Martin Grumet | Rutgers, The State University of New Jersey (original) (raw)
Papers by Martin Grumet
Cancer research, Jan 15, 1996
An important contributor to the malignancy of brain tumors is their ability to infiltrate the bra... more An important contributor to the malignancy of brain tumors is their ability to infiltrate the brain. Extracellular matrix molecules and cell adhesion molecules on cell surfaces play key roles in cell migration. In the present study, we used reaggregates of dissociated cells from freshly excised human brain tumors to analyze the migration of cells from human brain tumors of different types and grades on many different adhesion proteins adsorbed to glass substrates. Proteins were chosen based on their presence in normal or neoplastic nervous tissue, and included the extra-cellular matrix molecules fibronectin, collagens, fibrinogen, laminin, tenascin-C, thrombospondin, and the neuron-glia cell adhesion molecule, Ng-CAM. Cells from astrocytomas (n = 24) migrated on a variety of substrates, in contrast to cells from primitive neuroectodermal tumors cells (n=6), which only migrated well on laminin, fibronectin, or type IV collagen but not on the other substrates. Typically, migrating cel...
The Journal of cell biology, Jan 17, 2001
The structurally related cell adhesion molecules L1 and Nr-CAM have overlapping expression patter... more The structurally related cell adhesion molecules L1 and Nr-CAM have overlapping expression patterns in cerebellar granule cells. Here we analyzed their involvement in granule cell development using mutant mice. Nr-CAM-deficient cerebellar granule cells failed to extend neurites in vitro on contactin, a known ligand for Nr-CAM expressed in the cerebellum, confirming that these mice are functionally null for Nr-CAM. In vivo, Nr-CAM-null cerebella did not exhibit obvious histological defects, although a mild size reduction of several lobes was observed, most notably lobes IV and V in the vermis. Mice deficient for both L1 and Nr-CAM exhibited severe cerebellar folial defects and a reduction in the thickness of the inner granule cell layer. Additionally, anti-L1 antibodies specifically disrupted survival and maintenance of Nr-CAM-deficient granule cells in cerebellar cultures treated with antibodies. The combined results indicate that Nr-CAM and L1 play a role in cerebellar granule cell...
The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 15, 2000
Specialized paranodal junctions form between the axon and the closely apposed paranodal loops of ... more Specialized paranodal junctions form between the axon and the closely apposed paranodal loops of myelinating glia. They are interposed between sodium channels at the nodes of Ranvier and potassium channels in the juxtaparanodal regions; their precise function and molecular composition have been elusive. We previously reported that Caspr (contactin-associated protein) is a major axonal constituent of these junctions (Einheber et al., 1997). We now report that contactin colocalizes and forms a cis complex with Caspr in the paranodes and juxtamesaxon. These proteins coextract and coprecipitate from neurons, myelinating cultures, and myelin preparations enriched in junctional markers; they fractionate on sucrose gradients as a high-molecular-weight complex, suggesting that other proteins may also be associated with this complex. Neurons express two contactin isoforms that differ in their extent of glycosylation: a lower-molecular-weight phosphatidylinositol phospholipase C (PI-PLC)-resi...
Neurosurgery, 1997
Tenascin-C (TN) is an extracellular matrix glycoprotein with a characteristic six-armed structure... more Tenascin-C (TN) is an extracellular matrix glycoprotein with a characteristic six-armed structure. The aim of this study was to determine whether the concentration of TN in the cyst fluid of brain tumors can be used as a marker for angiogenesis and glioma grade. We investigated the expression of TN in the cyst wall and cyst fluid of human brain tumors by immunohistochemistry, immunoprecipitation, and immunoblotting. The tumors included 12 astrocytomas (5 glioblastoma multiforme tumors, 1 anaplastic astrocytoma, 1 low-grade astrocytoma, 4 juvenile pilocytic astrocytomas, and 1 mixed glioma), 2 dysembryoplastic neuroepithelial tumors, 3 craniopharyngiomas, 2 ependymomas, 2 metastatic carcinomas, 3 arachnoid cysts, 1 glial ependymal cyst, and 1 inflammatory cyst. We detected no expression of TN in the cyst fluids of the ependymomas, craniopharyngiomas, and nonpilocytic low-grade astrocytoma. By contrast, TN was detected in the cyst fluids of all the other tumors. Results of quantitativ...
