Distribution of laminin in the developing peripheral nervous system of the chick

During axonal elongation in the developing peripheral nervous system, the temporal and spatial distribution of adhesive molecules in extracellular matrices and on neighboring cell surfaces may provide "choices" of pathways for growth cone migration. The extracellular matrix glycoprotein laminin appears in early embryos and mediates neuronal adhesion and neurite extension in vitro. In this study, we have examined the distribution of laminin at early periods of peripheral nervous system development. The distribution of laminin, demonstrated by immunostaining frozen sections of chick embryos, was compared to the distribution of fibronectin and of early peripheral neurites as revealed with an antibody to a neurofilament-associated protein. Laminin is present in the neural tube basement membrane, in early ganglia, and in developing dorsal and ventral roots, where the laminin staining pattern parallels that of neurofilaments. In early ganglia and nerve roots, laminin immunostaining defines loose "meshworks" rather than basement membranes, which seem to form slightly later in these structures. In contrast, fibronectin is absent in neural tube basement membrane, ganglia, and nerve roots, although it is present along neural crest migratory pathways and in intersomitic spaces. Our observations of laminin distribution are consistent with the possibility that laminin provides an adhesive surface for neurite extension at some stages of early peripheral nervous system development.     

Avian vasculogenesis and the distribution of collagens I, IV, laminin, and fibronectin in the heart primordia

The heart-forming regions of the early embryo are composed of splanchnic mesoderm, endoderm, and the associated ECM. The ECM of the heart-forming regions in stage 7-9 chicken embryos was examined using immunofluorescence. Affinity purified antibodies to chicken collagens type I and IV, chicken fibronectin, and mouse laminin were used as probes. We report that (1) the basement membrane of the endoderm contains immunoreactive laminin and collagen IV; (2) the nascent basement membrane of the heart splanchnic mesoderm contains immunoreactive laminin, but not type IV collagen, and (3) the prominent ECM between the splanchnic mesoderm and the endoderm (the primitive-heart ECM) contains collagen IV, collagen I, fibronectin, but not laminin. In addition, we describe microscopic observations on the spatial relationship of cardiogenic cells to the primitive-heart ECM and the endodermal basement membrane.     

Molecular forms, binding functions, and developmental expression patterns of cytotactin and cytotactin-binding proteoglycan, an interactive pair of extracellular matrix molecules

Cytotactin is an extracellular matrix protein that is found in a restricted distribution and is related to developmental patterning at a number of neural and non-neural sites. It has been shown to bind specifically to other extracellular matrix components including a chondroitin sulfate proteoglycan (cytotactin-binding [CTB] proteoglycan) and fibronectin. Cell binding experiments have revealed that cytotactin interacts with neurons and fibroblasts. When isolated from brain, both cytotactin and CTB proteoglycan contain the HNK-1 carbohydrate epitope. Here, specific antibodies prepared against highly purified cytotactin and CTB proteoglycan were used to correlate the biochemical alterations and modes of binding of these proteins with their differential tissue expression as a function of time and place during chicken embryo development. It was found that, during neural development, both the levels of expression of cytotactin and CTB proteoglycan and of the molecular forms of each molecule varied, following different time courses. In addition, a novel Mr 250,000 form of cytotactin was detected that contained chondroitin sulfate. The intermolecular binding of cytotactin and CTB proteoglycan and the binding of cytotactin to fibroblasts were characterized further and found to be inhibited by EDTA, consistent with a dependence on divalent cations. Unlike the molecules from neural tissue, cytotactin and CTB proteoglycan isolated from non-neural tissues such as fibroblasts lacked the HNK-1 epitope. Nevertheless, the intermolecular and cellular binding activities of cytotactin isolated from fibroblast culture medium were comparable to those of the molecule isolated from brain, suggesting that the HNK-1 epitope is not directly involved in binding. Binding experiments involving enzymatically altered molecules that lack chondroitin sulfate suggested that this glycosaminoglycan is also not directly involved in binding. Although they clearly formed a binding couple, the spatial distributions of cytotactin and CTB proteoglycan in the embryo were not always coincident. They were similar in tissue sections from the cerebellum, gizzard, and vascular smooth muscle. In contrast, CTB proteoglycan was present in cardiac muscle where no cytotactin is present, and it was seen in cartilage throughout development unlike cytotactin, which was present only in immature chondrocytes. Cell culture experiments were consistent with the previous conclusion that cytotactin was specifically synthesized by glia, whereas CTB proteoglycan was specifically synthesized by neurons.(ABSTRACT TRUNCATED AT 400 WORDS)     

