Neural crest cell migration in relation to extracellular matrix organization in the embryonic axolotl trunk

Study on the biological mechanism of urolithin a on nasopharyngeal carcinoma in vitro

CONTEXT

Urolithin A (UroA) can inhibit the growth of many human cancer cells, but it has not be reported if UroA inhibits nasopharyngeal carcinoma (NPC) cells.

OBJECTIVE

To explore the inhibitory effect of UroA on NPC and potential mechanism in vitro.

MATERIALS AND METHODS

RNA-sequencing-based mechanistic prediction was conducted by comparing KEGG enrichment of 40 μM UroA-treated for 24 h with untreated CNE2 cells. The untreated cells were selected as control. After NPC cells were treated with 20-60 μM UroA, proliferation, migration and invasion of were measured by colony formation, wound healing and transwell experiments. Apoptosis, mitochondrial membrane potential (MMP), reactive oxygen species (ROS) were measured by flow cytometry, Hoechst 33342, Rhodamine 123, JC-1 staining and ROS assay methods, respectively. Gene and protein expression were measured by RT-qPCR and Western blotting assay.

RESULTS

RNA-sequencing and KEGG enrichment revealed UroA mainly altered the ECM receptor interaction pathway. UroA inhibited cells proliferation, epithelial-mesenchymal-transition pathway, migration and invasion with IC₅₀ values of 34.72 μM and 44.91 μM, induced apoptosis, MMP depolarization and increase ROS content at a concentration of 40 μM. UroA up-regulated E-cadherin, Bax/Bcl-2, c-caspase-3 and PARP proteins, while inhibiting COL4A1, MMP2, MMP9, N-cadherin, Vimentin and Snail proteins at 20-60 μM. Moreover, co-treatment of UroA (40 μM) and NAC (5 mM) could reverse the effect of UroA on apoptosis-related proteins.

DISCUSSION AND CONCLUSIONS

RNA-sequencing technology based on bioinformatic analyses may be applicable for studiying the mechanism of drugs for tumour treatment.

Switch-like enhancement of epithelial-mesenchymal transition by YAP through feedback regulation of WT1 and Rho-family GTPases

Collective cell migration occurs in many patho-physiological states, including wound healing and invasive cancer growth. The integrity of the expanding epithelial sheets depends on extracellular cues, including cell-cell and cell-matrix interactions. We show that the nano-scale topography of the extracellular matrix underlying epithelial cell layers can strongly affect the speed and morphology of the fronts of the expanding sheet, triggering partial and complete epithelial-mesenchymal transitions (EMTs). We further demonstrate that this behavior depends on the mechano-sensitivity of the transcription regulator YAP and two new YAP-mediated cross-regulating feedback mechanisms: Wilms Tumor-1-YAP-mediated downregulation of E-cadherin, loosening cell-cell contacts, and YAP-TRIO-Merlin mediated regulation of Rho GTPase family proteins, enhancing cell migration. These YAP-dependent feedback loops result in a switch-like change in the signaling and the expression of EMT-related markers, leading to a robust enhancement in invasive cell spread, which may lead to a worsened clinical outcome in renal and other cancers.

Reorganisation of the extracellular matrix (ECM) controls processes involving epithelial-mesenchymal transition (EMT). Here, the authors show that EMT occurring in epithelial cells on a fabricated nano-engineered cell adhesion surface is triggered by mechanical cues from the ECM.

Collective Cell Migration in Development

Collective cell migration is a key process in developmental biology, facilitating the bulk movement of cells in the morphogenesis of animal tissues. Predictive understanding in this field remains challenging due to the complexity of many interacting cells, their signalling, and microenvironmental factors - all of which can give rise to non-intuitive emergent behaviours. In this chapter we discuss biological examples of collective cell migration from a range of model systems, developmental stages, and spatial scales: border cell migration and haemocyte dispersal in Drosophila, gastrulation, neural crest migration, lateral line formation in zebrafish, and branching morphogenesis; as well as examples of developmental defects and similarities to metastatic invasion in cancer. These examples will be used to illustrate principles that we propose to be important: heterogeneity of cell states, substrate-free migration, contact-inhibition of locomotion, confinement and repulsive cues, cell-induced (or self-generated) gradients, stochastic group decisions, tissue mechanics, and reprogramming of cell behaviours. Understanding how such principles play a common, overarching role across multiple biological systems may lead towards a more integrative understanding of the causes and function of collective cell migration in developmental biology, and to potential strategies for the repair of developmental defects, the prevention and control of cancer, and advances in tissue engineering.

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.

Multidisciplinary approaches to understanding collective cell migration in developmental biology

Mathematical models are becoming increasingly integrated with experimental efforts in the study of biological systems. Collective cell migration in developmental biology is a particularly fruitful application area for the development of theoretical models to predict the behaviour of complex multicellular systems with many interacting parts. In this context, mathematical models provide a tool to assess the consistency of experimental observations with testable mechanistic hypotheses. In this review, we showcase examples from recent years of multidisciplinary investigations of neural crest cell migration. The neural crest model system has been used to study how collective migration of cell populations is shaped by cell–cell interactions, cell–environmental interactions and heterogeneity between cells. The wide range of emergent behaviours exhibited by neural crest cells in different embryonal locations and in different organisms helps us chart out the spectrum of collective cell migration. At the same time, this diversity in migratory characteristics highlights the need to reconcile or unify the array of currently hypothesized mechanisms through the next generation of experimental data and generalized theoretical descriptions.

Controlling the morphology and outgrowth of nerve and neuroglial cells: The effect of surface topography

Unlike other tissue types, like epithelial tissue, which consist of cells with a much more homogeneous structure and function, the nervous tissue spans in a complex multilayer environment whose topographical features display a large spectrum of morphologies and size scales. Traditional cell cultures, which are based on two-dimensional cell-adhesive culture dishes or coverslips, are lacking topographical cues and mainly simulate the biochemical microenvironment of the cells. With the emergence of micro- and nano-fabrication techniques new types of cell culture platforms are developed, where the effect of various topographical cues on cellular morphology, proliferation and differentiation can be studied. Different approaches (regarding the material, fabrication technique, topographical characteristics, etc.) have been implemented. The present review paper aims at reviewing the existing body of literature on the use of artificial micro- and nano-topographical features to control neuronal and neuroglial cells' morphology, outgrowth and neural network topology. The cell responses-from phenomenology to investigation of the underlying mechanisms- on the different topographies, including both deterministic and random ones, are summarized.

