Synthesis and effects of basement membrane components in cultured rat Schwann cells

Understanding the molecules of neural cell contacts: emerging patterns of structure and function

Neural cells make and break many contacts during their lifetime. The processes of neuroblast migration, axon elongation and guidance, synaptogenesis, myelination and synaptic rearrangement all require the selective formation and elimination of cell-cell and cell-substratum associations.

Non-myelin-forming Schwann cells proliferate rapidly during Wallerian degeneration in the rat sciatic nerve

Transection of a mixed peripheral nerve results in the degeneration of axons and breakdown of myelin in the distal stump. These events are accompanied by a sharp but transient Schwann cell proliferation. The present study seeks to determine whether both myelin-forming and non-myelin-forming Schwann cells enter a proliferative phase under these conditions, or whether the dividing cells are chiefly recruited from one or other of the Schwann cell populations. The macrophage recruitment into the transected distal stumps has also been timed and quantitated, since it has been suggested that macrophages are an important source of Schwann cell mitogens in degenerating peripheral nerves. Incorporation of [3H]-thymidine and autoradiography was used as a measure of cell proliferation, and cell type markers and immunohistochemistry were used to identify myelin-forming and non-myelin-forming Schwann cells. The cells were removed from the distal stump of the rat sciatic nerve and sympathetic trunk at various times after transection and proliferation measured during the first 24 h in culture. It was found that in the sciatic nerve, which contains a mixture of myelinated and unmyelinated fibres, both myelin-forming cells, identified by presence of the myelin protein Po, and non-myelin-forming cells (Po- cells) showed a substantial elevation in [3H]-thymidine labelling index at day 2 postoperatively, which was similar in magnitude for the two categories of cell. The proliferation rate of both Po+ and Po- cells remained elevated for up to 8 days after transection.(ABSTRACT TRUNCATED AT 250 WORDS)

Domains of laminin with growth-factor activity

Laminin and fragments (1, 1-4) containing the inner rod-like segments from its short arms, which consist of cysteine-rich, "EGF-like" repeats, stimulated thymidine incorporation in cultured cells possessing EGF receptors but had no effect on a cell line lacking this receptor. The response was comparable to that of EGF concerning effective concentrations, magnitude, time dependence, and synergistic enhancement by insulin. Other fragments (4 and 8) were inactive. Laminin and its active fragments could not compete with the binding of EGF to cells. There was no correlation between growth promotion and attachment of cells to a high affinity binding site present on laminin fragment 8. The data indicate that mitogenic effects induced by laminin and EGF proceed in some steps via related pathways and that different domains of laminin are involved in growth promotion and in adhesion and spreading of cells.

Detection of a nerve growth factor receptor on fetal human Schwann cells in culture: absence of the receptor on fetal human astrocytes

Cultures of human Schwann cells and astrocytes were established from fetal nerves and brains respectively. The human Schwann cells in culture expressed a nerve growth factor (NGF) receptor as determined by indirect immunofluorescence, autoradiography, and immunoprecipitation. In contrast, the human astrocytes in culture did not have an NGF receptor. Cultures of rat Schwann cells and astrocytes were also established for comparison, with similar results. The rat Schwann cells had an NGF receptor whereas the astrocytes did not. The functional significance of this NGF receptor on Schwann cells, as well as the lack of the receptor on astrocytes, is discussed.

Migration of Schwann cells and axons into developing chick forelimb muscles following removal of either the neural tube or the neural crest

A study has been made of the effects of neural crest and neural tube removal at the brachial level on the migration of Schwann cells and axons into the flexor digitorum profundus (fdp) and flexor carpi ulnaris (fcu) muscles of the avian forelimb. The identification of Schwann cells was based on the assumption that antibody HNK-1 uniquely labels these cells at the growing end of limb nerves. Myotubes and nerves were identified by using antibodies to myosin and to neurofilament protein, respectively. The removal of neural crest cells at stage 13 gave a complete Schwann cell-free embryo at the brachial level. Motor axons only grew to the base of the forelimb, forming a rudimentary plexus by stage 27, and failed to penetrate the limb. Removal of the neural tube at stage 13 did not prevent sensory axons from forming a plexus at the base of the limb; these axons subsequently developed into the brachialis longus inferior (bli n) and superior (bls n) nerves. By stage 27 the bli n had branched into the interosseus nerve (in n) and the medial-ulnar nerve (m-u n) trunks. However, unlike the result in control embryos, no nerves were detected amongst the developing fdp and fcu muscles, thus indicating that sensory axons do not grow into the muscles in the absence of motor axons. In contrast, Schwann cells were observed amongst the myotubes at the level of the in n and m-u nerve trunks. The present observations show that motor axons do not enter the limb bud and innervate limb muscles in the absence of Schwann cells. Furthermore, in the absence of motor axons (neural-tube-removed embryos) sensory axons still enter the limb (behind migrating Schwann cells) but fail to innervate developing muscles even though Schwann cells are present among the developing myotubes.

Evidence that an RGD-dependent receptor mediates the binding of oligodendrocytes to a novel ligand in a glial-derived matrix

A simple adhesion assay was used to measure the interaction between rat oligodendrocytes and various substrata, including a matrix secreted by glial cells. Oligodendrocytes bound to surfaces coated with fibronectin, vitronectin and a protein component of the glial matrix. The binding of cells to all of these substrates was inhibited by a synthetic peptide (GRGDSP) modeled after the cell-binding domain of fibronectin. The component of the glial matrix responsible for the oligodendrocyte interaction is a protein which is either secreted by the glial cells or removed from serum by products of these cultures; serum alone does not promote adhesion to the same extent as the glial-derived matrix. The interaction of cells with this glial-derived matrix requires divalent cations and is not mediated by several known RGD-containing extracellular proteins, including fibronectin, vitronectin, thrombospondin, type I and type IV collagen, and tenascin.

