Imaging neural crest cell dynamics during formation of dorsal root ganglia and sympathetic ganglia

Rspo1 and Rspo3 are required for sensory lineage neural crest formation in mouse embryos

BACKGROUND

R-spondins (Rspos) are secreted proteins that modulate Wnt/β-catenin signaling. At the early stages of spinal cord development, Wnts (Wnt1, Wnt3a) and Rspos (Rspo1, Rspo3) are co-expressed in the roof plate, suggesting that Rspos are involved in development of dorsal spinal cord and neural crest cells in cooperation with Wnt ligands.

RESULTS

Here, we found that Rspo1 and Rspo3, as well as Wnt1 and Wnt3a, maintained roof-plate-specific expression until late embryonic stages. Rspo1- and Rspo3-double-knock-out (dKO) embryos partially exhibited the phenotype of Wnt1 and Wnt3a dKO embryos. While the number of Ngn2-positive sensory lineage neural crest cells is reduced in Rspo-dKO embryos, development of dorsal spinal cord, including its size and dorso-ventral patterning in early development, elongation of the roof plate, and proliferation of ependymal cells, proceeded normally. Consistent with these slight defects, Wnt/β-catenin signaling was not obviously changed in developing spinal cord of dKO embryos.

CONCLUSIONS

Our results show that Rspo1 and Rspo3 are dispensable for most developmental processes involving roof plate-derived Wnt ligands, except for specification of a subtype of neural crest cells. Thus, Rspos may modulate Wnt/β-catenin signaling in a context-dependent manner.

The differences in the anatomy of the thoracolumbar and sacral autonomic outflow are quantitative

PURPOSE

We have re-evaluated the anatomical arguments that underlie the division of the spinal visceral outflow into sympathetic and parasympathetic divisions.

METHODOLOGY

Using a systematic literature search, we mapped the location of catecholaminergic neurons throughout the mammalian peripheral nervous system. Subsequently, a narrative method was employed to characterize segment-dependent differences in the location of preganglionic cell bodies and the composition of white and gray rami communicantes.

RESULTS AND CONCLUSION

One hundred seventy studies were included in the systematic review, providing information on 389 anatomical structures. Catecholaminergic nerve fibers are present in most spinal and all cranial nerves and ganglia, including those that are known for their parasympathetic function. Along the entire spinal autonomic outflow pathways, proximal and distal catecholaminergic cell bodies are common in the head, thoracic, and abdominal and pelvic region, which invalidates the "short-versus-long preganglionic neuron" argument. Contrary to the classically confined outflow levels T1-L2 and S2-S4, preganglionic neurons have been found in the resulting lumbar gap. Preganglionic cell bodies that are located in the intermediolateral zone of the thoracolumbar spinal cord gradually nest more ventrally within the ventral motor nuclei at the lumbar and sacral levels, and their fibers bypass the white ramus communicans and sympathetic trunk to emerge directly from the spinal roots. Bypassing the sympathetic trunk, therefore, is not exclusive for the sacral outflow. We conclude that the autonomic outflow displays a conserved architecture along the entire spinal axis, and that the perceived differences in the anatomy of the autonomic thoracolumbar and sacral outflow are quantitative.

Human iPSC modeling recapitulates in vivo sympathoadrenal development and reveals an aberrant developmental subpopulation in familial neuroblastoma

Studies defining normal and disrupted human neural crest cell development have been challenging given its early timing and intricacy of development. Consequently, insight into the early disruptive events causing a neural crest related disease such as pediatric cancer neuroblastoma is limited. To overcome this problem, we developed an in vitro differentiation model to recapitulate the normal in vivo developmental process of the sympathoadrenal lineage which gives rise to neuroblastoma. We used human in vitro pluripotent stem cells and single-cell RNA sequencing to recapitulate the molecular events during sympathoadrenal development. We provide a detailed map of dynamically regulated transcriptomes during sympathoblast formation and illustrate the power of this model to study early events of the development of human neuroblastoma, identifying a distinct subpopulation of cell marked by SOX2 expression in developing sympathoblast obtained from patient derived iPSC cells harboring a germline activating mutation in the anaplastic lymphoma kinase (ALK) gene.

Description of trunk neural crest migration and peripheral nervous system formation in the Egyptian cobra Naja haje haje

The neural crest is a stem cell population that forms in the neurectoderm of all vertebrates and gives rise to a diverse set of cells such as sensory neurons, Schwann cells and melanocytes. Neural crest development in snakes is still poorly understood. From the point of view of evolutionary and comparative anatomy is an interesting topic given the unique anatomy of snakes. The aim of the study was to characterize how trunk neural crest cells (TNCC) migrate in the developing elapid snake Naja haje haje and consequently, look at the beginnings of development of neural crest derived sensory ganglia (DRG) and spinal nerves. We found that trunk neural crest and DRG development in Naja haje haje is like what has been described in other vertebrates and the colubrid snake strengthening our knowledge on the conserved mechanisms of neural crest development across species. Here we use the marker HNK1 to follow the migratory behavior of TNCC in the elapid snake Naja haje haje through stages 1-6 (1-9 days postoviposition). We observed that the TNCC of both snake species migrate through the rostral portion of the somite, a pattern also conserved in birds and mammals. The development of cobra peripheral nervous system, using neuronal and glial markers, showed the presence of spectrin in Schwann cell precursors and of axonal plexus along the length of the cobra embryos. In conclusion, cobra embryos show strong conserved patterns in TNCC and PNS development among vertebrates.

Implementing a multi-colour genetic marker analysis technique for embryology education

Embryology belongs to the basic sciences and is usually an integral part of the anatomy. The subject is traditionally taught by visual inspection of embryonic tissue slides stained with Haematoxylin and Eosin (H&E) to expose the dynamics of tissue histology as development proceeds. While combining in situ hybridization for gene expression analysis and immunostaining for protein expression analysis is an established technique for embryology research, the implementation of this tool in embryology teaching has not been described. The present study was conducted to assess the use of an online multi-colour gene expression analysis technique, alongside histological sections and diagrams, to improve students' understanding of embryology. The participants of this study were bachelor's students of Veterinary Medicine at the University of Khartoum. The method was also evaluated by distributing questionnaire items to Veterinary students via Google forms; subsequently, their responses were analysed qualitatively. The majority of students stated that the new technique was beneficial for their learning of embryology. The multi-colour images proved a more effective means for learning embryology than the traditional H&E image. Results from the students strengthen the belief in applying the multi-colour technique for better embryology course learning.

Ectopic dorsal root ganglion in cauda equina mimicking schwannoma in a child

Background

A heterotopic dorsal root ganglion (DRG) is sometimes observed in the vicinity of dysplastic neural structures during surgery for open spinal dysraphism; however, it is rarely associated with closed spinal dysraphism. Distinguish from neoplasms by preoperative imaging study is difficult. Although the embryopathogenesis of a heterotopic DRG has been speculated to be migration disorder of neural crest cells from primary neural tube, its details remain unelucidated.