STATEMENT OF SIGNIFICANCE

There is increasing evidence that physical cues, such as topography, can have a significant impact on the neural cell functions. With the aid of micro-and nanofabrication techniques, new types of cell culture platforms are developed and the effect of surface topography on the cells has been studied. The present review article aims at reviewing the existing body of literature reporting on the use of various topographies to study and control the morphology and functions of cells from nervous tissue, i.e. the neuronal and the neuroglial cells. The cell responses-from phenomenology to investigation of the underlying mechanisms- on the different topographies, including both deterministic and random ones, are summarized.

Cell migration: from tissue culture to embryos

Cell migration is a fundamental process that occurs during embryo development. Classic studies using in vitro culture systems have been instrumental in dissecting the principles of cell motility and highlighting how cells make use of topographical features of the substrate, cell-cell contacts, and chemical and physical environmental signals to direct their locomotion. Here, we review the guidance principles of in vitro cell locomotion and examine how they control directed cell migration in vivo during development. We focus on developmental examples in which individual guidance mechanisms have been clearly dissected, and for which the interactions among guidance cues have been explored. We also discuss how the migratory behaviours elicited by guidance mechanisms generate the stereotypical patterns of migration that shape tissues in the developing embryo.

Computational modelling of cell chain migration reveals mechanisms that sustain follow-the-leader behaviour

Follow-the-leader chain migration is a striking cell migratory behaviour observed during vertebrate development, adult neurogenesis and cancer metastasis. Although cell–cell contact and extracellular matrix (ECM) cues have been proposed to promote this phenomenon, mechanisms that underlie chain migration persistence remain unclear. Here, we developed a quantitative agent-based modelling framework to test mechanistic hypotheses of chain migration persistence. We defined chain migration and its persistence based on evidence from the highly migratory neural crest model system, where cells within a chain extend and retract filopodia in short-lived cell contacts and move together as a collective. In our agent-based simulations, we began with a set of agents arranged as a chain and systematically probed the influence of model parameters to identify factors critical to the maintenance of the chain migration pattern. We discovered that chain migration persistence requires a high degree of directional bias in both lead and follower cells towards the target. Chain migration persistence was also promoted when lead cells maintained cell contact with followers, but not vice-versa. Finally, providing a path of least resistance in the ECM was not sufficient alone to drive chain persistence. Our results indicate that chain migration persistence depends on the interplay of directional cell movement and biased cell–cell contact.

A drug delivery system for the treatment of peripheral nervous system injuries

Recent results in biomedical engineering and materials science and technology have brought about the development of novel bioactive materials by which the repair of peripheral nervous system injuries can be improved. The formation of scarring tissue, which represents a physical barrier to axon elongation, and the not oriented outgrowth of neurites are the two major obstacles for a complete recovery of physiological nerve function. This study mainly focuses on the analysis of biocompatible constructs for the controlled release of anti-scarring antibodies by means of fluorescence spectroscopy techniques.

Migratory patterns and developmental potential of trunk neural crest cells in the axolotl embryo

Using cell markers and grafting, we examined the timing of migration and developmental potential of trunk neural crest cells in axolotl. No obvious differences in pathway choice were noted for DiI-labeling at different lateral or medial positions of the trunk neural folds in neurulae, which contributed not only to neural crest but also to Rohon-Beard neurons. Labeling wild-type dorsal trunks at pre- and early-migratory stages revealed that individual neural crest cells migrate away from the neural tube along two main routes: first, dorsolaterally between the epidermis and somites and, later, ventromedially between the somites and neural tube/notochord. Dorsolaterally migrating crest primarily forms pigment cells, with those from anterior (but not mid or posterior) trunk neural folds also contributing glia and neurons to the lateral line. White mutants have impaired dorsolateral but normal ventromedial migration. At late migratory stages, most labeled cells move along the ventromedial pathway or into the dorsal fin. Contrasting with other anamniotes, axolotl has a minor neural crest contribution to the dorsal fin, most of which arises from the dermomyotome. Taken together, the results reveal stereotypic migration and differentiation of neural crest cells in axolotl that differ from other vertebrates in timing of entry onto the dorsolateral pathway and extent of contribution to some derivatives.

Evidence that some events of mammalian embryogenesis can result from differential growth, making migration unnecessary

Three events during mammalian embryogenesis were reexamined that traditionally have been considered to be migratory. Using reconstructions of serially sectioned rat and human embryos and computer imaging, this descriptive study reexamined the following: sclerotome formation from the somite, spinal ganglion formation from the neural crest, and thyroid, parathyroid, and thymus gland formations from pharyngeal endoderm. The aim was to determine if the positional changes of the developing structures could be explained by differential growth (i.e., changes in the size and shape of the embryo and its parts) rather than migration (i.e., structures moving from one region of the embryo to another). Embryos and many of their internal structures, especially the neural tube, rapidly change in size and shape during the period when migration is described, but these phenomena were not considered in past studies. Surface reference points were used in past investigations that also move as the embryo and its internal structures enlarge. Computer imaging makes it feasible for the first time to keep magnifications identical for each series of reconstructions, rendering each one equivalent to one frame of a motion picture film. Using this technique together with more centralized, less mobile reference points, the study concludes that the positional changes that occur during the three events can be explained by differential growth. Anat Rec (Part B: New Anat) 289B:53-63, 2006. (c) 2006 Wiley-Liss, Inc.

Cephalic neural crest cells and the evolution of craniofacial structures in vertebrates: morphological and embryological significance of the premandibular-mandibular boundary

The vertebrate head characteristically has two types of mesenchyme: the neural crest-derived ectomesenchyme and the mesoderm derived mesenchyme. Conserved patterns of development in various animal taxa imply the presence of shared inductive events for cephalic mesenchyme. These developmental programs can serve as developmental constraints that emerge as morphological homology of embryonic patterns. To understand the evolutionary changes in the developmental programs that shape the skull, we need to separate ancestral and derived patterns of vertebrate craniogenesis. This review deals with the terminology for neural crest cell subpopulations at each developmental stage, based on the topographical relationships and possible mechanisms for specification. The aim is to identify the changes that could have occurred in the evolutionary history of vertebrates. From comparisons of a lamprey species, Lethenteron japonicum, with gnathostomes it is clear that the initial distribution of cephalic crest cells is identical in the two animal lineages. In all vertebrate embryos, the trigeminal crest (TC) cells of an early pharyngula are subdivided into three subpopulations. At this stage, only the posterior subpopulation of the TC cells is specified as the mandibular arch, as compared to the more rostral components, the 'premandibular crest cells'. Later in development, the local specification patterns of the lamprey and the gnathostomes differ, so that homology cannot be established in the craniofacial primordia, including the oral apparatus. Therefore, embryological terminology should reflect these hierarchical patterns in developmental stages and phylogeny.

