Emerging Roles of Perivascular Mesenchymal Stem Cells in Synovial Joint Inflammation.

In contrast to the significant advances in our understanding of the mesenchymal stem cell (MSC) populations in bone marrow (BM), little is known about the MSCs that are resident in the synovial joint and their possible roles in the tissue homeostasis, chronic inflammation as well as in repair. Neural crest is a transient embryonic structure, generating multipotential MSC capable of migrating along peripheral nerves and blood vessels to colonize most tissue types. In adult, these MSC can provide functional stromal support as a stem cell niche for lymphocyte progenitors for instance in the BM and the thymus. Critically, MSC have major immunoregulatory activities to control adverse inflammation and infection. These MSC will remain associated to vessels (perivascular (p) MSC) and their unique expression of markers such as myelin P0 and transcription factors (e.g. Gli1 and FoxD1) has been instrumental to develop transgenic mice to trace the fate of these cells in health and disease conditions. Intriguingly, recent investigations of chronic inflammatory diseases argue for an emerging role of pMSC in several pathological processes. In response to tissue injuries and with the release of host cell debris (e.g. alarmins), pMSC can detach from vessels and proliferate to give rise to either lipofibroblasts, osteoblasts involved in the ossification of arteries and myofibroblasts contributing to fibrosis. This review will discuss currently available data that suggest a role of pMSC in tissue homeostasis and pathogenesis of the synovial tissue and joints. Graphical abstract.

CD34 defines melanocyte stem cell subpopulations with distinct regenerative properties.

Melanocyte stem cells (McSCs) are the undifferentiated melanocytic cells of the mammalian hair follicle (HF) responsible for recurrent generation of a large number of differentiated melanocytes during each HF cycle. HF McSCs reside in both the CD34+ bulge/lower permanent portion (LPP) and the CD34- secondary hair germ (SHG) regions of the HF during telogen. Using Dct-H2BGFP mice, we separate bulge/LPP and SHG McSCs using FACS with GFP and anti-CD34 to show that these two subsets of McSCs are functionally distinct. Genome-wide expression profiling results support the distinct nature of these populations, with CD34- McSCs exhibiting higher expression of melanocyte differentiation genes and with CD34+ McSCs demonstrating a profile more consistent with a neural crest stem cell. In culture and in vivo, CD34- McSCs regenerate pigmentation more efficiently whereas CD34+ McSCs selectively exhibit the ability to myelinate neurons. CD34+ McSCs, and their counterparts in human skin, may be useful for myelinating neurons in vivo, leading to new therapeutic opportunities for demyelinating diseases and traumatic nerve injury.

Depletion of Neural Crest-Derived Cells Leads to Reduction in Plasma Noradrenaline and Alters B Lymphopoiesis.

Hematopoietic stem cells and their lymphoid progenitors are supported by the bone marrow (BM) microenvironmental niches composed of various stromal cells and Schwann cells and sympathetic nerve fibers. Although neural crest (NC) cells contribute to the development of all the three, their function in BM is not well understood. In this study, NC-derived cells were ablated with diphtheria toxin in double-transgenic mice expressing NC-specific Cre and Cre-driven diphtheria toxin receptor with yellow fluorescent protein reporter. We found that yellow fluorescent protein-expressing, NC-derived nonhematopoietic cells in BM expressed hematopoietic factors Cxcl12 and stem cell factor The ablation of NC-derived cells led to a significant decrease in B cell progenitors but not in hematopoietic stem cells or myeloid lineage cells in BM. Interestingly, plasma noradrenaline was markedly decreased in these mice. The i.p. administration of 6-hydroxydopamine, a known neurotoxin for noradrenergic neurons, led to a similar phenotype, whereas the administration of a noradrenaline precursor in NC-ablated mice partially rescued this phenotype. Additionally, the continuous administration of adrenergic receptor ß antagonists partially decreased the number of B cell progenitors while preserving B lymphopoiesis in vitro. Taken together, our results indicate that NC-derived cell depletion leads to abnormal B lymphopoiesis partially through decreased plasma noradrenaline, suggesting this as a novel mechanism regulated by molecules released by the sympathetic neurons.

Accessory cells for ß-cell transplantation.