Case Description

We report a pediatric case with an ectopic DRG in cauda equina associated with a fatty terminal filum and bifid sacrum. The DRG mimicked a schwannoma in the cauda equina on preoperative magnetic resonance imaging. Laminotomy at L3 revealed that the tumor was entangled in the nerve roots, and small parts of the tumor were resected for biopsy. Histopathologically, the tumor consisted of ganglion cells and peripheral nerve fibers. Ki-67 immunopositive cells were observed at the periphery of the ganglion cells. These findings indicate the tumor comprised DRG tissue.

Conclusion

We report detailed neuroradiological, intraoperative and histological findings and discuss the embryopathogenesis of the ectopic DRG. One should be aware of the possibility of ectopic or heterotopic DRGs when cauda equina tumors are observed in pediatric patients with neurulation disorders.

The transcriptional portraits of the neural crest at the individual cell level

Since the discovery of this cell population by His in 1850, the neural crest has been under intense study for its important role during vertebrate development. Much has been learned about the function and regulation of neural crest cell differentiation, and as a result, the neural crest has become a key model system for stem cell biology in general. The experiments performed in embryology, genetics, and cell biology in the last 150 years in the neural crest field has given rise to several big questions that have been debated intensely for many years: "How does positional information impact developmental potential? Are neural crest cells individually multipotent or a mixed population of committed progenitors? What are the key factors that regulate the acquisition of stem cell identity, and how does a stem cell decide to differentiate towards one cell fate versus another?" Recently, a marriage between single cell multi-omics, statistical modeling, and developmental biology has shed a substantial amount of light on these questions, and has paved a clear path for future researchers in the field.

Microbial influences on gut development and gut-brain communication

The developmental programs that build and sustain animal forms also encode the capacity to sense and adapt to the microbial world within which they evolved. This is abundantly apparent in the development of the digestive tract, which typically harbors the densest microbial communities of the body. Here, we review studies in human, mouse, zebrafish and Drosophila that are revealing how the microbiota impacts the development of the gut and its communication with the nervous system, highlighting important implications for human and animal health.

Neuroblastoma differentiation in vivo excludes cranial tumors

Neuroblastoma (NB), the most common cancer in the first year of life, presents almost exclusively in the trunk. To understand why an early-onset cancer would have such a specific localization, we xenotransplanted human NB cells into discrete neural crest (NC) streams in zebrafish embryos. Here, we demonstrate that human NB cells remain in an undifferentiated, tumorigenic state when comigrating posteriorly with NC cells but, upon comigration into the head, differentiate into neurons and exhibit decreased survival. Furthermore, we demonstrate that this in vivo differentiation requires retinoic acid and brain-derived neurotrophic factor signaling from the microenvironment, as well as cell-autonomous intersectin-1-dependent phosphoinositide 3-kinase-mediated signaling, likely via Akt kinase activation. Our findings suggest a microenvironment-driven explanation for NB's trunk-biased localization and highlight the potential for induced differentiation to promote NB resolution in vivo.

Draxin inhibits chick trunk neural crest delamination and migration by increasing cell adhesion

The neural crest is a multipotent cell population that migrates extensively to play important roles during embryonic development. After acquiring motility, trunk neural crest cells delaminate from the spinal cord and migrate to various regions of the body. Several cellular adhesion molecules, such as vinculin, are involved in the regulation of neural crest delamination and migration. In the present study, we found that draxin could inhibit delamination and migration of neural crest cells from the chick spinal cord and abnormal aggregation of the migrating neural crest cells. In the presence of draxin, the resuspended neural crest regained its adhesive ability such that it was significantly increased. Overexpression of draxin caused increased vinculin expression in vivo. Our data indicate that draxin might control delamination and migration of chick trunk neural crest by increasing cell adhesion.

The embryonic trunk neural crest microenvironment regulates the plasticity and invasion of human neuroblastoma via TrkB signaling

Mistakes in trunk neural crest (NC) cell migration may lead to birth defects of the sympathetic nervous system (SNS) and neuroblastoma (NB) cancer. Receptor tyrosine kinase B (TrkB) and its ligand BDNF critically regulate NC cell migration during normal SNS development and elevated expression of TrkB is correlated with high-risk NB patients. However, in the absence of a model with in vivo interrogation of human NB cell and gene expression dynamics, the mechanistic role of TrkB in NB disease progression remains unclear. Here, we study the functional relationship between TrkB, cell invasion and plasticity of human NB cells by taking advantage of our validated in vivo chick embryo transplant model. We find that LAN5 (high TrkB) and SHSY5Y (moderate TrkB) human NB cells aggressively invade host embryos and populate typical NC targets, however loss of TrkB function significantly reduces cell invasion. In contrast, NB1643 (low TrkB) cells remain near the transplant site, but over-expression of TrkB leads to significant cell invasion. Invasive NB cells show enhanced expression of genes indicative of the most invasive host NC cells. In contrast, transplanted human NB cells down-regulate known NB tumor initiating and stem cell markers. Human NB cells that remain within the dorsal neural tube transplant also show enhanced expression of cell differentiation genes, resulting in an improved disease outcome as predicted by a computational algorithm. These in vivo data support TrkB as an important biomarker and target to control NB aggressiveness and identify the chick embryonic trunk neural crest microenvironment as a source of signals to drive NB to a less aggressive state, likely acting at the dorsal neural tube.

5-HT3 Signaling Alters Development of Sacral Neural Crest Derivatives That Innervate the Lower Urinary Tract

The autonomic nervous system derives from the neural crest (NC) and supplies motor innervation to the smooth muscle of visceral organs, including the lower urinary tract (LUT). During fetal development, sacral NC cells colonize the urogenital sinus to form pelvic ganglia (PG) flanking the bladder neck. The coordinated activity of PG neurons is required for normal urination; however, little is known about the development of PG neuronal diversity. To discover candidate genes involved in PG neurogenesis, the transcriptome profiling of sacral NC and developing PG was performed, and we identified the enrichment of the type 3 serotonin receptor (5-HT3, encoded by Htr3a and Htr3b). We determined that Htr3a is one of the first serotonin receptor genes that is up-regulated in sacral NC progenitors and is maintained in differentiating PG neurons. In vitro cultures showed that the disruption of 5-HT3 signaling alters the differentiation outcomes of sacral NC cells, while the stimulation of 5-HT3 in explanted fetal pelvic ganglia severely diminished neurite arbor outgrowth. Overall, this study provides a valuable resource for the analysis of signaling pathways in PG development, identifies 5-HT3 as a novel regulator of NC lineage diversification and neuronal maturation in the peripheral nervous system, and indicates that the perturbation of 5-HT3 signaling in gestation has the potential to alter bladder function later in life.