Nonadhesive nanotopography: Fibroblast response to poly(n-butyl methacrylate)-poly(styrene) demixed surface features

It is becoming clear that cells do not only respond to micrometric scale topography, but may also respond to topography at the nanometric scale. Nano-fabrication methods such as electron beam lithography are, however, expensive and time consuming. Polymer demixing of poly(styrene) and poly(4-bromostyrene) has been found to produce nano-scale islands of reproducible height, and the islands have been previously shown to effect cell events such as adhesion, spreading, proliferation, and differentiation. This study uses demixed poly(styrene) and poly(n-butyl methacrylate) to produce nano-islands with closer packing and narrower widths compared with those previously studied. Observations have been made of morphological and cytoskeletal changes in human fibroblasts interacting with 10- and 50-nm-high islands. The methods used included scanning electron microscopy, fluorescent microscopy, and optical microscopy. The results indicated that the cells do not respond differently to the 10-nm islands compared with planar samples but, in contrast, the 50-nm islands are nonadhesive.

Polymer-demixed nanotopography: control of fibroblast spreading and proliferation

Cell response to nanometric scale topography is a growing field. Nanometric topography production has traditionally relied on expensive and time-consuming techniques such as electron beam lithography. This presents disadvantages to the cell biologist in regard to material availability. New research is focusing on less expensive methods of nanotopography production for in vitro cell engineering. One such method is the spontaneous demixing of polymers (in this case polystyrene and polybromostyrene) to produce nanometrically high islands. This article observes fibroblast response to nanometric islands (13, 35, and 95 nm in height) produced by polymer demixing. Changes in cell morphology, cytoskeleton, and proliferation are observed by light, fluorescence, and scanning electron microscopy. Morphological features produced by cells in response to the materials were selected, and cell shape parameters were measured with shape-recognition software. The results showed that island height could either increase or reduce cell spreading and proliferation in relation to control, with 13-nm islands producing cells with the greatest area and 95 nm islands producing cells with the lowest areas. Interaction of filopodia with the islands could been seen to increase as island size was increased.

In vitro reaction of endothelial cells to polymer demixed nanotopography

The introduction of topography to material surfaces has been shown to strongly affect cell behaviour, and the effects of micrometric surface morphologies have been extensively characterised. Research is now starting to investigate the reaction of cells to nanometric topography. This study used polymer demixing of polystyrene and poly(4-bromostyrene) producing nanometrically high islands, and observed endothelial cell response to the islands. Three island heights were investigated; these were 13, 35 and 95 nm. The cells were seen to be more spread on the manufactured topographies than that on flat surfaces of similar chemistry. Other morphological differences were also noted by histology, fluorescence and scanning electron microscopy, with many arcuate cells noted on the test surfaces, and cytoskeletal alignment along the arcuate features. Of the nanotopographies, the 13 nm islands were seen to give the largest response, with highly spread cell morphologies containing well-defined cytoskeleton.

Increasing fibroblast response to materials using nanotopography: morphological and genetic measurements of cell response to 13-nm-high polymer demixed islands

It is becoming clear that cells can respond not only to micometric scale topography, but may also to nanometric scale topography. The production of reproducibly sized nanometric features has relied heavily on expensive and time-consuming methods of manufacture, such as electron beam lithography. Polymer demixing of polystyrene and polybromostyrene has been found to produce nanoscale islands of reproducible height, and the islands have been previously shown to effect cell spreading compared to planar surfaces. This study observes morphological, cytoskeletal, and molecular changes in fibroblast reaction to 13-nm-high islands. The methods employed include scanning electron microscopy, fluorescent microscopy, and 1718 gene microarray. The results show that the cells respond to the islands by broad gene up-regulation, notably in the areas of cell signaling, proliferation, cytoskeleton, and production of extracellular matrix proteins. Microscopical results provide confirmation of the microarray findings.

Mechanisms of early neural crest development: from cell specification to migration

The neural crest is a group of embryonic progenitors that forms during the process of neurulation by interactions that take place between the prospective epidermis and the specified neuroectoderm. Although initially an integral part of the neuroepithelium, neural crest cells separate from the central nervous system primordium by a process of epitheliomesenchymal transition and become a motile cell population. These mesenchymal cells then migrate through stereotypic pathways, some of which are common and others unique to various vertebrate species. Furthermore, the availability of distinct migratory pathways also differs according to embryonic stage and axial level. Studies have begun to address the molecular basis of neural crest specification, delamination, and migration. The present review summarizes some major advances in our understanding of the nature of the intercellular interactions and the molecules that mediate them during early phases of neural crest ontogeny.

Role of the extracellular matrix during neural crest cell migration

Once specified to become neural crest (NC), cells occupying the dorsal portion of the neural tube disrupt their cadherin-mediated cell-cell contacts, acquire motile properties, and embark upon an extensive migration through the embryo to reach their ultimate phenotype-specific sites. The understanding of how this movement is regulated is still rather fragmentary due to the complexity of the cellular and molecular interactions involved. An additional intricate aspect of the regulation of NC cell movement is that the timings, modes and patterns of NC cell migration are intimately associated with the concomitant phenotypic diversification that cells undergo during their migratory phase and the fact that these changes modulate the way that moving cells interact with their microenvironment. To date, two interplaying mechanisms appear central for the guidance of the migrating NC cells through the embryo: one involves secreted signalling molecules acting through their cognate protein kinase/phosphatase-type receptors and the other is contributed by the multivalent interactions of the cells with their surrounding extracellular matrix (ECM). The latter ones seem fundamental in light of the central morphogenetic role played by the intracellular signals transduced through the cytoskeleton upon integrin ligation, and the convergence of these signalling cascades with those triggered by cadherins, survival/growth factor receptors, gap junctional communications, and stretch-activated calcium channels. The elucidation of the importance of the ECM during NC cell movement is presently favoured by the augmenting knowledge about the macromolecular structure of the specific ECM assembled during NC development and the functional assaying of its individual constituents via molecular and genetic manipulations. Collectively, these data propose that NC cell migration may be governed by time- and space-dependent alterations in the expression of inhibitory ECM components; the relative ratio of permissive versus non-permissive ECM components; and the supramolecular assembly of permissive ECM components. Six multidomain ECM constituents encoded by a corresponding number of genes appear to date the master ECM molecules in the control of NC cell movement. These are fibronectin, laminin isoforms 1 and 8, aggrecan, and PG-M/version isoforms V0 and V1. This review revisits a number of original observations in amphibian and avian embryos and discusses them in light of more recent experimental data to explain how the interaction of moving NC cells with these ECM components may be coordinated to guide cells toward their final sites during the process of organogenesis.

