The neural cell adhesion molecule (NCAM) as a regulator of cell-cell interactions

Effects of chronic stress on contextual fear conditioning and the hippocampal expression of the neural cell adhesion molecule, its polysialylation, and L1

Chronic stress has been shown to induce time-dependent neurodegeneration in the hippocampus, ranging from a reversible damage to a permanent neuronal loss. This damage has been proposed to impair cognitive function in hippocampus-dependent learning tasks. In this study, we have used a 21-day restraint stress procedure in rats, previously reported to induce reversible atrophy of apical dendrites of CA3 pyramidal cells, to assess whether it may influence subsequent performance in the contextual fear conditioning task under experimental conditions involving high stress levels (1 mA shock intensity as the unconditioned stimulus). In addition, we were interested in the study of the possible cellular and molecular mechanisms involved in the reversible phase of neural damage. Cell adhesion molecules of the immunoglobulin superfamily, such as the neural cell adhesion molecule and L1, are cell-surface macromolecules that, through their recognition and adhesion properties, regulate cell-cell interactions and have been reported to play a key role in cognitive functioning. A second aim of this study was to evaluate whether chronic stress would modulate the expression of the neural cell adhesion molecule, its polysialylation, and L1 in the hippocampus. The results showed that chronic stress facilitated subsequent contextual fear conditioning. They also showed that chronically stressed rats displayed reduced hippocampal neural cell adhesion molecule, but increased polysialylated expression as well as a trend towards exhibiting increased L1 expression. In summary, these results support the view that a 21-day chronic stress regimen predisposes individuals to develop enhanced contextual fear conditioning responses. They also indicate that cell adhesion molecules might play a role in the structural remodelling that occurs in the hippocampus as a consequence of chronic stress exposure.

PSA-NCAM modulates BDNF-dependent survival and differentiation of cortical neurons

We show that the loss or inactivation of the polysialic acid (PSA) tail of neural cell adhesion molecule (NCAM) on rat cortical neurons in culture leads to reduced differentiation and survival. The mechanism by which this negative effect is mediated appears to involve the neuronal response to brain-derived neurotrophic factor (BDNF): (i) in the absence of PSA or in the presence of excess free PSA added to the culture medium, BDNF-induced cell signalling is reduced; (ii) the addition of exogenous BDNF to the medium reverses the effect of PSA loss or inactivation. These data suggest that PSA-NCAM, previously shown to modulate cell migration and plasticity, is needed for an adequate sensitivity of neurons to BDNF.

A nude mice model of human rhabdomyosarcoma lung metastases for evaluating the role of polysialic acids in the metastatic process

PSA is an oncodevelopmental antigen usually expressed in human tumors with high metastatic potential. Here we set up a metastatic model in nude mice by using TE671 cells, which strongly express PSA-NCAM. We observed the formation of lung metastases when TE671 cells were injected intravenously, intramuscularly, and intraperitoneally, but not subcutaneously. Intraperitoneal injections also induced peritoneal carcinosis, ascites, and liver metastases. To evaluate the putative role of PSA in the metastatic process we used a specific cleavage of PSA on NCAM by endoneuraminidase-N on intraperitoneal primary tumors. Mice with primary intramuscular tumors were taken as control. Repeated injections of endoneuraminidase-N led to a decrease in PSA expression in primary intraperitoneal nodules and ascites but not in intramuscular primary tumors. Endoneuraminidase-N also increased the delay in ascitic formation and decreased the number of lung or liver metastases in the case of intraperitoneal tumors but not in the case of intramuscular tumors. When metastases occurred in endoneuraminidase-N injected animals, they strongly expressed PSA-NCAM. Therefore, we established a relationship between PSA expression on the surface of primary tumor cells and the metastatic process.

Oligodendrocyte precursor migration and differentiation: combined effects of PSA residues, growth factors, and substrates

Using the oligosphere strategy (V. Avellana-Adalid et al., 1996, J. Neurosci. Res. 45, 558-570), we compared the migratory behavior of oligodendrocyte preprogenitors (OPP) that expressed the polysialylated form of the neural cell adhesion molecule (PSA-NCAM) and of GD3-positive oligodendrocyte progenitors (OP). To study the role of PSA in OPP migration, we used endoneuraminidase-N, which specifically cleaves PSA from NCAM. Kinetic data showed that (i) migration velocity decreased with time and was favored on polyornithine compared to Matrigel; (ii) cells emerging from spheres enriched in PSA-NCAM+ OPP migrated farther than those from spheres enriched in GD3+ OP, their migration being enhanced by the addition of growth factors; (iii) removal of PSA from NCAM moderately reduced OPP migration and induced their differentiation in GD3+ OP and GFAP+ astrocytes; (iv) blocking integrins reduced their migration, suggesting an alternative mechanism of migration. Altogether these data illustrate that motility and differentiation of OPP involve the combinatorial action of PSA-NCAM, molecules of the ECM and their receptors, and growth factors.

Biosynthetic incorporation of unnatural sialic acids into polysialic acid on neural cells

In this study we demonstrate that polysialyltransferases are capable of accepting unnatural substrates in terminally differentiated human neurons. Polysialyltransferases catalyze the glycosylation of the neural cell adhesion molecule (NCAM) with polysialic acid (PSA). The unnatural sialic acid analog, N-levulinoyl sialic acid (SiaLev), was incorporated into cell surface glycoconjugates including PSA by the incubation of cultured neurons with the metabolic precursor N-levulinoylmannosamine (ManLev). The ketone group within the levulinoyl side chain of SiaLev was then used as a chemical handle for detection using a biotin probe. The incorporation of SiaLev residues into PSA was demonstrated by protection from sialidases that can cleave natural sialic acids but not those bearing unnatural N-acyl groups. The presence of SiaLev groups on the neuronal cell surface did not impede neurite outgrowth or significantly affect the distribution of PSA on neuronal compartments. Since PSA is important in neural plasticity and development, this mechanism for modulating PSA structure might be useful for functional studies.

PSA-NCAM distinguishes reactive astrocytes in 6-OHDA-lesioned substantia nigra from those in the striatal terminal fields

6-hydroxydopamine (6-OHDA) lesion of the substantia nigra (SN) causes the appearance of reactive astrocytes not only in the SN but also in the striatal terminal fields, as measured by increased size of the cells and their processes, as well as enhanced expression of glial fibrillary acidic protein (GFAP) and an epitope recognized by monoclonal antibody 19D1. We now demonstrate that polysialylated neural cell adhesion molecule (PSA-NCAM) is induced on reactive astrocytes, as well as on large neurons, on the ipsilateral side of the 6-OHDA-lesioned SN. Colocalization of GFAP and PSA-NCAM was confirmed for reactive astrocytes using a confocal laser scanning microscope. Negligible amounts of PSA-NCAM reactivity were detected contralaterally, although colocalization was noted on astrocytes with sparse, significantly thinner processes. In contrast to the increase of GFAP in the lesioned striatum, few striatal astrocytes expressed PSA-NCAM. In agreement with these results, PSA-NCAM was detected on cultured reactive astrocytes from SN but not reactive striatal astrocytes. Double immunohistochemistry for proliferating cell nuclear antigen (PCNA), a marker of dividing cells, and GFAP demonstrated that reactive astrocytes in lesioned SN were PCNA-positive whereas those in striatum were not. Although NG2 chondroitin sulfate proteoglycan expression also increased in the lesioned SN, NG2 was not colocalized with PSA-NCAM, was not expressed on astrocytes, and labeled only oligodendrocyte precursor cells. Our results suggest that PSA-NCAM can act as a marker for reactive astrocytes only at the site of the lesion and not in the terminal fields, probably because it is reexpressed only when astrocytes divide.

