Fibronectin associated with the glial component of embryonic brain cell cultures

Wnt/β-catenin signaling pathway inhibits the proliferation and apoptosis of U87 glioma cells via different mechanisms

The Wnt signaling pathway is necessary for the development of the central nervous system and is associated with tumorigenesis in various cancers. However, the mechanism of the Wnt signaling pathway in glioma cells has yet to be elucidated. Small-molecule Wnt modulators such as ICG-001 and AZD2858 were used to inhibit and stimulate the Wnt/β-catenin signaling pathway. Techniques including cell proliferation assay, colony formation assay, Matrigel cell invasion assay, cell cycle assay and Genechip microarray were used. Gene Ontology Enrichment Analysis and Gene Set Enrichment Analysis have enriched many biological processes and signaling pathways. Both the inhibiting and stimulating Wnt/β-catenin signaling pathways could influence the cell cycle, moreover, reduce the proliferation and survival of U87 glioma cells. However, Affymetrix expression microarray indicated that biological processes and networks of signaling pathways between stimulating and inhibiting the Wnt/β-catenin signaling pathway largely differ. We propose that Wnt/β-catenin signaling pathway might prove to be a valuable therapeutic target for glioma.

Enhanced In Vitro Biocompatibility of Chemically Modified Poly(dimethylsiloxane) Surfaces for Stable Adhesion and Long-term Investigation of Brain Cerebral Cortex Cells

Studies on the mammalian brain cerebral cortex have gained increasing importance due to the relevance of the region in controlling critical higher brain functions. Interactions between the cortical cells and surface extracellular matrix (ECM) proteins play a pivotal role in promoting stable cell adhesion, growth, and function. Poly(dimethylsiloxane) (PDMS) based platforms have been increasingly used for on-chip in vitro cellular system analysis. However, the inherent hydrophobicity of the PDMS surface has been unfavorable for any long-term cell system investigations due to transitory physical adsorption of ECM proteins on PDMS surfaces followed by eventual cell dislodgement due to poor anchorage and viability. To address this critical issue, we employed the (3-aminopropyl)triethoxysilane (APTES) based cross-linking strategy to stabilize ECM protein immobilization on PDMS. The efficiency of surface modification in supporting adhesion and long-term viability of neuronal and glial cells was analyzed. The chemically modified surfaces showed a relatively higher cell survival with an increased neurite length and neurite branching. These changes were understood in terms of an increase in surface hydrophilicity, protein stability, and cell-ECM protein interactions. The modification strategy could be successfully applied for stable cortical cell culture on the PDMS microchip for up to 3 weeks in vitro.

Culturing and characterization of astrocytes isolated from juvenile rainbow trout (Oncorhynchus mykiss)

An access to brain cell cultures from fish would enable screening of possible neurotoxic chemicals contaminating the aquatic environment. In the present study, a protocol for a successful routine isolation and culturing of brain cells from juvenile rainbow trout was worked out. The coating material was shown to be of importance for cell proliferation. Cells grow better on a surface coated with laminin than on those coated with poly-L-lysine (PLL), poly-D-lysin (PDL) or poly-L-ornithine (PLO). The best cell growth was obtained on double-coated surfaces (PLL, PDL or PLO plus laminin). On such a culture substrate and with a seeding density of 1 x 10(7) cells/cm(2) confluence was obtained within 3-4 weeks at an incubation temperature of 18 degrees C. Approximately 95% of the cells were identified as astrocytes on the basis of a positive staining with antibodies against the astrocyte specific glial protein (GFAP). No oligodendrocytes or fibroblasts were identified in the cultures, and despite several efforts, neurons did not grow under the culture conditions used. When challenged with ligands known to awake a calcium transient in mammalian astrocytes, 44% of the cells responded to ATP with an increase in [Ca 2+](i), 38% to norepinephrine, 27% to 5-hydroxytryptamine, 7% to histamine and 6% to glutamate. Kainate, quisqualate and gamma-aminobutyric acid did not awake a calcium transient in the cells. Using a proper protocol, it is thus quite easy to get an almost pure culture of astrocyte, whereas neurones proved to very difficult to culture.