Development of neural crest in Xenopus

The neural crest is a unique cell population among embryonic cell types, displaying properties of both ectodermal and mesodermal lineages. Most of the recent studies examining the neural crest have been performed in avian embryos. Only in the first half of this century were amphibians extensively used. We first summarize this important older source of information, reviewing studies made since the turn of the century. Due to the increasingly detailed in cellular and molecular knowledge of the early development of Xenopus laevis, the remainder of the review focuses on this species. We describe the route of migration and fate of the neural crest and propose a new model of neural crest induction in which prospective cells are induced independently of the neural plate by a double gradient of a morphogen that patterns the entire ectoderm. This model is also discussed in a more general context in connection with the dorsoventral patterning of the neural tube. Finally, we discuss some ideas concerning neural crest evolution and propose a novel hypothesis about its phylogenetic origin.

Early- and late-migrating cranial neural crest cell populations have equivalent developmental potential in vivo

We present the first in vivo study of the long-term fate and potential of early-migrating and late-migrating mesencephalic neural crest cell populations, by performing isochronic and heterochronic quail-to-chick grafts. Both early- and late-migrating populations form melanocytes, neurons, glia, cartilage and bone in isochronic, isotopic chimeras, showing that neither population is lineage-restricted. The early-migrating population distributes both dorsally and ventrally during normal development, while the late-migrating population is confined dorsally and forms much less cartilage and bone. When the late-migrating population is substituted heterochronically for the early-migrating population, it contributes extensively to ventral derivatives such as jaw cartilage and bone. Conversely, when the early-migrating population is substituted heterochronically for the late-migrating population, it no longer contributes to the jaw skeleton and only forms dorsal derivatives. When the late-migrating population is grafted into a late-stage host whose neural crest had previously been ablated, it migrates ventrally into the jaws. Thus, the dorsal fate restriction of the late-migrating mesencephalic neural crest cell population in normal development is due to the presence of earlier-migrating neural crest cells, rather than to any change in the environment or to any intrinsic difference in migratory ability or potential between early- and late-migrating cell populations. These results highlight the plasticity of the neural crest and show that its fate is determined primarily by the environment.

Initial closure of the mesencephalic neural groove in the chick embryo involves a releasing zipping-up mechanism

According to a traditional viewpoint, initial closure of the anterior neural groove involves bilateral elevation of the edges of the neural plate, flattening of the midline area, subsequent convergence of the dorsal neural folds, and finally adhesion and fusion of the medial fold edges. In a transverse view, the shape of the neural groove thereby changes from V > U > toppled C > O. This sequence implicates that the neural groove is wide almost from its inception. In the present study, a new mechanism of initial closure is proposed, based on observations in living chick embryos and on light and scanning electron microscopic observations during neurulation in the presumptive mesencephalic region. The medial part of the neural plate invaginates in ventral direction. The walls of the arising neural groove appose, beginning in the depth, and make subsequent contact. During continued invagination the neural walls extend in ventral direction, the apposition/contact zone shifts in dorsal direction up to the neural folds and the neural walls separate ventrally, resulting in the incipient neural tube lumen. The mechanism is best compared with a zipping-up releasing model. In a transverse view, the shape of the neural groove changes from V > Y > I > O. While, according to the traditional view, the neural folds have to converge from a distance in order to contact each other, in the present mechanism the walls and folds are sequentially in contact by the ventro-dorsal zipping-up mechanism, thereby avoiding the possibility of mismatch of the neural folds. The above process is initiated over a considerable longitudinal distance along the neural plate, but only at the mesencephalic level does the dorsal shift of the contact zone become complete. At other levels of the neuraxis, the contact zone releases prematurely and the neural walls become widely separated well before their dorsal neural folds are in contact. These folds have to converge, therefore, in order to close, but their matching is facilitated by the alignment of the previously contacted neural folds at the mesencephalic level as well as by guidance underneath the vitelline membrane.

Detection and characterization of an activity which aligns mesodermal cells into parallel arrays

A cell line of mesodermal origin, FS9, was found to release a Cell Orienting Factor into its culture medium. In contrast with the random migration of controls, the orienting activity causes migrating mesenchymal cells to form an orderly "halo' surrounding tissue explants; individual cells and their cytoskeletons are elongated and parallel to each other but at right angle to the explant. No effect on the rate of cell movement was apparent. The orienting activity could be quantified by counting the number of cells found within strings radiating at right angles to a single tissue explant in the presence of FS9 conditioned medium or by using NIH image analysis. A dose dependent relationship with half maximal activity occurring at a 25% dilution of conditioned medium was observed. Cells that migrated randomly in the absence of conditioned medium became oriented within 4 h of exposure to 50% conditioned medium. Conversely, when the conditioned medium was removed, parallel alignment was rapidly lost. The orienting activity was found in conditioned media from a variety of mesodermal derivatives. Transformation of Balb/c 3T3 cells using EJ-ras oncogene led to augmented production of the activity. Furthermore, insulin was required in serum-free medium to support its production, Laminin, fibronectin and collagen and a range of pure cytokines, neither promoted nor inhibited orientation. Cell alignment was also unaffected by treatments which interfered with cell-substrate interactions and motility including the addition of the RGD peptide or anti-integrin beta 1 and beta 3 antibodies. A protein is likely to be involved since the activity was heat and trypsin sensitive and non-dialysable. The possibility is discussed that the orienting activity is a novel protein(s) which alters intercellular interactions to promote the formation of an aligned pattern by migrating mesenchymal cells.

