Lgr5 Marks Neural Crest Derived Multipotent Oral Stromal Stem Cells

Assessing the fate and contribution of Foxd1-expressing embryonic precursors and their progeny in palatal development, homeostasis and excisional repair

Oral mucosal tissues heal rapidly with minimal scarring, although palatal mucosa can be associated with excessive fibrosis in response to injury. Investigations on the balance between neovascularization and tissue repair suggests regulation of angiogenesis is an important determinant of repair versus scarring. Associated with pericyte mediated fibrosis in kidney injury, FoxD1 is implicated in growth centres during cranio-facial development, although which cell lineages are derived from these embryonic populations in development and in adult animals is unknown. Using a lineage tracing approach, we assessed the fate of embryonic Foxd1-expressing progenitor cells and their progeny in palatal development and during wound healing in adult mice. During palatal development as well as in post-natal tissues, Foxd1-lineage progeny were associated with the vasculature and the epineurium. Post-injury, de novo expression of FoxD1 was not detectable, although Foxd1-lineage progeny expanded while exhibiting low association with the fibroblast/myofibroblast markers PDGFα, PDGFβ, vimentin, α-smooth muscle actin, as well as the neuronal associated markers S100β and p75NTR. Foxd1-lineage progeny were primarily associated with CD146, CD31, and to a lesser extent CD105, remaining in close proximity to developing neovascular structures. Our findings demonstrate that FoxD1 derived cells are predominantly associated with the palatal vasculature and provide strong evidence that FoxD1 derived cells do not give rise to populations involved directly in the scarring of the palate.

Lgr5-expressing secretory cells form a Wnt inhibitory niche in cartilage critical for chondrocyte identity

Osteoarthritis is a degenerative joint disease that causes pain, degradation, and dysfunction. Excessive canonical Wnt signaling in osteoarthritis contributes to chondrocyte phenotypic instability and loss of cartilage homeostasis; however, the regulatory niche is unknown. Using the temporomandibular joint as a model in multiple species, we identify Lgr5-expressing secretory cells as forming a Wnt inhibitory niche that instruct Wnt-inactive chondroprogenitors to form the nascent synovial joint and regulate chondrocyte lineage and identity. Lgr5 ablation or suppression during joint development, aging, or osteoarthritis results in depletion of Wnt-inactive chondroprogenitors and a surge of Wnt-activated, phenotypically unstable chondrocytes with osteoblast-like properties. We recapitulate the cartilage niche and create StemJEL, an injectable hydrogel therapy combining hyaluronic acid and sclerostin. Local delivery of StemJEL to post-traumatic osteoarthritic jaw and knee joints in rabbit, rat, and mini-pig models restores cartilage homeostasis, chondrocyte identity, and joint function. We provide proof of principal that StemJEL preserves the chondrocyte niche and alleviates osteoarthritis.

Role of LGR5-positive mesenchymal cells in craniofacial development

Leucine Rich Repeat Containing G Protein-Coupled Receptor 5 (LGR5), a Wnt pathway member, has been previously recognised as a stem cell marker in numerous epithelial tissues. In this study, we used Lgr5-EGFP-CreERT2 mice to analyse the distribution of LGR5-positive cells during craniofacial development. LGR5 expressing cells were primarily located in the mesenchyme adjacent to the craniofacial epithelial structures undergoing folding, such as the nasopharyngeal duct, lingual groove, and vomeronasal organ. To follow the fate of LGR5-positive cells, we performed lineage tracing using an inducible Cre knock-in allele in combination with Rosa26-tdTomato reporter mice. The slight expansion of LGR5-positive cells was found around the vomeronasal organ, in the nasal cavity, and around the epithelium in the lingual groove. However, most LGR5 expressing cells remained in their original location, possibly supporting their signalling function for adjacent epithelium rather than exerting their role as progenitor cells for the craniofacial structures. Moreover, Lgr5 knockout mice displayed distinct defects in LGR5-positive areas, especially in the reduction of the nasopharyngeal duct, the alteration of the palatal shelves shape, abnormal epithelial folding in the lingual groove area, and the disruption of salivary gland development. The latter defect manifested as an atypical number and localisation of the glandular ducts. The gene expression of several Wnt pathway members (Rspo1-3, Axin2) was altered in Lgr5-deficient animals. However, the difference was not found in sorted EGFP-positive cells obtained from Lgr5^+/+ and Lgr5^−/− animals. Expression profiling of LGR5-positive cells revealed the expression of several markers of mesenchymal cells, antagonists, as well as agonists, of Wnt signalling, and molecules associated with the basal membrane. Therefore, LGR5-positive cells in the craniofacial area represent a very specific population of mesenchymal cells adjacent to the epithelium undergoing folding or groove formation. Our results indicate a possible novel role of LGR5 in the regulation of morphogenetic processes during the formation of complex epithelial structures in the craniofacial areas, a role which is not related to the stem cell properties of LGR5-positive cells as was previously defined for various epithelial tissues.

