PubMed Health⌕ Search

Biomedical subjects

U Rutishauser

Publications and source records attributed to U Rutishauser.

At least 55 records · Page 3Linked to original sources
PubMed1994

N-CAM mutation inhibits tangential neuronal migration and is phenocopied by enzymatic removal of polysialic acid.

The mutation of N-CAM in mice produces a phenotype dominated by an undersized olfactory bulb and accumulation of precursors in the subependymal layer. We demonstrate here that this defect can be duplicated by injection of an enzyme that specifically destroys the polysialic acid (PSA) moiety associated with N-CAM. Studies of BrdU-labeled and pyknotic cells suggest that this defect reflects a decrease in the rostral migration of olfactory precursors and not a change in the proliferation or rate of death of these cells. In addition to their ectopic location, these cells had fewer growth cone-like processes oriented along the migration route. In contrast to tangential movement, radial migration of granule cells in the olfactory bulb was not affected by loss of PSA. These results support the proposed role for PSA in cell translocation, discriminate between different mechanisms of cell migration, and provide insight as to the nature of the N-CAM mutant phenotype.

Animals↗
PubMed1994

Polysialic acid regulates growth cone behavior during sorting of motor axons in the plexus region.

Removal of polysialic acid (PSA) from N-CAM during the time when chick motoneuron axons are segregating into target-specific fascicles at the base of the limb was previously shown to result in motoneuron projection errors. Here, it is established that these errors are associated with altered growth cone behavior in the plexus. In contrast to control embryos, in which individual axons were observed to exhibit dramatic changes in direction and extensive divergence, axonal trajectories following the removal of PSA were relatively straight. To determine whether enhanced axon-axon fasciculation following PSA removal had prevented growth cones from responding appropriately to guidance cues at the base of the limb, we also examined the role of L1, a major mediator of axon-axon fasciculation in this system. Anti-L1 reversed the effects of PSA removal on both growth cone trajectories and projection errors. These results indicate that PSA plays a permissive role, attenuating axon-axon interactions in the plexus and thereby allowing the axonal reorganization that is essential for the formation of specific motoneuron projections.

Animals↗
PubMed1994

Expression of neural cell adhesion molecule (N-CAM) in rat islets and its role in islet cell type segregation.

Endocrine cell types are non-randomly distributed within pancreatic islets of Langerhans. In the rat, insulin-secreting B-cells occupy the core of the islets and are surrounded by A-, D- and PP-cells, secreting glucagon, somatostatin and pancreatic polypeptide, respectively. Furthermore, dissociated islet cells have the ability in vitro to form aggregates with the same cell-type organization as native islets (pseudoislets). These observations suggest that a differential expression of cell adhesion molecules (CAMs) might characterize B- and non-B-cells (A-, D- and PP-cells), and be in part responsible for the establishment and maintenance of islet architecture. Indirect immunofluorescence using antibodies against CAMs and islet hormones was performed on serial sections of the splenic and duodenal parts of the rat pancreas. Staining for the Ca(2+)-dependent CAM E-cadherin was detected on both exocrine and endocrine tissue and was uniform over the entire islet section, in both pancreatic regions. By contrast, staining for the Ca(2+)-independent neural CAM (N-CAM) was restricted to endocrine tissue and nerve endings. Furthermore, N-CAM staining of endocrine cells was stronger in the islet periphery, a region composed mostly of non-B-cells. Serial sections demonstrate that cells staining strongly for N-CAM in the splenic part correspond to glucagon cells and in the duodenal part to pancreatic polypeptide cells. Within pseudoislets in vitro a stronger staining for N-CAM was also observed on peripheral cells, corresponding to non-B-cells.

Animals↗
PubMed1993

Genetic deletion of a neural cell adhesion molecule variant (N-CAM-180) produces distinct defects in the central nervous system.

N-CAM is abundantly expressed in the nervous system in the form of numerous structural variants with characteristic distribution patterns and functional properties. N-CAM-180, the variant having the largest cytoplasmic domain, is expressed by all neurons. The N-CAM-180-specific exon 18 has been deleted to generate homozygous mice unable to express this N-CAM form. The most conspicuous mutant phenotype was in the olfactory bulb, where granule cells were both reduced in number and disorganized. In addition, precursors of these cells were found to be accumulated at their origin in the subependymal zone at the lateral ventricle. Analysis of the mutant in this region suggests that the mutant phenotype involves a defect in cell migration, possibly through specific loss of the polysialylated form of N-CAM-180, which is expressed in the migration pathway. Subtle but distinct abnormalities also were observed in other regions of the brain.

