Expression of cell-adhesion molecules in embryonic induction. I. Morphogenesis of nestling feathers

The potential relationship of cell adhesion to embryonic induction during feather formation was examined by immunohistochemical analysis of the spatiotemporal distribution of three cell-adhesion molecules (CAMs), neural CAM (N-CAM), liver CAM (L-CAM), and neuron-glia CAM (Ng-CAM), and of substrate molecules (laminin and fibronectin) in embryonic chicken skin. The N-CAM found at sites of embryonic induction in the feather was found to be similar to brain N-CAM as judged by immuno-cross-reactivity, migratory position in PAGE, and the presence of embryonic to adult conversion. In contrast to the N-CAM found in the brain, however, only one polypeptide of Mr 140,000 was seen. N-CAM-positive dermal condensations were distributed periodically under L-CAM-positive feather placodes at those sites where basement membranes are known to be disrupted. After initiation of induction, L-CAM-positive placode cells became transiently N-CAM-positive. N-CAM was asymmetrically concentrated in the dorsal region of the feather bud, while fibronectin was concentrated in the ventral region. During feather follicle formation, N-CAM was expressed in the dermal papilla and was closely apposed to the L-CAM-positive papillar ectoderm, while the dermal papilla showed no evidence of laminin or fibronectin. The collar epithelium was both N-CAM- and L-CAM-positive. During the formation of the feather filament, N-CAM appeared periodically and asymmetrically on basilar cells located in the valleys between adjacent barb ridges. In contrast to the two primary CAMs, Ng-CAM was found only on nerves supplying the feather and the skin. These studies indicate that at each site of induction during feather morphogenesis, a general pattern is repeated in which an epithelial structure linked by L-CAM is confronted with periodically propagating condensations of cells linked by N-CAM.     

Expression of cell adhesion molecules during embryonic induction. III. Development of the otic placode

During embryonic development, the inner ear develops from a placode into a richly differentiated structure with defined borders between neural and non-neural elements. In an effort to define the origin of such differentiation boundaries from the time of appearance of the placode, immunocytochemical methods have been used to map the developmental distributions of the cell adhesion molecules, N-CAM, L-CAM, and Ng-CAM, and the extracellular matrix molecules, cytotactin and fibronectin, in the cochlea of the chicken embryo. As the otic placode was induced by the underlying N-CAM-containing rhombencephalon and mesoderm, the placode expressed both N-CAM and L-CAM. During the period when the otic vesicle differentiated to give rise to the acoustic ganglion and to the differentiated structures of the cochlea, N-CAM increased in the innervated sensory regions while L-CAM increased in the non-sensory areas of the auditory epithelium adjacent to the sensory regions. During subsequent development, the differential expression of N-CAM and L-CAM again formed striking borders within the epithelium between the five morphologically and functionally distinct regions of the cochlea. This pattern of CAM expression is consistent with previous observations suggesting that primary CAMs of different binding specificities are expressed in two different modes to form borders at all sites of embryonic induction and at sites of further cytodifferentiation (K. L. Crossin, C -M. Chuong, and G. M. Edelman, 1985, Proc. Natl. Acad. Sci. USA 82, 6942-6946). Unlike inductive sites involving mesenchyme, however, the placode showed only changes in which an epithelium containing both CAMs loses one or the other or remains unchanged. As differentiation occurred during innervation of the sensory region, the secondary Ng-CAM appeared. Ng-CAM-positive fibers penetrated into the basilar papilla and Ng-CAM and the matrix protein cytotactin appeared within the epithelium in a radial pattern that was consistent with the previously described roles of these molecules in neurite movement. Immunoblot analyses confirmed the identity and biochemical properties of the CAMs and also revealed that N-CAM underwent embryonic to adult conversion during inner ear formation. These studies support the idea that CAMs are expressed in specific modal patterns in the cell collectives participating in inductive events, and strongly suggest that cellular regulation of these patterns is correlated with border formation.(ABSTRACT TRUNCATED AT 400 WORDS)     

Expression sequences and distribution of two primary cell adhesion molecules during embryonic development of Xenopus laevis

