Biomedical subjects

M Schachner

Publications and source records attributed to M Schachner.

At least 307 records · Page 17Linked to original sources

PubMed1990

Boundaries during normal and abnormal brain development: in vivo and in vitro studies of glia and glycoconjugates.

This paper focuses on transient boundaries of glia and glycoconjugates during development of the mouse central nervous system (CNS). Lectin-bound glycoconjugates, glial fibrillary acidic protein, and the J1/tenascin glycoprotein are distributed coextensively within boundaries around developing substructural arrangements (e.g., developing nuclei, and at a finer level, somatosensory cortical "barrels" related to individual facial vibrissae) throughout the CNS during pattern formation events. Electron microscopy has shown that the J1/tenascin glycoprotein, for example, is present in immature astrocytes, on glial and neuronal plasma membranes, and within the pericellular space that could be extracellular matrix (ECM). The findings presented on the expression of this well-characterized ECM molecule suggest that previously described glial and glycoconjugate boundaries reported by our group are in part composed of specific recognition molecules. The J1/tenascin glycoprotein, a chondroitin sulfate-containing antigen termed the 473 proteoglycan, and the adhesion molecule on glia are expressed within discrete boundary regions and associated axonal pathways. There, they may sculpture fine aspects of functional cytoarchitectonic arrangements and help guide axons to specific targets. The expression and developmental regulation of glycoproteins such as J1/tenascin may thus be integral events during pattern formation and synaptogenesis in the CNS. The presence of abnormal glial arrangements and glycoconjugate boundaries in the cortices of the genetic mutant mouse reeler, and findings on plasticity of boundaries following various perturbations, suggest that boundary expression is controlled by both genetic and epigenetic factors. Some future directions for studying developmental boundaries, including use of cultured explants for in vitro "bioassays," are also discussed.

Aging↗

PubMed1990

Oligodendrocyte-derived J1-160/180 extracellular matrix glycoproteins are adhesive or repulsive depending on the partner cell type and time of interaction.

We have studied the functional involvement of J1-160 and J1-180 in the interaction between oligodendrocytes and neurons, astrocytes, or L cells in short- and long-term adhesion assays using monoclonal antibodies directed against topographically distinct epitopes on the molecules. Whereas antibodies to mouse liver membranes and monoclonal antibody 597 do not interfere with neuron-oligodendrocyte or astrocyte-oligodendrocyte adhesion after 30 min of coculture, antibodies 596, 619, and 620 interfere with astrocyte to oligodendrocyte and neuron to oligodendrocyte adhesion. The adhesion of L cells to oligodendrocytes is not affected by the antibodies. When neurons or astrocytes are cultured on oligodendrocytes for more than 30 min, monoclonal antibody 619 continues to reduce adhesion of astrocytes to oligodendrocytes after 1 and 2 h. However, during this time period the antibody affects neuron to oligodendrocyte adhesion in a different manner. It does not interfere with adhesion of neurons to oligodendrocytes at 1 h and enhances the adhesion of neurons to oligodendrocytes after 2 h of coculture. After 6 and 24 h of coculture, antibody 619 does not affect the adhesion of neurons or astrocytes to oligodendrocytes, suggesting that other adhesive mechanisms are predominant at later times of interaction. At all times studied, neurons and astrocytes adhered well to the oligodendrocytes. To study the influence of the J1 molecules on neuronal interactions in the absence of other oligodendrocyte-derived cell surface components, purified J1-160 was coated as a substrate and neuron attachment was measured as a function of time. Two hours after plating neurons adhered well to J1-160, as they did to laminin, while cell detachment was subsequently observed from J1-160, but not from laminin. These results implicate J1-160 and J1-180 in a recognition process between oligodendrocytes and neurons or astrocytes, but not fibroblasts. This recognition process appears to merge into adhesion or stabilization of cell contacts for astrocytes and destabilization of cell interactions or repulsion for neurons. It is likely that these two opposite effects in cell behavior elicited by the J1 molecules result from differential intracellular responses to a cell surface trigger possibly mediated by different cell surface receptors and/or different consequences in intracellular signaling networks.

Animals↗

PubMed1990

The adhesion molecule on glia (AMOG) is a homologue of the beta subunit of the Na,K-ATPase.