Actins↗
PubMed1993

Adhesion molecules of the nervous system.

The structural and functional characterization of neural cell-cell adhesion molecules continues to progress at a rapid rate, exposing the complex nature of these large multidomain receptors and their intricate relationship with the cell. Over the past year, significant progress has been made in the description of multiple binding activities, signaling potentials, and cytoplasmic associations of cell-cell adhesion molecules. In addition, new modes for developmental regulation of adhesion molecule function have been identified.

Animals↗
PubMed1993

Regulation and activity-dependence of N-cadherin, NCAM isoforms, and polysialic acid on chick myotubes during development.

Muscle development in vivo involves a complex sequence of cell-cell interactions in which secondary myotubes first form in association with primary myotubes and subsequently separate from them. We show here that during this process N-cadherin and the different structural forms of NCAM are regulated in a pattern that involves both temporal changes in expression and localization to particular regions of the muscle cell surface. In particular, levels of N-cadherin on maturing myotubes are decreased, and the form of NCAM synthesized by the muscle changes from a transmembrane non-polysialylated to a lipid-linked polysialylated membrane protein. Moreover, while NCAM was distributed on all myotube surfaces, the polysialyated form of NCAM was restricted to regions of the myotube surface that had recently separated from neighboring cells. We previously found that blockade of nerve-induced activity by d-Tubocurarine perturbed muscle cell interactions, resulting in a failure of myotubes to separate. We now show that this activity blockade also alters adhesion molecule expression. First, N-cadherin was no longer down-regulated in maturing myotubes, and its persistence on the surfaces of mature myotubes may partly explain their failure to separate. Secondly, the developmental switch from transmembrane to lipid-linked NCAM did not occur, and polysialylated NCAM was no longer formed. As the unusual physical properties of PSA have been proposed to impede cell-cell interactions, this alteration would also be expected to compromise cell separation. Together, these results suggest that the regulated expression of both N-cadherin and NCAM isoforms including their polysialylation, is an essential mechanism for the normal separation of secondary myotubes from primary myotubes.

Animals↗
PubMed1992

Neural cell adhesion molecule in aged mouse muscle.

Expression of the neural cell adhesion molecule was compared in endplate and non-endplate regions of skeletal muscles of mature and old CBF-1 mice, in order to determine whether age-related changes in neuromuscular morphology were correlated with age changes in neural cell adhesion molecule expression. Three muscles were examined: two (soleus and sternomastoid) showed age-related regionalization of nerve terminals as one manifestation of increased synaptic remodelling while the third (diaphragm) did not. Relative neural cell adhesion molecule content in these muscles was measured by densitometry of immunoblots after concentration by affinity chromatography. Expression of the major 140,000 mol. wt form of neural cell adhesion molecule, which was most abundant in the endplate region, was increased in sternomastoid and soleus of old compared to adult mouse, but was unchanged with age in diaphragm. A 70,000-80,000 mol. wt presumably proteolytic polypeptide fragment of neural cell adhesion molecule was increased in immunoblots of all old muscles. Immunocytochemical studies of skeletal muscles showed no difference in neural cell adhesion molecule cellular distribution in mature vs old mice, but in motor nerve of sternomastoid, the number of neural cell adhesion molecule-positive nerve fibers was increased in old mice. Several lines of evidence indicated that partial denervation was rare in old CBF-1 mice, and therefore could not account for the findings above. Selective increase of 140,000 mol. wt neural cell adhesion molecule expression in the junctional regions of those muscles of old mice which show neuromuscular remodelling indicates that this adhesion molecule may play a role in the age-related instability of motor nerve terminals.

Aging↗
PubMed1992

Polysialic acid influences specific pathfinding by avian motoneurons.

