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1. Maurel, P, Einheber, S, Thaker, P, Lam, I, Salzer, JL. "The nectin-like proteins are internodal adhesion molecules required for myelination [Abstract]," Journal of neurochemistry 2008 MAR;104(1):84-85.   (ISI:000252815800201 #J0133638)    

2. Salzer, James L. "Switching myelination on and off [comment]," Journal of cell biology 2008 May 19;181(4):575-7.   (MEDL:18490509 PMID: 18490509 #J0138475)    

   Schwann cells are remarkably plastic cells that can both form and stably maintain myelin sheaths around axons and also rapidly dedifferentiate upon injury. New findings (Parkinson, D.B., A. Bhaskaran, P. Arthur-Farraj, L.A. Noon, A. Woodhoo, A.C. Lloyd, M.L. Feltri, L. Wrabetz, A. Behrens, R. Mirsky, and K.R. Jessen. 2008. J. Cell Biol. 181:625-637) indicate that the transition between these distinct states of differentiation is directed by the transcription factor Krox-20, which promotes and maintains myelination, and c-Jun, which antagonizes it. Cross-inhibition of these transcription factors serves to switch Schwann cells between the myelinated and dedifferentiated phenotypes, respectively.

3. Taveggia, Carla, Thaker, Pratik, Petrylak, Ashley, Caporaso, Gregg L, Toews, Arrel, Falls, Douglas L, Einheber, Steven, Salzer, James L. "Type III neuregulin-1 promotes oligodendrocyte myelination," Glia 2008 Feb;56(3):284-93.   (MEDL:18080294 PMID: 18080294 #J0135294)    

   The axonal signals that regulate oligodendrocyte myelination during development of the central nervous system (CNS) have not been established. In this study, we have examined the regulation of oligodendrocyte myelination by the type III isoform of neuregulin-1 (NRG1), a neuronal signal essential for Schwann cell differentiation and myelination. In contrast to Schwann cells, primary oligodendrocytes differentiate normally when cocultured with dorsal root ganglia (DRG) neurons deficient in type III NRG1. However, they myelinate type III NRG1-deficient neurites poorly in comparison to wild type cultures. Type III NRG1 is not sufficient to drive oligodendrocyte myelination as sympathetic neurons are not myelinated even with lentiviral-mediated expression of NRG1. Mice haploinsufficient for type III NRG1 are hypomyelinated in the brain, as evidenced by reduced amounts of myelin proteins and lipids and thinner myelin sheaths. In contrast, the optic nerve and spinal cord of heterozygotes are myelinated normally. Together, these results implicate type III NRG1 as a significant determinant of the extent of myelination in the brain and demonstrate important regional differences in the control of CNS myelination. They also indicate that oligodendrocyte myelination, but not differentiation, is promoted by axonal NRG1, underscoring important differences in the control of myelination in the CNS and peripheral nervous system (PNS).

4. Dzhashiashvili, Yulia, Zhang, Yanqing, Galinska, Jolanta, Lam, Isabel, Grumet, Martin, Salzer, James L. "Nodes of Ranvier and axon initial segments are ankyrin G-dependent domains that assemble by distinct mechanisms," Journal of cell biology 2007 Jun 4;177(5):857-70.   (MEDL:17548513 PMID: 17548513 #J0128340)    

   Axon initial segments (AISs) and nodes of Ranvier are sites of action potential generation and propagation, respectively. Both domains are enriched in sodium channels complexed with adhesion molecules (neurofascin [NF] 186 and NrCAM) and cytoskeletal proteins (ankyrin G and betaIV spectrin). We show that the AIS and peripheral nervous system (PNS) nodes both require ankyrin G but assemble by distinct mechanisms. The AIS is intrinsically specified; it forms independent of NF186, which is targeted to this site via intracellular interactions that require ankyrin G. In contrast, NF186 is targeted to the node, and independently cleared from the internode, by interactions of its ectodomain with myelinating Schwann cells. NF186 is critical for and initiates PNS node assembly by recruiting ankyrin G, which is required for the localization of sodium channels and the entire nodal complex. Thus, initial segments assemble from the inside out driven by the intrinsic accumulation of ankyrin G, whereas PNS nodes assemble from the outside in, specified by Schwann cells, which direct the NF186-dependent recruitment of ankyrin G.

5. Maurel, Patrice, Einheber, Steven, Galinska, Jolanta, Thaker, Pratik, Lam, Isabel, Rubin, Marina B, Scherer, Steven S, Murakami, Yoshinuri, Gutmann, David H, Salzer, James L. "Nectin-like proteins mediate axon Schwann cell interactions along the internode and are essential for myelination," Journal of cell biology 2007 Aug 27;178(5):861-74.   (MEDL:17724124 PMID: 17724124 #J0132468)    

   Axon-glial interactions are critical for the induction of myelination and the domain organization of myelinated fibers. Although molecular complexes that mediate these interactions in the nodal region are known, their counterparts along the internode are poorly defined. We report that neurons and Schwann cells express distinct sets of nectin-like (Necl) proteins: axons highly express Necl-1 and -2, whereas Schwann cells express Necl-4 and lower amounts of Necl-2. These proteins are strikingly localized to the internode, where Necl-1 and -2 on the axon are directly apposed by Necl-4 on the Schwann cell; all three proteins are also enriched at Schmidt-Lanterman incisures. Binding experiments demonstrate that the Necl proteins preferentially mediate heterophilic rather than homophilic interactions. In particular, Necl-1 on axons binds specifically to Necl-4 on Schwann cells. Knockdown of Necl-4 by short hairpin RNA inhibits Schwann cell differentiation and subsequent myelination in cocultures. These results demonstrate a key role for Necl-4 in initiating peripheral nervous system myelination and implicate the Necl proteins as mediators of axo-glial interactions along the internode.

6. Taveggia, Carla, Salzer, James L. "PARsing the events of myelination," Nature neuroscience 2007 Jan;10(1):17-8.   (MEDL:17189948 PMID: 17189948 #J0122272)    

7. Grijalva, I, Li, X, Marcillo, A, Salzer, JL, Levi, AD. "Expression of neurotrimin in the normal and injured adult human spinal cord," Spinal cord 2006 MAY;44(5):280-286.   (ISI:000237299000003 #J0114580)    

   Study design: Neurotrimin (Ntm) is a member of the family of neural cell adhesion molecules. Its expression pattern suggests that Ntm promotes axonal fasciculation, guides nerve fibers to specific targets and stabilizes synapses as it accumulates coincident with synaptogenesis. Strong labeling of Ntm was observed in motor and sensory areas of the postnatal rat cortex. It is not known whether Ntm is present in adult human spinal cord (SC). In the present study, a monoclonal antibody specific for Ntm (1B1), is applied to the first study of the expression of Ntm in normal and injured adult human SC. Objective: (1) To investigate the expression pattern of Ntm in adult normal human SC, and ( 2) to observe the changes of Ntm expression after SC injury and compare the differences between normal and injured adult human SC. Methods: Human SC tissue was obtained from necropsies of patients with (n5) and without (n4) SC injury. The 1B1 Ntm monoclonal antibody was used for immunohistochemical staining on parafin embedded sections with an ABC kit. Results: (1) In total, 12 slides were analyzed for each group from both cervical and thoracic levels. Motor neurons and Clarke's neurons and glial-like cells were mild to moderately positive in all uninjured SC specimens. ( 2) In injured SC, no staining was observed in the injury epicenter between two and three levels proximally and distally, but was detected five levels away. ( 3) In patients older than 67 years of age, Ntm-positive inclusions were present in the white matter of the SC with or without injury. ( 4) Some meningeal cells were strongly Ntm-positive, especially in the uninjured human SC. Conclusion: Ntm is expressed by motor and Clarke's neurons and glial cells in uninjured human SC. The downregulation of Ntm in the injured SC suggests that its expression is regulated by afferent input.

8. Koticha D, Maurel P, Zanazzi G, Kane-Goldsmith N, Basak S, Babiarz J, Salzer J, Grumet M. "Neurofascin interactions play a critical role in clustering sodium channels, ankyrin(G) and betaIV spectrin at peripheral nodes of Ranvier," Developmental biology (Orlando) 2006 May 1;293(1):1-12..   (MEDL:16566914 PMID: 16566914 #J0113056)    

   The Ig cell adhesion molecules (CAM) neurofascin (NF) and Nr-CAM are localized at developing nodes of Ranvier in peripheral myelinated axons prior to clustering of Na(+) channels. Different isoforms of NF are expressed on neurons and glia, and NF binding on both cells has been suggested to play roles in node and paranode formation. To clarify the role of NF further, we analyzed effects of NF-Fc fusion proteins in Schwann cell-DRG neuron myelinating cocultures. NF-Fc significantly inhibited nodal clustering of Na(+) channels, ankyrin(G), and betaIV spectrin, and modestly reduced Caspr clustering at paranodal junctions; it did not significantly affect lengths or numbers of myelin-positive segments, axon initial segments, or accumulations of phosphorylated-ERM proteins in Schwann cell nodal microvilli. NF-Fc binds to Schwann cells but little or no binding to DRG neurons was detected. The results suggest a critical early role for axonal NF in clustering of Na(+) channels at nodes of Ranvier via interactions with receptors on Schwann cells.

9. Murano M, Xiong X, Murano N, Salzer JL, Lafaille JJ, Tsiagbe VK. "Latent TGF-{beta}1-transduced CD4+ T cells suppress the progression of allergic encephalomyelitis," Journal of leukocyte biology 2006 Jan;79(1):140-6.   (MEDL:16244108 PMID: 16244108 #J0110068)    

   Systemic injection of small amounts of transforming growth factor-beta (TGF-beta), a cytokine produced by lymphoid and other cells, has a profound effect in protecting mice from the inflammatory demyelinating lesions of experimental allergic encephalomyelitis (EAE; an animal model for multiple sclerosis). However, TGF-beta has side-effects, which might be avoided if the cells producing TGF-beta can be delivered to the affected site in the nervous system to insure its local release in small amounts. Myelin basic protein (MBP)-specific, cloned CD4(+) T cells were engineered by retroviral transduction to produce latent TGF-beta. Studies about the spontaneous form of EAE in T cell receptor (TCR)-transgenic recombination-activating gene (RAG)-1(-/-) mice showed that essentially all of the MBP-specific, TCR-transgenic RAG-1(-/-) (BALB/cxB10.PL)F1 mice develop spontaneous EAE by the age of 11 weeks. By 12 weeks, 25-50% of the mice have died from disease. A single injection of TGF-beta1-transduced T helper cell type 1 (Th1) cells significantly protected the mice from EAE, and untransduced Th1 cells did not protect. MBP-specific BALB/c Th2 clones, transduced with TGF-beta1-internal ribosome entry site-green fluorescent protein (GFP) significantly reduced EAE induction by untransduced Th1 cells in RAG-1(-/-) B10.PL mice. Furthermore, the GFP(+) TGF-beta1-producing Th2 cells were detectable in the spinal cords of the injected mice.

