; as does glioma. It was, therefore, our hypothesis that elevated vitamin D concentration would increase glioma risk. We conducted a nested case-control study using specimens from the Janus Serum Bank cohort in Norway. Blood donors who were subsequently diagnosed with glioma (n = 592), between 1974 and 2007, were matched to donors without glioma (n = 1112) on date and age at blood collection and sex. We measured 25-hydroxyvitamin D [25(OH)D], an indicator of vitamin D availability, using liquid chromatography coupled with mass spectrometry. Seasonally adjusted odds ratios (ORs) and 95% confidence intervals (95% CIs) were estimated for each control quintile of 25(OH)D using conditional logistic regression. Among men diagnosed with high grade glioma >56, we found a negative trend (P = .04). Men diagnosed ≤ 56 showed a borderline positive trend (P = .08). High levels (>66 nmol/L) of 25(OH)D in men >56 were inversely related to high grade glioma from ≥2 yr before diagnosis (OR = 0.59; 95% CI = 0.38, 0.91) to ≥15 yr before diagnosis (OR = 0.61; 95% CI = 0.38,0.96). Our findings are consistent long before glioma diagnosis and are therefore unlikely to reflect preclinical disease.

Tendon development and diseases

Tendon is a uniaxial connective tissue component of the musculoskeletal system. Tendon is involved in force transmission between muscle and bone. Tendon injury is very common and debilitating but tendon repair remains a clinical challenge for orthopedic medicine. In vertebrates, tendon is mainly composed of type I collagen fibrils, displaying a parallel organization along the tendon axis. The tendon-specific spatial organization of type I collagen provides the mechanical properties for tendon function. In contrast to other components of the musculoskeletal system, tendon biology is poorly understood. An important goal in tendon biology is to understand the mechanisms involved in the production and assembly of type I collagen fibrils during development, postnatal formation, and healing processes in order to design new therapies for tendon repair. In this review we highlight the current understanding of the molecular and mechanical signals known to be involved in tenogenesis during development, and how development provides insights into tendon healing processes. WIREs Dev Biol 2016, 5:5-23. doi: 10.1002/wdev.201 For further resources related to this article, please visit the WIREs website.

FGF8 signaling sustains progenitor status and multipotency of cranial neural crest-derived mesenchymal cells in vivo and in vitro

The cranial neural crest (CNC) cells play a vital role in craniofacial development and regeneration. They are multi-potent progenitors, being able to differentiate into various types of tissues. Both pre-migratory and post-migratory CNC cells are plastic, taking on diverse fates by responding to different inductive signals. However, what sustains the multipotency of CNC cells and derivatives remains largely unknown. In this study, we present evidence that FGF8 signaling is able to sustain progenitor status and multipotency of CNC-derived mesenchymal cells both in vivo and in vitro. We show that augmented FGF8 signaling in pre-migratory CNC cells prevents cell differentiation and organogenesis in the craniofacial region by maintaining their progenitor status. CNC-derived mesenchymal cells with Fgf8 overexpression or control cells in the presence of exogenous FGF8 exhibit prolonged survival, proliferation, and multi-potent differentiation capability in cell cultures. Remarkably, exogenous FGF8 also sustains the capability of CNC-derived mesenchymal cells to participate in organogenesis such as odontogenesis. Furthermore, FGF8-mediated signaling strongly promotes adipogenesis but inhibits osteogenesis of CNC-derived mesenchymal cells in vitro. Our results reveal a specific role for FGF8 in the maintenance of progenitor status and in fate determination of CNC cells, implicating a potential application in expansion and fate manipulation of CNC-derived cells in stem cell-based craniofacial regeneration.

Localization and osteoblastic differentiation potential of neural crest-derived cells in oral tissues of adult mice

In embryos, neural crest cells emerge from the dorsal region of the fusing neural tube and migrate throughout tissues to differentiate into various types of cells including osteoblasts. In adults, subsets of neural crest-derived cells (NCDCs) reside as stem cells and are considered to be useful cell sources for regenerative medicine strategies. Numerous studies have suggested that stem cells with a neural crest origin persist into adulthood, especially those within the mammalian craniofacial compartment. However, their distribution as well as capacity to differentiate into osteoblasts in adults is not fully understood. To analyze the precise distribution and characteristics of NCDCs in adult oral tissues, we utilized an established line of double transgenic (P0-Cre/CAG-CAT-EGFP) mice in which NCDCs express green fluorescent protein (GFP) throughout their life. GFP-positive cells were scattered like islands throughout tissues of the palate, gingiva, tongue, and buccal mucosa in adult mice, with those isolated from the latter shown to form spheres, typical cell clusters composed of stem cells, under low-adherent conditions. Furthermore, GFP-positive cells had markedly increased alkaline phosphatase (a marker enzyme of osteoblast differentiation) activity and mineralization as shown by alizarin red staining, in the presence of bone morphogenetic protein (BMP)-2. These results suggest that NCDCs reside in various adult oral tissues and possess potential to differentiate into osteoblastic cells. NCDCs in adults may be a useful cell source for bone regeneration strategies.

