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Gomes DE, Witwer KW. L1CAM-associated extracellular vesicles: A systematic review of nomenclature, sources, separation, and characterization. JOURNAL OF EXTRACELLULAR BIOLOGY 2022; 1:e35. [PMID: 35492832 PMCID: PMC9045013 DOI: 10.1002/jex2.35] [Citation(s) in RCA: 25] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/09/2022] [Accepted: 02/24/2022] [Indexed: 12/20/2022]
Abstract
When released into biological fluids like blood or saliva, brain extracellular vesicles (EVs) might provide a window into otherwise inaccessible tissue, contributing useful biomarkers of neurodegenerative and other central nervous system (CNS) diseases. To enrich for brain EVs in the periphery, however, cell-specific EV surface markers are needed. The protein that has been used most frequently to obtain EVs of putative neuronal origin is the transmembrane L1 cell adhesion molecule (L1CAM/CD171). In this systematic review, we examine the existing literature on L1CAM and EVs, including investigations of both neurodegenerative disease and cancer through the lens of the minimal information for studies of EVs (MISEV), specifically in the domains of nomenclature usage, EV sources, and EV separation and characterization. Although numerous studies have reported L1CAM-associated biomarker signatures that correlate with disease, interpretation of these results is complicated since L1CAM expression is not restricted to neurons and is also upregulated during cancer progression. A recent study has suggested that L1CAM epitopes are present in biofluids mostly or entirely as cleaved, soluble protein. Our findings on practices and trends in L1CAM-mediated EV separation, enrichment, and characterization yield insights that may assist with interpreting results, evaluating rigor, and suggesting avenues for further exploration.
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Affiliation(s)
- Dimitria E. Gomes
- Cornell University College of Veterinary Medicine, Ithaca, New York, USA
- Department of Molecular and Comparative Pathobiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Kenneth W. Witwer
- Department of Molecular and Comparative Pathobiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
- The Richman Family Precision Medicine Centre of Excellence in Alzheimer’s Disease, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
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2
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Płatek R, Grycz K, Więckowska A, Czarkowska-Bauch J, Skup M. L1 Cell Adhesion Molecule Overexpression Down Regulates Phosphacan and Up Regulates Structural Plasticity-Related Genes Rostral and Caudal to the Complete Spinal Cord Transection. J Neurotrauma 2019; 37:534-554. [PMID: 31426714 DOI: 10.1089/neu.2018.6103] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
L1 cell adhesion molecule (L1CAM) supports spinal cord cellular milieu after contusion and compression lesions, contributing to neuroprotection, promoting axonal outgrowth, and reducing outgrowth-inhibitory molecules in lesion proximity. We extended investigations into L1CAM molecular targets and explored long-distance effects of L1CAM rostral and caudal to complete spinal cord transection (SCT) in adult rats. L1CAM overexpression in neurons and glia after Th10/Th11 SCT was achieved using adeno-associated viral vector serotype 5 (AAV5) injected into an L1-lumbar segment immediately after transection. At 5 weeks, a L1CAM mRNA profound decrease detected rostral and caudal to the transection site was alleviated by AAV5-L1CAM treatment, with increased endogenous L1CAM rostral to the SCT. Transected corticospinal tract fibers showed attenuated retraction after treatment, accompanied by a multi-segmental increase of lesion-reduced expression of adenylate cyclase 1 (Adcy1), synaptophysin, growth-associated protein 43, and myelin basic protein genes caudal to transection, and Adcy1 rostral to transection. In parallel, chondroitin sulfate proteoglycan phosphacan elevated after SCT was downregulated after treatment. Low-molecular L1CAM isoforms generated after spinalization indicated the involvement of sheddases in L1CAM processing and long-distance effects. A disintegrin and metalloproteinase (ADAM)10 sheddase immunoreactivity, stronger in AAV5-L1CAM than AAV5- enhanced green fluorescent protein (EGFP)-transduced motoneurons indicated local ADAM10 upregulation by L1CAM. The results suggest that increased L1CAM availability and penetration of diffusible L1CAM fragments post-lesion induce both local and long-distance neuronal and glial responses toward better neuronal maintenance, neurite growth, and myelination. Despite the fact that intervention promoted beneficial molecular changes, kinematic analysis of hindlimb movements showed minor improvement, indicating that spinalized rats require longer L1CAM treatment to regain locomotor functions.