The influence of polysialic acid (PSA) on the neural cell adhesion molecule on motoneuron outgrowth and pathway formation was investigated by determining its temporal and spatial pattern of expression and by the effect that its removal had on motoneuron projection patterns. Motoneurons first expressed PSA as their growth cones began to segregate into motoneuron pool-specific groups in the plexus region; furthermore, PSA levels differed between motoneurons projecting to different targets. When PSA was removed during the period of axonal segregation in the plexus region projection errors were common. However, later removal during the process of muscle nerve formation did not result in projection errors. These results suggest that PSA modulates interactions between motoneuron axons and guidance molecules in the plexus region during axonal pathfinding.

Animals↗
PubMed1992

Intercellular space is affected by the polysialic acid content of NCAM.

We have previously proposed that polysialic acid (PSA), which is attached to NCAM on the cell surface, can serve to regulate a variety of cell-cell interactions. The present study provides evidence that hydrated PSA influences a sufficiently large volume at the cell surface to exert broad steric effects, and that the removal of PSA in fact causes a detectable change in intercellular space. Using F11 neuron/neuroblastoma hybrid cells as a model system, the measured density and size of PSA suggests that a substantial fraction of the space between two apposed cell surface membranes could be sterically influenced by the presence of PSA. Specific enzymatic removal of PSA, which is similar in magnitude to changes that occur in many tissues during normal development, caused about a 25% decrease in the distance between two apposed cells. By contrast, removal of both heparan sulfate and chondroitin sulfate from the cells had no effect on this parameter. It is proposed that such changes in membrane-membrane distance could serve to alter selectively the efficiency of encounter between complementary receptors on apposing cells, and explain at least in part the broad biological influences of PSA.

Animals↗
PubMed1992

Identification of a peptide sequence involved in homophilic binding in the neural cell adhesion molecule NCAM.

The neural cell adhesion molecule NCAM is capable of mediating cell-cell adhesion via homophilic interactions. In this study, three strategies have been combined to identify regions of NCAM that participate directly in NCAM-NCAM binding: analysis of domain deletion mutations, mapping of epitopes of monoclonal antibodies, and use of synthetic peptides to inhibit NCAM activity. Studies on L cells transfected with NCAM mutant cDNAs using cell aggregation and NCAM-covasphere binding assays indicate that the third immunoglobulin-like domain is involved in homophilic binding. The epitopes of four monoclonal antibodies that have been previously shown to affect cell-cell adhesion mediated by NCAM were also mapped to domain 3. Overlapping hexapeptides were synthesized on plastic pins and assayed for binding with these monoclonal antibodies. One of them (PP) reacted specifically with the sequence KYSFNY. Synthetic oligopeptides containing the PP epitope were potent and specific inhibitors of NCAM binding activity. A substratum containing immobilized peptide conjugates also exhibited adhesiveness for neural retinal cells. Cell attachment was specifically inhibited by peptides that contained the PP-epitope and by anti-NCAM univalent antibodies. The shortest active peptide has the sequence KYSFNYDGSE, suggesting that this site is directly involved in NCAM homophilic interaction.

Amino Acid Sequence↗
PubMed1992

NCAM and its polysialic acid moiety: a mechanism for pull/push regulation of cell interactions during development?

Many cell adhesion molecules have a distinct pattern of expression and well-defined role in cell-cell recognition. In contrast, NCAM is broadly expressed and perturbations of its function affect many diverse aspects of embryonic development. Evidence has been obtained suggesting that the molecule and its polysialic acid moiety serve not only to contribute to specific interactions, but also to regulate overall cell-cell apposition. In this latter mode, the molecule can have both a positive and a negative effect on a wide variety of contact-dependent cellular events.

Animals↗
PubMed1992

Polysialic acid is required for optimal growth of axons on a neuronal substrate.

Formation of axonal pathways involves a variety of molecules that influence cell-cell interactions. The polysialic acid (PSA) moiety of the neural cell adhesion molecule (NCAM) is present on neuronal surfaces during process outgrowth. Our studies reveal that the removal of PSA causes a decrease in the rate of elongation of retinal cell processes on a substrate of neuronal membranes derived from chick tectum. This effect was partially reversed by antibodies against the L1 adhesion molecule, but not by antibodies against NCAM, N-cadherin, or beta 1-integrins. This predominant effect of PSA on L1 was also observed in short-term, cell-cell adhesion assays, suggesting that PSA promotes optimal outgrowth on neuronal substrates by limiting the consequences of L1-mediated adhesion.