Localization of epidermal growth factor receptors and putative neuroblasts in human subependymal zone

Studies in rodents and monkeys suggest that neuronal precursor cells continue to exist and differentiate well into adulthood in these species. These results challenge the long held assumption that neurogenesis does not occur in the postnatal human brain. We examined the rostral subependymal zone (SEZ) of postnatal human brain for expression of cell phenotypic markers that have been associated with neuronal precursors and neuroblasts in rodent brain. We found epidermal growth factor receptor (EGF-R) mRNA and protein to be expressed in infant, teen, young adult, and adult human SEZ. Some SEZ cells expressed the polysialic acid form of neural cell adhesion molecule (PSA-NCAM), characteristic of migrating neuroblasts, as well as class III beta-tubulin and Hu protein, characteristic of neuroblasts and early neurons. These neuroblast-like cells were negative for glial fibrillary acidic protein (GFAP), 2;,3;-cyclic nucleotide 3;-phosphohydrolase (CNPase), and vimentin, suggesting that they were not differentiating as glia. Our results show that neuroblast-like cells exist in the human SEZ and support the theory that SEZ of postnatal human brain has neurogenic potential.

N-CAM binding inhibits the proliferation of hippocampal progenitor cells and promotes their differentiation to a neuronal phenotype

Cell adhesion molecules (CAMs) play important roles during the development of the nervous system. On the basis of our previous observations that binding of the neural CAM (N-CAM) inhibits astrocyte proliferation and alters gene expression, we hypothesized that N-CAM may influence the balance between the proliferation and the differentiation of neural progenitor cells. Rat and mouse hippocampal progenitor cells were cultured and showed dependence on basic FGF for proliferation, immunoreactivity for nestin, the presence of limited numbers of differentiated cells, and the ability to generate glial cells and neurons under different culture conditions. Addition of soluble N-CAM reduced cell proliferation in a dose-dependent manner with no evidence of apoptosis. The inhibition of proliferation by N-CAM was accompanied by an induction of differentiation to the neuronal lineage, as indicated by a twofold increase in the percentage of microtubule-associated protein 2-positive cells even in the presence of mitogenic growth factors. Experiments using hippocampal cells from N-CAM knock-out mice indicated that N-CAM on the cell surface is not required for these effects, suggesting the existence of heterophilic signaling. These results support a role for N-CAM and N-CAM ligands in the inhibition of proliferation and the induction of neural differentiation of hippocampal neural progenitor cells.

Glycocalyx modulation is a physiological means of regulating cell adhesion

Here we present experimental evidence that phagocytic cells use modulation of specific components of their glycocalyx to regulate their binding capacity. Particles coated with antibodies specific for the CD32 medium affinity IgG receptor were driven along human monocytic THP-1 cells (expressing CD32) in a flow chamber operated at low shear rate. Surprisingly, only minimal adhesion was observed. However, when cells were activated by exposure to fibronectin-coated surfaces and/or soluble γ interferon, adhesion efficiency was dramatically increased, whereas the apparent glycocalyx thickness displayed 20% decrease, and the surface density of CD43/leukosialin carbohydrate epitopes displayed 30–40% decrease on activated cells. The existence of a causal link between adhesion increase and glycocalyx alteration was strongly supported by the finding that (i) both phenomena displayed similar kinetics, (ii) an inverse relationship between THP-1 cell binding capacity and glycocalyx density was demonstrated at the individual cell level, and (iii) adhesion enhancement could not be ascribed to an increased binding site density or improved functional capacity of activated cells. Additional experiments revealed that cell-to-particle adhesion resulted in delayed (i.e. more than a few minutes) egress of CD43/leukosialin from contact areas. Since the time scale of particle attachment was less than a second, surface mobility should not affect the potential of CD43 to impair the initial step of adhesion. Finally, studies performed with fluorescent lectins suggested that THP-1 cell activation and increased adhesive potential were related to a decrease of O-glysosylation rather than N-glycosylation of surface glycoproteins.

Differentiation and proliferation of pulmonary neuroendocrine cells

In this review article the morphological profiles of pulmonary neuroendocrine cells (PNEC) in experimental animals and humans are described. Although the mechanisms of differentiation and proliferation of neuroendocrine cells in the airway epithelium remain to be solved, several experimental studies using explant culture and cell culture systems of fetal animal lungs have been performed to clarify fundamental phenomena associated with neuroendocrine differentiation and proliferation. Experimental animal studies using chronic hypoxia, toxic substances and carcinogens have succeeded in inducing alterations in PNEC systems, and these studies have elucidated the reactions of PNEC in cell injury and inflammation, and functional aspects of PNEC in disease conditions. Human pulmonary neuroendocrine tumors include various histological subtypes, and show divergent morphological and biological varieties. Molecular abnormalities of small cell carcinoma, the most aggressive subtype of pulmonary neuroendocrine tumors, have been extensively studied, but the mechanism of neuroendocrine differentiation of this tumor is still largely unknown. PNEC share common phenotypes with neuronal cells, and developmental studies have begun contributed evidence that similar transcriptional networks, including active and repressive basic helix-loop-helix (bHLH) factors, function in the differentiation of both PNEC and neuronal cells. Such a bHLH network may also play a central role in determining cell differentiation in lung carcinomas. Further studies of the neuronal bHLH network, its regulatory system and related signal transduction pathways, will be required for understanding the mechanisms of neuroendocrine differentiation and proliferation in normal and pathological lung conditions.

Brain-derived neurotrophic factor restores long-term potentiation in polysialic acid-neural cell adhesion molecule-deficient hippocampus

The neural cell adhesion molecule (NCAM) and its polysialylated form (PSA-NCAM) contribute to long-term potentiation (LTP) in the CA1 hippocampus. Here we report that the deficient LTP found in slices prepared from NCAM knockout mice and in organotypic slice cultures treated with Endo-N, an enzyme that cleaves the PSA moiety of NCAM, can be rescued by brain-derived neurotrophic factor (BDNF). This effect is not reproduced by nerve growth factor, but can be obtained with high concentrations of NT4/5. The effect of BDNF cannot be accounted for by modifications of N-methyl-D-aspartate receptor-dependent responses or of high-frequency bursts. PSA-NCAM, however, could directly interact with BDNF. Exogenous application of PSA residues or recombinant PSA-NCAM also prevents LTP. Furthermore trkB phosphorylation, and thus BDNF signaling, is reduced in both NCAM knockout mice and Endo-N-treated slice cultures. These results suggest that one action of PSA-NCAM could be to sensitize pyramidal neurons to BDNF, thereby modulating activity-dependent synaptic plasticity.