10. Nave, Klaus-Armin, Salzer, James L. "Axonal regulation of myelination by neuregulin 1," Current opinion in neurobiology 2006 Oct;16(5):492-500.   (MEDL:16962312 PMID: 16962312 #J0121141)    

    Neuregulins comprise a family of epidermal growth factor-like ligands that interact with ErbB receptor tyrosine kinases to control many aspects of neural development. One of the most dramatic effects of neuregulin-1 is on glial cell differentiation. The membrane-bound neuregulin-1 type III isoform is an axonal ligand for glial ErbB receptors that regulates the early Schwann cell lineage, including the generation of precursors. Recent studies have shown that the amount of neuregulin-1 type III expressed on axons also dictates the glial phenotype, with a threshold level triggering Schwann cell myelination. Remarkably, neuregulin-1 type III also regulates Schwann cell membrane growth to adjust myelin sheath thickness to match axon caliber precisely. Whether this signaling system operates in central nervous system myelination remains an open question of major importance for human demyelinating diseases.

11. Zhang, Yueting, Taveggia, Carla, Melendez-Vasquez, Carmen, Einheber, Steven, Raine, Cedric S, Salzer, James L, Brosnan, Celia F, John, Gareth R. "Interleukin-11 potentiates oligodendrocyte survival and maturation, and myelin formation," Journal of neuroscience 2006 Nov 22;26(47):12174-85.   (MEDL:17122042 PMID: 17122042 #J0122142)    

    Mechanisms that regulate oligodendrocyte survival and myelin formation are an intense focus of research into myelin repair in the lesions of multiple sclerosis (MS). Although demyelination and oligodendrocyte loss are pathological hallmarks of the disease, increased oligodendrocyte numbers and remyelination are frequently observed in early lesions, but these diminish as the disease course progresses. In the current study, we used a microarray-based approach to investigate genes regulating repair in MS lesions, and identified interleukin-11 (IL-11) as an astrocyte-derived factor that potentiates oligodendrocyte survival and maturation, and myelin formation. IL-11 was induced in human astrocyte cultures by the cytokines IL-1beta and TGFbeta1, which are both prominently expressed in MS plaques. In MS tissue samples, IL-11 was expressed by reactive astrocytes, with expression particularly localized at the myelinated border of both active and silent lesions. Its receptor, IL-11R alpha, was expressed by oligodendrocytes. In experiments in human cultures in vitro, IL-11R alpha localized to immature oligodendrocytes, and its expression decreased during maturation. In cultures treated with IL-11, we observed a significant increase in oligodendrocyte number, and this was associated with enhanced oligodendrocyte survival and maturation. Importantly, we also found that IL-11 treatment was associated with significantly increased myelin formation in rodent CNS cocultures. These data are the first to implicate IL-11 in oligodendrocyte viability, maturation, and myelination. We suggest that this pathway may represent a potential therapeutic target for oligodendrocyte protection and remyelination in MS.

12. Melendez-Vasquez C, Carey DJ, Zanazzi G, Reizes O, Maurel P, Salzer JL. "Differential expression of proteoglycans at central and peripheral nodes of Ranvier," Glia 2005 Dec;52(4):301-8.   (MEDL:16035076 PMID: 16035076 #J0110069)    

    The nodes of Ranvier are regularly spaced gaps between myelin sheaths that are markedly enriched in voltage-gated sodium channels and associated proteins. Myelinating glia play a key role in promoting node formation, although the requisite glial signals remain poorly understood. In this study, we have examined the expression of glial proteoglycans in the peripheral and central nodes. We report that the heparan sulfate proteoglycan, syndecan-3, becomes highly enriched with PNS node formation; its ligand, collagen V, is also concentrated at the PNS nodes and at lower levels along the abaxonal membrane. The V1 isoform of versican, a chondroitin sulfate proteoglycan, is also present in the nodal gap. By contrast, CNS nodes are enriched in versican isoform V2, but not syndecan-3. We have examined the molecular composition of the PNS nodes in syndecan-3 knockout mice. Nodal components are normally expressed in mice deficient in syndecan-3, suggesting that it has a nonessential role in the organization of nodes in the adult. These results indicate that the molecular composition and extracellular environment of the PNS and CNS nodes of Ranvier are significantly distinct.

13. Taveggia C, Zanazzi G, Petrylak A, Yano H, Rosenbluth J, Einheber S, Xu X, Esper RM, Loeb JA, Shrager P, Chao MV, Falls DL, Role L, Salzer JL. "Neuregulin-1 type III determines the ensheathment fate of axons," Neuron 2005 Sep 1;47(5):681-94.   (MEDL:16129398 PMID: 16129398 #J0106855)    

    The signals that determine whether axons are ensheathed or myelinated by Schwann cells have long been elusive. We now report that threshold levels of neuregulin-1 (NRG1) type III on axons determine their ensheathment fate. Ensheathed axons express low levels whereas myelinated fibers express high levels of NRG1 type III. Sensory neurons from NRG1 type III deficient mice are poorly ensheathed and fail to myelinate; lentiviral-mediated expression of NRG1 type III rescues these defects. Expression also converts the normally unmyelinated axons of sympathetic neurons to myelination. Nerve fibers of mice haploinsufficient for NRG1 type III are disproportionately unmyelinated, aberrantly ensheathed, and hypomyelinated, with reduced conduction velocities. Type III is the sole NRG1 isoform retained at the axon surface and activates PI 3-kinase, which is required for Schwann cell myelination. These results indicate that levels of NRG1 type III, independent of axon diameter, provide a key instructive signal that determines the ensheathment fate of axons.

14. Melendez-Vasquez CV, Einheber S, Salzer JL. "Rho kinase regulates schwann cell myelination and formation of associated axonal domains," Journal of neuroscience 2004 Apr 21;24(16):3953-63.   (MEDL:15102911 PMID: 15102911 #J0067272)    

    The myelin sheath forms by the spiral wrapping of a glial membrane around an axon. The mechanisms involved are poorly understood but are likely to involve coordinated changes in the glial cell cytoskeleton. Because of its key role as a regulator of the cytoskeleton, we investigated the role of Rho kinase (ROCK), a major downstream effector of Rho, in Schwann cell morphology, differentiation, and myelination. Pharmacologic inhibition of ROCK activity results in loss of microvilli and stress fibers in Schwann cell cultures and strikingly aberrant myelination in Schwann cell-neuron cocultures; there was no effect on Schwann cell proliferation or differentiation. Treated Schwann cells branch aberrantly and form multiple, small, independent myelin segments along the length of axons, each with associated nodes and paranodes. This organization partially resembles myelin formed by oligodendrocytes rather than the single long myelin sheath characteristic of Schwann cells. ROCK regulates myosin light chain phosphorylation, which is robustly, but transiently, activated at the onset of myelination. These results support a key role of Rho through its effector ROCK in coordinating the movement of the glial membrane around the axon at the onset of myelination via regulation of myosin phosphorylation and actomyosin assembly. They also indicate that the molecular machinery that promotes the wrapping of the glial membrane sheath around the axon is distributed along the entire length of the internode.

15. Gollan L, Salomon D, Salzer JL, Peles E. "Caspr regulates the processing of contactin and inhibits its binding to neurofascin," Journal of cell biology 2003 Dec 22;163(6):1213-8.   (MEDL:14676309 PMID: 14676309 #J0069887)    

    Three cell adhesion molecules are present at the axoglial junctions that form between the axon and myelinating glia on either side of nodes of Ranvier. These include an axonal complex of contacin-associated protein (Caspr) and contactin, which was proposed to bind NF155, an isoform of neurofascin located on the glial paranodal loops. Here, we show that NF155 binds directly to contactin and that surprisingly, coexpression of Caspr inhibits this interaction. This inhibition reflects the association of Caspr with contactin during biosynthesis and the resulting expression of a low molecular weight (LMw), endoglycosidase H-sensitive isoform of contactin at the cell membrane, which remains associated with Caspr but is unable to bind NF155. Accordingly, deletion of Caspr in mice by gene targeting results in a shift from the LMw- to a HMw-contactin glycoform. These results demonstrate that Caspr regulates the intracellular processing and transport of contactin to the cell surface, thereby affecting its ability to interact with other cell adhesion molecules.

16. Melendez-Vasquez, CV, Einheber, S, Salzer, JL. "Rho-GTPases regulate Schwann cell morphology and myelination," Journal of neurochemistry 2003 MAY;85(9):30-30.   (ISI:000182828800108 #J0052504)    

17. Rios JC, Rubin M, St Martin M, Downey RT, Einheber S, Rosenbluth J, Levinson SR, Bhat M, Salzer JL. "Paranodal interactions regulate expression of sodium channel subtypes and provide a diffusion barrier for the node of Ranvier," Journal of neuroscience 2003 Aug 6;23(18):7001-11.   (MEDL:22786664 PMID: 12904461 #J0053135)    

    The node of Ranvier is a distinct domain of myelinated axons that is highly enriched in sodium channels and is critical for impulse propagation. During development, the channel subtypes expressed at the node undergo a transition from Nav1.2 to Nav1.6. Specialized junctions that form between the paranodal glial membranes and axon flank the nodes and are candidates to regulate their maturation and delineate their boundaries. To investigate these roles, we characterized node development in mice deficient in contactin-associated protein (Caspr), an integral junctional component. Paranodes in these mice lack transverse bands, a hallmark of the mature junction, and exhibit progressive disruption of axon-paranodal loop interactions in the CNS. Caspr mutant mice display significant abnormalities at central nodes; components of the nodes progressively disperse along axons, and many nodes fail to mature properly, persistently expressing Nav1.2 rather than Nav1.6. In contrast, PNS nodes are only modestly longer and, although maturation is delayed, eventually all express Nav1.6. Potassium channels are aberrantly clustered in the paranodes; these clusters are lost over time in the CNS, whereas they persist in the PNS. These findings indicate that interactions of the paranodal loops with the axon promote the transition in sodium channel subtypes at CNS nodes and provide a lateral diffusion barrier that, even in the absence of transverse bands, maintains a high concentration of components at the node and the integrity of voltage-gated channel domains.