Characterization of cortical astrocytes on materials of differing surface chemistry

The behavior of cortical astrocytes was evaluated on a number of medically relevant materials of differing physicochemical properties. This study describes cell attachment, DNA synthesis, production of extracellular matrix (ECM) proteins, and neuronal interactions of perinatal rat astrocytes in vitro. The number of attached astrocytes initially differed among the materials, decreasing with increasing material hydrophobicity. In contrast, the rate of DNA synthesis increased with increasing material hydrophobicity. With the exception of only one material, astrocytes reached confluence by 12 days in culture on all the materials tested. Furthermore, the expression of characteristic ECM proteins and the fundamental ability of astrocytes to support neuronal attachment and growth was qualitatively identical between populations of astrocytes on different materials. The ability of astrocytes to colonize different surfaces initially was mediated via adsorbed serum proteins, as reducing the capacity of a model surface to adsorb proteins inhibited astrocyte colonization for up to 2 weeks in culture. We propose that astrocytes are relatively insensitive to differences in surface chemistries so long as the proteins necessary for cellular attachment are capable of adsorbing to the material to some extent. It seems likely that the ability of astrocytes to produce and remodel a matrix creates a surface environment that eventually becomes similar regardless of the surface chemistry of the underlying material.

Expression of s-laminin and laminin in the developing rat central nervous system

The extracellular matrix component, s-laminin, is a homologue of the B1 subunit of laminin. S-laminin is concentrated in the synaptic cleft at the neuromuscular junction and contains a site that is adhesive for motor neurons, suggesting that it may influence neuromuscular development. To ascertain whether s-laminin may also play roles in the genesis of the central nervous system, we have examined its expression in the brain and spinal cord of embryonic and postnatal rats. S-laminin was not detectable in synapse-rich areas of adults. However, s-laminin was present in discrete subsets of three laminin-containing structures: (1) In the developing cerebral cortex, laminin and s-laminin were expressed in the subplate, a transient layer through which neuroblasts migrate and cortical afferents grow. Both laminin and s-laminin disappeared as embryogenesis proceeded; however, laminin was more widely distributed and present longer than s-laminin. (2) In the developing spinal cord, laminin was present throughout the pia. In contrast, s-laminin was concentrated in the pia that overlies the floor plate, a region in which extracellular cues have been postulated to guide growing axons. (3) In central capillaries, s-laminin appeared perinatally, an interval during which the blood-brain barrier matures. In contrast, laminin was present in capillary walls of both embryos and adults. To extend our immunohistochemical results, we used biochemical methods to characterize s-laminin in brain. We found that authentic s-laminin mRNA is present in the embryonic brain, but that brain-derived s-laminin differs (perhaps by a posttranslational modification) from that derived from nonneural tissues. We also used tissue culture methods to show that glia are capable of synthesizing "brain-like" s-laminin, and of assembling it into an extracellular matrix. Thus, glia may be one cellular source of s-laminin in brain. Together, these results demonstrate that s-laminin is present in the developing central nervous system, and raise the possibility that this molecule may influence developmental processes.

Fibronectin-like immunoreactivity in Helisoma buccal ganglia: evidence that an endogenous fibronectin-like molecule promotes neurite outgrowth

We examined the distribution of fibronectin-like (FNL) immunoreactivity associated with intact buccal ganglia, cell-cultured buccal ganglia neurons and nonneuronal cells, and brain-conditioned medium from the snail Helisoma. In addition, the possible roles of fibronectin in the regulation of neurite outgrowth were studied. Immunofluorescent staining for FNL antigens revealed intense staining in patches and fibrous arrays over the connective tissue sheaths of buccal ganglia and nerve trunks. Within the ganglia, heavy staining was seen surrounding neurons and in track-like arrangements. In cell cultures, specific staining was associated with nonneuronal cell surfaces and to a lesser degree with the surface of identified neurons. In addition, a noncellular, substrate-bound component of brain-conditioned medium displayed FNL immunoreactivity. Since cultured Helisoma neurons require a substrate-associated, brain-derived conditioning factor (CF) in order to elaborate neurites with motile growth cones, we tested whether the FNL immunoreactive substance might act as a neuritotropic agent. Fibronectin antiserum suppressed, in a dose-dependent manner, the CF-induced sprouting of identified neurons in isolated cell culture. When added at increasing concentrations to neurons already growing in response to CF, fibronectin antiserum exerted a biphasic effect on neurite elongation; outgrowth was accelerated at low, but inhibited at high, antiserum concentrations. In contrast, growth cone structures associated with motility (filopodia and lamellipodia) were progressively reduced by increasing levels of antiserum. A short peptide derived from fibronectin's cell-binding domain (Arg-Gly-Asp-Ser) also greatly reduced neurite outgrowth. The combined results of this study indicate an abundance of FNL immunoreactive molecules within the CNS of Helisoma, their probable production by nonneuronal cells, and their function as a substrate-associated component of CF which promotes growth cone filopodial and lamellipodial activity.