Promotion of periostin expression contributes to the migration of Schwann cells

Neuregulin ligands and their ErbB receptors are important for the development of Schwann cells, the glial cells of the peripheral nervous system (PNS). ErbB3 deficiency is characterized by a complete loss of Schwann cells along axons of the peripheral nerves, impaired fasciculation and neuronal cell death. We performed comparative gene expression analysis of dorsal root ganglia (DRG) explant cultures from ErbB3-deficient and wild-type mice in order to identify genes that are involved in Schwann cell development and migration. The extracellular matrix (ECM) gene periostin was found to exhibit the most prominent down regulation in ErbB3-deficient DRG. Expression analysis revealed that the periostin-expressing cell population in the PNS corresponds to Schwann cell precursors and Schwann cells, and is particularly high in migratory Schwann cells. Furthermore, stimulation of Schwann cells with neuregulin-1 (NRG1) or transforming growth factor β (TGFβ-1) resulted in an upregulation of periostin expression. Interestingly, DRG explant cultures of periostin-deficient mice revealed a significant reduction of the number of migrating Schwann cells. These data demonstrate that the expression of periostin is stimulated by ErbB ligand NRG1 and influences the migration of Schwann cell precursors.

Wnt/β-Catenin Signaling Pathway in Skin Carcinogenesis and Therapy

Cooperating with other signaling pathways, Wnt signaling controls cell proliferation, morphology, motility, and embryonic development destination and maintains the homeostasis of tissues including skin, blood, intestine, and brain by regulating somatic stem cells and their niches throughout adult life. Abnormal regulation of Wnt pathways leads to neoplastic proliferation in these tissues. Recent research shows that Wnt signaling is also associated with the regulation of cancer stem cells (CSCs) through a similar mechanism to that observed in normal adult stem cells. Thus, the Wnt/β-catenin signaling pathway has been intensively studied and characterized. For this review, we will focus on the regulation of the Wnt/β-catenin signaling pathway in skin cancer. With the important role in stemness and skin CSC proliferation, the Wnt/β-catenin signaling pathway and its elements have the potential to be targets for skin cancer therapy.

Molecular control of the neural crest and peripheral nervous system development

A transient and unique population of multipotent stem cells, known as neural crest cells (NCCs), generate a bewildering array of cell types during vertebrate development. An attractive model among developmental biologists, the study of NCC biology has provided a wealth of knowledge regarding the cellular and molecular mechanisms important for embryogenesis. Studies in numerous species have defined how distinct phases of NCC specification, proliferation, migration, and survival contribute to the formation of multiple functionally distinct organ systems. NCC contributions to the peripheral nervous system (PNS) are well known. Critical developmental processes have been defined that provide outstanding models for understanding how extracellular stimuli, cell-cell interactions, and transcriptional networks cooperate to direct cellular diversification and PNS morphogenesis. Dissecting the complex extracellular and intracellular mechanisms that mediate the formation of the PNS from NCCs may have important therapeutic implications for neurocristopathies, neuropathies, and certain forms of cancer.

Neural crest cell evolution: how and when did a neural crest cell become a neural crest cell

As vertebrates evolved from protochordates, they shifted to a more predatory lifestyle, and radiated and adapted to most niches of the planet. This process was largely facilitated by the generation of novel vertebrate head structures, which were derived from neural crest cells (NCC). The neural crest is a unique vertebrate cell population that is frequently termed the "fourth germ layer" because it forms in conjunction with the other germ layers and contributes to a diverse array of cell types and tissues including the craniofacial skeleton, the peripheral nervous system, and pigment cells among many other tissues and cell types. NCC are defined by their origin at the neural plate border, via an epithelial-to-mesenchymal transition (EMT), together with multipotency and polarized patterns of migration. These defining characteristics, which evolved independently in the germ layers of invertebrates, were subsequently co-opted through their gene regulatory networks to form NCC in vertebrates. Moreover, recent data suggest that the ability to undergo an EMT was one of the latter features co-opted by NCC. In this review, we discuss the potential origins of NCC and how they evolved to contribute to nearly all tissues and organs throughout the body, based on paleontological evidence together with an evaluation of the evolution of molecules involved in NCC development and their migratory cell paths.

The Origin and Role of Autophagy in the Formation of Cytoplasmic Granules in Canine Lingual Granular Cell Tumors

Granular cell tumors (GCTs) are histologically characterized by polygonal neoplastic cells with abundant eosinophilic cytoplasmic granules. In humans, these cells are considered to be derived from Schwann cells, and the cytoplasmic granules are assumed to be autophagosomes or autophagolysosomes. However, the origin and nature of the cytoplasmic granules in canine GCTs have not been well characterized. The present study examined 9 canine lingual GCTs using immunohistochemistry, transmission electron microscopy (TEM), and cell culture and xenotransplantation experiments. In some cases, the tumor cells expressed S100, CD133, and desmin. The cytoplasmic granules were positive for LC3, p62, NBR1, and ubiquitin. TEM revealed autophagosome-like structures in the cytoplasm of the granule-containing cells. The cultured GCT cells were round to spindle shaped and expressed S100, nestin, Melan-A, CD133, LC3, p62, NBR1, and ubiquitin, suggesting that they were of neural crest origin, redifferentiated into melanocytes, and exhibited upregulated autophagy. The xenotransplanted tumors consisted of spindle to polygonal cells. Only a few cells contained cytoplasmic granules, and some had melanin pigments in their cytoplasm. The xenotransplanted cells expressed S100, nestin, Melan-A, and CD133. P62 and ubiquitin were detected, regardless of the presence or absence of cytoplasmic granules, while LC3 and NBR1 were detected only in the neoplastic cells containing cytoplasmic granules. These findings suggest that some xenotransplanted cells redifferentiated into melanocytes and that autophagy was upregulated in the cytoplasmic granule-containing cells. In conclusion, canine lingual GCTs originate from the neural crest and develop cytoplasmic granules via autophagy. In addition, the microenvironment of GCT cells affects their morphology.

