Asymmetric expression in somites of cytotactin and its proteoglycan ligand is correlated with neural crest cell distribution

Analysis of proteoglycan expression in developing chicken brain: characterization of a heparan sulfate proteoglycan that interacts with the neural cell adhesion molecule

In the present study we have characterized the major proteoglycans of chick brain, focusing on their pattern of expression in development and on identifying the heparan sulfate proteoglycan (HSPG) that binds to the neural cell adhesion molecule (NCAM). The major chondroitin sulfate proteoglycans (CSPG) are a heterogeneous group of molecules with an average MW of 450 kDa. Protein core analysis reveals multiple protein cores between 100 and 350 kDa. The HSPGs are somewhat smaller, with an average MW of 350 kDa, and the major brain HSPG possesses a 250 kDa protein core. During development the relative percentage of HSPG decreases from approximately 50% of total sulfate-labeled PG at E6 to 25% by E10. In order to begin to characterize the HSPG that interacts with NCAM, we initially used an antiserum produced against a HSPG which was previously shown to copurify with NCAM (Cole and Burg: Exp Cell Res 182:44-60, 1989). This antiserum immunoprecipitated a HSPG core protein of 250 kDa, corresponding to the major HSPG of chick brain. We also show that the major brain HSPG binds to a synthetic peptide that encodes the heparan sulfate-binding domain of NCAM, and that monoclonal antibodies to a recently identified chick retinal HSPG recognize this NCAM-binding HSPG. This HSPG was immunopurified from E10 chick brain using the 6D2 monoclonal antibody, and has been shown to bind an affinity column containing the heparan sulfate-binding peptide of NCAM. Consistent with its ability to bind NCAM, we show that the intact 6D2 HSPG inhibits cell adhesion to a HBD peptide substratum, and also binds chick brain cells when employed as a substratum.

Early stages of chick somite development

We report on the formation and early differentiation of the somites in the avian embryo. The somites are derived from the avian embryo. The somites are derived from the mesoderm which, in the body (excluding the head), is subdivided into four compartments: the axial, paraxial, intermediate and lateral plate mesoderm. Somites develop from the paraxial mesoderm and constitute the segmental pattern of the body. They are formed in pairs by epithelialization, first at the cranial end of the paraxial mesoderm, proceeding caudally, while new mesenchyme cells enter the paraxial mesoderm as a consequence of gastrulation. After their formation, which depends upon cell-cell and cell-matrix interactions, the somites impose segmental pattern upon peripheral nerves and vascular primordia. The newly formed somite consists of an epithelial ball of columnar cells enveloping mesenchymal cells within a central cavity, the somitocoel. Each somite is surrounded by extracellular matrix material connecting the somite with adjacent structures. The competence to form skeletal muscle is a unique property of the somites and becomes realized during compartmentalization, under control of signals emanating from surrounding tissues. Compartmentalization is accompanied by altered patterns of expression of Pax genes within the somite. These are believed to be involved in the specification of somite cell lineages. Somites are also regionally specified, giving rise to particular skeletal structures at different axial levels. This axial specification appears to be reflected in Hox gene expression. MyoD is first expressed in the dorsomedial quadrant of the still epithelial somite whose cells are not yet definitely committed. During early maturation, the ventral wall of the somite undergoes an epithelio-mesenchymal transition forming the sclerotome. The sclerotome later becomes subdivided into rostral and caudal halves which are separated laterally by von Ebner's fissure. The lateral part of the caudal half of the sclerotome mainly forms the ribs, neural arches and pedicles of vertebrae, whereas within the lateral part of the rostral half the spinal nerve develops. The medially migrating sclerotomal cells form the peri-notochordal sheath, and later give rise to the vertebral bodies and intervertebral discs. The somitocoel cells also contribute to the sclerotome. The dorsal half of the somite remains epithelial and is referred to as the dermomyotome because it gives rise to the dermis of the back and the skeletal musculature. the cells located within the lateral half of the dermomyotome are the precursors of the muscles of the hypaxial domain of the body, whereas those in the medial half are precursors of the epaxial (back) muscles.(ABSTRACT TRUNCATED AT 400 WORDS)

Macrophages, microglia, and astrocytes are rapidly activated after crush injury of the goldfish optic nerve: a light and electron microscopic analysis

Several matrix and adhesion molecules in fish optic nerve, which are constitutively expressed, are increased during axonal regeneration and are primarily associated with nonneuronal cells (W.P. Battisti, Y. Shinar, M. Schwartz, P. Levitt, and M. Murray [1992] J. Neurocytol. 21:557-573). The current study examines the reactions of specific cell types to optic nerve crush and axonal regeneration. The goldfish optic nerve contains macroglia and microglia as well as a population of monocyte-derived cells (granular macrophages) unique to goldfish. Two cell types were OX-42 positive (granular macrophages and microglia), indicating monocyte lineage, each with a distinct morphology and distribution within the nerve. Within hours of the optic nerve crush, the number of OX-42-labeled cell profiles increased near the crush site, remained elevated during the time axons were elongating, and then declined. Microglia, but not granular macrophages, were phagocytically active. Astrocytes are readily identified in the normal optic nerve, but they exhibited marked morphologic changes within hours of injury, which is consistent with the contribution these cells make to the altered environment. Oligodendroglia could not be reliably identified in regenerating optic nerves until myelin was formed. A comparison of the distribution of OX-42-labeled cells with that of transforming growth factor beta-1 (TGF-beta 1) and tenascin suggests that these molecules are expressed by granular macrophages. Tenascin staining may be additionally associated with astrocytes and/or microglia. The rapid response of these nonneuronal cells to injury, their rapid phagocytic activity, and the secretion of growth-promoting factors by these cells likely contributes to the environment that supports robust regeneration by optic axons in the goldfish.

Differential effects of cytotactin/tenascin fusion proteins on intracellular pH and cell morphology

Cytotactin/tenascin is a multidomain extracellular matrix protein that inhibits both cell spreading and intracellular alkalinization. The protein has multiple different domains which are homologous to regions in epidermal growth factor, fibronectin, and fibrinogen. In previous studies, we produced nonoverlapping fusion proteins corresponding to these domains and examined their effects on cell attachment and spreading. Based on their ability either to promote or to inhibit cell attachment, two of these fusion proteins were shown to be adhesive and two were shown to be counteradhesive. To determine how the adhesive and counteradhesive activities of different cytotactin/tenascin domains alter intracellular pH (designated pHi), we have measured pHi, in NIH3T3 and U251MG cells in the presence of the cytotactin/tenascin fusion proteins and intact cytotactin/tenascin, as well as fibronectin. Cells incubated in the presence of intact cytotactin/tenascin or of the counteradhesive fusion proteins had a pHi lower than control cells. In contrast, the presence of the adhesive fusion proteins or of fibronectin caused cells to have higher pHi values than control cells. When two fragments were simultaneously presented, one of which alone increased pHi and the other of which alone decreased pHi, the predominant effect was that of lowered pHi. Incubation with an RGD-containing peptide derived from the cytotactin/tenascin sequence inhibited alkalinization promoted by the adhesive fragment containing the second through sixth fibronectin type III repeats that was known to bind to integrins. Incubation of the cells with heparinase I or III inhibited the intracellular alkalinization of cells plated in the presence of the other adhesive fusion protein containing the fibrinogen domain, suggesting that heparan sulfate proteoglycans were involved in these pHi changes. The activity of protein kinase C appeared to be important for the changes in pHi mediated by all of the proteins. The protein kinase C inhibitor Calphostin C blocked the rise in pHi elicited by the adhesive fusion proteins and by fibronectin. Moreover, activation of protein kinase C by the addition of phorbol esters increased the pHi in cells plated on cytotactin/tenascin or counteradhesive fusion proteins and reversed their effects. The results of this study support the hypothesis that cytotactin/tenascin can bind to multiple cell surface receptors and thereby elicit different physiological responses. Decreases in pHi are correlated with the phenomenon of counteradhesion whereas the ability to increase pHi is associated with cell attachment via at least two different types of cell surface receptors. The data raise the possibility that binding of cytotactin/tenascin may influence primary cellular processes such as migration and proliferation through the differential regulation of pHi.