Regulation of Schwann cell nerve growth factor receptor by cyclic adenosine 3',5'-monophosphate

Previous studies indicated that Schwann cells in immature nerves express nerve growth factor (NGF) receptors, and that this expression is down regulated during development but re-induced by Wallerian degeneration. It was also shown that immature Schwann cells are induced to express galactocerebroside and other molecules characteristic of mature Schwann cells by either contact with an axon or treatment with the cyclic adenosine 3',5'-monophosphate (cAMP) analogues dibutyryl cAMP (dbcAMP) and 8-bromo cAMP or the adenylate cyclase activator forskolin. In the present study, NGF receptors on the surface of cultured Schwann cells were demonstrated by binding of an anti-rat NGF receptor monoclonal antibody or of radioiodinated NGF. Treatment of cultured Schwann cells with cAMP analogues or forskolin resulted in a progressive decrease in both immunoreactive NGF receptors and radioiodinated NGF binding. The cultured Schwann cells contained a polyadenylated RNA species homologous with human melanoma NGF receptor mRNA in sequence and size. The amount of this NGF mRNA was lower in cAMP analogue-treated than in untreated Schwann cells.

Extracellular fluid conditioned during peripheral nerve regeneration stimulates Schwann cell adhesion, migration and proliferation

Schwann cell movement and proliferation occur during peripheral nerve regeneration and remyelination. We asked whether soluble factors promoting these activities were present in fluid surrounding rat sciatic nerves regenerating across a 10-mm gap bridged by a silicone tube. In this model, regenerated and remyelinated axons extend across the gap by 28 days following nerve transection and tube implantation. Fluid conditioned by cells participating in nerve regeneration (RCF) was assayed for its ability to promote Schwann cell adhesion, migration and proliferation in vitro. RCFs collected at post-transectional days 1-28 were equally effective in promoting Schwann cell-substratum adhesion. In contrast, the motility-promoting activity of RCF was minimal at 1-2 days following nerve-transection, peaked at 7 days and remained elevated through 21 days. The RCF peak response was 87-fold greater than control. Schwann cell proliferative activity of RCF exhibited peaks of activity at 1 and 14 days post-transection. The biological potency of this fluid for each activity assayed in vitro correlated well with the behavior of Schwann cells chronicled during nerve repair in vivo. These findings suggest that soluble factors promoting Schwann cell adhesion, migration, and proliferation accumulate extracellularly during peripheral nerve regeneration and remyelination.

The extracellular matrix of the central and peripheral nervous systems: structure and function

The extracellular matrix (ECM) is the naturally occurring substrate upon which cells migrate, proliferate, and differentiate. The ECM functions as a biological adhesive that maintains the normal cytoarchitecture of different tissues and defines the key spatial relationships among dissimilar cell types. A loss of coordination and an alteration in the interactions between mesenchymal cells and epithelial cells separated by an ECM are thought to be fundamental steps in the development and progression of cancer. Although a substantial body of knowledge has been accumulated concerning the role of the ECM in most other tissues, much less is known of the structure and function of the ECM in the nervous system. Recent experiments in mammalian systems have shown that an increased knowledge of the ECM in the nervous system can lead to a better understanding of complex neurobiological processes under developmental, normal, and pathological conditions. This review focuses on the structure and function of the ECM in the peripheral and central nervous systems and on the importance of ECM macromolecules in axonal regeneration, cerebral edema, and cerebral neoplasia.

In vitro studies on adult cardiac myocytes: attachment and biosynthesis of collagen type IV and laminin

The interactions between adult rat cardiac myocytes and the basement membrane components collagen type IV and laminin were investigated in attachment experiments and biosynthesis studies and by immunofluorescence staining. Adult myocytes attached equally well to native collagen type IV and laminin but did not attach to collagen type IV solubilized with pepsin (P-CIV) or to collagen type I. However, when laminin was used to coat P-CIV, attachment was enhanced. Affinity-purified antibodies against laminin inhibited the attachment of myocytes to dishes coated with native collagen type IV, indicating that cell surface-bound laminin mediated attachment of the cells to this substrate. Immunofluorescence staining of freshly isolated myocytes, using antibodies against laminin or collagen type IV, revealed the presence of laminin but not of collagen type IV on the surface of freshly isolated cells, indicating that during the isolation procedure collagen IV was removed from the cell surface. Metabolic labeling followed by immunoprecipitation demonstrated synthesis of both laminin and collagen type IV in cardiac myocytes as they progressed into culture over a 14-day period. This synthesis was accompanied by the deposition of the collagen type IV and laminin into distinctly different patterns as revealed by immunofluorescence staining. As the cells progressed into culture, newly synthesized laminin formed a network radiating from the center of the reorganizing cell into the pseudopods. The laminin was redistributed and remodeled with time in culture to form a dense layer beneath the cell. Collagen type IV was also synthesized with time in culture, but the pattern was a much finer network as opposed to the denser pattern of laminin staining. These studies demonstrate that adult cardiac myocytes synthesize and remodel the basement membrane as they adapt to the culture environment.

The neurite-promoting domain of human laminin promotes attachment and induces characteristic morphology in non-neuronal cells

The interaction of cells with laminin and laminin fragments was studied in short-term cell attachment assays. Neurite-promoting chymotrypsin fragments of laminin were isolated using a monoclonal antibody which blocks neurite outgrowth on laminin. The fragments were shown, by electron microscopy after rotary shadowing and by immunological reactivity with different monoclonal antibodies, to contain only the distal end of the long arm. These fragments promoted the attachment and spreading of glioma, sarcoma, carcinoma, muscle, and endodermal cells to the same extent as intact laminin. The attachment was unaffected by peptides containing the RGD sequence. The morphology of the cells on the chymotrypsin fragments was indistinguishable from that on intact laminin but different from the morphology of the same cells on fibronectin. Light microscopy and scanning electron microscopy showed extensive process formation on laminin but not on fibronectin suggestive of increased cell motility in response to laminin. We conclude that the neurite-promoting domain of laminin contains a major site of interaction for non-neuronal cells and that this site induces a cellular response in certain non-neuronal cells that is unique to laminin.

