Endogenous lectin CSL is present on the membrane of cilia of rat brain ependymal cells

Msx1-Deficient Mice Fail to Form Prosomere 1 Derivatives, Subcommissural Organ, and Posterior Commissure and Develop Hydrocephalus

Msx1 is a regulatory gene involved in epithelio-mesenchymal interactions in limb formation and organogenesis. In the embryonic CNS, the Msx1 gene is expressed along the dorsal midline. Msx1 mutant mice have been obtained by insertion of the nlacZ gene in the Msx1 homeodomain. The most important features of homozygous mutants that we observed were the absence or malformation of the posterior commissure (PC) and of the subcommissural organ (SCO), the collapse of the cerebral aqueduct, and the development of hydrocephalus. Heterozygous mutants developed abnormal PC and reduced SCO, as revealed by specific antibodies against SCO secretory glycoproteins. About one third of the heterozygous mutants also showed hydrocephalus. Other defects displayed by homozygous mutants were ependymal denudation, subventricular cavitations and edema, and underdevelopment of the pineal gland and subfornical organ. Some homozygous mutants developed both SCO and PC, probably as a consequence of genetic redundancy with Msx2. However, these mutants did not show SCO-immunoreactive glycoproteins and displayed obstructive hydrocephalus. This suggests that Msx1 is necessary for the synthesis of SCO glycoproteins, which would then be required for the maintenance of an open aqueduct.

Ependymal development, proliferation, and functions: a review

A survey of the literature shows that proliferation of ependyma occurs largely during the embryonic and early postnatal periods of development in most species. Differentiation of these cells proceeds along particular regional and temporal gradients as does the expression of various cytoskeletal (vimentin, cytokeratins, glial fibrillary acidic protein) and secretory proteins (S-100). Turnover declines significantly postnatally, and only low levels of residual activity persist into adulthood under normal conditions. Although the reported response of ependyma to injury is somewhat equivocal, only limited regenerative capacity appears to exist and to varying degrees in different regions of the neuraxis. Proliferation has been most often observed in response to spinal cord injury. Indeed, the ependyma plays a significant role in the initiation and maintenance of the regenerative processes in the spinal cord of inframammalian vertebrates. In the human, however, ependyma appears never to regenerate at any age nor re-express cytoskeletal proteins characteristic of immature cells. The functions of ependyma including tanycytes, a specialized form of ependymal cell that persists into adulthood within circumscribed regions of the nervous system, are still largely speculative. Fetal unlike mature ependyma is believed to be secretory and is believed to play a role in neurogenesis, neuronal differentiation/axonal guidance, transport, and support. In the adult brain, mature ependyma is not merely an inert lining but may regulate the transport of ions, small molecules, and water between the cerebrospinal fluid and neuropil and serve an important barrier function that protects neural tissue from potentially harmful substances by mechanisms that are still incompletely understood.

Spinal cord compression injury in guinea pigs: structural changes of endothelium and its perivascular cell associations after blood-brain barrier breakdown and repair

This study examines morphological changes of the blood-brain barrier (BBB) after spinal cord compression. The lowest thoracic segment (T13) of female guinea pigs was injured and the BBB was tested from 7 days to 5.5 months postinjury using intravenously injected horseradish peroxidase (HRP) as a tracer. Tracer leakage in the injured segment was verified with the light microscope and the fine structure of capillaries was examined. Diffuse tissue staining was observed at T13 up to 2 weeks following injury. A leaky BBB correlated with expected changes in the fine structure of endothelial cell junctions. These were predominantly nonoverlapping cell junctions which, in many instances, were separated by clefts between adjacent cells. At early survival times, numerous capillary profiles with juxtaposed astrocyte foot processes were noted in addition to altered cell associations. Complete sealing of the BBB against interstitial HRP leakage was not observed until 17 days postinjury. After the first week, some of the endothelial cells were contacted by macrophages, processes of perivascular microglia, and processes of swollen and degenerating astrocytes. Perivascular spaces varied in extent and contained amorphous deposits of extracellular materials in addition to supernumerary layers of basal lamina. The early changes were followed by profound tissue restructuring due to loss of both neurons and glia. At longer survival times the BBB to HRP repaired. Endothelial cells formed complex overlapping junctions with zonulae occludentes. Most of the capillaries in the injured segment were no longer in direct contact with astrocyte foot processes, although reactive astrocytes constituted the predominant cell type in the remaining gray matter. Substantial expansion of perivascular spaces was evident. The cytoplasm of endothelial cells had numerous pinocytotic vesicles. Perivascular spaces contained layers of assembled collagen arranged perpendicularly to each other in addition to amorphous matrix materials. The findings suggest that decoupling of astrocyte foot processes from endothelial cell surfaces does not prevent reformation of tight junctions. It remains to be examined what effects the larger perivascular spaces, extracellular matrix deposits, and changes of cell associations may have on transport systems and ionic buffering. The data are relevant for estimating an opportune time for application of barrier-impermeable drugs to the lesion area.