The Journal of cell biology, 1994
We have previously shown that aggregation of microbeads coated with N-CAM and Ng-CAM is inhibited... more We have previously shown that aggregation of microbeads coated with N-CAM and Ng-CAM is inhibited by incubation with soluble neurocan, a chondroitin sulfate proteoglycan of brain, suggesting that neurocan binds to these cell adhesion molecules (Grumet, M., A. Flaccus, and R. U. Margolis. 1993. J. Cell Biol. 120:815). To investigate these interactions more directly, we have tested binding of soluble 125I-neurocan to microwells coated with different glycoproteins. Neurocan bound at high levels to Ng-CAM and N-CAM, but little or no binding was detected to myelin-associated glycoprotein, EGF receptor, fibronectin, laminin, and collagen IV. The binding to Ng-CAM and N-CAM was saturable and in each case Scatchard plots indicated a high affinity binding site with a dissociation constant of approximately 1 nM. Binding was significantly reduced after treatment of neurocan with chondroitinase, and free chondroitin sulfate inhibited binding of neurocan to Ng-CAM and N-CAM. These results indica...
Journal of Cell Biology, 1986
Immunocytochemical methods were used to show that Ng-CAM (the neuron-glia cell adhesion molecule)... more Immunocytochemical methods were used to show that Ng-CAM (the neuron-glia cell adhesion molecule), N-CAM (the neural cell adhesion mole- cule), 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 anti- bodies to both CAMs but not by antibodies to cytotac-
Receptor protein tyrosine phosphatase b (RPTP b ) is expressed as soluble and receptor forms with... more Receptor protein tyrosine phosphatase b (RPTP b ) is expressed as soluble and receptor forms with common extracellular regions consisting of a car- bonic anhydrase domain (C), a fibronectin type III re- peat (F), and a unique region called S. We showed pre- viously that a recombinant Fc fusion protein with the C domain ( b C) binds to contactin
The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 5, 2003
Molecular events involved in Na+ channel clustering at the node of Ranvier have been investigated... more Molecular events involved in Na+ channel clustering at the node of Ranvier have been investigated during early development. NrCAM, an ankyrinG-binding protein, precedes Na+ channels at cluster sites adjacent to the tips of Schwann cell processes. Both Na+ channel and ankyrinG sequestration at developing nodes are delayed in NrCAM null mutants. The action of NrCAM is manifest locally at individual nodes, rather than affecting overall neuronal expression, and is linked to glial interactions. During remyelination, Na+ channel clusters at new nodes are initially labile, and anchoring to the cytoskeleton appears to grow progressively with time. The distance between Na+ channel clusters across remyelinating Schwann cells (nascent internodes) increases markedly from 83 to 274 microm during node formation, arguing against schemes in which the loci of nodes are fixed in advance by the axon. A hypothesis for node formation in which axonal Na+ channels move by lateral diffusion from regions of...
Trends in Biochemical Sciences, 1998
Receptor-like protein tyrosine phosphatase beta (RPTP beta) shows structural and functional simil... more Receptor-like protein tyrosine phosphatase beta (RPTP beta) shows structural and functional similarity to cell adhesion molecules (CAMs). It binds to several neuronal CAMs and extracellular matrix (ECM) proteins that combine to form cell-recognition complexes. Here, the authors discuss the implications of such complexes for intercellular signaling, and the regulation of RPTP activity by cell-cell and cell-ECM contact.
The Journal of Cell Biology, 1985
The Journal of Cell Biology, 1980
Polylysine was found to induce polymerization of muscle actin in a low ionic strength buffer cont... more Polylysine was found to induce polymerization of muscle actin in a low ionic strength buffer containing 0 .4 mM MgC12. The rate of induced polymerization was dependent on the amount and on the molecular size of the polylysine added . A similar effect was obtained by adding actin nuclei (containing about 2-4 actin subunits) cross-linked by p-NN'-phenylenebismaleimide to G-actin under the same conditions, suggesting that the effect ofpolylysine is due to promotion of the formation of actin nuclei . Polymerization induced by polylysine and by crosslinked actin nuclei was inhibited by low concentrations (10-8-10 -s M) of cytochalasins . Binding experiments showed that actin filaments, but not actin monomers, contained high-affinity binding sites for [3 H]cytochalasin B (one site per 600 actin monomers) . The relative affinity of several cytochalasins for these sites (determined by competitive displacement of [3 H]dihydrocytochalasin B) was : cytochalasin D > cytochalasin E -dihydrocytochalasin B . The results of this study suggest that cytochalasins inhibit nuclei-induced actin polymerization by binding to highly specific sites at the point of monomer addition, i .e ., the elongation site, in actin nuclei and filaments .