Despite recent advances, insulin therapy remains a treatment, not a cure, for diabetes mellitus with persistent risk of glycaemic alterations and life-threatening complications. Restoration of the endogenous ß-cell mass through regeneration or transplantation offers an attractive alternative. Unfortunately, signals that drive ß-cell regeneration remain enigmatic and ß-cell replacement therapy still faces major hurdles that prevent its widespread application. Co-transplantation of accessory non-islet cells with islet cells has been shown to improve the outcome of experimental islet transplantation. This review will highlight current travails in ß-cell therapy and focuses on the potential benefits of accessory cells for islet transplantation in diabetes.

Impaired Cellular Immunity in the Murine Neural Crest Conditional Deletion of Endothelin Receptor-B Model of Hirschsprung's Disease.

Hirschsprung's disease (HSCR) is characterized by aganglionosis from failure of neural crest cell (NCC) migration to the distal hindgut. Up to 40% of HSCR patients suffer Hirschsprung's-associated enterocolitis (HAEC), with an incidence that is unchanged from the pre-operative to the post-operative state. Recent reports indicate that signaling pathways involved in NCC migration may also be involved in the development of secondary lymphoid organs. We hypothesize that gastrointestinal (GI) mucosal immune defects occur in HSCR that may contribute to enterocolitis. EdnrB was deleted from the neural crest (EdnrBNCC-/-) resulting in mutants with defective NCC migration, distal colonic aganglionosis and the development of enterocolitis. The mucosal immune apparatus of these mice was interrogated at post-natal day (P) 21-24, prior to histological signs of enterocolitis. We found that EdnrBNCC-/- display lymphopenia of their Peyer's Patches, the major inductive site of GI mucosal immunity. EdnrBNCC-/- Peyer's Patches demonstrate decreased B-lymphocytes, specifically IgM+IgDhi (Mature) B-lymphocytes, which are normally activated and produce IgA following antigen presentation. EdnrBNCC-/- animals demonstrate decreased small intestinal secretory IgA, but unchanged nasal and bronchial airway secretory IgA, indicating a gut-specific defect in IgA production or secretion. In the spleen, which is the primary source of IgA-producing Mature B-lymphocytes, EdnrBNCC-/- animals display decreased B-lymphocytes, but an increase in Mature B-lymphocytes. EdnrBNCC-/- spleens are also small and show altered architecture, with decreased red pulp and a paucity of B-lymphocytes in the germinal centers and marginal zone. Taken together, these findings suggest impaired GI mucosal immunity in EdnrBNCC-/- animals, with the spleen as a potential site of the defect. These findings build upon the growing body of literature that suggests that intestinal defects in HSCR are not restricted to the aganglionic colon but extend proximally, even into the ganglionated small intestine and immune cells.

Development of the juxta-oral organ in rat embryo.

The aim of this work is to clarify the development and morphology of the juxta-oral organ (JOO) in rat embryos from Day (E)14 to 19. Furthermore, in the region of the JOO, an analysis was made of the expression of the monoclonal antibody HNK-1, which recognizes cranial neural-crest cells. In this study, we report that JOO develops from an epithelial condensation at the end of the transverse groove of the primitive mouth at E14. During E15, it invaginates and is disconnected from the oral epithelium. At E16, the JOO forms an solid epithelial cord with three parts (anterior, middle, and posterior) and is related to the masseter, temporal, medial pterygoid, and tensor veli palatini muscles. During E17-19, no significant changes were detected in their position. Both the mesenchyme caudal to the anlage of the JOO at E14, as well as the mesenchyme that surrounds the bud of the JOO at E15, expressed positivity for HNK-1. Our results suggest that the mesenchyme surrounding the JOO at E15 could emit some inductive signal for the JOO to reach its position at E16. This work shows for the first time that the cranial neural-crest-derived mesenchyme participates in the development of the JOO.

HNK-1 immunoreactivity during early morphogenesis of the head region in a nonmodel vertebrate, crocodile embryo.

The present study examines HNK-1 immunoidentification of a population of the neural crest (NC) during early head morphogenesis in the nonmodel vertebrate, the crocodile (Crocodylus niloticus) embryos. Although HNK-1 is not an exclusive NC marker among vertebrates, temporospatial immunoreactive patterns found in the crocodile are almost consistent with NC patterns derived from gene expression studies known in birds (the closest living relatives of crocodiles) and mammals. In contrast to birds, the HNK-1 epitope is immunoreactive in NC cells at the neural fold level in crocodile embryos and therefore provides sufficient base to assess early migratory events of the cephalic NC. I found that crocodile NC forms three classic migratory pathways in the head: mandibular, hyoid, and branchial. Further, I demonstrate that, besides this classic phenotype, there is also a forebrain-derived migratory population, which consolidates into a premandibular stream in the crocodile. In contrast to the closely related chick model, crocodilian premandibular and mandibular NC cells arise from the open neural tube suggesting that species-specific heterochronic behavior of NC may be involved in the formation of different vertebrate facial phenotypes.