Bioinformatic analysis of nematode migration-associated genes identifies novel vertebrate neural crest markers

Neural crest cells are highly motile, yet a limited number of genes governing neural crest migration have been identified by conventional studies. To test the hypothesis that cell migration genes are likely to be conserved over large evolutionary distances and from diverse tissues, we searched for vertebrate homologs of genes important for migration of various cell types in the invertebrate nematode and examined their expression during vertebrate neural crest cell migration. Our systematic analysis utilized a combination of comparative genomic scanning, functional pathway analysis and gene expression profiling to uncover previously unidentified genes expressed by premigratory, emigrating and/or migrating neural crest cells. The results demonstrate that similar gene sets are expressed in migratory cell types across distant animals and different germ layers. Bioinformatics analysis of these factors revealed relationships between these genes within signaling pathways that may be important during neural crest cell migration.

Role of p75 neurotrophin receptor in stem cell biology: more than just a marker

p75(NTR), the common receptor for both neurotrophins and proneurotrophins, has been widely studied because of its role in many tissues, including the nervous system. More recently, a close relationship between p75(NTR) expression and pluripotency has been described. p75(NTR) was shown to be expressed in various types of stem cells and has been used to prospectively isolate stem cells with different degrees of potency. Here, we give an overview of the current knowledge on p75(NTR) in stem cells, ranging from embryonic to adult stem cells, and cancer stem cells. In an attempt to address its potential role in the control of stem cell biology, the molecular mechanisms underlying p75(NTR) signaling in different models are also highlighted. p75(NTR)-mediated functions include survival, apoptosis, migration, and differentiation, and depend on cell type, (pro)neurotrophin binding, interacting transmembrane co-receptors expression, intracellular adaptor molecule availability, and post-translational modifications, such as regulated proteolytic processing. It is therefore conceivable that p75(NTR) can modulate cell-fate decisions through its highly ramified signaling pathways. Thus, elucidating the potential implications of p75(NTR) activity as well as the underlying molecular mechanisms of p75(NTR) will shed new light on the biology of both normal and cancer stem cells.

The effects of tumor location on diagnostic criteria for canine malignant peripheral nerve sheath tumors (MPNSTs) and the markers for distinction between canine MPNSTs and canine perivascular wall tumors

Canine malignant peripheral nerve sheath tumors (MPNSTs) occur not only in the peripheral nervous system (PNS) but also in soft tissue and various organs (non-PNS). The most important diagnostic criterion is proof of peripheral nerve sheath origin. This is difficult in non-PNS MPNSTs, and its differential diagnosis is challenging. Canine perivascular wall tumors (PWTs) also commonly arise in soft tissue. Their histopathological features are quite similar to those of canine MPNSTs, making their differential diagnosis challenging. To elucidate whether the morphological features are applicable to diagnose non-PNS MPNSTs and to demonstrate useful markers for distinction between canine MPNSTs and PWTs, the authors examined 30 canine MPNSTs and 31 PWTs immunohistochemically for S100, nestin, NGFR, Olig2, claudin-1, CD57, PRX, α-SMA, desmin, and calponin. Among canine MPNSTs, the PNS tumors displayed significantly higher S100 and Olig2 expression than the non-PNS tumors. The expression levels of the other markers did not differ significantly, suggesting that the same morphological diagnostic criteria are applicable regardless of their location. The PWT cells displayed significantly weaker immunoreactivity than MPNSTs to markers used except α-SMA and desmin. Cluster analysis sorted most canine MPNSTs and PWTs into 2 distinctly different clusters, whereas 3 MPNSTs and 6 PWTs were assigned to the opposing cluster. These 3 MPNSTs were negative for almost all markers, while these 6 PWTs were positive for only neuronal markers. In particular, NGFR and Olig2 were almost negative in the rest of PWT cases. These findings suggest that NGFR and Olig2 are useful to distinguish these 2 tumors.

Stem Cell-Based Tissue Engineering for Regenerative Medicine

The applications of stem cells in tissue engineering will show great promise in generating tailor-made tissue/organs for clinical applications. This paper gives a review on a broad spectrum of areas in stem cell-based tissue engineering including neuron repair, cardiac patches, skin regeneration, gene therapy and cartilage tissue engineering. This paper is intended to serve as an informative tutorial for scientists and physicians from fields other than stem cells and tissue engineering. It will shed light on various strategies of target tissue/organ repair involving stem cells.