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Affiliation(s)
- Rafał Płatek
- Nencki Institute of Experimental Biology, Warsaw, Poland
| | - Kamil Grycz
- Nencki Institute of Experimental Biology, Warsaw, Poland
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3
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Modulation of cell-cell interactions for neural tissue engineering: Potential therapeutic applications of cell adhesion molecules in nerve regeneration. Biomaterials 2019; 197:327-344. [DOI: 10.1016/j.biomaterials.2019.01.030] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2018] [Revised: 12/08/2018] [Accepted: 01/20/2019] [Indexed: 12/21/2022]
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4
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He Q, Man L, Ji Y, Zhang S, Jiang M, Ding F, Gu X. Comparative Proteomic Analysis of Differentially Expressed Proteins between Peripheral Sensory and Motor Nerves. J Proteome Res 2012; 11:3077-89. [DOI: 10.1021/pr300186t] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
- Qianru He
- Jiangsu Key Laboratory of Neuroregeneration, Nantong University, Nantong, Jiangsu Province 226001,
P. R. China
| | - Lili Man
- Jiangsu Key Laboratory of Neuroregeneration, Nantong University, Nantong, Jiangsu Province 226001,
P. R. China
| | - Yuhua Ji
- Jiangsu Key Laboratory of Neuroregeneration, Nantong University, Nantong, Jiangsu Province 226001,
P. R. China
| | - Shuqiang Zhang
- Jiangsu Key Laboratory of Neuroregeneration, Nantong University, Nantong, Jiangsu Province 226001,
P. R. China
| | - Maorong Jiang
- Jiangsu Key Laboratory of Neuroregeneration, Nantong University, Nantong, Jiangsu Province 226001,
P. R. China
| | - Fei Ding
- Jiangsu Key Laboratory of Neuroregeneration, Nantong University, Nantong, Jiangsu Province 226001,
P. R. China
| | - Xiaosong Gu
- Jiangsu Key Laboratory of Neuroregeneration, Nantong University, Nantong, Jiangsu Province 226001,
P. R. China
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5
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Kim J, Lilliehook C, Dudak A, Prox J, Saftig P, Federoff HJ, Lim ST. Activity-dependent alpha-cleavage of nectin-1 is mediated by a disintegrin and metalloprotease 10 (ADAM10). J Biol Chem 2010; 285:22919-26. [PMID: 20501653 DOI: 10.1074/jbc.m110.126649] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Nectin-1 is known to undergo ectodomain shedding by alpha-secretase and subsequent proteolytic processing by gamma-secretase. How secretase-mediated cleavage of nectin-1 is regulated in neuronal cells and how nectin-1 cleavage affects synaptic adhesion is poorly understood. We have investigated alpha-and gamma-secretase-mediated processing of nectin-1 in primary cortical neurons and identified which protease acts as a alpha-secretase. We report here that NMDA receptor activation, but not stimulation of AMPA or metabotropic glutamate receptors, resulted in robust alpha- and gamma-secretase cleavage of nectin-1 in mature cortical neurons. Cleavage of nectin-1 required influx of Ca(2+) through the NMDA receptor, and activation of calmodulin, but was not dependent on calcium/calmodulin-dependent protein kinase II (CaMKII) activation. We found that ADAM10 is the major secretase responsible for nectin-1 ectodomain cleavage in neurons and the brain. These observations suggest that alpha- and gamma-secretase processing of nectin-1 is a Ca(2+)/calmodulin-regulated event that occurs under conditions of activity-dependent synaptic plasticity and ADAM10 and gamma-secretase are responsible for these cleavage events.
