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M Schachner

Publications and source records attributed to M Schachner.

At least 217 records · Page 12Linked to original sources
PubMed1994

The L2/HNK-1 carbohydrate is carried by the myelin associated glycoprotein and sulphated glucuronyl glycolipids in muscle but not cutaneous nerves of adult mice.

We have previously shown that myelinating Schwann cells associated with motor, but not sensory, axons in peripheral nerves of adult mice express the L2/HNK-1 carbohydrate epitope. This carbohydrate structure carried by glycolipids and neural cell adhesion molecules has been suggested to specifically foster regrowth of motor as opposed to sensory axons after infliction of a lesion. To determine which molecular components may be the carriers of the L2 carbohydrate in motor axon-associated myelinating Schwann cells, we have isolated the purely sensory, cutaneous branch and the mixed sensory and motor muscle branch of the femoral nerve of adult mice, isolated the myelin fraction thereof and analysed the molecules expressing the L2 carbohydrate by several immunochemical methods. L2 immunoreactivity in myelin of the muscle branch was four to five times higher than that of the cutaneous branch. The 110 kDa L2-immunoreactive glycoprotein in myelin of the muscle branch, which is not L2-immunoreactive in the cutaneous branch, was identified as the myelin-associated glycoprotein by a combination of immunoprecipitation and Western blot analysis. Myelin extraction with organic solvents additionally revealed the two L2-carrying glycolipids, which amounted to approximately 40 ng glycolipid/mg dry weight in myelin of the muscle branch, whereas no significant amounts of the L2 glycolipids were found in myelin of the cutaneous branch. These observations suggest an astonishing degree of differential regulation of carbohydratesynthesizing activities in myelinating Schwann cells.

Animals↗
PubMed1994

Transient production of TGF-beta 2 by postnatal cerebellar neurons and its effect on neuroblast proliferation.

The beta transforming growth factors (TGF-beta) are suggested to regulate developmental processes since they are distinctly expressed during embryogenesis and exert pleiotropic effects on cell growth and differentiation, In the present study the expression of TGF-beta isoforms was investigated in the postnatal and adult mouse brain. As shown by in situ hybridization, TGF-beta 2 was expressed in the choroid plexus, hippocampus, dentate gyrus and cerebellar Purkinje neurons, both postnatally and in adults. Furthermore, TGF-beta 2 expression was observed postnatally in immature cerebellar neurons of both the external and internal granule cell layers. In the external granule cell layer, the frequency of TGF-beta2 transcripts increased until postnatal day 10 and declined thereafter. In contrast to TGF-beta 2, no TGF-beta 1 mRNA was detected in cerebellar granule cells. TGF-beta 3 expression was widely distributed in postnatal brains although at very low levels. The significance of TGF-beta 2 production by cerebellar granule cells was further investigated using cultures of small cerebellar neurons. In these cultures reverse polymerase chain reaction analysis revealed expression of TGF-beta 2 but low or almost undetectable levels of TGF-beta 1 or -beta 3 mRNAs. Likewise, only TGF-beta 2 protein in its latent form was identified in the culture supernatant; the release of TGF-beta 2 was maximal during the second day in vitro. Furthermore, TGF-beta was found to inhibit the proliferation of cultured small cerebellar neurons. Taken together, these data suggest that TGF-beta 2 is involved in the regulation of postnatal development of the cerebellum.

Animals↗
PubMed1994

The extracellular matrix molecule janusin regulates neuronal morphology in a substrate- and culture time-dependent manner.

Janusin is an extracellular matrix glycoprotein with structural homology to tenascin. In search of extracellular matrix components which govern the differentiation of neurons in the central nervous system, we have investigated the influence of janusin on the differentiation of hippocampal neurons in vitro. Janusin coated onto nitrocellulose was a good substrate for attachment of cell bodies and neurite outgrowth after 21 h of culture. Most cells exhibited a polarized morphology with one long major neurite and one or two short minor neurites. When janusin was coated onto a polyornithine-conditioned plastic surface, it increased the polarity of neurons in that the length of major neurites was increased and the length and number of minor neurites were decreased when compared with the control polyornithine-conditioned plastic without janusin. As we have shown before for tenascin, laminin and fibronectin, polarization was preceded by an increase in the number and length of all neurites during the first hours after cell plating. This study therefore adds janusin to the increasing number of extracellular matrix glycoproteins which promote axonal but not dendritic growth.

Animals↗
PubMed1994

Tenascin mRNA isoforms in the developing mouse brain.