On the Genesis of Neuroblastoma and Glioma

As the emergence of cancer is most frequent in proliferating tissues, replication errors are considered to be at the base of this disease. This review concentrates mainly on two neural cancers, neuroblastoma and glioma, with completely different backgrounds that are well documented with respect to their ontogeny. Although clinical data on other cancers of the nervous system are available, usually little can be said about their origins. Neuroblastoma is initiated in the embryo at a moment when the nervous system (NS) is in full expansion and occasionally genomic damage can lead to neoplasia. Glioma, to the contrary, occurs in the adult brain supposed to be mostly in a postmitotic state. According to current consensus, neural stem cells located in the subventricular zone (SVZ) in the adult are thought to accumulate enough genomic mutations to diverge on a carcinogenic course leading to diverse forms of glioma. After weighing the pros and cons of this current hypothesis in this review, it will be argued that this may be improbable, yielding to the original old concept of glial origin of glioma.

Intracerebroventricular administration of nerve growth factor induces gliogenesis in sensory ganglia, dorsal root, and within the dorsal root entry zone

Previous studies indicated that intracerebroventricular administration of nerve growth factor (NGF) leads to massive Schwann cell hyperplasia surrounding the medulla oblongata and spinal cord. This study was designed to characterize the proliferation of peripheral glial cells, that is, Schwann and satellite cells, in the trigeminal ganglia and dorsal root ganglia (DRG) of adult rats during two weeks of NGF infusion using bromodeoxyuridine (BrdU) to label dividing cells. The trigeminal ganglia as well as the cervical and lumbar DRG were analyzed. Along the entire neuraxis a small number of dividing cells were observed within these regions under physiological condition. NGF infusion has dramatically increased the generation of new cells in the neuronal soma and axonal compartments of sensory ganglia and along the dorsal root and the dorsal root entry zone. Quantification of BrdU positive cells within sensory ganglia revealed a 2.3- to 3-fold increase in glial cells compared to controls with a similar response to NGF for the different peripheral ganglia examined. Immunofluorescent labeling with S100β revealed that Schwann and satellite cells underwent mitosis after NGF administration. These data indicate that intracerebroventricular NGF infusion significantly induces gliogenesis in trigeminal ganglia and the spinal sensory ganglia and along the dorsal root entry zone as well as the dorsal root.

Characterization of cultured multipotent zebrafish neural crest cells

The neural crest is a unique cell population associated with vertebrate evolution. Neural crest cells (NCCs) are characterized by their multipotent and migratory potentials. While zebrafish is a powerful genetic model organism, the isolation and culture of zebrafish NCCs would provide a useful adjunct to fully interrogate the genetic networks that regulate NCC development. Here we report for the first time the isolation, in vitro culture, and characterization of NCCs from zebrafish embryos. NCCs were isolated from transgenic sox10:egfp embryos using fluorescence activated cell sorting and cultured in complex culture medium without feeder layers. NCC multilineage differentiation was determined by immunocytochemistry and real-time qPCR, cell migration was assessed by wound healing assay, and the proliferation index was calculated by immunostaining against the mitosis marker phospho-histone H3. Cultured NCCs expressed major neural crest lineage markers such as sox10, sox9a, hnk1, p75, dlx2a, and pax3, and the pluripotency markers c-myc and klf4. We showed that the cultured NCCs can be differentiated into multiple neural crest lineages, contributing to neurons, glial cells, smooth muscle cells, melanocytes, and chondrocytes. We applied the NCC in vitro model to study the effect of retinoic acid on NCC development. We showed that retinoic acid had a profound effect on NCC morphology and differentiation, significantly inhibited proliferation and enhanced cell migration. The availability of high numbers of NCCs and reproducible functional assays offers new opportunities for mechanistic studies of neural crest development, in genetic and chemical biology applications.

Insights into neural crest development and evolution from genomic analysis

The neural crest is an excellent model system for the study of cell type diversification during embryonic development due to its multipotency, motility, and ability to form a broad array of derivatives ranging from neurons and glia, to cartilage, bone, and melanocytes. As a uniquely vertebrate cell population, it also offers important clues regarding vertebrate origins. In the past 30 yr, introduction of recombinant DNA technology has facilitated the dissection of the genetic program controlling neural crest development and has provided important insights into gene regulatory mechanisms underlying cell migration and differentiation. More recently, new genomic approaches have provided a platform and tools that are changing the depth and breadth of our understanding of neural crest development at a “systems” level. Such advances provide an insightful view of the regulatory landscape of neural crest cells and offer a new perspective on developmental as well as stem cell and cancer biology.

Accumulating mutations in series of haplotypes at the KIT and MITF loci are major determinants of white markings in Franches-Montagnes horses

Coat color and pattern variations in domestic animals are frequently inherited as simple monogenic traits, but a number are known to have a complex genetic basis. While the analysis of complex trait data remains a challenge in all species, we can use the reduced haplotypic diversity in domestic animal populations to gain insight into the genomic interactions underlying complex phenotypes. White face and leg markings are examples of complex traits in horses where little is known of the underlying genetics. In this study, Franches-Montagnes (FM) horses were scored for the occurrence of white facial and leg markings using a standardized scoring system. A genome-wide association study (GWAS) was performed for several white patterning traits in 1,077 FM horses. Seven quantitative trait loci (QTL) affecting the white marking score with p-values p≤10(-4) were identified. Three loci, MC1R and the known white spotting genes, KIT and MITF, were identified as the major loci underlying the extent of white patterning in this breed. Together, the seven loci explain 54% of the genetic variance in total white marking score, while MITF and KIT alone account for 26%. Although MITF and KIT are the major loci controlling white patterning, their influence varies according to the basic coat color of the horse and the specific body location of the white patterning. Fine mapping across the MITF and KIT loci was used to characterize haplotypes present. Phylogenetic relationships among haplotypes were calculated to assess their selective and evolutionary influences on the extent of white patterning. This novel approach shows that KIT and MITF act in an additive manner and that accumulating mutations at these loci progressively increase the extent of white markings.