Changing patterns of peanut agglutinin labelling in the dorsal cochlear nucleus correspond to axonal ingrowth

Various studies have suggested that glycoconjugates may influence connectivity and lamination in the developing central nervous system and may function as barriers to neuritic extension. It has been proposed that the peanut agglutinin lectin labels a glycoconjugate subserving a barrier function. We chose to investigate the distribution of this peanut-agglutinin-labelled glycoconjugate in the dorsal cochlear nucleus of the developing hamster since the development of the dorsal cochlear nucleus is well characterised and its axons obey laminar boundaries. The distribution of peanut agglutinin label throughout the cochlear nucleus delineated zones that cochlear axons fail to invade. In the dorsal cochlear nucleus, laminar differences were reduced on postnatal d 13 and virtually disappearing by postnatal d 23. Label in the molecular layer dissipated as axons and dendrites grew into this layer. These patterns of peanut agglutinin binding correspond to axonal ingrowth and are consistent with a barrier function for glycoconjugates in the molecular layer.

Specific roles of the alpha V beta 1, alpha V beta 3 and alpha V beta 5 integrins in avian neural crest cell adhesion and migration on vitronectin

To identify potentially important extracellular matrix adhesive molecules in neural crest cell migration, the possible role of vitronectin and its corresponding integrin receptors was examined in the adhesion and migration of avian neural crest cells in vitro. Adhesion and migration on vitronectin were comparable to those found on fibronectin and could be almost entirely abolished by antibodies against vitronectin and by RGD peptides. Immunoprecipitation and immunocytochemistry analyses revealed that neural crest cells expressed primarily the alpha V beta 1, alpha V beta 3 and alpha V beta 5 integrins as possible vitronectin receptors. Inhibition assays of cellular adhesion and migration with function-perturbing antibodies demonstrated that adhesion of neural crest cells to vitronectin was mediated essentially by one or more of the different alpha V integrins, with a possible preeminence of alpha V beta 1, whereas cell migration involved mostly the alpha V beta 3 and alpha V beta 5 integrins. Immunofluorescence labeling of cultured motile neural crest cells revealed that the alpha V integrins are differentially distributed on the cell surface. The beta 1 and alpha V subunits were both diffuse on the surface of cells and in focal adhesion sites in association with vinculin, talin and alpha-actinin, whereas the alpha V beta 3 and alpha V beta 5 integrins were essentially diffuse on the cell surface. Finally, vitronectin could be detected by immunoblotting and immunohistochemistry in the early embryo during the ontogeny of the neural crest. It was in particular closely associated with the surface of migrating neural crest cells. In conclusion, our study indicates that neural crest cells can adhere to and migrate on vitronectin in vitro by an RGD-dependent mechanism involving at least the alpha V beta 1, alpha V beta 3 and alpha V beta 5 integrins and that these integrins may have specific roles in the control of cell adhesion and migration.

Development of sensory innervation in chick skin: comparison of nerve fibre and chondroitin sulphate distributions in vivo and in vitro

In bird skin, nerve fibres develop in the dermis but do not enter the epidermis. In co-cultures of 7-day-old chick embryo dorsal root ganglia and epidermis, the neurites also avoid the epidermis. Previous studies have shown that chondroitin sulphate proteoglycans may be involved. Chondroitin sulphate has therefore been visualized by immunocytochemistry, using the monoclonal antibody CS-56, both in vivo and in vitro using light and electron microscopy. Its distribution was compared to those of 2 other chondroitin sulphate epitopes and to that of the growing nerve fibres. In cultures of epidermis from 7-day-old embryonic chicks, immunoreactivity is found uniformly around the epidermal cells while at 7.5 days the distribution in dermis is heterogeneous, and particularly marked in feather buds. In vivo, chondroitin sulphate immunoreactivity is detected in the epidermis, on the basal lamina, on the surfaces of fibroblasts and along collagen fibrils. This localization is complementary to the distribution of cutaneous nerves. Chondroitin sulphate in the basal lamina could prevent innervation of the epidermis and the dermal heterogeneities could partly explain the nerve fibres surrounding the base of the feathers. Chondroitin sulphate could therefore be important for neural guidance in developing chick skin.

Rostro-caudal polarity in the avian somite related to paraxial segmentation. A study on HNK-1, tenascin and neurofilament expression

Segmental organization of the vertebrate body is one of the major patterns arising during embryonic development. Somites that play an important role in this process show intrinsic patterns of gene expression and differentiation. The somites become polarized in all three dimensions, rostrocaudal, mediolateral and dorsoventral, the quadrants giving rise to several tissue components. The timing of polarization was studied by means of antibodies against HNK-1, tenascin and neurofilament. Whole mounts and serial sections of quail and chick embryos show that somites are already polarized at the moment of their segregation from the segmental plate. The rostral hemisomite carries the HNK-1 epitope preferentially, while the caudal hemisomite stains more strongly for tenascin. HNK-1-stained areas in the segmental plate strongly relate to the notochordal sheath, suggesting that axial structures determine the fate of paraxial structures. Neural crest cells were only seen to colonize the rostral part of a somite after they had differentiated into HNK-1 positive cells. Their colonization pattern seems to be guided by the segmental organization of the somite. Moreover, this somite organization probably dictates the organization of both sensory and motor fibres converging towards the segmental dorsal root ganglia, justifying a shift in the connections between neural tube and somites. This segmental shift takes place over one quarter of a somite length in a rostral direction.

Expression of the extracellular matrix glycoprotein tenascin in the somatosensory cortex of the mouse during postnatal development: an immunocytochemical and in situ hybridization analysis

Layer 4 of the rodent somatosensory cortex contains the barrel field which is the cortical representation of the whisker pad located on the contralateral side of the face. Each barrel within the barrel field is related one to one to its corresponding whisker both anatomically and physiologically. The astrocyte-derived extracellular matrix glycoprotein tenascin has been shown by immunocytochemistry to delineate the boundaries between barrels during their formation until the end of the second postnatal week. The present study describes the anatomical localization of tenascin mRNA expressing cells in the somatosensory cortex of the mouse from birth to postnatal day 15. During this time, a general down-regulation of tenascin-specific message was observed as a function of the state of maturation, with layers 5 and 6 down-regulating the message earlier than layers 1 and 2/3. Tenascin (as detected by immunocytochemistry) also revealed this gradual down-regulation with maturation. Layer 4 of the somatosensory cortex was different in that, with the onset of formation of barrel field boundaries at postnatal day 3, tenascin protein and mRNA were down-regulated more in layer 4 than in the upper and the lower layers of the somatosensory cortex and, interestingly, not in layer 4 of adjacent cortical areas. At postnatal day 6 tenascin immunoreactivity was most clearly distinguished in the barrel field boundaries while tenascin-specific mRNA was no longer detectable in layer 4. Down-regulation of tenascin message was also seen at P6 at the level of the enlarged barrel corresponding to an early postnatal lesioned row of whiskers. At postnatal day 15, tenascin protein and mRNA were no longer detectable in the somatosensory cortex. Distribution of glial fibrillary acidic protein immunoreactivity did not reveal any preferential accumulation of GFAP-positive radial glial processes in barrel field hollows versus barrel field boundaries at any stage.