Studies of chicken embryos have demonstrated that cell adhesion molecules are important in embryonic induction and are expressed in defined sequences during embryogenesis and histogenesis. To extend these observations and to provide comparable evidence for heterochronic changes in such sequences during evolution, the local distributions of the neural cell adhesion molecule (N-CAM) and of the liver cell adhesion molecule (L-CAM) were examined in Xenopus laevis embryos by immunohistochemical and biochemical techniques. Because of the technical difficulties presented by the existence of multiple polypeptide forms of CAMs and by autofluorescence of yolk-containing cells, special care was taken in choosing and characterizing antibodies, fluorophores, and embedding procedures. Both N-CAM and L-CAM were found at low levels in pregastrulation embryos. During gastrulation, N-CAM levels increased in the presumptive neural epithelium and decreased in the endoderm, but L-CAM continued to be expressed in all cells including endodermal cells. During neurulation, the level of N-CAM expression in the neural ectoderm increased considerably, while remaining constant in non-neural ectoderm and diminishing in the somites; in the notochord, N-CAM was expressed transiently. Prevalence modulation was also seen at all sites of secondary induction: both CAMs increased in the sensory layer of the ectoderm during condensation of the placodes. During organogenesis, the expression of L-CAM gradually diminished in the nervous system while N-CAM expression remained high. In all other organs examined, the amount of one or the other CAM decreased, so that by stage 50 these two molecules were expressed in non-overlapping territories. Embryonic and adult tissues were compared to search for concordance of CAM expression at later stages. With few exceptions, the tissue distributions of N-CAM and L-CAM were similar in the frog and in the chicken from early times of development. In contrast to previous observations in the chicken and in the mouse, N-CAM expression was found to be high in the adult liver of Xenopus, whereas L-CAM expression was low. In the adult brain, N-CAM was expressed as three components of apparent molecular mass 180, 140, and 120 kD, respectively; in earlier stages of development only the 140-kD component could be detected. In the liver, a single N-CAM band appears at 160 kD, raising the possibility that this band represents an unusual N-CAM polypeptide. L-CAM appeared at all stages as a 124-kD molecule.(ABSTRACT TRUNCATED AT 400 WORDS)     

Adhesion molecules during somitogenesis in the avian embryo

In avian embryos, somites constitute the morphological unit of the metameric pattern. Somites are epithelia formed from a mesenchyme, the segmental plate, and are subsequently reorganized into dermatome, myotome, and sclerotome. In this study, we used somitogenesis as a basis to examine tissue remodeling during early vertebrate morphogenesis. Particular emphasis was put on the distribution and possible complementary roles of adhesion-promoting molecules, neural cell adhesion molecule (N-CAM), N-cadherin, fibronectin, and laminin. Both segmental plate and somitic cells exhibited in vitro calcium-dependent and calcium-independent systems of cell aggregation that could be inhibited respectively by anti-N-cadherin and anti-N-CAM antibodies. In vivo, the spatio-temporal expression of N-cadherin was closely associated with both the formation and local disruption of the somites. In contrast, changes in the prevalence of N-CAM did not strictly accompany the remodeling of the somitic epithelium into dermamyotome and sclerotome. It was also observed that fibronectin and laminin were reorganized secondarily in the extracellular spaces after CAM-mediated contacts were modulated. In an in vitro culture system of somites, N-cadherin was lost on individual cells released from somite explants and was reexpressed when these cells reached confluence and established intercellular contacts. In an assay of tissue dissociation in vitro, antibodies to N-cadherin or medium devoid of calcium strongly and reversibly dissociated explants of segmental plates and somites. Antibodies to N-CAM exhibited a smaller disrupting effect only on segmental plate explants. In contrast, antibodies to fibronectin and laminin did not perturb the cohesion of cells within the explants. These results emphasize the possible role of cell surface modulation of CAMs during the formation and remodeling of some transient embryonic epithelia. It is suggested that N-cadherin plays a major role in the control of tissue remodeling, a process in which N-CAM is also involved but to a lesser extent. The substratum adhesion molecules, fibronectin and laminin, do not appear to play a primary role in the regulation of these processes but may participate in cell positioning and in the stabilization of the epithelial structures.     