Role of Sp5 as an essential early regulator of neural crest specification in xenopus

BACKGROUND

The neural crest (NC) is a multipotent embryonic cell population, which is induced by an integration of secreted signals including BMP, Wnt, and FGF and, subsequently, NC cell fates are specified by a regulatory network of specific transcription factors. This study was undertaken to identify a role of Sp5 transcription factor in vertebrates.

RESULTS

Xenopus Sp5 is expressed in the prospective neural crest regions from gastrulation through the tadpole stages in early development. Knockdown of Sp5 caused severe defects in craniofacial cartilage, pigmentation, and dorsal fin. Gain- and loss-of-function of Sp5 led to up- and down-regulation of the expression of NC markers in the neural fold, respectively. In contrast, Sp5 had no effect on neural induction and patterning. Sp5 regulated the expression of neural plate border (NPB) specifiers, Msx1 and Pax3, and these regulatory factors recovered the expression of NC marker in the Sp5-deficient embryos. Depletion of Sp5 impaired NC induction by Wnt/β-catenin or FGF signal, whereas its co-expression rescued NC markers in embryos in which either signal was blocked.

CONCLUSIONS

These results suggest that Sp5 functions as a critical early factor in the genetic cascade to regulate NC induction downstream of Wnt and FGF pathways.

The ubiquitin ligase Nedd4 regulates craniofacial development by promoting cranial neural crest cell survival and stem-cell like properties

The integration of multiple morphogenic signalling pathways and transcription factor networks is essential to mediate neural crest (NC) cell induction, delamination, survival, stem-cell properties, fate choice and differentiation. Although the transcriptional control of NC development is well documented in mammals, the role of post-transcriptional modifications, and in particular ubiquitination, has not been explored. Here we report an essential role for the ubiquitin ligase Nedd4 in cranial NC cell development. Our analysis of Nedd4(-/-) embryos identified profound deficiency of cranial NC cells in the absence of structural defects in the neural tube. Nedd4 is expressed in migrating cranial NC cells and was found to positively regulate expression of the NC transcription factors Sox9, Sox10 and FoxD3. We found that in the absence of these factors, a subset of cranial NC cells undergo apoptosis. In accordance with a lack of cranial NC cells, Nedd4(-/-) embryos have deficiency of the trigeminal ganglia, NC derived bone and malformation of the craniofacial skeleton. Our analyses therefore uncover an essential role for Nedd4 in a subset of cranial NC cells and highlight E3 ubiquitin ligases as a likely point of convergence for multiple NC signalling pathways and transcription factor networks.

Human foreskin fibroblast-like stromal cells can differentiate into functional hepatocytic cells

Foreskin fibroblast-like stromal cells (FDSCs) are progenitors isolated from human tissue that can differentiate into diverse cell types. Many types of stem cells can differentiate into hepatocyte-like cells, which could be used for drug testing or in liver regeneration therapy, but whether FDSCs can be converted into functional hepatocytes is unknown. FDSCs show divergent properties when cultured in distinct media, forming spheres in Dulbecco's modified Eagle's medium (DMEM) containing F12, epidermal growth factor (EGF), and basic fibroblast growth factor (b-FGF), but have fibroblast-like morphology when cultured in DMEM-based growth medium. Both cell populations express the typical mesenchymal stem cell markers CD90, CD105, and CD73, but the p75 neurotrophin receptor (p75NTR) was detected only in FDSC spheres. Both types of FDSCs can differentiate into hepatocyte-like cells, which express typical liver markers, including albumin and hepatocyte paraffin 1 (Hep Par1), along with liver-specific biological activities. When plasmids containing the human hepatitis B virus (HBV) genome were transfected transiently into FDSCs, differentiated hepatocyte-like cells secrete large amounts of HBe and HBs antigens. FDSCs could be used for clinical hepatic therapy and/or serve as a model of HBV.

Ancestral Myf5 gene activity in periocular connective tissue identifies a subset of fibro/adipogenic progenitors but does not connote a myogenic origin

Extraocular muscles (EOM) represent a unique muscle group that controls eye movements and originates from head mesoderm, while the more typically studied body and limb muscles are somite-derived. Aiming to investigate myogenic progenitors (satellite cells) in EOM versus limb and diaphragm of adult mice, we have been using flow cytometry in combination with myogenic-specific Cre-loxP lineage marking for cell isolation. While analyzing cells from the EOM of mice that harbor Myf5(Cre)-driven GFP expression, we identified in addition to the expected GFP(+) myogenic cells (presumably satellite cells), a second dominant GFP(+) population distinguished as being Sca1(+), non-myogenic, and exhibiting a fibro/adipogenic potential. This unexpected population was not only unique to EOM compared to the other muscles but also specific to the Myf5(Cre)-driven reporter when compared to the MyoD(Cre) driver. Histological studies of periocular tissue preparations demonstrated the presence of Myf5(Cre)-driven GFP(+) cells in connective tissue locations adjacent to the muscle masses, including cells in the vasculature wall. These vasculature-associated GFP(+) cells were further identified as mural cells based on the presence of the specific XLacZ4 transgene. Unlike the EOM satellite cells that originate from a Pax3-negative lineage, these non-myogenic Myf5(Cre)-driven GFP(+) cells appear to be related to cells of a Pax3-expressing origin, presumably derived from the neural crest. In all, our lineage tracing based on multiple reporter lines has demonstrated that regardless of common ancestral expression of Myf5, there is a clear distinction between periocular myogenic and non-myogenic cell lineages according to their mutually exclusive antecedence of MyoD and Pax3 gene activity.