Specification and segmentation of the paraxial mesoderm

Somite formation in the mouse embryo begins with the recruitment of mesenchymal cells into the paraxial mesoderm. Cells destined for the paraxial mesoderm are recruited from a progenitor population found first in the embryonic ectoderm and later in the primitive streak and the tail bud. Experimental evidence suggests that the allocation of precursor cells to different mesodermal lineages may be related to the site at which the cells ingress through the primitive streak. An increasing number of genes, such as those encoding growth factor and transcription factors, are now known to be expressed in the primitive streak. It is not known whether the specification of mesodermal cell fate has any relationship with the activity of genes that are expressed in the restricted cell populations of the primitive streak. Somitomeres, which are spherical clusters of mesenchymal cells in the presomitic mesoderm, presage the segmentation of somites in the paraxial mesoderm. The somitomeric organization denotes a pre-pattern of segmentation that defines the physical boundary and the bilateral symmetry of the mesodermal segments in the body axis. The establishment of new somitomeres seems to require the interaction of a resident cell population in the presomitic mesoderm and the incoming primitive streak cells. Cell mixing, which occurs in the somitomeres prior to somite segmentation, poses problems in understanding the developmental role of the somitomere and the real significance of the partitioning of the node-derived and primitive streak-derived cells in the mesodermal segments. In the presomitic mesoderm, the expression of some genes that encode transcription factors, growth factors or tyrosine kinase receptor, and the localization of certain cell adhesion molecules are closely associated with distinct morphogenetic events, such as cell clustering in the presomitic mesoderm and the formation of epithelial somites. There is, however, very little direct relationship between the spatial pattern of gene expression and the somitomeric organization in the presomitic mesoderm. Results of somite transplantation experiments suggest that both the segmental address and the morphogenetic characteristics of the somite may be determined during somite segmentation. Regional identity of the paraxial mesodermal segment is conferred by the expression of a combination of Hox genes in the sclerotome and probably other lineage-specific genes that are subject to imprinting. Superimposed on the global metameric pattern, two orthogonal polarities of cell differentiation are endowed in each mesodermal segment. The rostro-caudal polarity is established prior to somite segmentation. This polarity is later manifested by the subdivision of the sclerotome and the alliance of the neural crest cells and motor axons with the rostral half-somite.(ABSTRACT TRUNCATED AT 400 WORDS)

Tenascin: does it play a role in epidermal morphogenesis and homeostasis?

Tenascin is a large glycoprotein of the extracellular matrix. Its complex multidomain structure, along with its unique distribution during embryogenesis, inflammation, wound healing, and tumorigenesis suggest this protein may play a significant role in regulating cell proliferation, migration, and differentiation. In this review I will summarize the structural features of tenascin and its localization in skin and discuss some of the potential roles of tenascin in the regulation of keratinocyte biology.

Development of the spinal nerves in the mouse with special reference to innervation of the axial musculature

Development of the mouse spinal nerves was studied. On E11 (11th day of gestation), the primitive spinal nerve fascicle extended ventrally in the anterior half of the sclerotome. Spinal nerves in the forelimb region united with each other to form the primitive brachial plexus. Their terminal segment was covered by a peculiar cell mass. On E12, five primary branches developed along the primitive spinal nerve trunk. The ramus dorsalis was originally a cutaneous nerve, supplying two series of branches to the skin of the back. The medial series was derived from the dorsal ramus of C2-C8, and the lateral series from C8 and the more caudal dorsal rami. Nerves of the former series took the presegmental course through the intermyotomic space, while those of the latter the postsegmental course. The ramus cutaneous lateralis was a nerve that took the presegmental course to become cutaneous. The ramus intercostalis externus was a muscle branch whose distribution was restricted within the segment. The ramus anterior was a muscle branch from the end of the primitive spinal nerve trunk. The ramus visceralis connected a thoracic nerve with the para-aortic sympathetic cell cord. On E13-16 the ramus anterior secondarily gave off a cutaneous branch (ramus cutaneous anterior). The ramus intercostalis externus extended ventrally deep to the intercostalis externus muscle, crossing just caudal to the ramus cutaneous lateralis that secondarily gave off branches to the obliquus externus abdominis muscle.

Nervous tissue proteoglycans

The structure, biosynthesis, localization, and possible functional roles of nervous tissue glycosaminoglycans and proteoglycans were last reviewed several years ago. Since that time, there has been an exponential increase in publications on the neurobiology of proteoglycans. This review will therefore focus on reports which have appeared in the period after 1988, and especially on those concerning the properties of individual characterized nervous tissue proteoglycans. Related areas such as the regulation of glycosaminoglycan biosynthesis and the roles of cell surface proteoglycans in adhesion and growth control are covered in other contributions to this special topic issue.

Mammalian neural crest and neural crest derivatives

In the mammalian embryonic trunk, neural crest cells emigrate from the closed neural tube in a cranio-caudal sequences and appear to have similar migration pathways and derivatives to those of avian embryos. In the cranial region, however, there are mammalian-specific features, which are related to the mammalian-specific pattern of cranial neurulation. Midbrain and rostral hindbrain neural crest cells emigrate from widely open neural folds; caudal hindbrain crest emigrates in a caudo-rostral sequence, following the sequence of neural tube closure in this region. The forebrain is also a source of neural crest cells at early stages of neurulation; both forebrain and midbrain crest cells contribute to the frontonasal mesenchyme, although their relative contributions have not been analysed. Few studies have provided direct information about mammalian neural crest cell derivatives. Studies on the effects of retinoid excess on craniofacial development provide indirect evidence that mammalian cranial neural crest, like that of avian embryos, includes two populations whose differentiated phenotype and morphological tissue structure are determined prior to emigration. Retinoid-induced shortening of the preotic hindbrain leads to abnormal migration pathways of the neural crest cells that normally migrate into the mandibular arch to form Meckel's cartilage, so that an ectopic Meckel's cartilage-like structure forms in the maxillary region of the face. Slow descent of the heart in retinoid-exposed embryos enables the "wrong" crest cell population to populate the wall of the truncus arteriosus. These observations correlate well with observations of retinoid-induced craniofacial and heart abnormalities in human infants.

Different forms of 130 kD connective tissue protein are specific for boundaries in the nervous system and basement membrane of muscle cells in leech

The nervous system and muscle tissue of the leech express two different organ-specific forms of connective tissue protein. The nervous system-specific form appears in regional boundaries separating cell bodies, axonal tracts and areas of the neuropile during late embryogenesis. In contrast, the muscle-specific form appears earlier during development in the basement membrane of muscle cells. In extraction experiments both forms behave like extracellular matrix proteins and because of their molecular weight, are considered members of a group of cell type-specific 130 kD proteins (leech gp130s). However, the two forms differ in their posttranslational modification. As determined by Con A and lentil lectin affinity chromatography, only the nervous system-specific, but not the muscle-specific form, has fucosylated and high mannose N-linked carbohydrates. These differences in the developmental onset and glycosylation suggest that nervous system-specific and muscle-specific connective tissue proteins are regulated differently and participate in different molecular interactions.

Morphogenesis of the avian trunk neural crest: use of morphological techniques in elucidating the process

Morphological data generated from light and electron microscopy form the basis of our understanding of avian morphogenesis. Because chicken embryos are readily and cheaply obtained and are easily accessible for experimental manipulation, morphogenetic processes have been studied extensively in this species. Such studies have allowed us to identify the cells involved during morphogenesis, observe the shape changes or cellular translocations that accompany a morphogenetic process, and determine the timing of these events. Elucidation of the molecular basis of morphogenesis has awaited the integration of several additional approaches. Among these are experimental embryology, which has allowed us to understand cellular behavior associated with morphogenesis; immunocytochemistry, which has identified the macromolecular cues that regulate cell movements and the environmental factors that control them; and molecular techniques, which will permit us eventually to clarify the genetic regulation of morphogenesis. Although current research in development is heavily biased towards molecular biology, morphological studies continue to frame the questions that are now being addressed using molecular techniques. This review focuses on the cells of the neural crest as a model system where questions of avian morphogenesis have been profitably addressed.

