Isolation of a stem cell for neurons and glia from the mammalian neural crest

Mechanism of inflammatory response and therapeutic effects of stem cells in ischemic stroke: current evidence and future perspectives

Ischemic stroke is a leading cause of death and disability worldwide, with an increasing trend and tendency for onset at a younger age. China, in particular, bears a high burden of stroke cases. In recent years, the inflammatory response after stroke has become a research hotspot: understanding the role of inflammatory response in tissue damage and repair following ischemic stroke is an important direction for its treatment. This review summarizes several major cells involved in the inflammatory response following ischemic stroke, including microglia, neutrophils, monocytes, lymphocytes, and astrocytes. Additionally, we have also highlighted the recent progress in various treatments for ischemic stroke, particularly in the field of stem cell therapy. Overall, understanding the complex interactions between inflammation and ischemic stroke can provide valuable insights for developing treatment strategies and improving patient outcomes. Stem cell therapy may potentially become an important component of ischemic stroke treatment.

Chemical Coaxing of Mesenchymal Stromal Cells by Drug Repositioning for Nestin Induction

Mesenchymal stromal cells (MSCs) display heterogeneity in origin and functional role in tissue homeostasis. Subsets of MSCs derived from the neural crest express nestin and serve as niches in bone marrow, but the possibility of coaxing MSCs into nestin-expresing cells for enhanced supportive activity is unclear. In this study, as an approach to the chemical coaxing of MSC functions, we screened libraries of clinically approved chemicals to identify compounds capable of inducing nestin expression in MSCs. Out of 2000 clinical compounds, we chose vorinostat as a candidate to coax the MSCs into neural crest-like fates. When treated with vorinostat, MSCs exhibited a significant increase in the expression of genes involved in the pluripotency and epithelial-mesenchymal transition (EMT), as well as nestin and CD146, the markers for pericytes. In addition, these nestin-induced MSCs exhibited enhanced differentiation towards neuronal cells with the upregulation of neurogenic markers, including SRY-box transcription factor 2 (Sox2), SRY-box transcription factor 10 (Sox10) and microtubule associated protein 2 (Map2) in addition to nestin. Moreover, the coaxed MSCs exhibited enhanced supporting activity for hematopoietic progenitors without supporting leukemia cells. These results demonstrate the feasibility of the drug repositioning of MSCs to induce neural crest-like properties through the chemical coaxing of cell fates.

Single-cell Profiling of Reprogrammed Human Neural Stem Cells Unveils High Similarity to Neural Progenitors in the Developing Central Nervous System

BACKGROUND

Similar to induced pluripotent cells (iPSCs), induced neural stem cells (iNSCs) can be directly converted from human somatic cells such as dermal fibroblasts and peripheral blood monocytes. While previous studies have demonstrated the resemblance of iNSCs to neural stem cells derived from primary sources and embryonic stem cells, respectively, a comprehensive analysis of the correlation between iNSCs and their physiological counterparts remained to be investigated.

METHODS

Nowadays, single-cell sequencing technologies provide unique opportunities for in-depth cellular benchmarking of complex cell populations. Our study involves the comprehensive profiling of converted human iNSCs at a single-cell transcriptomic level, alongside conventional methods, like flow cytometry and immunofluorescence stainings.

RESULTS

Our results show that the iNSC conversion yields a homogeneous cell population expressing bona fide neural stem cell markers. Extracting transcriptomic signatures from published single cell transcriptomic atlas data and comparison to the iNSC transcriptome reveals resemblance to embryonic neuroepithelial cells of early neurodevelopmental stages observed in vivo at 5 weeks of development.

CONCLUSION

Our data underscore the physiological relevance of directly converted iNSCs, making them a valuable in vitro system for modeling human central nervous system development and establishing translational applications in cell therapy and compound screening.

Advancements in self-assembling peptides: Bridging gaps in 3D cell culture and electronic device fabrication

Self-assembling peptides (SAPs) show promise in creating synthetic microenvironments that regulate cellular function and tissue repair. Also, the precise π-π interactions and hydrogen bonding within self-assembled peptide structures enable the creation of quantum confined structures, leading to reduced band gaps and the emergence of semiconductor properties within the superstructures. This review emphasizes the need for standardized 3D cell culture methods and electronic devices based on SAPs for monitoring cell communication and controlling cell surface morphology. Additionally, the gap in understanding the relationship between SAP peptide sequences and nanostructures is highlighted, underscoring the importance of optimizing peptide deposition parameters, which affect charge transport and bioactivity due to varying morphologies. The potential of peptide nanofibers as extracellular matrix mimics and the introduction of the zone casting method for improved film deposition are discussed within this review, aiming to bridge knowledge gaps and offer insights into fields like tissue engineering and materials science, with the potential for groundbreaking applications at the interface of biology and materials engineering.

Neural Stem Cell-based Regenerative Therapy: A New Approach to Diabetes Treatment

Diabetes mellitus (DM) is the most common metabolic disorder that occurs due to the loss, or impaired function of insulin-secreting pancreatic beta cells, which are of two types - type 1 (T1D) and type 2 (T2D). To cure DM, the replacement of the destroyed pancreatic beta cells of islet of Langerhans is the most widely practiced treatment. For this, isolating neuronal stem cells and cultivating them as a source of renewable beta cells is a significant breakthrough in medicine. The functions, growth, and gene expression of insulin-producing pancreatic beta cells and neurons are very similar in many ways. A diabetic patient's neural stem cells (obtained from the hippocampus and olfactory bulb) can be used as a replacement source of beta cells for regenerative therapy to treat diabetes. The same protocol used to create functional neurons from progenitor cells can be used to create beta cells. Recent research suggests that replacing lost pancreatic beta cells with autologous transplantation of insulin-producing neural progenitor cells may be a perfect therapeutic strategy for diabetes, allowing for a safe and normal restoration of function and a reduction in potential risks and a long-term cure.

Enteric neurospheres retain the capacity to assemble neural networks with motile and metamorphic gliocytes and ganglia

BACKGROUND

Neurosphere medium (NSM) and self-renewal medium (SRM) were widely used to isolate enteric neural stem cells (ENSCs) in the form of neurospheres. ENSCs or their neurosphere forms were neurogenic and gliogenic, but the compelling evidence for their capacity of assembling enteric neural networks remained lacking, raising the question of their aptitude for rebuilding the enteric nervous system (ENS) in ENSC therapeutics. It prompted us to explore an effective culture protocol or strategy for assembling ENS networks, which might also be employed as an in vitro model to simplify the biological complexity of ENS embedded in gut walls.

METHODS

NSM and SRM were examined for their capacity to generate neurospheres in mass culture of dispersed murine fetal enterocytes at serially diluted doses and assemble enteric neural networks in two- and three-dimensional cell culture systems and ex vivo on gut explants. Time-lapse microphotography was employed to capture cell activities of assembled neural networks. Neurosphere transplantation was performed via rectal submucosal injection.

RESULTS

In mass culture of dispersed enterocytes, NSM generated discrete units of neurospheres, whereas SRM promoted neural network assembly with neurospheres akin to enteric ganglia. Both were highly affected by seeding cell doses. SRM had similar ENSC mitosis-driving capacity to NSM, but was superior in driving ENSC differentiation in company with heightened ENSC apoptosis. Enteric neurospheres were motile, capable of merging together. It argued against their clonal entities. When nurtured in SRM, enteric neurospheres proved competent to assemble neural networks on two-dimensional coverslips, in three-dimensional hydrogels and on gut explants. In the course of neural network assembly from enteric neurospheres, neurite extension was preceded by migratory expansion of gliocytes. Assembled neural networks contained motile ganglia and gliocytes that constantly underwent shapeshift. Neurospheres transplanted into rectal submucosa might reconstitute myenteric plexuses of recipients' rectum.