Insights into pigmentary phenomena provided by grafting and chimera formation in the axolotl

The expression of pigmentation patterns in axolotl pigmentary mutants was observed following three types of experimental manipulations including chimera formation, reciprocal neural crest grafts, of gonadal primordia. Three pigmentary genes were utilized including the wild type (D), white (d), and albino (a). In chimeras between white and albino embryos, melanoblasts from the white half crossed the graft interface to differentiate in albino skin. Neural crest grafts from white embryos to albinos provided melanophores of white origin that were capable of differentiation in albino skin. Grafts of gonadal primordia from albino to white embryos provided albino germ cells that formed unpigmented ovocytes together with dark ovocytes: white ovocytes from the albino grafted ovary, and dark ovocytes from the host ovary. The donor albino white ectoderm included in the graft was able to support the differentiation of melanophores, iridophores, and xanthophores that invaded the graft ectoderm from the neural crest of the white host. It was concluded that manifestation of the white or wild phenotypes may be related to the possible presence or absence of inhibiting or stimulating pigmentary factors in the skin. This possibility was discussed in the light of recent discoveries of such factors as Agouti Signaling Protein (ASP) from mammalian skin.

Distribution of keratan sulphate and chondroitin sulphate in wild type and white mutant axolotl embryos during neural crest cell migration

In embryos of the white mutant axolotl, prospective pigment cells are unable to migrate from the neural crest (NC) due to a deficiency in the subepidermal extracellular matrix (ECM). This raises the question of the molecular nature of this functional defect. Some PGs can inhibit cell migration on ECM molecules in vitro, and an excess of this class of molecules in the migratory pathways of neural crest cells might cause the restricted migration of prospective pigment cells seen in the white mutant embryo. In the present study, we use several monoclonal antibodies against epitopes on keratan sulphate (KS) and chondroitin sulphate (CS) and LM immunofluorescence to examine the distribution of these glycosaminoglycans at initial (stage 30) and advanced (stage 35) stages of neural crest cell migration. Most KS epitopes are more widely distributed in the white mutant than in the wild type embryo, whereas CS epitopes show very similar distributions in mutant and wild type embryos. This is confirmed quantitatively by immunoblotting: certain KS epitopes are more abundant in the white mutant. TEM immunogold staining reveals that KS as well as CS are present both in the basal lamina and in the interstitial ECM in both types of embryos. It remains to be investigated whether the abundance of certain KS epitopes in the white mutant embryo might contribute to the deficiency in supporting pigment cell migration shown by its ECM.

Effects of extracellular matrix molecules on subepidermal neural crest cell migration in wild type and white mutant (dd) axolotl embryos

Migration of neural crest (NC) derived pigment cells is restricted in the white mutant (dd) axolotl embryo (Ambystoma mexicanum). Transplantations between mutant and wild type embryos show that the extracellular matrix (ECM) of the white mutant is unable to support the migration of prospective pigment cells in wild type embryos (Löfberg et al., 1989, Dev. Biol. 131:168-181). In the present study, we test the effects of various purified ECM molecules on NC cell migration in the subepidermal migratory pathway of wild type (D/-) and white mutant (dd) axolotl embryos. We adsorbed the ECM molecules onto membrane microcarriers, which were then implanted under the epidermis. Fibronectin (FN), tenascin (TN), collagens I and VI, and a chick aggrecan stimulated migration in both types of embryos. Laminin-nidogen, rat chondrosarcoma aggrecan, and shark aggrecan stimulated migration in dd embryos but did not affect migration in D/- embryos. Collagen III, fibromodulin and bovine aggrecan had no effect on migration in either type of embryo. NC cells did not migrate on control microcarriers, which lacked ECM molecules. Some cells observed contacting, and presumably migrating on, coated microcarriers could be identified as pigment cells by their ultrastructure. Enzymatic digestion in vivo with chondroitinase ABC had no effect on NC cell migration. The neutral or stimulatory effect of the aggrecans is surprising; when tested in vitro they inhibited NC cell migration. The effect of three-dimensionality and other molecules present either in the embryonic ECM or in solution may overcome the inhibitory effect of aggrecans.

Guidance of oligodendrocytes and their progenitors by substratum topography

Oligodendrocyte progenitors arise in subventricular zones and migrate extensively during development before differentiating into mature oligodendrocytes, which myelinate nerve tracts in the central nervous system. We have used microfabricated substrata, containing periodic patterns of contours similar to those of central nervous system axons to assess the influence in vitro of substratum topography on oligodendrocytes isolated from 7 day rat optic nerve. Antiganglioside antibody A2B5 positive oligodendrocyte-type 2 astrocyte progenitors, and galactocerebroside positive and myelin basic protein positive oligodendrocytes, were highly aligned by surface contours as small as 100 nm depth and 260 nm repeat spacing. Rat optic nerve astrocytes also aligned on surface contours, but rat hippocampal and cerebellar neurons were unresponsive. Oligodendrocytes demonstrated enhanced parallel extension of their processes on narrow repeating topography in an arrangement similar to that found in the intact optic nerve. This is in marked contrast to the phenotype displayed by this cell type on planar substrata. Neither oligodendrocytes nor oligodendrocyte-type 2 astrocyte progenitors showed high-order F-actin cytoskeletal networks; thus their alignment on gratings is unlikely to result from deformation of actin cables and focal contacts. In contrast, aligned astrocytes showed striking arrangements of actin stress fibres. These results establish glial cells as potentially the most topographically sensitive cell types within the central nervous system. Furthermore, the topographical pattern inducing maximal alignment of oligodendrocyte lineage cells corresponds to the diameters of single axons within the 7 day optic nerve. Thus the migration of oligodendrocyte-type 2 astrocyte progenitors and axonal ensheathment by oligodendrocytes may be guided by axonal topography within the developing nerve.