PSA-NCAM: an important regulator of hippocampal plasticity

The Neural Cell Adhesion Molecule (NCAM) serves as a temporally and spatially regulated modulator of a variety of cell-cell interactions. This review summarizes recent results of studies aimed at understanding its regulation of expression and biological function, thereby focussing on its polysialylated isoforms (PSA-NCAM). The detailed analysis of the expression of PSA and NCAM in the hippocampal mossy fiber system and the morphological consequences of PSA-NCAM deficiency in mice support the notion that the levels of expression of NCAM are important not only for the regulation and maintenance of structural changes, such as migration, axonal growth and fasciculation, but also for activity-induced plasticity. There is evidence that PSA-NCAM can specifically contribute to a presynaptic form of plasticity, namely long-term potentiation at hippocampal mossy fiber synapses. This is consistent with previous observations that NCAM-deficient mice show deficits in spatial learning and exploratory behavior. Furthermore, our data points to an important role of the hypothalamic-pituitary-adrenal axis, which is the principle adaptive response of the organism to environmental challenges, in the control of PSA-NCAM expression in the hippocampal formation. In particular, we evidence an inhibitory influence of corticosterone on PSA-NCAM expression.

Synaptic target recognition at Drosophila neuromuscular junctions

Every synaptogenesis begins with "synaptic target recognition," a cell-cell recognition event in which a neuron and its target stably adhere. Despite its importance in developing nervous systems, synaptic target recognition has been difficult to study in complex systems. The relatively simple and genetically accessible Drosophila NMJ model system provides a repertoire of target recognition cues. We describe how these molecules control the targeting of specific growth cones in either a positive (synaptogenic) or negative (anti-synaptogenic) manner. We also propose two alternate signaling paradigms to explain how these initial cell recognition events are coupled to the intracellular signaling pathways that begin the process of synapse maturation.

Polysialyltransferase-1 autopolysialylation is not requisite for polysialylation of neural cell adhesion molecule

Polysialyltransferase-1 (PST; ST8Sia IV) is one of the alpha2, 8-polysialyltransferases responsible for the polysialylation of the neural cell adhesion molecule (NCAM). The presence of polysialic acid on NCAM has been shown to modulate cell-cell and cell-matrix interactions. We previously reported that the PST enzyme itself is modified by alpha2,8-linked polysialic acid chains in vivo. To understand the role of autopolysialylation in PST enzymatic activity, we employed a mutagenesis approach. We found that PST is modified by five Asn-linked oligosaccharides and that the vast majority of the polysialic acid is found on the oligosaccharide modifying Asn-74. In addition, the presence of the oligosaccharide on Asn-119 appeared to be required for folding of PST into an active enzyme. Co-expression of the PST Asn mutants with NCAM demonstrated that autopolysialylation is not required for PST polysialyltransferase activity. Notably, catalytically active, non-autopolysialylated PST does not polysialylate any endogenous COS-1 cell proteins, highlighting the protein specificity of polysialylation. Immunoblot analyses of NCAM polysialylation by polysialylated and non-autopolysialylated PST suggests that the NCAM is polysialylated to a higher degree by autopolysialylated PST. We conclude that autopolysialylation of PST is not required for, but does enhance, NCAM polysialylation.

JLP5B9: new monoclonal antibody against polysialylated neural cell adhesion molecule is of value in phenotyping lung cancer

Non-small-cell lung cancer (NSCLC) is currently one of the most prevalent malignant tumors. It displays a wide variety of phenotypes which includes neuroendocrine markers commonly found on small-cell lung cancers (SCLC) such as the neural cell adhesion molecule (NCAM) and in particular its highly polysialylated isoform, embryonic NCAM (eNCAM). NSCLC with neuroendocrine differentiation may represent a subset of tumors whose cells have a more aggressive biological behavior. A tumor marker that distinguishes this latter sub-type could be of clinical relevance. Accordingly, we have raised a monoclonal antibody of the IgM type (JLP5B9) directed against capsular polysaccharides of N. meningitidis B which bears polysialic acid groups. We have demonstrated that JLP5B9 recognizes eNCAM with high affinity and that it is specifically directed against the polysialic acid moieties of NCAM. JLP5B9 was also found to react with human SCLC, NSCLC and neuroblastoma cell lines. We then used JLP5B9 as a specific probe for the detection of tissue eNCAM and found that it was expressed on up to 20% of tumor cells obtained from 5 out of 13 patients with NSCLC. This mAb deserves further investigation to evaluate its potential as a tool for serodiagnosis of lung cancer.

Role of carbohydrate structures in CEA-mediated intercellular adhesion

Human carcinoembryonic antigen (CEA) is a member of a family of cell surface glycoproteins representing a subset of the immunoglobulin superfamily and is a major tumor marker. CEA has been demonstrated to function in vitro, at least, as a homotypic intercellular adhesion molecule. CEA can also inhibit the differentiation of several different cell types and contribute to tumorigenesis, an activity that requires CEA-CEA interactions. Post-translational modifications that could modulate CEA-CEA binding are therefore of interest. CEA is heavily glycosylated with 28 consensus sites for the addition of asparagine-linked carbohydrate structures, leading to a molecule with a bottle brush-like structure. In order to modulate the glycosylation of CEA, we transfected the functional cDNA of CEA into Chinese hamster ovary (CHO) mutant cells, Lec1, Lec2, and Lec8, which are deficient in enzymes responsible for various steps in the glycosylation processing pathway. Aggregation assays of cells in suspension were performed with stable CEA transfectants of these cell lines and showed that all of the aberrant CEA glycoforms could still mediate adhesion. In addition, the specificity of adhesion of these glycoforms was unchanged, as shown by homotypic and heterotypic adhesion assays between the transfectants. Lec1 and Lec2 transfectants did, however, show an increased speed and final extent of aggregation, which is consistent with models in which sugar structures interfere with binding through protein domains. Lec8 transfectants, on the other hand, with more truncated sugar structures than Lec2, showed less aggregation than wild type (WT) transfectants. We therefore conclude that carbohydrates do not determine the adhesion property of CEA or its specificity, in spite of the unusually high degree of glycosylation; they do, however, modulate the strength of adhesion.

Molecular cloning and characterization of a novel bacteriophage-associated sialidase

Bacteriophage 63D, previously isolated from sewage, is associated with alpha-2,8-linked polysialic acid degrading activity. We cloned a DNA fragment containing the sialidase gene from a 63D phage genomic library and the enzyme was functionally expressed in Escherichia coli. Determination of the nucleotide sequence of the fragment revealed that it contained one open reading frame (ORF) coding for a 108-kDa polypeptide consisting of 984 amino acid residues. The fragment had promoter sequences similar to the E. coli consensus promoters for sigma70. The deduced amino acid sequence of the central region of the ORF showed homology to those of phages K1F (51.6% identity) and PK1E (51.7% identity) endosialidases. Two Asp-box motifs that are widely found in sialidases were conserved. Purification of the soluble enzyme from lysed culture broth of infected E. coli yielded a 90-kDa protein upon SDS polyacrylamide gel electrophoresis, suggesting that the primary translational product is processed to the mature 90-kDa protein. The molecular mass of the enzyme was determined as 360 kDa by gel filtration, indicating that the native enzyme was probably a tetramer of identical 90-kDa subunits.

Electrical and chemical synaptic transmission as an interacting system

It is proposed that presynaptic potassium efflux triggered by the nerve impulse may generate either excitatory or inhibitory responses depending on the neurotransmitter which more or less steadily impregnates the postsynaptic membrane. The jelly intersynaptic matrix may potentiate the efficiency of inoic intersynaptic signals. The synaptic vesicles are proposed to shuttle mitochondrial ATP towards the presynaptic membrane, thereby supplying the energy necessary to restore the membrane polarity after synaptic transmission. Plain structural data and currently accepted functional antecedents appear to justify the proposal.