Implantation of a nerve protector embedded with human GMSC-derived Schwann-like cells accelerates regeneration of crush-injured rat sciatic nerves

BACKGROUND

Peripheral nerve injuries (PNIs) remain one of the great clinical challenges because of their considerable long-term disability potential. Postnatal neural crest-derived multipotent stem cells, including gingiva-derived mesenchymal stem cells (GMSCs), represent a promising source of seed cells for tissue engineering and regenerative therapy of various disorders, including PNIs. Here, we generated GMSC-repopulated nerve protectors and evaluated their therapeutic effects in a crush injury model of rat sciatic nerves.

METHODS

GMSCs were mixed in methacrylated collagen and cultured for 48 h, allowing the conversion of GMSCs into Schwann-like cells (GiSCs). The phenotype of GiSCs was verified by fluorescence studies on the expression of Schwann cell markers. GMSCs encapsulated in the methacrylated 3D-collagen hydrogel were co-cultured with THP-1-derived macrophages, and the secretion of anti-inflammatory cytokine IL-10 or inflammatory cytokines TNF-α and IL-1β in the supernatant was determined by ELISA. In addition, GMSCs mixed in the methacrylated collagen were filled into a nerve protector made from the decellularized small intestine submucosal extracellular matrix (SIS-ECM) and cultured for 24 h, allowing the generation of functionalized nerve protectors repopulated with GiSCs. We implanted the nerve protector to wrap the injury site of rat sciatic nerves and performed functional and histological assessments 4 weeks post-surgery.

RESULTS

GMSCs encapsulated in the methacrylated 3D-collagen hydrogel were directly converted into Schwann-like cells (GiSCs) characterized by the expression of S-100β, p75NTR, BDNF, and GDNF. In vitro, co-culture of GMSCs encapsulated in the 3D-collagen hydrogel with macrophages remarkably increased the secretion of IL-10, an anti-inflammatory cytokine characteristic of pro-regenerative (M2) macrophages, but robustly reduced LPS-stimulated secretion of TNF-1α and IL-1β, two cytokines characteristic of pro-inflammatory (M1) macrophages. In addition, our results indicate that implantation of functionalized nerve protectors repopulated with GiSCs significantly accelerated functional recovery and axonal regeneration of crush-injured rat sciatic nerves accompanied by increased infiltration of pro-regenerative (M2) macrophages while a decreased infiltration of pro-inflammatory (M1) macrophages.

CONCLUSIONS

Collectively, these findings suggest that Schwann-like cells converted from GMSCs represent a promising source of supportive cells for regenerative therapy of PNI through their dual functions, neurotrophic effects, and immunomodulation of pro-inflammatory (M1)/pro-regenerative (M2) macrophages.

A Narrative Review: Gingival Stem Cells as a Limitless Reservoir for Regenerative Medicine

The gingival tissue can be collected in an easy way and represent an accessible source to isolate gingival-derived mesenchymal stem cells (GMSCs). GMSCs are a subpopulation of dental-derived mesenchymal stem cells that show the mesenchymal stem cells (MSCs) features, such as differentiation abilities and immunomodulatory properties. Dental-derived stem cells are also expandable in vitro with genomic stability and the possibility to maintain the stemness properties over a prolonged period of passages. Moreover, several preclinical studies have documented that the extracellular vesicles (EVs) released from GMSCs possess similar biological functions and therapeutic effects. The EVs may represent a promising tool in the cell-free regenerative therapy approach. The present review paper summarized the GMSCs, their multi-lineage differentiation capacities, immunomodulatory features, and the potential use in the treatment of several diseases in order to stimulate tissue regeneration. GMSCs should be considered a good stem cell source for potential applications in tissue engineering and regenerative dentistry.