18. Salzer JL. "Polarized domains of myelinated axons," Neuron 2003 Oct 9;40(2):297-318.   (MEDL:22919825 PMID: 14556710 #J0053042)    

    The entire length of myelinated axons is organized into a series of polarized domains that center around nodes of Ranvier. These domains, which are crucial for normal saltatory conduction, consist of distinct multiprotein complexes of cell adhesion molecules, ion channels, and scaffolding molecules; they also differ in their diameter, organelle content, and rates of axonal transport. Juxtacrine signals from myelinating glia direct their sequential assembly. The composition, mechanisms of assembly, and function of these molecular domains will be reviewed. I also discuss similarities of this domain organization to that of polarized epithelia and present emerging evidence that disorders of domain organization and function contribute to the axonopathies of myelin and other neurologic disorders.

19. Gil OD, Zhang L, Chen S, Ren YQ, Pimenta A, Zanazzi G, Hillman D, Levitt P, Salzer JL. "Complementary expression and heterophilic interactions between igLON family members neurotrimin and LAMP," Journal of neurobiology 2002 Jun 5;51(3):190-204.   (MEDL:0 PMID: 11984841 #J0030235) Full Text Link!   

    Neurotrimin (Ntm) and the limbic system-associated membrane protein (LAMP) are members of the IgLON (LAMP, OBCAM, Ntm) family of glycorylphosphatidylinositol anchored neural cell adhesion molecules. We previously reported that LAMP and Ntm promote adhesion and neurite outgrowth via a homophilic mechanism, suggesting that these proteins promote the formation of specific neuronal circuits by homophilic interactions. In this report, we have further characterized the expression and binding specificity of Ntm. Using a newly generated monoclonal antibody to Ntm, we demonstrated that this protein is largely expressed in a complementary pattern to that of LAMP in the nervous system, with co-expression at a few sites. Ntm is expressed at high levels in sensory-motor cortex and, of particular note, is transiently expressed in neurons of cortical barrel fields and corresponding thalamic 'barreloids.' Binding of a recombinant, soluble form of Ntm to CHO cells expressing either Ntm or LAMP demonstrates that Ntm and LAMP interact both homophilically and heterophilically. In contrast to conventional growth-promoting activity of Ig superfamily members, LAMP strongly inhibits the outgrowth of Ntm-expressing dorsal root ganglion (DRG) neurons in a heterophilic manner. These anatomical and functional data support the concept that homophilic and heterophilic interactions between IgLON family members are likely to play a role in the specification of neuronal projections via growth promoting and inhibiting effects, respectively. Copyright 2002 Wiley Periodicals, Inc. J Neurobiol 51: 190-204, 2002.

20. Hempstead BL, Salzer JL. "Neurobiology. A glial spin on neurotrophins [Comment]," Science 2002 Nov 8;298(5596):1184-6.   (MEDL:22312006 PMID: 12424359 #J0046693) Full Text Link!   

21. Melendez-Vasquez, CV, Einheber, S, Salzer, JL. "Role of Rho-GTPases in the control of Schwann cell morphology and nodal microvilli formation [abstract]," Molecular biology of the cell 2002 NOV;13(4):56A-56A.   (ISI:000179569100314 #J0050833)    

22. Rambukkana A, Zanazzi G, Tapinos N, Salzer JL. "Contact-Dependent Demyelination by Mycobacterium leprae in the Absence of Immune Cells," Science 2002 May 3;296(5569):927-31.   (MEDL:21984703 PMID: 11988579 #J0030236) Full Text Link!   

    Demyelination results in severe disability in many neurodegenerative diseases and nervous system infections, and it is typically mediated by inflammatory responses. Mycobacterium leprae, the causative organism of leprosy, induced rapid demyelination by a contact-dependent mechanism in the absence of immune cells in an in vitro nerve tissue culture model and in Rag1-knockout (Rag1(-/-)) mice, which lack mature B and T lymphocytes. Myelinated Schwann cells were resistant to M. leprae invasion but undergo demyelination upon bacterial attachment, whereas nonmyelinated Schwann cells harbor intracellular M. leprae in large numbers. During M. leprae-induced demyelination, Schwann cells proliferate significantly both in vitro and in vivo and generate a more nonmyelinated phenotype, thereby securing the intracellular niche for M. leprae.

23. Rambukkana, A, Zanuzzi, G, Tapinos, N, Salzer, JL. "Mycobacterium leprae and demyelination - Response," Science 2002 AUG 30;297(5586):1476-1476.   (ISI:000177697300022 #J0100927)    

24. Salzer JL. "Nodes of Ranvier come of age," Trends in neurosciences 2002 Jan;25(1):2-5.   (MEDL:21660889 PMID: 11801321 #J0030237) Full Text Link!   

    Sodium channel subtypes are frequently coexpressed within neurons. Recent studies demonstrate that targeting of specific channel subtypes to distinct membrane domains of axons is regulated by local signals from myelinating glia; they also show that channel subtypes are sequentially expressed at nodes of Ranvier, indicating an unexpected regulation in the composition of these domains.

25. Bhat MA, Rios JC, Lu Y, Garcia-Fresco GP, Ching W, St Martin M, Li J, Einheber S, Chesler M, Rosenbluth J, Salzer JL, Bellen HJ. "Axon-glia interactions and the domain organization of myelinated axons requires neurexin IV/Caspr/Paranodin," Neuron 2001 May;30(2):369-83.   (MEDL:21289247 PMID: 11395000 #J0030239) Full Text Link!   

    Myelinated fibers are organized into distinct domains that are necessary for saltatory conduction. These domains include the nodes of Ranvier and the flanking paranodal regions where glial cells closely appose and form specialized septate-like junctions with axons. These junctions contain a Drosophila Neurexin IV-related protein, Caspr/Paranodin (NCP1). Mice that lack NCP1 exhibit tremor, ataxia, and significant motor paresis. In the absence of NCP1, normal paranodal junctions fail to form, and the organization of the paranodal loops is disrupted. Contactin is undetectable in the paranodes, and K(+) channels are displaced from the juxtaparanodal into the paranodal domains. Loss of NCP1 also results in a severe decrease in peripheral nerve conduction velocity. These results show a critical role for NCP1 in the delineation of specific axonal domains and the axon-glia interactions required for normal saltatory conduction.

26. Chen S, Gil O, Ren YQ, Zanazzi G, Salzer JL, Hillman DE. "Neurotrimin expression during cerebellar development suggests roles in axon fasciculation and synaptogenesis," Journal of neurocytology 2001 Nov;30(11):927-37.   (MEDL:22260408 PMID: 12373100 #J0046344) Full Text Link!   

    We investigated the temporal expression of the neural cell adhesion molecule, neurotrimin, in the rat cerebellum and the brainstem from birth to adulthood using immunoreactive labeling. A wave of expression accompanied the development of projection pathways extending from brainstem nuclei (pons/inferior olive) through the cerebellar peduncles into the arbor vitae and disappeared with myelination by P14. Immuno-EM revealed expression of neurotrimin on the surface of unmyelinated axons but not on astrocytes or oligodendroglia. With the development of the molecular and internal granular layers, intense labeling occurred on the surface of parallel fiber bundles, granule cells and mossy fibers. With synaptogenesis, each excitatory junction was labeled by the immunoreaction. By P21, neurotrimin reactivity decreased on the surfaces of neuronal somata, dendrites and axons but remained at excitatory synaptic contact sites in both the molecular and granular layers. The spatial-temporal expression pattern of neurotrimin suggests that this adhesion molecule plays a role in axonal fasciculation of specific cerebellar systems and may also be involved in the formation of excitatory synapses and their stabilization into adulthood.

27. Lustig M, Zanazzi G, Sakurai T, Blanco C, Levinson SR, Lambert S, Grumet M, Salzer JL. "Nr-CAM and neurofascin interactions regulate ankyrin G and sodium channel clustering at the node of Ranvier," Current biology. CB 2001 Nov 27;11(23):1864-9.   (MEDL:21585387 PMID: 11728309 #J0030238) Full Text Link!   

    Voltage-dependent sodium (Na(+)) channels are highly concentrated at nodes of Ranvier in myelinated axons and play a key role in promoting rapid and efficient conduction of action potentials by saltatory conduction. The molecular mechanisms that direct their localization to the node are not well understood but are believed to involve contact-dependent signals from myelinating Schwann cells and interactions of Na(+) channels with the cytoskeletal protein, ankyrin G. Two cell adhesion molecules (CAMs) expressed at the axon surface, Nr-CAM and neurofascin, are also linked to ankyrin G and accumulate at early stages of node formation, suggesting that they mediate contact-dependent Schwann cell signals to initiate node development. To examine the potential role of Nr-CAM in this process, we treated myelinating cocultures of DRG (dorsal root ganglion) neurons and Schwann cells with an Nr-CAM-Fc (Nr-Fc) fusion protein. Nr-Fc had no effect on initial axon-Schwann cell interactions, including Schwann cell proliferation, or on the extent of myelination, but it strikingly and specifically inhibited Na(+) channel and ankyrin G accumulation at the node. Nr-Fc bound directly to neurons and clustered and coprecipitated neurofascin expressed on axons. These results provide the first evidence that neurofascin plays a major role in the formation of nodes, possibly via interactions with Nr-CAM.

28. Melendez-Vasquez CV, Rios JC, Zanazzi G, Lambert S, Bretscher A, Salzer JL. "Nodes of Ranvier form in association with ezrin-radixin-moesin (ERM)-positive Schwann cell processes," Proceedings of the National Academy of Sciences of the United States of America 2001 Jan 30;98(3):1235-40.   (MEDL:21107699 PMID: 11158623 #J0029116) Full Text Link!   

    In the adult peripheral nerve, microvillous processes of myelinating Schwann cells project to the nodes of Ranvier; their composition and physiologic function have not been established. As the ezrin-radixin-moesin (ERM) proteins are expressed in the microvilli of many epithelial cells, we have examined the expression and distribution of these proteins in Schwann cells and neurons in vitro and in vivo. Cultured Schwann cells express high levels of all three proteins and the ezrin-binding protein 50, whereas neurons express much lower, although detectable, levels of radixin and moesin. Ezrin is specific for Schwann cells. All three ERM proteins are expressed predominantly at the membrane of cultured Schwann cells, notably in their microvilli. In vivo, the ERM proteins are concentrated strikingly in the nodal processes of myelinating Schwann cells. Because these processes are devoid of myelin proteins, they represent a unique compartment of the myelinating Schwann cell. During development, the ERM proteins become concentrated at the ends of Schwann cells before myelin basic protein expression, demonstrating that Schwann cells are polarized longitudinally at the onset of myelination. ERM-positive Schwann cell processes overlie and are associated closely with nascent nodes of Ranvier, identified by clusters of ankyrin G. Ankyrin accumulation at the node precedes that of Caspr at the paranodes and therefore does not depend on the presence of mature paranodal junctions. These results demonstrate that nodes of Ranvier in the peripheral nervous system form in contact with specialized processes of myelinating Schwann cells that are highly enriched in ERM proteins.