Spatiotemporal contribution of neuromesodermal progenitor-derived neural cells in the elongation of developing mouse spinal cord

AIMS

During vertebrate development, the posterior end of the embryo progressively elongates in a head-to-tail direction to form the body plan. Recent lineage tracing experiments revealed that bi-potent progenitors, called neuromesodermal progenitors (NMPs), produce caudal neural and mesodermal tissues during axial elongation. However, their precise location and contribution to spinal cord development remain elusive.

MAIN METHODS

Here we used NMP-specific markers (Sox2 and BraT) and a genetic lineage tracing system to localize NMP progeny in vivo.

KEY FINDINGS

Sox2 and BraT double positive cells were initially located at the tail tip, but were later found in the caudal neural tube, which is a unique feature of mouse development. In the neural tube, they produced neural progenitors (NPCs) and contributed to the spinal cord gradually along the AP axis during axial elongation. Interestingly, NMP-derived NPCs preferentially contributed to the ventral side first and later to the dorsal side at the lumbar spinal cord level, which may be associated with atypical junctional neurulation in mice.

SIGNIFICANCE

Our current observations detail the contribution of NMP progeny to spinal cord elongation and provide insights into how different species uniquely execute caudal morphogenesis.

Development of the sympathetic trunks in human embryos

Although the development of the sympathetic trunks was first described >100 years ago, the topographic aspect of their development has received relatively little attention. We visualised the sympathetic trunks in human embryos of 4.5–10 weeks post‐fertilisation, using Amira 3D‐reconstruction and Cinema 4D‐remodelling software. Scattered, intensely staining neural crest‐derived ganglionic cells that soon formed longitudinal columns were first seen laterally to the dorsal aorta in the cervical and upper thoracic regions of Carnegie stage (CS)14 embryos. Nerve fibres extending from the communicating branches with the spinal cord reached the trunks at CS15‐16 and became incorporated randomly between ganglionic cells. After CS18, ganglionic cells became organised as irregular agglomerates (ganglia) on a craniocaudally continuous cord of nerve fibres, with dorsally more ganglionic cells and ventrally more fibres. Accordingly, the trunks assumed a “pearls‐on‐a‐string” appearance, but size and distribution of the pearls were markedly heterogeneous. The change in position of the sympathetic trunks from lateral (para‐aortic) to dorsolateral (prevertebral or paravertebral) is a criterion to distinguish the “primary” and “secondary” sympathetic trunks. We investigated the position of the trunks at vertebral levels T2, T7, L1 and S1. During CS14, the trunks occupied a para‐aortic position, which changed into a prevertebral position in the cervical and upper thoracic regions during CS15, and in the lower thoracic and lumbar regions during CS18 and CS20, respectively. The thoracic sympathetic trunks continued to move further dorsally and attained a paravertebral position at CS23. The sacral trunks retained their para‐aortic and prevertebral position, and converged into a single column in front of the coccyx. Based on our present and earlier morphometric measurements and literature data, we argue that differential growth accounts for the regional differences in position of the sympathetic trunks.

Tracking the movement of individual avian neural crest cells in vitro

The origin, migratory pathways and adult derivatives of neural crest cells (NCCs) are well known. However, less is known about how these cells migrate. In this study, in a laboratory based in a low-resource setting, a hanging drop culture assay was utilised to study the movement of individual avian trunk neural crest cells. Mode of migration by means of lamellipodia and filopodia was studied in live cell cultures with a laser scanning confocal microscope and Airyscan module. Both distance migrated and speed of migration were calculated. NCCs migrated in a chain soon after emerging from the explanted neural tube, but were more dispersed and had random movements when they reached the periphery of the culture. While the distances travelled by these NCCs were less and the cells were slower on gelatine than on other extracellular matrices reported in the literature, the assay afforded detailed observation of actin filament distribution and cytoplasmic protrusions. The study has provided unique evidence of individual NCC movements in vitro, in a simple hanging drop assay optimized for the study of NCCs. The assay could be used for further analysis of the behaviour of NCCs on different extracellular matrices or with targeted action.

Physiological electric fields induce directional migration of mammalian cranial neural crest cells

During neurulation, cranial neural crest cells (CNCCs) migrate long distances from the neural tube to their terminal site of differentiation. The pathway traveled by the CNCCs defines the blueprint for craniofacial construction, abnormalities of which contribute to three-quarters of human birth defects. Biophysical cues like naturally occurring electric fields (EFs) have been proposed to be one of the guiding mechanisms for CNCC migration from the neural tube to identified position in the branchial arches. Such endogenous EFs can be mimicked by applied EFs of physiological strength that has been reported to guide the migration of amphibian and avian neural crest cells (NCCs), namely galvanotaxis or electrotaxis. However, the behavior of mammalian NCCs in external EFs has not been reported. We show here that mammalian CNCCs migrate towards the anode in direct current (dc) EFs. Reversal of the field polarity reverses the directedness. The response threshold was below 30 ​mV/mm and the migration directedness and displacement speed increased with increase in field strength. Both CNCC line (O9-1) and primary mouse CNCCs show similar galvanotaxis behavior. Our results demonstrate for the first time that the mammalian CNCCs respond to physiological EFs by robust directional migration towards the anode in a voltage-dependent manner.

Expression of Connexins 37, 43 and 45 in Developing Human Spinal Cord and Ganglia

Direct intercellular communication via gap junctions has an important role in the development of the nervous system, ranging from cell migration and neuronal differentiation to the formation of neuronal activity patterns. This study characterized and compared the specific spatio-temporal expression patterns of connexins (Cxs) 37, 43 and 45 during early human developmental stages (since the 5th until the 10th developmental week) in the spinal cord (SC) and dorsal root ganglia (DRG) using double immunofluorescence and transmission electron microscopy. We found the expression of all three investigated Cxs during early human development in all the areas of interest, in the SC, DRG, developing paravertebral ganglia of the sympathetic trunk, notochord and all three meningeal layers, with predominant expression of Cx37. Comparing the expression of different Cxs between distinct developmental periods, we did not find significant differences. Specific spatio-temporal pattern of Cxs expression might reflect their relevance in the development of all areas of interest via cellular interconnectivity and synchronization during the late embryonic and early fetal period of human development.

The development of somatosensory neurons: Insights into pain and itch

Primary nociceptors are a heterogeneous class of peripheral somatosensory neurons, responsible for detecting noxious, pruriceptive, and thermal stimuli. These neurons are further divided into several molecularly defined subtypes that correlate with their functional sensory modalities and morphological features. During development, all nociceptors arise from a common pool of embryonic precursors, and then segregate progressively into their mature specialized phenotypes. In this review, we summarize the intrinsic transcriptional programs and extrinsic trophic factor signaling mechanisms that interact to control nociceptor diversification. We also discuss how recent transcriptome profiling studies have significantly advanced the field of sensory neuron development.