Animals↗
PubMed1991

Phosphorylation-dependent regulation of axon fasciculation.

Axons often grow along other axons to produce bundles called fascicles, and a number of cell adhesion molecules (CAMs) found on axon surfaces contribute to this process. The surprising observation that Fab fragments against individual CAMs can completely block fascicle formation suggests that the different axon-associated CAMs are functionally linked. The present studies investigate whether such a linkage might reflect intracellular regulatory mechanisms. Results obtained with chicken retinal explants in culture indicate that fasciculation is highly sensitive to cytoplasmic protein phosphorylation by means of a mechanism that does not alter levels of CAM expression. Moreover, the potent effect of individual Fabs on fasciculation disappears with enhanced phosphorylation. These observations suggest that growing axons possess a general regulatory process for the multiple CAMs that participate in fasciculation.

Animals↗
PubMed1991

Proteolytic modification of neural cell adhesion molecule (NCAM) by the intracellular proteinase calpain.

The neural cell adhesion molecule, NCAM, is concentrated in synaptic regions and thus may contribute to the formation and maintenance of connections between brain cells. We present evidence that the cytoplasmic domain of NCAM can be experimentally modified by the intracellular calcium-dependent proteinase, calpain. This degradation could provide a mechanism for rapidly uncoupling and reorganizing synaptic contacts.

Animals↗
PubMed1991

Formation of the retinal ganglion cell and optic fiber layers.

The early development of retinal ganglion cell and the optic fiber layers has been studied by examining the morphology of differentiating retinal ganglion cells using immunoelectron microscopy and a monoclonal antibody against neuron-specific beta-tubulin. This antibody identified retinal ganglion cells during the stages of their most active differentiation and axonogenesis prior to maturation of other retinal neurons. The changing morphology of retinal ganglion cells during these early stages is consistent with a differentiation sequence in which axonogenesis and translocation of the cell body to the vitreal surface occur while the cell is still attached to the vitreal margin through its vitreal endfeet. Thus, the mechanism of retinal ganglion cell axon generation and soma migration to the vitreal surface appears to involve maintenance of this attachment which may act as both a focus for axon differentiation and an anchor for directed nuclear translocation to the vitreal margin.

Animals↗
PubMed1991

Polysialic acid on the surface of axons regulates patterns of normal and activity-dependent innervation.

Studies of the cell-cell adhesion molecules NCAM and L1 have indicated that their combined action is an important determinant in establishing normal patterns of muscle innervation. Moreover, they participate in activity-dependent changes in axonal sprouting. Recent findings in vivo, however, suggest that the central variable in both events is not altered NCAM or L1 expression, but rather changes in the amount of polysialic acid (PSA) at the cell surface. This finding is consistent with the proposed role of PSA as a regulator of cell-cell interactions. Because these molecular entities are present in most of the nervous system, it is likely that this mechanism can influence many aspects of axonal behavior during development and regeneration.

Animals↗
PubMed1991

NCAM polysialic acid can regulate both cell-cell and cell-substrate interactions.

We have proposed previously that the polysialic acid (PSA) moiety of NCAM can influence membrane-membrane apposition, and thereby serve as a selective regulator of a variety of contact-dependent cell interactions. In this study, cell and tissue culture models are used to obtain direct evidence that the presence of PSA on the surface membrane can affect both cell-cell and cell-substrate interactions. Using a neuroblastoma/sensory neuron cell hybrid, it was found that removal of PSA with a specific neuraminidase (endo-N) augments cell-cell aggregation mediated by the L1 cell adhesion molecule as well as cell attachment to a variety of tissue culture substrates. In studies of embryonic spinal cord axon bundling, which involves both cell-cell and cell-substrate interactions, the pronounced defasciculation produced by removal of PSA is most easily explained by an increase in cell-substrate interaction. The fact that in both studies NCAM's intrinsic adhesion function was found not to be an important variable further illustrates that regulation of the cell surface by PSA can extend beyond binding mediated by the NCAM polypeptide.

Animals↗