Neuropilins define distinct populations of neural crest cells

Identification and characterization of intermediate states in mammalian neural crest cell epithelial to mesenchymal transition and delamination

Epithelial to mesenchymal transition (EMT) is a cellular process that converts epithelial cells to mesenchymal cells with migratory potential in developmental and pathological processes. Although originally considered a binary event, EMT in cancer progression involves intermediate states between a fully epithelial and a fully mesenchymal phenotype, which are characterized by distinct combinations of epithelial and mesenchymal markers. This phenomenon has been termed epithelial to mesenchymal plasticity (EMP), however, the intermediate states remain poorly described and it's unclear whether they exist during developmental EMT. Neural crest cells (NCC) are an embryonic progenitor cell population that gives rise to numerous cell types and tissues in vertebrates, and their formation and delamination is a classic example of developmental EMT. However, whether intermediate states also exist during NCC EMT and delamination remains unknown. Through single-cell RNA sequencing of mouse embryos, we identified intermediate NCC states based on their transcriptional signature and then spatially defined their locations in situ in the dorsolateral neuroepithelium. Our results illustrate the importance of cell cycle regulation and functional role for the intermediate stage marker Dlc1 in facilitating mammalian cranial NCC delamination and may provide new insights into mechanisms regulating pathological EMP.

Identification and characterization of intermediate states in mammalian neural crest cell epithelial to mesenchymal transition and delamination

Epithelial to mesenchymal transition (EMT) is a cellular process that converts epithelial cells to mesenchymal cells with migratory potential in both developmental and pathological processes. Although originally considered a binary event, EMT in cancer progression involves intermediate states between a fully epithelial and a fully mesenchymal phenotype, which are characterized by distinct combinations of epithelial and mesenchymal markers. This phenomenon has been termed epithelial to mesenchymal plasticity (EMP), however, the intermediate states remain poorly described and it's unclear whether they exist during developmental EMT. Neural crest cells (NCC) are an embryonic progenitor cell population that gives rise to numerous cell types and tissues in vertebrates, and their formation is a classic example of developmental EMT. An important feature of NCC development is their delamination from the neuroepithelium via EMT, following which NCC migrate throughout the embryo and undergo differentiation. NCC delamination shares similar changes in cellular state and structure with cancer cell invasion. However, whether intermediate states also exist during NCC EMT and delamination remains unknown. Through single cell RNA sequencing, we identified intermediate NCC states based on their transcriptional signature and then spatially defined their locations in situ in the dorsolateral neuroepithelium. Our results illustrate the progressive transcriptional and spatial transitions from premigratory to migratory cranial NCC during EMT and delamination. Of note gene expression and trajectory analysis indicate that distinct intermediate populations of NCC delaminate in either S phase or G2/M phase of the cell cycle, and the importance of cell cycle regulation in facilitating mammalian cranial NCC delamination was confirmed through cell cycle inhibition studies. Additionally, transcriptional knockdown revealed a functional role for the intermediate stage marker Dlc1 in regulating NCC delamination and migration. Overall, our work identifying and characterizing the intermediate cellular states, processes, and molecular signals that regulate mammalian NCC EMT and delamination furthers our understanding of developmental EMP and may provide new insights into mechanisms regulating pathological EMP.

Single-cell sequencing reveals increased LAMB3-positive basal keratinocytes and ZNF90-positive fibroblasts in autologous cultured epithelium

Autologous cultured epithelium grafting (ACEG) presents a promising treatment for refractory vitiligo, yet concerns regarding infections and immunological reactions hinder its surgical use due to serum and feeder dependencies. Addressing this, we culture autologous epithelium under serum- and feeder-free (SFF) conditions, comparing its safety and efficacy with serum- and feeder-dependent (SFD) conditions in stable vitiligo patients, and we discover no significant differences in repigmentation between the SFF and SFD grafts. Single-cell RNA transcriptomics on SFF- and SFD-cultured epithelium alongside healthy skin reveal increased populations of LAMB3+ basal keratinocytes and ZNF90+ fibroblasts in the SFF sheets. Functional analyses showcase active cellular metabolism in LAMB3+ basal keratinocytes, vital in extracellular matrix homeostasis, while ZNF90+ fibroblasts demonstrate increased differentiation, essential in collagen formation for cell adhesion. Importantly, these cell populations in SFF sheets exhibit enhanced interactions with melanocytes compared to SFD sheets. Further, knockdown experiments of LAMB3 in keratinocytes and ZNF90 in fibroblasts lead to a downregulation in melanocyte ligand-receptor-related genes. Overall, SFF sheets demonstrate comparable efficacy to SFD sheets, offering superior safety. LAMB3+ basal keratinocytes and ZNF90+ fibroblasts act as potential drivers behind repigmentation in ACEG under SFF conditions. This study provides translational insights into ACEG repigmentation and potential therapeutic targets for vitiligo.