29. Scherer SS; Salzer JL. "Axon-Schwann cell interactions during peripheral nerve degeneration and regeneration," In: Glial cell development : basic principles and clinical relevance / Jessen KR; Richardson WD (Eds.)    Oxford ; New York : Oxford University Press, 2001. p. 165-196    (offline #C0001356)

30. Zanazzi G, Einheber S, Westreich R, Hannocks MJ, Bedell-Hogan D, Marchionni MA, Salzer JL. "Glial growth factor/neuregulin inhibits Schwann cell myelination and induces demyelination," Journal of cell biology 2001 Mar 19;152(6):1289-99.   (MEDL:21157407 PMID: 11257128 #J0023195) Full Text Link!   

    During development, neuregulin-1 promotes Schwann cell proliferation and survival; its role in later events of Schwann cell differentiation, including myelination, is poorly understood. Accordingly, we have examined the effects of neuregulin-1 on myelination in neuron-Schwann cell cocultures. Glial growth factor (GGF), a neuregulin-1 isoform, significantly inhibited myelination by preventing axonal segregation and ensheathment. Basal lamina formation was not affected. Treatment of established myelinated cultures with GGF resulted in striking demyelination that frequently began at the paranodes and progressed to the internode. Demyelination was dose dependent and accompanied by dedifferentiation of Schwann cells to a promyelinating stage, as evidenced by reexpression of the transcription factor suppressed cAMP-inducible POU; a significant proportion of cells with extensive demyelination also proliferated. Two other Schwann cell mitogens, fibroblast growth factor-2 and transforming growth factor-beta, inhibited myelination but did not cause demyelination, suggesting this effect is specific to the neuregulins. The neuregulin receptor proteins, erbB2 and erbB3, are expressed on ensheathing and myelinating Schwann cells and rapidly phosphorylated with GGF treatment. GGF treatment of myelinating cultures also induced phosphorylation of phosphatidylinositol 3-kinase, mitogen-activated protein kinase, and a 120-kD protein. These results suggest that neuronal mitogens, including the neuregulins, may inhibit myelination during development and that activation of mitogen signaling pathways may contribute to the initial demyelination and subsequent Schwann cell proliferation observed in various pathologic conditions.

31. Einheber S, Salzer JL. "A glial investment of axons defrayed [Comment]," Neuron 2000 Dec;28(3):627-8.   (MEDL:21094469 PMID: 11163251 #J0046346) Full Text Link!   

32. Maurel P, Salzer JL. "Axonal regulation of Schwann cell proliferation and survival and the initial events of myelination requires PI 3-kinase activity," Journal of neuroscience 2000 Jun 15;20(12):4635-45.   (MEDL:20304938 PMID: 10844033 #J0008897) Full Text Link!   

    In this report, we have investigated the signaling pathways that are activated by, and mediate the effects of, the neuregulins and axonal contact in Schwann cells. Phosphatidylinositol 3-kinase (PI 3-kinase) and mitogen-activated protein kinase kinase (MAPK kinase) are strongly activated in Schwann cells by glial growth factor (GGF), a soluble neuregulin, and by contact with neurite membranes; both kinase activities are also detected in Schwann cell-DRG neuron cocultures. Inhibition of the PI 3-kinase, but not the MAP kinase, pathway reversibly inhibited Schwann cell proliferation induced by GGF and neurites. Cultured Schwann cells undergo apoptosis after serum deprivation and can be rescued by GGF or contact with neurites; these survival effects were also blocked by inhibition of PI 3-kinase. Finally, we have examined the role of these signaling pathways in Schwann cell differentiation in cocultures. At early stages of coculture, inhibition of PI 3-kinase, but not MAPK kinase, blocked Schwann cell elongation and subsequent myelination but did not affect laminin deposition. Later, after Schwann cells established a one-to-one relationship with axons, inhibition of PI 3-kinase did not block myelin formation, but the myelin sheaths that formed were shorter, and the rate of myelin protein accumulation was markedly decreased. PI 3-kinase inhibition had no observable effect on the maintenance of myelin sheaths in mature myelinated cocultures. These results indicate that activation of PI 3-kinase by axonal factors, including the neuregulins, promotes Schwann cell proliferation and survival and implicate PI 3-kinase in the early events of myelination.

33. Ng V, Zanazzi G, Timpl R, Talts JF, Salzer JL, Brennan PJ, Rambukkana A. "Role of the cell wall phenolic glycolipid-1 in the peripheral nerve predilection of Mycobacterium leprae," Cell 2000 Oct 27;103(3):511-24.   (MEDL:20531887 PMID: 11081637 #J0046348) Full Text Link!   

    The cell wall of pathogenic mycobacteria is abundant with complex glycolipids whose roles in disease pathogenesis are mostly unknown. Here, we provide evidence for the involvement of the specific trisaccharide unit of the phenolic glycolipid-1 (PGL-1) of Mycobacterium leprae in determining the bacterial predilection to the peripheral nerve. PGL-1 binds specifically to the native laminin-2 in the basal lamina of Schwann cell-axon units. This binding is mediated by the alpha(2LG1, alpha2LG4, and alpha2LG5 modules present in the naturally cleaved fragments of the peripheral nerve laminin alpha2 chain, and is inhibited by the synthetic terminal trisaccharide of PGL-1. PGL-1 is involved in the M. leprae invasion of Schwann cells through the basal lamina in a laminin-2-dependent pathway. The results indicate a novel role of a bacterial glycolipid in determining the nerve predilection of a human pathogen.

34. Peles E, Salzer JL. "Molecular domains of myelinated axons," Current opinion in neurobiology 2000 Oct;10(5):558-65.   (MEDL:20538855 PMID: 11084317 #J0046347) Full Text Link!   

    Myelinated axons are organized into specific domains as the result of interactions with glial cells. Recently, distinct protein complexes of cell adhesion molecules, Na(+) channels and ankyrin G at the nodes, Caspr and contactin in the paranodes, and K(+) channels and Caspr2 in the juxtaparanodal region have been identified, and new insights into the role of the paranodal junctions in the organization of these domains have emerged.

35. Rios JC, Melendez-Vasquez CV, Einheber S, Lustig M, Grumet M, Hemperly J, Peles E, Salzer JL. "Contactin-associated protein (Caspr) and contactin form a complex that is targeted to the paranodal junctions during myelination," Journal of neuroscience 2000 Nov 15;20(22):8354-64.   (MEDL:20524373 PMID: 11069942 #J0046349) Full Text Link!   

    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)-resistant form is associated specifically with Caspr in the paranodes, whereas a higher-molecular-weight form of contactin, not associated with Caspr, is present in central nodes of Ranvier. These results suggest that the targeting of contactin to different axonal domains may be determined, in part, via its association with Caspr. Treatment of myelinating cocultures of Schwann cells and neurons with RPTPbeta-Fc, a soluble construct containing the carbonic anhydrase domain of the receptor protein tyrosine phosphatase beta (RPTPbeta), a potential glial receptor for contactin, blocks the localization of the Caspr/contactin complex to the paranodes. These results strongly suggest that a preformed complex of Caspr and contactin is targeted to the paranodal junctions via extracellular interactions with myelinating glia.

36. Tikoo R, Zanazzi G, Shiffman D, Salzer J, Chao MV. "Cell cycle control of Schwann cell proliferation: role of cyclin-dependent kinase-2," Journal of neuroscience 2000 Jun 15;20(12):4627-34.   (MEDL:20304937 PMID: 10844032 #J0013527) Full Text Link!   

    Schwann cell proliferation is regulated by multiple growth factors and axonal signals. However, the molecules that control growth arrest of Schwann cells are not well defined. Here we describe regulation of the cyclin-dependent kinase-2 (CDK2) protein, an enzyme that is necessary for the transition from G1 to S phase. Levels of CDK2 protein were elevated in proliferating Schwann cells cultured in serum and forskolin. However, when cells were grown with either serum-free media or at high densities, CDK2 levels declined to low levels. The decrease in CDK2 levels was associated with growth arrest of Schwann cells. The modulation of CDK2 appears to be regulated at the transcriptional level, because CDK2 mRNA levels and its promoter activity both decline during cell cycle arrest. Furthermore, analysis of the CDK2 promoter suggests that Sp1 DNA binding sites are essential for maximal activation in Schwann cells. Together, these data suggest that CDK2 may represent a significant target of developmental signals that regulate Schwann cell proliferation and that this regulation is mediated, in part, through regulation of Sp1 transcriptional activity.

37. Canoll PD, Kraemer R, Teng KK, Marchionni MA, Salzer JL. "GGF/neuregulin induces a phenotypic reversion of oligodendrocytes," Molecular & cellular neurosciences 1999 Feb;13(2):79-94.   (MEDL:99210387 PMID: 10192767 #J0000179) Full Text Link!   

    We have previously shown that glial growth factor (GGF), a member of the neuregulin (NRG) family of growth factors, is a mitogen and survival factor for oligodendrocyte progenitors in cell culture and blocks their differentiation at the pro-oligodendrocyte stage (P. D. Canoll et al., 1996, Neuron 17, 229-243). We now show that GGF is able to induce differentiated oligodendrocytes to undergo a phenotypic reversion characterized by loss of MBP expression, reexpression of the intermediate filament protein nestin, reorganization of the actin cytoskeleton, and a dramatic reduction in the number of processes per cell. TUNEL analysis demonstrates that GGF is not cytotoxic for mature oligodendrocytes, but rather enhances their survival. GGF also induces the rapid activation of the PI 3-kinase and MAP kinase signaling pathways. These results further support a role for the NRGs in promoting the proliferation and survival of and inhibiting the differentiation of cells in the oligodendrocyte lineage and demonstrate that oligodendrocytes that differentiate in culture retain a substantial degree of phenotypic plasticity. Copyright 1999 Academic Press.

38. Ching W, Zanazzi G, Levinson SR, Salzer JL. "Clustering of neuronal sodium channels requires contact with myelinating Schwann cells," Journal of neurocytology 1999 Apr-May;28(4-5):295-301.   (MEDL:20204285 PMID: 10739572 #J0009071) Full Text Link!   