Endogenous immunoreactive glia maturation factor-like molecule in cultured rat Schwann cells

Using the monoclonal antibody G2-09 raised against bovine glia maturation factor (GMF), we demonstrated that cultured rat Schwann cells and Schwannoma cells, but not their conditioned media, possessed endogenous GMF-like immunoreactivity. The presence of immunoreactive GMF correlated well with GMF bioactivity. The GMF-like factor in Schwann cells was characterized by immunodotting, immunofluorescence, immunoadsorption and immunoblotting. Immunofluorescence confirmed the intracellular location of GMF. Immunoadsorption completely eliminated the GMF-like bioactivity from the cell extracts. Immunoblotting identified a protein band with a molecular weight of 14,000. Thus, the evidence strongly supports the argument that the GMF-like factor in rat Schwann cells is identical with GMF from the bovine brain. The GMF-like molecule in Schwannoma cells showed properties similar to those in Schwann cells, but for unknown reasons was not detectable by immunofluorescence. The presence of GMF in cultured rat Schwann cells suggests that the factor may play a role in the peripheral nervous system.

Structural requirements for the stimulation of neurite outgrowth by two variants of laminin and their inhibition by antibodies

Laminin derived from the Engelbreth-Holm-Swarm (EHS) tumor and a lamininlike molecule synthesized by RN22 Schwannoma cells both stimulate rapid neurite outgrowth, consistent with a common neurite-promoting site. However, antilaminin antisera can only inhibit the activity of the EHS laminin. The blocking antibodies in such sera are directed against the terminal heparin-binding domain of the laminin long arm (Edgar, D., R. Timpl, and H. Thoenen. 1984. EMBO [Eur. Mol. Biol. Organ.] J. 3: 1463-1468). These epitopes are demonstrated by immunoblotting to be part of the A chain and to be absent in RN22 laminin, showing (through metabolic labeling) that the cells synthesized little if any 440-kD A chain. This indicates that the antibody inhibition was probably due to steric hindrance, a common neurite-promoting site, apparently not being antigenic in native molecules. Antibodies raised against a 25-kD proteolytic fragment derived from the long arm of laminin were then used as probes to identify other potential neurite-promoting structures. Although these antibodies do not cross-react with native laminin, they recognized the B chains of denatured EHS and RN22 molecules on immunoblots. The antibodies also bound to the large proteolytic fragment, derived from the long arm of laminin that contains the neurite-promoting site, thus inhibiting its activity. Taken together, these results point to the localization of normally nonantigenic, defined, B chain sequences within or close to the neurite-promoting site of laminin.

Laminin, fibronectin and type IV collagen in BM-like material from cultured arterial smooth muscle cells

1. The intra- and extracellular distribution of fibronectin and laminin was studied by immunofluorescence in cultures of rabbit and human arterial smooth muscle cells. 2. Basement membrane (BM)-like material was isolated from the cell layer of arterial smooth muscle cells cultures and analysed by sodium dodecyl sulphate gel electrophoresis (SDS-PAGE) and immunoblotting. The major 220-240 kD component of arterial BM-like material was identified as fibronectin. Also a 200 kD fibronectin band was observed. 3. The 200 kD subunit of laminin was contained in isolated BM-like material, but no slower migrating laminin chains were detected. 4. Collagens were prepared from pepsinized BM-like material. The band pattern as resolved by SDS-PAGE and silver staining suggested that type IV collagen is the major collagen of arterial BM-like material.

Laminin alters cell shape and stimulates motility and proliferation of murine skeletal myoblasts

Proliferating skeletal myoblasts show multiple specific responses to laminin, one of the major glycoprotein components of basement membranes. Using MM14Dy myoblasts, a myogenic cell strain derived from a normal adult mouse skeletal muscle, we show in this study that substrate-bound laminin but not other matrix proteins such as collagens or fibronectin specifically and rapidly induces the outgrowth of cell processes, resulting in bipolar, spindle-shaped cells. This effect is independent from the presence of collagens or serum, and was also observed in primary cultures of fetal mouse skeletal myoblasts. The outgrowth of cell processes on laminin is associated with a dramatic stimulation of cell motility: MM14 myoblasts migrate about five times faster on laminin than on fibronectin. In another series of experiments the effect of laminin and fibronectin on thymidine uptake and proliferation of myoblasts was tested. On top of a type I collagen substrate which was provided to ensure complete adhesion even at low doses of laminin or fibronectin, laminin stimulated myoblast proliferation and incorporation of [3H]thymidine in a dose-dependent manner. The stimulation is two- to threefold higher than on dishes coated with equivalent amounts of fibronectin and is observed both in the presence and in the absence of serum. These results suggest that laminin, a major component of the muscle basal lamina, may be actively involved in the development and regeneration of skeletal muscle.

Role of basement membranes in cell differentiation

Extracellular matrices have diverse biological effects, including promoting the growth and differentiation of various cells of epithelial origin. The components of one of these matrices, the basement membrane, are discussed, as well as studies using these components alone or in combination with cells in culture. The particular response observed varies with the cell type examined and appears to be dependent on multiple interactions with components of the matrix. Potential uses for a basement membrane-derived matrix in vitro and in vivo are being developed.

Control of peripheral glial cell proliferation: a comparison of the division rates of enteric glia and Schwann cells and their response to mitogens

The enteric nervous system comprises neurons and a relatively homogeneous population of glial cells, which differ considerably from those found in other parts of the peripheral nervous system and resemble more closely astrocytes from the central nervous system. It provides a simple model system for the study of neuron/glial interactions and glial cell development. In this study the proliferation rates of purified populations of enteric glia and Schwann cells and their response to several mitogens in vitro were compared. Enteric glial cells divided at a much higher rate than Schwann cells in both serum-containing and serum-free media. This difference in their basal proliferation rates was the major difference seen between the two cell types. Both cell populations were stimulated to divide by fibroblast growth factor and glial growth factor but not by epidermal growth factor. Enteric glial cells and Schwann cells proliferated at a greater rate on a basement membrane-like extracellular matrix produced by corneal endothelial cells, laminin, and fibronectin than on poly-L-lysine-coated glass coverslips. The magnitude of stimulation was greater for Schwann cells, presumably due to their lower basal division rates. Like Schwann cells, enteric glial cells were stimulated to divide by two agents which elevate intracellular cAMP, cholera toxin, and dibutyryl cAMP.