The ependyma: a protective barrier between brain and cerebrospinal fluid

This review summarizes the current scientific literature concerning the ependymal lining of the cerebral ventricles of the brain with an emphasis on selective barrier function and protective roles for the common ependymal cell. Topics covered include the development, morphology, protein and enzyme expression including reactive changes, and pathology. Some cells lining the neural tube are committed at an early stage to becoming ependymal cells. They serve a secretory function and perhaps act as a cellular/axonal guidance system, particularly during fetal development. In the mature mammalian brain ependymal cells possess the structural and enzymatic characteristics necessary for scavenging and detoxifying a wide variety of substances in the CSF, thus forming a metabolic barrier at the brain-CSF interface.

Presence of anti-CSL antibodies in the cerebrospinal fluid of patients: a sensitive and specific test in the diagnosis of multiple sclerosis

The carbohydrate-binding protein (lectin) CSL is an antigen involved in the stabilization of the myelin structure by interacting with the carbohydrate moiety of myelin glycoproteins. Since anti-CSL Fab fragments were able to produce destruction of CNS myelin in vitro, CSL was considered as a potential immunological target in multiple sclerosis. The presence of anti-CSL antibodies has been examined in the cerebrospinal fluid of 1388 different patients with various neurological diseases. It is concluded that the presence of anti-CSL antibodies in the cerebrospinal fluid of patients less than 50 years old constitutes a very sensitive and specific test for multiple sclerosis.

Glycoproteins and lectins in cell adhesion and cell recognition processes

The discovery of endogenous lectins having specific and high affinity for the carbohydrate portions of glycoproteins has opened up new directions in the field of cell adhesion and cell recognition. Two endogenous lectins, termed as CSL and R1, initially isolated from the rat cerebellum and having a wide distribution in mammalian tissues, have been shown to participate in essential mechanisms of cell adhesion. The membrane-bound lectin R1 seems to be involved in transient recognition between neuronal cells, followed by elimination of the glycoprotein ligands at the surface of the recognized cell. In contrast, CSL is a molecule involved in adhesion between various normal or transformed cells since it participates in the formation of tight junctions. The glycoprotein ligands recognized with higher affinity by these two lectins seem to possess a special structure which defines a sub-class of oncofetal HNK-1 glycans. The over-expression of the glycoprotein ligands of these lectins in most transformed cells provides new tools for understanding the underlying mechanism of malignant transformation as well as the generation of signals through cell adhesion.

Malignant transformation in hepatocytes is associated with the general increase of glycoprotein ligands specifically binding to the endogenous lectin CSL

Several hepatoma cell lines and hepatic ascite tumour cells were studied for the presence of glycoprotein ligands of an endogenous lectin, the "Cerebellar Soluble Lectin" (CSL). This lectin is also present in hepatocytes in vivo and in vitro and can be detected biochemically and immunologically. In transformed cells, the level of CSL glycoprotein ligands is increased 50-fold as compared to the control cells. Such an increase is not observed for the ligands of the plant lectin, concanavalin A, which is, as CSL, a D-mannose-binding lectin. These results indicated that the changes in glycans during malignant transformation, in these cells, is specifically important for minor glycans binding to CSL.

