Biomedical subjects

A Faissner

Publications and source records attributed to A Faissner.

At least 55 records · Page 3Linked to original sources

PubMed1995

Cell and matrix specialisations of rhombomere boundaries.

Hindbrain segments, rhombomeres, define distinct cellular and molecular domains which furnish the ground plan for important aspects of neural and cranial development. In this study, further evidence is presented that the interfaces between rhombomeres, rhombomere boundaries, contain both cells and extracellular matrix with specialised characteristics. Cells at rhombomere boundaries show temporally and spatially distinct expression patterns of developmentally important genes. Towards the end of the developmental period when rhombomeres are present, a fan-shaped array of cells at rhombomere boundaries, that constitute the ventricular ridge, shows decreased expression of two genes (Hoxb-1 and Krox-20), which earlier in development were expressed in all cells of specific rhombomeres. In contrast, these boundary cells show increased expression of another gene, Pax-6, which earlier in development has a rhombomere-specific expression pattern. A specialised identity for boundary cells is further suggested by increased labelling with an anti-vimentin antibody at rhombomere boundaries, indicating that at least some boundary cells are radial glia or glial precursors. In addition to distinct cellular properties, the extracellular domain at rhombomere boundaries is also specialised. Chondroitin sulphate proteoglycan (CSPG) immunoreactivity is increased and, as revealed by immuno-electron microscopy, localised to extracellular spaces. CSPG is also enriched in boundaries regenerated after ablation, or boundaries generated ectopically by rhombomere transplantation. We propose that rhombomere boundaries form their characteristic morphology at the interface between groups of cells with differing molecular characteristics, representing different cell states. A specialised band of cells then develops at the interface. Both the boundary cells and extracellur matrix have characteristics which could be important in later events of neural development such as axon guidance and cell migration.

Animals↗

PubMed1995

Boundaries and inhibitory molecules in developing neural tissues.

Numerous studies of the past decade have illuminated the importance of intercellular adhesion events for neural pattern formation. It has been documented that members of the Ig and cadherin gene superfamilies, that glycoproteins and, probably to some extent, proteoglycans of the extracellular matrix play a role in this context. Recent observations suggest that, in addition to adhesive interactions, repulsive and/or inhibitory phenoma are also of importance in regulating neural pattern formation. Several molecules are under study which are considered possible mediators of inhibitory interactions in the nervous system. The hypothesis has been advanced that some of these might be partially responsible for restrictive, boundary-like properties ascribed to glial cells in developing and regenerating tissues. The current review summarizes these studies and focusses on molecular aspects of boundary and compartmentation phenomena.

Animals↗

PubMed1995

Identification of the border between fibronectin type III homologous repeats 2 and 3 of the neural cell adhesion molecule L1 as a neurite outgrowth promoting and signal transducing domain.

To determine the domains of the neural cell adhesion molecule L1 involved in neurite outgrowth, we have generated monoclonal antibodies against L1 and investigated their effects on neurite outgrowth of small cerebellar neurons in culture. When the 10 antibodies were coated as substrate, only antibody 557.B6, which recognizes an epitope represented by a synthetic peptide comprising amino acids 818 to 832 at the border between the fibronectin type III homologous repeats 2 and 3, was as efficacious as L1 in promoting neurite outgrowth, increasing intracellular levels of Ca2+, and stimulating the turnover of inositol phosphates. These findings suggest that neurite outgrowth and changes in these second messengers are correlated. Such a correlation was confirmed by the ability of Ca2+ channel antagonists and pertussis toxin to inhibit neurite outgrowth on L1 and antibody 557.B6. These observations indicate for the first time a distinct site on cell surface-bound L1 as a prominent signal-transducing domain through which the recognition events appear to be funneled to trigger neurite outgrowth, increase turnover of inositol phosphates, and elevate intracellular levels of Ca2+.

Amino Acid Sequence↗

PubMed1995

Gliosis and axonal sprouting in the hippocampus of epileptic rats are associated with an increase of tenascin-C immunoreactivity.

Temporal lobe epilepsy is associated with neuronal death, gliosis and sprouting of mossy fibres in the hippocampus of human and rats. In the present study we show that immunoreactivity for tenascin-C (an extracellular matrix glycoprotein) increase in the hippocampus of epileptic rats. However, this increase was only observed in the cases displaying neuronal cell loss and glial reaction (i.e. after kainate treatment but not after kindling). Tenascin-C increase was particularly striking at Ammon's horn, where the antibody labelled both reactive astrocytes (confirmed by double-labelling experiments) and axonal plasma membranes. In the molecular layer tenascin-C immunoreactivity remained unchanged in both kindled or kainate treated rats. It is interesting that increased tenascin-C immunoreactivity was observed within zones in which axonal regeneration did not occur (the CA3 area in kainate-treated animals) whereas zones in which reactive synaptogenesis occurred (such as the CA3 area of kindled rats or the molecular layer of both kindled and kainate-treated rats) were devoid of tenascin-C immunoreactivity. We infer from these results that tenascin-C impedes the terminal sprouting of mossy fibres in CA3 of kainate-treated rats.