Harnessing 3D collagen hydrogel-directed conversion of human GMSCs into SCP-like cells to generate functionalized nerve conduits

Achieving a satisfactory functional recovery after severe peripheral nerve injuries (PNI) remains one of the major clinical challenges despite advances in microsurgical techniques. Nerve autografting is currently the gold standard for the treatment of PNI, but there exist several major limitations. Accumulating evidence has shown that various types of nerve guidance conduits (NGCs) combined with post-natal stem cells as the supportive cells may represent a promising alternative to nerve autografts. In this study, gingiva-derived mesenchymal stem cells (GMSCs) under 3D-culture in soft collagen hydrogel showed significantly increased expression of a panel of genes related to development/differentiation of neural crest stem-like cells (NCSC) and/or Schwann cell precursor-like (SCP) cells and associated with NOTCH3 signaling pathway activation as compared to their 2D-cultured counterparts. The upregulation of NCSC-related genes induced by 3D-collagen hydrogel was abrogated by the presence of a specific NOTCH inhibitor. Further study showed that GMSCs encapsulated in 3D-collagen hydrogel were capable of transmigrating into multilayered extracellular matrix (ECM) wall of natural NGCs and integrating well with the aligned matrix structure, thus leading to biofabrication of functionalized NGCs. In vivo, implantation of functionalized NGCs laden with GMSC-derived NCSC/SCP-like cells (designated as GiSCs), significantly improved the functional recovery and axonal regeneration in the segmental facial nerve defect model in rats. Together, our study has identified an approach for rapid biofabrication of functionalized NGCs through harnessing 3D collagen hydrogel-directed conversion of GMSCs into GiSCs.

A Model of Waardenburg Syndrome Using Patient-Derived iPSCs With a SOX10 Mutation Displays Compromised Maturation and Function of the Neural Crest That Involves Inner Ear Development

Waardenburg syndrome (WS) is an autosomal dominant inherited disorder that is characterized by sensorineural hearing loss and abnormal pigmentation. SOX10 is one of its main pathogenicity genes. The generation of patient-specific induced pluripotent stem cells (iPSCs) is an efficient means to investigate the mechanisms of inherited human disease. In our work, we set up an iPSC line derived from a WS patient with SOX10 mutation and differentiated into neural crest cells (NCCs), a key cell type involved in inner ear development. Compared with control-derived iPSCs, the SOX10 mutant iPSCs showed significantly decreased efficiency of development and differentiation potential at the stage of NCCs. After that, we carried out high-throughput RNA-seq and evaluated the transcriptional misregulation at every stage. Transcriptome analysis of differentiated NCCs showed widespread gene expression alterations, and the differentially expressed genes (DEGs) were enriched in gene ontology terms of neuron migration, skeletal system development, and multicellular organism development, indicating that SOX10 has a pivotal part in the differentiation of NCCs. It's worth noting that, a significant enrichment among the nominal DEGs for genes implicated in inner ear development was found, as well as several genes connected to the inner ear morphogenesis. Based on the protein-protein interaction network, we chose four candidate genes that could be regulated by SOX10 in inner ear development, namely, BMP2, LGR5, GBX2, and GATA3. In conclusion, SOX10 deficiency in this WS subject had a significant impact on the gene expression patterns throughout NCC development in the iPSC model. The DEGs most significantly enriched in inner ear development and morphogenesis may assist in identifying the underlying basis for the inner ear malformation in subjects with WS.