Regional differences in the expression of laminin isoforms during mouse neural tube development

Many significant human birth defects originate around the time of neural tube closure or early during post-closure nervous system development. For example, failure of the neural tube to close generates anencephaly and spina bifida, faulty cell cycle progression is implicated in primary microcephaly, while defective migration of neuroblasts can lead to neuronal migration disorders such as lissencephaly. At the stage of neural tube closure, basement membranes are becoming organised around the neuroepithelium, and beneath the adjacent non-neural surface ectoderm. While there is circumstantial evidence to implicate basement membrane dynamics in neural tube and surface ectodermal development, we have an incomplete understanding of the molecular composition of basement membranes at this stage. In the present study, we examined the developing basement membranes of the mouse embryo at mid-gestation (embryonic day 9.5), with particular reference to laminin composition. We performed in situ hybridization to detect the mRNAs of all eleven individual laminin chains, and immunohistochemistry to identify which laminin chains are present in the basement membranes. From this information, we inferred the likely laminin variants and their tissues of origin: that is, whether a given basement membrane laminin is contributed by epithelium, mesenchyme, or both. Our findings reveal major differences in basement composition along the body axis, with the rostral neural tube (at mandibular arch and heart levels) exhibiting many distinct laminin variants, while the lumbar level where the neural tube is just closing shows a much simpler laminin profile. Moreover, there appears to be a marked difference in the extent to which the mesenchyme contributes laminin variants to the basement membrane, with potential contribution of several laminins rostrally, but no contribution caudally. This information paves the way towards a mechanistic analysis of basement membrane laminin function during early neural tube development in mammals.     

Distribution and expression of two interactive extracellular matrix proteins, cytotactin and cytotactin-binding proteoglycan, during development of Xenopus laevis. I. Embryonic development.

An immunohistochemical study of the localization of cytotactin and cytotactin-binding (CTB) proteoglycan throughout embryonic development of the anuran Xenopus laevis reveals that both appear in a restricted pattern related to specific morphogenetic events. CTB proteoglycan expression is first detected during gastrulation at the blastopore lip. Later, it is seen in the archenteron roof around groups of cells forming the notochord, somites and neural plate. Cytotactin first appears after neurulation, and is restricted to the intersomitic regions. Both molecules appear along the migratory pathways of neural crest cells in the trunk and tail. Later, cytotactin is present at sites where neural crest cells differentiate, around the aorta and in the smooth muscle coat of the gut; CTB proteoglycan is absent from these sites. In the head, cytotactin is initially restricted to the regions between cranial somites, while CTB proteoglycan is distributed throughout the cranial mesenchyme. The expression of both molecules is later associated with key events in chondrogenesis during the development of the skull. After chondrogenesis, CTB proteoglycan is distributed throughout the cartilage matrix, while cytotactin is restricted to a thin perichondrial deposit. Both molecules are expressed in developing brain. These findings are compared to studies of the chick embryo and although distinct anatomical differences exist between frog and chick, the expression of these molecules is associated with similar developmental processes in both species. These include mesoderm segmentation, neural crest cell migration and differentiation, cartilage development, and central nervous system histogenesis.     

Neural crest migration in 3D extracellular matrix utilizes laminin, fibronectin, or collagen