Cytoplasmic domain is not essential for the cell adhesion activities of gicerin, an Ig-superfamily molecule

Gicerin is a cell adhesion molecule in the immunoglobulin (Ig) superfamily and is expressed abundantly during development in the nervous system. It has homophilic cell adhesion activity and also has heterophilic binding activity with NOF (neurite outgrowth factor) and mediates neurite extension. There are two isoforms of gicerin, one with a short (s-gicerin) and the other with a longer cytoplasmic domain (l-gicerin). We have reported that s-gicerin possesses stronger activities than l-gicerin during cell aggregation, in NOF-binding, and in neurite extension. In this study, we established cell lines which expressed a mutant-gicerin whose cytoplasmic domain was deleted and we compared the above three biological activities of the mutant-gicerin with those of s- and l-gicerin. We found that the mutant-gicerin retained all these activities, but the activities were weaker than those of s-gicerin and almost the same as those of l-gicerin. We concluded that the cytoplasmic domain of gicerin is not essential for optimal adhesive activities of gicerin, but might be involved in the regulation of its activities.

Immunocytochemical assessment of bone marrow aspirates for monitoring response to chemotherapy in small-cell lung cancer patients

Recent reports have suggested that tumour cell immunodetection in bone marrow of small-cell lung cancer patients is by far more frequent than found cytohistologically and may have clinical relevance. This study evaluates primarily the efficacy of chemotherapy as method of in vivo purging, but also the relationship of marrow involvement with survival. A total of 112 bone marrow aspirates from 30 chemo-naïve patients were stained twice using anti-NCAM antibodies, first at diagnosis and then after chemotherapy (24 patients) or at disease progression (six patients). Marrow contamination was associated with lower survival (P = 0.002), and was also detected in 7/17 patients conventionally staged as having limited disease. At multivariate analysis, marrow involvement was an independent factor of unfavourable prognosis (P = 0.033). The amount of tumour contamination, before and after chemotherapy, remained unchanged also in responders and even in the subset of patients with apparent limited disease. Following chemotherapy, bone marrow became tumour negative only in 25% of initially positive responders and in none of non-responders. Our results indicate that (i) chemotherapy is not effective in purging bone marrow even in chemo-responsive patients and (ii) a subset of patients with limited disease and negative bone marrow aspirates might have a more favourable prognosis.

Neuronal progenitor-like cells expressing polysialylated neural cell adhesion molecule are present on the ventricular surface of the adult rat brain and spinal cord

In the adult rodent brain, it is now well established that neurons are continuously generated from proliferating neuronal progenitor cells located in the subventricular zone of the lateral ventricle (SVZ) and the dentate gyrus of the hippocampus. Recently, it has been shown that neurons can also be generated in vitro from various regions of the adult brain and spinal cord ventricular neuroaxis. As the highly polysialylated neural cell adhesion molecule (PSA-NCAM) has been shown to be specifically expressed by neuronal progenitor cells of the SVZ and the hippocampus, the present study was designed to determine whether cells expressing this molecule could be detected in the vicinity of the ventricular system of the adult rat brain and spinal cord. After double or triple immunostaining for different neuronal and glial markers, confocal microscopy was used to examine the surface of the ventricular neuroaxis in either 40- to 50-microm-thick transverse vibratome sections cut through different brain regions, or in 200- to 300-microm-thick tissue slices including the intact surface of the brain ventricles or of the spinal cord central canal. In untreated rats, PSA-NCAM, microtubule associated protein 2 (MAP2) and class III-beta-tubulin were found to be associated with a number of neuron-like cells located on the surface of the third and fourth ventricles and of the spinal cord central canal. The proliferation of the PSA-NCAM-immunoreactive (IR) neuron-like cells detected on the surface of the third and fourth ventricles was not affected by injection of epidermal growth factor (EGF) or basic fibroblast growth factor (bFGF) into these ventricles, but was stimulated by the combined injection of EGF + bFGF. These data indicate that cells exhibiting features of neuronal progenitors are present on the ependymal surface of the adult rat brain and spinal cord ventricular axis.

Cortical auditory dysfunction in children with oral clefts: relation with cleft type

OBJECTIVE

Up to 46% of individuals with oral clefts suffer from language-learning disabilities. The degree of these disabilities varies according to cleft type. The pathogenesis of cognitive malfunctioning or its relationship with cleft type is not known. We investigated persistence of auditory short-term memory (STM) that is implicitly involved in language-specific perception in children with clefts, grouped using fine-graded cleft classification.

METHODS

Cortical evoked potentials were recorded in 78 children with non-syndromic oral clefts and in 32 healthy peers. A mismatch negativity (MMN) potential that indexes preattentive detection of change in auditory input was obtained in response to tone sounds. In order to test durability of short-term memory traces, sounds were presented with three stimulation rates.

RESULTS

With slowest stimulation, MMN amplitudes were reduced in cleft children as compared to the healthy peers (P < 0.00065). Only cleft-lip children did not significantly differ from controls. Among isolated palatal clefts, the more posteriorly delimited the cleft was, the smaller was the amplitude of MMN. MMNs of smallest amplitudes were obtained in the subgroup of complete unilateral cleft of lip and palate.

CONCLUSIONS

Reduced MMN amplitudes, found in cleft children, imply deficiency in auditory STM trace maintenance. This dysfunction is likely to contribute to their language and learning disabilities. The MMN diminution with shorter/more posterior clefts suggests that differences in auditory cortex function are one of the underlying mechanisms of the cleft type-malcogniton association.

Developmental methylmercury administration alters cerebellar PSA-NCAM expression and Golgi sialyltransferase activity

Brain dysmorphogenesis and persistent psychomotor disturbances are hallmarks of developmental methylmercury (MeHg) exposure, but the molecular mechanisms underlying these effects are poorly understood. Targets of developmental MeHg exposure include neural cell adhesion molecules (NCAMs), sialoglycoconjugate molecules whose proper temporal and spatial expression is important at all stages of neurodevelopment and especially during synaptic structuring. To investigate the effects of MeHg on the temporal expression of NCAM during development, rat pups were dosed with 7.0 mg/kg MeHgCl (s.c.) on alternate days from postnatal days (PNDs) 3-13 and killed on PNDs 15, 30 and 60. Brain MeHg concentrations were determined in a subset of litters injected with CH(3)203Hg. Expression of NCAM180 protein and of NCAM180 polysialylation was examined in whole cerebellum homogenates, cerebellar synaptosomes and isolated cerebellar growth cones by Western blotting and immunocytochemical staining. NCAM sialyltransferase activity was assayed in preparations of purified Golgi apparatus from the cerebelli of rats treated in vivo, or following in vitro incubation with 0, 1, 2.5, or 7.5 microM MeHg for 2 h. At PND15, no change in NCAM180 protein expression was observed in any cerebellar preparations, but decreased polysialylation of NCAM180 was observed in cerebellar whole homogenates, synaptosomes and isolated growth cones. At PND30, both NCAM180 protein expression and NCAM180 polysialylation were elevated in whole homogenate preparations but not in synaptosomes. NCAM180 expression in MeHg-treated rats was similar to controls at PND60, 47 days after the last methylmercury administration. In vivo studies of cerebellar Golgi sialyltransferase activity revealed significant reductions in PND15 MeHg-treated rats as compared to controls, but no changes in sialyltransferase activity in PND30 and PND60 animals. In vitro experiments revealed decreasing sensitivity of cerebellar sialyltransferases to MeHg as the developmental age of the rat increased. Toxic perturbation of the developmentally-regulated expression of polysialylated NCAM during brain formation may disturb the stereotypic formation of neuronal contacts and could contribute to the behavioral and morphological disturbances observed following MeHg poisoning.