N-CAM and N-cadherin are specifically expressed in xanthophores, but not in the other types of pigment cells, melanophores, and iridiphores

Little is known about cell-cell communication in pigment cells, whereas a number of signalling molecules have been implicated to control their migration, differentiation, and proliferation. We set out to investigate the expression of cell adhesion molecules (CAMs) in the three different types of pigment cells in poikilotherms, Oryzias latipes and Xenopus laevis. In the present experiments, the expression of N-CAM and N-cadherin in the pigment cells in vitro was examined by immunocytochemistry. Melanophores and xanthophores were isolated and cultured from scales or skins, while iridophores were harvested from skins or peritoneum. The results showed that N-CAM and N-cadherin were specifically expressed in xanthophores, but not in melanophores or iridophores in both O. latipes and X. laevis. N-CAM and N-cadherin basically colocalized in the restricted regions of xanthophores, although the N-caderin-expressed region was broader than the N-CAM-expressed region in the same cell. The incidence of N-cadherin expression was higher than that of N-CAM expression. N-CAM and N-cadherin were expressed at the tip or the base of dendrites, or at the edge between dendrites in dendritic xanthophores. N-CAM and N-cadherin usually localized in small and narrow regions of xanthophores. This distribution pattern was essentially similar in xanthophores with round morphology, which exhibited spot, band, or semicircular immunoreactive regions on the peripheral edge of the cells. The difference in the distribution of pigment granules within the cells, culture period, fixatives, or immunofluorescent markers used in the experiments did not alter the immunostaining pattern.

Movement of embryonic chick sympathetic neurons on laminin in vitro is preceded by neurite extension

Chick sympathetic neurons (E-9) are capable of moving on a laminin substrate but not on more adhesive substrates in vitro. The effect of laminin is dose-dependent and reduced by the addition of anti-laminin antibodies, whereas soluble laminin does not stimulate movement. The onset of neuronal movement is preceded by, and highly correlated with, the onset of neurite formation. The addition of 1,2 dioctanoyl-sn-glycerol (DAG), a stimulator or protein kinase C that has been shown to inhibit neurite outgrowth, was found to delay both process formation and neuronal movement but did not affect the correlation between these two measures. These results support the conclusion that laminin stimulates primary neuronal movement in vitro and suggest that the mechanism underlying movement involves process formation followed by "towing" of the cell body by the advancing process. The similarities of this in vitro behavior to that observed in vivo suggest that similar mechanisms may underlie neuronal movement in the developing nervous system as suggested by Morest (Z Anat Entwicklungsgesch 130:265-305, 1970) and Liesi (EMBO J 4:1163-1170, 1985; Exp Neurol 117:103-113, 1992).

Adhesion molecules in neural crest development

Peripheral nerve cells, various endocrine and pigment cells and cranial connective tissue cells of vertebrates stem mainly from the embryonic neural crest. This originates with the central nervous system, but the crest cells detach from this tissue, via a decrease of cell-cell adhesion involving, particularly, a reduction of the adherens junction cell adhesive molecule A-CAM. This epithelio-mesenchymal transformation allows crest cells to migrate along pathways that are defined partly by the distribution of substrate adhesion molecules, the archetype being fibronectin, an extracellular matrix molecule recognized by integrin receptors on crest cells. Many other molecules, however, may act in the same way. In contrast, some molecules may define migration pathways by reducing adhesion; chondroitin sulfate proteoglycan is a candidate for this role. Pathway selection is most likely achieved by balanced combinations of molecules that promote and reduce adhesion. Cessation of migration, in the case of the nervous ganglia, correlated with re-expression of cell-cell adhesion molecules like A-CAM and others, consistent with an adhesive basis, although functional tests have not yet been performed. The development of the neural crest system provides a useful model that emphasizes the role of adhesion in morphogenesis.

Molecular mechanisms of neural crest cell attachment and migration on types I and IV collagen

We have examined the mechanisms involved in the interaction of avian neural crest cells with collagen types I and IV (Col I and IV) during their adhesion and migration in vitro. For this purpose native Col IV was purified from chicken tissues, characterized biochemically and ultrastructurally. Purified chicken Col I and Col IV, and various proteolytic fragments of the collagens, were used in quantitative cell attachment and migration assays in conjunction with domain-specific collagen antibodies and antibodies to avian integrin subunits. Neural crest cells do not distinguish between different macromolecular arrangements of Col I during their initial attachment, but do so during their migration, showing a clear preference for polymeric Col I. Interaction with Col I is mediated by the alpha 1 beta 1 integrin, through binding to a segment of the alpha 1(I) chain composed of fragment CNBr3. Neural crest cell attachment and migration on Col IV involves recognition of conformation-dependent sites within the triple-helical region and the noncollagenous, carboxyl-terminal NC1 domain. This recognition requires integrity of inter- and intrachain disulfide linkages and correct folding of the molecule. Moreover, there also is evidence that interaction sites within the NC1 domain may be cryptic, being exposed during migration of the cells in the intact collagen as a result of the prolonged cell-substratum contact. In contrast to Col I, neural crest cell interaction with Col IV is mediated by beta 1-class integrins other than alpha 1 beta 1.

The development of the neural crest in amphibians

Our review deals with the development of the neural crest (NC) in amphibians. We will consider relevant aspects of evolution, ontogeny, migration and differentiation, and investigate principal problems such as the regulation of NC cell determination, pathway selection and destination recognition. Earlier data and more recent findings will be presented. The NC probably evolved about 440 million years ago from the anlagen of epidermal nerve plexuses in protochordates. In urodele amphibians, the prospective NC is already present in the early gastrula as a narrow band of ectodermal cells between the prospective epidermis and the prospective neural plate. The NC proper develops later from the apices of the neural folds and forms, after neural fold fusion, a transient cellular ridge on the dorsal surface of the neural tube. NC cells migrate extensively into various body regions and give rise to a wide variety of derivatives including the mesenchymal elements of the skull, the neural and glial precursors of the peripheral nervous system and the pigment cells. NC cell migration is stimulated by components of the extracellular matrix (ECM) and may conveniently be analyzed in the system of wild-type (dark) and white mutant axolotl embryos. Skeletal elements of the head derive from cranial NC cells following an interaction with pharyngeal endoderm. Other derivatives of the NC are the ganglia of the peripheral nervous system in the head (sensory ganglia; mostly mixed origin with placodal material) and trunk (spinal, sympathetic and enteric ganglia). Pigment cells also derive from the NC and become arranged into uniform or banded pigment patterns.

From the crest to the periphery: control of pigment cell migration and lineage segregation

Pigment cells are one of many cell types derived from the neural crest. This review focuses on the mechanisms that control the timing and pathways of migration of pigment cells into the epidermis and determinants that control the differentiation of pigment cells. Several factors may control the timing and pattern of pigment cell migration in the dorsolateral space including the loss of inhibitory molecules in the pathway, the appearance of chemotactic molecules emanating from the dispersing dermatome, and the differentiation of pigment cells, which may be the only neural crest derivative capable of utilizing the substratum found in the dorsolateral path. Control of pigment cell differentiation remains controversial. A working model presented in this review suggests that multipotent neural crest cells that disperse ventrally upon separation from the neural tube preserve neurogenic ability and lose melanogenic ability, whereas those cells that are arrested at the entrance to the dorsolateral path lose neurogenic ability so that the population becomes primarily melanogenic. During the time that the latter population is arrested in migration it is speculated that the neural crest cells are exposed to an environment comprised of specific extracellular matrix molecules and/or growth factors that enhance pigment cell differentiation.