The extracellular matrix glycoprotein tenascin is expressed in the developing mouse cerebellum as a group of four protein species of different molecular weights. The difference is most likely due to alternative splicing which is known to occur in tenascin mRNA within the region of the fibronectin type III repeats. In order to systematically analyze tenascin mRNA isoforms that would account for this heterogeneity, tenascin splice variants were isolated from mouse brain by the polymerase chain reaction (PCR). In agreement with Northern blot analysis, amplification by PCR revealed a general decrease in tenascin mRNA expression during development from embryonic and early postnatal to adult stages. This decrease was more pronounced for isoforms of high molecular weight compared to those of low molecular weight. In accord with the observations at the protein level, four splice variants were found to be predominantly expressed, containing insertions of either six, five, or one fibronectin type III repeat, or comprising no insertion. In addition, a minor splice variant with an insertion of four fibronectin type III repeats was isolated. Three of the isolated mRNA splice variants have not yet been described for mouse tenascin. Among them, an isoform containing six alternatively spliced repeats was found to include a novel fibronectin type III repeat. The sequence of this repeat displays 96.7% similarity to a corresponding type III repeat in human tenascin, revealing a strict evolutionary conservation between tenascin molecules from different species in the region of alternative splicing. Southern blot analysis of the amplified mRNA isoforms showed that the novel mouse type III repeat is confined to splice variants with an insertion of six fibronectin type III repeats. Furthermore, in situ hybridization on sections from mouse embryos indicated that tenascin-specific mRNAs containing the novel type III repeat are predominantly expressed in the central nervous system.

Animals↗
PubMed1994

Differential, LFA-1-sensitive effects of antibodies to nectadrin, the heat-stable antigen, on B lymphoblast aggregation and signal transduction.

Nectadrin, the heat-stable antigen (HSA), is a highly glycosylated GPI-linked glycoprotein that can undergo homophilic and heterophilic binding. In the present work we have examined short-term effects of nectadrin antibodies on splenic B lymphoblast aggregation and signal transduction. Monoclonal antibody 79 inhibited cell aggregation and induced an intracellular Ca++ signal in the absence of cross-linking. Both these effects were perturbed in the presence of LFA-1 antibodies. Nectadrin antibody M1/69 and polyclonal nectadrin antibodies stimulated cell aggregation, did not induce a Ca++ signal, and their effects were functionally independent of LFA-1. These results suggest that nectadrin may concomitantly mediate primary and activate secondary adhesion mechanisms whereby each of these processes may be related to a different signal transduction pathway.

Animals↗
PubMed1994

Restricted localization of L1 and N-CAM at sites of contact between Schwann cells and neurites in culture.

Schwann cell-axon contacts in developing and regenerating peripheral nerve in situ contain high levels of the recognition molecules L1 and N-CAM, while the molecules are not detectable at the ab-axonal cell surface of Schwann cells. To investigate whether Schwann cells, axons, or both contribute to the localization of the molecules at Schwann cell-axon contacts, a heterologous cell culture system consisting of Schwann cells from mice and neurons from chicken was investigated by immunoelectron microscopy using species-specific L1 and N-CAM antibodies. We showed that Schwann cells expressed both molecules only at sites of contact between Schwann cells and neurites and other Schwann cells. Schwann cells not in contact with other cells expressed both molecules on their entire cell surface. In contrast, neurites expressed G4, an L1-related molecule in chicken, on their entire cell surface independently of whether they were in contact with other cells or not. Thus, cultured Schwann cells localize L1 and N-CAM selectively at cell contact sites and may thereby stabilize their attachment to the neighboring cellular partners.

Animals↗
PubMed1994

Spatiotemporal pattern of expression of tenascin-like molecules in a developing insect olfactory system.

During the development of the olfactory (antennal) lobe of the moth Manduca sexta, olfactory sensory axons induce glomerular branching patterns in their target neurons. Glial cells, by surrounding the developing glomerular template, are thought to mediate the developmental influence of olfactory axons on these branching patterns. Previous studies have demonstrated that, in the absence of glia, neurons in the antennal lobe branch in an aglomerular fashion, even in the presence of competent antennal axons (Oland and Tolbert, 1988, J. Comp. Neurol. 278:377-387; Oland et al., 1988, J. Neurosci. 8:353-367). We have begun to explore the molecular basis by which glial cells could influence patterns of neurite branching. For this work, we have utilized immunocytochemical techniques and a partial biochemical analysis to demonstrate that molecules antigenically similar and comparable in size to mammalian tenascin are localized on the neuropil-associated glial cells that form borders around glomeruli in the developing antennal lobe. These tenascin-like molecules associated with neuropilar glia are present at critical stages of glomerulus development; tenascin-like immunoreactivity declines after glomeruli form and become stabilized. Neither the arrival nor the absence of antennal axons in the lobe induces changes in either the molecular forms or the amounts of tenascin-like molecules. The spatiotemporal pattern of expression of tenascin-like molecules suggests that they are in a position to participate in the formation of a glomerular neuropil and could form a molecular barrier that constrains neurite outgrowth strictly to glomeruli.