The Journal of Cell Biology, 1988
The neuron-glia cell adhesion molecule (Ng-CAM) is present in the central nervous system on postm... more The neuron-glia cell adhesion molecule (Ng-CAM) is present in the central nervous system on postmitotic neurons and in the periphery on neurons and Schwann cells. It has been implicated in binding between neurons and between neurons and glia. To understand the molecular mechanisms of Ng-CAM binding, we analyzed the aggregation of chick Ng-CAM either immobilized on 0.5-~tm beads (Covaspheres) or reconstituted into liposomes. The results were correlated with the binding of these particles to different types of cells as well as with cell-cell binding itself. Both Ng-CAM-Covaspheres and Ng-CAM liposomes individually self-aggregated, and antibodies against Ng-CAM strongly inhibited their aggregation; the rate of aggregation increased approximately with the square of the concentration of the beads or the liposomes. Much higher rates of aggregation were observed when the ratio of Ng-CAM to lipid in the liposome was increased. Radioiodinated Ng-CAM on Covaspheres and in liposomes bound both to neurons and to glial cells and in each case antibodies against Ng-CAM inhibited 50-90% of the binding. Control preparations of fibroblasts and meningeal cells did not exhibit significant binding.
The Journal of Cell Biology, 1986
The neuron-glia cell adhesion molecule (Ng-CAM) has been identified in mammalian brain tissue and... more The neuron-glia cell adhesion molecule (Ng-CAM) has been identified in mammalian brain tissue and PC 12 pheochromocytoma ceils as Mr 200,000 and Mr 230,000 species, respectively. When PC12 cells were treated with nerve growth factor (NGF), the amount of Ng-CAM at the cell surface was increased approximately threefold, whereas the amount of the neural cell adhesion molecule (N-CAM) remained unchanged. An NGF-inducible large external glycoprotein (NILE) has been previously identified by its enhanced expression in NGFtreated PC 12 cells. Ng-CAM and NILE are similar in molecular weight, expression during development, and responsiveness to NGF in PC I2 cells, suggesting that the two molecules are related. In addition, antibodies to Ng-CAM and NILE cross-reacted and the molecules had similar peptide maps after limited proteolysis. Moreover, antibodies to Ng-CAM inhibited fasciculation of neurites, a functional property shared with NILE. The results show that cell adhesion molecules can respond selectively to growth factors and suggest that NILE is, in fact, mammalian Ng-CAM.
The Journal of Cell Biology, 1986
Peripheral nerve injury results in short-term and long-term changes in both neurons and glia. In ... more 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-
The Journal of Cell Biology, 1986
Individual neurons can express both the neural cell adhesion molecule (N-CAM) and the neuron-glia... more Individual neurons can express both the neural cell adhesion molecule (N-CAM) and the neuron-glia cell adhesion molecule (Ng-CAM) at their cell surfaces. To determine how the functions of the two molecules may be differentially controlled, we have used specific antibodies to each cell adhesion molecule (CAM) to perturb its function, first in brain membrane vesicle aggregation and then in tissue culture assays testing the fasciculation of neurite outgrowths from cultured dorsal root ganglia, the migration of granule cells in cerebellar explants, and the formation of histological layers in the developing retina. Our strategy was
The Journal of Cell Biology, 1991
The neuron-glia cell adhesion molecule (Ng-CAM) mediates both neuron-neuron and neuron-glia adhes... more The neuron-glia cell adhesion molecule (Ng-CAM) mediates both neuron-neuron and neuron-glia adhesion; it is detected on SDS-PAGE as a predominant 135-kD glycoprotein, with minor components of 80, 190, and 210 kD. We have isolated cDNA clones encoding the entire sequence of chicken Ng-CAM. The predicted extracellular region includes six immunoglobulin-like domains followed by five fibronectin-type III repeats, structural features that are characteristic of several neural CAMs of the N-CAM superfamily. The amino acid sequence of chicken Ng-CAM is most similar to that of mouse L1 but the overall identity is only 40% and Ng-CAM contains a short fibronectin-like segment with an RGD sequence that has no counterpart in L1. These findings suggest that Ng-CAM and L1 may not be equivalent molecules in chicken and mouse.