An endogenous lectin and one of its neuronal glycoprotein ligands are involved in contact guidance of neuron migration

In the central nervous system, postmitotic neurons migrate along astrocytic processes to reach their adult position. The molecular mechanisms of this guided migration are not clearly defined, although some steps have been shown to involve proteases and cell adhesion molecules. We report that monovalent antibodies (Fab fragments) raised against an endogenous cerebellar soluble lectin (CSL) completely inhibit neuronal migration in cultures of cerebellar explants at concentrations as low as 50 micrograms/ml. A similar inhibition pattern was obtained with Fab fragments prepared against one of the endogenous glycoprotein ligands of CSL, the 31-kDa glycoprotein (this glycoprotein is a membrane-bound glycoprotein specifically occurring, in the cerebellum, at the surface of immature neurons). We propose that this lectin-glycoprotein interaction supports the adhesion between neurons and the astrocyte guide during the migration of cerebellar immature neurons.

Detection and mapping of endogenous receptors for carrier-immobilized constituents of glycoconjugates (lectins) by labelled (neo)glycoproteins and by affinity chromatography in human adult mesencephalon, pons, medulla oblongata and cerebellum

Different carrier-immobilized carbohydrate moieties were employed as tools to detect respective binding sites glycohistochemically and glycobiochemically. Besides ascertaining their presence the pattern of endogenous sugar receptors (lectins) in different regions of the human central nervous system was mapped to reveal any non-uniform expression. A strong and specific staining with biotinylated neoglycoproteins, exposing different sugar moieties as ligands, indicated the presence of sugar receptors in the nuclei, neuronal pathways and accessory structures such as ependyma cells, plexus chorioideus, intra- and extracerebral vessels and leptomeninges localized in the mesencephalon, in the pons, in the medulla oblongata and in the cerebellum. Significant differences were seen for various neuroanatomical regions like nerve cells in the basal and central regions of the nuclei pontis in the glycohistochemically detected level of expression of endogenous sugar receptors (lectins). The used approach with carbohydrate constituents of cellular glycoconjugates as ligands in search of specific receptors complemented studies on the localization of glycoconjugates with sugar-specific tools like plant lectins. Exemplary glycobiochemical investigations on the medulla oblongata and cerebellum were performed to investigate the molecular nature of sugar receptors detected glycohistochemically. Despite notable overall similarities, carbohydrate-binding proteins of differing molecular weight can be isolated from these two regions of the central nervous system, namely in the case of receptors with specificity to beta-galactoside termini, to N-acetyl-D-galactosamine and N-acetyl-D-glucosamine and to D-xylose. These combined glycohistochemical and glycobiochemical results serve as a guideline for exploring the physiological relevance of the detected regional differences.

Antibodies to cerebellar soluble lectin CSL in multiple sclerosis

Cerebrospinal fluid samples from 239 patients with various neurological disorders were tested for the presence of autoantibodies to an endogenous mannose-binding protein, the cerebellar soluble lectin CSL, by means of an immunoblotting test with rat CSL as antigen. 47 of 51 patients with multiple sclerosis were positive for anti-CSL compared with 30 of 188 patients with other neurological disorders. 14 of the 30 false-positive patients were over 60 years old, an age group not typical of multiple sclerosis patients. The specificity of the test for multiple sclerosis was 85% and the sensitivity 93.5%. The possibility that CSL is an important immunological target in multiple sclerosis allows new insights into the possible causes and development of this disorder.

Regional differences in the distribution of endogenous receptors for carbohydrate constituents of cellular glycoconjugates, especially lectins, in cortex, hippocampus, basal ganglia and thalamus of adult human brain

Ten different types of labelled neoglycoproteins, exposing glycohistochemically pivotal carbohydrate moieties that mostly are constituents of naturally occurring glycoconjugates with an aromatic spacer, were synthesized. The panel was applied to fixed, paraffin-embedded sections of different cortical regions and white matter, of hippocampal gyrus, basal ganglia, thalamus nuclei and adjacent areas of adult human brain to comprehensively map the presence of respective binding sites in these parts. Compliance with accepted criteria for specificity of binding was routinely ascertained. Overall, not a uniform binding pattern, but a distinct distribution with regional differences on the level of specific cytoplasmic and nuclear staining in nerve cells was determined, fiber structures being generally labelled with medium or strong intensity. For example, among the neurons localized in the five cortical laminae the binding of N-acetyl-D-galactosamine varied from strong to undetectable. Biochemical analysis, employing carbohydrate residues as affinity ligands in chromatography, proved that the neuroanatomically different regions exhibited a pattern of receptors with notable similarities. These results on endogenous binding sites for glycoconjugates, especially lectins, are complementary to assessment of localization of cellular glycoconjugates by plant lectins and carbohydrate-specific monoclonal antibodies. They are thus a further obligatory step to substantiate the physiological roles of recognitive protein-carbohydrate interactions in the central nervous system.