    Efficient and rapid conduction of action potentials by saltatory conduction requires the clustering of voltage-gated sodium channels at nodes of Ranvier. This clustering results from interactions between neurons and myelinating glia, although it has not been established whether this glial signal is contact-dependent or soluble. To investigate the nature of this signal, we examined sodium channel clustering in co-cultures of embryonic rat dorsal root ganglion neurons and Schwann cells. Cultures maintained under conditions promoting or preventing myelination were immunostained with antibodies against the alpha subunit of the sodium channel and against ankyrin(G), a cytoskeletal protein associated with these channels. Consistent with previous in vivo studies (Vabnick et al., 1996), sodium channels and ankyrin G cluster at the onset of myelination. These clusters form adjacent to the ends of the myelinating Schwann cells and appear to fuse to form mature nodes. In contrast, sodium channels and ankyrin G do not cluster in neurons grown alone or in co-cultures where myelination is precluded by growing cells in defined media. Conditioned media from myelinating co-cultures also failed to induce sodium channel or ankyrin G clusters in cultures of neurons alone. Finally, no clusters develop in the amyelinated portions of suspended fascicles of dorsal root ganglia explants despite being in close proximity to myelinated segments in other areas of the dish. These results indicate that clustering of sodium channels requires contact with myelinating Schwann cells.

39. Ching, W, Zanazzi, G, Levinson, S R, Salzer, J L. "Sodium channel clustering at the node of Ranvier requires contact with myelinating Schwann cells [abstract]," Abstracts (Society for Neuroscience) 25(1-2): 999, 1999 October 23-28.   (BIOSIS:200000144746 #J0017065)    

40. Galbiati F, Volonte D, Gil O, Zanazzi G, Salzer JL, Sargiacomo M, Scherer PE, Engelman JA, Schlegel A, Parenti M, Okamoto T, Lisanti MP. "Expression of caveolin-1 and -2 in neurons [abstract]," Journal of neurochemistry 1999;72:S87-S87.   (offline #J0003793)    

41. Lustig, M, Zanazzi, G, Sakurai, T, Blanco, C, Salzer, J, Grumet, M. "Interactions of Nr-CAM are critical for clustering of ankyrin and sodium channels at the node of Ranvier [abstract]," Abstracts (Society for Neuroscience) 25(1-2): 999, 1999 October 23-28.   (BIOSIS:200000144745 #J0017066)    

42. Poliak S, Gollan L, Martinez R, Custer A, Einheber S, Salzer JL, Trimmer JS, Shrager P, Peles E. "Caspr2, a new member of the neurexin superfamily, is localized at the juxtaparanodes of myelinated axons and associates with K+ channels," Neuron 1999 Dec;24(4):1037-47.   (MEDL:20088303 PMID: 10624965 #J0031120) Full Text Link!   

    Rapid conduction in myelinated axons depends on the generation of specialized subcellular domains to which different sets of ion channels are localized. Here, we describe the identification of Caspr2, a mammalian homolog of Drosophila Neurexin IV (Nrx-IV), and show that this neurexin-like protein and the closely related molecule Caspr/Paranodin demarcate distinct subdomains in myelinated axons. While contactin-associated protein (Caspr) is present at the paranodal junctions, Caspr2 is precisely colocalized with Shaker-like K+ channels in the juxtaparanodal region. We further show that Caspr2 specifically associates with Kv1.1, Kv1.2, and their Kvbeta2 subunit. This association involves the C-terminal sequence of Caspr2, which contains a putative PDZ binding site. These results suggest a role for Caspr family members in the local differentiation of the axon into distinct functional subdomains.

43. Rios, J C, Lustig, M, Grumet, M, Gollan, L, Peles, E, Hemperly, J J, Salzer, J L. "Caspr and contactin co-localize in the paranodal and internodal membranes of myelinated axons [abstract]," Abstracts (Society for Neuroscience) 25(1-2): 999, 1999 October 23-28.   (BIOSIS:200000144747 #J0017064)    

44. Salzer JL. "Creating barriers: a new role for Schwann cells and Desert hedgehog [Comment]," Neuron 23(4):627-9, 1999 Aug.   (MEDL:99409952 PMID: 10482226 #J0000390) Full Text Link!   

45. Galbiati F, Volonte D, Gil O, Zanazzi G, Salzer JL, Sargiacomo M, Scherer PE, Engelman JA, Schlegel A, Parenti M, Okamoto T, Lisanti MP. "Expression of caveolin-1 and -2 in differentiating PC12 cells and dorsal root ganglion neurons: caveolin-2 is up-regulated in response to cell injury," Proceedings of the National Academy of Sciences of the United States of America 1998 Aug 18;95(17):10257-62.   (MEDL:98374339 PMID: 9707634 #J0046350) Full Text Link!   

    Caveolae are cholesterol/sphingolipid-rich microdomains of the plasma membrane that have been implicated in signal transduction and vesicular trafficking. Caveolins are a family of caveolae-associated integral membrane proteins. Caveolin-1 and -2 show the widest range of expression, whereas caveolin-3 expression is restricted to muscle cell types. It has been previously reported that little or no caveolin mRNA species are detectable in the brain by Northern blot analyses or in neuroblastoma cell lines. However, it remains unknown whether caveolins are expressed within neuronal cells. Here we demonstrate the expression of caveolin-1 and -2 in differentiating PC12 cells and dorsal root ganglion (DRG) neurons by using mono-specific antibody probes. In PC12 cells, caveolin-1 expression is up-regulated on day 4 of nerve growth factor (NGF) treatment, whereas caveolin-2 expression is transiently up-regulated early in the differentiation program and then rapidly down-regulated. Interestingly, caveolin-2 is up-regulated in response to the mechanical injury of differentiated PC12 cells; up-regulation of caveolin-2 under these conditions is strictly dependent on continued treatment with NGF. Robust expression of caveolin-1 and -2 is also observed along the entire cell surface of DRG neurons, including high levels on growth cones. These findings demonstrate that neuronal cells express caveolins.

46. Gil OD, Zanazzi G, Struyk AF, Salzer JL. "Neurotrimin mediates bifunctional effects on neurite outgrowth via homophilic and heterophilic interactions," Journal of neuroscience 1998 Nov 15;18(22):9312-9325.   (MEDL:99019749 PMID: 9801370 #J0002400) Full Text Link!   

    Neurotrimin (Ntm) together with the limbic system-associated membrane protein (LAMP) and the opioid-binding cell adhesion molecule (OBCAM) comprise the IgLON family of neural cell adhesion molecules. These glycosylphosphatidylinositol (GPI)-anchored proteins are expressed in distinct neuronal systems. In the case of Ntm, its expression pattern suggests a role in the development of thalamocortical and pontocerebellar projections (Struyket al., 1995). We have now characterized Ntm's function in cell adhesion and in neurite outgrowth. Cross-linking studies of transfected cells show that Ntm forms noncovalent homodimers and multimers at the cell surface. Ntm mediates homophilic adhesion, as evidenced by the reaggregation of the transfected cells and the specific binding of an Ntm-Fc chimera to these cells. Consistent with these results, Ntm-Fc binds to neurons that express Ntm at high levels, e.g., dorsal root ganglion (DRG) and hippocampal neurons. It does not bind to DRG neurons treated with phosphatidylinositol-specific phospholipase C (PI-PLC) or to sympathetic neurons that do not express Ntm or other members of the IgLON family at significant levels. Ntm promotes the outgrowth of DRG neurons, even after PI-PLC treatment, suggesting that its effects on outgrowth are mediated by heterophilic interactions. Of particular note, both membrane-bound and soluble Ntm inhibit the outgrowth of sympathetic neurons. These results strongly suggest that Ntm, and other members of the IgLON family, regulate the development of neuronal projections via attractive and repulsive mechanisms that are cell type specific and are mediated by homophilic and heterophilic interactions.

47. Rambukkana A, Yamada H, Zanazzi G, Mathus T, Salzer JL, Yurchenco PD, Campbell KP, Fischetti VA. "Role of alpha-dystroglycan as a Schwann cell receptor for Mycobacterium leprae [see comments]," Science 282(5396):2076-9, 1998 Dec 11.   (MEDL:99069624 PMID: 9851927 #J0003086) Full Text Link!   

    alpha-Dystroglycan (alpha-DG) is a component of the dystroglycan complex, which is involved in early development and morphogenesis and in the pathogenesis of muscular dystrophies. Here, alpha-DG was shown to serve as a Schwann cell receptor for Mycobacterium leprae, the causative organism of leprosy. Mycobacterium leprae specifically bound to alpha-DG only in the presence of the G domain of the alpha2 chain of laminin-2. Native alpha-DG competitively inhibited the laminin-2-mediated M. leprae binding to primary Schwann cells. Thus, M. leprae may use linkage between the extracellular matrix and cytoskeleton through laminin-2 and alpha-DG for its interaction with Schwann cells.

48. Salzer JL, Lovejoy L, Linder MC, Rosen C. "Ran-2, a glial lineage marker, is a GPI-anchored form of ceruloplasmin," Journal of neuroscience research 1998 Oct 15;54(2):147-57.   (MEDL:99002323 PMID: 9788274 #J0002562) Full Text Link!   

    Cell interactions in the nervous system are frequently mediated by surface proteins that are attached to the membrane by a glycosyl phosphatidylinositol (GPI) anchor. In this study, we have characterized the expression of such proteins on glial cells. We have detected a major GPI-anchored protein on astrocytes and Schwann cells, with a molecular weight of 140 kD. When Schwann cells were treated with forskolin to promote a myelinating phenotype, expression of this 140-kD protein dramatically decreased, whereas another GPI-anchored protein of 80 kD was strongly induced; expression of other integral membrane proteins were likewise dramatically altered. The size and pattern of expression of the 140-kD protein suggested that it might correspond to the Ran-2 antigen, a glial lineage marker. This notion was confirmed by immunoprecipitating this 140-kD protein with the Ran-2 monoclonal antibody. The Ran-2 antigen is expressed over the entire Schwann cell surface in a punctate fashion; it is removed by phosphatidylinositol phospholipase C treatment, thereby confirming that it is GPI-anchored. When Schwann cells are cocultured with neurons, the Ran-2 antigen initially concentrates at sites of Schwann cell contact with neurons, suggesting that it may play a role in early Schwann cell-neuron interactions; it is then downregulated. Protein sequencing of the Ran-2 antigen immunopurified from rat brain membranes showed complete identity over two extended segments with the copper binding protein ceruloplasmin. These findings indicate that astrocytes and Schwann cells express a novel GPI-anchored form of ceruloplasmin and suggest that this GPI form plays a role in axonal-glial interactions.

49. Shen YJ, DeBellard ME, Salzer JL, Roder J, Filbin MT. "Myelin-associated glycoprotein in myelin and expressed by Schwann cells inhibits axonal regeneration and branching," Molecular & cellular neurosciences 1998 Sep;12(1-2):79-91.   (MEDL:98445471 PMID: 9770342 #J0003165) Full Text Link!   