CONCLUSION

Enteric neurospheres mass-produced in NSM might assemble neural networks in SRM-immersed two- or three-dimensional environments and on gut explants, and reconstitute myenteric plexuses of the colon after rectal submucosal transplantation. Our results also shed first light on the dynamic entity of ENS and open the experimental avenues to explore cellular activities of ENS and facilitate ENS demystification.

Generation of Schwann cell derived melanocytes from hPSCs identifies pro-metastatic factors in melanoma

The neural crest (NC) is highly multipotent and generates diverse lineages in the developing embryo. However, spatiotemporally distinct NC populations display differences in fate potential, such as increased gliogenic and parasympathetic potential from later migrating, nerve-associated Schwann cell precursors (SCPs). Interestingly, while melanogenic potential is shared by both early migrating NC and SCPs, differences in melanocyte identity resulting from differentiation through these temporally distinct progenitors have not been determined. Here, we leverage a human pluripotent stem cell (hPSC) model of NC temporal patterning to comprehensively characterize human NC heterogeneity, fate bias, and lineage development. We captured the transition of NC differentiation between temporally and transcriptionally distinct melanogenic progenitors and identified modules of candidate transcription factor and signaling activity associated with this transition. For the first time, we established a protocol for the directed differentiation of melanocytes from hPSCs through a SCP intermediate, termed trajectory 2 (T2) melanocytes. Leveraging an existing protocol for differentiating early NC-derived melanocytes, termed trajectory 1 (T1), we performed the first comprehensive comparison of transcriptional and functional differences between these distinct melanocyte populations, revealing differences in pigmentation and unique expression of transcription factors, ligands, receptors and surface markers. We found a significant link between the T2 melanocyte transcriptional signature and decreased survival in melanoma patients in the cancer genome atlas (TCGA). We performed an in vivo CRISPRi screen of T1 and T2 melanocyte signature genes in a human melanoma cell line and discovered several T2-specific markers that promote lung metastasis in mice. We further demonstrated that one of these factors, SNRPB, regulates the splicing of transcripts involved in metastasis relevant functions such as migration, cell adhesion and proliferation. Overall, this study identifies distinct developmental trajectories as a source of diversity in melanocytes and implicates the unique molecular signature of SCP-derived melanocytes in metastatic melanoma.

Establishment of a novel in vitro co-culture system of enteric neurons and Caco-2 cells for evaluating the effect of enteric nervous system on transepithelial transport of drugs

The gastrointestinal tract is innervated by extrinsic autonomic nerves and intrinsic enteric nervous system (ENS). However, the role of ENS in drug absorption has remained to be clarified. To investigate the effect of ENS on drug transport across the intestinal epithelial cells, we established a novel co-culture system of Caco-2 cells and enteric neurons differentiated from neural crest stem (NCS)-like cells isolated from mouse longitudinal muscle/myenteric plexus (LMMP). Immunostaining analysis revealed that the proportions of neuron, glia, and NCS-like cells were only <5 % at population in the primary culture of LMMP cells. Therefore, we proliferated NCS-like cells and differentiated them into neuronal cells and successfully increased the neuronal cell population upto about 40 %. Then, the differentiated neuronal cells were co-cultured with Caco-2 cell monolayers, and we found that the co-culture significantly decreased the transepithelial electrical resistance and enhanced the transport of fluorescein isothiocyanate-labeled dextran-4 across Caco-2 cell monolayers, suggesting that the enteric neurons would function to open the tight junction and facilitate the drug transport via the paracellular route. On the other hand, no changes in the permeability of antipyrine were observed, suggesting that the enteric neurons would not affect the passive transport via the transcellular pathway.

Development and In Vitro Differentiation of Schwann Cells

Schwann cells are glial cells of the peripheral nervous system. They exist in several subtypes and perform a variety of functions in nerves. Their derivation and culture in vitro are interesting for applications ranging from disease modeling to tissue engineering. Since primary human Schwann cells are challenging to obtain in large quantities, in vitro differentiation from other cell types presents an alternative. Here, we first review the current knowledge on the developmental signaling mechanisms that determine neural crest and Schwann cell differentiation in vivo. Next, an overview of studies on the in vitro differentiation of Schwann cells from multipotent stem cell sources is provided. The molecules frequently used in those protocols and their involvement in the relevant signaling pathways are put into context and discussed. Focusing on hiPSC- and hESC-based studies, different protocols are described and compared, regarding cell sources, differentiation methods, characterization of cells, and protocol efficiency. A brief insight into developments regarding the culture and differentiation of Schwann cells in 3D is given. In summary, this contribution provides an overview of the current resources and methods for the differentiation of Schwann cells, it supports the comparison and refinement of protocols and aids the choice of suitable methods for specific applications.

Keratinocyte Growth Factor Stimulates Growth of p75+ Neural Crest Lineage Cells During Middle Ear Cholesteatoma Formation in Mice

During development, cranial neural crest (NC) cells display a striking transition from collective to single-cell migration and undergo a mesenchymal-to-epithelial transformation to form a part of the middle ear epithelial cells (MEECs). While MEECs derived from NC are known to control homeostasis of the epithelium and repair from otitis media, paracrine action of keratinocyte growth factor (KGF) promotes the growth of MEECs and induces middle ear cholesteatoma (cholesteatoma). The animal model of cholesteatoma was previously established by transfecting a human KGF-expression vector. Herein, KGF-inducing cholesteatoma was studied in Wnt1-Cre/Floxed-enhanced green fluorescent protein (EGFP) mice that conditionally express EGFP in the NC lineages. The cytokeratin 14-positive NC lineage expanded into the middle ear and formed cholesteatoma. Moreover, the green fluorescent protein-positive NC lineages comprising the cholesteatoma tissue expressed p75, an NC marker, with high proliferative activity. Similarly, a large number of p75-positive cells were observed in human cholesteatoma tissues. Injections of the immunotoxin murine p75-saporin induced depletion of the p75-positive NC lineages, resulting in the reduction of cholesteatoma in vivo. The p75 knockout in the MEECs had low proliferative activity with or without KGF protein in vitro. Controlling p75 signaling may reduce the proliferation of NC lineages and may represent a new therapeutic target for cholesteatoma.

Neurofibroma Development in Neurofibromatosis Type 1: Insights from Cellular Origin and Schwann Cell Lineage Development

BACKGROUND

Neurofibromatosis type 1 (NF1), a genetic tumor predisposition syndrome that affects about 1 in 3000 newborns, is caused by mutations in the NF1 gene and subsequent inactivation of its encoded neurofibromin. Neurofibromin is a tumor suppressor protein involved in the downregulation of Ras signaling. Despite a diverse clinical spectrum, one of several hallmarks of NF1 is a peripheral nerve sheath tumor (PNST), which comprises mixed nervous and fibrous components. The distinct spatiotemporal characteristics of plexiform and cutaneous neurofibromas have prompted hypotheses about the origin and developmental features of these tumors, involving various cellular transition processes.

METHODS

We retrieved published literature from PubMed, EMBASE, and Web of Science up to 21 June 2022 and searched references cited in the selected studies to identify other relevant papers. Original articles reporting the pathogenesis of PNSTs during development were included in this review. We highlighted the Schwann cell (SC) lineage shift to better present the evolution of its corresponding cellular origin hypothesis and its important effects on the progression and malignant transformation of neurofibromas.