Neuropilin 1 (NRP1) Positively Regulates Adipogenic Differentiation in C3H10T1/2 Cells

Neuropilin 1 (NRP1), a non-tyrosine kinase receptor for several ligands, is highly expressed in many kinds of mesenchymal stem cells (MSCs), but its function is poorly understood. In this study, we explored the roles of full-length NRP1 and glycosaminoglycan (GAG)-modifiable NRP1 in adipogenesis in C3H10T1/2 cells. The expression of full-length NRP1 and GAG-modifiable NRP1 increased during adipogenic differentiation in C3H10T1/2 cells. NRP1 knockdown repressed adipogenesis while decreasing the levels of Akt and ERK1/2 phosphorylation. Moreover, the scaffold protein JIP4 was involved in adipogenesis in C3H10T1/2 cells by interacting with NRP1. Furthermore, overexpression of non-GAG-modifiable NRP1 mutant (S612A) greatly promoted adipogenic differentiation, accompanied by upregulation of the phosphorylated Akt and ERK1/2. Taken together, these results indicate that NRP1 is a key regulator that promotes adipogenesis in C3H10T1/2 cells by interacting with JIP4 and activating the Akt and ERK1/2 pathway. Non-GAG-modifiable NRP1 mutant (S612A) accelerates the process of adipogenic differentiation, suggesting that GAG glycosylation is a negative post-translational modification of NRP1 in adipogenic differentiation.

Role of Neuropilin-2-mediated signaling axis in cancer progression and therapy resistance

Neuropilins (NRPs) are transmembrane proteins involved in vascular and nervous system development by regulating angiogenesis and axon guidance cues. Several published reports have established their role in tumorigenesis. NRPs are detectable in tumor cells of several cancer types and participate in cancer progression. NRP2 is also expressed in endothelial and immune cells in the tumor microenvironment and promotes functions such as lymphangiogenesis and immune suppression important for cancer progression. In this review, we have taken a comprehensive approach to discussing various aspects of NRP2-signaling in cancer, including its regulation, functional significance in cancer progression, and how we could utilize our current knowledge to advance the studies and target NRP2 to develop effective cancer therapies.

SEMAPHORINS and their receptors: focus on the crosstalk between melanoma and hypoxia

Hypoxia, a condition of oxygen deprivation, is considered a hallmark of tumor microenvironment regulating several pathways and promoting cancer progression and resistance to therapy. Semaphorins, a family of about 20 secreted, transmembrane and GPI-linked glycoproteins, and their cognate receptors (plexins and neuropilins) play a pivotal role in the crosstalk between cancer and stromal cells present in the tumor microenvironment. Many studies reported that some semaphorins are involved in the development of a permissive tumor niche, guiding cell-cell communication and, consequently, the development and progression, as well as the response to therapy, of different cancer histotypes, including melanoma.

In this review we will summarize the state of art of semaphorins regulation by hypoxic condition in cancer with different origin. We will also describe evidence about the ability of semaphorins to affect the expression and activity of transcription factors activated by hypoxia, such as hypoxia-inducible factor-1. Finally, we will focus our attention on findings reporting the role of semaphorins in melanocytes transformation, melanoma progression and response to therapy. Further studies are necessary to understand the mechanisms through which semaphorins induce their effect and to shed light on the possibility to use semaphorins or their cognate receptors as prognostic markers and/or therapeutic targets in melanoma or other malignancies.

Gbx2 Is Required for the Migration and Survival of a Subpopulation of Trigeminal Cranial Neural Crest Cells

The development of key structures within the mature vertebrate hindbrain requires the migration of neural crest (NC) cells and motor neurons to their appropriate target sites. Functional analyses in multiple species have revealed a requirement for the transcription factor gastrulation-brain-homeobox 2 (Gbx2) in NC cell migration and positioning of motor neurons in the developing hindbrain. In addition, loss of Gbx2 function studies in mutant mouse embryos, Gbx2^neo, demonstrate a requirement for Gbx2 for the development of NC-derived sensory neurons and axons constituting the mandibular branch of the trigeminal nerve (CNV). Our recent GBX2 target gene identification study identified multiple genes required for the migration and survival of NC cells (e.g., Robo1, Slit3, Nrp1). In this report, we performed loss-of-function analyses using Gbx2^neo mutant embryos, to improve our understanding of the molecular and genetic mechanisms regulated by Gbx2 during anterior hindbrain and CNV development. Analysis of Tbx20 expression in the hindbrain of Gbx2^neo homozygotes revealed a severely truncated rhombomere (r)2. Our data also provide evidence demonstrating a requirement for Gbx2 in the temporal regulation of Krox20 expression in r3. Lastly, we show that Gbx2 is required for the expression of Nrp1 in a subpopulation of trigeminal NC cells, and correct migration and survival of cranial NC cells that populate the trigeminal ganglion. Taken together, these findings provide additional insight into molecular and genetic mechanisms regulated by Gbx2 that underlie NC migration, trigeminal ganglion assembly, and, more broadly, anterior hindbrain development.

