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N Ratner

Publications and source records attributed to N Ratner.

At least 55 records · Page 3Linked to original sources
PubMed1992

Neurofibromin, a predominantly neuronal GTPase activating protein in the adult, is ubiquitously expressed during development.

The onset of manifestations of the common, autosomal dominantly inherited disease type 1 neurofibromatosis (NF1) is usually in childhood. To begin to understand the pathogenesis of NF1, we analyzed the developmental pattern of expression of the protein product of the NF1 gene, neurofibromin, by Western blotting and immunohistochemistry using the rat as a model system. Neurofibromin is uniformly distributed throughout embryonic day 10 and 12 rat embryos. By embryonic day 16, neurofibromin immunoreactivity is enriched in neurons of the cortical plate, in peripheral ganglia, and in developing CNS and PNS fiber tracts, but remains detectable outside the nervous system. Expression decreases in nonneural tissues by postnatal day 6, and neurofibromin is greatly decreased (lung, adrenal cortex, skin) or absent (skeletal muscle, cartilage) in adult tissues except for brain, spinal cord, peripheral nerve, and adrenal medulla. Transient expression of neurofibromin during development in many tissues suggests the importance of this GTPase-activating protein in morphogenesis and organ growth. A separate role is proposed for neurofibromin in growing axons and in the mature nervous system.

Animals↗
PubMed1992

Schwann cells and cells in the oligodendrocyte lineage proliferate in response to a 50,000 dalton membrane-associated mitogen present in developing brain.

The neuronal cell surface is believed to carry a mitogenic signal for peripheral glial cells. We have purified a mitogen from fetal bovine brain membranes that, in common with the PNS neuronal mitogen, stimulates the proliferation of Schwann cells in vitro and binds heparin. The purified mitogen has an apparent molecular weight of 50,000 daltons as estimated by elution of activity from non-reducing polyacrylamide gels. Since the developing central nervous system is a rich source of mitogen, we tested whether the protein is mitogenic for one or more cell types isolated from the developing brain. Purified mitogen was added to enriched cultures of astrocytes or developing oligodendrocytes, or to microglial cells. The analyses demonstrated that the protein is mitogenic for developing oligodendrocytes but not astrocytes or microglial cells. These results suggest that during development a membrane-associated mitogen present in the brain might regulate the proliferation of developing oligodendrocytes, and consequently, the population size of oligodendrocytes in the brain.

Animals↗
PubMed1992

S100 is present in developing chicken neurons and Schwann cells and promotes motor neuron survival in vivo.

We used polyclonal antisera recognizing S100, a small acidic protein highly enriched in nervous tissue, to stain sections of embryonic chicken lumbosacral spinal cord and hindlimb. S100 immunoreactivity was detected in developing sensory neurons of the dorsal root ganglia (DRG) and motor neurons of the ventral spinal cord as early as embryonic day (E) 5, and staining persisted through hatching. In contrast, expression of S100 first became apparent in Schwann cells at E13, just before myelination, and was not detected in developing skin or muscle. Since S100 beta was present in motor and sensory neurons and is known to promote neuronal survival and neurite extension in vitro (Winningham-Major, Staecker, Barger, Coats, and Van Eldik, 1989), we tested the ability of S100 to promote neuron survival in an in ovo survival assay. Addition of S100 to chick embryos in ovo during the period of naturally occurring motor neuron cell death resulted in a significant increase in motor neuron survival, but had no effect on the in vivo survival of sensory neurons in the DRG. The findings that S100 is present in spinal motor neurons and that the addition of S100 enhances the survival of these cells in vivo are consistent with the possibility that S100 may act as a naturally occurring neuron survival factor during development.