A monoclonal antibody to Schwann cell surface membrane recognizes a cAMP inducible epitope

A monoclonal antibody to the surface membrane of rat Schwann cells was generated. This antibody bound to Schwann cell surface but not to fibroblasts in mixed neonatal sciatic nerve cultures. It did not bind to cells in newborn rat brain or corpus callosum cultures that contained oligodendrocytes, astrocytes, fibroblasts and neurons. The target antigen for this monoclonal antibody disappeared from Schwann cell surface after 5 days in culture. At this time, addition of 10(-3) M 8-bromo cyclic AMP or 10(-3) M dibutyryl cyclic AMP resulted in the reappearance within 2 days, of the target antigen on Schwann cell surface membrane. The reappearance of this epitope parallels that of surface galactocerebroside on Schwann cells when incubated with cAMP analogues. Re-expression of the target antigen for this monoclonal antibody in the presence of cAMP is evidence that cAMP may be a signal for synthesis of a variety of myelin molecules and as such could be a signal for myelination of axons by Schwann cells.

Release of autocrine growth factor by primary and immortalized Schwann cells

Schwann cells derived from neonatal rat sciatic nerve are quiescent in culture unless treated with specific mitogens. The use of glial growth factor (GGF) and forskolin has been found to be an effective method for stimulating proliferation of Schwann cells on a poly(L-lysine) substratum while maintaining their ability to myelinate axons in vitro. We find that repetitive passaging of Schwann cells with GGF and forskolin results in the loss of normal growth control; the cells are able to proliferate without added mitogens. The immortalized cells grow continuously in the absence of added growth factor and in the presence or absence of serum yet continue to express distinctive Schwann cell-surface antigens. The cells can associate with axons in culture, deposit a basal lamina, and ensheath axons, but they gradually lose their capacity to myelinate axons. The immortalized cells release growth-promoting activity into their culture medium. The released activity is effective in stimulating proliferation of primary Schwann cells that retain normal growth properties. Extracellular matrix molecules (laminin and fibronectin) augment the response of primary Schwann cells to the secreted mitogen. Quiescent primary Schwann cells also secrete a growth factor into their culture medium, but its activity is detectable only in the presence of added laminin or fibronectin. The results suggest that both normal and immortalized Schwann cells secrete an autocrine growth factor. Response to the autocrine factor appears to entail a multicomponent mechanism. Unlike primary cells, immortalized Schwann cells have the capacity to secrete all of the necessary components and to respond to them constitutively.

Effects of inhibition of proteoglycan synthesis on the differentiation of cultured rat Schwann cells

Schwann cells synthesize two heparan sulfate proteoglycans, one that is a component of the Schwann cell basement membrane and a smaller one that is an integral component of the Schwann cell plasma membrane. To determine the functions of these molecules, Schwann cell-nerve cell cultures were grown in medium containing a specific inhibitor of proteoglycan biosynthesis, 4-methylumbelliferyl-beta-D-xyloside. Treatment with 1 mM beta-D-xyloside caused a 90% reduction in the accumulation of 35SO4-labeled proteoglycans in the cell layer of the cultures. Gel filtration analysis revealed that both the basement membrane and plasma membrane proteoglycans were affected. Inhibition of proteoglycan biosynthesis was accompanied by an inhibition of laminin deposition into extracellular matrix as determined by immunostaining of cultures and by immunoblotting of cell-associated proteins. This occurred even though there was no decrease in the amount of laminin detected in the medium of beta-D-xyloside-treated cultures. Deposition of collagen type IV was similarly affected. In addition, there was no myelin produced in beta-D-xyloside treated cultures. However, when beta-xyloside-treated cultures were supplied with exogenous basement membrane, Schwann cells produced numerous myelin segments. These results indicate that Schwann cell proteoglycans play an essential role in basement membrane assembly, and that the integral plasma membrane proteoglycan is not required for the basement membrane to exert its effects on Schwann cell differentiation.

Characterization of retinal pigment epithelial cells cultured on microporous filters

Retinal pigment epithelium (RPE) cultured on microporous filter supports was compared to RPE cultured on plastic and evaluated for features characteristic of RPE in vivo. RPE cells grown on filters were cuboidal, formed junctional complex structures between cells, and had elaborate microvilli and basal infoldings similar to RPE in vivo, while RPE grown on plastic also formed intercellular junctions but appeared squamous and had few microvilli and basal infoldings. RPE grown on filters or plastic secreted an extracellular matrix at the basal surface and ingested isolated rat rod outer segments at the apical surface. RPE grown on filters coated with laminin or fibronectin became confluent more rapidly than RPE grown on uncoated filters, while RPE grown at the same density on filters coated with collagen type I did not become confluent. The laminin and fibronectin coatings did not alter the RPE cell morphology; however, cells seeded on collagen-coated filters grew in large disorganized clusters. RPE grown on laminin-coated filters formed functional tight junctions as evidenced by the capacity of RPE monolayers to prevent the bulk flow of medium and the passage of trypan blue across the filter. Radiolabeled sucrose and inulin were used to measure the paracellular flux through the tight junctions between cells. The passage of these tracers was linear over time, with the lower molecular weight tracer, sucrose, passing through the monolayer more readily than inulin. Values for the flux of radiolabeled bovine serum albumin across RPE monolayers fell between values for sucrose and inulin. The results from these studies show that RPE monolayers cultured on laminin-coated filters maintain a morphology similar to that of RPE in vivo, are capable of ingesting rod outer segments, and form a selectively permeable barrier to various tracers. This culture system should be useful for studies of transepithelial transport, secretion, endocytosis and exocytosis that require independent control of the extracellular environment at the apical and basolateral cell surfaces.