CONCLUSIONS

In this review, we summarized the vast array of evidence obtained on the full range of neurofibroma development based on cellular and molecular pathogenesis. By integrating findings relating to tumor formation, growth, and malignancy, we hope to reveal the role of SC lineage shift as well as the combined impact of additional determinants in the natural history of PNSTs.

Microarrayed human bone marrow organoids for modeling blood stem cell dynamics

In many leukemia patients, a poor prognosis is attributed either to the development of chemotherapy resistance by leukemic stem cells (LSCs) or to the inefficient engraftment of transplanted hematopoietic stem/progenitor cells (HSPCs) into the bone marrow (BM). Here, we build a 3D in vitro model system of bone marrow organoids (BMOs) that recapitulate several structural and cellular components of native BM. These organoids are formed in a high-throughput manner from the aggregation of endothelial and mesenchymal cells within hydrogel microwells. Accordingly, the mesenchymal compartment shows partial maintenance of its self-renewal and multilineage potential, while endothelial cells self-organize into an interconnected vessel-like network. Intriguingly, such an endothelial compartment enhances the recruitment of HSPCs in a chemokine ligand/receptor-dependent manner, reminiscent of HSPC homing behavior in vivo. Additionally, we also model LSC migration and nesting in BMOs, thus highlighting the potential of this system as a well accessible and scalable preclinical model for candidate drug screening and patient-specific assays.

Advances in construction and modeling of functional neural circuits in vitro

Over the years, techniques have been developed to culture and assemble neurons, which brought us closer to creating neuronal circuits that functionally and structurally mimic parts of the brain. Starting with primary culture of neurons, preparations of neuronal culture have advanced substantially. Development of stem cell research and brain organoids has opened a new path for generating three-dimensional human neural circuits. Along with the progress in biology, engineering technologies advanced and paved the way for construction of neural circuit structures. In this article, we overview research progress and discuss perspective of in vitro neural circuits and their ability and potential to acquire functions. Construction of in vitro neural circuits with complex higher-order functions would be achieved by converging development in diverse major disciplines including neuroscience, stem cell biology, tissue engineering, electrical engineering and computer science.

A cholinergic neuroskeletal interface promotes bone formation during postnatal growth and exercise

The autonomic nervous system is a master regulator of homeostatic processes and stress responses. Sympathetic noradrenergic nerve fibers decrease bone mass, but the role of cholinergic signaling in bone has remained largely unknown. Here, we describe that early postnatally, a subset of sympathetic nerve fibers undergoes an interleukin-6 (IL-6)-induced cholinergic switch upon contacting the bone. A neurotrophic dependency mediated through GDNF-family receptor-α2 (GFRα2) and its ligand, neurturin (NRTN), is established between sympathetic cholinergic fibers and bone-embedded osteocytes, which require cholinergic innervation for their survival and connectivity. Bone-lining osteoprogenitors amplify and propagate cholinergic signals in the bone marrow (BM). Moderate exercise augments trabecular bone partly through an IL-6-dependent expansion of sympathetic cholinergic nerve fibers. Consequently, loss of cholinergic skeletal innervation reduces osteocyte survival and function, causing osteopenia and impaired skeletal adaptation to moderate exercise. These results uncover a cholinergic neuro-osteocyte interface that regulates skeletogenesis and skeletal turnover through bone-anabolic effects.

Isolation and Culture of Cranial Neural Crest Cells from the First Branchial Arch of Mice

Craniofacial anomalies (CFA) are a diverse group of deformities, which affect the growth of the head and face. Dysregulation of cranial neural crest cell (NCC) migration, proliferation, differentiation, and/or cell fate specification have been reported to contribute to CFA. Understanding of the mechanisms through which cranial NCCs contribute for craniofacial development may lead to identifying meaningful clinical targets for the prevention and treatment of CFA. Isolation and culture of cranial NCCs in vitro facilitates screening and analyses of molecular cellular mechanisms of cranial NCCs implicated in craniofacial development. Here, we present a method for the isolation and culture of cranial NCCs harvested from the first branchial arch at early embryonic stages. Morphology of isolated cranial NCCs was similar to O9-1 cells, a cell line for neural crest stem cells. Moreover, cranial NCCs isolated from a transgenic mouse line with enhanced bone morphogenetic protein (BMP) signaling in NCCs showed an increase in their chondrogenic differentiation capacity, suggesting maintenance of their in vivo differentiation potentials observed in vitro. Taken together, our established method is useful to visualize cellular behaviors of cranial NCCs.

Reactive Oxygen Species: Angels and Demons in the Life of a Neuron

Reactive oxygen species (ROS) have emerged as regulators of key processes supporting neuronal growth, function, and plasticity across lifespan. At normal physiological levels, ROS perform important roles as secondary messengers in diverse molecular processes such as regulating neuronal differentiation, polarization, synapse maturation, and neurotransmission. In contrast, high levels of ROS are toxic and can ultimately lead to cell death. Excitable cells, such as neurons, often require high levels of metabolic activity to perform their functions. As a consequence, these cells are more likely to produce high levels of ROS, potentially enhancing their susceptibility to oxidative damage. In addition, because neurons are generally post-mitotic, they may be subject to accumulating oxidative damage. Thus, maintaining tight control over ROS concentration in the nervous system is essential for proper neuronal development and function. We are developing a more complete understanding of the cellular and molecular mechanisms for control of ROS in these processes. This review focuses on ROS regulation of the developmental and functional properties of neurons, highlighting recent in vivo studies. We also discuss the current evidence linking oxidative damage to pathological conditions associated with neurodevelopmental and neurodegenerative disorders.

Oligodendroglia Generated From Adult Rat Adipose Tissue by Direct Cell Conversion

Obtaining oligodendroglial cells from dispensable tissues would be of great interest for autologous or immunocompatible cell replacement therapy in demyelinating diseases, as well as for studying myelin-related pathologies or testing therapeutic approaches in culture. We evaluated the feasibility of generating oligodendrocyte precursor cells (OPCs) from adult rat adipose tissue by expressing genes encoding transcription factors involved in oligodendroglial development. Adipose-derived mesenchymal cells were lentivirally transduced with tetracycline-inducible Sox10, Olig2, Zfp536, and/or Nkx6.1 transgenes. Immunostaining with the OPC-specific O4 monoclonal antibody was used to mark oligodendroglial induction. O4- and myelin-associated glycoprotein (MAG)-positive cells emerged after 3 weeks when using the Sox10 + Olig2 + Zfp536 combination, followed in the ensuing weeks by GFAP-, O1 antigen-, p75NTR (low-affinity NGF receptor)-, and myelin proteins-positive cells. The O4⁺ cell population progressively expanded, eventually constituting more than 70% of cells in culture by 5 months. Sox10 transgene expression was essential for generating O4⁺ cells but was insufficient for inducing a full oligodendroglial phenotype. Converted cells required continuous transgene expression to maintain their glial phenotype. Some vestigial characteristics of mesenchymal cells were maintained after conversion. Growth factor withdrawal and triiodothyronine (T₃) supplementation generated mature oligodendroglial phenotypes, while FBS supplementation produced GFAP⁺- and p75NTR⁺-rich cultures. Converted cells also showed functional characteristics of neural-derived OPCs, such as the expression of AMPA, NMDA, kainate, and dopaminergic receptors, as well as similar metabolic responses to differentiation-inducing drugs. When co-cultured with rat dorsal root ganglion neurons, the converted cells differentiated and ensheathed multiple axons. We propose that functional oligodendroglia can be efficiently generated from adult rat mesenchymal cells by direct phenotypic conversion.