Animals↗
PubMed1992

The protein product of the neurofibromatosis type 1 gene is expressed at highest abundance in neurons, Schwann cells, and oligodendrocytes.

von Recklinghausen's neurofibromatosis (NF1) is a common inherited human disease. The events leading to patient symptoms from inheritance of a defective NF1 gene are unknown. Since knowledge of the distribution of the normal NF1 gene product should improve understanding of the pathogenesis of the disease, we raised antibodies against peptides coded by portions of the recently cloned human NF1 cDNA. These antibodies specifically recognize a 220 kd protein (neurofibromin) in both human and rat spinal cord. Neurofibromin is most abundant in the nervous system. Immunostaining of tissue sections indicates that neurons, oligodendrocytes, and nonmyelinating Schwann cells contain neurofibromin while astrocytes and myelinating Schwann cells do not. These results suggest a function for neurofibromin in the normal nervous system. Some NF1 disease manifestations, such as Schwann cell tumors and learning disabilities, may result from abnormalities in the cells that express neurofibromin.

Animals↗
PubMed1991

P0 is an early marker of the Schwann cell lineage in chickens.

We have generated a monoclonal antibody, termed 1E8, that is specific for myelinating and nonmyelinating Schwann cells in mature chickens. 1E8 first stains cells at the edge of the neural crest; later, cells located between the neural tube and somites and in the sclerotome are immunopositive. Double labeling with HNK-1 indicates that these 1E8-positive cells represent a subset of neural crest cells in the ventral migratory pathways. 1E8-positive cells are later associated with the dorsal and ventral roots and with extending nerve trunks. In Western blots, 1E8 reacts with proteins comigrating with P0. Immunodepletion experiments establish that all P0 molecules carry the 1E8 determinant. The developmental distribution of P0, as determined by 1E8 immunoreactivity, differs from that reported for P0 in mammals and suggests that, in chicken, P0 is an early marker for the Schwann cell lineage.

Animals↗
PubMed1991

Expression of P30, a protein with adhesive properties, in Schwann cells and neurons of the developing and regenerating peripheral nerve.

P30 is a heparin-binding protein with adhesive and neurite outgrowth-promoting properties present at high levels in the developing rat central nervous system (Rauvala, H., and R. Pihlaskari. 1987 J. Biol. Chem. 262:16625-16635). Partial sequencing of p30 has revealed homology or identity with HMG-1 (Rauvala, H., J. Merenmies, R. Pihlaskari, M. Korkolainen, M.-L. Huhtala, and P. Panula. 1988. J. Cell Biol. 107:2292-2305), a 28-kD protein that was originally purified from the thymus (Goodwin, G.H., C. Sanders, and E. W. Johns. 1973. Eur. J. Biochem. 38:14-19) which binds DNA in vitro. We have analyzed the distribution of p30 in the developing rat peripheral nervous system (PNS). P30 was detected by immunohistochemistry and Western blot analysis using antibodies raised against intact p30 and against a synthetic peptide corresponding to the amino terminus of the p30 molecule. P30 was localized to nonnuclear compartments of neurons and peripheral glial cells (Schwann cells). P30 immunoreactivity of PNS neurons persisted into adulthood. In contrast, Schwann cell staining decreased after the second postnatal week and was not detectable in adult animals. Neuron-Schwann cell contact was correlated with diminished p30 levels in Schwann cells. Schwann cells of the normal adult sciatic nerve did not express p30; however, when deprived of axonal contact by nerve transection, the Schwann cells of the distal nerve stained intensely for p30. In addition, when Schwann cells and dorsal root ganglion neurons were grown in coculture, Schwann cells that were associated with neurites were not as intensely stained by anti-p30 as Schwann cells that were not in contact with neurons. The pattern of p30 expression during development and regeneration, and its apparent regulation by cell-cell contact suggests that p30 plays a role in the interaction between neurons and Schwann cells during morphogenesis of peripheral nerves.

Aging↗
PubMed1990

Mitogen accumulation in von Recklinghausen neurofibromatosis.