A fibronectin-like molecule is present in the developing cat cerebral cortex and is correlated with subplate neurons

The subplate is a transient zone of the developing cerebral cortex through which postmitotic neurons migrate and growing axons elongate en route to their adult positions within the cortical plate. To learn more about the cellular interactions that occur in this zone, we have examined whether fibronectins (FNs), a family of molecules known to promote migration and elongation in other systems, are present during the fetal and postnatal development of the cat's cerebral cortex. Three different anti-FN antisera recognized a single broad band with an apparent molecular mass of 200-250 kD in antigen-transfer analyses (reducing conditions) of plasma-depleted (perfused) whole fetal brain or synaptosome preparations, indicating that FNs are present at these ages. This band can be detected as early as 1 mo before birth at embryonic day 39. Immunohistochemical examination of the developing cerebral cortex from animals between embryonic day 46 and postnatal day 7 using any of the three antisera revealed that FN-like immunoreactivity is restricted to the subplate and the marginal zones, and is not found in the cortical plate. As these zones mature into their adult counterparts (the white matter and layer 1 of the cerebral cortex), immunostaining gradually disappears and is not detectable by postnatal day 70. Previous studies have shown that the subplate and marginal zones contain a special, transient population of neurons (Chun, J. J. M., M. J. Nakamura, and C. J. Shatz. 1987. Nature (Lond.). 325:617-620). The FN-like immunostaining in the subplate and marginal zone is closely associated with these neurons, and some of the immunostaining delineates them. Moreover, the postnatal disappearance of FN-like immunostaining from the subplate is correlated spatially and temporally with the disappearance of the subplate neurons. When subplate neurons are killed by neurotoxins, FN-like immunostaining is depleted in the lesioned area. These observations show that an FN-like molecule is present transiently in the subplate of the developing cerebral cortex and, further, is spatially and temporally correlated with the transient subplate neurons. The presence of FNs within this zone, but not in the cortical plate, suggests that the extracellular milieu of the subplate mediates a unique set of interactions required for the development of the cerebral cortex.

Sialosyl cholesterol induces morphological and biochemical differentiations of glioblasts without intracellular cyclic AMP level rise

Synthesized sialosyl cholesterols, alpha- and beta-D-N-acetylneuraminyl cholesterols (alpha-SC and beta-SC), induced the morphological conversion of normal rat glioblasts from a flat epithelioid morphology to an astrocytic process-bearing (stellate) morphology resembling the conversion by glia maturation factor (GMF). The stellogenic effects were rapid and detectable within 1 h after drug stimulation, and irrelevant to the intracellular cyclic adenosine monophosphate (cAMP) levels. The morphological alteration was ascertained by the fluorescence-visualization of cytoskeletons: alpha-SC elicited the reorganization of GFA protein network to the formation of bundles, the destruction of stress fiber, and the redistribution as plasmalemmal constituents. alpha-SC also evoked biological differentiations represented by an elevation of glial marker proteins, S-100 protein and GFA protein. The results provide a possibility that SC incorporated into plasma membrane may cause morphologically and biochemically astrocyte-like differentiations of glioblast through the alteration of membrane characteristics, the cytoskeletal anchorages to the membrane, the affinity of receptors, and/or the postreceptor responses distinct from cAMP-production system.