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Affiliation(s)
- Jinsook Kim
- Neuroscience Department, Georgetown University Medical Center, Washington, D. C. 20057, USA
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6
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Wieringa PA, Wiertz RWF, de Weerd E, Rutten WLC. Bifurcating microchannels as a scaffold to induce separation of regenerating neurites. J Neural Eng 2010; 7:16001. [PMID: 20054102 DOI: 10.1088/1741-2560/7/1/016001] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Many neural interfacing strategies, such as the sieve electrode and the cultured probe, rely on neurite growth to establish neural contact. But this growth is subject to natural fasciculation, compromising the effectiveness of these interfacing strategies by reducing potential selectivity. This in vitro study shows that the fasciculation mechanism can be manipulated by providing an appropriate microchannel scaffold to guide and influence growth, thereby achieving a high degree of selectivity. The microchannels employed have a bifurcation from a primary channel into two secondary channels. This bifurcating microstructure was able to support and promote fasciculated growth over 70% of the time for microchannels widths of 2.5, 5, 10 and 20 microm. Fasciculation is shown to be a strong force during ingrowth, with the initiation of neurite separation related to random spatial exploration. Narrower microchannels initiate separated growth better. Once separated growth starts fasciculation results in an even distribution of neurite growth across the bifurcation. The reduction from 20 microm to 10 microm wide channels also resulted in a 3-fold decrease in ingrowing neurites performing 180 degrees turns to exit the microchannel via the entrance. No neurite turning was observed for both the 5 and 2.5 microm wide channels.
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Affiliation(s)
- P A Wieringa
- Neurotechnology Group/BSS, MIRA Institute, University of Twente, Enschede, The Netherlands.
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7
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Hagiyama M, Ichiyanagi N, Kimura KB, Murakami Y, Ito A. Expression of a soluble isoform of cell adhesion molecule 1 in the brain and its involvement in directional neurite outgrowth. THE AMERICAN JOURNAL OF PATHOLOGY 2009; 174:2278-89. [PMID: 19435791 PMCID: PMC2684192 DOI: 10.2353/ajpath.2009.080743] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 02/19/2009] [Indexed: 11/20/2022]
Abstract
Cell adhesion molecule 1 (CADM1), an immunoglobulin superfamily member, is expressed on superior cervical ganglion neurites and mediates cell-cell adhesion by trans-homophilic binding. In addition to the membrane-bound form, we have previously shown that a soluble form (sCADM1) generated by alternative splicing possesses a stop codon immediately downstream of the immunoglobulin-like domain. Here, we demonstrate the presence of sCADM1 in vivo and its possible role in neurite extension. sCADM1 appears to be a stromal protein because extracellular-restricted, but not intracellular-restricted, anti-CADM1 antibody stained stromal protein-rich extract from mouse brains. Murine plasmacytoma cells, P3U1, were modified to secrete sCADM1 fused with either immunoglobulin (Ig)G Fc portion (sCADM1-Fc) or its deletion form that lacks the immunoglobulin-like domain (DeltasCADM1-Fc). When P3U1 derivatives expressing sCADM1-Fc or DeltasCADM1-Fc were implanted into collagen gels, Fc-fused proteins were present more abundantly around the cells. Superior cervical ganglion neurons, parental P3U1, and either derivative were implanted into collagen gels separately, and co-cultured for 4 days. Bodian staining of the gel sections revealed that most superior cervical ganglion neurites turned toward the source of sCADM1-Fc, but not DeltasCADM1-Fc. Furthermore, immunofluorescence signals for sCADM1-Fc and membrane-bound CADM1 were co-localized on the neurite surface. These results show that sCADM1 appears to be involved in directional neurite extension by serving as an anchor to which membrane-bound CADM1 on the neurites can bind.