Surface micromorphology and cellular interactions

Contact guidance induced by the topographical properties of the underlying substratum is of great importance in morphogenesis and also influences the interaction of tissue cells with implanted material. A large body of evidence has accumulated since the first detection of this phenomenon in 1910. Several major hypotheses have been developed to explain the observed cell behaviour. The technological progress enabled researchers to produce pure substrata with a defined and controlled surface microgeometry. Based on these specimens, it could be demonstrated that cytoskeletal structures and receptors forming focal adhesions most likely are involved in contact guidance. In a study using human gingival fibroblasts, the reaction of these cells to a regular surface microstructure of 1 micron pitch and 1 micron depth was tested. After two days on the microstructured samples, all the cells showed a strong alignment to the topography of the surface. Transmission electron microscopy revealed that the cells either bridged the grooves or conformed to the surface structures. The latter confirms earlier investigations with porous subcutaneous implants, where the inflammatory reaction and the formation of a fibrous tissue capsule was reduced due to enhanced tissue adhesion.

Localization of fibronectin in the frog skin

In this review, we present structural and ultrastructural localizations of fibronectin (FN) in the larval and adult skin of the frog (Rana esculenta) either in in vivo or in in vitro conditions. The ventral skin of the tadpole contains membrane-associated FN-plaques disposed around the epidermal and dermal cells during their climactic rearrangement. Moreover, lines of fibrillar FN are detected inside the breaks opened in the derived collagen. The ventral skin of the adult frog reveals FN distributed in the three superimposed tissues forming the skin, i.e. the epidermis, the dermis and the subcutaneous tissue. In vivo, the epidermis is devoid of FN except for the mitochondria-rich cells (MRCs) which contain FN cytoplasmic granules. The dermis reveals two distinct collagenous networks showing FN localizations. A vertically-oriented network formed by thick tracts contains axis of fibrillar FN connecting the upper dermis devoid of FN to the FN-rich subcutaneous tissue. In contiguity with an horizontally-oriented network comprises thin tracts formed by clear spaces separating the superimposed collagen bundles of the dermal stratum compactum. These tracts contain aligned FN-granules. Inside the thick and thin tracts, the dermal and pigment cells present membrane-associated In vitro (in organ culture conditions) MRCs of the epidermis maintain their FN localization and, in addition, the stratum germinativum cells show cytoplasmic FN granules. Epidermal cells, in the vicinity of the cut edges of the cultivated skin fragment, modify their shape and acquire membrane-associated FN-plaques located between desmosomes. The FN localizations in these two collagenous networks of the dermis remain unchanged. In the same way, the FN-rich subcutaneous tissue is unmodified. In summary, the FN distribution in the larval skin is related to the cell rearrangement during the metamorphic climax, and, in the adult skin to the cell migration during the wound healing process and the pigment cell patterning. The cell migration is demonstrated, in organ culture conditions, by antiFN serum used as an experimental tool. FN is an important substrate used in the dermal breaks of the larval skin, and in the dermal tracts of the adult skin, both allowing the dermal and pigment cell migration.

Segregation and early dispersal of neural crest cells in the embryonic zebrafish

We have exploited our ability to visualize and follow individual cells in situ, in the living embryo, to study the development of trunk neural crest in the embryonic zebrafish. In most respects, the development of zebrafish trunk neural crest is similar to the development of trunk neural crest in other species: zebrafish trunk neural crest cells segregate from the dorsal neural keel in a rostrocaudal sequence, migrate ventrally along two pathways, and give rise to neurons of the peripheral nervous system, Schwann cells, and pigment cells. However, some aspects of the development of zebrafish trunk neural crest differ from those of other vertebrates: zebrafish trunk neural crest cells are significantly larger and fewer in number than those in avian embryos and the locations of their migratory pathways are slightly different. This initial description of neural crest development in the zebrafish embryo provides the foundation for future experimental studies.

Descriptive and experimental analysis of the dispersion of neural crest cells along the dorsolateral path and their entry into ectoderm in the chick embryo

We have characterized the dispersion of neural crest cells along the dorsolateral path in the trunk of the chicken embryo and experimentally investigated the control of neural crest cell entry into this path. The distribution of putative neural crest cells was analyzed in plastic sections of embryos that had been incubated for 24 hr in HNK-1 antibody, a procedure that we show successfully labels neural crest cells in the dorsolateral path and ectoderm. In accord with earlier observations, crest cells delay entering the dorsolateral path until a day or more after their counterparts have colonized the ventral path. However, once crest cells enter, they disperse rapidly through the path dorsal to the somite but still delay migrating dorsal to the intersegmental space. During dispersion, crest cells invade the ectoderm at sites associated with local disruptions in the basal lamina which may be caused by crest cells. Finally, deleting the dermamyotome releases an inhibition of neural crest cell migration: crest cells enter the dorsolateral path precociously. We speculate that the epithelial dermatome may transiently produce inhibitory substances and that emerging dermis may provide a long-distance, stimulatory cue.

Inhibition of neural crest cell differentiation by embryo ectodermal extract

The white mutation in Mexican axolotls has long been thought to be a defect associated with the embryonic extracellular environment, but not with embryonic neural crest cells. Thus it was believed that pigment cells in white axolotls disappear from the skin during early development, not because they are intrinsically defective but because they have no choice but to move into an unfavorable environment. We present evidence to suggest that: (1) white neural crest cells are in fact intrinsically different from dark (wild-type) cells, and (2) an inhibitor is produced in white embryonic ectoderm that actively suppresses the migration, differentiation, and survival of pigment cells in this animal. How these observations fit into the existing body of literature on the white mutant and a model for how the white phenotype might develop are discussed.