Contribution of neural crest-derived cells in the embryonic and adult thymus.

Neural crest (NC)-derived mesenchyme has previously been shown to play an important role in the development of fetal thymus. Using Wnt1-Cre and Sox10-Cre mice crossed to Rosa26(eYfp) reporter mice, we have revealed NC-derived mesenchymal cells in the adult murine thymus. We report that NC-derived cells infiltrate the thymus before day 13.5 of embryonic development (E13.5) and differentiate into cells with characteristics of smooth muscle cells associated with large vessels, and pericytes associated with capillaries. In the adult organ at 3 mo of age, these NC-derived perivascular cells continue to be associated with the vasculature, providing structural support to the blood vessels and possibly regulating endothelial cell function.

Transcription factor c-Myb is involved in the regulation of the epithelial-mesenchymal transition in the avian neural crest.

Multipotential neural crest cells (NCCs) originate by an epithelial-mesenchymal transition (EMT) during vertebrate embryogenesis. We show for the first time that the key hematopoietic factor c-Myb is synthesized in early chick embryos including the neural tissue and participates in the regulation of the trunk NCCs. A reduction of endogenous c-Myb protein both in tissue explants in vitro and in embryos in ovo, prevented the formation of migratory NCCs. A moderate over-expression of c-myb in naive intermediate neural plates triggered the EMT and NCC migration probably through cooperation with BMP4 signaling because (i) BMP4 activated c-myb expression, (ii) elevated c-Myb caused accumulation of transcripts of the BMP4 target genes msx1 and slug, and (iii) the reduction of c-Myb prevented the BMP4-induced formation of NCCs. The data show that in chicken embryos, the c-myb gene is expressed prior to the onset of hematopoiesis and participates in the formation and migration of the trunk neural crest.

Comparison of c-Fos immunoreactivity in pancreatic beta cells and cells with neural crest origin in rats: an immunohistochemical study.

Although a neural crest origin has been proposed for pancreatic beta cells, these cells are known to possess many similarities with neuronal cells. These similarities give rise to the hypothesis that undifferentiated neural crest cells can be transformed into beta cells. The objective of this study was to compare beta-cells and undifferentiated neural crest cells with respect to c-Fos immunoreactivity (c-Fos-IR), which plays a crucial role in certain cellular and biological processes and is used as a neuronal activity marker. For the purpose of the study, c-Fos-IR has been analysed by immunohistochemical methods in rat pancreatic beta cells, pulpal undifferentiated ectomesenchimal cells (PUECs) that are known to have a neural crest origin, and in small intestine fibroblasts which do not have a neural crest origin, in formaline-fixed, paraffin-embedded sections. There were no significant differences between beta-cells and PUECs in c-Fos-IR (p > 0.05) but there was a highly significant difference between fibroblasts and the other two type of cells ( p < 0.001). These results give rise to and support the suggestion that PUECs can be transformed into beta-cells.

Generation and characterization of monoclonal antibodies to the neural crest.

The generation of monoclonal antibodies (MAbs) specific for quail neural crest may provide valuable tools for studying the differentiation of embryonic precursor cells. Unfortunately, relatively few antibodies are available because of the difficulty in obtaining sufficient cells for in vivo immunization strategies. We have overcome this problem by using intrasplenic immunization with formaldehyde-fixed cells harvested from neural crest cultures. In addition, booster injections of cultured whole-embryo cells were administered intraperitoneally. Following two fusions, a total of 18 hybridomas were generated with antibody reactivity to the cytoplasm of neural crest cells. Furthermore, 32 were reactive against both somite (a noncrest mesodermal control) and crest cultures, whilst 15 were not reactive. Out of those hybridomas reactive with neural crest, six designated 160D, 164D, OE, 12E, 120E and 124E were further characterized. Interestingly MAb supernatants OE, 12E, 120E, and 124E exhibited reactivity against some but not all neural crest cells suggesting that they might recognise subpopulations. Immunoglobulin isotyping of supernatants revealed that 4 (160D, 164D, OE, and 120E) were IgM and 2 (12E and 124E) were IgG(2b). On assessing their reactivity against human tissue sections, all six hybridoma supernatants cross-reacted with neuroendocrine cells within appendix, colon and rectum. These MAbs could provide novel reagents for the understanding of neural crest development.