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Affiliation(s)
- Man Hagiyama
- Division of Molecular Pathology, Department of Cancer Biology, Institute of Medical Science, The University of Tokyo, 4-6-1, Shirokanedai, Minato-ku, Tokyo 108-8639, Japan
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8
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Pruessmeyer J, Ludwig A. The good, the bad and the ugly substrates for ADAM10 and ADAM17 in brain pathology, inflammation and cancer. Semin Cell Dev Biol 2009; 20:164-74. [DOI: 10.1016/j.semcdb.2008.09.005] [Citation(s) in RCA: 159] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2008] [Revised: 09/11/2008] [Accepted: 09/15/2008] [Indexed: 10/21/2022]
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9
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Baculovirus expression and bioactivity of a soluble 140kDa extracellular cleavage fragment of L1 neural cell adhesion molecule. Protein Expr Purif 2008; 57:172-9. [DOI: 10.1016/j.pep.2007.10.006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2007] [Revised: 10/08/2007] [Accepted: 10/11/2007] [Indexed: 11/21/2022]
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10
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Maretzky T, Schulte M, Ludwig A, Rose-John S, Blobel C, Hartmann D, Altevogt P, Saftig P, Reiss K. L1 is sequentially processed by two differently activated metalloproteases and presenilin/gamma-secretase and regulates neural cell adhesion, cell migration, and neurite outgrowth. Mol Cell Biol 2005; 25:9040-53. [PMID: 16199880 PMCID: PMC1265787 DOI: 10.1128/mcb.25.20.9040-9053.2005] [Citation(s) in RCA: 186] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The immunoglobulin superfamily recognition molecule L1 plays important functional roles in the developing and adult nervous system. Metalloprotease-mediated cleavage of this adhesion molecule has been shown to stimulate cellular migration and neurite outgrowth. We demonstrate here that L1 cleavage is mediated by two distinct members of the disintegrin and metalloprotease family, ADAM10 and ADAM17. This cleavage is differently regulated and leads to the generation of a membrane bound C-terminal fragment, which is further processed through gamma-secretase activity. Pharmacological approaches with two hydroxamate-based inhibitors with different preferences in blocking ADAM10 and ADAM17, as well as loss of function and gain of function studies in murine embryonic fibroblasts, showed that constitutive shedding of L1 is mediated by ADAM10 while phorbol ester stimulation or cholesterol depletion led to ADAM17-mediated L1 cleavage. In contrast, N-methyl-d-aspartate treatment of primary neurons stimulated ADAM10-mediated L1 shedding. Both proteases were able to affect L1-mediated adhesion and haptotactic migration of neuronal cells. In particular, both proteases were involved in L1-dependent neurite outgrowth of cerebellar neurons. Thus, our data identify ADAM10 and ADAM17 as differentially regulated L1 membrane sheddases, both critically affecting the physiological functions of this adhesion protein.
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11
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Yasuda H, Terada M, Maeda K, Kogawa S, Sanada M, Haneda M, Kashiwagi A, Kikkawa R. Diabetic neuropathy and nerve regeneration. Prog Neurobiol 2003; 69:229-85. [PMID: 12757748 DOI: 10.1016/s0301-0082(03)00034-0] [Citation(s) in RCA: 185] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Diabetic neuropathy is the most common peripheral neuropathy in western countries. Although every effort has been made to clarify the pathogenic mechanism of diabetic neuropathy, thereby devising its ideal therapeutic drugs, neither convinced hypotheses nor unequivocally effective drugs have been established. In view of the pathologic basis for the treatment of diabetic neuropathy, it is important to enhance nerve regeneration as well as prevent nerve degeneration. Nerve regeneration or sprouting in diabetes may occur not only in the nerve trunk but also in the