    The mammalian CNS does not regenerate after injury due largely to myelin-specific inhibitors of axonal growth. The PNS, however, does regenerate once myelin is cleared and myelin proteins are down-regulated by Schwann cells. Myelin-associated glycoprotein (MAG), a sialic acid binding protein, is a potent inhibitor of neurite outgrowth when presented to neurons in culture. Here, we present additional evidence that strongly supports the suggestion that MAG contributes to the overall inhibitory properties of myelin. When myelin from MAG-/- mice is used as a substrate, axonal length is 100 and 60% longer for neonatal cerebellar and older DRG neurons, respectively, compared to MAG+/+ myelin. The converse is true for neurites from neonatal DRG neurons, which are twice as long on MAG+/+ relative to MAG-/- myelin, consistent with MAG's dual role of promoting axonal growth from neonatal DRG neurons but inhibiting growth in older DRG and all other postnatal neurons examined. Furthermore, desialylating neurons reverses inhibition by CNS myelin by 45%. Contrary to previous reports, under these conditions PNS myelin is also inhibitory for axonal regeneration. Importantly, results using PNS MAG-/- myelin as a substrate suggest that MAG contributes to this inhibition. Finally, when Schwann cells not expressing MAG and permissive for axonal growth are induced to express MAG by retroviral infection, not only is axonal outgrowth greatly inhibited by these cells but so also is neurite branching. This suggests for the first time that MAG not only affects axonal regeneration but may also play a role in the control of axonal sprouting. Copyright 1998 Academic Press.

50. Einheber S, Zanazzi G, Ching W, Scherer S, Milner TA, Peles E, Salzer JL. "The axonal membrane protein Caspr, a homologue of neurexin IV, is a component of the septate-like paranodal junctions that assemble during myelination," Journal of cell biology 1997 Dec 15;139(6):1495-1506.   (MEDL:98060845 PMID: 9396755 #J0002383) Full Text Link!   

    We have investigated the potential role of contactin and contactin-associated protein (Caspr) in the axonal-glial interactions of myelination. In the nervous system, contactin is expressed by neurons, oligodendrocytes, and their progenitors, but not by Schwann cells. Expression of Caspr, a homologue of Neurexin IV, is restricted to neurons. Both contactin and Caspr are uniformly expressed at high levels on the surface of unensheathed neurites and are downregulated during myelination in vitro and in vivo. Contactin is downregulated along the entire myelinated nerve fiber. In contrast, Caspr expression initially remains elevated along segments of neurites associated with nascent myelin sheaths. With further maturation, Caspr is downregulated in the internode and becomes strikingly concentrated in the paranodal regions of the axon, suggesting that it redistributes from the internode to these sites. Caspr expression is similarly restricted to the paranodes of mature myelinated axons in the peripheral and central nervous systems; it is more diffusely and persistently expressed in gray matter and on unmyelinated axons. Immunoelectron microscopy demonstrated that Caspr is localized to the septate-like junctions that form between axons and the paranodal loops of myelinating cells. Caspr is poorly extracted by nonionic detergents, suggesting that it is associated with the axon cytoskeleton at these junctions. These results indicate that contactin and Caspr function independently during myelination and that their expression is regulated by glial ensheathment. They strongly implicate Caspr as a major transmembrane component of the paranodal junctions, whose molecular composition has previously been unknown, and suggest its role in the reciprocal signaling between axons and glia.

51. Marchionni MA, Grinspan JB, Canoll PD, Mahanthappa NK, Salzer JL, Scherer SS. "Neuregulins as potential neuroprotective agents," Annals of the New York Academy of Sciences 1997 Oct 15;825:348-65.   (MEDL:98036740 PMID: 9370000 #J0046351)    

52. Rambukkana A, Salzer JL, Yurchenco PD, Tuomanen EI. "Neural targeting of Mycobacterium leprae mediated by the G domain of the laminin-alpha2 chain," Cell 1997 Mar 21;88(6):811-21.   (MEDL:97236501 PMID: 9118224 #J0020696) Full Text Link!   

    We report that the molecular basis of the neural tropism of Mycobacterium leprae is attributable to the specific binding of M. leprae to the laminin-alpha2 (LN-alpha2) chain on Schwann cell-axon units. Using recombinant fragments of LN-alpha2 (rLN-alpha2), the M. leprae-binding site was localized to the G domain. rLN-alpha2G mediated M. leprae binding to cell lines and to sciatic nerves of dystrophic dy/dy mice lacking LN-alpha2, but expressing laminin receptors. Anti-beta4 integrin antibody attenuated rLN-alpha2G-mediated M. leprae adherence, suggesting that M. leprae interacts with cells by binding to beta4 integrin via an LN-alpha2G bridge. Our results indicate a novel role for the G domain of LN-2 in infection and reveal a model in which a host-derived bridging molecule determines nerve tropism of a pathogen.

53. Salzer JL. "Clustering sodium channels at the node of Ranvier: close encounters of the axon-glia kind," Neuron 1997 Jun;18(6):843-846.   (MEDL:97352456 PMID: 9208851 #J0002252) Full Text Link!   

54. Tang S, Shen YJ, DeBellard ME, Mukhopadhyay G, Salzer JL, Crocker PR, Filbin MT. "Myelin-associated glycoprotein interacts with neurons via a sialic acid binding site at ARG118 and a distinct neurite inhibition site," Journal of cell biology 1997 Sep 22;138(6):1355-66.   (MEDL:97444369 PMID: 9298990 #J0046352) Full Text Link!   

    Inhibitory components in myelin are largely responsible for the lack of regeneration in the mammalian CNS. Myelin-associated glycoprotein (MAG), a sialic acid binding protein and a component of myelin, is a potent inhibitor of neurite outgrowth from a variety of neurons both in vitro and in vivo. Here, we show that MAG's sialic acid binding site is distinct from its neurite inhibitory activity. Alone, sialic acid-dependent binding of MAG to neurons is insufficient to effect inhibition of axonal growth. Thus, while soluble MAG-Fc (MAG extracellular domain fused to Fc), a truncated form of MAG-Fc missing Ig-domains 4 and 5, MAG(d1-3)-Fc, and another sialic acid binding protein, sialoadhesin, each bind to neurons in a sialic acid- dependent manner, only full-length MAG-Fc inhibits neurite outgrowth. These results suggest that a second site must exist on MAG which elicits this response. Consistent with this model, mutation of arginine 118 (R118) in MAG to either alanine or aspartate abolishes its sialic acid-dependent binding. However, when expressed at the surface of either CHO or Schwann cells, R118-mutated MAG retains the ability to inhibit axonal outgrowth. Hence, MAG has two recognition sites for neurons, the sialic acid binding site at R118 and a distinct inhibition site which is absent from the first three Ig domains.

55. Canoll PD, Musacchio JM, Hardy R, Reynolds R, Marchionni MA, Salzer JL. "GGF/neuregulin is a neuronal signal that promotes the proliferation and survival and inhibits the differentiation of oligodendrocyte progenitors," Neuron 1996 Aug;17(2):229-43.   (MEDL:96374356 PMID: 8780647 #J0010303) Full Text Link!   

    We show that GGF/neuregulin is a mitogen for prooligodendrocytes (O4+/O1- cells), oligodendrocytes (O4+/O1+ cells), and type-2 astrocytes. Heregulin beta 1, another neuregulin isoform, is also mitogenic. The proliferative effect of glial growth factor (GGF) does not require, but is greatly potentiated by, serum factors. GGF also promotes the survival of pro-oligodendrocytes under serum-free conditions. High levels of GGF reversibly inhibit the differentiation and lineage commitment of oligodendrocyte progenitors and, in differentiated cultures, result in loss of O1 and myelin basic protein expression. All three erbB receptors are expressed by progenitors and are activated by GGF; the relative abundance of these receptors changes during differentiation. Finally, cortical neurons release a soluble mitogen for pro-oligodendrocytes that is specifically blocked by antibodies to GGF. These results implicate the neuregulins in the neuronal regulation of oligodendrocyte progenitor proliferation, survival, and differentiation.

56. Einheber S, Schnapp LM, Salzer JL, Cappiello ZB, Milner TA. "Regional and ultrastructural distribution of the alpha 8 integrin subunit in developing and adult rat brain suggests a role in synaptic function," Journal of comparative neurology 1996 Jun 17;370(1):105-34.   (MEDL:8797161 PMID: 8797161 #J0104945)    

    Integrins are heterodimeric cell adhesion molecules comprised of alpha and beta subunits that have been implicated in the regulation of neuronal migration, differentiation, and process outgrowth. They mediate both cell-extracellular matrix and cell-cell interactions. The integrin alpha 8 beta 1 is a receptor for fibronectin, tenascin, and vitronectin that has been localized to axonal tracts and several types of non-neuronal cells in chick embryos and to smooth muscle cells in adult mammalian tissues. In this report, we describe the distribution of the alpha 8 subunit in the developing and adult mammalian brain. By light microscopy, alpha 8 labeling in the rat brain was found predominantly in neurons. It was primarily localized within perikarya and dendrites, but was also observed in certain fiber tracts. alpha 8 immunoreactivity was most concentrated in the olfactory bulb, hippocampal formation, substantia nigra, ventral tegmental area, and superior olivary complex, but was also found at moderate levels in several regions including layer 5 of the cerebral cortex. alpha 8 labeling was detected as early as E16, peaked in most areas during the first 3 postnatal weeks, and persisted in the adult. Electron microscopic analysis of the adult hippocampal formation revealed a striking concentration of alpha 8 immunoreactivity in the spines and postsynaptic densities of dendrites. These results suggest that alpha 8 is involved in the regulation of axonal and dendritic growth of some neurons in the developing central nervous system (CNS) and provide ultrastructural evidence that integrins may participate in the formation, maintenance, or plasticity of synapses.

57. Marchionni MA, Kirk CJ, Isaacs IJ, Hoban CJ, Mahanthappa NK, Anton ES, Chen C, Wason F, Lawson D, Hamers FP, Canoll PD, Reynolds R, Cannella B, Meun D, Holt WF, Matthew WD, Chen LE, Gispen WH, Raine CS, Salzer JL, Gwynne DI. "Neuregulins as potential drugs for neurological disorders," Cold Spring Harbor symposia on quantitative biology 1996;61:459-72.   (MEDL:97389286 PMID: 9246474 #J0046353)    

58. Salzer JL, Colman DR. "In memoriam: Richard Paul Bunge," Neuron 1996 Nov;17(5):811-2.   (MEDL:97092694 PMID: 8938114 #J0010180) Full Text Link!   