AMOG (adhesion molecule on glia) is a Ca2(+)-independent adhesion molecule which mediates selective neuron-astrocyte interaction in vitro (Antonicek, H., E. Persohn, and M. Schachner. 1987. J. Cell Biol. 104:1587-1595). Here we report the structure of AMOG and its association with the Na,K-ATPase. The complete cDNA sequence of mouse AMOG revealed 40% amino acid identity with the previously cloned beta subunit of rat brain Na,K-ATPase. Immunoaffinity-purified AMOG and the beta subunit of detergent-purified brain Na,K-ATPase had identical apparent molecular weights, and were immunologically cross-reactive. Immunoaffinity-purified AMOG was associated with a protein of 100,000 Mr. Monoclonal antibodies revealed that this associated protein comprised the alpha 2 (and possibly alpha 3) isoforms of the Na,K-ATPase catalytic subunit, but not alpha 1. The monoclonal AMOG antibody that blocks adhesion was shown to interact with Na,K-ATPase in intact cultured astrocytes by its ability to increase ouabain-inhibitable 86Rb+ uptake. AMOG-mediated adhesion occurred, however, both at 4 degrees C and in the presence of ouabain, an inhibitor of the Na,K-ATPase. Both AMOG and the beta subunit are predicted to be extracellularly exposed glycoproteins with single transmembrane segments, quite different in structure from the Na,K-ATPase alpha subunit or any other ion pump. We hypothesize that AMOG or variants of the beta subunit of the Na,K-ATPase, tightly associated with an alpha subunit, are recognition elements for adhesion that subsequently link cell adhesion with ion transport.

Adenosine Triphosphatases↗

PubMed1990

The neural cell adhesion molecule N-CAM enhances L1-dependent cell-cell interactions.

On neural cells, the cell adhesion molecule L1 is generally found coexpressed with N-CAM. The two molecules have been suggested, but not directly shown, to affect each other's function. To investigate the possible functional relationship between the two molecules, we have characterized the adhesive interactions between the purified molecules and between cultured cells expressing them. Latex beads were coated with purified L1 and found to aggregate slowly. N-CAM-coated beads did not aggregate, but did so after addition of heparin. Beads coated with both L1 and N-CAM aggregated better than L1-coated beads. Strongest aggregation was achieved when L1-coated beads were incubated together with beads carrying both L1 and N-CAM. In a binding assay, the complex of L1 and N-CAM bound strongly to immobilized L1, but not to the cell adhesion molecules J1 or myelin-associated glycoprotein. N-CAM alone did not bind to these glycoproteins. Cerebellar neurones adhered to and sent out processes on L1 immobilized on nitrocellulose. N-CAM was less effective as substrate. Neurones interacted most efficiently with the immobilized complex of L1 and N-CAM. They adhered to this complex even when its concentration was at least 10 times lower than the lowest concentration of L1 found to promote adhesion. The complex became adhesive for cells only when the two glycoproteins were preincubated together for approximately 30 min before their immobilization on nitrocellulose. The adhesive properties between cells that express L1 only or both L1 and N-CAM were also studied. ESb-MP cells, which are L1-positive, but N-CAM negative, aggregated slowly under low Ca2+. Their aggregation could be completely inhibited by antibodies to L1 and enhanced by addition of soluble N-CAM to the cells before aggregation. N2A cells, which are L1 and N-CAM positive aggregated well under low Ca2+. Their aggregation was partially inhibited by either L1 or N-CAM antibodies and almost completely by the combination of both antibodies. N2A and ESb-MP cells coaggregated rapidly and their interaction was similarly inhibited by L1 and N-CAM antibodies. These results indicate that L1 is involved in two types of binding mechanisms. In one type, L1 serves as its own receptor with slow binding kinetics. In the other, L1 is modulated in the presence of N-CAM on one cell (cis-binding) to form a more potent receptor complex for L1 on another cell (trans-binding).

Animals↗

PubMed1990

Functional cooperation between the neural adhesion molecules L1 and N-CAM is carbohydrate dependent.