Effects of different immunolabeling techniques on the detection of small-cell lung cancer cells in bone marrow

Recent reports have suggested that the immunodetection of tumor cells in bone marrow of small-cell lung cancer (SCLC) patients is by far more effective than traditional cytohistological methods and that this may be clinically relevant. This study aimed to evaluate whether the level of detection of tumor cells in bone marrow is affected by different immunostaining methods. Using two anti-NCAM monoclonal antibodies (MAbs), we compared four different "sandwich" methods on cytospin preparations of the N592 human SCLC cell line and of bone marrow aspirates from 37 SCLC patients. Our data indicate that the combination of the alkaline phosphatase-anti-alkaline phosphatase and streptavidin-biotin-alkaline phosphatase complex methods provides the best results in terms of sensitivity and specificity, and of intensity of immunoreaction and absence of staining background. Moreover, bone marrow micrometastases detected by this method were prognostically relevant and identified, among patients with apparently limited disease according to conventional staging procedures, a subgroup with shorter survival. We suggest that the choice of a sensitive immunostaining technique may significantly increase the detection rate of SCLC cells in bone marrow, mirroring the biological aggressiveness of the disease.

A role for fasciclin II in the guidance of neuronal migration

The insect cell adhesion receptor fasciclin II is expressed by specific subsets of neural and non-neural cells during embryogenesis and has been shown to control growth cone motility and axonal fasciculation. Here we demonstrate a role for fasciclin II in the guidance of migratory neurons. In the developing enteric nervous system of the moth Manduca sexta, an identified set of neurons (the EP cells) undergoes a stereotyped sequence of migration along the visceral muscle bands of the midgut prior to their differentiation. Probes specific for Manduca fasciclin II show that while the EP cells express fasciclin II throughout embryogenesis, their muscle band pathways express fasciclin II only during the migratory period. Manipulations of fasciclin II in embryonic culture using blocking antibodies, recombinant fasciclin II fragments, and enzymatic removal of glycosyl phosphatidylinositol-linked fasciclin II produced concentration-dependent reductions in the extent of EP cell migration. These results support a novel role for fasciclin II, indicating that this homophilic adhesion molecule is required for the promotion or guidance of neuronal migration.

Arcadlin is a neural activity-regulated cadherin involved in long term potentiation

Neural activity results in long term changes that underlie synaptic plasticity. To examine the molecular basis of activity-dependent plasticity, we have used differential cloning techniques to identify genes that are rapidly induced in brain neurons by synaptic activity. Here, we identify a novel cadherin molecule Arcadlin (activity-regulated cadherin-like protein). arcadlin mRNA is rapidly and transiently induced in hippocampal granule cells by seizures and by N-methyl-D-aspartate-dependent synaptic activity in long term potentiation. The extracellular domain of Arcadlin is most homologous to protocadherin-8; however, the cytoplasmic region is distinct from that of any cadherin family member. Arcadlin protein is expressed at the synapses and shows a homophilic binding activity in a Ca2+-dependent manner. Furthermore, application of Arcadlin antibody reduces excitatory postsynaptic potential amplitude and blocks long term potentiation in hippocampal slices. Its close homology with cadherins, its rapid inducibility by neural activity, and its involvement in synaptic transmission suggest that Arcadlin may play an important role in activity-induced synaptic reorganization underlying long term memory.

Multistratified expression of polysialic acid and its relationship to VAChT-containing neurons in the inner plexiform layer of adult rat retina

We investigated the localization of polysialic acid (PSA), neural cell adhesion molecule (NCAM), and vesicular acetylcholine transporter (VAChT) in adult rat retina by using immunofluorescence with a confocal laser scanning microscope. Western blot analysis showed a typical broad smear of PSA and isoforms of NCAM (120, 140, and 180 kD). PSA immunofluorescence revealed multistratification in the inner plexiform layer (IPL). Dual immunostaining for PSA and NCAM exhibited the selective co-expression of PSA and NCAM on Müller cells. Moreover, dual immunolabeling for PSA and VAChT completely separated the five strata in the IPL. Strata 1, 3, and 5 were immunoreactive for PSA and Strata 2 and 4 for VAChT. These results suggest the possibility that PSA molecules on Müller cells are spatially related to ON and OFF retinal channels in the IPL.

Up-regulation of the alpha2,6-sialyltransferase messenger ribonucleic acid increases glycoconjugates containing alpha2, 6-linked sialic acid residues in granulosa cells during follicular atresia of porcine ovaries

The sugar chains in cellular glycoconjugates have many biological functions. Extensive morphological development and remodeling occur in the ovary of female animals. This caused us to study glycobiological characteristics of ovarian cells, particularly granulosa cells that undergo apoptosis during follicular atresia. The lectin Sambucus sieboldiana agglutinin (SSA) specific for Siaalpha2,6Gal/GalNAc showed positive staining for granulosa cells only in atretic follicles of porcine ovaries by lectin histochemistry. Lectin blot analysis for SSA demonstrated specific glycoproteins only in atretic follicles. Furthermore, we performed analysis of backbone structures of SSA-positive glycans carried by granulosa cell glycoproteins increased during atresia by glycosidase treatment. Most of these structures were Siaalpha2,6Galbeta1,4GlcNAc on complex-type N-glycans, suggesting that only ST6Gal I of four distinct alpha2,6-sialyltransferases catalyzes alpha2,6-sialic acid transfer in most of the increased glycoproteins of granulosa cells during follicular atresia. Reverse transcription-polymerase chain reaction analysis demonstrated that the expression of ST6Gal I mRNA was up-regulated in granulosa cells during atresia. These results suggested that the alteration of glycoconjugates by ST6Gal I in granulosa cells during atresia is involved in some processes of ovarian follicular atresia and granulosa cell apoptosis.

Developmental patterns of GalBeta1,3(4)GlcNAc alpha2,3-sialyltransferase (ST3Gal III) expression in the mouse: in situ hybridization using DIG-labeled RNA probes

Sialic acids are key determinants for biological processes, such as cell-cell interaction and differentiation. Sialyltransferases contribute to the diversity in carbohydrate structure through their attachment of sialic acid in various terminal positions on glycolipid and glycoprotein (N-linked and O-linked) carbohydrate groups. Galbeta 1,3(4)GlcNAc alpha2,3-sialyltransferase (ST3Gal III) is involved in the biosynthesis of sLe(x)and sLe(a) known as selectin ligands and tumor-associated carbohydrate structures. The appearance and differential distribution of ST3Gal III mRNA during mice embryogenesis [embryonic (E) days; E9, E11, E13, E15] were investigated by in situ hybridization with digoxigenin-labeled RNA probes coupled with alkaline phosphatase detection. On E9, all tissues were positive for ST3Gal III mRNA expression, whereas ST3Gal III mRNA on E11 was not detected throughout all tissues. On E13, ST3Gal III mRNA was expressed in different manner in various tissues. In this stage, ST3Gal III mRNA was positive only in the liver, pancreas and bladder. On E15, specific signal for ST3Gal III was detected in the liver, lung and forebrain. These results indicate that ST3GAI III is differently expressed at developmental stages of mice embryo, and this may be importantly related with regulation of organogenesis in mice.