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PubMed1995

Increased axon regeneration in astrocytes grown in the presence of proteoglycan synthesis inhibitors.

We have recently reported that the critical difference between astrocytic cell lines that are good or poor promoters of axon growth lies in the extracellular matrix. We demonstrated that much of this difference between matrix produced by permissive and non-permissive cell lines could be ascribed to one or more dermatan/keratan sulphate proteoglycans and that these proteoglycans are able to block the neurite-promoting effect of laminin. These proteoglycans are also produced by cultures of primary astrocytes. In the present study, we have demonstrated that treatment of both astrocytic cell lines and primary astrocytes with inhibitors of proteoglycan synthesis, beta-D-xylosides and sodium chlorate, can strongly influence the axon growth promoting properties of both matrix and whole cells. Dorsal root ganglia grown on matrix or in conditioned medium from cultures treated with beta-D-xylosides or sodium chlorate had twice as many axons and the axons grew to twice the length as in control cultures. Following treatment of Neu7 cells with proteoglycan synthesis inhibitors there was also a significant reduction in the ability of Neu7 conditioned medium to block the neurite-promoting effect of laminin. Dorsal root ganglia grown on Neu7 cells treated with sodium chlorate extended 2 to 3 times the number of axons for approximately 300 mm longer distance than on control cultures. Treatment of Neu7 cells with beta-D-xylosides, however, did not make the cells less inhibitory to axon growth. We have also examined the effects of proteoglycan synthesis inhibitors on three-dimensional primary astrocyte cultures, which closely mimic the in vivo effects of astrocytes on axon growth.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1995

Focal brain injury and upregulation of a developmentally regulated extracellular matrix protein.

Tenascin is an extracellular matrix glycoprotein expressed during both normal development and neoplastic growth in both neural and nonneural tissues. During development of the central nervous system (CNS), tenascin is synthesized by glial cells, in particular by immature astrocytes, and is concentrated in transient boundaries around emerging groups of functionally distinct neurons. In the mature CNS, only low levels of the glycoprotein can be detected. The present study demonstrates that following trauma to the adult human cerebral cortex, discrete populations of reactive astrocytes upregulate their expression of tenascin and dramatically increase their transcription of the tenascin gene. The enhanced expression of tenascin may be involved in CNS wound healing, and may also affect neurite growth within and around a brain lesion.

Adult↗

PubMed1995

Tenascin knockout mice: barrels, boundary molecules, and glial scars.

In light of a previous report suggesting that the brains of tenascin-deficient animals are grossly normal, we have studied the somatosensory cortical barrel field and injured cerebral cortex in postnatal homozygous tenascin knockout, heterozygote, and normal wild-type mice. Nissl staining, cytochrome oxidase, and Dil axonal tracing of thalamocortical axonal projections to the somatosensory cortex, all reveal the formation of normal barrels in the first postnatal week in homozygous knockout mice that cannot be distinguished from heterozygote or normal wild-type barrels. In addition to confirming the absence of tenascin in knockout animals, and reporting apparently reduced levels of the glycoprotein in barrel boundaries of heterozygote animals using well-characterized antibodies and immunocytochemistry, we also studied the DSD-1-PG proteoglycan, another developmentally regulated molecule known to be associated with transient glial/glycoconjugate boundaries that surround developing barrels; DSD-1-PG was also found to be expressed in barrel boundaries in apparently normal time frames in tenascin knockout mice. Peanut agglutinin (PNA) binding of galactosyl-containing glycoconjugates also revealed barrel boundaries in all three genotypes. We also examined the expression of tenascin-R, a paralog of tenascin-C (referred to here simply as tenascin). As previously reported, tenascin-R is prominently expressed in subcortical white matter, and we found it was not expressed in the barrel boundaries in any of the genotypes. Thus, the absence of tenascin does not result in a compensatory expression of tenascin-R in the barrel boundaries. Finally, we studied wounds of the cerebral cortex in the late postnatal mouse. The astroglial scar formed, for the most part, in the same time course and spatial distribution in the wild-type and tenascin knockout mice. However, there may be some differences in the extent of gliosis between the knockout and the wild type that warrant further study. Roles for boundary molecules like tenascin during brain pattern formation and injury are reconsidered in light of these findings on barrel development and cortical lesions in tenascin-deficient mice.