The neural cell adhesion molecules L1 and N-CAM have been suggested to interact functionally by formation of a complex between the two molecules (Kadmon, G., A. Kowitz, P. Altevogt, and M. Schachner. 1990. J. Cell Biol. 110:193-208). To determine the molecular mechanisms underlying this functional cooperation, we have studied the contribution of carbohydrates to the association of the two molecules at the cell surface. Aggregation or adhesion between L1- and N-CAM-positive neuroblastoma N2A cells was reduced when the synthesis of complex and/or hybrid glycans was modified by castanospermine. Fab fragments of polyclonal antibodies to L1 inhibited aggregation and adhesion of castanospermine-treated cells almost completely, whereas untreated cells were inhibited by approximately 50%. Fab fragments of polyclonal antibodies to N-CAM did not interfere with the interaction between castanospermine-treated cells, whereas they inhibited aggregation or adhesion of untreated cells by approximately 50%. These findings indicate that cell interactions depending both on L1 and N-CAM ("assisted homophilic" binding) can be reduced to an L1-dominated interaction ("homophilic binding"). Treatment of cells with the carbohydrate synthesis inhibitor swainsonine did not modify cell aggregation in the absence or presence of antibodies compared with untreated cells, indicating that castanospermine-sensitive, but swainsonine-insensitive glycans are involved. To investigate whether the appropriate carbohydrate composition is required for an association of L1 and N-CAM in the surface membrane (cis-interaction) or between L1 on one side and L1 and N-CAM on the other side of interacting partner cells (trans-interaction), an L1-positive lymphoid tumor cell line was coaggregated with and adhered to neuroblastoma cells in the various combinations of castanospermine-treated and untreated cells. The results show that it is the cis-interaction between L1 and N-CAM that depends on the appropriate carbohydrate structures.

Alkaloids↗

PubMed1990

Expression of the adhesion molecules L1, N-CAM and J1/tenascin during development of the murine small intestine.

We have previously studied the immunohistological localization of the three adhesion molecules L1, N-CAM and J1/tenascin in adult mouse small intestine and shown that L1 expression in epithelial crypt cells underlies the adhesion of these cells to one another [63]. To obtain further insight into the functional roles of L1, N-CAM and J1/tenascin in this organ we studied their expression starting at embryonic day 14 during embryonic and early postnatal morphogenesis and during epithelial cell migration in the adult. Expression of L1 was restricted to neural cells until approximately postnatal day 5, when L1 started to be detectable on crypt but not on villus cells, predominantly on the basolateral membrane infoldings. As in brain, L1-specific mRNA was approximately 6 kb in size. L1 from intestine appears to differ from the brain-derived equivalent in possessing a higher level of glycosylation. N-CAM was detectable from embryonic day 14 onward in neural and also in mesenchymal cells. Expression by smooth muscle cells decreased during development. In the villus core, N-CAM was strongly detectable at contact sites between smooth muscle cells forming the cellular scaffold of the villus. From embryonic day 14 onward, N-CAM appeared in both 180- and 140-kDa forms. J1/tenascin was present in both neural and mesenchymal cells from embryonic day 14 onward. Starting at embryonic day 17, J1/tenascin appeared concentrated at the boundary between mesenchyme and epithelium in an increasing gradient from the crypt base to the villus top. From embryonic day 14 onward J1/tenascin consisted of the 190- and 220-kDa components. J1/tenascin from intestine differed from brain-derived J1 in its carbohydrate composition. These observations show that the three adhesion molecules are expressed by distinct cell populations and may serve as cell-type-specific markers in pathologically altered intestinal tissue.

Animals↗

PubMed1990

Production and characterization of monoclonal antibodies to the major peripheral myelin glycoprotein P0.

Several monoclonal antibodies were generated against the major glycoprotein P0 of human peripheral nervous system myelin. Antibodies were selected for their reactivity with P0 in Western blots. The antibodies were of the immunoglobulin G subclass and reacted with the glycopeptidase F-treated P0, indicating that the reactive epitope resides in the protein backbone. In fresh frozen and paraffin-embedded sections of central and peripheral nervous system of rat and human, P0 antibody 592 reacted with myelin sheaths of peripheral, but not central, nervous system.

Animals↗

PubMed1990

Binding of the J1 adhesion molecules to extracellular matrix constituents.