Extracellular matrix in healing CO2 laser incision wound

Extracellular matrix components laminin, Type IV collagen, Type III collagen, and fibronectin, of laser-treated rat tongue mucosa were studied over a healing period of 28 days by using immunohistochemical and electron microscopic techniques. Their distribution and amount in laser wounds was compared with that in scalpel incisions and normal tongue mucosa. Laser treatment caused an extensive destruction of both epithelial and stromal cells but left much of the connective tissue matrix intact. Basement membranes, in particular, appeared to resist laser irradiation. During the study period the laser-induced lesions healed through reparative synthesis of matrix proteins which led to filling of the tissue defects. The regenerative processes with concomitant re-epithelialization took place more slowly in laser-treated than in scalpel incision wounds. The relative resistance of the matrix proteins against laser irradiation and the slow removal and replacement of the residual matrix is suggested to account at least partially for the lack of scarring and contraction frequently observed in laser-treated areas.

Human amnion membrane serves as a substratum for growing axons in vitro and in vivo

The epithelial cell layer of human amnion membrane can be removed while the basement membrane and stromal surfaces remain morphologically intact. Such a preparation has been used as a substratum for the in vitro culture of dissociated neurons. Embryonic motor neurons from chick ciliary ganglion attached to both surfaces but grew extensive neurites only on the basement membrane. On cross sections of rolled amnion membranes, regenerating axons of cultured neurons were guided along pathways of basement membrane that were immunoreactive with an antibody to laminin. In addition, when rolled amnion membranes were implanted into a lesion cavity between the rat septum and hippocampus, cholinergic neurons extended axons through the longitudinally oriented implant into the hippocampus. Thus, this amnion preparation can serve as a bridge to promote axonal regeneration in vivo in damaged adult brain.

Motoneurone survival and neurite regeneration requirements: the role of dorsal root ganglion cells during development

The effect of dissociated dorsal root ganglion cells on the survival of motoneurones in vitro from differently aged chick embryos has been studied. Homogeneous cultures of motoneurones were prepared from 5-8-day embryos, using a cell sorter; dorsal root ganglion cells were obtained from 8-day embryos. The survival of motoneurones from 5-day and 6-day embryos was not enhanced above controls by the presence of dorsal root ganglion cells; however, the survival of motoneurones from older embryos was greatly increased, reaching a maximum of over 80% for 8-day embryonic motoneurones. In contrast, the number of motoneurones that had regenerated neurites when co-cultured with dorsal root ganglion cells for 24 h decreased with the motoneurone age at plating, from 51% at 5 days to less than 10% for 7- and 8-day motoneurones. The survival-enhancing effects were probably mediated by cell contact between the motoneurones and processes of the dorsal root ganglion cells: conditioned media from high-density cultures of dorsal root ganglion cells could not be shown to significantly enhance the survival of motoneurones above that of control levels. The possibility that the ganglion cells exert this survival enhancing effect by depolarizing the motoneurones was examined by exposing 8-day sorted motoneurones to 47 mM potassium; this did not effect the survival of the motoneurones relative to control levels. The stage dependency of the survival of motoneurones on different neurotrophic factors and the dorsal root ganglion cell is discussed.

Basement membrane proteins produced by Schwann cells and in neurofibromatosis

Mouse Schwann cells and rat RN22 schwannoma cells cultured in the absence of neurons and fibroblasts produce typical basement membrane proteins. Heparan sulfate proteoglycan (low density form), nidogen, and protein BM-40 were identified by radioimmunoassays, immunoblotting, and by immunoprecipitation after metabolic labeling. The cells also produce a laminin-like protein that differs from authentic laminin by a reduced A chain content and lack of antigenic determinants located in the long arm of laminin. Laminin possessing A and B chains is, however, produced by PYS-2 teratocarcinoma cells grown under the same conditions. Laminin from Schwann cell culture medium promotes neurite outgrowth, and this activity could be immunoprecipitated but not blocked by various antibodies against authentic laminin. In addition, Schwann cell laminin is found complexed noncovalently with nidogen. Sulfate incorporation revealed the synthesis of proteoglycans and entactin. A similar set of proteins and in addition collagen IV could be demonstrated in neurofibroma tissue by immunohistology, and were localized to the laminae densae of the multilayered basement membranes around Schwann cells and capillaries. Laminin purified from 0.5 M NaCl neurofibroma tissue extracts possessed both A and B chains. Nidogen was identified in a partially degraded form.

Role of laminin and fibronectin in selecting myogenic versus fibrogenic cells from skeletal muscle cells in vitro

Growth of embryonic skeletal muscle occurs by fusion of multinucleated myotubes with differentiated, fusion-capable myoblasts. Selective recognition seems to prevent fusion of myotubes with nonmyogenic cells such as muscle fibroblasts, endothelial cells, or nerve cells, but the nature of the signal is as yet unknown. Here we provide evidence that one of the selection mechanisms may be the enhanced affinity for laminin of myogenic cells as compared to fibrogenic cells. Growing myotubes in myoblast cultures accumulate laminin and type IV collagen on their surface in patches and strands as the first step in assembling a continuous basal lamina on mature myofibers (U. Kühl, R. Timpl, and K. von der Mark (1982), Dev. Biol. 93, 344-359). Fibronectin, on the other hand, assembles into an intercellular fibrous meshwork not associated with the free myotube surface. Over a brief time period (10-20 min) myoblasts from embryonic mouse thigh muscle adhere faster to laminin than do fibroblasts from the same tissue; these adhere faster to fibronectin. When a mixture of the cells is plated for 20 min on laminin/type IV collagen substrates, only myogenic cells adhere, giving rise to cultures with more than 90% fusion after 2 weeks; on fibronectin/type I collagen in the same time primarily fibroblastic cells adhere, giving rise to cultures with less than 10% nuclei in myotubes. The differential affinities of myoblasts for basement membrane constituents and of fibroblasts for interstitial connective tissue components may play a role in sorting out myoblasts from fibroblasts in skeletal muscle development.