Multiple integrins mediate cell attachment to cytotactin/tenascin

To identify potential cell surface receptors for chicken cytotactin (CT), we have characterized the ability of recombinant fusion proteins spanning the proximal fibronectin (FN) type III repeats of the molecule to support attachment of glioma and carcinoma cell lines. The third FN type III repeat, which contains the RGD tripeptide, supported cell attachment and cell spreading; however, mutation of RGD to RAD did not result in significant loss of either activity. In addition, the same repeat of mouse CT, which contains a natural mutant, RVD, also supported cell attachment and spreading, although at a lower level; both activities were increased by mutation of the RVD sequence to RGD. Studies utilizing RGD-containing peptides and well-characterized antibodies to integrins indicated that cell attachment to the third FN type III repeat was mediated by at least two different integrin receptors of the alpha v subtype. Additional cellular receptors may also be involved in cell attachment to CT. For example, an antibody to the beta 1 subfamily of integrins partially inhibited binding of cells to intact CT but did not inhibit cell binding to the third FN type III repeat. These findings suggest that the RGD site in CT is able to mediate cell attachment to integrins and thus is not a cryptic adhesion site. They also open the possibility that the functions of CT in processes such as counteradhesion, cell migration, cell proliferation, and cell differentiation may be mediated in part by interaction with multiple integrins.

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.

Dual function of tenascin: simultaneous promotion of neurite growth and inhibition of glial migration

The extracellular matrix molecule tenascin is expressed within the developing peripheral nervous system, first by migrating neural crest cells and later by satellite (Schwann precursor) cells at the growing tips of peripheral nerves. Here we found that the neurite promoting activity of tenascin for sensory neurons is developmentally regulated: very young sensory ganglia of stage 23 (4 days old) embryos grew neurites on tenascin as fast as on laminin and fibronectin. The growth response of older (day 7 and 9) ganglia on laminin and fibronectin was similar to that of 4-day-old ganglia, while on tenascin neurite growth occurred only after a lag phase and at a slower rate. Neurite growth on tenascin was inhibited by antibodies to beta 1 integrin and by heparin. While tenascin promotes neurite outgrowth of peripheral neurons, we found that it does not allow satellite cell migration when it is present on the substratum, and it inhibits migration of satellite cells on fibronectin when added in soluble form. In contrast, soluble tenascin did not significantly alter the rate of neurite growth on tenascin, fibronectin or laminin substrata, although neurites were straighter and less attached. When isolated satellite cells were added to neurites grown on tenascin, they preferentially adhered to and elongated along neurite surfaces. Using patterned substrata of tenascin versus fibronectin or laminin confirmed that tenascin borders allow neurites to pass but act as barriers to migrating satellite cells. We postulate that tenascin or related molecules with dual functions in cell adhesion are important for peripheral nerve morphogenesis. Tenascin allows axonal growth, but may restrict random satellite cell migration into the fibronectin-rich mesenchyme, thereby inducing the compaction of nerve fascicles.

Immunohistochemical evaluation of epidermis overlying basal cell carcinomas

We have examined the character and carcinogenic properties of the normal-appearing epidermis overlying basal cell carcinomas by immunohistochemical methods, employing a series of monoclonal antibodies. The labelling index was significantly increased in the atrophic epidermis overlying basal cell carcinomas (solid type, n = 20), compared with the epidermis overlying or adjacent to squamous cell carcinoma (n = 20), keratoacanthoma (n = 10), dermatofibroma (n = 10), neurofibroma (n = 10), soft fibroma (n = 10), pyogenic granuloma (n = 10) and cutaneous leiomyoma (n = 5). Cells which expressed epidermal growth factor (EGF) receptor were detected in all layers of the epidermis over the basal cell carcinomas, but not the other tumours. Basement membrane-related antigens, including bullous pemphigoid antigen and GB3 antigen, were decreased in the epidermis. AE1, the monoclonal antibody against basal cell keratin, reacted with the uppermost layers of the normal-appearing epidermis overlying the basal cell carcinomas. ICAM-1 expression was very weak in the overlying epidermis. The dermis subjacent to the proliferating epidermis showed staining for transforming growth factor-alpha (TGF-alpha), strong positive PECAM-1 staining of endothelium, and numerous HLA-DR-positive cells. From these results, we suggest that the proliferative activity in the epidermis overlying basal cell carcinomas is not a state induced by the dermal infiltrate, but represents carcinogenic activity of the epidermis.

Nervous tissue proteoglycans

The structure, biosynthesis, localization, and possible functional roles of nervous tissue glycosaminoglycans and proteoglycans were last reviewed several years ago. Since that time, there has been an exponential increase in publications on the neurobiology of proteoglycans. This review will therefore focus on reports which have appeared in the period after 1988, and especially on those concerning the properties of individual characterized nervous tissue proteoglycans. Related areas such as the regulation of glycosaminoglycan biosynthesis and the roles of cell surface proteoglycans in adhesion and growth control are covered in other contributions to this special topic issue.

Tissue variation of two large chondroitin sulfate proteoglycans (PG-M/versican and PG-H/aggrecan) in chick embryos

PG-M and PG-H, chick large chondroitin sulfate proteoglycans corresponding to versican (fibroblast-type proteoglycan) and aggrecan (cartilage-characteristic proteoglycan), respectively, which are found in mammals, have been characterized in various tissues of chick embryos. Their distribution and the compositions of the core molecules were analyzed by immunofluorescence staining and immunoblotting, respectively, using various monospecific antibodies. Molecules reactive to a monoclonal antibody to the PG-M core protein (designated MY-174) were distributed in various tissues, including aorta, lung, cornea, brain, skeletal muscle and dermis. Immunoblotting with MY-174 of the chondroitinase ABC-digested tissue extracts showed a tissue variation of MY-174-reactive core molecules (550-kD, 500-kD, 450-kD, and 350-300-kD). In contrast, PG-H, besides massive occurrence in cartilage, was only found in a few tissues such as aorta and brain. In addition, PG-H in aorta, cornea, and skin was atypical in structure, because it lacked keratan sulfate. The expression of PG-M in developing chick embryos was then examined. PG-M was found in some developmentally active areas, such as the perinotochordal mesenchyme between notochord and neural tube, the basement membranes facing neuroepithelial cells, and condensing mesenchymal cells in limb buds, suggesting some functions distinctive of the developing tissues.

Adaptation of a non-radioactive in situ hybridization method to electron microscopy: detection of tenascin mRNAs in mouse cerebellum with digoxigenin-labelled probes and gold-labelled antibodies

In this study we describe a method for the detection of mRNAs at the ultrastructural level using a non-radioactive in situ hybridization method based on digoxigenin-labelled cRNA probes and gold-labelled digoxigenin-specific antibodies. We applied this protocol to an analysis of the expression of the extracellular matrix protein tenascin in the developing cerebellar cortex of the mouse. To gain an impression of the sensitivity attainable with digoxigenin-labelled probes, we first established at the light microscopic level that the hybridization signal obtained with the non-radioactive probe is as sensitive as that obtained with a 35S-labelled probe. The non-radioactive hybridization protocol was then combined with electron microscopic post-embedding and immunogold detection techniques. Tenascin-specific, digoxigenin-labelled cRNA probes were hybridized to ultrathin sections of Lowicryl K4M-embedded tissue and the probe/target mRNA hybrids were detected using gold-labelled antibodies to digoxigenin. In agreement with the observations from in situ hybridization at the light microscopic level, specific labelling was observed in Golgi epithelial cells in the region of the Purkinje cell layer and cells in the internal granular layer, which could be identified as astrocytes by ultrastructural criteria. Labelling was detectable in association with free ribosomes and ribosomes of the rough endoplasmic reticulum. In addition, focal hybridization signals were occasionally found in the nucleus. No signal was observed in Golgi epithelial cells or astrocytes using sense or in any other cerebellar cell type using either sense or anti-sense probes. The described in situ hybridization technique uses ultrastructural criteria to associate the presence of a given mRNA species with a particular cell type. Additionally, it provides information about the target mRNA's subcellular distribution, thus offering the possibility to study intracellular transport of particular mRNAs.