Potential Therapeutic Strategies and Substances for Facial Nerve Regeneration Based on Preclinical Studies

Despite advances in microsurgical technology and an improved understanding of nerve regeneration, obtaining satisfactory results after facial nerve injury remains a difficult clinical problem. Among existing peripheral nerve regeneration studies, relatively few have focused on the facial nerve, particularly how experimental studies of the facial nerve using animal models play an essential role in understanding functional outcomes and how such studies can lead to improved axon regeneration after nerve injury. The purpose of this article is to review current perspectives on strategies for applying potential therapeutic methods for facial nerve regeneration. To this end, we searched Embase, PubMed, and the Cochrane library using keywords, and after applying exclusion criteria, obtained a total of 31 qualifying experimental studies. We then summarize the fundamental experimental studies on facial nerve regeneration, highlighting recent bioengineering studies employing various strategies for supporting facial nerve regeneration, including nerve conduits with stem cells, neurotrophic factors, and/or other therapeutics. Our summary of the methods and results of these previous reports reveal a common feature among studies, showing that various neurotrophic factors arising from injured nerves contribute to a microenvironment that plays an important role in functional recovery. In most cases, histological examinations showed that this microenvironmental influence increased axonal diameter as well as myelination thickness. Such an analysis of available research on facial nerve injury and regeneration represents the first step toward future therapeutic strategies.

Gingiva-Derived Mesenchymal Stem Cells: Potential Application in Tissue Engineering and Regenerative Medicine - A Comprehensive Review

A unique subpopulation of mesenchymal stem cells (MSCs) has been isolated and characterized from human gingival tissues (GMSCs). Similar to MSCs derived from other sources of tissues, e.g. bone marrow, adipose or umbilical cord, GMSCs also possess multipotent differentiation capacities and potent immunomodulatory effects on both innate and adaptive immune cells through the secretion of various types of bioactive factors with immunosuppressive and anti-inflammatory functions. Uniquely, GMSCs are highly proliferative and have the propensity to differentiate into neural cell lineages due to the neural crest-origin. These properties have endowed GMSCs with potent regenerative and therapeutic potentials in various preclinical models of human disorders, particularly, some inflammatory and autoimmune diseases, skin diseases, oral and maxillofacial disorders, and peripheral nerve injuries. All types of cells release extracellular vesicles (EVs), including exosomes, that play critical roles in cell-cell communication through their cargos containing a variety of bioactive molecules, such as proteins, nucleic acids, and lipids. Like EVs released by other sources of MSCs, GMSC-derived EVs have been shown to possess similar biological functions and therapeutic effects on several preclinical diseases models as GMSCs, thus representing a promising cell-free platform for regenerative therapy. Taken together, due to the easily accessibility and less morbidity of harvesting gingival tissues as well as the potent immunomodulatory and anti-inflammatory functions, GMSCs represent a unique source of MSCs of a neural crest-origin for potential application in tissue engineering and regenerative therapy.

Between Fate Choice and Self-Renewal-Heterogeneity of Adult Neural Crest-Derived Stem Cells

Stem cells of the neural crest (NC) vitally participate to embryonic development, but also remain in distinct niches as quiescent neural crest-derived stem cell (NCSC) pools into adulthood. Although NCSC-populations share a high capacity for self-renewal and differentiation resulting in promising preclinical applications within the last two decades, inter- and intrapopulational differences exist in terms of their expression signatures and regenerative capability. Differentiation and self-renewal of stem cells in developmental and regenerative contexts are partially regulated by the niche or culture condition and further influenced by single cell decision processes, making cell-to-cell variation and heterogeneity critical for understanding adult stem cell populations. The present review summarizes current knowledge of the cellular heterogeneity within NCSC-populations located in distinct craniofacial and trunk niches including the nasal cavity, olfactory bulb, oral tissues or skin. We shed light on the impact of intrapopulational heterogeneity on fate specifications and plasticity of NCSCs in their niches in vivo as well as during in vitro culture. We further discuss underlying molecular regulators determining fate specifications of NCSCs, suggesting a regulatory network including NF-κB and NC-related transcription factors like SLUG and SOX9 accompanied by Wnt- and MAPK-signaling to orchestrate NCSC stemness and differentiation. In summary, adult NCSCs show a broad heterogeneity on the level of the donor and the donors' sex, the cell population and the single stem cell directly impacting their differentiation capability and fate choices in vivo and in vitro. The findings discussed here emphasize heterogeneity of NCSCs as a crucial parameter for understanding their role in tissue homeostasis and regeneration and for improving their applicability in regenerative medicine.