Expression of the cell adhesion molecules, L-CAM and N-CAM during avian scale development

To examine the involvement of cell adhesion molecules in the inductive epithelial-mesenchymal interactions during avian scale development, a study of the spatiotemporal distribution of L-CAM and N-CAM was undertaken. During scutate scale development, L-CAM and N-CAM are expressed together in cells of the transient embryonic layers destined to be lost at hatching. The ongoing linkage of the cells of these layers by both CAMs sets them apart, early in development, as unique cell populations. L-CAM and N-CAM were also expressed simultaneously at the basal surface of the early germinative cells where signal transduction is presumed to occur. In spite of the differences in cell shape, adhesion, density and proliferative state between populations of epidermal placode and interplacode cells, the expression of L-CAM and N-CAM appeared to be uniform and nondiscriminating for these discrete cell lineages. The same pattern of L-CAM and N-CAM expression was observed during morphogenesis of reticulate scales that develop without placode formation. While L-CAM and N-CAM are present during the early stages of scale development and most likely function in cell adhesion, the data do not support a role for these adhesion molecules in the formation of the morphogenetically critical placode and interplacode cell populations. In both scale types, L-CAM became predominantly epithelial, and N-CAM became predominantly dermal as histogenesis occurred. Initially, N-CAM was concentrated near the basal lamina where it may be involved in the reciprocal epidermal-dermal interactions required for morphogenesis. However, as development of the scales progressed, N-CAM disappeared from the tissues. L-CAM expression continued in the epidermis and was intense on all suprabasal cells undergoing differentiation into either an alpha-stratum or beta-stratum. However, L-CAM was more prevalent on the basal cells of alpha-keratinizing regions than on the basal cells of beta-keratinizing regions.     

cDNAs of cell adhesion molecules of different specificity induce changes in cell shape and border formation in cultured S180 cells

The liver cell adhesion molecule (L-CAM) and N-cadherin or adherens junction-specific CAM (A-CAM) are structurally related cell surface glycoproteins that mediate calcium-dependent adhesion in different tissues. We have isolated and characterized a full-length cDNA clone for chicken N-cadherin and used this clone to transfect S180 mouse sarcoma cells that do not normally express N-cadherin. The transfected cells (S180cadN cells) expressed N-cadherin on their surfaces and resembled S180 cells transfected with L-CAM (S180L cells) in that at confluence they formed an epithelioid sheet and displayed a large increase in the number of adherens and gap junctions. In addition, N-cadherin in S180cadN cells, like L-CAM in S180L cells, accumulated at cellular boundaries where it was colocalized with cortical actin. In S180L cells and S180cadN cells, L-CAM and N-cadherin were seen at sites of adherens junctions but were not restricted to these areas. Adhesion mediated by either CAM was inhibited by treatment with cytochalasin D that disrupted the actin network of the transfected cells. Despite their known structural similarities, there was no evidence of interaction between L-CAM and N-cadherin. Doubly transfected cells (S180L/cadN) also formed epithelioid sheets. In these cells, both N-cadherin and L-CAM colocalized at areas of cell contact and the presence of antibodies to both CAMs was required to disrupt the sheets of cells. Studies using divalent antibodies to localize each CAM at the cell surface or to perturb their distributions indicated that in the same cell there were no interactions between L-CAM and N-cadherin molecules. These data suggest that the Ca(++)-dependent CAMs are likely to play a critical role in the maintenance of epithelial structures and support a model for the segregation of CAM mediated binding. They also provide further support for the so-called precedence hypothesis that proposes that expression and homophilic binding of CAMs are necessary for formation of junctional structures in epithelia.     

Mechanism of skin morphogenesis. I. Analyses with antibodies to adhesion molecules tenascin, N-CAM, and integrin.