The J1 glycoproteins can be obtained in multiple forms in the soluble fraction of developing and adult mouse brain tissue. They are recovered as two forms of apparent molecular weights of 160,000 and 180,000 (J1-160) from adult mouse brain and as forms of apparent molecular weights of 200,000 and 220,000 (J1-220) from developing brain. J1-160 and J1-220 share common epitopes but are considered as separate entities, with J1-220 being immunochemically closely related if not identical to tenascin. Based on the observation that J1 immunoreactivity appears on basement membrane and interstitial collagens after denervation of the neuromuscular junction in adult rodents, we became interested in investigating the binding properties of J1 glycoproteins to extracellular matrix constituents in vitro. Both J1-160 and J1-220 bound to collagens type I-VI and IX but not to laminin, fibronectin, bovine serum albumin, or gelatin under hypotonic buffer conditions. Under isotonic buffer conditions, J1-220 bound to all collagen types, whereas J1-160 bound only to collagen types V and VI with values that could be examined by Scatchard analysis. Binding of J1-220 to collagens displayed two binding constants (KD) between 1.5 and 4.4 X 10(-9) and 1.8 and 5.5 X 10(-8) M, respectively, under hypotonic buffer conditions and a single KD of 2.1-8.0 X 10(-8) M under isotonic buffer conditions. Binding of J1-160 to collagens had an apparent KD of 1.9-8.0 X 10(-9) M under hypotonic buffer conditions. Under isotonic buffer conditions, binding constants of J1-160 to collagen types V and VI were approximately 2 X 10(-8) M. Binding of J1-220 to collagen type I could be inhibited by J1-220, J1-160, and collagen type VI but not by fibronectin or gelatin. Conversely, binding of J1-160 was inhibited by J1-220, J1-160, and collagen type VI (in order of decreasing efficacy of competition). J1-160 and J1-220 were retained on a heparin-agarose column and eluted in a salt gradient at approximately 0.5 M NaCl. The formation of the J1-heparin complexes was inhibited 100-fold more efficiently by heparin than by chondroitin sulfate. These experiments show that J1 glycoproteins resemble in many respects the extracellular matrix constituents fibronectin, laminin, vitronectin, and von Willebrand factor.

Animals↗

PubMed1990

Fibroblast-derived J1 adhesion glycoproteins show binding properties to extracellular matrix constituents different from those of central nervous system origin.

The J1 extracellular adhesion molecule from mouse brain consists of several immunochemically related glycoproteins of different molecular weights and distinct functional properties. Like the brain J1 glycoproteins, the fibroblast-derived J1 glycoproteins interact with all collagen types tested (collagen G and types I-IV and IX), as measured by binding of 125I-labeled J1 glycoproteins to immobilized collagens. As tested for collagen type I, this binding can be inhibited more effectively by chondroitin sulfate than by heparin. After electrophoretic separation and transfer to nitrocellulose, fibroblast-derived J1 only binds to a limited number of collagen types (collagen types I, VI, and IX and G), whereas brain-derived J1 glycoproteins bind to all collagen types tested (collagen types I-VI and IX and G). These results show that fibroblast-derived J1 glycoproteins, although immunochemically related to J1 glycoproteins from brain, differ from these in their binding specificities to extracellular matrix constituents.

Animals↗

PubMed1990

Isolation and biochemical characterization of a neural proteoglycan expressing the L5 carbohydrate epitope.

The monoclonal L5 antibody reacts with an N-glycosidically linked carbohydrate structure which is present on the neural cell adhesion molecule L1, neural chondroitin sulfate proteoglycans, and other not yet identified glycosylated proteins. Using this antibody, we isolated and characterized proteoglycans from adult mouse brain and cultured astrocytes biosynthetically labeled with Na2 35SO4 and a 3H-amino acid mixture. Our data suggest that the L5 proteoglycans of both sources are identical in their biochemical properties. The apparent molecular mass of the L5 proteoglycan is approximately 500 kDa. Digestion of the iodinated L5 proteoglycan from mouse brain and of the [35S]methionine-labeled L5 proteoglycan from cultured astrocytes with proteinase-free chondroitinases ABC and AC revealed three major core proteins with apparent molecular masses of approximately 380, 360, and 260 kDa. These represent molecularly distinct protein cores.

Animals↗

PubMed1990

Studies of the initiation of myelination by Schwann cells.