Animals↗
PubMed1994

In vitro analyses of neurite outgrowth indicate a potential role for tenascin-like molecules in the development of insect olfactory glomeruli.

Tenascin-like material is associated with glial cells that form borders around developing glomerular units in the olfactory (antennal) lobe of the moth Manduca sexta and is present at critical stages of glomerulus formation (Krull et al., 1994, J. Neurobiol. 25:515-534). Tenascin-like immunoreactivity declines in the mature lobe, coincident with a wave of synapse formation within the glomeruli and glomerulus stabilization. Tenascin-like molecules associated with neuropilar glia are in the correct position to influence the branching patterns of growing neurites by constraining them to glomeruli. In this study, we examine the growth of cultured moth antennal-lobe neurons in response to mouse CNS tenascin. Uniform tenascin provides a poor substrate for cell-body attachment and neurite outgrowth. Neuronal cell bodies provided with a striped substratum consisting of tenascin and concanavalin-A (con-A)/laminin attach preferentially to con-A/laminin lanes. Most neurons restrict their branching to con-A/laminin lanes both at early and later times in culture but others send processes across multiple tenascin and con-/laminin lanes in an apparently indiscriminate manner. Tenascin can inhibit the neuritic outgrowth of most antennal-lobe neurons, and this raises the possibility that the tenascin-like molecules associated with neuropilar glia in vivo act to constrain growing neurites to glomeruli. Thus, glial cells, acting in concert with olfactory axons, might act to promote glomerular patterns of branching by antennal-lobe neurons.

Animals↗
PubMed1994

Determination of structural elements of the L2/HNK-1 carbohydrate epitope required for its function.

The L2/HNK-1 carbohydrate epitope has been shown to carry an unusual 3'-sulfoglucuronic acid linked O-glycosidically through a neolactosyl-type backbone to a ceramide residue. Using monoclonal antibodies, the same or a closely related epitope has also been detected N-glycosidically linked to glycoproteins, amongst them several neural cell adhesion molecules. We used synthetic glycolipids carrying sulfated or non-sulfated glucuronic acid attached to ceramide through glycans of different length to show that not only the sulfated glucuronic acid but also the neolactosyl-type backbone is essential for the recognition of the L2/HNK-1 carbohydrate by a monoclonal antibody, its binding to laminin and its role in neural cell migration and outgrowth of processes from neurons and astrocytes.

Animals↗
PubMed1994

Expression of the extracellular matrix glycoprotein tenascin in the somatosensory cortex of the mouse during postnatal development: an immunocytochemical and in situ hybridization analysis.

Layer 4 of the rodent somatosensory cortex contains the barrel field which is the cortical representation of the whisker pad located on the contralateral side of the face. Each barrel within the barrel field is related one to one to its corresponding whisker both anatomically and physiologically. The astrocyte-derived extracellular matrix glycoprotein tenascin has been shown by immunocytochemistry to delineate the boundaries between barrels during their formation until the end of the second postnatal week. The present study describes the anatomical localization of tenascin mRNA expressing cells in the somatosensory cortex of the mouse from birth to postnatal day 15. During this time, a general down-regulation of tenascin-specific message was observed as a function of the state of maturation, with layers 5 and 6 down-regulating the message earlier than layers 1 and 2/3. Tenascin (as detected by immunocytochemistry) also revealed this gradual down-regulation with maturation. Layer 4 of the somatosensory cortex was different in that, with the onset of formation of barrel field boundaries at postnatal day 3, tenascin protein and mRNA were down-regulated more in layer 4 than in the upper and the lower layers of the somatosensory cortex and, interestingly, not in layer 4 of adjacent cortical areas. At postnatal day 6 tenascin immunoreactivity was most clearly distinguished in the barrel field boundaries while tenascin-specific mRNA was no longer detectable in layer 4. Down-regulation of tenascin message was also seen at P6 at the level of the enlarged barrel corresponding to an early postnatal lesioned row of whiskers. At postnatal day 15, tenascin protein and mRNA were no longer detectable in the somatosensory cortex. Distribution of glial fibrillary acidic protein immunoreactivity did not reveal any preferential accumulation of GFAP-positive radial glial processes in barrel field hollows versus barrel field boundaries at any stage.