Stage specific glycosylation pattern for lactoseries carbohydrates in the developing chick retina

Based on the idea of differentiation-related changes in the glycosylation pattern of neurons, the expression of two cell surface oligosaccharide epitopes, N-acetyl-lactosamine (NALA), and its sulpho-glucuronyl derivative (HNK-1), was studied, by immunohistochemistry and Western blot experiments, in the developing chick retina beginning on day 2 of incubation (E2) until day 18 post-hatching. NALA was detectable on neuroepithelial cells as soon as the primary optic vesicles formed, and this pattern continued until E3. During subsequent retinal development NALA expression became progressively restricted in concert with the appearance of postmitotic neurons as revealed by neurite outgrowth, and with the formation of synaptic contacts until it disappeared at the end of the incubation period. The pattern of NALA expression was the inverse of HNK-1 which was detected for the first time at E3 on postmitotic ganglion cells accumulating at the vitreal surface. The number of HNK-1+ cells steadily increased until around E10, when the entire neural epithelium was labelled. Synchronously to synaptogenesis, most neurons lost their HNK-1 immunoreactivity. At the time of hatching the adult-like pattern was found, characterised by subpopulations of labelled horizontal, bipolar, amacrine, and ganglion cells. Immunoblot experiments demonstrated transient NALA glycosylation of protein bands, partially identical in their apparent molecular weight to those proteins with HNK-1 glycosylation. The observed temporospatial changes in the glycosylation patterns of distinct proteins during retinal development suggest NALA as a suitable marker for neuronal proliferation, and HNK-1 for differentiation and establishment of final synaptic configuration.

Sialylation of E-cadherin does not change the spontaneous or ET-18-OMe-mediated aggregation of MCF-7 human breast cancer cells

We have investigated the role of sialylation on cell-cell adhesion mediated by E-cadherin. Two MCF-7 human breast cancer cell variants were studied: MCF-7/AZ cells showed a spontaneous cell-cell adhesion in the fast and slow aggregation assay. whereas the adhesion deficient MCF-7/6 cell variant failed to form larger aggregates, suggesting that E-cadherin was not functional under the conditions of both assays. We measured the sialyltransferase activities using Galbeta1-3GalNAcalpha-O-benzyl and Galbeta1-4GlcNAcalpha-O-benzyl as acceptor substrates as well as mRNA levels of four sialyltransferases, ST3Gal I, ST3Gal III, ST3Gal IV, ST6Gal I, using multiplex RT-PCR in MCF-7 cell variants. The alpha2-6 and alpha2-3 sialylation of E-cadherin was investigated by immuno-blot using Sambucus nigra agglutinin and Maackia amurensis agglutinin. Compared to the adhesion-proficient MCF-7/AZ cells, the adhesion-deficient MCF-7/6 cell line apparently lacks ST6Gal I mRNA, has a lower ST3Gal I mRNA, a lower ST3Gal I sialyltransferase activity, and no alpha2-3 linked sialic acid moieties on E-cadherin. The potential anti-cancer drug 1-O-octadecyl-2-O-methylglycero-3-phosphocholine (ET-18-OMe, 48 h, 25 microg/ml) belonging to the class of alkyllysophospholipids restored the E-cadherin function in the adhesion-deficient MCF-7/6 cells as evidenced by an increased aggregation. ET-18-OMe caused loss of ST6Gal I mRNA in MCF-7/AZ cells but no changes of sialyltransferase activities or sialic acid moieties on E-cadherin could be observed. We conclude that Ca2+-dependent, E-cadherin-specific homotypic adhesion of MCF-7/AZ or MCF-7/6 cells treated with ET-18-OMe was not affected by sialylation of E-cadherin.

Nerve cell adhesion molecule expression in squamous cell carcinoma of the head and neck: a predictor of propensity toward perineural spread

OBJECTIVE

To evaluate head and neck squamous cell carcinomas (SCCAs) for the expression of nerve cell adhesion molecule (N-CAM). We propose that expression of N-CAM by tumor cells may be associated with perineural invasion in SCCA of the head and neck.

METHODS

Seventy-six archived specimens of histologically proven SCCA were analyzed by immunohistochemistry for the expression of N-CAM. Positive and negative controls were used to assess staining. Two sections of each specimen were reviewed for the presence of perineural invasion. A retrospective chart review was performed for each patient that corresponded to the above specimens.

RESULTS

Perineural invasion was present in 28 (37%) of the 76 patients evaluated for the expression of N-CAM. N-CAM expression was demonstrated in 38 (50%) of the 76 specimens. The incidence of N-CAM expression was significantly associated with perineural invasion (P = .002). There was no significant association between the presence of staining or the presence of perineural invasion and the incidence of locoregional recurrence, distant metastasis, or survival status; however, the mean follow-up was only 13.6 months (range, 1-49 mo).

CONCLUSION

There is a positive correlation between the presence of N-CAM expression and perineural invasion in SCCA of the head and neck. The expression of this adhesion molecule by tumor cells may facilitate both homophilic cell-to-cell and heterophilic cell-to-substrate adhesion, thereby enabling the tumor cells to use the perineural tissues or neural cells, or both as a conduit for perineural spread.

Expression of gicerin, a cell adhesion molecule, in the abnormal retina in silver plumage color mutation of Japanese quail (Coturnix japonica)

Silver plumage color mutant (B/B) quail has an abnormal retina characterizing the transdifferentiation of retinal pigment epithelium (RPE) following the retinal separation in the early developmental stage. In the present study; (i) the expression of gicerin, an immunoglobulin-superfamily cell adhesion molecule, was examined in the retina of B/B quail. In the wild-type quail, gicerin protein was enriched in the apical membrane (facing the neural retina, NR) of RPE cells on embryonic day (E) 4 and then appeared also in NR cells from E5. However, in the B/B retina, no gicerin expression was found in the transdifferentiation area of RPE prior to the retinal separation. (ii) In addition to this, microinjection of anti-gicerin polyclonal antibody into the eyeball of wild-type quail on E3 caused the retinal separation and induced the transdifferentiation of RPE into new NR. These observations suggest that the decrease of gicerin expression might participate in the retinal separation and RPE-transdifferentiation in B/B quail.

Involvement of gicerin, a cell adhesion molecule, in development and regeneration of oviduct and metastasis of oviductal adenocarcinomas of the chicken

Gicerin is a novel cell adhesion molecule in the immunoglobulin superfamily and has both homophilic adhesion and heterophilic adhesive activity to neurite outgrowth factor (NOF), an extracellular matrix protein in the laminin family. We investigated the possible involvement of gicerin in oviductal development, regeneration, and metastasis of oviductal adenocarcinomas of the chicken. In the oviductal epithelium, gicerin was expressed strongly during development, disappeared after maturation, and reappeared during regeneration. NOF was constitutively expressed in the basement membrane of the epithelium. These molecules were expressed strongly in oviductal adenocarcinomas in both primary and metastatic lesions in the mesentery. An anti-gicerin antibody inhibited the attachment of adenocarcinoma cells to the mesentery in vitro. Many cells migrated from adenocarcinoma tissues on NOF, which were inhibited by an anti-gicerin antibody. These results suggest that gicerin might play a role in oviductal development and regeneration and also in the metastasis of adenocarcinomas.