Bioprinting: From Tissue and Organ Development to in Vitro Models

Bioprinting techniques have been flourishing in the field of biofabrication with pronounced and exponential developments in the past years. Novel biomaterial inks used for the formation of bioinks have been developed, allowing the manufacturing of in vitro models and implants tested preclinically with a certain degree of success. Furthermore, incredible advances in cell biology, namely, in pluripotent stem cells, have also contributed to the latest milestones where more relevant tissues or organ-like constructs with a certain degree of functionality can already be obtained. These incredible strides have been possible with a multitude of multidisciplinary teams around the world, working to make bioprinted tissues and organs more relevant and functional. Yet, there is still a long way to go until these biofabricated constructs will be able to reach the clinics. In this review, we summarize the main bioprinting activities linking them to tissue and organ development and physiology. Most bioprinting approaches focus on mimicking fully matured tissues. Future bioprinting strategies might pursue earlier developmental stages of tissues and organs. The continuous convergence of the experts in the fields of material sciences, cell biology, engineering, and many other disciplines will gradually allow us to overcome the barriers identified on the demanding path toward manufacturing and adoption of tissue and organ replacements.

Putative roles of SLC7A5 (LAT1) transporter in pain

Large amino acid transporter 1 (LAT1), also known as SLC7A5, is an essential amino acid transporter that forms a heterodimeric complex with the glycoprotein cell-surface antigen heavy chain (4F2hc (CD98, SLC3A2)). Within nociceptive pathways, LAT1 is expressed in the dorsal root ganglia and spinal cord. Although LAT1 expression is upregulated following spinal cord injury, little is known about LAT1 in neuropathic pain. To date, only circumstantial evidence supports LAT1/4F2hc's role in pain. Notably, LAT1's expression and regulation link it to key cell types and pathways implicated in pain. Transcriptional regulation of LAT1 expression occurs via the Wnt/frizzled/β-catenin signal transduction pathway, which has been shown to be involved in chronic pain. The LAT1/4F2hc complex may also be involved in pain pathways related to T- and B-cells. LAT1's expression induces activation of the mammalian target of rapamycin (mTOR) signaling axis, which is involved in inflammation and neuropathic pain. Similarly, hypoxia and cancer induce activation of hypoxia-inducible factor 2 alpha, promoting not only LAT1's expression but also mTORC1's activation. Perhaps the strongest evidence linking LAT1 to pain is its interactions with key voltage-gated ion channels connected to nociception, namely the voltage-gated potassium channels Kv1.1 and Kv1.2 and the voltage-gated sodium channel Nav1.7. Through functional regulation of these channels, LAT1 may play a role in governing the excitatory to inhibitory ratio which is altered in chronic neuropathic pain states. Remarkably, the most direct role for LAT1 in pain is to mediate the influx of gabapentin and pregabalin, two first-line neuropathic pain drugs, that indirectly inhibit high voltage-activated calcium channel auxiliary subunit α2δ-1. In this review, we discuss the expression, regulation, relevant signaling pathways, and protein interactions of LAT1 that may link it to the development and/or maintenance of pain. We hypothesize that LAT1 expressed in nociceptive pathways may be a viable new target in pain.

The development of the trunk neural crest in the turtle Trachemys scripta

BACKGROUND

The neural crest is a group of multipotent cells that give rise to a wide variety of cells, especially portion of the peripheral nervous system. Neural crest cells (NCCs) show evolutionary conserved fate restrictions based on their axial level of origin: cranial, vagal, trunk, and sacral. While much is known about these cells in mammals, birds, amphibians, and fish, relatively little is known in other types of amniotes such as snakes, lizards, and turtles. We attempt here to provide a more detailed description of the early phase of trunk neural crest cell (tNCC) development in turtle embryos.

RESULTS

In this study, we show, for the first time, migrating tNCC in the pharyngula embryo of Trachemys scripta by vital-labeling the NCC with DiI and through immunofluorescence. We found that (a) tNCC form a line along the sides of the trunk NT; (b) The presence of late migrating tNCC on the medial portion of the somite; (c) The presence of lateral mesodermal migrating tNCC in pharyngula embryos; (d) That turtle embryos have large/thick peripheral nerves.

CONCLUSIONS

The similarities and differences in tNCC migration and early PNS development that we observe across sauropsids (birds, snake, gecko, and turtle) suggests that these species evolved some distinct NCC pathways.

Mechanisms of Neural Crest Migration

Neural crest cells are a transient embryonic cell population that migrate collectively to various locations throughout the embryo to contribute a number of cell types to several organs. After induction, the neural crest delaminates and undergoes an epithelial-to-mesenchymal transition before migrating through intricate yet characteristic paths. The neural crest exhibits a variety of migratory behaviors ranging from sheet-like mass migration in the cephalic regions to chain migration in the trunk. During their journey, neural crest cells rely on a range of signals both from their environment and within the migrating population for navigating through the embryo as a collective. Here we review these interactions and mechanisms, including chemotactic cues of neural crest cells' migration.

Pulling in models of cell migration

There are numerous biological scenarios in which populations of cells migrate in crowded environments. Typical examples include wound healing, cancer growth, and embryo development. In these crowded environments cells are able to interact with each other in a variety of ways. These include excluded-volume interactions, adhesion, repulsion, cell signaling, pushing, and pulling. One popular way to understand the behavior of a group of interacting cells is through an agent-based mathematical model. A typical aim of modellers using such representations is to elucidate how the microscopic interactions at the cell-level impact on the macroscopic behavior of the population. At the very least, such models typically incorporate volume-exclusion. The more complex cell-cell interactions listed above have also been incorporated into such models; all apart from cell-cell pulling. In this paper we consider this under-represented cell-cell interaction, in which an active cell is able to "pull" a nearby neighbor as it moves. We incorporate a variety of potential cell-cell pulling mechanisms into on- and off-lattice agent-based volume exclusion models of cell movement. For each of these agent-based models we derive a continuum partial differential equation which describes the evolution of the cells at a population level. We study the agreement between the agent-based models and the continuum, population-based models and compare and contrast a range of agent-based models (accounting for the different pulling mechanisms) with each other. We find generally good agreement between the agent-based models and the corresponding continuum models that worsens as the agent-based models become more complex. Interestingly, we observe that the partial differential equations that we derive differ significantly, depending on whether they were derived from on- or off-lattice agent-based models of pulling. This hints that it is important to employ the appropriate agent-based model when representing pulling cell-cell interactions.