Immuno-characterisation of neuroendocrine cells of the rat thymus gland in vitro and in vivo.

Primary cell cultures and organ fragments of rat thymus were characterised by use of a panel of antibodies raised against the neural adhesion molecule L1, tyrosine hydroxylase, protein gene product 9.5, nerve growth factor, calcitonin gene-related peptide, glial fibrillary acidic protein, vimentin, pan-cytokeratin, a ganglioside of neural crest and neuroendocrine cells (A2B5), and thymulin (4 beta). Immunoreactivity for neural markers only was identified in a single morphology (nerve-like) of cell in culture and throughout the adult thymus as fine, tortuous staining. Immunoreactivity for endocrine markers only was identified in polygonal epithelial-like cells in culture, throughout viable tissue in fragment culture and in the subcapsular cortex of the adult thymus. Immunoreactivity for both endocrine and neural markers was identified in three distinct morphologies in cell culture: elongate, spherical, and stellate. Similar results were observed in the mitotic periphery of the cultured fragments and in the medulla and cortico-medullary junction of the adult thymus. Cells with immunoreactivity to A2B5 were present in primary and fragment cultures and occurred throughout the adult thymus. The apparent diversity of cell immunoreactivity in primary and fragment thymic cultures suggests that numerous neural and endocrine factors may be required for the development and/or regeneration of the thymic microenvironment.

The brain and thymus have much in common: a functional analysis of their microenvironments.

Research into the neural and immune systems has begun to converge. Since the first reports that interleukins play important roles in both systems and that lymphocytes secrete neuronal factors, scientists have been surprised by the ever-increasing list of interactions. Here, Rolf Mentlein and Marion Kendall examine the major supporting cells of the brain and thymus - astrocytes and thymic epithelial cells - the similar neuroectodermal origin of which could explain such fundamental analogies.

Phosphotyrosine signalling as a regulator of neural crest cell adhesion and motility.

We demonstrate that neural crest cell-cell adhesion, cell-substrate adhesion, and ultimately cell motility, are highly dependent on the balanced action of tyrosine kinases and tyrosine phosphatases. Neural crest cell migration on fibronectin is diminished in the presence of the tyrosine phosphatase inhibitor vanadate or tyrosine kinase inhibitor herbimycin A, while cadherin-rich cell-cell adhesions are significantly increased. In contrast, cells treated with the kinase inhibitor genistein have decreased motility, rearrange rapidly and reversibly into a pavement-like monolayer, but have no increase in cadherin interactions. Genistein-sensitive tyrosine kinases may therefore abrogate a latent sensitivity of neural crest cells to contact-mediated inhibition of movement. Furthermore, we show that the activity of herbimycin A-sensitive kinases is necessary for focal adhesion formation in these cells. Moreover, the size and distribution of these adhesions are acutely sensitive to the actions of tyrosine phosphatases and genistein-sensitive kinases. We propose that in migrating neural crest cells there is a balance in phosphotyrosine signalling which minimises both cell-cell adhesion and contact inhibition of movement, while enhancing dynamic cell-substrate interactions and thus the conditions for motility.

Immunoreactivity of neural crest-derived cells in thymic tissue developing under the rat kidney capsule.

In order to study the functional development of a thymus in an experimental model, small pieces of adult rat thymic tissue were cultured for 9 days and implanted under the kidney capsule of littermates. The tissues were examined with a panel of antibodies raised against thymic and neural factors and neural crest cells at intervals from 5 to 13 days. At 5 days post-implantation, there were groups of L1+ cells within the implants that reacted with antibodies raised against neural and neural crest cell markers. L1+ cells were highly mitotic, rounded cells measuring 8.7 +/- 0.6 micrometer in diameter. Double immunostaining with different combinations of antibodies showed that 94% of the L1+ cells were also TH+, and many were HNK-1/NCAM+, PGP 9.5+, NGF+, chromogranin A+, VIP+, S100+, CGRP+, GAD+, and A2B5+. A few were also pan-cytokeratin+. These results indicate that these cells are derived from neural crest derived cells and belong to the neuroepithelial line of development. The L1+ cells were most numerous before nerves appeared (about Day 9) and reduced in number and extent as the thymus differentiated. The neural crest cells occasionally had long cytoplasmic extensions, but it was not possible to decide if they formed the nerves that appeared in the implants. Adult thymuses also contained a population of L1+ and HNK-1/NCAM+ cells, mainly in the subcapsular cortex, the septa, and the medulla. These cells could be a source of neural crest cells able to repopulate the implant. The adult thymus may always contain a reservoir of cells potentially capable of producing neuropeptides and transmitter factors required for thymic growth and regeneration.