Development, Diversity, and Neurogenic Capacity of Enteric Glia

Enteric glia are a fascinating population of cells. Initially identified in the gut wall as the "support" cells of the enteric nervous system, studies over the past 20 years have unveiled a vast array of functions carried out by enteric glia. They mediate enteric nervous system signalling and play a vital role in the local regulation of gut functions. Enteric glial cells interact with other gastrointestinal cell types such as those of the epithelium and immune system to preserve homeostasis, and are perceptive to luminal content. Their functional versatility and phenotypic heterogeneity are mirrored by an extensive level of plasticity, illustrated by their reactivity in conditions associated with enteric nervous system dysfunction and disease. As one of the hallmarks of their plasticity and extending their operative relationship with enteric neurons, enteric glia also display neurogenic potential. In this review, we focus on the development of enteric glial cells, and the mechanisms behind their heterogeneity in the adult gut. In addition, we discuss what is currently known about the role of enteric glia as neural precursors in the enteric nervous system.

Single-cell transcriptomic analysis of zebrafish cranial neural crest reveals spatiotemporal regulation of lineage decisions during development

Neural crest (NC) cells migrate throughout vertebrate embryos to give rise to a huge variety of cell types, but when and where lineages emerge and their regulation remain unclear. We have performed single-cell RNA sequencing (RNA-seq) of cranial NC cells from the first pharyngeal arch in zebrafish over several stages during migration. Computational analysis combining pseudotime and real-time data reveals that these NC cells first adopt a transitional state, becoming specified mid-migration, with the first lineage decisions being skeletal and pigment, followed by neural and glial progenitors. In addition, by computationally integrating these data with RNA-seq data from a transgenic Wnt reporter line, we identify gene cohorts with similar temporal responses to Wnts during migration and show that one, Atp6ap2, is required for melanocyte differentiation. Together, our results show that cranial NC cell lineages arise progressively and uncover a series of spatially restricted cell interactions likely to regulate such cell-fate decisions.

Tatarakis et al. provide a single-cell transcriptomic timeline of cranial neural crest (NC) development in zebrafish and address long-standing questions surrounding the integration of NC cell migration and lineage specification. They find that lineages are specified mid-migration. These fate decisions correspond to shifts in Wnt signaling, and lineages rapidly segregate.

Cell Fate Decisions in the Neural Crest, from Pigment Cell to Neural Development

The neural crest shows an astonishing multipotency, generating multiple neural derivatives, but also pigment cells, skeletogenic and other cell types. The question of how this process is controlled has been the subject of an ongoing debate for more than 35 years. Based upon new observations of zebrafish pigment cell development, we have recently proposed a novel, dynamic model that we believe goes some way to resolving the controversy. Here, we will firstly summarize the traditional models and the conflicts between them, before outlining our novel model. We will also examine our recent dynamic modelling studies, looking at how these reveal behaviors compatible with the biology proposed. We will then outline some of the implications of our model, looking at how it might modify our views of the processes of fate specification, differentiation, and commitment.

Review: The Role of Wnt/β-Catenin Signalling in Neural Crest Development in Zebrafish

The neural crest (NC) is a multipotent cell population in vertebrate embryos with extraordinary migratory capacity. The NC is crucial for vertebrate development and forms a myriad of cell derivatives throughout the body, including pigment cells, neuronal cells of the peripheral nervous system, cardiomyocytes and skeletogenic cells in craniofacial tissue. NC induction occurs at the end of gastrulation when the multipotent population of NC progenitors emerges in the ectodermal germ layer in the neural plate border region. In the process of NC fate specification, fate-specific markers are expressed in multipotent progenitors, which subsequently adopt a specific fate. Thus, NC cells delaminate from the neural plate border and migrate extensively throughout the embryo until they differentiate into various cell derivatives. Multiple signalling pathways regulate the processes of NC induction and specification. This review explores the ongoing role of the Wnt/β-catenin signalling pathway during NC development, focusing on research undertaken in the Teleost model organism, zebrafish (Danio rerio). We discuss the function of the Wnt/β-catenin signalling pathway in inducing the NC within the neural plate border and the specification of melanocytes from the NC. The current understanding of NC development suggests a continual role of Wnt/β-catenin signalling in activating and maintaining the gene regulatory network during NC induction and pigment cell specification. We relate this to emerging models and hypotheses on NC fate restriction. Finally, we highlight the ongoing challenges facing NC research, current gaps in knowledge, and this field's potential future directions.

Age of the donor affects the nature of in vitro cultured human dental pulp stem cells

Objectives

The dental pulp stem cells (DPSCs) of six donors (three young donors aged < 19 years and three adult donors aged > 25 and < 30 years) were characterized for their stem cell marker expression and differentiation potential to study the effect of donor age on DPSCs in vitro.

Methods

DPSCs were cultured in αMEM supplemented with 20% fetal calf serum (conventional conditions) or on fibronectin-coated flasks with neurobasal medium supplemented with B27, bFGF and EGF (alternative conditions). DPSCs were characterized by immunofluorescence staining to detect the neural crest/mesenchymal stem cells markers P75 and CD146, respectively. The differentiation potential was tested by the induction of DPSCs into osteogenic, adipogenic and glial lineages and then by detecting the corresponding markers osteocalcin, lipidtox and S100ß, respectively.

Results

The DPSCs of the young donors expressed CD146 only under the conventional conditions and expressed P75 regardless of the culture conditions. However, the DPSCs of adult donors expressed CD146 only under the alternative conditions and expressed P75 only under conventional conditions. Only the DPSCs of the young donors differentiated into the glial linage. The DPSCs of the adult donors differentiated more efficiently into the adipogenic linage. Osteogenic differentiation was comparable.

Conclusion

Donor age affects the expression of stem cell markers and differentiation potential of DPSCs. Moreover, the effect of culture conditions on DPSCs is age dependent.

Cyclical fate restriction: a new view of neural crest cell fate specification

Neural crest cells are crucial in development, not least because of their remarkable multipotency. Early findings stimulated two hypotheses for how fate specification and commitment from fully multipotent neural crest cells might occur, progressive fate restriction (PFR) and direct fate restriction, differing in whether partially restricted intermediates were involved. Initially hotly debated, they remain unreconciled, although PFR has become favoured. However, testing of a PFR hypothesis of zebrafish pigment cell development refutes this view. We propose a novel 'cyclical fate restriction' hypothesis, based upon a more dynamic view of transcriptional states, reconciling the experimental evidence underpinning the traditional hypotheses.