The Journal of Cell Biology, 1984
By means of a multistage quantitative assay, we have identified a new kind of cell adhesion molec... more By means of a multistage quantitative assay, we have identified a new kind of cell adhesion molecule (CAM) on neuronal cells of the chick embryo that is involved in their adhesion to glial cells. The assay used to identify the binding component (which we name neuron-glia CAM or Ng-CAM) w~s,designed to distinguish between homotypic binding (e .g., neuron to neuron) and heterotypic binding (e .g., neuron to glia) . This distinction was essential because a single neuron might simultaneously carry different CAMS separately mediating each of these interactions . The adhesion of neuronal cells to glial cells in vitro was previously found to be inhibited by Fab' fragments prepared from antisera against neuronal membranes but not by Fab' fragments against N-CAM, the neural cell adhesion molecule. This suggested that neuron-glia adhesion is mediated by specific cell surface molecules different from previously isolated CAMS . To verify that this was the case, neuronal membrane vesicles were labeled internally with 6-carboxyfluorescein and externally with 125 1-labeled antibodies to N-CAM to block their homotypic binding. Labeled vesicles bound to glial cells but not to fibroblasts during a 30-min incubation period . The specific binding of the neuronal vesicles to glial cells was measured by fluorescence microscopy and gamma spectroscopy of the 125 1 label . Binding increased with increasing concentrations of both glial cells and neuronal vesicles . Fab' fragments prepared from anti-neuronal membrane sera that inhibited binding between neurons and glial cells were also found to inhibit neuronal vesicle binding to glial cells .
The Journal of Cell Biology, 1991
We have identified and characterized a new
The Journal of Cell Biology, 1985
This study represents a global survey of the times of the first appearance of the neuron-glia cel... more This study represents a global survey of the times of the first appearance of the neuron-glia cell adhesion molecule (Ng-CAM) in various regions and on particular cells of the chick embryonic nervous system. Ng-CAM, originally characterized by means of an in vitro binding assay between glial cells and brain membrane vesicles, first appears in development at the surface of early postmitotic neurons. By 3 d in the chick embryo, the first neurons detected by antibodies to Ng-CAM are located in the ventral neural tube; these precursors of motor neurons emit well-stained fibers to the periphery. To identify locations of appearance of Ng-CAM in the peripheral nervous system (PNS), we used a monoclonal antibody called NC-1 that is specific for neural crest cells in early embryos to show the presence of numerous crest cells in the neuritic outgrowth from the neural tube; neither these crest cells nor those in ganglion rudiments bound anti-Ng-CAM antibodies. The earliest neurons in the PNS stained by anti-Ng-CAM appeared by 4 d of development in the cranial ganglia. At later stages and progressively, all the neurons and neurities of the PNS were found to contain Ng-CAM both in vitro and in vivo. Many central nervous system (CNS) neurons also showed Ng-CAM at these later stages, but in the CNS, the molecule was mostly associated with neuronal processes (mainly axons) rather than with cell bodies; this regional distribution at the neuronal cell surface is an example of polarity modulation.
The Journal of Cell Biology, 1994
Phosphacan is a chondroitin sulfate proteoglycan produced by glial cells in the central nervous s... more Phosphacan is a chondroitin sulfate proteoglycan produced by glial cells in the central nervous system, and represents the extracellular domain of a receptor-type protein tyrosine phosphatase (RPTP zeta/beta). We previously demonstrated that soluble phosphacan inhibited the aggregation of microbeads coated with N-CAM or Ng-CAM, and have now found that soluble 125I-phosphacan bound reversibly to these neural cell adhesion molecules, but not to a number of other cell surface and extracellular matrix proteins. The binding was saturable, and Scatchard plots indicated a single high affinity binding site with a Kd of approximately 0.1 nM. Binding was reduced by approximately 15% after chondroitinase treatment, and free chondroitin sulfate was only moderately inhibitory, indicating that the phosphacan core glycoprotein accounts for most of the binding activity. Immunocytochemical studies of embryonic rat spinal phosphacan, Ng-CAM, and N-CAM have overlapping distributions. When dissociated neurons were incubated on dishes coated with combinations of phosphacan and Ng-CAM, neuronal adhesion and neurite growth were inhibited. 125I-phosphacan bound to neurons, and the binding was inhibited by antibodies against Ng-CAM and N-CAM, suggesting that these CAMs are major receptors for phosphacan on neurons. C6 glioma cells, which express phosphacan, adhered to dishes coated with Ng-CAM, and low concentrations of phosphacan inhibited adhesion to Ng-CAM but not to laminin and fibronectin. Our studies suggest that by binding to neural cell adhesion molecules, and possibly also by competing for ligands of the transmembrane phosphatase, phosphacan may play a major role in modulating neuronal and glial adhesion, neurite growth, and signal transduction during the development of the central nervous system.