Environmental influences on neural crest cell migration

Neural crest cells migrate extensively and interact with numerous tissues and extracellular matrix components during their movement. Cell marking techniques have shown that neural crest cells in the trunk of the avian embryo migrate through the anterior, but not posterior, half of each sclerotome and avoid the region around the notochord. A possible mechanism to account for this migratory pattern is that neural crest cells may be inhibited from entering the posterior sclerotome and the perinotochordal space. Thus, interactions with other tissue may prescribe the pattern of neural crest cell migration in the trunk. In contrast, interactions between neural crest cells and the extracellular matrix may mediate the primary interactions controlling neural crest cells migration in the head region.

Interaction of astrochondrin with extracellular matrix components and its involvement in astrocyte process formation and cerebellar granule cell migration

We have recently characterized a chondroitin sulfate proteoglycan from the murine central nervous system which is expressed by astrocytes in vitro and carries the L2/HNK-1 and L5 carbohydrate structures. In the present study, we provide evidence that its three core proteins of different size are similar in their proteolytic peptide maps and thus designate this group of structurally related molecules astrochondrin. During development, astrochondrin and the L5 carbohydrate were hardly detectable in the brain of 14-d-old mouse embryos by Western blot analysis. Expression of astrochondrin and the L5 epitope was highest at postnatal day 8, the peak of cerebellar granule cell migration and Bergmann glial process formation, and decreased to weakly detectable levels in the adult. Immunocytochemical localization of astrochondrin in the cerebellar cortex of 6-d-old mice showed association of immunoreactivity with the cell surface of astrocytes, including Bergmann glial processes and astrocytes in the internal granular layer or prospective white matter. Endfeet of astrocytes contacting the basal lamina of endothelial and meningeal cells and contact sites between Bergmann glial processes and granule cells also showed detectable levels of astrochondrin. Furthermore, granule cell axons in the molecular layer were astrochondrin immunoreactive. In the adult, astrochondrin immunoreactivity was weakly present in the internal granular layer and white matter. Both Fab fragments of polyclonal antibodies to astrochondrin and monovalent fragments of the L5 monoclonal antibody reduced the formation of processes of mature GFAP-positive astrocytes on laminin and collagen type IV, but not on fibronectin as substrata. Interestingly, the initial attachment of astrocytic cell bodies was not disturbed by these antibodies. Antibodies to astrochondrin also reduced the migration of granule cells in the early postnatal mouse cerebellar cortex. In a solid phase radioligand binding assay, astrochondrin was shown to bind to the extracellular matrix components laminin and collagen type IV, being enhanced in the presence of Ca2+, but not to fibronectin, J1/tenascin or other neural recognition molecules. Furthermore, astrochondrin interacted with collagen types III and V, less strongly with collagen types I, II, and IX, but not with collagen type VI. The interaction of astrochondrin with collagen types III and V was saturable and susceptible to increasing ionic strength, and could be competed by chondroitin sulfate, heparin, and dextran sulfate, but not by hyaluronic acid, glucose-6-phosphate, or neuraminic acid.(ABSTRACT TRUNCATED AT 400 WORDS)

Tenascin expression in the mouse: in situ localization and induction in vitro by bFGF

The glycoprotein tenascin is found in the extracellular matrix in regions of cell motility, cell proliferation, and tissue modelling. We have used novel tenascin cDNA probes to localize tenascin transcripts in the developing mouse and to study the regulation of tenascin expression by growth factors in vitro. At postnatal day 1 tenascin mRNAs are abundant in regions of bone and cartilage formation, as well as in the ependymal layer of the central nervous system. Previous studies have demonstrated that transforming growth factor-beta type 1 (TGF-beta 1) can induce tenascin expression in vitro. As TGF-beta 1 is absent or scarce in the developing brain, it is likely that other growth factors, alone or in addition to TGF-beta 1, may regulate tenascin expression during development. Therefore, we have compared the effects of TGF-beta 1 and a growth factor that is found in both developing connective tissue and the central nervous system, basic fibroblast growth factor (bFGF), on tenascin expression in a mouse embryo fibroblast cell line (Swiss 3T3 cells). Immuno-slot blot analysis of Swiss 3T3 cell-conditioned culture medium demonstrates that bFGF is a more potent inducer of tenascin expression than TGF-beta 1. Furthermore, bFGF and TGF-beta 1 have an additive effect on levels of tenascin, but not fibronectin, in the conditioned medium. Western blots revealed that different forms of tenascin are induced by bFGF and TGF-beta 1: the tenascin induced by the former has a molecular mass of approximately 250 kDa, the latter induces an approximately 200 kDa form of tenascin. The induction of large tenascin by bFGF was confirmed by northern blot analysis, which revealed increased levels of an 8 kb tenascin transcript after 24 h by as little as 4 ng/ml of bFGF in serum-free medium. Thus bFGF, alone or in combination with TGF-beta 1, is a potential regulator of tenascin expression in vitro. bFGF may alter not only the relative abundance of tenascin and fibronectin in the extracellular matrix, but also the splice variant of tenascin expressed by a given cell type.

Development of the dorsal root ganglion in a teleost, Oreochromis mossambicus (Peters)

The precursor crest cells of the spinal dorsal root ganglia (DRG) in the tilapia, Oreochromis mossambicus, were analysed by HNK-1 antibody staining, scanning electron microscopy, and DiI labeling techniques. The ontogeny of the DRG was followed in the embryos and young fry of the fish. Neural crest cells which contribute to the formation of the DRG were observed to commence their migration in the trunk region after 40 hours postfertilization. They do not penetrate the somites but travel through the space between the neural tube and the somite. Crest cells destined to become the DRG accumulate at the midsomitic region where the ventral root exits. At 50 to 80 hours postfertilization, they differentiate and become bipolar sensory cells. The DRG continues to grow and develop right through hatching at 115 hours. During the early larval stages, crest cells accumulate around the ventral root and the DRG eventually fuses with the motor root, giving rise to a situation in which the DRG contains not only the sensory cells but also motor fibres. The mixed nature of the DRG was confirmed by HRP retrograde labeling. We believe that this is the first report in describing the formation of the DRG in a teleost.

Alpha 1 beta 1 integrin on neural crest cells recognizes some laminin substrata in a Ca(2+)-independent manner

Neural crest cells migrate along pathways containing laminin and other extracellular matrix molecules. In the present study, we functionally and biochemically identify an alpha 1 beta 1 integrin heterodimer which bears the HNK-1 epitope on neural crest cells. Using a quantitative cell adhesion assay, we find that this heterodimer mediates attachment to laminin substrata prepared in the presence of Ca2+. Interestingly, neural crest cells bind to laminin-Ca2+ substrata in the presence or absence of divalent cations in the cell attachment medium. In contrast, the attachment of neural crest cells to laminin substrata prepared in the presence of EDTA, heparin, Mg2+, or Mn2+ requires divalent cations. Interactions with these laminin substrata are mediated by a different integrin heterodimer, since antibodies against beta 1 but not alpha 1 integrins inhibit neural crest cell attachment. Thus, the type of laminin substratum appears to dictate the choice of laminin receptor used by neural crest cells. The laminin conformation is determined by the ratio of laminin to Ca2+, though incorporation of heparin during substratum polymerization alters the conformation even in the presence of Ca2+. Once polymerized, the substratum appears stable, not being altered by soaking in either EDTA or divalent cations. Our findings demonstrate: (a) that the alpha 1 beta 1 integrin can bind to some forms of laminin in the absence of soluble divalent cations; (b) that substratum preparation conditions alter the conformation of laminin such that plating laminin in the presence of Ca2+ and/or heparin modulates its configuration; and (c) that neural crest cells utilize different integrins to recognize different laminin conformations.