Laminin immunohistochemistry: a simple method to visualize and quantitate vascular structures in the mammalian brain

Immunohistochemistry using antiserum against the basement membrane glycoprotein laminin, was shown to be an excellent marker for brain blood vessels. Throughout the brain of mice, rats, guinea pigs, monkeys and humans, the basement membrane of the vascular structures were strongly laminin-positive. The neuropil itself was laminin-negative, whereas a positive reaction was observed in the meaninges. When the laminin antiserum was preabsorbed with its proper antigen, no specific fluorescence was observed. Using India ink perfusion as a comparative method, it was found that probably all vascular structures were also visualized with laminin immunohistochemistry. Laminin immunofluorescence was found well-suited for computer-assisted quantitative image analysis of brain vascularity. As expected in the periphery, the basement membrane of many other structures except blood vessels such as endoneurium, epithelium and smooth muscle cells were laminin-positive. Although the vascular network was also strongly laminin-immunoreactive, it was difficult to differentiate between blood vessels and non-vascular structures in the periphery as compared to the central nervous system. In conclusion, laminin immunohistochemistry has proven to be a simple, useful and specific method to study vascular structures in the central nervous system and an excellent alternative to more conventional and laborious methods such as perfusion with India ink.

S-100 protein and laminin: immunocytochemical markers for human Schwann cells in vitro

Human fetal and adult Schwann cells, which had been maintained in culture for 5 weeks according to an explant-reexplantation technique, were labeled by immunoperoxidase using antibodies directed against S-100 protein and laminin in order to find specific antigenic markers. Immunocytochemical analysis of the distribution of both proteins showed that they were expressed in long-term cultures. The localization of S-100 protein and laminin in long-term cultures indicated that the expression of these proteins by human Schwann cells was not axon-dependent and also occurred in absence of myelin synthesis.

Schwann cell myelination: induction by exogenous basement membrane-like extracellular matrix

Exposing rat Schwann cells co-cultured with nerve cells to a reconstituted basement membrane induced the formation of myelin segments by Schwann cells. This occurred in a serum-free culture medium in which, in the absence of this matrix, Schwann cells proliferate but fail to differentiate. This reconstituted basement membrane was prepared from solubilized extracellular matrix proteins synthesized by a basement membrane-producing murine tumor. The major constituents of this reconstituted matrix are collagen type IV, laminin, heparan sulfate proteoglycan, entactin, and nidogen. The matrix also elicited striking morphological changes in Schwann cells, inducing them to spread longitudinally along the nerve fibers (a necessary early step in the process of ensheathment of nerve fibers). Several observations indicated that the effect of the matrix was exerted directly on Schwann cells and not indirectly through an effect on nerve cells. First, the matrix-induced cell spreading occurred only in areas in which Schwann cells directly contacted the matrix; Schwann cells that were associated with the same nerve fibers but that did not themselves directly contact the matrix did not exhibit spreading. Second, the matrix-induced alteration in Schwann cell morphology was observed in cultures in which the nerve cells were removed. These results provide direct evidence that basement membrane contact induces normal Schwann cell differentiation, and support the idea that Schwann cell differentiation in vivo may be regulated by the appearance of the basement membrane, which normally envelops terminally differentiating Schwann cells.

Requisites for growth and myelination of urodele sensory neurons in tissue culture

We describe a system for long-term culture of adult salamander dorsal root ganglia and present initial observations on the regulation of nonneuronal cell proliferation in this system. Observations of the region of axonal outgrowth in these cultures indicated that, on the one hand, fibroblasts proliferate equally well with neurons present or absent. Schwann cells, on the other hand, require not only the presence of neurons but also proximity to or contact with their neurites. These results indicate that neural tissue is not mitogenic for all cell types represented in the limb regeneration blastema. Further, we describe, for the first time, myelination of salamander axons in vitro. The critical factors found to be required for this high degree of differentiation were the use of long culture periods and addition to the culture medium of ascorbic acid, which is shown to promote extracellular matrix deposition. These observations correlate with extensive observations made on mammalian tissues in vitro, indicating a linkage between deposition of extracellular matrix and full expression of other Schwann cell functions. We anticipate this culture system will be useful in studies of limb blastema cell proliferation.

Regulation of cell attachment and cell number by fibronectin and laminin

We have examined the effect of laminin and fibronectin on the attachment and growth on type IV collagen of a line of mouse epithelial cells and a strain of adult human fibroblasts. Laminin stimulated attachment of the epidermal cells and fibronectin stimulated fibroblast attachment. At high concentrations (100 micrograms/ml), the attachment proteins altered the growth of cells in culture. The epidermal cells grew better in media containing fibronectin-free serum supplemented with laminin. Fibroblasts, on the other hand, grew best in media containing serum supplemented with fibronectin. These data suggest that laminin promotes epithelial cell growth whereas fibronectin promotes fibroblast growth. This observation was confirmed when these cells were cocultured in the presence of the attachment proteins or of their respective antibodies. The mouse epidermal cells grew best when laminin was added to cocultures of fibroblasts and epithelial cells. Fibroblasts grew best in the presence of antibody to laminin and poorly in the presence of antibody to fibronectin. Thus, fibronectin and laminin may participate in the regulation of cell populations in vivo and may be involved in epithelial-mesenchymal interactions.