Most, but not all, patients with von Recklinghausen neurofibromatosis develop tumors (neurofibromas) that contain large numbers of Schwann cells and fibroblasts. To begin to understand the molecular events that contribute to cell proliferation in these benign tumors, we have analyzed extracts of neurofibromas to determine whether they contain mitogens for Schwann cells or fibroblasts, or both. Schwann cell and fibroblast mitogens are present in neurofibroma extracts. All the neurofibromas analyzed contain a Schwann cell mitogen similar to a neuronal cell surface molecule known to stimulate Schwann cell proliferation during normal development; this mitogen also stimulates fibroblast proliferation. Basic fibroblast growth factor is present in 60% of tumors evaluated. Accumulation of mitogenic substances may contribute to the growth of neurofibromas.

Cell Division↗
PubMed1990

Angiogenic and invasive properties of neurofibroma Schwann cells.

Neurofibromas are benign tumors from patients with von Recklinghausen Neurofibromatosis (NF1) that are comprised primarily of Schwann cells. These Schwann cells are found both in association with axons and in the extracellular matrix that is prevalent in neurofibromas, and in which fibroblasts are also abundant. An unresolved question has been whether cells in neurofibromas are normal cells or are intrinsically abnormal. We have tested the hypothesis that cells in neurofibromas are abnormal and have shown that neurofibroma Schwann cells, unlike normal Schwann cells, promote angiogenesis in the chick chorioallantoic membrane model system, and invade basement membranes in this system. In contrast, neurofibroma fibroblasts neither promote angiogenic reactions nor invade basement membranes. When injected into nude mice, neurofibroma Schwann cells do not form progressive tumors. These results suggest that NF1 Schwann cells differ from normal Schwann cells, that they are preneoplastic, and that genetic and/or epigenetic changes in Schwann cells may be required for development of peripheral nerve tumors in NF1.

Allantois↗
PubMed1988

The neuronal cell-surface molecule mitogenic for Schwann cells is a heparin-binding protein.

The cell surface of embryonic peripheral neurons provides a mitogenic stimulus for Schwann cells. We report (i) the solubilization of this mitogenic activity from rat dorsal root ganglion neurons grown in tissue culture and (ii) the solubilization and partial purification of mitogenic activity from neonatal rat brains. Extracted mitogenic activity is peripheral rather than intrinsic to the membrane, stable after extraction, and active as a mitogen in the absence of serum (the most stringent criterion defining the neuronal mitogen). We have previously provided evidence suggesting that a neuronal cell-surface heparan sulfate proteoglycan is required for expression of the neurons' mitogenic activity. We now show that mitogenic activity can be extracted from the membrane dissociated from proteoglycan as assayed by its ability to bind to immobilized heparin. After dissociation, low concentrations of heparin (1 micrograms/ml) inhibit the ability of the mitogen to stimulate Schwann cell division. Basic fibroblast growth factor (FGF) is weakly mitogenic for Schwann cells, but it is not present in mitogenic brain extracts (based on immunoblotting). Immunodepletion experiments with specific antibodies to FGF indicate that the mitogenic activity extracted from neurons is not a form of this heparin-binding mitogen. Acidic FGF is not mitogenic for Schwann cells and is not present in mitogenic brain extracts. We suggest that these and previous data indicate the neurite mitogen is a proteoglycan-growth factor complex that limits mitogenic activity to the axonal surface, protects mitogen against inactivation by other proteoglycans, and provides for effective presentation of mitogen to the Schwann cell.

Animals↗
PubMed1986

Specific asparagine-linked oligosaccharides are not required for certain neuron-neuron and neuron-Schwann cell interactions.