59. Struyk AF, Rosen C, Salzer JL. "Role of GPI anchored proteins in neural cell adhesion," Advances in molecular & cell biology 1996;16:?-?.   (offline #J0102904)    

60. EINHEBER, S, MILNER, T, GIANCOTTI, F, SALZER, J. "POTENTIAL ROLE OF INTEGRINS IN MYELINATION [Abstract]," Journal of neurochemistry 1995 AUG;65(4):S69-S69.   (ISI:A1995RC60100269 #J0149128)    

61. Einheber S, Hannocks MJ, Metz CN, Rifkin DB, Salzer JL. "Transforming growth factor-beta 1 regulates axon/Schwann cell interactions," Journal of cell biology 1995 Apr;129(2):443-458.   (MEDL:95238541 PMID: 7536747 #J0003336)    

    We have investigated the potential regulatory role of TGF-beta in the interactions of neurons and Schwann cells using an in vitro myelinating system. Purified populations of neurons and Schwann cells, grown alone or in coculture, secrete readily detectable levels of the three mammalian isoforms of TGF-beta; in each case, virtually all of the TGF-beta activity detected is latent. Expression of TGF-beta 1, a major isoform produced by Schwann cells, is specifically and significantly downregulated as a result of axon/Schwann cell interactions. Treatment of Schwann cells or Schwann cell/neuron cocultures with TGF-beta 1, in turn, has dramatic effects on proliferation and differentiation. In the case of purified Schwann cells, treatment with TGF-beta 1 increases their proliferation, and it promotes a pre- or nonmyelinating Schwann cell phenotype characterized by increased NCAM expression, decreased NGF receptor expression, inhibition of the forskolin-mediated induction of the myelin protein P0, and induction of the Schwann cell transcription factor suppressed cAMP-inducible POU protein. Addition of TGF-beta 1 to the cocultures inhibits many of the effects of the axon on Schwann cells, antagonizing the proliferation induced by contact with neurons, and, strikingly, blocking myelination. Ultrastructural analysis of the treated cultures confirmed the complete inhibition of myelination and revealed only rudimentary ensheathment of axons. Associated defects of the Schwann cell basal lamina and reduced expression of laminin were also detected. These effects of TGF-beta 1 on Schwann cell differentiation are likely to be direct effects on the Schwann cells themselves which express high levels of TGF-beta 1 receptors when cocultured with neurons. The regulated expression of TGF-beta 1 and its effects on Schwann cells suggest that it may be an important autocrine and paracrine mediator of neuron/Schwann cell interactions. During development, TGF-beta 1 could serve as an inhibitor of Schwann cell proliferation and myelination, whereas after peripheral nerve injury, it may promote the transition of Schwann cells to a proliferating, nonmyelinating phenotype, and thereby enhance the regenerative response.

62. Pedraza L, Spagnol G, Latov N, Salzer JL. "Biosynthesis and regulation of expression of the HNK-1 epitope on myelin-associated glycoprotein in a transfected cell model system," Journal of neuroscience research 1995 Apr 15;40(6):716-27.   (MEDL:7543157 PMID: 7543157 #J0104240)    

    The HNK-1 antibody recognizes a carbohydrate epitope expressed by many cell adhesion molecules in the nervous system that has been proposed to be an important adhesive determinant. This epitope is particularly prominent on the myelin-associated glycoprotein (MAG) and is related to the antigenic target in an autoimmune mediated demyelinating neuropathy. Elucidation of the mechanisms underlying the biosynthesis and regulation of expression of the HNK-1 epitope is therefore likely to have important functional and clinical implications. In order to investigate its biosynthesis and the regulation of its expression, we have expressed both human and rat MAG in several different cell lines by retroviral infection. These studies indicate that the cellular milieu determines whether the HNK-1 epitope is expressed on the MAG polypeptide and provide an explanation for the significant variation in HNK-1 levels that has been noted in different species. Using a transfected human neuroblastoma line, we have determined that this epitope is present on the fourth and/or fifth immunoglobulin-like domain of rat MAG and that it is added intracellularly, probably in the trans Golgi. Finally we have found that expression of the HNK-1 epitope is increased by activation of different second messenger systems, providing direct evidence that its expression can be regulated independently from that of the MAG polypeptide.

63. Salzer JL. "Mechanisms of adhesion between axons and glial cells," In: The axon : structure, function, and pathophysiology / Waxman S; Kocsis J; Syts P (Eds.)    New York : Oxford University Press, 1995. p. 164-184    (offline #C0001348)

64. Struyk AF, Canoll PD, Wolfgang MJ, Rosen CL, D'Eustachio P, Salzer JL. "Cloning of neurotrimin defines a new subfamily of differentially expressed neural cell adhesion molecules," Journal of neuroscience 1995 Mar;15(3 Pt 2):2141-2156.   (MEDL:95198094 PMID: 7891157 #J0001368)    

    Previous studies in the laboratory indicated that glycosylphosphatidylinositol (GPI)-anchored proteins may generate diversity of the cell surface of different neuronal populations (Rosen et al., 1992). In this study, we have extended these findings and surveyed the expression of GPI-anchored proteins in the developing rat CNS. In addition to several well characterized GPI-anchored cell adhesion molecules (CAMs), we detected an unidentified broad band of 65 kDa that is the earliest and most abundantly expressed GPI-anchored species in the rat CNS. Purification of this protein band revealed that it is comprised of several related proteins that define a novel subfamily of immunoglobulin-like (Ig) CAMs. One of these proteins is the opiate binding-cell adhesion molecule (OBCAM). We have isolated a cDNA encoding a second member of this family, that we have termed neurotrimin, and present evidence for the existence of additional family members. Like OBCAM, with which it shares extensive sequence identity, neurotrimin contains three immunoglobulin-like domains. Both proteins are encoded by distinct genes that may be clustered on the proximal end of mouse chromosome 9. Characterization of the expression of neurotrimin and OBCAM in the developing CNS by in situ hybridization reveals that these proteins are differentially expressed during development. Neurotrimin is expressed at high levels in several developing projection systems: in neurons of the thalamus, subplate, and lower cortical laminae in the forebrain and in the pontine nucleus, cerebellar granule cells, and Purkinje cells in the hindbrain. Neurotrimin is also expressed at high levels in the olfactory bulb, neural retina, dorsal root ganglia, spinal cord, and in a graded distribution in the basal ganglia and hippocampus. OBCAM has a much more restricted distribution, being expressed at high levels principally in the cortical plate and hippocampus. These results suggest that these proteins, together with other members of this family, provide diversity to the surfaces of different neuronal populations that could be important in the specification of neuronal connectivity.

65. Einheber S, Milner TA, Giancotti F, Salzer JL. "Axonal regulation of Schwann cell integrin expression suggests a role for alpha 6 beta 4 in myelination," Journal of cell biology 1993 Dec;123(5):1223-1236.   (MEDL:94064783 PMID: 8245127 #J0000710)    

    Ensheathment and myelination of axons by Schwann cells in the peripheral nervous system requires contact with a basal lamina. The molecular mechanism(s) by which the basal lamina promotes myelination is not known but is likely to reflect the activity of integrins expressed by Schwann cells. To initiate studies on the role of integrins during myelination, we characterized the expression of two integrin subunits, beta 1 and beta 4, in an in vitro myelination system and compared their expression to that of the glial adhesion molecule, the myelin-associated glycoprotein (MAG). In the absence of neurons, Schwann cells express significant levels of beta 1 but virtually no beta 4 or MAG. When Schwann cells are cocultured with dorsal root ganglia neurons under conditions promoting myelination, expression of beta 4 and MAG increased dramatically in myelinating cells, whereas beta 1 levels remained essentially unchanged. (In general agreement with these findings, during peripheral nerve development in vivo, beta 4 levels also increase during the period of myelination in sharp contrast to beta 1 levels which show a striking decrease.) In cocultures of neurons and Schwann cells, beta 4 and MAG appear to colocalize in nascent myelin sheaths but have distinct distributions in mature sheaths, with beta 4 concentrated in the outer plasma membrane of the Schwann cell and MAG localized to the inner (periaxonal) membrane. Surprisingly, beta 4 is also present at high levels with MAG in Schmidt-Lanterman incisures. Immunoprecipitation studies demonstrated that primary Schwann cells express beta 1 in association with the alpha 1 and alpha 6 subunits, while myelinating Schwann cells express alpha 6 beta 4 and possibly alpha 1 beta 1. beta 4 is also downregulated during Wallerian degeneration in vitro, indicating that its expression requires continuous Schwann cell contact with the axon. These results indicate that axonal contact induces the expression of beta 4 during Schwann cell myelination and suggest that alpha 6 beta 4 is an important mediator of the interactions of myelinating Schwann cells with the basal lamina.

66. EINHEBER, S, GIANCOTTI, FG, SALZER, JL. "EXPRESSION AND DISTRIBUTION OF THE ALPHA-6-BETA-4-INTEGRIN IN MYELINATING SCHWANN-CELLS [Abstract]," Molecular biology of the cell 1992 SEP;3(4):A130-A130.   (ISI:A1992JR25500754 #J0089287)    

67. Rosen CL, Lisanti MP, Salzer JL. "Expression of unique sets of GPI-linked proteins by different primary neurons in vitro," Journal of cell biology 1992 May;117(3):617-27.   (MEDL:92242307 PMID: 1349305 #J0012070)    

    We have surveyed the proteins expressed at the surface of different primary neurons as a first step in elucidating how axons regulate their ensheathment by glial cells. We characterized the surface proteins of dorsal root ganglion neurons, superior cervical ganglion neurons, and cerebellar granule cells which are myelinated, ensheathed but unmyelinated, and unensheathed, respectively. We found that the most abundant proteins are common to all three types of neurons. Reproducible differences in the composition of the integral membrane proteins (enriched by partitioning into a Triton X-114 detergent phase) were detected. These differences were most striking when the expression of glycosylphosphatidyl-inositol (GPI)-anchored membrane proteins by these different neurons was compared. Variations in the relative abundance and degree of glycosylation of several well known GPI-anchored proteins, including Thy-1, F3/F11, and the 120-kD form of the neural cell adhesion molecule (N-CAM), and an abundant 60-kD GPI-linked protein were observed. In addition, we have identified several potentially novel GPI-anchored glycoproteins on each class of neurons. These include a protein that is present only on superior cervical ganglion neurons and is 90 kD; an abundant protein of 69 kD that is essentially restricted in its expression to dorsal root ganglion neurons; and proteins of 38 and 31 kD that are expressed only on granule cell neurons. Finally, the relative abundance of the three major isoforms of N-CAM was found to vary significantly between these different primary neurons. These results are the first demonstration that nerve fibers with diverse ensheathment fates differ significantly in the composition of their surface proteins and suggest an important role for GPI-anchored proteins in generating diversity of the neuronal cell surface.