The prognostic value of leucine-rich repeat-containing G-protein (Lgr5) and its impact on clinicopathological features of colorectal cancer

Introduction

Colorectal cancer (CRC) constitutes one of the most prevalent malignancies in the world. Recent research suggests that cancer stem cells (CSCs) are responsible for tumor cell’s malignant behavior in CRC. This study has been designed to determinate clinical implications of CSC markers: CD44, DCLK1, Lgr5, and ANXA2 in CRC.

Materials and methods

The study was performed on tissue samples which were collected from 89 patients undergoing colectomy. Formalin-fixed paraffin-embedded tissue blocks with representative tumor areas were identified and corded. Immunohistochemical staining was performed using anti-CD44, anti-LGR5, anti-ANXA2, and anti-DCLK1 antibodies. The H-score system was utilized to determine the immunointensity of CRC cells.

Results

The lower expression of Lgr5 was significantly correlated with the presence of lymph-node metastases (p = 0.011), while high expression of Lgr5 was statistically significant in vascular invasion in examined cancer tissue samples (p = 0.027). Moreover, a high H-score value of Lgr5 expression was significantly related to a reduced overall survival rate (p = 0.043).

Conclusion

Our results suggest a strong relationship between CSC marker Lgr5 and vascular invasion, presence of lymph-node metastasis, and overall poor survival. The presence of Lgr5 might be an unfavorable prognostic factor, and its high level in cancer tissue is related to an aggressive course. This marker could also be used to access the effectiveness of the treatment.

Lgr5 in cancer biology: functional identification of Lgr5 in cancer progression and potential opportunities for novel therapy

Cancer remains one of the leading lethal diseases worldwide. Identifying biomarkers of cancers might provide insights into the strategies for the development of novel targeted anti-cancer therapies. Leucine-rich repeat-containing G protein-coupled receptor 5 (Lgr5) has been recently discovered as a candidate marker of cancer stem cell populations. Aberrant increased expression of Lgr5 may represent one of the most common molecular alterations in some human cancers, leading to long-term potentiation of canonical Wnt/β-catenin signaling. On the other hand, however, Lgr5-mediated suppression in canonical Wnt/β-catenin signaling has also been reported in certain cancers, such as B cell malignancies. Until now, therapeutic approaches targeting Lgr5-associated signaling axis are not yet clinically available. Increasing evidence have indicated that endogenous Lgr5+ cell population is implicated in tumor initiation, progression, and metastasis. This review is to summarize our current knowledge about the importance of Lgr5 in cancer biology and the underlying molecular mechanisms of Lgr5-mediated tumor-promoting/suppressive activities, as well as potentially useful preventive strategies in treating tumor. Therefore, targeted therapeutic modulation of Lgr5+ cancer cell population by targeting Wnt/β-catenin signaling through targeted drug delivery system or targeted genome editing might be promising for potential novel anti-cancer treatments. Simultaneously, combination of therapeutics targeting both Lgr5+ and Lgr5- cancer cells may deserve further consideration considering the plasticity of cancer cells. Also, a more specific targeting of cancer cells using double biomarkers may be much safer and more effective for anti-cancer therapy.

Isolation and Characterization of Neural Crest-Derived Stem Cells From Adult Ovine Palatal Tissue

Adult mammalian craniofacial tissues contain limited numbers of post-migratory neural crest-derived stem cells. Similar to their embryonic counterparts, these adult multipotent stem cells can undergo multi-lineage differentiation and are capable of contributing to regeneration of mesodermal and ectodermal cells and tissues in vivo. In the present study, we describe for the first time the presence of Nestin-positive neural crest-derived stem cells (NCSCs) within the ovine hard palate. We show that these cells can be isolated from the palatal tissue and are able to form neurospheres. Ovine NCSCs express the typical neural crest markers Slug and Twist, exhibit high proliferative and migratory activity and are able to differentiate into α smooth muscle cells and β-III-tubulin expressing ectodermal cells. Finally, we demonstrate that oNCSCs are capable of differentiating into osteogenic, adipogenic and chondrogenic cells. Taken together, our results suggest that oNCSCs could be used as model cells to assess the efficacy and safety of autologous NCSC transplantation in a large animal model.