Interactions of neural glycosaminoglycans and proteoglycans with protein ligands: assessment of selectivity, heterogeneity and the participation of core proteins in binding

The method of affinity coelectrophoresis was used to study the binding of nine representative glycosaminoglycan (GAG)-binding proteins, all thought to play roles in nervous system development, to GAGs and proteoglycans isolated from developing rat brain. Binding to heparin and non-neural heparan and chondroitin sulfates was also measured. All nine proteins-laminin-1, fibronectin, thrombospondin-1, NCAM, L1, protease nexin-1, urokinase plasminogen activator, thrombin, and fibroblast growth factor-2-bound brain heparan sulfate less strongly than heparin, but the degree of difference in affinity varied considerably. Protease nexin-1 bound brain heparan sulfate only 1.8-fold less tightly than heparin (Kdvalues of 35 vs. 20 nM, respectively), whereas NCAM and L1 bound heparin well (Kd approximately 140 nM) but failed to bind detectably to brain heparan sulfate (Kd>3 microM). Four proteins bound brain chondroitin sulfate, with affinities equal to or a few fold stronger than the same proteins displayed toward cartilage chondroitin sulfate. Overall, the highest affinities were observed with intact heparan sulfate proteoglycans: laminin-1's affinities for the proteoglycans cerebroglycan (glypican-2), glypican-1 and syndecan-3 were 300- to 1800-fold stronger than its affinity for brain heparan sulfate. In contrast, the affinities of fibroblast growth factor-2 for cerebroglycan and for brain heparan sulfate were similar. Interestingly, partial proteolysis of cerebroglycan resulted in a >400-fold loss of laminin affinity. These data support the views that (1) GAG-binding proteins can be differentially sensitive to variations in GAG structure, and (2) core proteins can have dramatic, ligand-specific influences on protein-proteoglycan interactions.

Neural cell adhesion molecule (N-CAM) is required for cell type segregation and normal ultrastructure in pancreatic islets

Classical cell dissociation/reaggregation experiments with embryonic tissue and cultured cells have established that cellular cohesiveness, mediated by cell adhesion molecules, is important in determining the organization of cells within tissue and organs. We have employed N-CAM-deficient mice to determine whether N-CAM plays a functional role in the proper segregation of cells during the development of islets of Langerhans. In N-CAM-deficient mice the normal localization of glucagon-producing alpha cells in the periphery of pancreatic islets is lost, resulting in a more randomized cell distribution. In contrast to the expected reduction of cell-cell adhesion in N-CAM-deficient mice, a significant increase in the clustering of cadherins, F-actin, and cell-cell junctions is observed suggesting enhanced cadherin-mediated adhesion in the absence of proper N-CAM function. These data together with the polarized distribution of islet cell nuclei and Na+/K+-ATPase indicate that islet cell polarity is also affected. Finally, degranulation of beta cells suggests that N-CAM is required for normal turnover of insulin-containing secretory granules. Taken together, our results confirm in vivo the hypothesis that a cell adhesion molecule, in this case N-CAM, is required for cell type segregation during organogenesis. Possible mechanisms underlying this phenomenon may include changes in cadherin-mediated adhesion and cell polarity.

Fasciclin II and Beaten path modulate intercellular adhesion in Drosophila larval visual organ development

Previous studies demonstrated that Fasciclin II and Beaten path are necessary for regulating cell adhesion events that are important for motoneuron development in Drosophila. We observe that the cell adhesion molecule Fasciclin II and the secreted anti-adhesion molecule Beaten path have additional critical roles in the development of at least one set of sensory organs, the larval visual organs. Taken together, phenotypic analysis, genetic interactions, expression studies and rescue experiments suggest that, in normal development, secretion of Beaten path by cells of the optic lobes allows the Fasciclin II-expressing larval visual organ cells to detach from the optic lobes as a cohesive cell cluster. Our results also demonstrate that mechanisms guiding neuronal development may be shared between motoneurons and sensory organs, and provide evidence that titration of adhesion and anti-adhesion is critical for early steps in development of the larval visual system.

Expression of polysialylated NCAM but not L1 or N-cadherin by regenerating adult mouse optic fibers in vitro

This study asks if there might be irreversible maturational changes in adult neurons that limit their capacity to regenerate. Retina from adult and embryonic mouse were placed in culture on laminin substrates so that regenerating adult optic fibers could be compared to growing embryonic fibers. Several cell adhesion molecules (CAMs) known to mediate the growth of embryonic neurites on astrocytes were assayed by immunocytochemistry: L1, N-cadherin, and NCAM. Thy 1.2, a potential CAM with inhibitory activity, was also examined. As in vivo, embryonic fibers were found to express both L1 and N-cadherin. In contrast, regenerating adult fibers had no detectable amounts of either of these CAMs. N-Cadherin is normally down regulated during development so its absence in adult fibers suggests it can not be reexpressed during regeneration. L1 is normally found in the proximal regions of adult optic fibers so its absence indicates it is not expressed or transported in regenerating fibers. Adult regenerating fibers expressed high levels of Thy 1.2, which was undetectable in embryonic optic fibers. Thy 1.2 is normally found in mature fibers, indicating this phenotypic feature is preserved during regeneration. Both adult and embryonic fibers showed strong reactivity for NCAM, which in vivo is normally found in embryonic and at lower levels in adult fibers. Surprisingly, both embryonic and regenerating adult fibers expressed high levels of polysialic acid, which is normally absent in adult fibers. NCAM may be one of few CAMs available to adult optic fibers for regeneration on astrocytes.

Myelin does not influence the choice behaviour of entorhinal axons but strongly inhibits their outgrowth length in vitro

Myelin is crucial for the stabilization of the entorhinohippocampal projection during late development and is a non-permissive substrate for regrowing axons after lesion in the adult brain. We used two in vitro assays to analyse the impact of myelin on rat entorhinohippocampal projection neurons. A stripe assay was used to study the impact of myelin on the choice behaviour of axons from the entorhinal cortex (EC). Given a choice between alternating hippocampal membrane lanes from developmental stages ranging from early postnatal to adult, EC axons preferred to extend on early postnatal hippocampal membranes. Neither the neutralization of myelin-associated factors by a specific antibody (IN-1) nor the separation of myelin from membranes interfered with the axons' choice behaviour. The entorhinal axons showed no preference in the membrane combination of adult and myelin-free adult hippocampal membranes. These stripe assay experiments demonstrate that support for EC axon choice in the developing hippocampus is maturation-dependent and is not influenced by myelin. The application of IN-1 in the outgrowth assay and the separation of myelin from membranes, enhanced elongation of outgrowing entorhinal axons on adult hippocampal membranes, whereas a control antibody did not. This shows that myelin-associated factors have a strong inhibitory effect on the outgrowth length of entorhinal axons. In conclusion, we suggest that axonal elongation in the entorhinohippocampal system during development is strongly influenced by myelin-associated growth inhibition factors and that specific target finding of entorhinal axons is regulated by a different mechanism.