Chemotaxis of human gingival epithelial cells to laminin. A mechanism for epithelial cell apical migration

Laminin, a large glycoprotein (Mr = 10(6)) and a major component of basement membrane, is shown here to be a potent chemoattractant for human gingival epithelial cells. Laminin stimulated chemotaxis and chemokinesis of gingival epithelial cells in the modified Boyden chamber assay. This effect appeared to be laminin receptor mediated. Gingival epithelial cells were shown to bind laminin (Kd = 2.0 nM) with 10,000 to 30,000 binding sites per cell. Antilaminin antibody, which inhibited laminin binding, inhibited the chemotactic response of epithelial cells to laminin, while antifibronectin was without effect. Fibronectin was not as potent a chemoattractant as laminin. Other biological response modifiers were also tested; of these, Type IV collagen and epidermal growth factor were active as chemoattractants, although not as effective in inducing chemotaxis as laminin. The data indicate that laminin and other components of basement membrane may be important in regulating the migration and growth of gingival epithelial cells.

Cell shape and motility of oligodendrocytes cultured without neurons

Oligodendrocytes, the myelin-forming cells of the central nervous system (CNS), were cultured from newborn rat brain and optic nerve to study how they differentiate in vitro in the absence of neurons. By use of galactocerebroside (GC) as a reference marker, the development of the cell phenotype was studied with video-enhanced differential interference contrast microscopy, immunofluorescence and electron microscopy. After a few days in culture, oligodendrocytes extend 5 to 10 main processes that are very rich in microtubules, but they did not stain with a monoclonal antibody reacting with all known classes of intermediate filaments. The number of processes can vary with the substrate on which the cells are grown; fewer processes form on laminin than on polylysine coated glass. Oligodendrocytes, in a fashion similar to that of neurons appear to keep their body immobile while the long processes grow. However, while neurons display motile activities mostly at the end of the cell processes called growth cones, the oligodendrocytes display motile, actin rich filopodia and lamellipodia along the entire length of all processes. The outgrowth of motile processes from oligodendrocytes sometimes occurs preferentially towards neighboring astrocytes. Oligodendrocyte processes display intense bidirectional movement of cytoplasmic organelles. Movement of surface components also occurs since GC molecules cross-linked by antibodies move from the processes towards the cell body. Thus, oligodendrocytes cultured without neurons develop on schedule a complex phenotype similar to their in vivo counterpart. In addition, their processes are capable of specific motile activities which may function in vivo to find the target axon and to transport myelin membrane components at the site of myelin assembly.

Laminin promotes rabbit neutrophil motility and attachment

Polymorphonuclear neutrophils (PMN) traverse basement membrane to reach sites of infection. We have studied the role of laminin, a specific basement membrane component, in this process using three assay systems. In the Boyden chamber, laminin was found to stimulate chemotaxis of neutrophils while fibronectin did not. Co-incubation of cells with antibody to laminin blocked this chemotaxis, while antibody to fibronectin was without effect. In the human amnion system, neutrophils were shown to penetrate through the tissue when the peptide chemoattractant f-Met-Leu-Phe was placed on the opposing side. Antibody to laminin, but not to fibronectin, blocked this penetration. In an attachment assay system, laminin, but not fibronectin, was found to increase dispase-treated neutrophil attachment to type IV (basement membrane) collagen-coated plastic and to a plastic substrate itself. Electrophoretic analysis of PMN extract indicated the presence of laminin, and indirect immunofluorescence suggested that laminin is localized on the surface of the neutrophils. These data suggest that PMN can bind laminin on their cell surfaces, use laminin to attach to basement (type IV) membrane collagen, and migrate toward a gradient of laminin. These properties may be important for the passage of neutrophils from the circulation to sites of infection.

Schwann cell marker defined by a monoclonal antibody (224-58) with species cross-reactivity. I. Cellular localization

We have demonstrated by indirect immunofluorescence the cellular localization of a monoclonal antibody (mAb 224-58), produced after immunization of a mouse with human central nervous system (CNS) myelin. Serologically, mAb 224-58 was found to be specific for 3'-sulfomonogalactosylglycolipids, namely 3'-sulfogalactosylceramide (SGC) and 3'-sulfogalactosyl 1-O-alkyl ether 2-O-acylglycerol (seminolipid). This mAb did not bind to SGC-containing tissues such as kidney, liver, spleen, or brain, nor to muscle. However mAb 224-58 did stain positively mouse, rat, and human peripheral nerve sections. In these latter sections, mAb 224-58 was bound to Schwann cell bodies and processes. The specificity of mAb 224-58 for Schwann cells was ascertained on teased rat sciatic nerves and rat Schwann cell cultures. Cells positive for mAb 224-58 were also positive for laminin, and negative for Thy 1-1 antigens both in teased fibers and Schwann cell cultures. In addition, in teased nerve preparations, mAb 224-58-positive cells were also galactosylceramide (GalC)- and SGC-positive. Isolated Schwann cells also expressed 224-58 antigen, even after prolonged time in culture. On testis sections, which contain both SGC and seminolipid, the SGC-positive cells, i.e., the spermatogonia, were always 224-58-negative. But the other germinal cells were 224-58-positive. This suggests that although 224-58 does not discriminate between SGC and seminolipid in serological tests, these lipids in their naturally occurring membrane acquire a spatial configuration that renders them distinguishable to their respective antibody.

Human endothelial cells are chemotactic to endothelial cell growth factor and heparin

The response of human endothelial cell migration to various extracellular matrix components and growth factors has been assessed. Human endothelial cells demonstrate increased chemotaxis and chemokinesis when placed in a modified Boyden chamber with endothelial cell growth factor (ECGF) used at a concentration of 10(-9) M. Anti-ECGF antibody inhibits the chemotactic response. Heparin (10(-8) to 10(-10) M) was also chemotactic and was shown to potentiate the chemotactic activity of ECGF. Although laminin, fibronectin, the polypeptide (epidermal, fibroblast, and nerve) growth factors, and collagen types I, II, III, IV, and V demonstrate a chemotactic response, these activities were one third to one half less than observed with ECGF. These data suggest that ECGF and heparin may play a significant role as response modifiers of human endothelial cell migration which may be relevant to tumor metastasis, wound healing, and atherogenesis.