The trunk neural crest originates by transformation of dorsal neuroepithelial cells into mesenchymal cells that migrate into embryonic interstices. Fibronectin (FN) is thought to be essential for the process, although other extracellular matrix (ECM) molecules are potentially important. We have examined the ability of three dimensional (3D) ECM to promote crest formation in vitro. Neural tubes from stage 12 chick embryos were suspended within gelling solutions of either basement membrane (BM) components or rat tail collagen, and the extent of crest outgrowth was measured after 22 hr. Fetal calf serum inhibits outgrowth in both gels and was not used unless specified. Neither BM gel nor collagen gel contains fibronectin. Extensive crest migration occurs into the BM gel, whereas outgrowth is less in rat tail collagen. Addition of fibronectin or embryo extract (EE), which is rich in fibronectin, does not increase the extent of neural crest outgrowth in BM, which is already maximal, but does stimulate migration into collagen gel. Removal of FN from EE with gelatin-Sepharose does not remove the ability of EE to stimulate migration. Endogenous FN is localized by immunofluorescence to the basal surface of cultured neural tubes, but is not seen in the proximity of migrating neural crest cells. Addition of the FN cell-binding hexapeptide GRGDSP does not affect migration into either the BM gel or the collagen gel with EE, although it does block spreading on FN-coated plastic. Thus, although crest cells appear to use exogenous fibronectin to migrate on planar substrata in vitro, they can interact with 3D collagenous matrices in the absence of exogenous or endogenous fibronectin. In BM gels, the laminin cell-binding peptide, YIGSR, completely inhibits migration of crest away from the neural tube, suggesting that laminin is the migratory substratum. Indeed, laminin as well as collagen and fibronectin is present in the embryonic ECM. Thus, it is possible that ECM molecules in addition to or instead of fibronectin may serve as migratory substrata for neural crest in vivo.     

Ontogenesis of the murine hepatic extracellular matrix: an immunohistochemical study

To define the role of the extracellular matrix (ECM) in hepatogenesis, we examined the temporal and spatial deposition of fibronectin, laminin and collagen types I and IV in 12.5-21.5 day fetal and 1, 7 and 14 day postnatal rat livers. In early fetal liver, discontinuous deposits of the four ECM components studied were present in the perisinusoidal space, with laminin being the most prevalent. All basement membrane zones contained collagen type IV and laminin, including those of the capsule (mesothelial), portal vein radicles and bile ductules. Fibronectin had a distribution similar to that of collagen type IV early in gestation. However, at later gestational dates, fibronectin distribution in the portal triads approached that of collagen type I, being present in the interstitial connective tissues; whereas, collagen type IV and laminin were restricted to vascular and biliary basement membrane zones in those regions. The cytoplasm of some sinusoidal lining cells and hepatocytes reacted with antibodies to extracellular matrix components. By electron microscopy the immunoreactive material was localized in the endoplasmic reticulum, indicating the ability of these cells to synthesize these ECM proteins. Biliary ductular cells had prominent intracytoplasmic staining for laminin and collagen type IV from day 19.5 gestation until 7 days of postnatal life, but lacked demonstrable fibronectin or collagen type I. These results demonstrate that by 12.5 days of gestation the rat liver anlage has deposited a complex extracellular matrix in the perisinusoidal space. The prevalence of laminin in the developing hepatic lobules suggests a possible role for this glycoprotein in hepatic morphogenesis. In view of the intimate association of the hepatic lobular extracellular matrix with the developing vasculature, we hypothesize that laminin provides a scaffold of the developing liver, but once the ontogenesis is complete, intrahepatic perisinusoidal laminin expression is suppressed.     

Distribution and expression of two interactive extracellular matrix proteins, cytotactin and cytotactin-binding proteoglycan, during development of Xenopus laevis. II. Metamorphosis.

During metamorphosis of Xenopus laevis the extracellular matrix (ECM) proteins cytotactin and cytotactin-binding (CTB) proteoglycan and the cell adhesion molecules N-CAM and Ng-CAM, appear in highly restricted patterns determined by immunofluorescence histology. During limb development, cytotactin appears from the earliest stages in a meshwork of ECM fibrils associated with migrating mesenchymal cells forming the limb bud. Cytotactin also appears in the ECM between the apical limb ectoderm and mesenchyme. Later, both cytotactin and CTB proteoglycan appear co-localized within the central (prechondrogenic) limb mesenchyme. During chondrogenesis in these areas, cytotactin becomes restricted to perichondrium, while CTB proteoglycan is expressed throughout the cartilage matrix. The premyogenic mesenchyme surrounding the chondrogenic areas expressed N-CAM. Later, N-CAM is concentrated at the myogenic foci where cytotactin appears at sites of nerve/muscle contact and in tendons. Expression of these molecules in the blastemas of regenerating limbs was also studied, and during development of the central nervous system, stomach, and small intestine. Analysis of the expression patterns of cytotactin and CTB proteoglycan throughout development and metamorphosis reveals several consistent themes. The expression of these molecules is highly dynamic, often transient, and associated with key morphogenetic events. Cytotactin appears at multiple sites where cells undergo a transition from an undifferentiated, migratory phenotype to a differentiated phenotype. One or both molecules appear at several sites of border formation between disparate cell collectives, and CTB proteoglycan expression is associated with chondrogenesis.     