Cellular and molecular bases of axonal pathfinding during embryogenesis of the fish central nervous system

The accessibility of the zebrafish embryo offers unique possibilities to study the mechanisms that guide growing axons in the developing vertebrate central nervous system. This review examines the current understanding of the pathfinding decisions by the growing axons, their substrates, and the recognition molecules that mediate axon-substrate interactions. The detailed analysis of pathfinding at the level of individual axons demonstrates that growing axons chose their paths unerringly. To do so, they rely on cues presented by their environment, in particular by neuroepithelial cells. Our understanding of the molecular bases of axon-substrate interactions is increasing. Members of most classes of recognition molecules have been identified in fish. Experimental evidence for the functions of these molecules in the zebrafish nervous system is accumulating. In the future, this analysis is expected to profit greatly from genetic screens that have recently been initiated.

In vivo autopolysialylation and localization of the polysialyltransferases PST and STX

A select group of mammalian proteins have been shown to possess alpha2,8-polysialylated oligosaccharide chains. The best studied of these proteins is the neural cell adhesion molecule (NCAM). Polysialylation of NCAM has been shown to decrease NCAM-dependent and independent cell adhesion. PST (ST8Sia IV) and STX (ST8Sia II) are the two polysialyltransferases responsible for NCAM polysialylation. Recent studies revealed that PST itself is autopolysialylated in vitro (Muhlenhoff, M., Eckhardt, M., Bethe, A., Frosch, M., and Gerardy-Schahn, R. (1996) EMBO J. 15, 6943-6950). Here we report studies on the biosynthesis and localization of the PST and STX polysialyltransferases. Both PST and STX are expressed as high molecular mass, polydisperse forms that are associated with the cell and found soluble in the medium. Analysis of these high molecular mass forms by glycosidase digestion and serial immunoprecipitation/immunoblot experiments demonstrated that PST and STX are autopolysialylated in vivo. Indirect immunofluorescence microscopy and immunoprecipitation analyses demonstrated that autopolysialylated PST and STX are localized in the Golgi, on the cell surface, and in the extracellular space. The cell surface and extracellular localization of these polysialylated polysialyltransferases suggest that their polysialic acid chains, like those of NCAM, may modulate cell interactions.

Studies on the binding of wheat germ agglutinin (Triticum vulgaris) to O-glycans

The binding profile of Triticum vulgaris (WGA, wheat germ) agglutinin to 23 O-glycans (GalNAc alpha1-->Ser/Thr containing glycoproteins, GPs) was quantitated by the precipitin assay and its specific interactions with O-glycans were confirmed by the precipitin inhibition assay. Of the 28 glycoforms tested, six complex O-glycans (hog gastric mucins, one human blood group A active and two precursor cyst GPs) reacted strongly with WGA and completely precipitated the lectin added. All of the other human blood group A active O-glycans and human blood group precursor GPs also reacted well with the lectin and precipitated over two-thirds of the agglutinin used. They reacted 4-50 times stronger than N-glycans (asialo-fetuin and asialo-human alpha1 acid GP). The binding of WGA to O-glycans was inhibited by either p-NO2-phenyl alpha,betaGlcNAc or GalNAc. From these results, it is highly possible that cluster (multivalent) effects through the high density of weak inhibitory determinants on glycans, such as GalNAc alpha1-->Ser/Thr (Tn), GalNAc at the nonreducing terminal, GlcNAc beta1--> at the non-reducing end and/or as an internal residue, play important roles in precipitation, while the GlcNAc beta1-->4GlcNAc disaccharide may play a minor role in the precipitation of mammalian glycan-WGA complexes.

LHRH neurons migrate into the trigeminal nerve when the developing olfactory nerve fibers are physically interrupted in chick embryos

Most LHRH neurons actively migrate from the olfactory epithelium to the forebrain during embryonic days (ED) 3.5-8. When a small piece of the membrane filter was placed on the central course of the olfactory nerve in ED 3.5-5 chick embryos, LHRH neurons deviated from their regular migratory course at ED 6.5-7.5 to follow a route along the PSA-NCAM-positive medial and lateral nasal branches of the ophthalmic nerve of the trigeminal nerve. The olfactory nerve fibers which were specifically immunoreactive for somatostatin also deviated into the ophthalmic nerve. Enzymatic removal of PSA using endoneuraminidase did not interfere with the migration of LHRH neurons into the ophthalmic nerve bundle of the trigeminal nerve. The presence of structural supports seems to be primarily of importance in the migration of LHRH neurons along the olfactory and trigeminal nerve bundles. PSA may be less important for the migration of the LHRH neurons along peripheral neural elements.

Purification and characterization of a glucuronyltransferase involved in the biosynthesis of the HNK-1 epitope on glycoproteins from rat brain

The glucuronyltransferase involved in the biosynthesis of the HNK-1 epitope on glycoproteins was purified to an apparent homogeneity from the Nonidet P-40 extract of 2-week postnatal rat forebrain by sequential chromatographies on CM-Sepharose CL-6B, UDP-GlcA-Sepharose 4B, asialo-orosomucoid-Sepharose 4B, Matrex gel Blue A, Mono Q, HiTrap chelating, and HiTrap heparin columns. The purified enzyme migrated as a 45-kDa protein upon SDS-polyacrylamide gel electrophoresis under reducing conditions, but eluted as a 90-kDa protein upon Superose gel filtration in the presence of Nonidet P-40, suggesting that the enzyme forms homodimers under non-denatured conditions. The enzyme transferred glucuronic acid to various glycoprotein acceptors bearing terminal N-acetyllactosamine structure such as asialo-orosomucoid, asialo-fetuin, and asialo-neural cell adhesion molecule, whereas little activity was detected to paragloboside, a precursor glycolipid of the HNK-1 epitope on glycolipids. These results suggested that the enzyme is specifically associated with the biosynthesis of the HNK-1 epitope on glycoproteins. Sphingomyelin was specifically required for expression of the enzyme activity. Stearoyl-sphingomyelin (18:0) was the most effective, followed by palmitoyl-sphingomyelin (16:0) and lignoceroyl-sphingomyelin (24:0). Interestingly, activity was demonstrated only for sphingomyelin with a saturated fatty acid, i.e. not for that with an unsaturated fatty acid, regardless of the length of the acyl group.

A role for polysialic acid in neural cell adhesion molecule heterophilic binding to proteoglycans

The neural cell adhesion molecule (NCAM) is known to participate in both homophilic and heterophilic binding, the latter including mechanisms that involve interaction with proteoglycans. The polysialic acid (PSA) moiety of NCAM can serve as a negative regulator of homophilic binding, but indirect evidence has suggested that PSA can also be involved in heterophilic binding. We have examined this potential positive role for PSA in terms of the adhesion of PSA-expressing mouse F11 cells and chick embryonic brain cells to substrates composed of the purified heparan sulfate proteoglycans agrin and 6C4. This adhesion was specifically inhibited by polyclonal anti-NCAM Fab antibodies, monoclonal anti-PSA antibodies, PSA itself, and enzymatic removal of either PSA or heparan sulfate side chains. By contrast, the adhesion was not affected by chondroitinase, and cell binding to laminin was not inhibited by any of these treatments. A specific NCAM-heparan sulfate interaction in this adhesion was further indicated by its inhibition with monoclonal anti-NCAM Fab antibodies that recognize the known heparin-binding domain of NCAM and with the HBD-2 peptide derived from this region, but not with antibodies directed against other regions of the protein including the homophilic binding region. Together, the results suggest that PSA can act in vitro either as a receptor in NCAM heterophilic adhesion or as a promoter of binding between heparan sulfate proteoglycans and the NCAM heparin-binding domain.