Cancer research, Jan 15, 1996
An important contributor to the malignancy of brain tumors is their ability to infiltrate the bra... more An important contributor to the malignancy of brain tumors is their ability to infiltrate the brain. Extracellular matrix molecules and cell adhesion molecules on cell surfaces play key roles in cell migration. In the present study, we used reaggregates of dissociated cells from freshly excised human brain tumors to analyze the migration of cells from human brain tumors of different types and grades on many different adhesion proteins adsorbed to glass substrates. Proteins were chosen based on their presence in normal or neoplastic nervous tissue, and included the extra-cellular matrix molecules fibronectin, collagens, fibrinogen, laminin, tenascin-C, thrombospondin, and the neuron-glia cell adhesion molecule, Ng-CAM. Cells from astrocytomas (n = 24) migrated on a variety of substrates, in contrast to cells from primitive neuroectodermal tumors cells (n=6), which only migrated well on laminin, fibronectin, or type IV collagen but not on the other substrates. Typically, migrating cel...
The Journal of cell biology, Jan 17, 2001
The structurally related cell adhesion molecules L1 and Nr-CAM have overlapping expression patter... more The structurally related cell adhesion molecules L1 and Nr-CAM have overlapping expression patterns in cerebellar granule cells. Here we analyzed their involvement in granule cell development using mutant mice. Nr-CAM-deficient cerebellar granule cells failed to extend neurites in vitro on contactin, a known ligand for Nr-CAM expressed in the cerebellum, confirming that these mice are functionally null for Nr-CAM. In vivo, Nr-CAM-null cerebella did not exhibit obvious histological defects, although a mild size reduction of several lobes was observed, most notably lobes IV and V in the vermis. Mice deficient for both L1 and Nr-CAM exhibited severe cerebellar folial defects and a reduction in the thickness of the inner granule cell layer. Additionally, anti-L1 antibodies specifically disrupted survival and maintenance of Nr-CAM-deficient granule cells in cerebellar cultures treated with antibodies. The combined results indicate that Nr-CAM and L1 play a role in cerebellar granule cell...
The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 15, 2000
Specialized paranodal junctions form between the axon and the closely apposed paranodal loops of ... more Specialized paranodal junctions form between the axon and the closely apposed paranodal loops of myelinating glia. They are interposed between sodium channels at the nodes of Ranvier and potassium channels in the juxtaparanodal regions; their precise function and molecular composition have been elusive. We previously reported that Caspr (contactin-associated protein) is a major axonal constituent of these junctions (Einheber et al., 1997). We now report that contactin colocalizes and forms a cis complex with Caspr in the paranodes and juxtamesaxon. These proteins coextract and coprecipitate from neurons, myelinating cultures, and myelin preparations enriched in junctional markers; they fractionate on sucrose gradients as a high-molecular-weight complex, suggesting that other proteins may also be associated with this complex. Neurons express two contactin isoforms that differ in their extent of glycosylation: a lower-molecular-weight phosphatidylinositol phospholipase C (PI-PLC)-resi...
Neurosurgery, 1997
Tenascin-C (TN) is an extracellular matrix glycoprotein with a characteristic six-armed structure... more Tenascin-C (TN) is an extracellular matrix glycoprotein with a characteristic six-armed structure. The aim of this study was to determine whether the concentration of TN in the cyst fluid of brain tumors can be used as a marker for angiogenesis and glioma grade. We investigated the expression of TN in the cyst wall and cyst fluid of human brain tumors by immunohistochemistry, immunoprecipitation, and immunoblotting. The tumors included 12 astrocytomas (5 glioblastoma multiforme tumors, 1 anaplastic astrocytoma, 1 low-grade astrocytoma, 4 juvenile pilocytic astrocytomas, and 1 mixed glioma), 2 dysembryoplastic neuroepithelial tumors, 3 craniopharyngiomas, 2 ependymomas, 2 metastatic carcinomas, 3 arachnoid cysts, 1 glial ependymal cyst, and 1 inflammatory cyst. We detected no expression of TN in the cyst fluids of the ependymomas, craniopharyngiomas, and nonpilocytic low-grade astrocytoma. By contrast, TN was detected in the cyst fluids of all the other tumors. Results of quantitativ...