Getting direction(s): The Eph/ephrin signaling system in cell positioning

In vertebrates, the Eph/ephrin family of signaling molecules is a large group of membrane-bound proteins that signal through a myriad of mechanisms and effectors to play diverse roles in almost every tissue and organ system. Though Eph/ephrin signaling has functions in diverse biological processes, one core developmental function is in the regulation of cell position and tissue morphology by regulating cell migration and guidance, cell segregation, and boundary formation. Often, the role of Eph/ephrin signaling is to translate patterning information into physical movement of cells and changes in morphology that define tissue and organ systems. In this review, we focus on recent advances in the regulation of these processes, and our evolving understanding of the in vivo signaling mechanisms utilized in distinct developmental contexts.

Hijacking of Embryonic Programs by Neural Crest-Derived Neuroblastoma: From Physiological Migration to Metastatic Dissemination

In the developing organism, complex molecular programs orchestrate the generation of cells in adequate numbers, drive them to migrate along the correct pathways towards appropriate territories, eliminate superfluous cells, and induce terminal differentiation of survivors into the appropriate cell-types. Despite strict controls constraining developmental processes, malignancies can emerge in still immature organisms. This is the case of neuroblastoma (NB), a highly heterogeneous disease, predominantly affecting children before the age of 5 years. Highly metastatic forms represent half of the cases and are diagnosed when disseminated foci are detectable. NB arise from a transient population of embryonic cells, the neural crest (NC), and especially NC committed to the establishment of the sympatho-adrenal tissues. The NC is generated at the dorsal edge of the neural tube (NT) of the vertebrate embryo, under the action of NC specifier gene programs. NC cells (NCCs) undergo an epithelial to mesenchymal transition, and engage on a remarkable journey in the developing embryo, contributing to a plethora of cell-types and tissues. Various NCC sub-populations and derived lineages adopt specific migratory behaviors, moving individually as well as collectively, exploiting the different embryonic substrates they encounter along their path. Here we discuss how the specific features of NCC in development are re-iterated during NB metastatic behaviors.

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

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

The Neural Crest: A Remarkable Model System for Studying Development and Disease

Neural crest cells are the embryonic precursors of most neurons and all glia of the peripheral nervous system, pigment cells, some endocrine components, and connective tissue of the head, face, neck, and heart. Following induction, crest cells undergo an epithelial to mesenchymal transition that enables them to migrate along specific pathways culminating in their phenotypic differentiation. Researching this unique embryonic population has revealed important understandings of basic biological and developmental principles. These principles are likely to assist in clarifying the etiology and help in finding strategies for the treatment of neural crest diseases, collectively termed neurocristopathies. The progress achieved in neural crest research is made feasible thanks to the continuous development of species-specific in vivo and in vitro paradigms and more recently the possibility to produce neural crest cells and specific derivatives from embryonic or induced pluripotent stem cells. All of the above assist us in elucidating mechanisms that regulate neural crest development using state-of-the art cellular, molecular, and imaging approaches.

A chemotactic model of trunk neural crest cell migration

Trunk neural crest cells follow a common ventral migratory pathway but are distributed into two distinct locations to form discrete sympathetic and dorsal root ganglia along the vertebrate axis. Although fluorescent cell labeling and time-lapse studies have recorded complex trunk neural crest cell migratory behaviors, the signals that underlie this dynamic patterning remain unclear. The absence of molecular information has led to a number of mechanistic hypotheses for trunk neural crest cell migration. Here, we review recent data in support of three distinct mechanisms of trunk neural crest cell migration and develop and simulate a computational model based on chemotactic signaling. We show that by integrating the timing and spatial location of multiple chemotactic signals, trunk neural crest cells may be accurately positioned into two distinct targets that correspond to the sympathetic and dorsal root ganglia. In doing so, we honor the contributions of Wilhelm His to his identification of the neural crest and extend the observations of His and others to better understand a complex question in neural crest cell biology.

Predicting neuroblastoma using developmental signals and a logic-based model

Genomic information from human patient samples of pediatric neuroblastoma cancers and known outcomes have led to specific gene lists put forward as high risk for disease progression. However, the reliance on gene expression correlations rather than mechanistic insight has shown limited potential and suggests a critical need for molecular network models that better predict neuroblastoma progression. In this study, we construct and simulate a molecular network of developmental genes and downstream signals in a 6-gene input logic model that predicts a favorable/unfavorable outcome based on the outcome of the four cell states including cell differentiation, proliferation, apoptosis, and angiogenesis. We simulate the mis-expression of the tyrosine receptor kinases, trkA and trkB, two prognostic indicators of neuroblastoma, and find differences in the number and probability distribution of steady state outcomes. We validate the mechanistic model assumptions using RNAseq of the SHSY5Y human neuroblastoma cell line to define the input states and confirm the predicted outcome with antibody staining. Lastly, we apply input gene signatures from 77 published human patient samples and show that our model makes more accurate disease outcome predictions for early stage disease than any current neuroblastoma gene list. These findings highlight the predictive strength of a logic-based model based on developmental genes and offer a better understanding of the molecular network interactions during neuroblastoma disease progression.

The intriguing nature of dorsal root ganglion neurons: Linking structure with polarity and function

Dorsal root ganglion (DRG) neurons are the first neurons of the sensory pathway. They are activated by a variety of sensory stimuli that are then transmitted to the central nervous system. An important feature of DRG neurons is their unique morphology where a single process -the stem axon- bifurcates into a peripheral and a central axonal branch, with different functions and cellular properties. Distinctive structural aspects of the two DRG neuron branches may have important implications for their function in health and disease. However, the link between DRG axonal branch structure, polarity and function has been largely neglected in the field, and relevant information is rather scattered across the literature. In particular, ultrastructural differences between the two axonal branches are likely to account for the higher transport and regenerative ability of the peripheral DRG neuron axon when compared to the central one. Nevertheless, the cell intrinsic factors contributing to this central-peripheral asymmetry are still unknown. Here we critically review the factors that may underlie the functional asymmetry between the peripheral and central DRG axonal branches. Also, we discuss the hypothesis that DRG neurons may assemble a structure resembling the axon initial segment that may be responsible, at least in part, for their polarity and electrophysiological features. Ultimately, we suggest that the clarification of the axonal ultrastructure of DRG neurons using state-of-the-art techniques will be crucial to understand the physiology of this peculiar cell type.

The convergent roles of CD271/p75 in neural crest-derived melanoma plasticity

The embryonic microenvironment is an important source of signals that promote multipotent cells to adopt a specific fate and direct cells along distinct migratory pathways. Yet, the ability of the embryonic microenvironment to retain multipotent progenitors or reprogram de-differentiated cells is less clear. Mistakes in cell differentiation or migration often result in developmental defects and tumorigenesis, including aggressive cancers that share many characteristics with embryonic progenitor cells. This is a striking feature of the vertebrate neural crest, a multipotent and highly migratory cell population first identified by His (1868) with the potential to metamorphose into aggressive melanoma cancer. In this perspective, we address the roles of CD271/p75 in tumor initiation, phenotype switching and reprogramming of metastatic melanoma and discuss the convergence of these roles in melanoma plasticity.