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

Polyclonal antibodies against NCAM and tenascin delay endplate reinnervation.

Experiments were performed to block molecules with antibodies which are upregulated in nerve and muscle following denervation. The delay in endplate reinnervation was taken as a measure for their involvement in regeneration. Gluteus maximus muscles of 86 male CBA/J mice were hemidenervated by freezing the caudal gluteal nerve at a defined position. The degree of reinnervation was evaluated in identified endplates by repeated vital staining of ACh receptors with rhodaminated alpha-bungarotoxin and of axons with 4Di-2ASP. Normally, endplates were completely reinnervated by 13-14 days (108 endplates in seven muscles). After daily application of polyclonal antibodies against NCAM or tenascin, reinnervation was significantly delayed. Preimmune serum, rabbit immunoglobulins or saline did not show this effect. Several monoclonal antibodies against NCAM (H-28) and tenascin (576, 578, 630, 633) showed a tendency but no significant effect. It is concluded that both NCAM and tenascin, upregulated after denervation, are involved in axon guidance and/or endplate reinnervation.

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

Effects of complete and incomplete tumor promoters on hair growth, angiogenesis, and tenascin expression in the skin of NMRI mice.

Although the phorbol esters 12-O-tetradecanoylphorbol-13-acetate (TPA) and 12-O-retinoylphorbol-13-acetate (RPA) are almost equipotent inducers of an inflammatory and hyperplastic response in NMRI mouse skin, TPA acts as a converting or complete and RPA as a non-converting or incomplete skin tumor promoter. Bearing in mind the converting effect of skin wounding and TGF beta, we have addressed the question of a relationship between conversion and stromal events. For this purpose we have compared the effects of TPA and RPA on dermal angiogenesis, hair regrowth and the expression of tenascin in NMRI mouse skin in vivo. In the reticular part of the dermis, shaving alone induced angiogenesis peaking at day 14, concomitant with hair regrowth. While TPA exhibited a stimulatory effect on both parameters, RPA suppressed shaving-induced angiogenesis and delayed the onset of hair regrowth. Whether this difference in the phorbol ester effects being consistent with the working hypothesis is critical for conversion, remains to be shown. In the papillary dermis, however, RPA was more potent than TPA in inducing vascularization and tenascin expression. The kinetics of both responses corresponded to the time course of hyperproliferation induced by the phorbol esters in the overlaying epidermis, i.e. may be related to promotion proper, rather than conversion.

Animals↗

PubMed1994

An inhibitor of neurite outgrowth produced by astrocytes.

We have produced a number of astrocytic cell lines, some of which promote abundant neurite outgrowth, some of which are poor promoters of neurite outgrowth. The critical difference between these lines lies in the extracellular matrix, cell lines that are good promoters of axon growth producing a matrix that promotes axon growth, cell lines that are poor promoters of axon growth producing a non-permissive matrix. We were unable to find any consistent correlations between promotion of axon growth and production of proteases, protease inhibitors, N-cadherin, growth cone collapsing activity, and several extracellular matrix molecules. In the present study we have compared the least permissive of our cell lines, Neu7, with the most permissive, A7. Medium conditioned by the cell lines has the same properties as the matrix, since dorsal root ganglia (DRGs) grown in conditioned medium from the Neu7 line grow axons poorly, while DRGs grown in medium conditioned by A7 or primary astrocytes grow many long axons. Since matrix produced by all the cell lines contains large amounts of laminin, we looked to see whether the cells were producing laminin-blocking activity. Medium from the Neu7 line blocked laminin, while that from the A7 and primary astrocytes did not. However, when the conditioned media were heat-treated to remove neurite-promoting activity, they all had laminin-blocking activity: the blocking activity is heat stable. The neurite-promoting properties of the conditioned media therefore probably reflect a balance between promoting molecules and blockers.(ABSTRACT TRUNCATED AT 250 WORDS)

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↗

PubMed1994

Tenascin glycoproteins in developing neural tissues: only decoration?