The Journal of cell biology, 1994
We have previously shown that aggregation of microbeads coated with N-CAM and Ng-CAM is inhibited... more We have previously shown that aggregation of microbeads coated with N-CAM and Ng-CAM is inhibited by incubation with soluble neurocan, a chondroitin sulfate proteoglycan of brain, suggesting that neurocan binds to these cell adhesion molecules (Grumet, M., A. Flaccus, and R. U. Margolis. 1993. J. Cell Biol. 120:815). To investigate these interactions more directly, we have tested binding of soluble 125I-neurocan to microwells coated with different glycoproteins. Neurocan bound at high levels to Ng-CAM and N-CAM, but little or no binding was detected to myelin-associated glycoprotein, EGF receptor, fibronectin, laminin, and collagen IV. The binding to Ng-CAM and N-CAM was saturable and in each case Scatchard plots indicated a high affinity binding site with a dissociation constant of approximately 1 nM. Binding was significantly reduced after treatment of neurocan with chondroitinase, and free chondroitin sulfate inhibited binding of neurocan to Ng-CAM and N-CAM. These results indica...
Journal of Cell Biology, 1986
Immunocytochemical methods were used to show that Ng-CAM (the neuron-glia cell adhesion molecule)... more Immunocytochemical methods were used to show that Ng-CAM (the neuron-glia cell adhesion molecule), N-CAM (the neural cell adhesion mole- cule), 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 anti- bodies to both CAMs but not by antibodies to cytotac-
Receptor protein tyrosine phosphatase b (RPTP b ) is expressed as soluble and receptor forms with... more Receptor protein tyrosine phosphatase b (RPTP b ) is expressed as soluble and receptor forms with common extracellular regions consisting of a car- bonic anhydrase domain (C), a fibronectin type III re- peat (F), and a unique region called S. We showed pre- viously that a recombinant Fc fusion protein with the C domain ( b C) binds to contactin
The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 5, 2003
Molecular events involved in Na+ channel clustering at the node of Ranvier have been investigated... more Molecular events involved in Na+ channel clustering at the node of Ranvier have been investigated during early development. NrCAM, an ankyrinG-binding protein, precedes Na+ channels at cluster sites adjacent to the tips of Schwann cell processes. Both Na+ channel and ankyrinG sequestration at developing nodes are delayed in NrCAM null mutants. The action of NrCAM is manifest locally at individual nodes, rather than affecting overall neuronal expression, and is linked to glial interactions. During remyelination, Na+ channel clusters at new nodes are initially labile, and anchoring to the cytoskeleton appears to grow progressively with time. The distance between Na+ channel clusters across remyelinating Schwann cells (nascent internodes) increases markedly from 83 to 274 microm during node formation, arguing against schemes in which the loci of nodes are fixed in advance by the axon. A hypothesis for node formation in which axonal Na+ channels move by lateral diffusion from regions of...
Trends in Biochemical Sciences, 1998
Receptor-like protein tyrosine phosphatase beta (RPTP beta) shows structural and functional simil... more Receptor-like protein tyrosine phosphatase beta (RPTP beta) shows structural and functional similarity to cell adhesion molecules (CAMs). It binds to several neuronal CAMs and extracellular matrix (ECM) proteins that combine to form cell-recognition complexes. Here, the authors discuss the implications of such complexes for intercellular signaling, and the regulation of RPTP activity by cell-cell and cell-ECM contact.
The Journal of Cell Biology, 1985
The Journal of Cell Biology, 1980
Polylysine was found to induce polymerization of muscle actin in a low ionic strength buffer cont... more Polylysine was found to induce polymerization of muscle actin in a low ionic strength buffer containing 0 .4 mM MgC12. The rate of induced polymerization was dependent on the amount and on the molecular size of the polylysine added . A similar effect was obtained by adding actin nuclei (containing about 2-4 actin subunits) cross-linked by p-NN'-phenylenebismaleimide to G-actin under the same conditions, suggesting that the effect ofpolylysine is due to promotion of the formation of actin nuclei . Polymerization induced by polylysine and by crosslinked actin nuclei was inhibited by low concentrations (10-8-10 -s M) of cytochalasins . Binding experiments showed that actin filaments, but not actin monomers, contained high-affinity binding sites for [3 H]cytochalasin B (one site per 600 actin monomers) . The relative affinity of several cytochalasins for these sites (determined by competitive displacement of [3 H]dihydrocytochalasin B) was : cytochalasin D > cytochalasin E -dihydrocytochalasin B . The results of this study suggest that cytochalasins inhibit nuclei-induced actin polymerization by binding to highly specific sites at the point of monomer addition, i .e ., the elongation site, in actin nuclei and filaments .