Large disulfide-stabilized proteoglycan complexes are synthesized by the epidermis of axolotl embryos

Proteoglycans (PGs) synthesized by the epidermis during stages crucial to the subepidermal migration of neural crest cells in the trunk of the axolotl (Ambystoma mexicanum, Urodela, Amphibia) embryo were studied. The glycosaminoglycan chains were biosynthetically labeled with [35S]sulfate in vitro during a period corresponding to the onset of migration. After extraction with guanidine HCl, the radiolabeled PGs were separated according to size by molecular-sieve chromatography on Sepharose CL-2B under dissociative conditions. This resulted in the separation of high-molecular-weight PGs, which eluted in the void volume, and low-molecular-weight PGs, eluting in a broad peak with a mean Kav of 0.7. The large PGs were also found to elute in the void volume when chromatographed on a Sephacryl S-1000 column. The low-molecular-weight PGs contained heparan sulfate and chondroitin sulfate (CS) and were not further characterized. The glycosaminoglycan component of the high-molecular-weight PG was completely degraded by chondroitinase ABC, while a large portion was resistant to chondroitinase AC, indicating the presence of dermatan sulfate (DS). These CS/DS chains were of unusually large size (Mr approximately 150,000) as estimated by chromatography on Sepharose CL-4B, relating the elution position to hyaluronan standards. Moreover, the chains were found to have a lower surface charge density than standard CS, and may therefore be undersulfated. After reduction and alkylation the high-molecular-weight PGs were included on both Sepharose CL-2B and Sephacryl S-1000 columns, eluting at Kav 0.2 and 0.4, respectively. Hence, the high-molecular-weight material appears to consist of large PG complexes, stabilized by intermolecular disulfide bonds. A CS/DSPG of similar size as the reduced monomeric form of the high-molecular-weight PG was found in small amounts in the total extract of 35S-labeled material.

Extracellular matrix of the developing heart in normal and cardiac lethal mutant axolotls, Ambystoma mexicanum

As part of an ongoing study of heart development in normal and cardiac lethal mutant axolotls (Mexican salamanders) we examined the extracellular matrix (ECM) by microscopical methods. With scanning electron microscopy we are unable to detect ECM on the apical surface of cells of the early cardiogenic mesoderm. During the period of lateral plate migration, which coincides with the period of cardiogenic induction of mesoderm by anterior endoderm, there is little ECM, aside from some microfibrils, on the basal surface of the endoderm or mesoderm of the pharyngeal region. Later, a basal lamina (BL) is found on the endoderm and along portions of the developing endocardial and myocardial tubes. By the time of heartbeat initiation the BLs are complete and invested with striated collagen-like fibrils that are sparsely distributed in the "cardiac jelly" of normal and mutant hearts. Striated fibril deposition, which increases with time, is generally random in orientation, with the exception of some regions where there is a preferred directionality. During the post-hatching period striated fibrils appear in the subepicardial space. In addition, branching fibers that are probably elastin appear in the bulbus arteriosus. In these later stages the density of fibrils in the cardiac lethal mutant heart is much less than normal. Indirect immunofluorescent microscopy reveals laminin and fibronectin in the basal laminae of the endocardial and myocardial tubes of both normal and cardiac lethal mutant hearts. In addition, punctate and fibrillar staining for fibronectin, and punctate staining for laminin are found in the cardiac jelly. These matrix proteins are not abundant at the apical (exterior) surface of the myocardium until the epicardium appears.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of fetal bovine serum and serum-free conditions on white and dark axolotl neural crest explants

Neural crest cells from both white mutant and dark (wildtype) axolotls (Ambystoma mexicanum) were cultured in increasing concentrations of fetal bovine serum (FBS; 2 to 20%). For each explant, the total number of cells that migrated and the percent of differentiated melanophores were recorded. At concentrations of FBS above 2% melanophore differentiation was essentially equivalent (32 to 59%) for both the white and dark neural crest cultures, but subtle differences in cell behavior and differentiation were found between the two phenotypes. By contrast there was a significant difference in the percent melanization of cells in serum-free control cultures, wherein melanophore differentiation in dark neural crest cultures was, on average, 18% compared to 5% in white cultures. Thus, contrary to all previously published work, white and dark neural crest cells are not intrinsically equivalent. Our culture results are discussed with regard to the probable in vivo conditions that cause the white phenotype.

Inhibition of neural crest cell migration by aggregating chondroitin sulfate proteoglycans is mediated by their hyaluronan-binding region

We have recently shown that the large hyaluronan-aggregating chondroitin sulfate proteoglycan from cartilage (PG-LA) is unfavorable as a substrate for neural crest cell migration in vitro and that this macromolecule inhibits cell dispersion on fibronectin substrates when included in the medium (R. Perris and S. Johansson, 1987, J. Cell Biol. 105, 2511-2521). In this study we present data on the specificity of the migration-repressing activity of PG-LA and data on the molecular mechanisms by which the proteoglycan might impair neural crest cell motility. Soluble PG-LA potently impaired cell migration on substrates of laminin/laminin-nidogen, vitronectin, and collagen types I, III, IV, and VI. When tested in solid-phase binding assays, PG-LA bound avidly to substrates of collagen types I-III and V. Conversely, minimal amounts of the proteoglycan bound to substrates of laminin-nidogen, vitronectin, collagen types IV and VI, and fibronectin or to a proteolytic fragment encompassing its cell-binding domain (105 kDa). Preincubation of these substrates with soluble PG-LA prior to plating of the cells had no effect on their locomotory behavior. These results indicate that PG-LA affects neural crest cell movement primarily through an interaction with the cell surface, rather than by association with the cell motility-promoting substrate molecules. The molecular interaction of soluble PG-LA with neural crest cells was further examined by analyzing the effects of isolated domains of the proteoglycan on cell migration on fibronectin. Addition of chondroitin sulfate chains, the core protein free of glycosaminoglycans, the isolated hyaluronan-binding region (HABr), or a proteolytic fragment corresponding to the keratan sulfate-enriched domain of the PG-LA to neural crest cells migrating on fibronectin or the 105-kDa fibronectin fragment had no significant effect on their motility. After reduction and alkylation, PG-LA was considerably less efficient in perturbing cell movement on fibronectin substrates and virtually ineffective in altering migration on the 105-kDa fragment. In the presence of hyaluronan fragments of 16-30 monosaccharides in length, or an antiserum against the HABr, the migration repressing activity of PG-LA was reduced in a dose-dependent fashion. Furthermore, the inhibitory action of PG-LA was significantly reduced by treatment of the cells with Streptomyces hyaluronidase.(ABSTRACT TRUNCATED AT 400 WORDS)