Identification, isolation and characterization of human LGR5-positive colon adenoma cells

The intestine is maintained by stem cells located at the base of crypts and distinguished by the expression of LGR5. Genetically engineered mouse models have provided a wealth of information about intestinal stem cells, whereas less is known about human intestinal stem cells owing to difficulty detecting and isolating these cells. We established an organoid repository from patient-derived adenomas, adenocarcinomas and normal colon, which we analyzed for variants in 71 colorectal cancer (CRC)-associated genes. Normal and neoplastic colon tissue organoids were analyzed by immunohistochemistry and fluorescent-activated cell sorting for LGR5. LGR5-positive cells were isolated from four adenoma organoid lines and were subjected to RNA sequencing. We found that LGR5 expression in the epithelium and stroma was associated with tumor stage, and by integrating functional experiments with LGR5-sorted cell RNA sequencing data from adenoma and normal organoids, we found correlations between LGR5 and CRC-specific genes, including dickkopf WNT signaling pathway inhibitor 4 (DKK4) and SPARC-related modular calcium binding 2 (SMOC2). Collectively, this work provides resources, methods and new markers to isolate and study stem cells in human tissue homeostasis and carcinogenesis.

Neural Crest Stem-Like Cells Non-genetically Induced from Human Gingiva-Derived Mesenchymal Stem Cells Promote Facial Nerve Regeneration in Rats

Non-genetic induction of somatic cells into neural crest stem-like cells (NCSCs) is promising for potential cell-based therapies for post-traumatic peripheral nerve regeneration. Here, we report that human gingiva-derived mesenchymal stem cells (GMSCs) could be reproducibly and readily induced into NCSCs via non-genetic approaches. Compared to parental GMSCs, induced NCSC population had increased expression in NCSC-related genes and displayed robust differentiation into neuronal and Schwann-like cells. Knockdown of the expression of Yes-associated protein 1 (YAP1), a critical mechanosensor and mechanotransducer, attenuated the expression of NCSC-related genes; specific blocking of RhoA/ROCK activity and non-muscle myosin II (NM II)-dependent contraction suppressed YAP1 and NCSC-related genes and concurrently abolished neural spheroid formation in NCSCs. Using a rat model of facial nerve defect, implantation of NCSC-laden nerve conduits promoted functional regeneration of the injured nerve. These promising findings demonstrate that induced NCSCs derived from GMSCs represent an easily accessible and promising source of neural stem-like cells for peripheral nerve regeneration.

Dynamics of Proliferative and Quiescent Stem Cells in Liver Homeostasis and Injury

BACKGROUND & AIMS

Adult liver stem cells are usually maintained in a quiescent/slow-cycling state. However, a proliferative population, marked by leucine-rich repeat-containing G-protein coupled receptor 5 (LGR5), was recently identified as an important liver stem cell population. We aimed to investigate the dynamics and functions of proliferative and quiescent stem cells in healthy and injured livers.

METHODS

We studied LGR5-positive stem cells using diphtheria toxin receptor and green fluorescent protein (GFP) knock-in mice. In these mice, LGR5-positive cells specifically coexpress diphtheria toxin receptor and the GFP reporter. Lineage-tracing experiments were performed in mice in which LGR5-positive stem cells and their daughter cells expressed a yellow fluorescent protein/mTmG reporter. Slow-cycling stem cells were investigated using GFP-based, Tet-on controlled transgenic mice. We studied the dynamics of both stem cell populations during liver homeostasis and injury induced by carbon tetrachloride. Stem cells were isolated from mouse liver and organoid formation assays were performed. We analyzed hepatocyte and cholangiocyte lineage differentiation in cultured organoids.

RESULTS

We did not detect LGR5-expressing stem cells in livers of mice at any stage of a lifespan, but only following liver injury induced by carbon tetrachloride. In the liver stem cell niche, where the proliferating LGR5⁺ cells are located, we identified a quiescent/slow-cycling cell population, called label-retaining cells (LRCs). These cells were present in the homeostatic liver, capable of retaining the GFP label over 1 year, and expressed a panel of progenitor/stem cell markers. Isolated single LRCs were capable of forming organoids that could be carried in culture, expanded for months, and differentiated into hepatocyte and cholangiocyte lineages in vitro, demonstrating their bona fide stem cell properties. More interestingly, LRCs responded to liver injury and gave rise to LGR5-expressing stem cells, as well as other potential progenitor/stem cell populations, including SOX9- and CD44-positive cells.