Glial fibrillary acidic protein, vimentin and fibronectin in primary cultures of human glioma and fetal brain

The expression of glial fibrillary acidic protein (GFAP), vimentin and fibronectin (Fn) was studied in cells cultured from human glioma and fetal brain by indirect immunofluorescence (IIF) microscopy and multiple labelling experiments. In the primary cultures a major part (20%-70%) of the cells usually displayed both GFAP and vimentin and the rest of the cells only vimentin. A prominent variation in GFAP and vimentin fluorescence intensity sometimes made interpretation of double IIF stainings difficult. However, occasional GFAP-positive cells appeared vimentin negative in primary glioma cultures, whereas in fetal brain primary cultures cells that were preferentially GFAP positive also showed at least a weak vimentin immunoreactivity. Only a fraction of the cells, roughly corresponding to the GFAP-negative cells, were Fn positive in the primary cultures. As judged by double IIF, the GFAP-positive cells were usually Fn negative, while the Fn-positive cells were vimentin positive. This could also be demonstrated in triple IIF experiments. During serial subcultivation the amount of cells expressing GFAP decreased, while the number of Fn-positive cells increased. By the third to fourth passage GFAP positivity was usually lost, all cells expressed vimentin and most cells also Fn. The results of the present study demonstrate a general coexpression of GFAP and vimentin in cultured astroglial cells, in addition to cells expressing only vimentin. Interestingly, occasional glioma cells seem to contain GFAP as the only intermediate filament protein as detected by immunocytochemistry.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of transformation on the expression of laminin and fibronectin by neural cells

We have studied laminin and fibronectin expression in a collection of rat cerebellar neural cell lines transformed with a mutant of Rous sarcoma virus which is temperature sensitive for transformation. We show that regardless of their neuronal or glial properties the cell lines produce both laminin and fibronectin. Laminin is expressed in similar amounts in cell lines grown at either the permissive or nonpermissive temperature for transformation, while fibronectin is generally expressed at higher levels in cells kept at the nonpermissive temperature. To provide further evidence that neural cells can produce laminin and fibronectin, double label immunofluorescence studies were conducted on primary cerebellar cultures. Both laminin and fibronectin were found to be present in the primary culture, and laminin was found to be associated with a subpopulation of astrocytes.

Fibronectin is expressed by astrocytes cultured from embryonic and early postnatal rat brain

In early primary cultures from newborn rat brain, few glial fibrillary acidic protein (GFAP)-positive glial cells expressed intracytoplasmic immunoreactivity for fibronectin. After the second week in culture, however, fibronectin was expressed by a distinct population of GFAP-positive flat astrocytes, irrespective of which brain region was studied. In cerebellar cultures, these cells were more abundant than in cortical or neostriatal cultures and often formed a major population of the GFAP-positive cells. The difference in fibronectin expression between cerebellum and the other areas studied was statistically significant. When cultures were started from 9-day-old postnatal rat brain, fibronectin-positive astrocytes appeared earlier than in those from newborn animals, in all areas studied. Further, especially in the case of cerebellum, the number of fibronectin-positive astrocytes increased as a function of time in culture. In cultures started from whole brains of 12-day-old rat embryos, fibronectin was expressed within 24 h in culture by all the cells with morphology of flat astrocytes, positive for vimentin but negative for GFAP. These results indicate that astrocytes cultured from newborn and early postnatal rat brain are a heterogeneous population of cells: depending on the brain region studied and also depending on the age of brain tissue or the time in culture, less than 1-60% of the GFAP-positive flat astrocytes expressed fibronectin. This, together with the fact that fibronectin was present in early embryonic brain cells in culture, suggests that fibronectin may be a prerequisite for the development or interactions of brain cells.