Stem cells, evolutionary aspects and pathology of the adrenal medulla: A new developmental paradigm

The mammalian adrenal gland is composed of two main components; the catecholaminergic neural crest-derived medulla, found in the center of the gland, and the mesoderm-derived cortex producing steroidogenic hormones. The medulla is composed of neuroendocrine chromaffin cells with oxygen-sensing properties and is dependent on tissue interactions with the overlying cortex, both during development and in adulthood. Other relevant organs include the Zuckerkandl organ containing extra-adrenal chromaffin cells, and carotid oxygen-sensing bodies containing glomus cells. Chromaffin and glomus cells reveal a number of important similarities and are derived from the multipotent nerve-associated descendants of the neural crest, or Schwann cell precursors. Abnormalities in complex developmental processes during differentiation of nerve-associated and other progenitors into chromaffin and oxygen-sensing populations may result in different subtypes of paraganglioma, neuroblastoma and pheochromocytoma. Here, we summarize recent findings explaining the development of chromaffin and oxygen-sensing cells, as well as the potential mechanisms driving neuroendocrine tumor initiation.

Neuropilins guide preganglionic sympathetic axons and chromaffin cell precursors to establish the adrenal medulla

The adrenal medulla is composed of neuroendocrine chromaffin cells that secrete adrenaline into the systemic circulation to maintain physiological homeostasis and enable the autonomic stress response. How chromaffin cell precursors colonise the adrenal medulla and how they become connected to central nervous system-derived preganglionic sympathetic neurons remain largely unknown. By combining lineage tracing, gene expression studies, genetic ablation and the analysis of mouse mutants, we demonstrate that preganglionic axons direct chromaffin cell precursors into the adrenal primordia. We further show that preganglionic axons and chromaffin cell precursors require class 3 semaphorin (SEMA3) signalling through neuropilins (NRP) to target the adrenal medulla. Thus, SEMA3 proteins serve as guidance cues to control formation of the adrenal neuroendocrine system by establishing appropriate connections between preganglionic neurons and adrenal chromaffin cells that regulate the autonomic stress response.

Summary: A new role is revealed for semaphorin/neuropilin signalling in guiding preganglionic sympathetic axons and chromaffin cell precursors into the adrenal primordia, ensuring correct regulation of the autonomic stress response.

The neural crest and evolution of the head/trunk interface in vertebrates

The migration and distribution patterns of neural crest (NC) cells reflect the distinct embryonic environments of the head and trunk: cephalic NC cells migrate predominantly along the dorsolateral pathway to populate the craniofacial and pharyngeal regions, whereas trunk crest cells migrate along the ventrolateral pathways to form the dorsal root ganglia. These two patterns thus reflect the branchiomeric and somitomeric architecture, respectively, of the vertebrate body plan. The so-called vagal NC occupies a postotic, intermediate level between the head and trunk NC. This level of NC gives rise to both trunk- and cephalic-type (circumpharyngeal) NC cells. The anatomical pattern of the amphioxus, a basal chordate, suggests that somites and pharyngeal gills coexist along an extensive length of the body axis, indicating that the embryonic environment is similar to that of vertebrate vagal NC cells and may have been ancestral for vertebrates. The amniote-like condition in which the cephalic and trunk domains are distinctly separated would have been brought about, in part, by anteroposterior reduction of the pharyngeal domain.

Neural crest and cancer: Divergent travelers on similar paths

Neural crest cells are multipotent progenitors that dynamically interpret diverse microenvironments to migrate significant distances as a loosely associated collective and contribute to many tissues in the developing vertebrate embryo. Uncovering details of neural crest migration has helped to inform a general understanding of collective cell migration, including that which occurs during cancer metastasis. Here, we discuss several commonalities and differences of neural crest and cancer cell migration and behavior. First, we focus on some of the molecular pathways required for the initial specification and potency of neural crest cells and the roles of many of these pathways in cancer progression. We also describe epithelial-to-mesenchymal transition, which plays a critical role in initiating both neural crest migration and cancer metastasis. Finally, we evaluate studies that demonstrate myriad forms of cell-cell and cell-environment communication during neural crest and cancer collective migration to highlight the remarkable similarities in their molecular and cell biological regulation.