Fibronectin and laminin in the extracellular matrix and basement membrane of sea urchin embryos

Fibronectin and laminin have been found in the extracellular matrix and in the basement membrane of sea urchin embryos during early development. These glycoproteins are also found on the cell surfaces of the outer epithelial layer and on the secondary mesenchyme cells within the blastocoel. The similarity of functions of the extracellular matrix and basement membrane is discussed, as is the similarity of their molecular components. These observations suggest the possibility that fibronectin and laminin form a continuous matrix surrounding the cells which links the outer ECM (hyaline layer) to the inner ECM (basement membrane). Such a network could coordinate the various activities of the embryo during early morphogenesis.     

Immunofluorescent analysis of fibronectin and laminin distribution in the vl mutant mouse

Summary The distribution of fibronectin and laminin was determined in the basement membrane surrounding the caudal neural tube and at the site of initial apposition of the caudal neural folds by means of indirect immunofluorescence histochemistry on 9.0- to 10.5-day mouse embryos fixed in Carnoy's solution and serially sectioned in paraffin. At early phases of development of normal (+/+) and abnormal (vl/vl) embryos the dorsolateral neural basement membrane overlying putative neural crest cells caudal to the hindlimb shows a patchy fibronectin reaction, with laminin virtually absent. In older embryos, both components are present but are discontinuous overlying the neural crest. The results suggest that since discontinuities occur in the basement membrane of abnormal as well as normal embryos, the neural crest cells are not prevented from emigrating from the abnormal neural tube; thus the faulty neural fold fusion that characterizesvl/vl embryos does not appear to be due to a suppression of emigration by the basement membrane. The results also demonstrate the advantages and reliability of embedding in paraffin for analysis of serially sectioned pathological material by means of indirect immunofluorescence, provided that normal controls and abnormals are processed simultaneously.     

Distribution of integrins and their ligands in the trunk of Xenopus laevis during neural crest cell migration

We have examined the distribution in Xenopus embryos of beta 1 subunits of integrin, as recognized by cross-reactive antibodies against the avian integrin beta 1 subunit. These antibodies recognize a doublet of bands of approximately 120 kD in Xenopus embryos. The distribution pattern of these integrin cell surface receptors was compared with that of two possible ligands, fibronectin and laminin, in the extracellular matrix during the time of neural crest cell migration. Integrin immunoreactivity in the early neurula was observed lightly outlining somite and epidermal cells and the notochord. The integrin immunostaining increased with developmental age and was observed on most cell types in the embryo but was particularly notable in the intersomitic clefts through which motoraxons grow. The immunoreactivity in this region was not, however, wholly on the axon surfaces, since intersomitic integrin remained detectable in embryos in which the neural tube had been ablated. Fibronectin and laminin were more extensively distributed than integrin at all stages examined. Immunoreactivity for both was observed around the neural tube, notochord, somites, epidermis, dorsal mesentery, and lateral plate mesoderm. The distribution of laminin and fibronectin around the somites was particularly interesting since it was non-uniform and similar to that of integrin. Strongest staining was observed in the intersomitic clefts, and weakest staining was observed on the medial surface of the somites, which faces the neural tube and notochord. The major differences in distribution pattern between the fibronectin and laminin immunoreactivities were that only fibronectin was detected in the mesenchyme of the dorsal fin. Our results demonstrate that a molecule homologous to avian integrin is present in Xenopus embryos during neural crest cell migration and motoraxon outgrowth. Its presence in the intersomitic clefts and on the surface of many embryonic cell types together with the abundant distribution of its ligands are consistent with a potentially important developmental function in neurite outgrowth and/or muscle development.     