Simultaneous labelling of basal lamina components and acetylcholinesterase at the neuromuscular junction

A double labelling technique has been developed which permits the concomitant localization of basal lamina constituents together with acetylcholinesterase in mouse skeletal muscles. First, using the protein A-gold technique, type IV collagen and laminin were revealed on basal laminae ensheathing skeletal muscle fibres. The immunolabelling for both proteins was higher in synaptic than extrasynaptic regions. At synaptic sites the anti-type IV collagen immunolabelling exhibited an asymmetry; it was more intense on the portion of basal lamina closest to the postsynaptic membrane, whereas the anti-laminin immunolabelling was more uniformly distributed. It was also observed that the laminin immunoreactivity associated with Schwann and perineural cells was higher than that of skeletal muscle fibres. Secondly, the two basal lamina antigens were revealed simultaneously with another synaptic protein, acetylcholinesterase, using a refined cytochemical technique prior to the immunolabelling. The cytochemical reaction, which facilitates the location of endplates, did not alter the immunolabelling pattern. This double labelling procedure permits ready comparison of the distributions of type IV collagen and laminin with that of acetylcholinesterase, and may prove to be a useful approach in studies on synaptic components in developing and diseased muscle.

Laminin detection in normal and retinitis pigmentosa human retina

Epiretinal membrane formation in the posterior pole is an almost constant feature of eyes with retinitis pigmentosa. Using a modified direct immunofluorescence reaction, we demonstrated a strong reaction with antilaminin in a band-like pattern on the inner retinal surface of 3 eyes with retinitis pigmentosa. There were also strongly-laminin-positive pigmented and unpigmented cells scattered throughout the degenerated retinas. This pattern was in sharp contrast to that seen in normal retinas, where the linear band of reaction at the internal limiting membrane was faint and accompanied by a zone of reaction at the level of the outer limiting membrane. Quantitation of laminin by ELISA revealed a six- to ten-fold increase (per mg protein) in retinitis pigmentosa retinas, as compared with normal. Since both glial and retinal pigmented epithelial cells can synthesize and deposit laminin, both may participate in the gliosis that occurs during the course of retinitis pigmentosa.

A neuronal cell surface heparan sulfate proteoglycan is required for dorsal root ganglion neuron stimulation of Schwann cell proliferation

Axons of dorsal root ganglion neurons express on their surfaces one or more proteins which are mitogenic for Schwann cells (Salzer, J., R. P. Bunge, and L. Glaser, 1980, J. Cell Biol., 84:767-778). Incubation of co-cultures of dorsal root ganglion neurons and Schwann cells with 4-methylumbelliferyl-beta-D-xyloside, an inhibitor of proteoglycan biosynthesis, decreases the mitogenic response of the Schwann cell by over 95%. The effect of the beta-D-xyloside has been localized to the neurons; pretreatment of neurons but not of Schwann cells with the inhibitor causes a marked reduction of the mitogenic response. In addition, Schwann cells treated with beta-D-xyloside are still mitogenically responsive to soluble Schwann cell mitogens (cholera toxin and glial growth factor). Neurons treated with heparitinase and membrane vesicles prepared from heparitinase-treated neurons show diminished mitogenicity for Schwann cells, while other proteoglycan lyases have no effect. We conclude that a cell surface heparan sulfate proteoglycan is a component of the Schwann cell mitogen present on the surface of dorsal root ganglion neurons.

Tissue culture studies of neurofibromatosis: effects of axolemmal fragments and cyclic adenosine 3',5'-monophosphate analogues on proliferation of Schwann-like and fibroblast-like neurofibroma cells

Six dermal neurofibromas obtained from 5 patients with neurofibromatosis were dissociated and the cells were plated on polylysine-coated glass. Two principal cell types were observed in the cultures: elongated and bipolar Schwann-like cells (SLCs), and polymorphic flattened fibroblast-like cells (FLCs). Indirect immunofluorescence demonstrated that SLCs expressed surface laminin but not surface fibronectin; FLCs expressed surface fibronectin but were only weakly positive for surface laminin. Tritiated thymidine autoradiography demonstrated that cultured SLCs proliferated slowly (labeling index, 0.7 to 4.0%), whereas FLCs divided more rapidly (labeling index, 7.5 to 26.4%). Axolemmal fragments prepared from human or rat central nervous system specimens adhered to SLCs derived from each of the 6 neurofibromas, but not to FLCs. Axolemmal fragments induced a marked proliferative response of SLCs from 2 of the 6 neurofibromas but had no effect on proliferation of SLCs from the other 4 neurofibromas or FLCs from any of the 6 neurofibromas. In one patient from whom 2 neurofibromas were obtained, SLCs from one neurofibroma responded to axolemmal fragments, while SLCs from the other did not. Treatment of the cultures with 0.1 mM cyclic adenosine 3'5'-monophosphate (cAMP) analogue, 8-bromo cAMP, caused marked inhibition of proliferation of both SLCs and FLCs derived from all 6 neurofibromas. The same concentration of another cAMP analogue, dibutyryl cAMP, inhibited proliferation of SLCs but not of FLCs.

Biological activities of laminin

Laminin is a multifunctional protein with diverse biological activities. Like fibronectin, it can influence cell adhesion, growth, morphology, differentiation, migration, and agglutination as well as the assembly of the extracellular matrix. Laminin primarily affects cells of epithelial origin, and the response varies depending on the cell. Because most differentiated cells are difficult to maintain in culture, laminin may be an important supplement in studies on cell differentiation in vitro.

Modulation of the metastatic activity of melanoma cells by laminin and fibronectin

Metastatic mouse melanoma cells have a high affinity for the basement membrane and the ability to degrade it; these properties may allow tumor cells to invade the membrane and disseminate. In this study it was found that the metastatic potential of mouse melanoma cells varied when the cells were exposed in culture to fibronectin or laminin. After removal of fibronectin or exposure to laminin, the cells had an increased affinity for basement membrane collagen, were more invasive of basement membranes in vitro, and produced more lung colonies in vivo. These changes are correlated with and may be due to an increase in the laminin-binding capacity of the tumor cell surface.