dermis and around dorsal root ganglion neurons, thereby being implicated in the generation of pain sensation. Thus, inadequate nerve regeneration unequivocally contributes to the pathophysiologic mechanism of diabetic neuropathy. In this context, the research on nerve regeneration in diabetes should be more accelerated. Indeed, nerve regenerative capacity has been shown to be decreased in diabetic patients as well as in diabetic animals. Disturbed nerve regeneration in diabetes has been ascribed at least in part to all or some of decreased levels of neurotrophic factors, decreased expression of their receptors, altered cellular signal pathways and/or abnormal expression of cell adhesion molecules, although the mechanisms of their changes remain almost unclear. In addition to their steady-state changes in diabetes, nerve injury induces injury-specific changes in individual neurotrophic factors, their receptors and their intracellular signal pathways, which are closely linked with altered neuronal function, varying from neuronal survival and neurite extension/nerve regeneration to apoptosis. Although it is essential to clarify those changes for understanding the mechanism of disturbed nerve regeneration in diabetes, very few data are now available. Rationally accepted replacement therapy with neurotrophic factors has not provided any success in treating diabetic neuropathy. Aside from adverse effects of those factors, more rigorous consideration for their delivery system may be needed for any possible success. Although conventional therapeutic drugs like aldose reductase (AR) inhibitors and vasodilators have been shown to enhance nerve regeneration, their efficacy should be strictly evaluated with respect to nerve regenerative capacity. For this purpose, especially clinically, skin biopsy, by which cutaneous nerve pathology including nerve regeneration can be morphometrically evaluated, might be a safe and useful examination.
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Affiliation(s)
- Hitoshi Yasuda
- Division of Neurology, Department of Medicine, Shiga University of Medical Science, Seta, Otsu, Japan.
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12
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Mechtersheimer S, Gutwein P, Agmon-Levin N, Stoeck A, Oleszewski M, Riedle S, Postina R, Fahrenholz F, Fogel M, Lemmon V, Altevogt P. Ectodomain shedding of L1 adhesion molecule promotes cell migration by autocrine binding to integrins. J Cell Biol 2001; 155:661-73. [PMID: 11706054 PMCID: PMC2198870 DOI: 10.1083/jcb.200101099] [Citation(s) in RCA: 304] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The L1 adhesion molecule plays an important role in axon guidance and cell migration in the nervous system. L1 is also expressed by many human carcinomas. In addition to cell surface expression, the L1 ectodomain can be released by a metalloproteinase, but the biological function of this process is unknown. Here we demonstrate that membrane-proximal cleavage of L1 can be detected in tumors and in the developing mouse brain. The shedding of L1 involved a disintegrin and metalloproteinase (ADAM)10, as transfection with dominant-negative ADAM10 completely abolishes L1 release. L1-transfected CHO cells (L1-CHO) showed enhanced haptotactic migration on fibronectin and laminin, which was blocked by antibodies to alpha v beta 5 and L1. Migration of L1-CHO cells, but not the basal migration of CHO cells, was blocked by a metalloproteinase inhibitor, indicating a role for L1 shedding in the migration process. CHO and metalloproteinase-inhibited L1-CHO cells were stimulated to migrate by soluble L1-Fc protein. The induction of migration was blocked by alpha v beta 5-specific antibodies and required Arg-Gly-Asp sites in L1. A 150-kD L1 fragment released by plasmin could also stimulate CHO cell migration. We propose that ectodomain-released L1 promotes migration by autocrine/paracrine stimulation via alpha v beta 5. This regulatory loop could be relevant for migratory processes under physiological and pathophysiological conditions.