To understand cell interactions during induction of skin appendages, we studied the roles of adhesion molecules N-CAM, tenascin, integrin, and fibronectin during feather development. Tenascin appeared in a periodic pattern on epithelia and was so far the earliest molecule detected in placodes. Three placode domains were identified: the anterior was positive for tenascin, the distal positive for N-CAM, and the posterior lacking both. Integrin appeared in dermal-epidermal junctions of placodes. In feather buds, sagittal sections revealed a transient anterior-posterior asymmetry with tenascin and N-CAM enriched in the anterior mesoderm. Tangential sections revealed a lateral-medial asymmetry with tenascin distributed in a ring shape and N-CAM in an "X" shape. Integrin was diffusely distributed within buds. Later tenascin and N-CAM were enriched in dermal papilla, the inducer of skin appendages. Perturbation of embryonic skin explant cultures with antibodies showed that anti-integrin beta 1 and anti-fibronectin blocked epithelial-mesenchymal interaction, anti-N-CAM caused uneven segregation of mesenchymal condensation, and anti-tenascin inhibited feather bud elongation. Dose-response curves showed gradual effects by these antibodies. The results indicated that these adhesion molecules are independently regulated and each contributes in different phases during morphogenesis of skin appendages.     

Avian feather development: relationships between morphogenesis and keratinization

Morphogenesis and expression of the alpha and beta keratin polypeptides are controlled by epidermal-dermal interactions during development of avian skin derivatives. We have examined the relationship between morphogenesis of the embryonic feather and expression of the feather alpha and beta keratins by routine histology, indirect-immunofluorescence, and SDS-PAGE. Initially beta keratins are expressed only in the feather sheath. Following barb ridge morphogenesis beta keratins can be detected in the barb ridge, coincident with the differentiation of barb ridge cells into eight distinct morphological types. Beta keratinization occurs in gradients; from feather apex to base, and from periphery of the barb ridge to the interior. The onset of beta keratinization in the barb ridges is paralleled by an increase in the major feather beta keratin polypeptides, as detected by SDS-PAGE. The alpha keratins are present in both the periderm and feather sheath at early stages of feather development, but become greatly reduced after hatching, when the down feather emerges from the sheath.     

Antibodies to cell surface ganglioside GD3 perturb inductive epithelial-mesenchymal interactions

Most epithelial sheets emerge during embryogenesis by a branching and growth of the epithelium. The surrounding mesenchyme is crucial for this process. We report that branching morphogenesis and the formation of a new epithelium from the mesenchyme in the embryonic kidney can be blocked by a monoclonal antibody reacting with a surface glycolipid, disialoganglioside GD3. In contrast, a more than 10-fold excess of antibodies to adhesive glycoproteins (N-CAM, L-CAM, fibronectin) fails to inhibit morphogenesis. Although the anti-GD3 antibody affected epithelial development, the disialoganglioside GD3 was expressed not in the epithelium, but in the mesenchyme surrounding the developing epithelia. The data raise the intriguing possibility that the anti-GD3 antibody inhibits epithelial development by interfering with epithelial-mesenchymal interactions.     

beta-catenin in epithelial morphogenesis: conversion of part of avian foot scales into feather buds with a mutated beta-catenin

We explored the role of beta-catenin in chicken skin morphogenesis. Initially beta-catenin mRNA was expressed at homogeneous levels in the epithelia over a skin appendage tract field which became transformed into a periodic pattern corresponding to individual primordia. The importance of periodic patterning was shown in scaleless mutants, in which beta-catenin was initially expressed normally, but failed to make a punctuated pattern. To test beta-catenin function, a truncated armadillo fragment was expressed in developing chicken skin from the RCAS retrovirus. This produced a variety of phenotypic changes during epithelial appendage morphogenesis. In apteric and scale-producing regions, new feather buds with normal-appearing follicle sheaths, dermal papillae, and barb ridges were induced. In feather tracts, short, wide, and curled feather buds with abnormal morphology and random orientation formed. Epidermal invaginations and placode-like structures formed in the scale epidermis. PCNA staining and the distribution of molecular markers (SHH, NCAM, Tenascin-C) were characteristic of feather buds. These results suggest that the beta-catenin pathway is involved in modulating epithelial morphogenesis and that increased beta-catenin pathway activity can increase the activity of skin appendage phenotypes. Analogies between regulated and deregulated new growths are discussed.     