Tenascin glycoproteins constitute a growing family of extracellular matrix molecules that are transiently expressed by astrocytes during the development of the central nervous system (CNS). In some areas, tenascin distribution is discrete and tenascin boundaries delineate emerging functional processing units, for example, in the somatosensory cortex. The intact adult CNS displays low levels of expression and up-regulation of tenascin after lesion or in glial tumors. In vitro studies using the purified glycoprotein, bacterially expressed tenascin fusion proteins, monoclonal antibodies, and defined cell culture models have established that tenascin glycoproteins possess cell-binding sites for neural cells, support neuronal migration and the formation of neurites. On the other hand, tenascin also embodies repulsive, inhibitory properties that could serve to conceal neuronal assemblies and to segregate emerging fiber tracts. These functional properties are encoded by distinct domains of the molecule and suggest that tenascin glycoproteins are involved in neural pattern formation and regeneration. This interpretation is discussed with reference to a recent report that the elimination of the tenascin gene does not cause obvious abnormalities of neural tissues.

Animals↗

PubMed1993

Growth and degeneration of axons on astrocyte surfaces: effects on extracellular matrix and on later axonal growth.

Cultured astrocytes deposit an extracellular matrix which has been shown by immunocytochemistry to react with antibodies to tenascin, laminin, and fibronectin. Neuronal-glial interaction down-regulates these components of the matrix, causing a reduction in extracellular matrix localized to areas of contact with axons. Axons used for these experiments were from embryonic rat retinal explants. In some experiments explants were removed from the co-cultures and their axons allowed to degenerate. Degeneration of axons did not reverse the local reduction of extracellular matrix brought about by axon outgrowth. The period of axon outgrowth studied was 4-5 days; the period of degeneration was 2-3 days. Astrocytes alone, astrocytes with intact retinal explants, and astrocytes with 2-day degenerated retinal axons were tested for their ability to support neurite outgrowth from embryonic rat cortical neurons. Neurite outgrowth occurred on all astrocyte cultures. Cortical neurite lengths, measured 2 days after plating, were not significantly different between astrocytes alone and astrocytes with degenerated retinal axons. However, there was a tendency for neurites to be shorter on astrocytes with intact retinal axons present. Two conclusions may be drawn from these results. First, the state of differentiation of astrocytes, as marked by their assembly of extracellular matrix, is altered by contact with axons. Second, degeneration of axons alone, in the absence of other cell types, is not a sufficient signal to reestablish assembly of extracellular matrix. However, neither is it a sufficient signal to render astrocytes inhospitable to further axonal outgrowth or regeneration.

Animals↗

PubMed1993

Differential expression of tenascin after denervation, damage or paralysis of mouse soleus muscle.

The expression of the extracellular matrix molecule tenascin was studied by immunocytochemistry and Western blotting in soleus muscles of adult mice after nerve damage (denervation), muscle injury (induced by enforced running or freezing) and functional block of synaptic transmission (botulinum toxin). Enhanced expression of tenascin in the extracellular spaces around focally damaged muscle fibres was found already 10 h after onset of running on a motor-driven treadmill which causes muscle injury in soleus muscle. Tenascin expression reached a peak at 2-3 days post-exercise, after which it declined gradually and became undetectable by two weeks after injury. Similarly, cryo-damage of soleus muscles in situ led to upregulation of tenascin. Chronic muscle denervation after sciatic nerve transection caused a persistent (studied up to 31 days) expression of tenascin at denervated endplates and in intramuscular nerve branches but not in other tissue compartments. Local application of botulinum toxin Type A, which results in muscle inactivity but not in tissue degeneration, however, did not induce tenascin expression 12 h to 12 days post-injection. Expression of tenascin after denervation and muscle damage, but its absence after paralysis, were verified by SDS-PAGE and Western blot analysis. Independent of the type of injury (muscle, nerve or both) the known major isoforms of mouse tenascin, as judged by M(r) comparison, were re-expressed, with no preponderance of individual M(r) forms. These results show that tenascin expression in adult muscles is induced by both axon and muscle fibre damage but not by muscle inactivity. In contrast, NCAM, in accordance with previous observations, showed enhanced expression both as a result of inactivity and in association with tissue repair.

Animals↗

PubMed1993

Tenascin glycoproteins in neural pattern formation: facets of a complex picture.

It is generally accepted that neuron-glia interactions play an important role in the regulation of neural development. For example, astrocytes are thought to guide migrating neuronal precursors and advancing growth cones to their destination. In addition, astrocytes have recently been ascribed a function in the segregation of forming neuronal assemblies and fiber tracts and are believed to hinder regeneration of lesioned adult central nervous system (CNS) structures. Therefore molecules that might specifically mediate neuron-glia interactions in the CNS attract considerable interest. The growing family of tenascin glycoproteins may play a key role in this context. Tenascin glycoproteins are transiently expressed by astrocytes in the nervous system and affect neuronal morphogenesis and behavior in definable ways. The present review discusses functional properties and examines seemingly contradictory effects of these extracellular matrix constituents.

Animals↗