Neuregulin-1 is a chemoattractant and chemokinetic molecule for trunk neural crest cells

BACKGROUND

Trunk neural crest cells migrate rapidly along characteristic pathways within the developing vertebrate embryo. Proper trunk neural crest cell migration is necessary for the morphogenesis of much of the peripheral nervous system, melanocytes, and the adrenal medulla. Numerous molecules help guide trunk neural crest cell migration throughout the early embryo.

RESULTS

The trophic factor NRG1 is a chemoattractant through in vitro chemotaxis assays and in vivo silencing via a DN-erbB receptor. Interestingly, we also observed changes in migratory responses consistent with a chemokinetic effect of NRG1 in trunk neural crest velocity.

CONCLUSIONS

NRG1 is a trunk neural crest cell chemoattractant and chemokinetic molecule. Developmental Dynamics 247:888-902, 2018.. © 2018 Wiley Periodicals, Inc.

NGF reprograms metastatic melanoma to a bipotent glial-melanocyte neural crest-like precursor

Melanoma pathogenesis from normal neural crest-derived melanocytes is often fatal due to aggressive cell invasion throughout the body. The identification of signals that reprogram de-differentiated, metastatic melanoma cells to a less aggressive and stable phenotype would provide a novel strategy to limit disease progression. In this study, we identify and test the function of developmental signals within the chick embryonic neural crest microenvironment to reprogram and sustain the transition of human metastatic melanoma to a neural crest cell-like phenotype. Results reveal that co-culture of the highly aggressive and metastatic human melanoma cell line C8161 upregulate a marker of melanosome formation (Mart-1) in the presence of embryonic day 3.5 chick trunk dorsal root ganglia. We identify nerve growth factor (NGF) as the signal within this tissue driving Mart-1 re-expression and show that NGF receptors trkA and p75 cooperate to induce Mart-1 re-expression. Furthermore, Mart-1 expressing C8161 cells acquire a gene signature of poorly aggressive C81-61 cells. These data suggest that targeting NGF signaling may yield a novel strategy to reprogram metastatic melanoma toward a benign cell type.

Summary: We identify and test the function of nerve growth factor to reprogram human metastatic melanoma cells to a less aggressive phenotype. This article has an associated First Person interview with the first author of the paper as part of the supplementary information.

Asymmetric localization of DLC1 defines avian trunk neural crest polarity for directional delamination and migration

Following epithelial-mesenchymal transition, acquisition of avian trunk neural crest cell (NCC) polarity is prerequisite for directional delamination and migration, which in turn is essential for peripheral nervous system development. However, how this cell polarization is established and regulated remains unknown. Here we demonstrate that, using the RHOA biosensor in vivo and in vitro, the initiation of NCC polarization is accompanied by highly activated RHOA in the cytoplasm at the cell rear and its fluctuating activity at the front edge. This differential RHOA activity determines polarized NC morphology and motility, and is regulated by the asymmetrically localized RhoGAP Deleted in liver cancer (DLC1) in the cytoplasm at the cell front. Importantly, the association of DLC1 with NEDD9 is crucial for its asymmetric localization and differential RHOA activity. Moreover, NC specifiers, SOX9 and SOX10, regulate NEDD9 and DLC1 expression, respectively. These results present a SOX9/SOX10-NEDD9/DLC1-RHOA regulatory axis to govern NCC migratory polarization.

Extrinsic mechanical forces mediate retrograde axon extension in a developing neuronal circuit

To form functional neural circuits, neurons migrate to their final destination and extend axons towards their targets. Whether and how these two processes are coordinated in vivo remains elusive. We use the zebrafish olfactory placode as a system to address the underlying mechanisms. Quantitative live imaging uncovers a choreography of directed cell movements that shapes the placode neuronal cluster: convergence of cells towards the centre of the placodal domain and lateral cell movements away from the brain. Axon formation is concomitant with lateral movements and occurs through an unexpected, retrograde mode of extension, where cell bodies move away from axon tips attached to the brain surface. Convergence movements are active, whereas cell body lateral displacements are of mainly passive nature, likely triggered by compression forces from converging neighbouring cells. These findings unravel a previously unknown mechanism of neuronal circuit formation, whereby extrinsic mechanical forces drive the retrograde extension of axons.How neuronal migration and axon growth coordinate during development is only partially understood. Here the authors use quantitative imaging to characterise the morphogenesis of the zebrafish olfactory placode and report an unexpected phenomenon, whereby axons extend through the passive movement of neuron cell bodies away from tethered axon tips.

DAN (NBL1) promotes collective neural crest migration by restraining uncontrolled invasion

Neural crest cells are both highly migratory and significant to vertebrate organogenesis. However, the signals that regulate neural crest cell migration remain unclear. In this study, we identify DAN as a novel factor that inhibits uncontrolled neural crest and metastatic melanoma invasion in a manner consistent with the inhibition of BMP signaling.

Neural crest cells are both highly migratory and significant to vertebrate organogenesis. However, the signals that regulate neural crest cell migration remain unclear. In this study, we test the function of differential screening-selected gene aberrant in neuroblastoma (DAN), a bone morphogenetic protein (BMP) antagonist we detected by analysis of the chick cranial mesoderm. Our analysis shows that, before neural crest cell exit from the hindbrain, DAN is expressed in the mesoderm, and then it becomes absent along cell migratory pathways. Cranial neural crest and metastatic melanoma cells avoid DAN protein stripes in vitro. Addition of DAN reduces the speed of migrating cells in vivo and in vitro, respectively. In vivo loss of function of DAN results in enhanced neural crest cell migration by increasing speed and directionality. Computer model simulations support the hypothesis that DAN restrains cell migration by regulating cell speed. Collectively, our results identify DAN as a novel factor that inhibits uncontrolled neural crest and metastatic melanoma invasion and promotes collective migration in a manner consistent with the inhibition of BMP signaling.

The zebrafish as a model for studying neuroblastoma

Neuroblastoma is a tumor arising in the peripheral sympathetic nervous system and is the most common cancer in childhood. Since most of the cellular and molecular mechanisms underlying neuroblastoma onset and progression remain unknown, the generation of new in vivo models might be appropriate to better dissect the peripheral sympathetic nervous system development in both physiological and disease states. This review is focused on the use of zebrafish as a suitable and innovative model to study neuroblastoma development. Here, we briefly summarize the current knowledge about zebrafish peripheral sympathetic nervous system formation, focusing on key genes and cellular pathways that play a crucial role in the differentiation of sympathetic neurons during embryonic development. In addition, we include examples of how genetic changes known to be associated with aggressive neuroblastoma can mimic this malignancy in zebrafish. Thus, we note the value of the zebrafish model in the field of neuroblastoma research, showing how it can improve our current knowledge about genes and biological pathways that contribute to malignant transformation and progression during embryonic life.