Study of the function and regulation of liver N-CAM in Xenopus laevis.

The liver of Xenopus laevis is a unique exception in terms of the cell adhesion molecules (CAM) which it expresses. In most species, hepatocytes are characterized by the expression of the epithelial Ca(2+)-dependent CAM E-cadherin or of closely related variants of this molecule (e.g., L-CAM); in Xenopus liver, however, the levels of expression of epithelial cadherins is very low while a thyroxine-inducible isoform of N-CAM is expressed in postmetamorphic hepatocytes. Since Xenopus liver N-CAM is localized in regions of contact between hepatocytes, it has been proposed that it might be involved in mediating hepatocyte adhesion in this species. In this study, we demonstrate that N-CAM can indeed act as a functional adhesion molecule in the liver of Xenopus and that its expression is correlated with a number of profound morphological changes of this organ. After thyroxine treatment, hepatocytes are no longer organized in long loose cords but in compact lobules of cells. Furthermore, at the ultrastructural level, plasma membranes are in much closer proximity with the appearance of electron-dense material in areas of closer contact. We have established two novel culture systems for premetamorphic Xenopus hepatocytes as adherent and non-adherent cells, and we describe the induction of expression of N-CAM in these cells. Given the difference in the profile of adhesion molecules present in the liver of Xenopus and of other species, our results are discussed in view of the importance of the expression of a specific set of cell adhesion molecules in defining the development of homologous organs in different species.     

Neuronal cell adhesion molecules and cytotactin are colocalized at the node of Ranvier

Immunocytochemical methods were used to show that Ng-CAM (the neuron-glia cell adhesion molecule), N-CAM (the neural cell adhesion molecule), and the extracellular matrix protein cytotactin are highly concentrated at nodes of Ranvier of the adult chicken and mouse. In contrast, unmyelinated axonal fibers were uniformly stained by specific antibodies to both CAMs but not by antibodies to cytotactin. Ultrastructural immunogold techniques indicated that both N-CAM and Ng-CAM were enriched in the nodal axoplasm and axolemma of myelinated fibers as well as within the nodal regions of the myelinating Schwann cell. At embryonic day 14, before myelination had occurred, small-caliber fibers of chick embryos showed periodic coincident accumulations of the two CAMs but not of cytotactin, with faint labeling in the axonal regions between accumulations. Cytotactin was found on Schwann cells and in connective tissue. By embryonic day 18, nodal accumulations of CAMs were first observed in a few medium- and large-caliber fibers. Immunoblot analyses indicated that embryonic to adult conversion of N-CAM and a progressive decrease in the amount of Ng-CAM and N-CAM occurred while nodes were forming. Sciatic nerves of mouse mutants with defects in cell interactions showed abnormalities in the distribution patterns and amount of Ng-CAM, N-CAM, and cytotactin that were consistent with the known morphological nodal disorders. In trembler (+/Tr), intense staining for both CAMs appeared all along the fibers and the amounts of N-CAM in the sciatic nerve were found to be increased. In mice with motor endplate disease (med/med), Ng-CAM and N-CAM, but not cytotactin, were localized in the widened nodes. Both trembler and med/med Schwann cells stained intensely for cytotactin, in contrast to normal Schwann cells which stained only slightly. All of these findings are consistent with the hypothesis that surface modulation of neuronal CAMs mediated by signals shared between neurons and glia may be necessary for establishing and maintaining the nodes of Ranvier.     