Distribution of a putative cell surface receptor for fibronectin and laminin in the avian embryo

The cell substratum attachment (CSAT) antibody recognizes a 140-kD cell surface receptor complex involved in adhesion to fibronectin (FN) and laminin (LM) (Horwitz, A., K. Duggan, R. Greggs, C. Decker, and C. Buck, 1985, J. Cell Biol., 101:2134-2144). Here, we describe the distribution of the CSAT antigen along with FN and LM in the early avian embryo. At the light microscopic level, the staining patterns for the CSAT receptor and the extracellular matrix molecules to which it binds were largely codistributed. The CSAT antigen was observed on numerous tissues during gastrulation, neurulation, and neural crest migration: for example, the surface of neural crest cells and the basal surface of epithelial tissues such as the ectoderm, neural tube, notochord, and dermomyotome. FN and LM immunoreactivity was observed in the basement membranes surrounding many of these epithelial tissues, as well as around the otic and optic vesicles. In addition, the pathways followed by cranial neural crest cells were lined with FN and LM. In the trunk region, FN and LM were observed surrounding a subpopulation of neural crest cells. However, neither molecule exhibited the selective distribution pattern necessary for a guiding role in trunk neural crest migration. The levels of CSAT, FN, and LM are dynamic in the embryo, perhaps reflecting that the balance of surface-substratum adhesions contributes to initiation, migration, and localization of some neural crest cell populations.     

Localization during development of alternatively spliced forms of cytotactin mRNA by in situ hybridization

Cytotactin, an extracellular glycoprotein found in neural and nonneural tissues, influences a variety of cellular phenomena, particularly cell adhesion and cell migration. Northern and Western blot analysis and in situ hybridization were used to determine localization of alternatively spliced forms of cytotactin in neural and nonneural tissues using a probe (CT) that detected all forms of cytotactin mRNA, and one (VbVc) that detected two of the differentially spliced repeats homologous to the type III repeats of fibronectin. In the brain, the levels of mRNA and protein increased from E8 through E15 and then gradually decreased until they were barely detectable by P3. Among the three cytotactin mRNAs (7.2, 6.6, and 6.4 kb) detected in the brain, the VbVc probe hybridized only to the 7.2-kb message. In isolated cerebella, the 220-kD polypeptide and 7.2-kb mRNA were the only cytotactin species present at hatching, indicating that the 220-kD polypeptide is encoded by the 7.2-kb message that contains the VbVc alternatively spliced insert. In situ hybridization showed cytotactin mRNA in glia and glial precursors in the ventricular zone throughout the central nervous system. In all regions of the nervous system, cytotactin mRNAs were more transient and more localized than the polypeptides. For example, in the radial glia, cytotactin mRNA was observed in the soma whereas the protein was present externally along the glial fibers. In the telencephalon, cytotactin mRNAs were found in a narrow band at the edge of a larger region in which the protein was wide-spread. Hybridization with the VbVc probe generally overlapped that of the CT probe in the spinal cord and cerebellum, consistent with the results of Northern blot analysis. In contrast, in the outermost tectal layers, differential hybridization was observed with the two probes. In nonneural tissues, hybridization with the CT probe, but not the VbVc probe, was detected in chondroblasts, tendinous tissues, and certain mesenchymal cells in the lung. In contrast, hybridization with both probes was observed in smooth muscle and lung epithelium. Both epithelium and mesenchyme expressed cytotactin mRNA in varying combinations: in the choroid plexus, only epithelial cells expressed cytotactin mRNA; in kidney, only mesenchymal cells; and in the lung, both of these cell types contained cytotactin mRNA. These spatiotemporal changes during development suggest that the synthesis of the various alternatively spliced cytotactin mRNAs is responsive to tissue-specific local signals and prompt a search for functional differences in the various molecular forms of the protein.     

Immunohistochemical localization of type IV collagen fibronectin and laminin in the juxtaglomerular apparatus of the rat kidney

The juxtaglomerular apparatus (JGA) is a complex structure containing several components: the vessels, the extraglomerular mesangium and the distal tubule. These structures include cellular elements and an extracellular matrix (ECM). Collagenous (type IV collagen) and noncollagenous components of the basement membranes were studied. The localization of type IV collagen and of two extracellular glycoproteins (laminin and fibronectin) was investigated using immunofluorescent and immunoperoxidase labelled antibodies. Type IV collagen and laminin have the same localization on the JGA basement membranes. On the other hand, fibronectin is limited to the entrance of the glomerular stalk. On electron microscopy, type IV collagen is found in the basement membrane while fibronectin is restricted to certain areas of the extracellular matrix. These findings confirm data concerning the distribution of these three components in basement membranes and allow a better understanding of the histoarchitecture of the juxtaglomerular apparatus.     