The rapid morphologic changes in Schwann cells and in their relationships to axons during the transition from the premyelinating to the myelinating state have been known for more than 15 years. The sorting of axons by dividing Schwann cells, the establishment of a 1:1 relationship between a postmitotic Schwann cell, and the onset of myelin sheath formation have all been described in detail. However, the chain of molecular events and mechanisms by which these morphologic changes are regulated has not been elucidated. In this chapter we have reviewed results that strongly suggest that the adhesion molecule L1 is one of the important determinants that mediate the elongation of the Schwann cell along the axon, and the extension of Schwann processes to engulf axons. Thus, L1 functions to promote the spreading of the Schwann cell process over the surface of the axon. L1 does not appear to be exclusively involved in the adhesion of Schwann cells to axons, in the activation of Schwann cell proliferation by axons, or in the induction of synthesis of extracellular matrix proteins. The results from the anti-L1 blocking experiments further provided clues for an understanding of how the expression of GalC and MAG, which are both likely to be involved in the initiation of myelination, are regulated. These results imply that the overall regulation of expression of these early myelin components could require controls other than a single signaling mechanism derived from contact with axons. We propose that the deposition of basal lamina or one of its components could also be involved. Finally, the results from anti-GalC-blocking experiments indicated that GalC is involved in the mechanism of early growth of the myelin spiral.

Animals↗

PubMed1990

Expression of J1/tenascin in the crypt-villus unit of adult mouse small intestine: implications for its role in epithelial cell shedding.

The localization of the extracellular matrix recognition molecule J1/tenascin was investigated in the crypt-villus unit of the adult mouse ileum by immunoelectron microscopic techniques. In the villus region, J1/tenascin was detected strongly in the extracellular matrix (ECM) between fibroblasts of the lamina propria. It was generally absent in the ECM at the interface between subepithelial fibroblasts and intestinal epithelium, except for some restricted areas along the epithelial basal lamina of villi, but not of crypts. These restricted areas corresponded approximately to the basal part of one epithelial cell. In J1/tenascin-positive areas, epithelial cells contacted the basal lamina with numerous microvillus-like processes, whereas in J1/tenascin-negative areas the basal surface membranes of epithelial cells contacted their basal lamina in a smooth and continuous apposition. In order to characterize the functional role of J1/tenascin in the interaction between epithelial cells and ECM, the intestinal epithelial cell line HT-29 was tested for its ability to adhere to different ECM components. Cells adhered to substratum-immobilized fibronectin, laminin and collagen types I to IV, but not to J1/tenascin. When laminin or collagen types I to IV were mixed with J1/tenascin, cell adhesion was as effective as without J1/tenascin. However, adhesion was completely abolished when cells were offered a mixture of fibronectin and J1/tenascin as substratum. The ability of J1/tenascin to reduce the adhesion of intestinal epithelial cells to their fibronectin-containing basal lamina suggests that J1/tenascin may be involved in the process of physiological cell shedding from the villus.

Animals↗

PubMed1990

Inhibition of Schwann cell myelination in vitro by antibody to the L1 adhesion molecule.

The specific axonal and Schwann cell surface molecules that mediate the initiation of myelination have not been identified. We have used cocultures of purified rat dorsal root ganglion neurons and Schwann cells and purified polyclonal antibodies to the L1 adhesion molecule to study the role of L1 in myelin formation. Schwann cells were first arrested in a basal-lamina-free premyelination stage (by serum/ascorbate deprivation), then manipulated to allow basal lamina deposition and myelination (by serum/ascorbate addition) in the absence or presence of anti-L1. Using electron microscopy, immunocytochemistry, and myelin sheath quantitation after Sudan-black staining, we determined the effect of anti-L1 on (1) basal lamina formation, (2) the segregation by Schwann cells of axons into a 1:1 relationship, (3) galactocerebroside (Gal-C) expression, (4) laminin deposition, and (5) myelin formation. Anti-L1 strongly blocked myelin formation, Gal-C expression, and axon segregation but did not block basal lamina formation. In controls, elongated Schwann cell processes completely covered the axons and exhibited uniform surface staining for laminin; in anti-L1-treated cultures, shortened Schwann cells, intensely stained for laminin, were observed in clusters separated by unstained lengths of axons. When 50 micrograms/ml exogenous purified laminin was added to the medium, Schwann cell length and laminin staining were similar in control and treated cultures. However, the inhibition of myelination of anti-L1 was not altered by the addition of laminin. Myelination was also inhibited with antigen-binding fragments (Fab) of polyclonal anti-L1, but an antibody to liver membranes did not block myelination. These results indicate that L1 is involved in the linear extension of Schwann cell processes along axons, the engulfment of axons, and the induction of myelin-specific components within the Schwann cell. We conclude that anti-L1 prevents myelination by blocking these events rather than by blocking basal lamina deposition.