The modulation of cell adhesion molecule expression and intercellular junction formation in the developing avian inner ear

The cells that constitute the membranous labyrinth in the vertebrate inner ear are all derived from a single embryonic source, namely, the otocyst. The mature inner ear epithelia contain different regions with highly differentiated cells, displaying a highly specialized cytoarchitecture. The present study was designed to determine the presence of adherens-type intercellular junctions in this tissue and study the expression of cell adhesion molecules (CAMs) associated with these junctions, namely, A-CAM and L-CAM, in the developing avian inner ear epithelia. The results presented here show that throughout the early otocyst, A-CAM is coexpressed with L-CAM. The formation of asymmetries between sensory and nonsensory areas in the epithelium is accompanied by the modulation of CAMs expression and the assembly of intercellular junctional complexes. A-CAM and L-CAM display reciprocal expression patterns, the former being expressed mostly in the mosaic sensory epithelium, while L-CAM becomes conspicuous in the nonsensory areas but its expression in the sensory region is markedly reduced. Adherens-type junctions and numerous desmosomes are found in the junctional complexes of early otocyst cells. The former persist to maturity of the various inner ear epithelia, whereas desmosomes disappear from junctional complexes of hair cells but remain in the intercellular junctional complexes of all other cell types in the membranous labyrinth. Thus, adherens type intercellular junctions comprise the only defined cytoskeleton-bound junction in mature hair cells. A-CAM-positive cells are also found in the region of the acoustic ganglion in early developmental stages but not in the mature neural elements.     

Cell Adhesion as a Basis of Pattern in Embryonic Development

The development of the modern methodologies of cell biologyin the fifties and sixties and of molecular biology in the seventiesand eighties has led to a reductionist view of embryonic developmentthat centers on the cell and the gene as the functional unitsof development. The functional units in most inductive and morphogeneticprocesses in the embryo are not single cells, however, but ratherare collectives of interacting cells that give rise to the tissuesand organs. Can these methodological developments reconcilea molecular analysis with the fact that form arises epigeneticallyfrom the increasing number of embryonic cells during development?To answer this question one must link genetic regulation tomechanochemical processes that coordinate cell division, cellmovement and cell death. Recent studies of cell adhesion suggestthat one such link is provided by cell adhesion molecules (CAMs)that mediate cell-cell binding. These studies suggest that CAMsare involved in defining cell collectives and their bordersas they interact during inductive events in morphogenesis. AlthoughCAMs cannot be considered the "cause" of induction, they playkey roles among the complex causal chains of inductive interactionsinvolving hormones and growth-factors, extracellular matrixcomponents and cellular receptors. We provide here a brief summaryof modern developments in the field centered about the functionof CAMs in morphogenesis and using recent experimental resultsin the developing feather as a paradigmatic example.     

Altered expression of neuronal cell adhesion molecules induced by nerve injury and repair

Peripheral nerve injury results in short-term and long-term changes in both neurons and glia. In the present study, immunohistological and immunoblot analyses were used to examine the expression of the neural cell adhesion molecule (N-CAM) and the neuron-glia cell adhesion molecule (Ng-CAM) within different parts of a functionally linked neuromuscular system extending from skeletal muscle to the spinal cord after peripheral nerve injury. Histological samples were taken from 3 to 150 d after crushing or transecting the sciatic nerve in adult chickens and mice. In unperturbed tissues, both N-CAM and Ng-CAM were found on nonmyelinated axons, and to a lesser extent on Schwann cells and myelinated axons. Only N-CAM was found on muscles. After denervation, the following changes were observed: The amount of N-CAM in muscle fibers increased transiently on the surface and in the cytoplasm, and in interstitial spaces between fibers. Restoration of normal N-CAM levels in muscle was dependent on reinnervation; in a chronically denervated state, N-CAM levels remained high. After crushing or cutting the nerve, the amount of both CAMs increased in the area surrounding the lesion, and the predominant form of N-CAM changed from a discrete Mr 140,000 component to the polydisperse high molecular weight embryonic form. Anti-N-CAM antibodies stained neurites, Schwann cells, and the perineurium of the regenerating sciatic nerve. Anti-Ng-CAM antibodies labeled neurites, Schwann cells and the endoneurial tubes in the distal stump. Changes in CAM distribution were observed in dorsal root ganglia and in the spinal cord only after the nerve was cut. The fibers within affected dorsal root ganglia were more intensely labeled for both CAMs, and the motor neurons in the ventral horn of the spinal cord of the affected segments were stained more intensely in a ring pattern by anti-N-CAM and anti-Ng-CAM than their counterparts on the side contralateral to the lesion. Taken together with the previous studies (Rieger, F., M. Grumet, and G. M. Edelman, J. Cell Biol. 101:285-293), these data suggest that local signals between neurons and glia may regulate CAM expression in the spinal cord and nerve during regeneration, and that activity may regulate N-CAM expression in muscle. Correlations of the present observations are made here with established events of nerve degeneration and suggest a number of roles for the CAMs in regenerative events.(ABSTRACT TRUNCATED AT 400 WORDS)     