Leader Cells Define Directionality of Trunk, but Not Cranial, Neural Crest Cell Migration

Collective cell migration is fundamental for life and a hallmark of cancer. Neural crest (NC) cells migrate collectively, but the mechanisms governing this process remain controversial. Previous analyses in Xenopus indicate that cranial NC (CNC) cells are a homogeneous population relying on cell-cell interactions for directional migration, while chick embryo analyses suggest a heterogeneous population with leader cells instructing directionality. Our data in chick and zebrafish embryos show that CNC cells do not require leader cells for migration and all cells present similar migratory capacities. In contrast, laser ablation of trunk NC (TNC) cells shows that leader cells direct movement and cell-cell contacts are required for migration. Moreover, leader and follower identities are acquired before the initiation of migration and remain fixed thereafter. Thus, two distinct mechanisms establish the directionality of CNC cells and TNC cells. This implies the existence of multiple molecular mechanisms for collective cell migration.

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CNC rely on cell-cell interactions to migrate directionally

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Leader cells dictate directionality to followers in the trunk NC population

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Leader and follower identities are acquired before the initiation of migration

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Leader and follower identities are non-interchangeable during migration

In vivo time-lapse imaging reveals extensive neural crest and endothelial cell interactions during neural crest migration and formation of the dorsal root and sympathetic ganglia

During amniote embryogenesis the nervous and vascular systems interact in a process that significantly affects the respective morphogenesis of each network by forming a "neurovascular" link. The importance of neurovascular cross-talk in the central nervous system has recently come into focus with the growing awareness that these two systems interact extensively both during development, in the stem-cell niche, and in neurodegenerative conditions such as Alzheimer's Disease and Amyotrophic Lateral Sclerosis. With respect to the peripheral nervous system, however, there have been no live, real-time investigations of the potential relationship between these two developing systems. To address this deficit, we used multispectral 4D time-lapse imaging in a transgenic quail model in which endothelial cells (ECs) express a yellow fluorescent marker, while neural crest cells (NCCs) express an electroporated red fluorescent marker. We monitored EC and NCC migration in real-time during formation of the peripheral nervous system. Our time-lapse recordings indicate that NCCs and ECs are physically juxtaposed and dynamically interact at multiple locations along their trajectories. These interactions are stereotypical and occur at precise anatomical locations along the NCC migratory pathway. NCCs migrate alongside the posterior surface of developing intersomitic vessels, but fail to cross these continuous streams of motile ECs. NCCs change their morphology and migration trajectory when they encounter gaps in the developing vasculature. Within the nascent dorsal root ganglion, proximity to ECs causes filopodial retraction which curtails forward persistence of NCC motility. Overall, our time-lapse recordings support the conclusion that primary vascular networks substantially influence the distribution and migratory behavior of NCCs and the patterned formation of dorsal root and sympathetic ganglia.

Studying the peripheral sympathetic nervous system and neuroblastoma in zebrafish

The zebrafish serves as an excellent model to study vertebrate development and disease. Optically clear embryos, combined with tissue-specific fluorescent reporters, permit direct visualization and measurement of peripheral nervous system formation in real time. Additionally, the model is amenable to rapid cellular, molecular, and genetic approaches to determine how developmental mechanisms contribute to disease states, such as cancer. In this chapter, we describe the development of the peripheral sympathetic nervous system (PSNS) in general, and our current understanding of genetic pathways important in zebrafish PSNS development specifically. We also illustrate how zebrafish genetics is used to identify new mechanisms controlling PSNS development and methods for interrogating the potential role of PSNS developmental pathways in neuroblastoma pathogenesis in vivo using the zebrafish MYCN-driven neuroblastoma model.

Physiological electrical signals promote chain migration of neuroblasts by up-regulating P2Y1 purinergic receptors and enhancing cell adhesion

Neuroblasts migrate as directed chains of cells during development and following brain damage. A fuller understanding of the mechanisms driving this will help define its developmental significance and in the refinement of strategies for brain repair using transplanted stem cells. Recently, we reported that in adult mouse there are ionic gradients within the extracellular spaces that create an electrical field (EF) within the rostral migratory stream (RMS), and that this acts as a guidance cue for neuroblast migration. Here, we demonstrate an endogenous EF in brain slices and show that mimicking this by applying an EF of physiological strength, switches on chain migration in mouse neurospheres and in the SH-SY5Y neuroblastoma cell line. Firstly, we detected a substantial endogenous EF of 31.8 ± 4.5 mV/mm using microelectrode recordings from explants of the subventricular zone (SVZ). Pharmacological inhibition of this EF, effectively blocked chain migration in 3D cultures of SVZ explants. To mimic this EF, we applied a physiological EF and found that this increased the expression of N-cadherin and β-catenin, both of which promote cell-cell adhesion. Intriguingly, we found that the EF up-regulated P2Y purinoceptor 1 (P2Y1) to contribute to chain migration of neuroblasts through regulating the expression of N-cadherin, β-catenin and the activation of PKC. Our results indicate that the naturally occurring EF in brain serves as a novel stimulant and directional guidance cue for neuronal chain migration, via up-regulation of P2Y1.

Imaging the Cell and Molecular Dynamics of Craniofacial Development: Challenges and New Opportunities in Imaging Developmental Tissue Patterning

The development of the vertebrate head requires cell-cell and tissue-tissue interactions between derivatives of the three germ layers to coordinate morphogenetic movements in four dimensions (4D: x, y, z, t). The high spatial and temporal resolution offered by optical microscopy has made it the main imaging modularity for capturing the molecular and cellular dynamics of developmental processes. In this chapter, we highlight the challenges and new opportunities provided by emerging technologies that enable dynamic, high-information-content imaging of craniofacial development. We discuss the challenges of varying spatial and temporal scales encountered from the biological and technological perspectives. We identify molecular and fluorescence imaging technology that can provide solutions to some of the challenges. Application of the techniques described within this chapter combined with considerations of the biological and technical challenges will aid in formulating the best image-based studies to extend our understanding of the genetic and environmental influences underlying craniofacial anomalies.

TrkB/BDNF signalling patterns the sympathetic nervous system

The sympathetic nervous system is essential for maintaining mammalian homeostasis. How this intricately connected network, composed of preganglionic neurons that reside in the spinal cord and post-ganglionic neurons that comprise a chain of vertebral sympathetic ganglia, arises developmentally is incompletely understood. This problem is especially complex given the vertebral chain of sympathetic ganglia derive secondarily from the dorsal migration of ‘primary' sympathetic ganglia that are initially located several hundred microns ventrally from their future pre-synaptic partners. Here we report that the dorsal migration of discrete ganglia is not a simple migration of individual cells but a much more carefully choreographed process that is mediated by extensive interactions of pre-and post-ganglionic neurons. Dorsal migration does not occur in the absence of contact with preganglionic axons, and this is mediated by BDNF/TrkB signalling. Thus BDNF released by preganglionic axons acts chemotactically on TrkB-positive sympathetic neurons, to pattern the developing peripheral nervous system.