Seq Your Destiny: Neural Crest Fate Determination in the Genomic Era

Neural crest stem/progenitor cells arise early during vertebrate embryogenesis at the border of the forming central nervous system. They subsequently migrate throughout the body, eventually differentiating into diverse cell types ranging from neurons and glia of the peripheral nervous system to bones of the face, portions of the heart, and pigmentation of the skin. Along the body axis, the neural crest is heterogeneous, with different subpopulations arising in the head, neck, trunk, and tail regions, each characterized by distinct migratory patterns and developmental potential. Modern genomic approaches like single-cell RNA- and ATAC-sequencing (seq) have greatly enhanced our understanding of cell lineage trajectories and gene regulatory circuitry underlying the developmental progression of neural crest cells. Here, we discuss how genomic approaches have provided new insights into old questions in neural crest biology by elucidating transcriptional and posttranscriptional mechanisms that govern neural crest formation and the establishment of axial level identity. Expected final online publication date for the Annual Review of Genetics, Volume 55 is November 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Mechanisms involved in selecting and maintaining neuroblastoma cancer stem cell populations, and perspectives for therapeutic targeting

Pediatric neuroblastomas (NBs) are heterogeneous, aggressive, therapy-resistant embryonal tumours that originate from cells of neural crest (NC) origin and in particular neuroblasts committed to the sympathoadrenal progenitor cell lineage. Therapeutic resistance, post-therapeutic relapse and subsequent metastatic NB progression are driven primarily by cancer stem cell (CSC)-like subpopulations, which through their self-renewing capacity, intermittent and slow cell cycles, drug-resistant and reversibly adaptive plastic phenotypes, represent the most important obstacle to improving therapeutic outcomes in unfavourable NBs. In this review, dedicated to NB CSCs and the prospects for their therapeutic eradication, we initiate with brief descriptions of the unique transient vertebrate embryonic NC structure and salient molecular protagonists involved NC induction, specification, epithelial to mesenchymal transition and migratory behaviour, in order to familiarise the reader with the embryonic cellular and molecular origins and background to NB. We follow this by introducing NB and the potential NC-derived stem/progenitor cell origins of NBs, before providing a comprehensive review of the salient molecules, signalling pathways, mechanisms, tumour microenvironmental and therapeutic conditions involved in promoting, selecting and maintaining NB CSC subpopulations, and that underpin their therapy-resistant, self-renewing metastatic behaviour. Finally, we review potential therapeutic strategies and future prospects for targeting and eradication of these bastions of NB therapeutic resistance, post-therapeutic relapse and metastatic progression.

Potential application of human neural crest-derived nasal turbinate stem cells for the treatment of neuropathology and impaired cognition in models of Alzheimer's disease

Background

Stem cell transplantation is a fascinating therapeutic approach for the treatment of many neurodegenerative disorders; however, clinical trials using stem cells have not been as effective as expected based on preclinical studies. The aim of this study is to validate the hypothesis that human neural crest-derived nasal turbinate stem cells (hNTSCs) are a clinically promising therapeutic source of adult stem cells for the treatment of Alzheimer’s disease (AD).

Methods

hNTSCs were evaluated in comparison with human bone marrow-derived mesenchymal stem cells (hBM-MSCs) according to the effect of transplantation on AD pathology, including PET/CT neuroimaging, immune status indicated by microglial numbers and autophagic capacity, neuronal survival, and cognition, in a 5 × FAD transgenic mouse model of AD.

Results

We demonstrated that hNTSCs showed a high proliferative capacity and great neurogenic properties in vitro. Compared with hBM-MSC transplantation, hNTSC transplantation markedly reduced Aβ42 levels and plaque formation in the brains of the 5 × FAD transgenic AD mice on neuroimaging, concomitant with increased survival of hippocampal and cortex neurons. Moreover, hNTSCs strongly modulated immune status by reducing the number of microglia and the expression of the inflammatory cytokine IL-6 and upregulating autophagic capacity at 7 weeks after transplantation in AD models. Notably, compared with transplantation of hBM-MSCs, transplantation of hNTSCs significantly enhanced performance on the Morris water maze, with an increased level of TIMP2, which is necessary for spatial memory in young mice and neurons; this difference could be explained by the high engraftment of hNTSCs after transplantation.

Conclusion

The reliable evidence provided by these findings reveals a promising therapeutic effect of hNTSCs and indicates a step forward the clinical application of hNTSCs in patients with AD.

Nasal Turbinate Mesenchymal Stromal Cells Preserve Characteristics of Their Neural Crest Origin and Exert Distinct Paracrine Activity

The sources of mesenchymal stromal cells (MSCs) for cell therapy trials are expanding, increasing the need for their characterization. Here, we characterized multi-donor, turbinate-derived MSCs (TB-MSCs) that develop from the neural crest, and compared them to bone marrow-derived MSCs (BM-MSCs). TB-MSCs had higher proliferation potential and higher self-renewal of colony forming cells, but lower potential for multi-lineage differentiation than BM-MSCs. TB-MSCs expressed higher levels of neural crest markers and lower levels of pericyte-specific markers. These neural crest-like properties of TB-MSCs were reflected by their propensity to differentiate into neuronal cells and proliferative response to nerve growth factors. Proteomics (LC-MS/MS) analysis revealed a distinct secretome profile of TB-MSCs compared to BM and adipose tissue-derived MSCs, exhibiting enrichments of factors for cell-extracellular matrix interaction and neurogenic signaling. However, TB-MSCs and BM-MSCs exhibited comparable suppressive effects on the allo-immune response and comparable stimulatory effects on hematopoietic stem cell self-renewal. In contrast, TB-MSCs stimulated growth and metastasis of breast cancer cells more than BM-MSCs. Altogether, our multi-donor characterization of TB-MSCs reveals distinct cell autonomous and paracrine properties, reflecting their unique developmental origin. These findings support using TB-MSCs as an alternative source of MSCs with distinct biological characteristics for optimal applications in cell therapy.

Umbilical artery tissue contains p75 neurotrophin receptor-positive pericyte-like cells that possess neurosphere formation capacity and neurogenic differentiation potential

INTRODUCTION

The p75 neurotrophin receptor (p75NTR) is known as an efficient marker for the prospective isolation of mesenchymal stem cells (MSCs) and neural crest-derived stem cells (NCSCs). To date, there is quite limited information concerning p75NTR-expressing cells in umbilical cord (UC), although UC is known as a rich source of MSCs. We show for the first time the localization, phenotype, and functional properties of p75NTR+ cells in UC.

METHODS

Human UC tissue sections were subjected to immunohistochemistry for MSC markers including p75NTR. Enzymatically isolated umbilical artery (UA) cells containing p75NTR+ cells were assessed for immunophenotype, clonogenic capacity, and differentiation potential. To identify the presence of neural crest-derived cells in the UA, P0-Cre/Floxed-EGFP reporter mouse embryos were used, and immunohistochemical analysis of UC tissue was performed.

RESULTS

Immunohistochemical analysis revealed that p75NTR+ cells were specifically localized to the subendothelial area of the UA and umbilical vein. The p75NTR+ cells co-expressed PDGFRβ, CD90, CD146, and NG2, phenotypic markers of MSCs and pericytes. Isolated UA cells possessed the potential to form neurospheres that further differentiated into neuronal and glial cell lineages. Genetic lineage tracing analysis showed that EGFP+ neural crest-derived cells were detected in the subendothelial area of UA with p75NTR immunoreactivity.

CONCLUSIONS

These results show that UA tissue harbors p75NTR+ pericyte-like cells in the subendothelial area that have the capacity to form neurospheres and the potential for neurogenic differentiation. The lineage tracing data suggests the p75NTR+ cells are putatively derived from the neural crest.

In vitro Modeling of Embryonal Tumors

A subset of pediatric tumors affects very young children and are thought to arise during fetal life. A common theme is that these embryonal tumors hijack developmental programs, causing a block in differentiation and, as a consequence, unrestricted proliferation. Embryonal tumors, therefore typically maintain an embryonic gene signature not found in their differentiated progeny. Still, the processes underpinning malignant transformation remain largely unknown, which is hampering therapeutic innovation. To gain more insight into these processes, in vitro and in vivo research models are indispensable. However, embryonic development is an extremely dynamic process with continuously changing cellular identities, making it challenging to define cells-of-origin. This is crucial for the development of representative models, as targeting the wrong cell or targeting a cell within an incorrect developmental time window can result in completely different phenotypes. Recent innovations in in vitro cell models may provide more versatile platforms to study embryonal tumors in a scalable manner. In this review, we outline different in vitro models that can be explored to study embryonal tumorigenesis and for therapy development.