CONCLUSIONS

Proliferative LGR5 cells are an intermediate stem cell population in the liver that emerge only during tissue injury. In contrast, LRCs are quiescent stem cells that are present in homeostatic liver, respond to tissue injury, and can give rise to LGR5 stem cells, as well as SOX9- and CD44-positive cells.

Quo vadis: tracing the fate of neural crest cells

The neural crest is a transient structure in vertebrate embryos that produces migratory cells with an astonishing developmental potential. While neural crest fate maps have originally been established through interspecies transplantation assays, dye labeling, and retroviral infection, more recent methods rely on approaches involving transgenesis and genome editing. These technologies allowed the identification of minor neural crest-derived cell populations in tissues of non-neural crest origin. Furthermore, in vivo multipotency at the single cell level and stage-dependent fate acquisitions were demonstrated using genetic technologies. Finally, recent reports indicate that neural crest-derived cells become activated in response to injury to secrete factors supporting tissue repair. Thus, neural crest-derived cells apparently contribute to tissue formation and regeneration by cell autonomous and non-autonomous mechanisms.

Requirement for Jagged1-Notch2 signaling in patterning the bones of the mouse and human middle ear

Whereas Jagged1-Notch2 signaling is known to pattern the sensorineural components of the inner ear, its role in middle ear development has been less clear. We previously reported a role for Jagged-Notch signaling in shaping skeletal elements derived from the first two pharyngeal arches of zebrafish. Here we show a conserved requirement for Jagged1-Notch2 signaling in patterning the stapes and incus middle ear bones derived from the equivalent pharyngeal arches of mammals. Mice lacking Jagged1 or Notch2 in neural crest-derived cells (NCCs) of the pharyngeal arches display a malformed stapes. Heterozygous Jagged1 knockout mice, a model for Alagille Syndrome (AGS), also display stapes and incus defects. We find that Jagged1-Notch2 signaling functions early to pattern the stapes cartilage template, with stapes malformations correlating with hearing loss across all frequencies. We observe similar stapes defects and hearing loss in one patient with heterozygous JAGGED1 loss, and a diversity of conductive and sensorineural hearing loss in nearly half of AGS patients, many of which carry JAGGED1 mutations. Our findings reveal deep conservation of Jagged1-Notch2 signaling in patterning the pharyngeal arches from fish to mouse to man, despite the very different functions of their skeletal derivatives in jaw support and sound transduction.

Neural crest stem cells and their potential therapeutic applications

The neural crest (NC) is a remarkable transient structure generated during early vertebrate development. The neural crest progenitors have extensive migratory capacity and multipotency, harboring stem cell-like characteristics such as self-renewal. They can differentiate into a variety of cell types from craniofacial skeletal tissues to the trunk peripheral nervous system (PNS). Multiple regulators such as signaling factors, transcription factors, and migration machinery components are expressed at different stages of NC development. Gain- and loss-of-function studies in various vertebrate species revealed epistatic relationships of these molecules that could be assembled into a gene regulatory network defining the processes of NC induction, specification, migration, and differentiation. These basic developmental studies led to the subsequent establishment and molecular validation of neural crest stem cells (NCSCs) derived by various strategies. We provide here an overview of the isolation and characterization of NCSCs from embryonic, fetal, and adult tissues; the experimental strategies for the derivation of NCSCs from embryonic stem cells, induced pluripotent stem cells, and skin fibroblasts; and recent developments in the use of patient-derived NCSCs for modeling and treating neurocristopathies. We discuss future research on further refinement of the culture conditions required for the differentiation of pluripotent stem cells into axial-specific NC progenitors and their derivatives, developing non-viral approaches for the generation of induced NC cells (NCCs), and using a genomic editing approach to correct genetic mutations in patient-derived NCSCs for transplantation therapy. These future endeavors should facilitate the therapeutic applications of NCSCs in the clinical setting.