Spinal muscular atrophy: a motor neuron disorder or a multi-organ disease?

Spinal muscular atrophy (SMA) is an autosomal recessive disorder that is the leading genetic cause of infantile death. SMA is characterized by loss of motor neurons in the ventral horn of the spinal cord, leading to weakness and muscle atrophy. SMA occurs as a result of homozygous deletion or mutations in Survival Motor Neuron-1 (SMN1). Loss of SMN1 leads to a dramatic reduction in SMN protein, which is essential for motor neuron survival. SMA disease severity ranges from extremely severe to a relatively mild adult onset form of proximal muscle atrophy. Severe SMA patients typically die mostly within months or a few years as a consequence of respiratory insufficiency and bulbar paralysis. SMA is widely known as a motor neuron disease; however, there are numerous clinical reports indicating the involvement of additional peripheral organs contributing to the complete picture of the disease in severe cases. In this review, we have compiled clinical and experimental reports that demonstrate the association between the loss of SMN and peripheral organ deficiency and malfunction. Whether defective peripheral organs are a consequence of neuronal damage/muscle atrophy or a direct result of SMN loss will be discussed.

The neural crest transcription factor Brn3a is expressed in melanoma and required for cell cycle progression and survival

Pigment cells and neuronal cells both are derived from the neural crest. Here, we describe the Pit-Oct-Unc (POU) domain transcription factor Brn3a, normally involved in neuronal development, to be frequently expressed in melanoma, but not in melanocytes and nevi. RNAi-mediated silencing of Brn3a strongly reduced the viability of melanoma cell lines and decreased tumour growth in vivo. In melanoma cell lines, inhibition of Brn3a caused DNA double-strand breaks as evidenced by Mre11/Rad50-containing nuclear foci. Activated DNA damage signalling caused stabilization of the tumour suppressor p53, which resulted in cell cycle arrest and apoptosis. When Brn3a was ectopically expressed in primary melanocytes and fibroblasts, anchorage-independent growth was increased. In tumourigenic melanocytes and fibroblasts, Brn3a accelerated tumour growth in vivo. Furthermore, Brn3a cooperated with proliferation pathways such as oncogenic BRAF, by reducing oncogene-induced senescence in non-malignant melanocytes. Together, these results identify Brn3a as a new factor in melanoma that is essential for melanoma cell survival and that promotes melanocytic transformation and tumourigenesis.

Integration of multiple signaling pathways determines differences in the osteogenic potential and tissue regeneration of neural crest-derived and mesoderm-derived calvarial bones

The mammalian skull vault, a product of a unique and tightly regulated evolutionary process, in which components of disparate embryonic origin are integrated, is an elegant model with which to study osteoblast biology. Our laboratory has demonstrated that this distinct embryonic origin of frontal and parietal bones confer differences in embryonic and postnatal osteogenic potential and skeletal regenerative capacity, with frontal neural crest derived osteoblasts benefitting from greater osteogenic potential. We outline how this model has been used to elucidate some of the molecular mechanisms which underlie these differences and place these findings into the context of our current understanding of the key, highly conserved, pathways which govern the osteoblast lineage including FGF, BMP, Wnt and TGFβ signaling. Furthermore, we explore recent studies which have provided a tantalizing insight into way these pathways interact, with evidence accumulating for certain transcription factors, such as Runx2, acting as a nexus for cross-talk.

Intervertebral disc-derived stem cells: implications for regenerative medicine and neural repair

STUDY DESIGN

An in vitro and in vivo evaluation of intervertebral disc (IVD)-derived stem/progenitor cells.

OBJECTIVE

To determine the chondrogenic, adipogenic, osteogenic, and neurogenic differentiation capacity of disc-derived stem/progenitor cells in vitro and neurogenic differentiation in vivo.

SUMMARY OF BACKGROUND DATA

Tissue repair strategies require a source of appropriate cells that could be used to replace dead or damaged cells and tissues such as stem cells. Here we examined the potential use of IVD-derived stem cells in regenerative medicine approaches and neural repair.

METHODS

Nonchondrodystrophic canine IVD nucleus pulposus (NP) cells were used to generate stem/progenitor cells (NP progenitor cells [NPPCs]) and the NPPCs were differentiated in vitro into chondrogenic, adipogenic, and neurogenic lineages and in vivo into the neurogenic lineage. NPPCs were compared with bone marrow-derived mesenchymal (stromal) stem cells in terms of the expression of stemness genes. The expression of the neural crest marker protein 0 and the Brachyury gene were evaluated in NP cells and NPPCs.