Immunolocalization of monoclonal antibody-defined extracellular matrix antigens in human brain tumors

The extracellular matrix is involved in many aspects of tumor cell biology, including tumor invasion and metastasis. 2A6 and 81C6 are murine monoclonal antibodies that identify glioma-mesenchymal extracellular matrix antigens. The 81C6 antigen is a high molecular weight glycoprotein composed of Mr 230,000 subunits. The expression of 2A6 antigen, 81C6 glycoprotein, fibronectin (FN), and laminin (LN) was examined immunohistochemically in ten malignant gliomas (MG) and four medulloblastomas (MBT). 2A6 and 81C6 were expressed in similar patterns by the neoplastic neuroepithelial cells in 9/10 MG and 1/4 MBT. The staining was typically diffuse and amorphous, without visualization of distinct cell bodies or processes. Less frequently, antigen was detected within tumor cell cytoplasm. In most tumors the staining was greatest in the perivascular regions. In two MG, 2A6 and 81C6 were expressed only by a subpopulation of neoplastic cells. Although intense staining was also associated with hyperplastic vascular and mesenchymal cells, many small and medium size blood vessels stained weakly or not at all. In contrast, FN and LN were expressed uniformly and intensely in the tumor vasculature, but were not expressed by neoplastic neuroepithelial cells. The 2A6 antigen and 81C6 glycoprotein are immunohistochemically distinct from FN and LN. These monoclonal antibody-defined antigens are heterogeneously expressed by neoplastic neuroepithelial cells and hyperplastic vascular-mesenchymal elements in MG and MBT. The 2A6 and 81C6 monoclonal antibodies will be useful reagents in the investigation of the extracellular matrix of malignant neuroepithelial neoplasms.

Products of cultured neuroglial cells: II. The production of fibronectin by C6 glioma cells

The possibility of fibronectin production by C6 glioma cells was examined with assays which require protein synthesis. Proteins produced by C6 cells using radiolabeled amino acid precursors were tested for affinity to collagen by binding to immobilized gelatin. The predominant collagen binding protein made by C6 coelectrophoresed with fibronectin synthesized by control fibroblasts and with the larger of the two proteins in unlabeled fibronectin when applied to polyacrylamide gels with sodium dodecyl sulfate (SDS). In addition, C6 produced a larger collagen binding protein of approximately 270,000 molecular weight. Solubilities in urea solutions of the collagen-binding proteins made by C6 cells and fibroblasts were similar. Immunofluorescence showed fibronectin associated with the C6 cell monolayer, but less abundant than the fibronectin associated with fibroblasts. Results provide evidence for the production of fibronectin by the C6 glioma cell line.

The control of cell motility during embryogenesis

Morphogenesis is the establishment during development of the complex organization of tissues and organs that characterizes the adult. In multicellular animals, one of the most important processes is morphogenetic movement, the translocation of individual cells or whole tissue rudiments from one site in the body to another. Active cellular locomotion is important in many situations of morphogenetic movement. Characteristically, cell migration in the embryo displays impressive precision: cells at defined sites in the embryo begin migration at particular stages of development, traverse precisely-characterized pathways during migration, and localize finally at particular sites in the body, in specific association with other tissues. One of the most challenging problems of experimental biology is the definition of the mechanisms that regulate the active migration of embryonic cells and tissues. Recent years have seen gratifying progress in this direction, with the definition and characterization of a number of processes of potential importance. This review describes selected instances of morphogenetic movement and contains a discussion of our current understanding of the problem of regulation of cell motility in the embryo.

Immunohistochemical localisation of macromolecules of the basement membrane and extracellular matrix of human gliomas and meningiomas

The distribution of type I, III, IV and V collagen in 35 gliomas and 20 meningiomas was studied by indirect immunofluorescence staining. In addition, the presence of fibronectin (FN) and laminin (LN) is also reported. In gliomas expression of type IV collagen and LN was found in the vessel walls and associated with the endothelial glomerulus-like proliferations. FN and type V collagens were located in proliferating vessel walls in a pattern corresponding both to the basement membrane and the perivascular matrix around the vessels. In the extracellular matrix of grade III and IV gliomas occasional faint intercellular fluorescence was also observed with both FN and type V collagen. Type I and III collagens were localised in the vessel walls and in the perivascular connective sheet. Glioma cells did not express any of the antigens investigated. In meningiomas, type IV and V collagens, LN and FN were found in vessel walls, whorls formations and psammoma bodies. These stainings support the hypothesis of a vascular origin of these psammoma bodies which were only found in syncytial and transitional meningiomas. Both type I and III collagens were detected in the perivascular connective tissue. In general, meningioma cells and extracellular matrix did not express any of these molecules, except in transitional meningiomas where occasional fluorescence was observed in extracellular matrix with type V collagen and FN.