To determine whether specific asparagine-linked (N-linked) oligosaccharides present in cell surface glycoproteins are required for cell-cell interactions within the peripheral nervous system, we have used castanospermine to inhibit maturation of N-linked sugars in cell cultures of neurons or neurons plus Schwann cells. Maximally 10-15% of the N-linked oligosaccharides on neuronal proteins have normal structure when cells are cultured in the presence of 250 micrograms/ml castanospermine; the remaining oligosaccharides are present as immature carbohydrate chains not normally found in these glycoproteins. Although cultures were treated for 2 wk with castanospermine, cells always remained viable and appeared healthy. We have analyzed several biological responses of embryonic dorsal root ganglion neurons, with or without added purified populations of Schwann cells, in the presence of castanospermine. We have observed that a normal complement of mature, N-linked sugars are not required for neurite outgrowth, neuron-Schwann cell adhesion, neuron-induced Schwann cell proliferation, or ensheathment of neurites by Schwann cells. Treatment of neuronal cultures with castanospermine increases the propensity of neurites to fasciculate. Extracellular matrix deposition by Schwann cells and myelination of neurons by Schwann cells are greatly diminished in the presence of castanospermine as assayed by electron microscopy and immunocytochemistry, suggesting that specific N-linked oligosaccharides are required for the expression of these cellular functions.

Alkaloids↗
PubMed1985

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.

Animals↗
PubMed1984

PC12 cells as a source of neurite-derived cell surface mitogen, which stimulates Schwann cell division.

Primary cultures of rat dorsal root ganglion Schwann cells were used to assay the efficacy of PC12 cells in stimulating Schwann cell proliferation. Co-cultures of PC12 cells and Schwann cells assayed by [3H]thymidine labeling followed by autoradiography showed proliferation of Schwann cells only where contact occurred between PC12 neurites and Schwann cells. Membranes derived from PC12 cells were shown to have many characteristics similar to membranes derived from sensory neurons; both could mimic whole cells in stimulating Schwann cell division; both were inactivated by mild heat treatment and by trypsinization, and both elevated intracellular cyclic AMP concentrations in Schwann cells 16 h after addition of membranes. We conclude that PC12 cells will be a valuable source for the isolation of the neuronal cell surface component which controls proliferation of Schwann cells during development of the peripheral nervous system.

Animals↗
PubMed1983

Structural organization of filamentous proteins in postsynaptic density.

Actin is one of the major protein constituents of the postsynaptic density (PSD), a characteristic structural entity subjacent to the postsynaptic membrane in excitatory synapses of the vertebrate central nervous system. In isolated purified PSD preparations, it is present to the extent of 29 +/- 2 micrograms/mg of total protein, 90% of which is in the filamentous (F-actin) form. Iodination by a discriminatory labeling technique demonstrates that actin is located on the surface of the PSD from which it can be stripped by treatment with a mixture of strong anionic detergents, leaving behind an insoluble core held together by disulfide bridges, consisting in part of tubulin and "PSD protein".

Actins↗
PubMed1983

Isolation of postsynaptic densities retaining their membrane attachment.

A method is described for the preparation of a subcellular fraction, 30-50% pure, of intact postsynaptic units from rat cerebral cortex. The isolation procedure is based on chemical dissociation of the synaptic cleft as described by Crawford, Osborne & Potter followed by sonication of the extracted membranes and separation of the postsynaptic units on a discontinuous sucrose gradient. This preparation provides the first practical procedure for the isolation of postsynaptic densities, prominent organelles of unknown function, without the use of detergents, enabling retention of the postsynaptic membrane in association with the postsynaptic density. The preparation shows enhanced binding of spiroperidol, a dopamine agonist, which, in conjunction with morphological evidence, indicates that the preparation is sufficiently intact to enable study of the interaction of the postsynaptic membrane with the postsynaptic density. Actin, alpha- and beta-tubulin and postsynaptic density protein constitute the major proteins in the preparation; they are present in amounts of 41, 54, 57 and 74 micrograms per mg protein, respectively; as compared to 54, 59, 55 and 9 micrograms per mg protein of the synaptic junctional membrane used as starting material. The utility of the preparation for a number of localization studies, including ion translocating adenosine 5'-triphosphatases, protein kinases and their substrates is discussed.

Actins↗