The Journal of Cell Biology, 1988
The neuron-glia cell adhesion molecule (Ng-CAM) is present in the central nervous system on postm... more The neuron-glia cell adhesion molecule (Ng-CAM) is present in the central nervous system on postmitotic neurons and in the periphery on neurons and Schwann cells. It has been implicated in binding between neurons and between neurons and glia. To understand the molecular mechanisms of Ng-CAM binding, we analyzed the aggregation of chick Ng-CAM either immobilized on 0.5-~tm beads (Covaspheres) or reconstituted into liposomes. The results were correlated with the binding of these particles to different types of cells as well as with cell-cell binding itself. Both Ng-CAM-Covaspheres and Ng-CAM liposomes individually self-aggregated, and antibodies against Ng-CAM strongly inhibited their aggregation; the rate of aggregation increased approximately with the square of the concentration of the beads or the liposomes. Much higher rates of aggregation were observed when the ratio of Ng-CAM to lipid in the liposome was increased. Radioiodinated Ng-CAM on Covaspheres and in liposomes bound both to neurons and to glial cells and in each case antibodies against Ng-CAM inhibited 50-90% of the binding. Control preparations of fibroblasts and meningeal cells did not exhibit significant binding.
The Journal of Cell Biology, 1986
The neuron-glia cell adhesion molecule (Ng-CAM) has been identified in mammalian brain tissue and... more The neuron-glia cell adhesion molecule (Ng-CAM) has been identified in mammalian brain tissue and PC 12 pheochromocytoma ceils as Mr 200,000 and Mr 230,000 species, respectively. When PC12 cells were treated with nerve growth factor (NGF), the amount of Ng-CAM at the cell surface was increased approximately threefold, whereas the amount of the neural cell adhesion molecule (N-CAM) remained unchanged. An NGF-inducible large external glycoprotein (NILE) has been previously identified by its enhanced expression in NGFtreated PC 12 cells. Ng-CAM and NILE are similar in molecular weight, expression during development, and responsiveness to NGF in PC I2 cells, suggesting that the two molecules are related. In addition, antibodies to Ng-CAM and NILE cross-reacted and the molecules had similar peptide maps after limited proteolysis. Moreover, antibodies to Ng-CAM inhibited fasciculation of neurites, a functional property shared with NILE. The results show that cell adhesion molecules can respond selectively to growth factors and suggest that NILE is, in fact, mammalian Ng-CAM.
The Journal of Cell Biology, 1986
Peripheral nerve injury results in short-term and long-term changes in both neurons and glia. In ... more 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-
The Journal of Cell Biology, 1986
Individual neurons can express both the neural cell adhesion molecule (N-CAM) and the neuron-glia... more Individual neurons can express both the neural cell adhesion molecule (N-CAM) and the neuron-glia cell adhesion molecule (Ng-CAM) at their cell surfaces. To determine how the functions of the two molecules may be differentially controlled, we have used specific antibodies to each cell adhesion molecule (CAM) to perturb its function, first in brain membrane vesicle aggregation and then in tissue culture assays testing the fasciculation of neurite outgrowths from cultured dorsal root ganglia, the migration of granule cells in cerebellar explants, and the formation of histological layers in the developing retina. Our strategy was
The Journal of Cell Biology, 1991
The neuron-glia cell adhesion molecule (Ng-CAM) mediates both neuron-neuron and neuron-glia adhes... more The neuron-glia cell adhesion molecule (Ng-CAM) mediates both neuron-neuron and neuron-glia adhesion; it is detected on SDS-PAGE as a predominant 135-kD glycoprotein, with minor components of 80, 190, and 210 kD. We have isolated cDNA clones encoding the entire sequence of chicken Ng-CAM. The predicted extracellular region includes six immunoglobulin-like domains followed by five fibronectin-type III repeats, structural features that are characteristic of several neural CAMs of the N-CAM superfamily. The amino acid sequence of chicken Ng-CAM is most similar to that of mouse L1 but the overall identity is only 40% and Ng-CAM contains a short fibronectin-like segment with an RGD sequence that has no counterpart in L1. These findings suggest that Ng-CAM and L1 may not be equivalent molecules in chicken and mouse.