RESULTS

NPPCs contain stem/progenitor cells and express "stemness" genes such as Sox2, Oct3/4, Nanog, CD133, Nestin, and neural cell adhesion molecule but differ from mesenchymal (stromal) stem cells in the higher expression of the Nanog gene by NPPCs. NPPCs do not express protein 0 or the Brachyury gene both of which are expressed by the totality of IVD NP cells. The percentage of NPPCs within the IVD is 1% of the total as derived by colony-forming assay. NPPCs are capable of differentiating along chondrogenic, adipogenic, and neurogenic lineages in vitro and into oligodendrocyte, neuron, and astroglial specific precursor cells in vivo within the compact myelin-deficient shiverer mouse.

CONCLUSION

We propose that the IVD NP represents a regenerative niche suggesting that the IVD could represent a readily accessible source of precursor cells for neural repair and regeneration.

Signals and switches in Mammalian neural crest cell differentiation

Neural crest cells (NCCs) comprise a multipotent, migratory cell population that generates a diverse array of cell and tissue types during vertebrate development. These include cartilage and bone, tendons, and connective tissue, as well as neurons, glia, melanocytes, and endocrine and adipose cells; this remarkable lineage potential persists into adult life. Taken together with a limited capacity for self-renewal, neural crest cells bear the hallmarks of stem and progenitor cells and are considered to be synonymous with vertebrate evolution. The neural crest has provided a system for exploring the mechanisms that govern developmental processes such as morphogenetic induction, cell migration, and fate determination. Today, much of the focus on neural crest cells revolves around their stem cell-like characteristics and potential for use in regenerative medicine. A thorough understanding of the signals and switches that govern mammalian neural crest patterning is central to potential therapeutic application of these cells and better appreciation of the role that neural crest cells play in vertebrate evolution, development, and disease.

Neural crest stem cell property of apical pulp cells derived from human developing tooth

Recent reports have described that NCSCs (neural crest-derived stem cells) are not only present in the embryonic neural crest but also in the adult tissues. Dental pulp is one of mesenchymal soft tissues origin from cranial neural crest cells, and thought to be a source of adult stem cells. Here, we investigated the existence of NCSC-like cells in apical pulp of human developing tooth. Human impacted third molars with immature apex freshly extracted were obtained. The cells derived from the apical pulp tissue not framed by dentin or the coronal pulp tissues were cultured by primary explant culture. APDCs (apical pulp-derived cells) and CPCs (coronal pulp cells) formed spheres under neurosphere culture condition. The number of spheres from APDCs was larger than that from CPCs. The sphere-forming cells derived from APDCs had self-renewal capacity, and expressed neural crest-associated markers (p75, Snail and Slug) and NSC (neural stem cell) markers (Nestin and Musashi1). The expression pattern of mesenchymal stem cell markers, CD105 and CD166, on the surface of sphere-forming cells derived APDCs was different from that of APDCs. These sphere-forming cells could differentiate into multiple mesenchymal lineages (osteoblasts, adipocytes, chondrocytes and smooth muscle cells) and neural lineage (neurons) in vitro, and generated ectopic bone tissues on the border of HA (hydroxyapatite) scaffold in vivo. The results of this study suggest that APDCs contain cells with characteristics of NCSCs reported previously in mice. Humans developing tooth with immature apex is an effective source of cells for neural crest lineage tissue regeneration.

Adult craniofacial stem cells: sources and relation to the neural crest

During the process of development, neural crest cells migrate out from their niche between the newly formed ectoderm and the neural tube. Thereafter, they give rise not only to ectodermal cell types, but also to mesodermal cell types. Cell types with neural crest ancestry consequently comprise a number of specialized varieties, such as ectodermal neurons, melanocytes and Schwann cells, as well as mesodermal osteoblasts, adipocytes and smooth muscle cells. Numerous recent studies suggest that stem cells with a neural crest origin persist into adulthood, especially within the mammalian craniofacial compartment. This review discusses the sources of adult neural crest-derived stem cells (NCSCs) derived from the cranium, as well as their differentiation potential and expression of key stem cell markers. Furthermore, the expression of marker genes associated with embryonic stem cells and the issue of multi- versus pluripotency of adult NCSCs is reviewed. Stringent tests are proposed, which, if performed, are anticipated to clarify the issue of adult NCSC potency. Finally, current pre-clinical and clinical data are discussed in light of the clinical impact of adult NCSCs.

Mesenspheres of neural crest-derived cells enriched from bone marrow stromal cell subpopulation

Neural crest-derived cells (NCCs) can be used for cell replacement therapy of neurodegenerative diseases and nerve injury, and it is of significance to open readily accessible tissue sources for NCCs due to their insufficient supply. In this study, we aimed to examine the possibility of enriching NCCs from bone marrow stromal cell (BMSC) subpopulation. The epidermal growth factor/fibroblast growth factor-2 (EGF/FGF2)-responsive BMSC subpopulation (BMSC-C2) was isolated from rat bone marrow by repetitive two-step condition culture. The BMSC-C2 subpopulation showed a long-term proliferative capacity and high cell growth rate, and possessed a significant sphere-forming ability. The mesenspheres derived from BMSC-C2 subpopulation were self-renewable and could express NCC markers, such as CD29, CD44, nestin, CD133 and p75(NTR). In particular, the mesenspheres could be induced to differentiate into neuron- and glia-like cells in vitro. Collectively, our results might provide a basis for in-depth studies of recruiting postmigratory NCCs from bone marrow and various neural crest-derived tissues.