Specific binding of cytotactin to sulfated glycolipids

The binding of the glial glycoprotein, cytotactin, to a variety of purified glycolipids was examined. Clear-cut evidence was found for binding of radiolabeled cytotactin to sulfatides purified from bovine brain, but the molecule did not bind to gangliosides or cerebrosides. The sulfatide binding was sensitive to pH and ionic strength and was dependent on the presence of divalent cations. Binding was inhibited by purified unlabeled cytotactin, by polyclonal antibodies to cytotactin, and by several monosaccharides and polysaccharides. It was not inhibited by fibronectin, a chondroitin sulfate proteoglycan, or the HNK-1 monoclonal antibody, all of which are known to bind to cytotactin. These findings raise the possibilities that sulfated glycolipids may function as cellular receptors for cytotactin and that binding by sulfatides may modulate the varied effects of cytotactin on cellular processes.

Cranial and trunk neural crest cells use different mechanisms for attachment to extracellular matrices

We have used a quantitative cell attachment assay to compare the interactions of cranial and trunk neural crest cells with the extracellular matrix (ECM) molecules fibronectin, laminin and collagen types I and IV. Antibodies to the beta 1 subunit of integrin inhibited attachment under all conditions tested, suggesting that integrins mediate neural crest cell interactions with these ECM molecules. The HNK-1 antibody against a surface carbohydrate epitope under certain conditions inhibited both cranial and trunk neural crest cell attachment to laminin, but not to fibronectin. An antiserum to alpha 1 intergrin inhibited attachment of trunk, but not cranial, neural crest cells to laminin and collagen type I, though interactions with fibronectin or collagen type IV were unaffected. The surface properties of trunk and cranial neural crest cells differed in several ways. First, trunk neural crest cells attached to collagen types I and IV, but cranial neural crest cells did not. Second, their divalent cation requirements for attachment to ECM molecules differed. For fibronectin substrata, trunk neural crest cells required divalent cations for attachment, whereas cranial neural crest cells bound in the absence of divalent cations. However, cranial neural crest cells lost this cation-independent attachment after a few days of culture. For laminin substrata, trunk cells used two integrins, one divalent cation-dependent and the other divalent cation-independent (Lallier, T. E. and Bronner-Fraser, M. (1991) Development 113, 1069–1081). In contrast, cranial neural crest cells attached to laminin using a single, divalent cation-dependent receptor system. Immunoprecipitations and immunoblots of surface labelled neural crest cells with HNK-1, alpha 1 integrin and beta 1 integrin antibodies suggest that cranial and trunk neural crest cells possess biochemically distinct integrins. Our results demonstrate that cranial and trunk cells differ in their mechanisms of adhesion to selected ECM components, suggesting that they are non-overlapping populations of cells with regard to their adhesive properties.

Characterization of multiple adhesive and counteradhesive domains in the extracellular matrix protein cytotactin

The extracellular matrix molecule cytotactin is a multidomain protein that plays a role in cell migration, proliferation, and differentiation during development. To analyze the structure-function relationships of the different domains of this glycoprotein, we have prepared a series of fusion constructs in bacterial expression vectors. Results obtained using a number of adhesion assays suggest that at least four independent cell binding regions are distributed among the various cytotactin domains. Two of these are adhesive; two others appear to be counteradhesive in that they inhibit cell attachment to otherwise favorable substrates. The adhesive regions were mapped to the fibronectin type III repeats II-VI and the fibrinogen domain. The morphology of the cells plated onto these adhesive fragments differed; the cells spread on the fibronectin type III repeats as they do on fibronectin, but remained round on the fibrinogen domain. The counteradhesive properties of the molecule were mapped to the EGF-like repeats and the last two fibronectin type III repeats, VII-VIII. The latter region also contained a cell attachment activity that was observed only after proteolysis of the cells. Several cell types were used in these analyses, including fibroblasts, neurons, and glia, all of which are known to bind to cytotactin. The different domains exert their effects in a concentration-dependent manner and can be inhibited by an excess of the soluble molecule, consistent with the hypothesis that the observed properties are mediated by specific receptors. Moreover, it appears that some of these receptors are restricted to particular cell types. For example, glial cells bound better than neurons to the fibrinogen domain and fibroblasts bound better than glia and neurons to the EGF fragment. These results provide a basis for understanding the multiple activities of cytotactin and a framework for isolating different receptors that mediate the various cellular responses to this molecule.

Neuronal cell adhesion molecule contactin/F11 binds to tenascin via its immunoglobulin-like domains

Adhesive interactions between neurons and extracellular matrix (ECM) play a key role in neuronal pattern formation. The prominent role played by the extracellular matrix protein tenascin/cytotactin in the development of the nervous system, tied to its abundance, led us to speculate that brain may contain yet unidentified tenascin receptors. Here we show that the neuronal cell adhesion molecule contactin/F11, a member of the immunoglobulin(Ig)-superfamily, is a cell surface ligand for tenascin in the nervous system. Through affinity chromatography of membrane glycoproteins from chick brain on tenascin-Sepharose, we isolated a major cell surface ligand of 135 kD which we identified as contactin/F11 by NH2-terminal sequencing. The binding specificity between contactin/F11 and tenascin was demonstrated in solid-phase assays. Binding of immunopurified 125I-labeled contactin/F11 to immobilized tenascin is completely inhibited by the addition of soluble tenascin or contactin/F11, but not by fibronectin. When the fractionated isoforms of tenascin were used as substrates, contactin/F11 bound preferentially to the 190-kD isoform. This isoform differs in having no alternatively spliced fibronectin type III domains. Our results imply that the introduction of these additional domains in some way disrupts the contactin/F11 binding site on tenascin. To localize the binding site on contactin/F11, proteolytic fragments were generated and characterized by NH2-terminal sequencing. The smallest contactin/F11 fragment which binds tenascin is 45 kD and also begins with the contactin/F11 NH2-terminal sequence. This implies that contactin/F11 binds to tenascin through a site within the first three Ig-domains.

Expression of tenascin mRNA in mesoderm during Xenopus laevis embryogenesis: the potential role of mesoderm patterning in tenascin regionalization

In Xenopus embryos, the extracellular matrix (ECM) protein tenascin (TN) is expressed dorsally in a very restricted pattern. We have studied the spatial and temporal expression of TN mRNA in tailbud-stage embryos by RNAase protection and in situ hybridization using a cDNA probe for Xenopus TN obtained by PCR amplification. We report that TN transcripts are principally expressed in cells dispersed around the neural tube and notochord as well as in myotome and sclerotome cells. No TN mRNA could be detected in lateral plate mesoderm, but expression was detectable beneath tail fin epidermis. In a second series of experiments, we studied the expression of TN mRNA and protein in combinations between animal and vegetal stage-6 blastomeres and in stage-8 blastula animal caps treated with activin A or basic fibroblastic growth factor (b-FGF). Isolated animal cap tissue cultured alone differentiates into epidermis, which expresses neither TN protein nor TN mRNA. TN expression is, however, elicited in response to isolated dorsal vegetal blastomeres and in response to high concentrations of activin, both of which treatments lead to formation of muscle and/or notochord. Low concentrations of activin, and ventral vegetal blastomeres, treatments that induce mesoderm of ventral character, are poor inducers of TN. However, b-FGF, which also induces ventral mesoderm, elicits strong expression. These results indicate that TN regionalization is a complex process, dependent both on the pattern of differentiation of mesodermal tissues and on the agent with which they are induced. The data further show that “ventral mesoderm” induced by low concentrations of activin is distinct from that induced by b-FGF, and imply that activin induces ventral mesoderm of the trunk while b-FGF induces posterior mesoderm of the tailbud.