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Affiliation(s)
- S Mechtersheimer
- Tumor Immunology Program, G0100, German Cancer Research Center, D-69120 Heidelberg, Germany
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Agarwala KL, Ganesh S, Suzuki T, Akagi T, Kaneko K, Amano K, Tsutsumi Y, Yamaguchi K, Hashikawa T, Yamakawa K. Dscam is associated with axonal and dendritic features of neuronal cells. J Neurosci Res 2001; 66:337-46. [PMID: 11746351 DOI: 10.1002/jnr.1226] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Dscam, a novel cell-adhesion molecule belonging to the Ig-superfamily mediates homophilic intercellular adhesion and is expressed abundantly in the nervous system during development. To gain better understanding on the role of Dscam in neuronal differentiation, we raised an antibody and characterized its protein product. Anti-Dscam antibody detected an approximately 200-kDa protein band in human and mouse brain lysates. Immunohistochemical studies showed that during embryonic development of mice, mouse Dscam is expressed throughout the neuronal tissues and also in nonneuronal tissues such as lung, liver, and limb buds. In adult brain Dscam expression is predominant in the cerebellum, hippocampus, and olfactory bulb. Immunofluorescence double labeling of hippocampal and cerebellar primary cultures revealed that Dscam is associated with axonal and dendritic processes. In view of its cellular localization and spatiotemporal expression pattern, we suggest that Dscam is involved in cell-cell interactions during axonal-dendritic development, and maintenance of functional neuronal networks.
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Affiliation(s)
- K L Agarwala
- Laboratory for Neurogenetics, RIKEN Brain Science Institute, Wako-shi, Saitama, Japan
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Chaisuksunt V, Zhang Y, Anderson PN, Campbell G, Vaudano E, Schachner M, Lieberman AR. Axonal regeneration from CNS neurons in the cerebellum and brainstem of adult rats: correlation with the patterns of expression and distribution of messenger RNAs for L1, CHL1, c-jun and growth-associated protein-43. Neuroscience 2001; 100:87-108. [PMID: 10996461 DOI: 10.1016/s0306-4522(00)00254-2] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Some neurons in the brain and spinal cord will regenerate axons into a living peripheral nerve graft inserted at the site of injury, others will not. We have examined the patterns of expression of four molecules thought to be involved in developmental and regenerative axonal growth, in the cerebellum and brainstem of adult rats, following the implantation into the cerebellum of peripheral nerve grafts. We also determined how the expression patterns observed correlate with the abilities of neurons in these regions to regenerate axons. Three days to 16 weeks after insertion of living tibial nerve autografts, neurons which had regenerated axons into the graft were retrogradely labelled from the distal extremity of the graft with cholera toxin conjugated to horseradish peroxidase, and sections through the cerebellum and brainstem were processed for visualization of transported tracer and/or hybridized with riboprobes to detect messenger RNAs for the cell recognition molecules L1 and CHL1 (close homologue of L1), growth-associated protein-43 and the cellular oncogene c-jun. Retrogradely labelled neurons were present in cerebellar deep nuclei close to the graft and in brainstem nuclei known to project to the cerebellum. Neurons in these same nuclei were found to have up-regulated expression of all four messenger RNAs. Individual retrogradely labelled neurons also expressed high levels of L1, CHL1, c-jun or growth-associated protein-43 messenger RNAs (and vice versa), and every messenger RNA investigated was co-localized with at least one other messenger RNA. Purkinje cells did not regenerate axons into the graft or up-regulate L1, CHL1 or growth-associated protein-43 messenger RNAs, but there was increased expression of c-jun messenger RNA in some Purkinje cells close to the graft. Freeze-killed grafts produced no retrograde labelling of neurons, and resulted in only transient and low levels of up-regulation of the tested molecules, mainly L1 and CHL1. These findings show that cerebellar deep nucleus neurons and precerebellar brainstem neurons, but not Purkinje cells, have a high propensity for axon regeneration, and that axonal regeneration by these neurons is accompanied by increased expression of L1, CHL1, c-jun and growth-associated protein-43. Furthermore, although the patterns of expression of the four molecules investigated are not identical in regenerating neuronal populations, it is probable that all four are up-regulated in all neurons whose axons regenerate into the grafts and that their up-regulation may be required for axon regeneration to occur. Finally, because c-jun up-regulation is seen in Purkinje cells close to the graft, unaccompanied by up-regulation of the other molecules investigated, c-jun up-regulation alone cannot be taken to reliably signify a regenerative response to axotomy.
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Affiliation(s)
- V Chaisuksunt
- Department of Anatomy and Developmental Biology, University College London, Gower Street, WC1E 6BT, London, UK
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