68. STRUYK, AF, ROSEN, CL, SALZER, JL. "CHARACTERIZATION OF THE OPIATE BINDING-CELL ADHESION MOLECULE - AN ABUNDANT GPI-ANCHORED PROTEIN IN THE RAT CNS [Abstract]," Molecular biology of the cell 1992 SEP;3(4):A358-A358.   (ISI:A1992JR25502078 #J0089297)    

69. Afar DE, Marius RM, Salzer JL, Stanners CP, Braun PE, Bell JC. "Cell adhesion properties of myelin-associated glycoprotein in L cell fibroblasts," Journal of neuroscience research 1991 Aug;29(4):429-36.   (MEDL:92167310 PMID: 1724267 #J0046355)    

    Myelin-associated glycoprotein (MAG) is a cell surface molecule expressed by oligodendrocytes and Schwann cells. In order to determine whether MAG expression can confer adhesive properties to cells which normally do not aggregate in suspension, the cDNA encoding the long form of MAG (L-MAG) was introduced into L cell fibroblasts by retroviral infection. Clonal L cell lines expressing MAG were then subjected to a cell aggregation assay. Our results indicate that L-MAG can function as an intercellular adhesion molecule in a heterologous cell system. A critical threshold value of L-MAG expression was required for cell aggregation to occur. The adhesive properties of these cells were specific to MAG, since monoclonal antibodies directed against its extracellular domain inhibited aggregation. Furthermore, the adhesion was found to be calcium- and temperature-independent. Cell sorting experiments demonstrated that L-MAG-expressing cells bind in a heterotypic fashion to parental L cell fibroblasts. These results suggest that L-MAG can function as a heterotypic cell adhesion molecule recognizing a cell surface molecule(s) expressed by L cells.

70. Pedraza L, Frey AB, Hempstead BL, Colman DR, Salzer JL. "Differential expression of MAG isoforms during development," Journal of neuroscience research 1991 Jun;29(2):141-8.   (MEDL:91366725 PMID: 1716323 #J0012702)    

    The myelin-associated glycoproteins (MAG) mediate the cell interactions of oligodendrocytes and Schwann cells with axons that are myelinated. MAG exists in two developmentally regulated isoforms: large MAG (L-MAG) and small MAG (S-MAG). In this paper, we have studied the tissue-specific and developmentally regulated alternative splicing of these isoforms using monospecific antibodies that recognize epitopes common to both isoforms or that are present only on L-MAG. In the central nervous system (CNS), L-MAG is the major form synthesized early in development, and it persists as a significant proportion of the MAG present in the adult. In the peripheral nervous system (PNS), L-MAG is expressed at modest levels during development; it is virtually absent in the adult. Thus, the expression of L-MAG is not limited to the CNS, as was formerly believed, suggesting that it plays a common role during the early stages of myelin formation by both oligodendrocytes and Schwann cells. In both the CNS and PNS, S-MAG is the predominant isoform in the adult. A higher-molecular-weight form of MAG is present in the PNS at low abundance, that is developmentally regulated, and appears to be a glycosylation variant. An analysis of the carbohydrate residues on MAG demonstrates that it contains both N-linked and O-linked sugars that could be modulated during development. These results suggest a possible mechanism for the regulation of MAG function during myelinogenesis via the expression of alternative isoforms and carbohydrate modifications.

71. Sperhac AM, Salzer JL. "A new developmental screening test. The Denver II," Journal of the American Academy of Nurse Practitioners 1991 Oct-Dec;3(4):152-7.   (MEDL:92162445 PMID: 1724169 #J0048289)    

    To maximize the potential of a child with a developmental delay, early detection and intervention is essential (Frankenburg and Thornton, 1989). The nurse practitioner who includes a developmental screening with the child's general assessment may detect a developmental delay during a routine office visit. The purpose of this article is to provide an overview of the Denver II, a new developmental screening test.

72. Afar DE, Salzer JL, Roder J, Braun PE, Bell JC. "Differential phosphorylation of myelin-associated glycoprotein isoforms in cell culture," Journal of neurochemistry 1990 Oct;55(4):1418-26.   (MEDL:90376125 PMID: 1697896 #J0046356)    

    The alternative splicing of myelin-associated glycoprotein (MAG) mRNA generates two isoforms that harbor distinct potential phosphorylation sites in their cytoplasmic tails. Here we characterize the in vivo phosphorylation of MAG isoforms in NIH 3T3 cells transfected with the cDNAs encoding the two isoforms of MAG. Our results demonstrate that the longer isoform, L-MAG, is phosphorylated constitutively mainly on serine, but also on threonine and tyrosine residues. This phosphorylation is subject to change by 12-O-tetradecanoylphorbol 13-acetate (TPA) and ammonium vanadate, but not by dibutyryl-cyclic AMP. The shorter isoform, S-MAG, is constitutively phosphorylated only on serine residues. While TPA and dibutyryl-cyclic AMP have no detectable effect, ammonium vanadate induces tyrosine and threonine phosphorylation in S-MAG. 32P labeling of v-src-transformed NIH 3T3 cells that express L-MAG also show that L-MAG is likely to be an in vivo substrate for pp60v-src tyrosine kinase activity. These results demonstrate that both MAG isoforms are phosphorylated in a heterologous cell system and that this phosphorylation is subject to pharmacological manipulation.

73. Owens GC, Boyd CJ, Bunge RP, Salzer JL. "Expression of recombinant myelin-associated glycoprotein in primary Schwann cells promotes the initial investment of axons by myelinating Schwann cells," Journal of cell biology 1990 Sep;111(3):1171-82.   (MEDL:90361743 PMID: 1697293 #J0046357)    

    Myelin-associated glycoprotein (MAG) is an integral membrane protein expressed by myelinating glial cells that occurs in two developmentally regulated forms with different carboxyterminal cytoplasmic domains (L-MAG and S-MAG). To investigate the role of MAG in myelination a recombinant retrovirus was used to introduce a MAG cDNA (L-MAG form) into primary Schwann cells in vitro. Stably infected populations of cells were obtained that constitutively expressed MAG at the cell surface without the normal requirement for neuronal contact to induce expression. Constitutive expression of L-MAG did not affect myelination. In long term co-culture with purified sensory neurons, the higher level of MAG expression on infected Schwann cells was reduced to control levels on cells that formed myelin. On the other hand, unlike normal Schwann cells, infected Schwann cells associated with nonmyelinated axons or undergoing Wallerian degeneration expressed high levels of MAG. This suggests that a posttranscriptional mechanism modulates MAG expression during myelination. Immunostaining myelinating cultures with an antibody specific to L-MAG showed that L-MAG was normally transiently expressed at the earliest stages of myelination. In short term co-culture with sensory neurons, infected Schwann cells expressing only L-MAG segregated and ensheathed larger axons after 4 d in culture provided that an exogenous basal lamina was supplied. Similar activity was rarely displayed by control Schwann cells correlating with the low level of MAG induction after 4 d. These data strongly suggest that L-MAG promotes the initial investment by Schwann cells of axons destined to be myelinated.

74. Pedraza L, Owens GC, Green LA, Salzer JL. "The myelin-associated glycoproteins: membrane disposition, evidence of a novel disulfide linkage between immunoglobulin-like domains, and posttranslational palmitylation," Journal of cell biology 1990 Dec;111(6 Pt 1):2651-61.   (MEDL:91115956 PMID: 1703542 #J0013132)    

    The myelin-associated glycoproteins (MAG) are members of the immunoglobulin gene superfamily that function in the cell interactions of myelinating glial cells with axons. In this paper, we have characterized the structural features of these proteins. The disposition of MAG in the bilayer as a type 1 integral membrane protein (with an extracellularly disposed amino terminus, single transmembrane segment, and cytoplasmic carboxy terminus) was demonstrated in protease protection studies of MAG cotranslationally inserted into microsomes in vitro and in immunofluorescent studies with site specific antibodies. A genetically engineered MAG cDNA, which lacks the putative membrane spanning segment, was constructed and shown to encode a secreted protein. These results confirm the identify of this hydrophobic sequence as the transmembrane segment. Sequencing of the secreted protein demonstrated the presence of a cleaved signal sequence and the site of signal peptidase cleavage. To characterize the disulfide linkage pattern of the ectodomain, we cleaved MAG with cyanogen bromide and used a panel of antibodies to coprecipitate specific fragments under nonreducing conditions. These studies provide support for a novel disulfide linkage between two of the immunoglobulin domains of the extracellular segment. Finally, we report that MAG is posttranslationally palmitylated via an intramembranous thioester linkage. Based on these studies, we propose a model for the conformation of MAG, including its RGD sequence, which is considered with regard to its function as a cell adhesion molecule.

75. Salzer JL, Pedraza L, Brown M, Struyk A, Afar D, Bell J. "Structure and function of the myelin-associated glycoproteins," Annals of the New York Academy of Sciences 1990;605:302-12.   (MEDL:91097177 PMID: 1702604 #J0046358)    

76. Salzer JL, Colman DR. "Mechanisms of cell adhesion in the nervous system: role of the immunoglobulin gene superfamily," Developmental neuroscience 1989;11(6):377-90.   (MEDL:90032430 PMID: 2680439 #J0007512)    

    The amino acid sequences of a large number of the cell surface proteins known to mediate cell-cell interactions in the nervous system have recently been reported. Many of these proteins are members of the immunoglobulin gene superfamily and have remarkably similar structures and amino acid sequences in their extracellular segments. We have termed this family of immunoglobulin-related cell adhesion molecules the Ig-CAMs. In this article, we review the structural features of the Ig-CAMs, discuss how these features may relate to the role of these proteins in mediating cell adhesion and cell signaling events, and finally consider the evolutionary origins of this family of proteins.

77. D'Eustachio P, Colman DR, Salzer JL. "Chromosomal location of the mouse gene that encodes the myelin-associated glycoproteins," Journal of neurochemistry 1988 Feb;50(2):589-93.   (MEDL:88089666 PMID: 2447245 #J0008157)    

    The two myelin-associated glycoprotein (MAG) species, designated large MAG (L-MAG) and small MAG (S-MAG), are believed to be generated by differential splicing from a single RNA transcript. We have now defined the genetic locus encoding the two MAG proteins in the mouse. Analysis of a panel of interspecies somatic cell hybrids indicated that all MAG coding sequences reside on chromosome 7. Following the inheritance of a restriction fragment length polymorphism associated with MAG coding sequences allowed the locus to be