From proliferation to target innervation: signaling molecules that direct sympathetic nervous system development

The sympathetic division of the autonomic nervous system includes a variety of cells including neurons, endocrine cells and glial cells. A recent study (Furlan et al. 2017) has revised thinking about the developmental origin of these cells. It now appears that sympathetic neurons and chromaffin cells of the adrenal medulla do not have an immediate common ancestor in the form a "sympathoadrenal cell", as has been long believed. Instead, chromaffin cells arise from Schwann cell precursors. This review integrates the new findings with the expanding body of knowledge on the signalling pathways and transcription factors that regulate the origin of cells of the sympathetic division of the autonomic nervous system.

Transcriptome profiling reveals expression signatures of cranial neural crest cells arising from different axial levels

Background

Cranial neural crest cells (NCCs) are a unique embryonic cell type which give rise to a diverse array of derivatives extending from neurons and glia through to bone and cartilage. Depending on their point of origin along the antero-posterior axis cranial NCCs are rapidly sorted into distinct migratory streams that give rise to axial specific structures. These migratory streams mirror the underlying segmentation of the brain with NCCs exiting the diencephalon and midbrain following distinct paths compared to those exiting the hindbrain rhombomeres (r). The genetic landscape of cranial NCCs arising at different axial levels remains unknown.

Results

Here we have used RNA sequencing to uncover the transcriptional profiles of mouse cranial NCCs arising at different axial levels. Whole transcriptome analysis identified over 120 transcripts differentially expressed between NCCs arising anterior to r3 (referred to as r1-r2 migratory stream for simplicity) and the r4 migratory stream. Eight of the genes differentially expressed between these populations were validated by RT-PCR with 2 being further validated by in situ hybridisation. We also explored the expression of the Neuropilins (Nrp1 and Nrp2) and their co-receptors and show that the A-type Plexins are differentially expressed in different cranial NCC streams.

Conclusions

Our analyses identify a large number of genes differentially regulated between cranial NCCs arising at different axial levels. This data provides a comprehensive description of the genetic landscape driving diversity of distinct cranial NCC streams and provides novel insight into the regulatory networks controlling the formation of specific skeletal elements and the mechanisms promoting migration along different paths.

Electronic supplementary material

The online version of this article (doi:10.1186/s12861-017-0147-z) contains supplementary material, which is available to authorized users.

The loss of scents: do defects in olfactory sensory neuron development underlie human disease?

The olfactory system is a fascinating and beguiling sensory system: olfactory sensory neurons detect odors underlying behaviors essential for mate choice, food selection, and escape from predators, among others. These sensory neurons are unique in that they have dendrites contacting the outside world, yet their first synapse lies in the central nervous system. The information entering the central nervous system is used to create odor memories that play a profound role in recognition of individuals, places, and appropriate foods. Here, the structure of the olfactory epithelium is given as an overview to discuss the origin of the olfactory placode, the plasticity of the olfactory sensory neurons, and finally the origins of the gonadotropin-releasing hormone neuroendocrine cells. For the purposes of this review, the development of the peripheral sensory system will be analyzed, incorporating recently published studies highlighting the potential novelties in development mechanisms. Specifically, an emerging model where the olfactory epithelium and olfactory bulb develop simultaneously from a continuous neurectoderm patterned at the end of gastrulation, and the multiple origins of the gonadotropin-releasing hormone neuroendocrine cells associated with the olfactory sensory system development will be presented. Advances in the understanding of the basic mechanisms underlying olfactory sensory system development allows for a more thorough understanding of the potential causes of human disease.

Sympathoadrenal neural crest cells: the known, unknown and forgotten?

Neural crest cells (NCCs) are highly migratory progenitor cells that give rise to a vast array of differentiated cell types. One of their key derivatives is the autonomic nervous system (ANS) that is comprised in part from chromaffin cells of the adrenal medulla and organ of Zuckerkandl, the sympathetic chain and additional prevertebral ganglia such as the celiac ganglia, suprarenal ganglia and mesenteric ganglia. In this review we discuss recent advances toward our understanding of how the NCC precursors of the ANS migrate to their target regions, how they are instructed to differentiate into the correct cell types, and the morphogenetic signals controlling their development. Many of these processes remain enigmatic to developmental biologists worldwide. Taking advantage of lineage tracing mouse models one of our own aims is to address the morphogenetic events underpinning the formation of the ANS and to identify the molecular mechanisms that help to segregate a mixed population of NCCs into pathways specific for the sympathetic ganglia, sensory ganglia or adrenal medulla.