Animals↗
PubMed1994

Neural recognition molecules in disease and regeneration.

The genetic analysis of inherited human diseases of the nervous system and the characterization of transgenic mice deficient in neural recognition molecules is opening up a new dimension in understanding the cellular and molecular mechanisms underlying neuro-developmental and -degenerative diseases, as well as in delineating the functions of recognition molecules in cell-cell interactions. Progress in identifying recognition molecules that inhibit neurite outgrowth and further characterization of the mechanisms that promote neurite outgrowth are shedding more light on the processes of regeneration in the mature nervous system. In the adult, recognition functions are fine-tuned by glycan moeities associated with neural recognition molecules, and successful neurite outgrowth is likely to depend on the delicate balance between growth-promoting and inhibitory recognition cues.

Animals↗
PubMed1994

Isolation of a neural chondroitin sulfate proteoglycan with neurite outgrowth promoting properties.

Proteoglycans are expressed in various tissues on cell surfaces and in the extracellular matrix and display substantial heterogeneity of both protein and carbohydrate constituents. The functions of individual proteoglycans of the nervous system are not well characterized, partly because specific reagents which would permit their isolation are missing. We report here that the monoclonal antibody 473HD, which binds to the surface of early differentiation stages of murine astrocytes and oligodendrocytes, reacts with the chondroitin sulfate/dermatan sulfate hybrid epitope DSD-1 expressed on a central nervous system chondroitin sulfate proteoglycan designated DSD-1-PG. When purified from detergent-free postnatal days 7 to 14 mouse brain extracts, DSD-1-PG displays an apparent molecular mass between 800-1,000 kD with a prominent core glycoprotein of 350-400 kD. Polyclonal anti-DSD-1-PG antibodies and monoclonal antibody 473HD react with the same molecular species as shown by immunocytochemistry and sequential immunoprecipitation performed on postnatal mouse cerebellar cultures, suggesting that the DSD-1 epitope is restricted to one proteoglycan. DSD-1-PG promotes neurite outgrowth of embryonic day 14 mesencephalic and embryonic day 18 hippocampal neurons from rat, a process which can be blocked by monoclonal antibody 473HD and by enzymatic removal of the DSD-1-epitope. These results show that the hybrid glycosaminoglycan structure DSD-1 supports the morphological differentiation of central nervous system neurons.

Animals↗
PubMed1994

Degeneration of neural cells in the central nervous system of mice deficient in the gene for the adhesion molecule on Glia, the beta 2 subunit of murine Na,K-ATPase.

We generated mice, null mutant in the adhesion molecule on glia (AMOG), the beta 2 subunit of the murine Na,K-ATPase gene. These mice exhibit motor incoordination at 15 d of age, subsequently tremor and paralysis of extremities, and die at 17-18 d after birth. At these ages, the mutants have enlarged ventricles, degenerating photoreceptor cells, and swelling and degeneration of astrocytic endfeet, leading to vacuoles adjoining capillaries of brain stem, thalamus, striatum, and spinal cord. In tissue homogenates from entire brains of 16-17-d-old mutants, Na,K-ATPase activity and expression of the beta 1 subunit of the Na,K-ATPase and of the neural adhesion molecules L1, N-CAM, and MAG appear normal. We suggest that the mutant phenotype can be related primarily to reduced pump activity, with neural degeneration as a possible consequence of osmotic imbalance.

Adenosine Triphosphatases↗
PubMed1994

Characterization of Pax-6 and Hoxa-1 binding to the promoter region of the neural cell adhesion molecule L1.

The neural cell adhesion molecule L1, a member of the immunoglobulin superfamily, mediates cell interactions in the developing and regenerating nervous system of mammals and is also detectable in the immune system and in the epithelia of intestine, skin, lung, and kidney. This diverse pattern of expression begs the question as to the regulatory mechanisms underlying transcription of the L1 gene. We demonstrate here that the paired domain and homeodomain containing Pax-6 protein binds to three different sites in the promoter region of the L1 gene. The promoter proximal binding site is also recognized by Hoxa-1 and lies approximately 60 bp upstream from the transcription start site only few base pairs upstream of a putative binding site for the TFII-I transcription initiation factor. On the basis of this sequence, we have characterized the binding of Pax-6 and explored two modes of its DNA binding activities.