Animals↗

PubMed1990

[Tube-free translaryngeal superposed jet ventilation].

Microsurgical operations on the larynx require sufficient space for the surgeon in order to achieve the best surgical result. After preliminary experimental studies we integrated two jets of a specific size into the Kleinsasser tube. Simultaneously, we developed a "superimposed jet-ventilation system", which consists of a low-frequency jet ventilation and superimposed high-frequency jet ventilation. Respiration was maintained with a mixture of oxygen and air, whereby an additional increase in air and volume via the Kleinsasser tube, which is open on the outside, can be sustained on account of the Venturi effect. We tested this tubeless translaryngeal superimposed jet-ventilation system in 48 patients. Anesthesia was carried out by continuous intravenous administration of Propofol and intermittent doses of Sufentanil and Vecuronium as required. The clinical results showed optimal ventilation without hypercapnia. The arterial pC0(2) levels were below 42 mmHg. The arterial p0(2) levels were above 120 mmHg with a FIO2 of 40%. No complications were observed with regard to respiration during any of the operations. The surgeon had optimal conditions to carry out the operation. Because of the absence of a plastic tube, inhalation anesthetics and nitrous oxide, laryngeal laser surgery is another field of application for which this form of tubeless jet ventilation is excellently suited. We tested it with 12 patients, and no complications due to laser anesthesia were observed. We consider this form of a tubeless superimposed translaryngeal jet ventilation to be a great improvement in microlaryngeal surgery.

Adult↗

PubMed1989

Immunoelectron-microscopic localization of the 180 kD component of the neural cell adhesion molecule N-CAM in postsynaptic membranes.

In order to investigate the expression of cell adhesion molecules in synapses, we have studied the localization of the neural cell adhesion molecule N-CAM in the cerebellum and hippocampus of adult mice by immunocytological and immunochemical methods. Of the three molecular components of N-CAM with relative molecular masses (Mr) of 120, 140, and 180 kD, N-CAM 120 is not detectable in synaptosomal membranes, whereas N-CAM 140 is expressed on both pre- and postsynaptic membranes and N-CAM 180 is restricted to postsynaptic sites, with localization of the N-CAM 180-specific epitope in postsynaptic densities. Specificity of immunoreactivity is indicated by the observation that antibodies to the neural cell adhesion molecule L1 do not label synaptic membranes, whereas antibodies to two major components of postsynaptic densities, actin and erythrocyte spectrin, react with synaptic structures. Interestingly, N-CAM 180 is only detectable in subpopulations of synapses in the intact tissue. Isolated synaptosomes, opened for unimpeded accessibility of antibody by hypoosmotic treatment, also reveal a partial expression of N-CAM 180 in that 67% are labeled by antibodies to N-CAM 180, while antibodies to actin and erythrocyte spectrin react with 95% and 88% of all synaptosomes, respectively. N-CAM 180 does not appear to be differentially expressed in synapses of a particular morphological type, but is detectable in all types of synapses in the cerebellum and hippocampus, except for mossy fiber synapses and synapses between basket and Purkinje cells, which are generally N-CAM 180-negative. Since N-CAM 180 has been shown to be characteristic of stabilized or stabilizing cell contacts, possibly by its association with the cytoskeleton-membrane linker protein spectrin (Pollerberg et al.: J. Cell Biol. 101:1921-1929, '85; Nature 324:462-465, '86; Cell Tissue Res. 250:227-236, '87), we would like to suggest N-CAM 180 plays an important role in determining the stability of contacts between pre- and postsynaptic membranes and state of synaptic activity.

Animals↗

PubMed1989

Immunohistological localization of the adhesion molecules L1, N-CAM, and MAG in the developing and adult optic nerve of mice.