Treatment and Prevention of Neurocristopathies

Neurocristopathies form a heterogeneous group of rare diseases caused by abnormal development of neural crest cells. Heterogeneity of neurocristopathies directly relates to the nature of these migratory and multipotent cells, which generate dozens of specialized cell types throughout the body. Neurocristopathies are thus characterized by congenital malformations of tissues/organs that otherwise appear to have very little in common, such as the craniofacial skeleton and enteric nervous system. Treatment options are currently very limited, mainly consisting of corrective surgeries. Yet, as reviewed here, analyses of normal and pathological neural crest development in model organisms have opened up the possibility for better treatment options involving cellular and molecular approaches. These approaches provide hope that some neurocristopathies might soon be curable or preventable.

Mutational Landscape of Virus- and UV-Associated Merkel Cell Carcinoma Cell Lines Is Comparable to Tumor Tissue

Simple Summary

Merkel cell carcinoma (MCC) is an aggressive, rare skin cancer which is caused either by a virus or chronic UV exposure. For both forms, distinct genetic alterations have been described; however, these observations were mostly made in tumor tissue. Since cancer cell lines are frequently used as preclinical models to investigate biological function, we considered it necessary to establish the genomic landscape of MCC cell lines by whole-exome sequencing. We confirmed the presence of UV-induced DNA damage, a high number of mutations and several coding mutations in virus-negative cell lines which were absent in virus-positive cell lines; these, however, harbored characteristic copy number variations, suggesting some virally caused genetic instability. Knowing the genomic features of MCC cell lines validates previous, and facilitates upcoming, experimental studies to discover their biological and translational relevance.

Abstract

Merkel cell carcinoma (MCC) is a rare, highly aggressive cutaneous malignancy that is either associated with the integration of the Merkel cell polyomavirus or chronic UV exposure. These two types of carcinogenesis are reflected in characteristic mutational features present in MCC tumor lesions. However, the genomic characteristics of MCC cell lines used as preclinical models are not well established. Thus, we analyzed the exomes of three virus-negative and six virus-positive MCC cell lines, all showing a classical neuroendocrine growth pattern. Virus-negative cell lines are characterized by a high tumor mutational burden (TMB), UV-light-induced DNA damage, functionally relevant coding mutations, e.g., in RB1 and TP53, and large amounts of copy number variations (CNVs). In contrast, virus-positive cell lines have a low TMB with few coding mutations and lack prominent mutational signatures, but harbor characteristic CNVs. One of the virus-negative cell lines has a local MYC amplification associated with high MYC mRNA expression. In conclusion, virus-positive and -negative MCC cell lines with a neuroendocrine growth pattern resemble mutational features observed in MCC tissue samples, which strengthens their utility for functional studies.

Reemergence of neural crest stem cell-like states in melanoma during disease progression and treatment

Melanoma is the deadliest of all skin cancers due to its high metastatic potential. In recent years, advances in targeted therapy and immunotherapy have contributed to a remarkable progress in the treatment of metastatic disease. However, intrinsic or acquired resistance to such therapies remains a major obstacle in melanoma treatment. Melanoma disease progression, beginning from tumor initiation and growth to acquisition of invasive phenotypes and metastatic spread and acquisition of treatment resistance, has been associated with cellular dedifferentiation and the hijacking of gene regulatory networks reminiscent of the neural crest (NC)—the developmental structure which gives rise to melanocytes and hence melanoma. This review summarizes the experimental evidence for the involvement of NC stem cell (NCSC)‐like cell states during melanoma progression and addresses novel approaches to combat the emergence of stemness characteristics that have shown to be linked with aggressive disease outcome and drug resistance.

Sox10 Functions as an Inducer of the Direct Conversion of Keratinocytes Into Neural Crest Cells

Neural crest cells (NCCs) are highly migratory multipotent cells that play critical roles in embryogenesis. The generation of NCCs is controlled by various transcription factors (TFs) that are regulated by each other and combine to form a regulatory network. We previously reported that the conversion of mouse fibroblasts into NCCs was achieved by the overexpression of only one TF, Sox10; therefore, Sox10 may be a powerful inducer of the conversion of NCCs. We herein investigated whether Sox10 functions in the direct conversion of other somatic cells into NCCs. Sox10 directly converted bone marrow-derived mesenchymal cells, but not keratinocytes, into P75+ NCCs. However, by the co-expression of four TFs (Snail1, Snail2, Twist1, and Tcfap2a) that are involved in NCC generation, but unable convert cells into NCCs, Sox10 converted keratinocytes into P75+ NCCs. P75+ NCCs mainly differentiated into glial cells, and to a lesser extent into neuronal cells. On the other hand, when Sox10 was expressed after the four TF expression, which mimicked the expression order in in vivo NCC generation, it converted keratinocytes into multipotent NCCs. These results demonstrate that Sox10 functions as an inducer of direct conversion into NCCs in cooperation with the TFs involved in NCC generation. The sequence of expression of the inducer and cooperative factors is important for the conversion of somatic cells into bona fide target cells.

Neural crest lineage analysis: from past to future trajectory

Since its discovery 150 years ago, the neural crest has intrigued investigators owing to its remarkable developmental potential and extensive migratory ability. Cell lineage analysis has been an essential tool for exploring neural crest cell fate and migration routes. By marking progenitor cells, one can observe their subsequent locations and the cell types into which they differentiate. Here, we review major discoveries in neural crest lineage tracing from a historical perspective. We discuss how advancing technologies have refined lineage-tracing studies, and how clonal analysis can be applied to questions regarding multipotency. We also highlight how effective progenitor cell tracing, when combined with recently developed molecular and imaging tools, such as single-cell transcriptomics, single-molecule fluorescence in situ hybridization and high-resolution imaging, can extend the scope of neural crest lineage studies beyond development to regeneration and cancer initiation.

A unique neuroendocrine cell model derived from the human foetal neural crest

PURPOSE

Nowadays, no human neuroendocrine cell models derived from the neural crest are available. In this study, we present non-transformed long-term primary Neural Crest Cells (NCCs) isolated from the trunk region of the neural crest at VIII-XII gestational weeks of human foetuses obtained from voluntary legal abortion.

METHODS AND RESULTS

In NCC, quantitative real-time RT PCR demonstrated the expression of neural crest specifier genes, such as Snail1, Snail2/SLUG, Sox10, FoxD3, c-Myc, and p75NTR. Moreover, these cell populations expressed stemness markers (such as Nanog and nestin), as well as markers of motility and invasion (TAGLN, MMP9, CXCR4, and CXCR7), and of neuronal/glial differentiation (MAP2, GFAP, SYP, and TAU). Functional analysis demonstrated that these cells not only possessed high migration properties, but most importantly, they expressed markers of sympatho-adrenal lineage, such as ASCL1 and tyrosine hydroxylase (TH). Moreover, the expression of TH increased after the induction with two different protocols of differentiation towards neuronal and sympatho-adrenal phenotypes. Finally, exposure to conditioned culture media from NCC induced a mature phenotype in a neuronal cell model (namely SH-SY5Y), suggesting that NCC may also act like Schwann precursors.