Human adult periodontal ligament-derived cells integrate and differentiate after implantation into the adult mammalian brain

Previous studies suggest that neural crest (NC)-derived stem cells may reside in NC derivatives including the human periodontal ligament (hPDL). The isolation and manipulation of autologous NC-derived cells could be an accessible source of adult neural stem cells for their use in cell replacement and gene transfer to the diseased central nervous system. In this study, we examined the expression of NC markers and neural differentiation potential of hPDL-derived cells both in vitro and in vivo. In vitro we found that hPDL-derived cells expressed stem cell markers (Oct3/4, Nestin, Sox2, and Musashi-1) and a subset of NC cell markers (Slug, p75(NTR), Twist, and Sox9). hPDL-derived cells differentiated into neural-like cells based on cellular morphology and neural marker expression (TUJ1, MAP2, MAP1b, GAD65/67, GABA, NeuN, ChAT, GAT1, synaptophysin, GFAP, NG2, and O4). In vivo, hPDL-derived cells survive, migrate, and give rise to DCX(+), NF-M(+), GABA(+), GFAP(+), and NG2(+) cells after grafting the adult mouse brain. Some of the grafted hPDL-derived cells were located in stem cell niches such as the ventricular epithelium and the subventricular zone of the anterolateral ventricle wall as well as in the subgranular zone of the hippocampal dentate gyrus. Thus, the hPDL contains stem cells that originate from the NC and can differentiate into neural cells. The engraftment and differentiation properties of hPDL-derived cells in the adult brain indicate that they are a potential stem cell source to be used in neuroregenerative and/or neurotrophic medicine.

Loss of pannexin 1 attenuates melanoma progression by reversion to a melanocytic phenotype

Pannexin 1 (Panx1) is a channel-forming glycoprotein expressed in different cell types of mammalian skin. We examined the role of Panx1 in melanoma tumorigenesis and metastasis since qPCR and Western blots revealed that mouse melanocytes exhibited low levels of Panx1 while increased Panx1 expression was correlated with tumor cell aggressiveness in the isogenic melanoma cell lines (B16-F0, -F10, and -BL6). Panx1 shRNA knockdown (Panx1-KD) generated stable BL6 cell lines, with reduced dye uptake, that showed a marked increase in melanocyte-like cell characteristics including higher melanin production, decreased cell migration and enhanced formation of cellular projections. Western blotting and proteomic analyses using 2D-gel/mass spectroscopy identified vimentin and β-catenin as two of the markers of malignant melanoma that were down-regulated in Panx1-KD cells. Xenograft Panx1-KD cells grown within the chorioallantoic membrane of avian embryos developed tumors that were significantly smaller than controls. Mouse-Alu qPCR of the excised avian embryonic organs revealed that tumor metastasis to the liver was significantly reduced upon Panx1 knockdown. These data suggest that while Panx1 is present in skin melanocytes it is up-regulated during melanoma tumor progression, and tumorigenesis can be inhibited by the knockdown of Panx1 raising the possibility that Panx1 may be a viable target for the treatment of melanoma.

Direct reprogramming of melanocytes to neural crest stem-like cells by one defined factor

Mouse and human somatic cells can either be reprogrammed to a pluripotent state or converted to another lineage with a combination of transcription factors suggesting that lineage commitment is a reversible process. Here we show that only one factor, the active intracellular form of Notch1, is sufficient to convert mature pigmented epidermal-derived melanocytes into functional multipotent neural crest (NC) stem-like cells. These induced NC stem cells (iNCSCs) proliferate as spheres under stem cell media conditions, re-express NC-related genes, and differentiate into multiple NC-derived mesenchymal and neuronal lineages. Moreover, iNCSCs are highly migratory and functional in vivo. These results demonstrate that mature melanocytes can be reprogrammed toward their primitive NC cell precursors through the activation of a single stem cell-related pathway. Reprogramming of melanocytes to iNCSCs may provide an alternate source of NCSCs for neuroregenerative applications.

Neural crest progenitors and stem cells: from early development to adulthood

In the vertebrate embryo, the neural crest forms transiently in the dorsal neural primordium to yield migratory cells that will invade nearly all tissues and later, will differentiate into bones and cartilages, neurons and glia, endocrine cells, vascular smooth muscle cells and melanocytes. Due to the amazingly diversified array of cell types it produces, the neural crest is an attractive model system in the stem cell field. We present here in vivo and in vitro studies of single cell fate, which led to the discovery and the characterization of stem cells in the neural crest of avian and mammalian embryos. Some of the key issues in neural crest cell diversification are discussed, such as the time of segregation of mesenchymal vs. neural/melanocytic lineages, and the origin and close relationships between the glial and melanocytic lineages. An overview is also provided of the diverse types of neural crest-like stem cells and progenitors, recently identified in a growing number of adult tissues in animals and humans. Current and future work, in which in vivo lineage studies and the use of injury models will complement the in vitro culture analysis, should help in unraveling the properties and function of neural crest-derived progenitors in development and disease.