Comparison of gene expression of extracellular matrix molecules in brain microvascular endothelial cells and astrocytes.

By use of random-primed cDNA probes the expression of extracellular matrix molecules in cerebral microvascular endothelial cells (cEC) and in astrocytes from mouse brain was examined. Two phenotypically different batches of cloned cEC were used. Expression of major adhesive ECM molecules, constituting the endothelial basement membrane (i.e., fibronectin, laminin A, B and collagen IV) and of other attachment factors, such as SPARC (osteonectin), tenascin and thrombospondin 1, was examined. We have demonstrated that cEC of different morphology display variations in the expression of fibronectin (FN), thrombospondin 1 (TSP1) and collagen IV (C IV). Astrocytes were shown to contain FN, TSP1, TN and SPARC mRNA. Unexpectedly, SPARC mRNA could not be detected in any of the capillary endothelial cells examined. Therefore, we suggest that astrocytes are likely to be involved in endothelial differentiation and function in the central nervous system via ECM molecule secretion.     

Distribution of laminin and collagens during avian neural crest development

The distribution of type I, III and IV collagens and laminin during neural crest development was studied by immunofluorescence labelling of early avian embryos. These components, except type III collagen, were present prior to both cephalic and trunk neural crest appearance. Type I collagen was widely distributed throughout the embryo in the basement membranes of epithelia as well as in the extracellular spaces associated with mesenchymes. Type IV collagen and laminin shared a common distribution primarily in the basal surfaces of epithelia and in close association with developing nerves and muscle. In striking contrast with the other collagens and laminin, type III collagen appeared secondarily during embryogenesis in a restricted pattern in connective tissues. The distribution and fate of laminin and type I and IV collagens could be correlated spatially and temporally with morphogenetic events during neural crest development. Type IV collagen and lamin disappeared from the basal surface of the neural tube at sites where neural crest cells were emerging. During the course of neural crest cell migration, type I collagen was particularly abundant along migratory pathways whereas type IV collagen and laminin were distributed in the basal surfaces of the epithelia lining these pathways but were rarely seen in large amounts among neural crest cells. In contrast, termination of neural crest cell migration and aggregation into ganglia were correlated in many cases with the loss of type I collagen and with the appearance of type IV collagen and laminin among the neural crest population. Type III collagen was not observed associated with neural crest cells during their development. These observations suggest that laminin and both type I and IV collagens may be involved with different functional specificities during neural crest ontogeny. (i) Type I collagen associated with fibronectins is a major component of the extracellular spaces of the young embryo. Together with other components, it may contribute to the three-dimensional organization and functions of the matrix during neural crest cell migration. (ii) Type III collagen is apparently not required for tissue remodelling and cell migration during early embryogenesis. (iii) Type IV collagen and laminin are important components of the basal surface of epithelia and their distribution is consistent with tissue remodelling that occurs during neural crest cell emigration and aggregation into ganglia.     

Distribution and functional role of laminin during induction of the embryonic axis in the chick embryo

Laminin is a major glycoprotein of basement membranes and has been shown to promote cell adhesion, and movement of various nonepithelial cells and tumour cells. Using antibodies to laminin in paraffin sections and cultured embryos, we have studied the distribution of laminin and its involvement in the first morphogenetic events, beginning with the first extensive cellular migrations and interactions that result in the induction of the primitive streak (PS) and of the neural plate in the early chick embryo. Laminin immunogold labeling was not detected in the blastoderm at stage X. At stage XIII, laminin immunoreactivity was detected at the ventral surface of the epiblast and in the entire hypoblast. The intense labeling of the hypoblast indicated that these cells are active in laminin synthesis. Extracellular matrix (ECM) started accumulating as the first embryonic spaces were forming, before the morphogenetic movements of gastrulation were initiated. Immunogold labeling revealed a punctate pattern of laminin distribution in the ECM in the blastocoele, and in the space below the neural plate. Laminin, which is a multidomain molecule known to interact with other molecules of the ECM and with the cell surface, could serve as the scaffold for highly specific contact points of migrating cells and for the folding of epithelial sheets during this time in the developing embryo. We incubated blastoderms at stages X and XIII with laminin antibodies (1:30 dilution) for 4 h, then cultured the blastoderms further in plain egg albumin. The laminin antibodies did not interfere with triggering of PS cell movements, but perturbed the normal migration pattern of these cells. A normal PS did not form and, as a consequence, the embryonic axis was not induced.(ABSTRACT TRUNCATED AT 250 WORDS)     