Light-microscopic immunocytochemical localization of fibronectin in the developing rat lung

The development of the rat lung is a process of continuing morphological change. Indications from work in other mammalian systems suggest that fibronectin may be important in the control of this process. The present study has examined embryonic, neonatal, and adult lung tissue of the rat by means of the peroxidase-antiperoxidase (PAP) technique to demonstrate fibronectin at the light-microscopic level. Positive reaction was observed with anti-fibronectin serum in all stages examined. Control sections treated with pre-immune serum or no primary serum gave negative results in each case. Fibronectin in adult tissue was localized to the alveolar surface and alveolar basal lamina. Neonatal tissue showed fibronectin on pulmonary tubule walls and in basal lamina while embryonic tissue revealed localization of the protein in the basal lamina and in association with small groups of cells at the base of septal buds. These findings suggest a role for fibronectin in the control of rat lung development. The results are discussed in terms of the known functions of fibronectin as a preliminary matrix for the subsequent deposition of collagenous connective tissue, as a cellular adhesion protein, and as surface-bound material for cellular migration.

Guidance of myogenic cell migration by oriented deposits of fibronectin

Fibronectin mediates myoblast-substratum attachment; one region of the molecule binds directly to the cell surface, while others bind to collagen, glycosaminoglycans, and other fibronectin molecules. There is evidence to suggest that fibronectin-containing extracellular matrices guide cell migration in vivo. We describe a method for producing regular deposits of fibronectin in vitro that can serve as a model system for studying cell-substrate interactions, cell orientation, and contact guidance. The novel culture substrate is prepared by allowing an aqueous solution of fibronectin and urea to dry in a culture dish and then washing away the urea crystals. Myogenic cells in vitro adhere to, align with, and migrate along, parallel streaks of fibronectin. This leads to the formation of myotubes that are long and thin, with little branching. Myogenic clones are highly elongated in the direction of the deposits, in contrast with the roughly circular clones seen in conventional cultures. Fibroblasts and limb bud mesenchymal cells align with fibronectin deposits, assuming a bipolar shape.

Effect of glia maturation factor on glial fibrillary acidic protein and fibronectin: a comparative study on glioblasts and fibroblasts using immunofluorescence

Glia maturation factor (GMF) was tested on separate cultures of glioblasts and fibroblasts isolated from the same rate fetuses. The astrocytic marker glial fibrillary acidic (GFA) protein and the fibroblast marker fibronectin were visualized with immunofluorescence. Before GMF stimulation, glioblasts showed only background fluorescence for GFA protein and fibronectin. After GMF stimulation, glioblasts showed intense fluorescence for GFA protein, especially in the processes and end-feet. GMF-stimulated glioblasts also showed a slight increase in intracellular fluorescence for fibronectin, mainly in the perinuclear cytoplasm but never in the process terminals. At no time was extracellular fibronectin observed in glioblast cultures. In contrast, fibroblast cultures formed an extensive extracellular network of fibronectin whether or not they were exposed to GMF. GFA protein never showed up in fibroblast cultures regardless of stimulation by GMF. The results indicate that GMF stimulates an increase of GFA protein in glial processes and confirms the astrocytic nature of these glioblasts.

Immunochemical analysis of fibronectin using monoclonal antibodies

Cloned hybrid cell lines secreting antibodies directed against human plasma fibronectin were prepared according to the methods of Kohler and Milstein (Kohler, G. and Milstein, C. (1975) Nature (London) 256, 495-497 and (1976) Eur. J. Immunol. 6, 511-519). The specificity of each monoclonal antibody for fibronectin was established from autoradiograms of radioimmunoprecipitates following SDS-polyacrylamide gel electrophoresis. The monoclonal antibodies were reactive with both native and SDS-denatured fibronectin. Ascites fluids obtained from infected isogenic mice precipitated 85-95% of the 125I-labelled fibronectin radioactivity in indirect radioimmunoprecipitation tests. Localization of specific epitopes to restricted regions of the fibronectin molecule was carried out by monitoring monoclonal antibody binding to proteolytic fragments. Of the five monoclonal antibodies analyzed in this study, three recognized determinants which resided in the terminal 35 kDa region of the fibronectin monomer. Furthermore, these epitopes were localized to fragments as small as 20 kDa. Competition studies carried out using plasma fibronectins isolated from different species revealed that three monoclonal antibodies recognized sites which were relatively conserved, while two monoclonal antibodies recognized epitopic sequences which were unique to the human protein. The corresponding anti-fibronectin serum also demonstrated discriminatory capabilities. Immunofluorescent analysis of human fibroblasts grown in vitro demonstrated that all the monoclonal antibodies tested were reactive with pericellular fibronectin.