CONCLUSION

This unique human cell model provides a solid tool for future studies addressing the bases of human neural crest-derived neuroendocrine tumours.

Sox10 Is a Specific Biomarker for Neural Crest Stem Cells in Immunohistochemical Staining in Wistar Rats

Objective

Neural crest stem cells (NCSCs) are prototypically migratory cells immigrating from the dorsal neural tube to specific embryonic sites where they generate a variety of cell types. A lot of biomarkers for NCSCs have been identified. However, which biomarkers are the most specific is still unclear.

Methods

The rat embryos harvested in embryonic day 9 (E9), E9.5, E10, E10.5, E11, E12, E13, and E14 were paraffin-embedded and sectioned in transverse. NCSCs were spatiotemporally demonstrated by immunohistochemical staining with RET, p75NTR, Pax7, and Sox10. NCSCs were isolated, cultured, and stained with RET, p75NTR, Pax7, and Sox10.

Results

In the paraffin sections of rat embryos, the immunohistochemical staining of RET, p75NTR, and Sox10 can all be used in demonstrating NCSCs. Sox10 was positive mainly in NCSCs while RET and p75NTR were positive not only in NCSCs but also in other tissue cells. In primary culture cells, Sox10 was mainly in the nucleus of NCSCs, RET was mainly in the membrane, and p75NTR was positive in cytoplasm and membrane.

Conclusions

Sox10 is the specific marker for immunohistochemical staining of NCSCs in paraffin sections. In cultured cells, Sox10, p75NTR, and RET presented a similar staining effect.

The development, patterning and evolution of neural crest cell differentiation into cartilage and bone

Neural crest cells are a vertebrate-specific migratory, multipotent cell population that give rise to a diverse array of cells and tissues during development. Cranial neural crest cells, in particular, generate cartilage, bone, tendons and connective tissue in the head and face as well as neurons, glia and melanocytes. In this review, we focus on the chondrogenic and osteogenic potential of cranial neural crest cells and discuss the roles of Sox9, Runx2 and Msx1/2 transcription factors and WNT, FGF and TGFβ signaling pathways in regulating neural crest cell differentiation into cartilage and bone. We also describe cranioskeletal defects and disorders arising from gain or loss-of-function of genes that are required for patterning and differentiation of cranial neural crest cells. Finally, we discuss the evolution of skeletogenic potential in neural crest cells and their function as a conduit for intraspecies and interspecies variation, and the evolution of craniofacial novelties.

Isolation and characterization of neural crest-like progenitor cells in human umbilical cord blood

Introduction

Neural crest (NC)-like stem/progenitor cells provide an attractive cell source for regenerative medicine because of their multipotent property and ease of isolation from adult tissue. Although human umbilical cord blood (HUCB) is known to be a rich source of stem cells, the presence of the NC-like stem/progenitor cells in HUCB remains to be elucidated. In this study, we have isolated NC-like progenitor cells using an antibody to p75 neurotrophin receptor (p75NTR) and examined their phenotype and stem cell function in vitro.

Methods

To confirm whether p75NTR⁺ NC-derived cells are present in cord blood, flow cytometric analysis of cord blood derived from P0-Cre/Floxed-EGFP reporter mouse embryos was performed. Freshly isolated HUCB mononuclear cells was subjected to flow cytometry to detect p75NTR⁺ cells and determined their immunophenotype. HUCB p75NTR⁺ cells were then collected by immunomagnetic separation and their immunophenotype, clonogenic potential, gene expression profile, and multilineage differentiation potential were examined.

Results

NC-derived EGFP⁺ cells co-expressing p75NTR was detected in cord blood of P0-Cre/Floxed-EGFP reporter mice. We found that freshly isolated HUCB mononuclear cells contained 0.23% of p75NTR⁺ cells. Isolated p75NTR⁺ cells from HUCB efficiently formed neurospheres and could differentiate into neuronal and glial cell lineages. The p75NTR⁺ cells expressed a set of NC-associated genes and undifferentiated neural cell marker genes before and after the culture.

Conclusions

These findings revealed that HUCB contained the p75NTR⁺ NC-like progenitor cell population which have the self-renewal capacity and the potential to differentiate into both neuronal and glial cell lineages.

Establishing Primary Cultures of Trunk Neural Crest Cells

Neural crest cells constitute a unique population of progenitor cells with extensive stem cell capacities able to navigate throughout various environments in the embryo and are a source of multiple cell types, including neurons, glia, melanocytes, smooth muscles, endocrine cells, cardiac cells, and also skeletal and supportive tissues in the head. Neural crest cells are not restricted to the embryo but persist as well in adult tissues where they provide a reservoir of stem cells with great therapeutic promise. Many fundamental questions in cell, developmental, and stem cell biology can be addressed using this system. During the last decades there has been an increased availability of elaborated techniques, animal models, and molecular tools to tackle neural crest cell development. However, these approaches are often very challenging and difficult to establish and they are not adapted for rapid functional investigations of mechanisms driving cell migration and differentiation. In addition, they are not adequate for collecting pure populations of neural crest cells usable in large scale analyses and for stem cell studies. Transferring and adapting the neural crest system in tissue culture may then represent an attractive alternative, opening up numerous prospects. Here we describe a simple method for establishing primary cultures of neural crest cells derived from trunk neural tubes using the avian embryo as a source of cells. This protocol is suited for producing pure populations of neural crest cells that can be processed for cytological, cellular, and functional approaches aimed at characterizing their phenotype, behavior, and potential. © 2020 Wiley Periodicals LLC. Basic Protocol: Primary cultures of avian trunk neural crest cells Support Protocol: Adaptations for immunofluorescence labeling and videomicroscopy.

3D Printed Neural Regeneration Devices

Neural regeneration devices interface with the nervous system and can provide flexibility in material choice, implantation without the need for additional surgeries, and the ability to serve as guides augmented with physical, biological (e.g., cellular), and biochemical functionalities. Given the complexity and challenges associated with neural regeneration, a 3D printing approach to the design and manufacturing of neural devices could provide next-generation opportunities for advanced neural regeneration via the production of anatomically accurate geometries, spatial distributions of cellular components, and incorporation of therapeutic biomolecules. A 3D printing-based approach offers compatibility with 3D scanning, computer modeling, choice of input material, and increasing control over hierarchical integration. Therefore, a 3D printed implantable platform could ultimately be used to prepare novel biomimetic scaffolds and model complex tissue architectures for clinical implants in order to treat neurological diseases and injuries. Further, the flexibility and specificity offered by 3D printed in vitro platforms have the potential to be a significant foundational breakthrough with broad research implications in cell signaling and drug screening for personalized healthcare. This progress report examines recent advances in 3D printing strategies for neural regeneration as well as insight into how these approaches can be improved in future studies.

Multipotent stem cells with neural crest stem cells characteristics exist in bovine adipose tissue

Neural crest stem cells (NCSCs) often referred to as the fourth germ layer, comprise a migratory, stem and progenitor cell population and are synonymous with vertebrate evolution and development. The cells follow specific paths to migrate to different locations of the body where they generate a diverse array of cell types and tissues. There are NCSCs which are maintained in an undifferentiated state throughout the life in the animal tissues. Based on some cells migratory property, we successfully developed a separation strategy to isolate and identify a population of adipose-derived stem cells with neural crest stem cell features in adult bovine adipose tissues within minimally-invasive surgical procedures. The cells have a high degree of multi-potency and self-renewal capabilities, can be cultured and maintained in feeder-free adhesion conditions as monolayer cells, and also be able to grow in the suspension condition in the form of neurosphere. For the purpose of simple description, we name this type cell as bovine adipose-derived neural crest stem cell (baNCSC). Taken together our study describes a readily accessible source of multipotent baNCSC for autologous tissue engineer and cell-based therapeutic researches.