The structure of cell adhesion molecule uvomorulin. Insights into the molecular mechanism of Ca2+-dependent cell adhesion.

We have determined the amino acid sequence of the Ca2+-dependent cell adhesion molecule uvomorulin as it appears on the cell surface. The extracellular part of the molecule exhibits three internally repeated domains of 112 residues which are most likely generated by gene duplication. Each of the repeated domains contains two highly conserved units which could represent putative Ca2+-binding sites. Secondary structure predictions suggest that the putative Ca2+-binding units are located in external loops at the surface of the protein. The protein sequence exhibits a single membrane-spanning region and a cytoplasmic domain. Sequence comparison reveals extensive homology to the chicken L-CAM. Both uvomorulin and L-CAM are identical in 65% of their entire amino acid sequence suggesting a common origin for both CAMs.     

Significance of cell adhesion molecules, CD56/NCAM in particular, in human tumor growth and spreading

Cell adhesion molecules (CAM) represent a large group of cell surface protein moieties with distinctive biological functions. In physiological terms they ascertain cell to cell contact such as cell cohesion of epithelia, condition cell migration and transmigration via biological membranes such as blood vessel walls, provide means for homing cells in a new microenvironment etc. These features of CAM are exploited by tumor cells to grow and spread in a tumor bearing host. CD56/N-CAM antigen is 140 kD isoform of neural cell adhesion molecule. N-CAM belongs to the large Ig superfamily of CAMs. CD56 can be traced at various sites, including nervous tissue, neuro-muscular junctions, neuroendocrine and endocrine organs. It is well known as a differentiation antigen of natural killer (NK) cells. Its role and function are far from clear, but its adhesion properties are evident in cell-cell (homophilic) interactions. CD56 has been, however, demonstrated the cells various human malignancies. Tumors of the nervous system such as neuroblastoma, are well known to express this marker. Malignant lymphomas of T-NK cell origin bear CD56, as well as multiple myeloma, melanoma and some cancers of epithelial origin. These data suggest that CD56/N-CAM antigen is, in some unknown manner involved in tumor biology.     

Expression of extracellular matrix components fibronectin and laminin in the human fetal heart.

It has been well documented that the extracellular matrix components fibronectin and laminin promote or regulate morphogenesis of the myocardial cells in mammalian heart. However, their chronological change of expression (or localization) in the human heart remains elusive. In this study, fibronectin and laminin in the left ventricle of forty-two human fetuses aged from 8 to 26 weeks gestation and left ventricular tissues obtained from a 2-week old infant and two adults were investigated by Western blot analyses and indirect immunofluorescence technique with monoclonal antibodies. In the fetal heart, fibronectins were present along the endocardium, epicardium, and linings of larger blood vessels. In 14-16 weeks gestation, fibronectin immunofluorescence became stronger but not evenly dispersed in the interstitium. After 24 weeks gestation, they were strongly positive only in the relatively larger blood vessels, as well as those in the infant and adult cardiac tissues. Laminins were strongly positive along the endocardium and basement membrane of the myocardial cells and fibroblasts during fetal life. After birth, laminins formed fine fibrillar network along the basement membrane in association with the transverse tubules of myocardial cell; these morphological characteristics remained in the adult cardiac tissues. These results indicate that fibronectin expression is relatively constant during fetal life but decreases after birth; in contrast, laminin expression is not age-dependent and constant throughout the life.