The somitogenetic potential of cells in the primitive streak and the tail bud of the organogenesis-stage mouse embryo

The developmental potency of cells isolated from the primitive streak and the tail bud of 8.5- to 13.5-day-old mouse embryos was examined by analyzing the pattern of tissue colonization after transplanting these cells to the primitive streak of 8.5-day embryos. Cells derived from these progenitor tissues contributed predominantly to tissues of the paraxial and lateral mesoderm. Cells isolated from older embryos could alter their segmental fate and participated in the formation of anterior somites after transplantation to the primitive streak of 8.5-day host embryo. There was, however, a developmental lag in the recruitment of the transplanted cells to the paraxial mesoderm and this lag increased with the extent of mismatch of developmental ages between donor and host embryos. It is postulated that certain forms of cell-cell or cell-matrix interaction are involved in the specification of segmental units and that there may be age-related variations in the interactive capability of the somitic progenitor cells during development. Tail bud mesenchyme isolated from 13.5-day embryos, in which somite formation will shortly cease, was still capable of somite formation after transplantation to 8.5-day embryos. The cessation of somite formation is therefore likely to result from a change in the tissue environment in the tail bud rather than a loss of cellular somitogenetic potency.

The role of matrix molecules in regeneration of leech CNS

Extracellular matrix (ECM) molecules extracted from the leech central nervous system (CNS) provide substrates that induce extensive growth of processes of identified leech nerve cells in culture. Two ECM molecules, laminin and tenascin, have been identified. The laminin-like molecule has been purified and shown to be a cross-shaped molecule similar to vertebrate laminin with subunits of 340, 220, 180, and 160 kD. Purified laminin as a substrate induces rapid outgrowth of Retzius (R) and Anterior Pagoda (AP) cells in culture. The tenascin molecule has been partially purified. In electronmicrographs, leech tenascin, like vertebrate tenascin, has six arms of equal size joined in a central globule. Highly enriched fractions of leech tenascin induce rapid and extensive outgrowth of Retzius and AP cells in culture. Substrate molecules not only induce outgrowth of processes but also affect the growth patterns of individual nerve cells. Neurites are straight with few branches in laminin, but curved with profuse branches on tenascin. During regeneration of the CNS in the animal, laminin appears at new sites associated with growth cones. The appearance of laminin correlates with the accumulation of microglial cells. Thus, ECM molecules with growth-promoting activity for leech nerve cells in vitro appear to be involved in inducing regeneration and allowing the neurites to reconnect with former targets.

Communication compartments in the axial mesoderm of the chick embryo

Intracellular microinjection of the fluorescent tracer Lucifer Yellow into mesoderm cells along the rostrocaudal axis of the early chick embryo has revealed compartments where the intercellular diffusion of dye, presumably via gap junctions, is restricted at the borders between groups of cells. Cells in the segmental plate were dye-coupled, as were cells forming the epithelial somites. However, dye-coupling was not observed between different somites, nor was it observed between the outer epithelial cells and the cells in the somitocoele. On dispersal of the somite, dermatome cells were dye-coupled. However, sclerotome cells were found to be divided into rostral and caudal compartments separated by a group of cells bordering the intrasclerotomal fissure (of von Ebner) that also exhibited dye-coupling, restricted primarily to cells along the fissure. Some of these compartment borders can be accounted for by the presence of a morphological barrier which reduces cell-cell contact, but others are more difficult to explain, as there appears to be extensive cell-cell contact across the border. This would be analogous to some compartments found in insects. Some of the compartments also have borders similar to those described by cell lineage studies. The results also indicate that dye-coupling becomes restricted in a spatial and temporal manner as the mesodermal cells mature.

Expression of cell adhesion molecules during initiation and cessation of neural crest cell migration

Because of their distribution and known ability to promote neuronal adhesion, it has been proposed that N-CAM and N-cadherin are involved in the formation of the nervous system. Here, we examine the expression of these molecules during the initiation and cessation of trunk neural crest cell migration during the formation of the peripheral nervous system. Whereas other neural tube cells express N-cadherin, the dorsal neural tube containing neural crest precursors has little or no N-cadherin immunoreactivity. In contrast, N-CAM is expressed in the dorsal neural tube and on early migrating neural crest cells, from which it gradually disappears during migration. Both N-CAM and N-cadherin are absent from neural crest cells at advanced stages of migration. As neural crest cells cease migration and condense to form dorsal root and sympathetic ganglia, N-cadherin but not N-CAM is observed on the forming ganglia, identified by neurofilament expression and the aggregation of HNK-1 reactive cells. The results demonstrate that the absence of N-cadherin correlates with the onset of neural crest migration and its reappearance correlates with cessation of migration and precedes gangliogenesis.

A segmented pattern of cell death during development of the chick embryo

During the early development of the chick embryo, specific groups of cells die in characteristic patterns. In this study, Nile Blue sulphate staining was used to reveal a novel pattern of segmentally repeated cell death in the paraxial mesoderm of the chick prior to stage 23. This pattern varies according to the developmental stage of the embryo and shifts rostrocaudally, corresponding to progressing somite differentiation. Initially, during early somite differentiation, cell death is restricted to the rostral half of the somite (the rostral pattern of cell death). After the somite has differentiated into dermomyotome and sclerotome, dead cells appear in superficial tissues in a pyramidal pattern which lies in register (rostrocaudally) with the central part of the sclerotome. Finally, small bands of dying cells are seen between the neural tube and the expanding sclerotome. This third pattern (the ventral path) lies in register with the rostral part of the caudal half of the sclerotome. We show by fluorescent labelling of the migrating neural crest that these patterns of cell death correspond to the routes of neural crest migration. In addition, serial sectioning of stage 23 chick embryos confirms that the position of dying cells correlates with the known routes of neural crest migration and with the sites of development of certain neural crest-derived tissues.

Activation of the cytotactin promoter by the homeobox-containing gene Evx-1

Cytotactin is a morphoregulatory molecule of the extracellular matrix affecting cell shape, division, and migration that appears in a characteristic and complex site-restricted pattern during embryogenesis. The promoter region of the gene that encodes chicken cytotactin contains a variety of potential regulatory sequences. These include putative binding sites for homeodomain proteins and a phorbol 12-O-tetradecanoate 13-acetate response element (TRE)/AP-1 element, a potential target for transcription factors thought to be involved in growth-factor signal transduction. To determine the effects of homeobox-containing genes on cytotactin promoter activity, we conducted a series of cotransfection experiments on NIH 3T3 cells using cytotactin promoter-chloramphenicol acetyltransferase (CAT) reporter gene constructs and plasmids driving the expression of mouse homeobox genes Evx-1 and Hox-1.3. cotransfection with Evx-1 stimulated cytotactin promoter activity whereas cotransfection in control experiments with Hox-1.3 had no effect. To localize the sequences required for Evx-1 activation, we tested a series of deletions in the cytotactin promoter. An 89-base-pair region containing a consensus TRE/AP-1 element was found to be required for activation. An oligonucleotide segment containing this TRE/AP-1 site was found to confer Evx-1 inducibility on a simian virus 40 minimal promoter; mutation of the TRE/AP-1 site abolished this activity. To explore the potential role of growth factors in cytotactin promoter activation, chicken embryo fibroblasts, which are known to synthesize cytotactin, were first transfected with cytotactin promoter constructs and cultured under minimal conditions in 1% fetal bovine serum. Although the cells exhibited only low levels of CAT activity under these conditions, cells exposed for 12 h to 10% (vol/vol) fetal bovine serum showed a marked increase in CAT activity. Cotransfection with Evx-1 and cytotactin promoter constructs of cells cultured in 1% fetal bovine serum was sufficient, however, to produce high levels of CAT activity. These findings are consistent with the hypothesis that Evx-1, a homeobox-containing gene, may activate the cytotactin promoter by a mechanism involving a growth-factor signal transduction pathway. More generally, the results support the hypothesis that the place-dependent expression of morphoregulatory molecules may depend upon local cues provided by homeobox genes and their encoded proteins.