GDNF and ET-3 differentially modulate the numbers of avian enteric neural crest cells and enteric neurons in vitro.

Vagal (hindbrain) neural crest cells migrate rostrocaudally in the gut to establish the enteric nervous system. Glial-derived neurotrophic factor (GDNF) and its receptor(s), and endothelin-3 (ET-3) and its receptor, are crucial for enteric nervous system development. Mutations interrupting either of these signaling pathways cause aganglionosis in the gut, termed Hirschsprung's disease in humans. However, the precise functions of GDNF and ET-3 in enteric neurogenesis are still unknown. We isolated precursor cells of the enteric nervous system from the vagal level neural crest of E1.7 quail embryos prior to entry into the gut and from the developing midgut at stages corresponding to migrating (E4.7) and longer resident differentiating cells (E7) using HNK-1 immunoaffinity and magnetic beads. These cells were tested for their response to GDNF and ET-3 in culture. ET-3 and GDNF had little effect in vitro on the growth, survival, migration, or neurogenesis of E1.7 vagal neural crest cells. In contrast, GDNF increased the proliferation rate and numbers of enteric neural precursors isolated from the E4.7 and E7 gut. Also, many more neurons and neurites developed in cultures treated with GDNF, disproportionately greater than the effect on cell numbers. At high cell density and in the presence of serum, ET-3, and GDNF had an additive effect on proliferation of neuron precursor cells. In defined medium, or low cell density, ET-3 reduced cell proliferation, overriding the proliferative effect of GDNF. Regardless of the culture condition, the stimulatory effect of GDNF on neuron numbers was strikingly diminished by the simultaneous presence of ET-3. We propose first that GDNF promotes the proliferation in the migratory enteric neural precursor cell population once the cells have entered the gut and is especially crucial for the differentiation of these cells into nonmigrating, nonproliferating enteric neurons. Second, we suggest that ET-3 modulates the action of GDNF, inhibiting neuronal differentiation to maintain the precursor cell pool, so ensuring sufficient population numbers to construct the entire enteric nervous system. Third, we suggest that generalized defects in enteric neural precursor cell numbers and differentiation due to mutations in the ET-3 and GDNF systems are converted to distal gut neural deficiencies by the rostrocaudal migration pattern of the precursors. Fourth, we suggest that additional factors such as those found in serum and produced by the enteric neural cells themselves are likely also to be involved in enteric nervous system development and consequently in Hirschsprung's disease.

Up-regulated expression of decay-accelerating factor (CD55) confers increased complement resistance to sprouting neural cells.

We studied gene expression in relation to induced neural differentiation in a human neural crest-derived cell line, Paju. Messenger RNA isolated before and after treatment with phorbol 12-myristate 13-acetate was analyzed by differential display reverse transcription PCR. A strongly up-regulated expression of decay-accelerating factor (DAF, CD55) was found to parallel the induced neural sprouting while the expression of two other complement regulatory proteins (CD59/protectin, CD46/membrane cofactor protein) remained unaltered during neural differentiation. The increased membrane expression of DAF, which was also seen on neural processes and growth cones, conferred elevated resistance to complement-mediated lysis. Our findings suggest that in sprouting neurons DAF expression is up-regulated to provide additional complement resistance to pathfinding axons/dendrites invading new environment. It is also suggested that membrane expression of DAF may constitute a marker of growing and regenerating neurons.

[The distribution of intermediate filaments, histiocytic antigens and neural crest-related antigens in the adult dental pulp. An immunocytochemical approach]. / Distribuzione di filamenti intermedi, antigeni istiocitari e antigeni correlati alla cresta neurale nella polpa dentaria dell'adulto. Approccio immunocitochimico.