The signals that pattern the sympathetic nervous system are not fully understood. Here the authors show that the dorsal migration of the primary sympathetic ganglia in chick embryos is orchestrated by BDNF/TrkB signalling and requires contact with preganglionic axons.

The Role of Thrombin and Cell Contractility in Regulating Clustering and Collective Migration of Corneal Fibroblasts in Different ECM Environments

PURPOSE

We previously reported that extracellular matrix composition (fibrin versus collagen) modulates the pattern of corneal fibroblast spreading and migration in 3-D culture. In this study, we investigate the role of thrombin and cell contractility in mediating these differences in cell behavior.

METHODS

To assess cell spreading, corneal fibroblasts were plated on top of fibrillar collagen and fibrin matrices. To assess 3-dimensional cell migration, compacted collagen matrices seeded with corneal fibroblasts were embedded inside acellular collagen or fibrin matrices. Constructs were cultured in serum-free media containing platelet-derived growth factor (PDGF), with or without thrombin, the Rho kinase inhibitor Y-27632, and/or the myosin II inhibitor blebbistatin. We used 3-dimensional and 4-dimensional imaging to assess cell mechanical behavior, connectivity and cytoskeletal organization.

RESULTS

Thrombin stimulated increased contractility of corneal fibroblasts. Thrombin also induced Rho kinase-dependent clustering of cells plated on top of compliant collagen matrices, but not on rigid substrates. In contrast, cells on fibrin matrices coalesced into clusters even when Rho kinase was inhibited. In nested matrices, cells always migrated independently through collagen, even in the presence of thrombin. In contrast, cells migrating into fibrin formed an interconnected network. Both Y-27632 and blebbistatin reduced the migration rate in fibrin, but cells continued to migrate collectively.

CONCLUSIONS

The results suggest that while thrombin-induced actomyosin contraction can induce clustering of fibroblasts plated on top of compliant collagen matrices, it does not induce collective cell migration inside 3-D collagen constructs. Furthermore, increased contractility is not required for clustering or collective migration of corneal fibroblasts interacting with fibin.

Neural crest migration: trailblazing ahead

Embryonic cell migration patterns are amazingly complex in the timing and spatial distribution of cells throughout the vertebrate landscape. However, advances in in vivo visualization, cell interrogation, and computational modeling are extracting critical features that underlie the mechanistic nature of these patterns. The focus of this review highlights recent advances in the study of the highly invasive neural crest cells and their migratory patterns during embryonic development. We discuss these advances within three major themes and include a description of computational models that have emerged to more rapidly integrate and test hypothetical mechanisms of neural crest migration. We conclude with technological advances that promise to reveal new insights and help translate results to human neural crest-related birth defects and metastatic cancer.

Restricted expression of classic cadherins in the spinal cord of the chicken embryo

Classic cadherins belong to the family of cadherin genes and play important roles in neurogenesis, neuron migration, and axon growth. In the present study, we compared the expression patterns of 10 classic cadherins (Cdh2, Cdh4, Cdh6, Cdh7, Cdh8, Cdh9, Cdh11, Cdh12, Cdh18, and Cdh20) in the developing chicken spinal cord (SP) by in situ hybridization. Our results indicate that each of the investigated cadherins exhibits a spatially restricted and temporally regulated pattern of expression. At early developmental stages (E2.5–E3), Cdh2 is expressed throughout the neuroepithelial layer. Cdh6 is strongly positive in the roof plate and later also in the floor plate. Cdh7, Cdh11, Cdh12, and Cdh20 are expressed in restricted regions of the basal plate of the SP. At intermediate stages of development (E4–E10), specific expression profiles are observed for all investigated cadherins in the differentiating mantle layer along the dorsoventral, mediolateral, and rostrocaudal dimensions. Expression profiles are especially diverse for Cdh2, Cdh4, Cdh8, Cdh11, and Cdh20 in the dorsal horn, while different pools of motor neurons exhibit signal for Cdh6, Cdh7, Cdh8, Cdh9, Cdh12, and Cdh20 in the ventral horn. Interestingly, subpopulations of cells in the dorsal root ganglion express combinations of different cadherins. In the surrounding tissues, such as the boundary cap cells and the notochord, the cadherins are also expressed differentially. The highly regulated spatiotemporal expression patterns of the classic cadherins indicate that these genes potentially play multiple and diverse roles during the development of the SP and its surrounding tissues.

Developmental imaging: the avian embryo hatches to the challenge

The avian embryo provides a multifaceted model to study developmental mechanisms because of its accessibility to microsurgery, fluorescence cell labeling, in vivo imaging, and molecular manipulation. Early two-dimensional planar growth of the avian embryo mimics human development and provides unique access to complex cell migration patterns using light microscopy. Later developmental events continue to permit access to both light and other imaging modalities, making the avian embryo an excellent model for developmental imaging. For example, significant insights into cell and tissue behaviors within the primitive streak, craniofacial region, and cardiovascular and peripheral nervous systems have come from avian embryo studies. In this review, we provide an update to recent advances in embryo and tissue slice culture and imaging, fluorescence cell labeling, and gene profiling. We focus on how technical advances in the chick and quail provide a clearer understanding of how embryonic cell dynamics are beautifully choreographed in space and time to sculpt cells into functioning structures. We summarize how these technical advances help us to better understand basic developmental mechanisms that may lead to clinical research into human birth defects and tissue repair.

Cadherin dynamics during neural crest cell ontogeny

Cell membrane-associated junctional complexes mediate cell-cell adhesion, intercellular interactions, and other fundamental processes required for proper embryo morphogenesis. Cadherins are calcium-dependent transmembrane proteins at the core of adherens junctions and are expressed in distinct spatiotemporal patterns throughout the development of an important vertebrate cell type, the neural crest. Multipotent neural crest cells arise from the ectoderm as epithelial cells under the influence of inductive cues, undergo an epithelial-to-mesenchymal transition, migrate throughout the embryonic body, and then differentiate into multiple derivatives at predetermined destinations. Neural crest cells change their expressed cadherin repertoires as they undergo each new morphogenetic transition, providing insight into distinct functions of expressed cadherins that are essential for proper completion of each specific stage. Cadherins modulate neural crest cell morphology, segregation, migration, and tissue formation. This chapter reviews the knowledge base of cadherin regulation, expression, and function during the ontogeny of the neural crest.