Epidermal growth factor enhances the expression of an endogenous lectin in aggregating fetal brain cell cultures

Aggregating cell cultures prepared from fetal rat telencephalon express the two subunits [cerebellar soluble lectins (CSL) 1 and 2] of a soluble, mannose-specific endogenous lectin (CSL) in a development-dependent manner. Increased CSL synthesis was found at an early postmitotic stage as well as during the period of maximal myelination. Repetitive treatment of early cultures with epidermal growth factor (EGF, 3nM) caused a great stimulation of CSL biosynthesis. Immunocytochemical studies revealed particularly intense CSL-specific staining in small, EGF-responsive cells, presumably glial cells. Large quantities of CSL-immunoreactive material were found also in the extracellular space and on the external side of the plasma membrane, indicating abundant release of CSL. The present findings suggest that EGF or EGF-related factors in the brain are able to regulate the expression of an endogenous lectin, affecting brain ontogeny.

An endogenous lectin found in rat astrocyte cultures has a role in cell adhesion but not in cell proliferation

The presence of an endogenous cerebellar soluble lectin (CSL) has been demonstrated in cultured rat astrocytes by using immunocytochemical techniques. In these cells, the location of lectin CSL was found intracellularly as well as on the external surface of the plasma membrane of the cell bodies and processes, especially in the zones of contact between cells. This suggested that CSL could have a role in adhesion of astrocytes to sister cells. Kinetics of adhesion of astrocytes to culture dishes precoated with CSL showed a rapid binding of these cells. In confluent astrocyte cultures, anti-CSL Fab fragments affected the shape and organization of astrocytes (retraction of the cytoplasm), but they did not detach cells from the substratum. These results indicated that CSL has adhesive properties for astroglial cells and is probably involved 1) in adhesion of astrocytes to sister cells; 2) in binding of protoplasmic regions of astrocyte membrane to the substratum. Further support for these roles came from demonstration of the presence in cultures of glycoprotein ligands recognized by this lectin. The problem of the mitogenic properties of the lectin was also questioned. The addition of CSL to confluent astroglial cultures was able to stimulate only by 40% the proliferation of these cells at an optimal concentration of 5 micrograms CSL lectin/ml of culture medium. This indicated that CSL is not a powerful growth factor for astrocytes.

Location of a transiently expressed glycoprotein in developing cerebellum delineating its possible ontogenetic roles

The development pattern of a 31,000 mol. wt phosphatidyl inositol-anchored membrane glycoprotein was followed during development in mouse and rat cerebellum using monoclonal antibody 194-653. The epitope was developmentally regulated and particularly abundant in post mitotic precursors of granule cells, newly formed parallel fibres and unmyelinated axons of the white matter between the 5th and the 15th postnatal days. It decreased considerably thereafter. In the adult, a significant although relatively low staining was observed only in white matter. Observation at the ultrastructural level showed that most of the 31,000 mol. wt glycoprotein was very concentrated on neuronal plasma membranes. A little immunoreactivity was also found intracellularly at the perinuclear membrane of neuroblasts of the external germinal layer. The antigen was present in the coated pits and intracellularly in coated vesicles. Immunochemical studies indicated that 31,000 mol. wt antigen was very likely to be a previously identified transient concanavalin A-binding glycoprotein insoluble in neutral detergents (Reeber et al., 1981; Brain Res. 229, 53-65). It appeared to be one of the glycoprotein ligands for two endogenous mannosyl-lectins isolated from rat cerebellum (Zanetta et al., 1985, Devl. Brain Res. 17, 233-243, Zanetta et al., 1987, J. Neurochem. 49, 1250-1257). The affinity of the 31,000 mol. wt glycoprotein for the two endogenous lectins, together with its developmental pattern and localization indicate that it could be an important molecule for contact guidance during migration of neurons and for myelination and could take part in other ontogenetic steps.