Adult tissue-derived neural crest-like stem cells: Sources, regulatory networks, and translational potential

Neural crest (NC) cells are a multipotent stem cell population that give rise to a diverse array of cell types in the body, including peripheral neurons, Schwann cells (SC), craniofacial cartilage and bone, smooth muscle cells, and melanocytes. NC formation and differentiation into specific lineages takes place in response to a set of highly regulated signaling and transcriptional events within the neural plate border. Premigratory NC cells initially are contained within the dorsal neural tube from which they subsequently emigrate, migrating to often distant sites in the periphery. Following their migration and differentiation, some NC‐like cells persist in adult tissues in a nascent multipotent state, making them potential candidates for autologous cell therapy. This review discusses the gene regulatory network responsible for NC development and maintenance of multipotency. We summarize the genes and signaling pathways that have been implicated in the differentiation of a postmigratory NC into mature myelinating SC. We elaborate on the signals and transcription factors involved in the acquisition of immature SC fate, axonal sorting of unmyelinated neuronal axons, and finally the path toward mature myelinating SC, which envelope axons within myelin sheaths, facilitating electrical signal propagation. The gene regulatory events guiding development of SC in vivo provides insights into means for differentiating NC‐like cells from adult human tissues into functional SC, which have the potential to provide autologous cell sources for the treatment of demyelinating and neurodegenerative disorders.

Dissection, Culture and Analysis of Primary Cranial Neural Crest Cells from Mouse for the Study of Neural Crest Cell Delamination and Migration

Over the past several decades there has been an increased availability of genetically modified mouse models used to mimic human pathologies. However, the ability to study cell movements and differentiation in vivo is still very difficult. Neurocristopathies, or disorders of the neural crest lineage, are particularly challenging to study due to a lack of accessibility of key embryonic stages and the difficulties in separating out the neural crest mesenchyme from adjacent mesodermal mesenchyme. Here, we set out to establish a well-defined, routine protocol for the culture of primary cranial neural crest cells. In our approach we dissect out the mouse neural plate border during the initial neural crest induction stage. The neural plate border region is explanted and cultured. The neural crest cells form in an epithelial sheet surrounding the neural plate border, and by 24 h after explant, begin to delaminate, undergoing an epithelial-mesenchymal transition (EMT) to become fully motile neural crest cells. Due to our two-dimensional culturing approach, the distinct tissue populations (neural plate versus premigratory and migratory neural crest) can be readily distinguished. Using live imaging approaches, we can then identify changes in neural crest induction, EMT and migratory behaviors. The combination of this technique with genetic mutants will be a very powerful approach for understanding normal and pathological neural crest cell biology.

Molecular and cellular mechanisms underlying the evolution of form and function in the amniote jaw

The amniote jaw complex is a remarkable amalgamation of derivatives from distinct embryonic cell lineages. During development, the cells in these lineages experience concerted movements, migrations, and signaling interactions that take them from their initial origins to their final destinations and imbue their derivatives with aspects of form including their axial orientation, anatomical identity, size, and shape. Perturbations along the way can produce defects and disease, but also generate the variation necessary for jaw evolution and adaptation. We focus on molecular and cellular mechanisms that regulate form in the amniote jaw complex, and that enable structural and functional integration. Special emphasis is placed on the role of cranial neural crest mesenchyme (NCM) during the species-specific patterning of bone, cartilage, tendon, muscle, and other jaw tissues. We also address the effects of biomechanical forces during jaw development and discuss ways in which certain molecular and cellular responses add adaptive and evolutionary plasticity to jaw morphology. Overall, we highlight how variation in molecular and cellular programs can promote the phenomenal diversity and functional morphology achieved during amniote jaw evolution or lead to the range of jaw defects and disease that affect the human condition.

LKB1 specifies neural crest cell fates through pyruvate-alanine cycling

Metabolic processes underlying the development of the neural crest, an embryonic population of multipotent migratory cells, are poorly understood. Here, we report that conditional ablation of the Lkb1 tumor suppressor kinase in mouse neural crest stem cells led to intestinal pseudo-obstruction and hind limb paralysis. This phenotype originated from a postnatal degeneration of the enteric nervous ganglia and from a defective differentiation of Schwann cells. Metabolomic profiling revealed that pyruvate-alanine conversion is enhanced in the absence of Lkb1. Mechanistically, inhibition of alanine transaminases restored glial differentiation in an mTOR-dependent manner, while increased alanine level directly inhibited the glial commitment of neural crest cells. Treatment with the metabolic modulator AICAR suppressed mTOR signaling and prevented Schwann cell and enteric defects of Lkb1 mutant mice. These data uncover a link between pyruvate-alanine cycling and the specification of glial cell fate with potential implications in the understanding of the molecular pathogenesis of neural crest diseases.

Employing Endogenous NSCs to Promote Recovery of Spinal Cord Injury

Endogenous neural stem cells (NSCs) exist in the central canal of mammalian spinal cords. Under normal conditions, these NSCs remain quiescent and express FoxJ1. After spinal cord injury (SCI), the endogenous NSCs of a heterogeneous nature are activated and proliferate and migrate towards the lesion site and mainly differentiate into astrocytes to repair the injured tissue. In vitro, spinal cord NSCs are multipotent and can differentiate into neurons, astrocytes, and oligodendrocytes. The altered microenvironments after SCI play key roles on the fate determination of activated NSCs, especially on the neuronal specification potential. Studies show that the activated spinal cord NSCs can generate interneurons when transplanted into the adult hippocampus. In addition, the spinal cord NSCs exhibit low immunogenicity in a transplantation context, thus implicating a promising therapeutic potential on SCI recovery. Here, we summarize the characteristics of spinal cord NSCs, especially their properties after injury. With a better understanding of endogenous NSCs under normal and SCI conditions, we may be able to employ endogenous NSCs for SCI repair in the future.

Ex Vivo Culture and Manipulation of Mouse Neural Crest Cells from Primary Embryonic Tissue Explants

In vitro culture of neural crest cells allows for the manipulation and study of neural crest cell function in a cell-autonomous manner. While several stable neural crest cell lines exist, the transformed nature of these cells may not closely reflect the in vivo properties of neural crest cells, hence making molecular and functional analyses using these cell lines difficult to interpret. Here we describe a robust method to culture primary mouse neural crest cells ex vivo for several days to weeks in culture. We further describe a method for siRNA knockdown in these cells to study gene function. This culture method can also be adapted for other molecular analyses, including addition of small-molecule inhibitors and/or growth factors to the culture media, as well as culturing neural crest cells from knockout or genetically modified mice.

The diverse neural crest: from embryology to human pathology

We review here some of the historical highlights in exploratory studies of the vertebrate embryonic structure known as the neural crest. The study of the molecular properties of the cells that it produces, their migratory capacities and plasticity, and the still-growing list of tissues that depend on their presence for form and function, continue to enrich our understanding of congenital malformations, paediatric cancers and evolutionary biology. Developmental biology has been key to our understanding of the neural crest, starting with the early days of experimental embryology and through to today, when increasingly powerful technologies contribute to further insight into this fascinating vertebrate cell population.