Tenascin promotes cerebellar granule cell migration and neurite outgrowth by different domains in the fibronectin type III repeats

The extracellular matrix molecule tenascin has been implicated in neuron-glia recognition in the developing central and peripheral nervous system and in regeneration. In this study, its role in Bergmann glial process-mediated neuronal migration was assayed in vitro using tissue explants of the early postnatal mouse cerebellar cortex. Of the five mAbs reacting with nonoverlapping epitopes on tenascin, mAbs J1/tn1, J1/tn4, and J1/tn5, but not mAbs J1/tn2 and J1/tn3 inhibited granule cell migration. Localization of the immunoreactive domains by EM of rotary shadowed tenascin molecules revealed that the mAbs J1/tn4 and J1/tn5, like the previously described J1/tn1 antibody, bound between the third and fifth fibronectin type III homologous repeats and mAb J1/tn3 bound between the third and fifth EGF-like repeats. mAb J1/tn2 had previously been found to react between fibronectin type III homologous repeats 10 and 11 of the mouse molecule (Lochter, A., L. Vaughan, A. Kaplony, A. Prochiantz, M. Schachner, and A. Faissner. 1991. J. Cell Biol. 113:1159-1171). When postnatal granule cell neurons were cultured on tenascin adsorbed to polyornithine, both the percentage of neurite-bearing cells and the length of outgrowing neurites were increased when compared to neurons growing on polyornithine alone. This neurite outgrowth promoting effect of tenascin was abolished only by mAb J1/tn2 or tenascin added to the culture medium in soluble form. The other antibodies did not modify the stimulatory or inhibitory effects of the molecule. These observations indicate that tenascin influences neurite outgrowth and migration of cerebellar granule cells by different domains in the fibronectin type III homologous repeats.

Wound healing of the ocular surface

Wound healing is a complex, long-lasting regulatory sequence that involves expression of a number of genes, which are active during the individual's development. Some of the phenomena differ from normal tissue turnover and growth only quantitatively. This article reviews the current data on corneal wound healing, with particular reference to mesenchymal matrix proteins and their integrin receptors, to growth factors and to proteolytic enzymes. Some inflammatory mediators are also discussed. The theoretical basis for therapeutic interventions is also discussed briefly, in the light of present knowledge.

Macrophage functions are regulated by murine decidual and tumor extracellular matrices

Because of their paternal antigens, the fetus and placenta may be considered an allograft in the maternal host. Understanding the mechanisms which prevent maternal immunological rejection of the fetus remains a fundamental unsolved problem in immunology. We have previously reported that macrophages are inhibited by maternal decidual stromal cells residing at the maternal-fetal interface. In view of the central role of macrophages in cell-mediated immunity, this inhibition may contribute to preventing maternal antifetal responses. We now report that it was the solid phase signals embedded in the extracellular matrix (ECM) made by decidual cells which are responsible for inhibiting macrophage-mediated lysis of TNF-alpha-resistant P815 mastocytoma cells. The latter macrophage function is acquired after stimulation by interferon gamma and endotoxin. All these macrophage functions were also inhibited by ECM isolated from the Engelberth-Holm-Swarme (EHS) tumor. This tumor ECM has a similar biochemical composition to decidual ECM. This ECM inhibited the effector, as opposed to the stimulator, phase of macrophage-mediated tumor lysis. Laminin, type IV collagen, and heparan sulfate proteoglycans, the major known components of decidual and EHS ECMs, did not inhibit the above macrophage functions. Altogether these data indicate that macrophages were inhibited by solid phase signals embedded in decidual and EHS ECMs. Whether the solid phase signals in these two ECMs are biochemically identical remains to be determined. To our knowledge, such signals are a novel pathway of inhibiting macrophage functions which may be important in understanding the maternal-fetal immunologic relationship, and the pathogenesis of perinatal infections. Furthermore, the ability of EHS tumor ECM to inhibit macrophage functions may indicate that some tumors may defend themselves against host macrophage responses using solid phase signals. This may be important in understanding some host-tumor relationships.

Cytotactin binding: inhibition of stimulated proliferation and intracellular alkalinization in fibroblasts

Cytotactin is an extracellular matrix protein that is dynamically and transiently expressed in a place-dependent fashion during development by glial cells, fibroblasts, and several other cell types. In the present study, the effects of cytotactin on cell proliferation were examined in fibroblastic cells in culture. NIH 3T3 mouse cells plated on tissue culture substrata in the presence of soluble cytotactin remained rounded for longer periods than untreated control cells, similar to their response to cytotactin-coated substrates. These rounding effects could be prevented by pretreatment of the cells with nocodazole, a microtubule-disrupting agent. Cytotactin inhibited the proliferation of fibroblasts in culture in a dose- and time-dependent manner, and this inhibition occurred even after nocodazole treatment. In addition, the presence of cytotactin inhibited proliferation stimulated by growth factors or tumor promoter. These effects on cell growth were accompanied by an early inhibition of the intracellular alkalinization that normally occurs upon mitogenic stimulation by a number of growth-promoting agents. Together these observations suggest that cytotactin is an endogenous cell surface modulatory protein and provide a possible mechanism whereby cytotactin may contribute to pattern formation during development, regeneration, tumorigenesis, and wound healing.

Focal adhesion integrity is downregulated by the alternatively spliced domain of human tenascin

Tenascin, together with thrombospondin and SPARC, form a family of matrix proteins that, when added to bovine aortic endothelial cells, caused a dose-dependent reduction in the number of focal adhesion-positive cells to approximately 50% of albumin-treated controls. For tenascin, a maximum response was obtained with 20-60 micrograms/ml of protein. The reduction in focal adhesions in tenascin-treated spread cells was observed 10 min after addition of the adhesion modulator, reached the maximum by 45 min, and persisted for at least 4 h in the continued presence of tenascin. This effect was fully reversible, was independent of de novo protein synthesis, and was neutralized by a polyclonal antibody to tenascin. Monoclonal antibodies to specific domains of tenascin (mAbs 81C6 and 127) were used to localize the active site to the alternatively spliced segment of tenascin. Furthermore, a recombinant protein corresponding to the alternatively spliced segment (fibronectin type III domains 6-12) was expressed in Escherichia coli and was active in causing loss of focal adhesions, whereas a recombinant form of a domain (domain 3) containing the RGD sequence had no activity. Chondroitin-6-sulfate effectively neutralized tenascin activity, whereas dermatan sulfate and chondroitin-4-sulfate were less active and heparan sulfate and heparin were essentially inactive. Studies suggest that galactosaminoglycans neutralize tenascin activity through interactions with cell surface molecules. Overall, our results demonstrate that tenascin, thrombospondin, and SPARC, acting as soluble ligands, are able to provoke the loss of focal adhesions in well-spread endothelial cells.