MATERIALS AND METHODS: Ten human healthy teeth were extracted for orthodontic or surgical purposes and processed for histological and immunocytochemical examination with the streptavidin-biotin-peroxidase method. Highly purified antibodies were used to reveal the distribution of intermediate filaments (vimentin, desmin, alpha-smooth muscle actin), histiocytic antigens (alpha-1-antitrypsin, lysozyme), neural and neural-crest-associated antigens (neuron-specific enolase, chromogranin-A, S-100, synaptophysin, glial fibrillary acidic protein, neurofilaments) in the adult pulp tissue. RESULTS: Vimentin immunostaining was strongly positive in the network of pulpal fibroblasts. Desmin and alpha-smooth muscle actin were present only in the vessel walls. Staining for alpha-1-antitrypsin and lysozyme reveals a number of macrophage-like cells in the central portion of the pulp. Macrophages were the most dominating immunocompetent cells. Negative immunostaining for chromogranin-A demonstrated the absence of neuroendocrine antigens in the adult dental pulp. Immunostaining for neuron-specific enolase, S-100 protein, synaptophysin, glial fibrillary acidic protein and neurofilaments were positive, with different intensity, in nerve fibres, but no pulp cell was found to be immunoreactive. CONCLUSIONS: The conclusion is drawn that the lack of labelling of pulp cells by the neural associated antibodies could be due to differentiation processes during tissue development.

Border controls at the mammalian spinal cord: late-surviving neural crest boundary cap cells at dorsal root entry sites may regulate sensory afferent ingrowth and entry zone morphogenesis.

Boundary caps (BCs) form when neural crest cells, migrating ventrally alongside the neural tube, arrest at sites where axons will enter and exit. However, nothing is known of their subsequent fate and functions. We have found late-surviving neural crest BC cell clusters at proximal dorsal root entry sites throughout rat spinal cord development. Sensory afferents cross BCs to enter the spinal cord, while exiting astrocyte processes, destined to form the dorsal root entry zone (DREZ) after birth, are temporarily stalled in their vicinity. To test whether contact with BC cells influences neurite outgrowth from dorsal root ganglia, neurons were cultured on embryonic dorsal root/spinal cord cryosections. Neurites that entered CNS territory preferentially extended over BC cells. Thus, BC cells could be instrumental in regulating afferent ingrowth and DREZ morphogenesis in mammalian spinal cord development.

New monoclonal antibody (4E9R) identifies mouse neural crest cells.

In order to analyze migration patterns of mouse neural crest cells, we produced a rat anti-mouse monoclonal antibody (4E9R) which identifies these cells. The distribution of 4E9R-immunoreactive cells was examined in migratory stages of mouse neural crest cells, ranging from embryonic day (Ed) 8.5 to 10.5. In the cephalic region of Ed 8.5 embryos, some mesencephalic mesenchymal cells close to neural folds were 4E9R-positive. In Ed 9.0-9.5 embryos, streams of 4E9R-immunoreactive cells extending from cranial neural tubes to maxillary processes and to first visceral arches were found in the lateral region and some of these cells were localized in presumptive trigeminal ganglia. In the same embryonic stages, 4E9R-positive cells were present in mesenchymal cells around the optic and otic vesicles. In the trunk region of Ed 9.5-10.5 embryos, 4E9R-positive cell masses were observed in dorsolateral spaces adjacent to neural tubes. The presence of 4E9R-immunoreactive cells in somitic segments was restricted within the anterior halves and these cells were seen under the dermomyotome and/or in the medial portion of the sclerotome. These cells colonized in presumptive dorsal root ganglia and in the surroundings of the dorsal aorta, the embryonic area in which sympathetic ganglia are formed. 4E9R-positive cells were also found just under the epidermis. These observations indicate that the distribution of 4E9R-positive cells is similar to that of amniote neural crest cells reported previously. Furthermore, the data suggest that the migratory behavior of mouse neural crest cells at trunk levels may be different between rostral and caudal levels within an anterior half of the sclerotome, and that sympathetic ganglia may be formed by neural crest cells migrating along "ventromedial pathways" as well as "ventrolateral pathways" at hindlimb-bud levels of mouse embryos. In primary cultures of mouse neural crest cells, approximately 80% of the cells were 4E9R-positive on culture day 2. Further, we have shown in cultures treated with colchicine or cytochalasin B that 4E9R antigens are present in intermediate filaments. When image analysis with a confocal laser scanning microscope was performed on primary cultures of mouse neural crest cells, the intracellular localization of 4E9R antigens in these cells was comparable to that of vimentin, which is a typical intermediate filament in most mesenchymal cells in embryonic stages examined. Since the distribution of 4E9R-positive cells and anti-vimentin-immunoreactive cells was different in mouse embryos, it is suggested that 4E9R antigens are vimentin-related and specifically expressed in a few cell types including mouse neural crest cells. These results indicate that a rat anti-mouse monoclonal antibody 4E9R is useful for the identification of mouse neural crest cells during the migratory stages.