Base Sequence↗
PubMed1994

Heat-stable antigen (CD24) as ligand for mouse P-selectin.

Heat-stable antigen (HSA)/CD24 is a cell surface molecule expressed by many cell types in the mouse. The molecule has an unusual structure because of its small protein core and extensive glycosylation. In order to study the functional role of the HSA-associated glycoconjugates we have isolated different forms of HSA. Using lectin analysis we provide evidence for extensive heterogeneity in carbohydrate composition and sialic acid linkage. Several HSA forms were recognized by mouse P-selectin-IgG but not E-selectin-IgG in ELISA. As expected, P-selectin-IgG also bound to L2/HNK-1-positive neural glycoproteins (L2-glycoproteins) and sulfatides but not to gangliosides and other control glycoproteins. The binding of P-selectin-IgG to L2-glycoproteins and HSA required bivalent cations. The reactivity to HSA was sensitive to sialidase treatment whereas the binding to L2-glycoproteins was not. Studies with alpha 2-6 sialytransferase indicated that alpha 2-6 linked sialic acid was not involved in the P-selectin binding to HSA. Surprisingly, an L2/HNK-1 specific antibody was found to cross-react with some HSA glycoforms and its binding correlated with P-selectin-IgG reactivity. L2/HNK-1-positive or L2/HNK-1-negative HSA glycoforms were also analyzed after coating to polystyrene beads. Only the L2/HNK-1-positive HSA coated beads were reactive with P-selectin-IgG and could bind to activated bend3 endothelioma cells expressing P-selectin whereas the L2/HNK-1-negative HSA beads did not. It is suggested that in its L2/HNK-1 modified form the HSA molecule on leukocytes could represent a ligand for P-selectin on endothelial cells or platelets.

Animals↗
PubMed1994

Tenascin-R (J1 160/180 inhibits fibronectin-mediated cell adhesion--functional relatedness to tenascin-C.

Cell adhesion and neurite outgrowth on fibronectin is a multistep process modulated by different extra- and intracellular signals. Fibronectin-mediated cell attachment and spreading can be affected in a negative way by tenascin-C, an extracellular matrix glycoprotein expressed in a temporally and spacially restricted manner during early morphogenesis. Tenascin-R (J1-160/180), consisting of two major isoforms of 160 kDa (tenascin-R 160) and 180 kDa (tenascin-R 180) in mammals, is an extracellular matrix glycoprotein of the central nervous system that shares high structural homologies with tenascin-C. Here we show that in relation to fibronectin-mediated adhesion, the two extracellular matrix molecules are also functionally closely related. When offered as mixed substrata with other extracellular matrix molecules, the two tenascin-R isoforms and tenascin-C derived from mouse brain selectively inhibit fibronectin-dependent cell adhesion and neurite outgrowth, and affect cell morphology of different mesenchymal and neural cells. This effect is partially due to interactions at the substrate level that result in a steric hindrance and/or conformational change of the cell binding sites of the fibronectin molecule. In addition, tenascin-R 180 and tenascin-C interact with cells by an RGD- and beta 1 integrin-independent mechanism, leading to cell rounding and detachment from such substrata. The expression of tenascin-R and tenascin-C in the nervous system at times and locations where fibronectin-mediated cellular processes take place may be related to the role of inhibitory signals in the extracellular matrix in the regulation of cell migration and differentiation in general.

Animals↗
PubMed1994

Tenascin demarcates the boundary between the myelinated and nonmyelinated part of retinal ganglion cell axons in the developing and adult mouse.

The molecular determinants controlling the topographically restricted distribution of neural cells in the mammalian CNS are largely unknown. In the mouse, myelin-forming oligodendrocytes are differentially distributed along retinal ganglion cell axons. These axons are myelin free intraretinally and in the most proximal (i.e., retinal) part of the optic nerve, but become myelinated in the distal (i.e., chiasmal) part of the optic nerve. Tenascin protein and mRNA are detectable in increased amounts at the retinal end of the developing optic nerve before the arrival of oligodendrocyte progenitor cells and are restricted to this region in the adult optic nerve. Tenascin is a nonadhesive substrate for oligodendrocytes and their progenitor cells in vitro when offered as a substrate in choice with polyornithine. These observations suggest that tenascin is critical for the establishment and maintenance of the restricted distribution of myelin-forming oligodendrocytes along retinal ganglion cell axons of the mouse.

Animals↗