Expression of hyaluronic acid-binding glycoprotein, hyaluronectin, in the developing rat embryo

Immunological and histological methods have been applied to the developing rat embryo to study the distribution of hyaluronectin (HN, a glycoprotein with hyaluronic acid-binding properties) previously shown to be present in the nervous system and in desmoplasias. HN was absent in the morula and the blastula and was first detected in the mesenchyme bordering the neural tube and somites on Day 10, i.e., at a time when hyaluronic acid is already widely dispersed in the mesenchyme. At this stage HN appeared to be closely associated with the basement membrane around the epithelial structures (somites, notochord, ectoderm) whereas the intercellular areas of mesenchyme were less strongly strained. The delineation of basement membranes decreased progressively, while the accumulation of HN increased in the cell-free areas of mesenchyme, giving a continuous, diffuse pattern. Differentiation of mesenchyme into vertebral cartilage and gut smooth muscle was accompanied by a progressive disappearance of HN. Even after streptomyces hyaluronidase or chondroitinase digestion the antigen was not unmasked in these tissues. The results are in agreement with the few observations made in the human. They suggest that HN could play a role, in association with fibronectin and glycosaminoglycans (hyaluronic acid), in the physiology of the embryonic extracellular matrix. HN appeared at a later stage in the embryonic nervous tissue; its distribution was extracellular in areas where both cell migration and proliferation occur.     

Appearance and distribution of entactin in the early chick embryo

Abstract. Entactin is a sulfated glycoprotein of basement membranes and recent data indicate that it may play a major role in extracellular matrix (ECM) assembly and in modulating the activities of the other molecular components. We investigated the time of appearance and subsequent distribution of entactin during the earliest stages of morphogenesis and its involvement in the first major cellular migrations and interactions in the chick embryo. Entactin is first detected in the epiblast and in the hypoblast at the blastula stage. The accumulating ECM displays intense presence of entactin in the space between the epiblast and the hypoblast at late blastula. Entactin is increasingly abundant in the neural plate and in the ECM and also at least transiently in many mesodermal tissues such as the notochord, the developing heart and somites in the early chick embryo. Immuno-gold labeling revealed a punctate pattern of entactin distribution in the ECM during the gastrula, neurula and at later stages and at all levels within the embryo. Because of its early appearance in more than one germ layer, entactin may be important in the formation of most embryonic structures. Entactin is detected at the same developmental time and co-localizes with laminin. Antibodies to entactin do not interfere with triggering of the first major cell movements but perturb directional migration of these cells. It would seem that entactin plays a functional role in the directed migration of cells and does not seem to affect cell adhesion during the period of the first morphogenetic events in the early chick embryo.     

Appearance and distribution of entactin in the early chick embryo

Abstract. Entactin is a sulfated glycoprotein of basement membranes and recent data indicate that it may play a major role in extracellular matrix (ECM) assembly and in modulating the activities of the other molecular components. We investigated the time of appearance and subsequent distribution of entactin during the earliest stages of morphogenesis and its involvement in the first major cellular migrations and interactions in the chick embryo. Entactin is first detected in the epiblast and in the hypoblast at the blastula stage. The accumulating ECM displays intense presence of entactin in the space between the epiblast and the hypoblast at late blastula. Entactin is increasingly abundant in the neural plate and in the ECM and also at least transiently in many mesodermal tissues such as the notochord, the developing heart and somites in the early chick embryo. Immunogold labeling revealed a punctate pattern of entactin distribution in the ECM during the gastrula, neurula and at later stages and at all levels within the embryo. Because of its early appearance in more than one germ layer, entactin may be important in the formation of most embryonic structures. Entactin is detected at the same developmental time and co-localizes with laminin. Antibodies to entactin do not interfere with triggering of the first major cell movements but perturb directional migration of these cells. It would seem that entactin plays a functional role in the directed migration of cells and does not seem to affect cell adhesion during the period of the first morphogenetic events in the early chick embryo.