Fibronectin promotes rat Schwann cell growth and motility

Techniques are now available for culturing well characterized and purified Schwann cells. Therefore, we investigated the role of fibronectin in the adhesion, growth, and migration of cultured rat Schwann cells. Double-immunolabeling shows that, in primary cultures of rat sciatic nerve, Schwann cells (90%) rarely express fibronectin, whereas fibroblasts (10%) exhibit a granular cytoplasmic and fibrillar surface-associated fibronectin. Secondary cultures of purified Schwann cells do not express fibronectin. Exogenous fibronectin has a small effect on promoting the adhesion of Schwann cells to the substrate and does not significantly affect cell morphology, but it produced a surface fibrillar network on fibronectin on the secondary Schwann cells. Tritiated thymidine autoradiography revealed that addition of fibronectin to the medium, even at low concentrations, markedly stimulates Schwann cell proliferation, in both primary and secondary cultures. In addition, when cell migration was measured in a Boyden chamber assay, fibronectin was found to moderately, but clearly, stimulate directed migration or chemotaxis.

Proliferation of glial-derived cells in defined media

A serum-free defined medium has been formulated that supports proliferation and morphologic differentiation of U-251 MGsp human and C6-2BD rat glioma cells. This defined medium consists of a basal medium supplemented with transferrin, fibroblast growth factor, hydrocortisone, selenium, biotin, and fibronectin (G2 medium). When U-251 cells were plated in G2 medium on poly-D-lysine precoated dishes, their growth rate was 77% and final cell density was 82% of serum-grown counterparts. The growth rate of C6 cells in G2 medium was 67% compared to cells cultured in serum supplemented medium. Although G2 medium supported the growth of human and rat glioma cells, LA-N-1 human neuroblastoma and WI-38 human fibroblast cells showed no increase in cell number when grown in G2 medium compared to basal medium. A similar formulation (G3 medium), lacking fibroblast growth factor and hydrocortisone, supported the proliferation of RN-22 rat schwannoma cells. Morphologic differences were observed between cells grown in the presence of serum and in defined media. All three glial cell lines changed from a flattened shape in serum supplemented medium to a more spherical appearance in defined medium. In addition, both U-251 and C6 cells developed numerous processes, some reaching several cell diameters in length. These defined media will facilitate studies of the growth and differentiation of glial-derived cells.

Distribution of the LETS protein (fibronectin) in rat cerebellum. An in vitro and in vivo developmental study

The distribution of the large, external, transformation-sensitive (LETS; fibronectin) protein was investigated in rat cerebellum, both in vitro and in vivo, by biochemical and immunocytochemical methods. Biochemical analyses indicated that LETS protein is not demonstrable on the surfaces of cerebellar neurons from postnatal rats maintained in cell culture for varying periods of time, but is present on the surfaces of at least some fraction of the total nonneuronal cell population in vitro. Indirect immunofluorescence microscopy with an anti-LETS antiserum substantiated these observations and further indicated that LETS-bearing cells of cerebellum maintained in vitro are probably of endothelial and fibroblastic origin. The LETS protein is arranged in a reticular network of filaments spanning the surfaces of the cells, and the filaments are often extensively interdigitated with each other. At all stages of development investigated (two days postnatal to adult) LETS antigen was observed in vivo to be primarily localized in the meninges covering the surface of the cerebellum and between folia, and in the walls of blood vessels within the tissue. Neuroblasts and neurons of the external and internal granule layers of the cerebellum, respectively, were negative for the presence of LETS antigen.