The Journal of Cell Biology, 1984
By means of a multistage quantitative assay, we have identified a new kind of cell adhesion molec... more By means of a multistage quantitative assay, we have identified a new kind of cell adhesion molecule (CAM) on neuronal cells of the chick embryo that is involved in their adhesion to glial cells. The assay used to identify the binding component (which we name neuron-glia CAM or Ng-CAM) w~s,designed to distinguish between homotypic binding (e .g., neuron to neuron) and heterotypic binding (e .g., neuron to glia) . This distinction was essential because a single neuron might simultaneously carry different CAMS separately mediating each of these interactions . The adhesion of neuronal cells to glial cells in vitro was previously found to be inhibited by Fab' fragments prepared from antisera against neuronal membranes but not by Fab' fragments against N-CAM, the neural cell adhesion molecule. This suggested that neuron-glia adhesion is mediated by specific cell surface molecules different from previously isolated CAMS . To verify that this was the case, neuronal membrane vesicles were labeled internally with 6-carboxyfluorescein and externally with 125 1-labeled antibodies to N-CAM to block their homotypic binding. Labeled vesicles bound to glial cells but not to fibroblasts during a 30-min incubation period . The specific binding of the neuronal vesicles to glial cells was measured by fluorescence microscopy and gamma spectroscopy of the 125 1 label . Binding increased with increasing concentrations of both glial cells and neuronal vesicles . Fab' fragments prepared from anti-neuronal membrane sera that inhibited binding between neurons and glial cells were also found to inhibit neuronal vesicle binding to glial cells .
The Journal of Cell Biology, 1991
We have identified and characterized a new
The Journal of Cell Biology, 1985
This study represents a global survey of the times of the first appearance of the neuron-glia cel... more This study represents a global survey of the times of the first appearance of the neuron-glia cell adhesion molecule (Ng-CAM) in various regions and on particular cells of the chick embryonic nervous system. Ng-CAM, originally characterized by means of an in vitro binding assay between glial cells and brain membrane vesicles, first appears in development at the surface of early postmitotic neurons. By 3 d in the chick embryo, the first neurons detected by antibodies to Ng-CAM are located in the ventral neural tube; these precursors of motor neurons emit well-stained fibers to the periphery. To identify locations of appearance of Ng-CAM in the peripheral nervous system (PNS), we used a monoclonal antibody called NC-1 that is specific for neural crest cells in early embryos to show the presence of numerous crest cells in the neuritic outgrowth from the neural tube; neither these crest cells nor those in ganglion rudiments bound anti-Ng-CAM antibodies. The earliest neurons in the PNS stained by anti-Ng-CAM appeared by 4 d of development in the cranial ganglia. At later stages and progressively, all the neurons and neurities of the PNS were found to contain Ng-CAM both in vitro and in vivo. Many central nervous system (CNS) neurons also showed Ng-CAM at these later stages, but in the CNS, the molecule was mostly associated with neuronal processes (mainly axons) rather than with cell bodies; this regional distribution at the neuronal cell surface is an example of polarity modulation.
The Journal of Cell Biology, 1994
Phosphacan is a chondroitin sulfate proteoglycan produced by glial cells in the central nervous s... more Phosphacan is a chondroitin sulfate proteoglycan produced by glial cells in the central nervous system, and represents the extracellular domain of a receptor-type protein tyrosine phosphatase (RPTP zeta/beta). We previously demonstrated that soluble phosphacan inhibited the aggregation of microbeads coated with N-CAM or Ng-CAM, and have now found that soluble 125I-phosphacan bound reversibly to these neural cell adhesion molecules, but not to a number of other cell surface and extracellular matrix proteins. The binding was saturable, and Scatchard plots indicated a single high affinity binding site with a Kd of approximately 0.1 nM. Binding was reduced by approximately 15% after chondroitinase treatment, and free chondroitin sulfate was only moderately inhibitory, indicating that the phosphacan core glycoprotein accounts for most of the binding activity. Immunocytochemical studies of embryonic rat spinal phosphacan, Ng-CAM, and N-CAM have overlapping distributions. When dissociated neurons were incubated on dishes coated with combinations of phosphacan and Ng-CAM, neuronal adhesion and neurite growth were inhibited. 125I-phosphacan bound to neurons, and the binding was inhibited by antibodies against Ng-CAM and N-CAM, suggesting that these CAMs are major receptors for phosphacan on neurons. C6 glioma cells, which express phosphacan, adhered to dishes coated with Ng-CAM, and low concentrations of phosphacan inhibited adhesion to Ng-CAM but not to laminin and fibronectin. Our studies suggest that by binding to neural cell adhesion molecules, and possibly also by competing for ligands of the transmembrane phosphatase, phosphacan may play a major role in modulating neuronal and glial adhesion, neurite growth, and signal transduction during the development of the central nervous system.