The localization of the cell adhesion molecules L1, neural cell adhesion molecule (N-CAM), and myelin-associated glycoprotein (MAG) was studied immunohistologically at the light and electron microscopic levels and immunochemically in the developing and adult mouse optic nerve and retina. The neural adhesion molecule L1 is strongly expressed on the shafts of fasciculating unmyelinated axons at all ages studied from embryonic day 15 through adulthood. Growth cones of retinal ganglion cell axons were weakly L1-positive or L1-negative when contacting glial cells. Unmyelinated axons were not only L1-positive when contacting each other but also when contacting glia, whereas contacts between glial cells were L1-negative at all developmental unmyelinated retinal nerve fiber layer or in the unmyelinated optic nerve head became L1-negative when enwrapped by myelin in the optic nerve proper. At all stages of development N-CAM showed profuse labeling on fasciculating axons, growth cones, and their contact sites with glial cells as well as contacts between glial cells. In contrast to L1, axons remained N-CAM-positive when becoming myelinated. Sometimes, N-CAM was found in compact myelin. However, N-CAM was absent from glial surfaces contacting basement membranes at the interface to meninges, blood vessels, and the vitreous body of the eye. MAG was first detectable intracellularly in oligodendrocytes associated with the endoplasmic reticulum and Golgi apparatus before it became apparent at the cell surface. There it was present on oligodendrocytes prior and during the first stages of ensheathment of axons, both on cell body and processes. After formation of compact myelin MAG remained strongly expressed periaxonally and was only weakly detectable in noncompacted myelin including inner mesaxon and paranodal loops. None of the adhesion molecules was detectable on extracellular matrix, in the meninges, or on endothelial cells. Immunochemical analysis of antigen expression at different developmental stages was in agreement with the immunohistological data. We infer from these observations that L1 is involved in stabilization not only of axon-axon, but also axon-glia contacts, while the more dynamic structure of the growth cone generally expresses less L1. A differential expression of L1 along the course of an axon--being present on its unmyelinated, but absent on its myelinated part--further supports the notion that L1 may be involved in the stabilization of axonal fascicles but not of axon-myelin contacts.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗

PubMed1989

Expression of cell adhesion molecules from the L2/HNK-1 family in cerebellar isografts in mice.

The expression of cell adhesion molecules and glial fibrillary acid protein (GFAP) was examined in isografts of embryonic mouse cerebellum. Donor embryonic cerebella with the meninges removed were implanted into the lateral cerebral ventricles of adult host animals and examined after 2-6 weeks. Indirect immunofluorescence staining was performed on fresh frozen sections, using antibodies against the cell adhesion molecules L1, N-CAM, J1, myelin associated glycoprotein (MAG), and their shared L2/HNK-1 carbohydrate epitope, as well as GFAP. Nissl staining revealed that a normal trilaminar cytoarchitecture developed in some areas of implanted cerebella. Antibodies against cell adhesion molecules showed patterns of immunoreactivity generally similar to those present during normal cerebellar development. Expression of the L2 epitope in normal cerebellum is transiently observed in the molecular layer and is primarily seen in the substantia medullaris of mature cerebellum. This pattern was altered in the grafts, with a persistent expression of the L2 epitope in the molecular layer and less pronounced L2 immunoreactivity in the substantia medullaris cerebelli. These results may reflect a retardation of granule neuron differentiation due to abnormal or missing efferents and afferents in transplanted cerebellum. Also, the characteristic GFAP-positive radially oriented elongated fibers of Bergmann glia were not detected, even though passage of granule cells from their germinating zone to the internal granular layer was observed. The data presented here suggest that the developmental appearance and pattern of expression of cell adhesion molecules during morphogenesis of the cerebellum occurs largely independently of the normal complement of afferent and efferent connections.

Animals↗

PubMed1989

Cells positive for the O4 surface antigen isolated by cell sorting are able to differentiate into astrocytes or oligodendrocytes.

Cells expressing the surface antigen O4 were isolated as pure populations from cultures of murine brain or cerebellum using fluorescence activated cell sorting. When these O4-positive cells were further cultured in the presence of fetal calf serum (FCS) many cells expressed both O4 and the astrocyte marker glial fibrillary acidic protein (GFAP) after 4 days of culture. Cells not exposed to FCS expressed O4, but never GFAP. GFAP-positive cells in the presence of fetal calf serum very rarely expressed the myelin associated glycoprotein (MAG) or O1, both of which are expressed on more differentiated oligodendrocytes, and never expressed O10 that is characteristic of even more mature oligodendrocytes. These results show that glial cells expressing O4, but not MAG, O1, O10 or GFAP are bipotential precursor cells able to differentiate into astrocytes or oligodendrocytes depending on the culture conditions and suggest that bipotentiality of glial precursor cells is retained up to a later developmental stage than that of the O2A progenitor cell.

Animals↗