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Galectins constitute a gene family of beta-galactoside-specific lectins that show high homology in their carbohydrate-binding site. They have been postulated to be involved in many biological events, but their specific functions are not yet well defined. Galectin-1 is a laminin binding protein that recognizes poly-N-acetyllactosamine chains on this major basement membrane glycoprotein. In this study, we analyzed the possibility that galectin-1 could modulate interactions between human melanoma cells and laminin. We demonstrated that A375 and A2058 cell lines express galectin-1 both intracellularly and on the cell surface. In an in vitro assay, recombinant galectin-1 increased melanoma cell attachment to laminin in a dose-dependent manner. This effect was abolished by lactose. Anti-galectin-1 inhibited adhesion of melanoma cells to laminin in a dose-dependent fashion. However, neither galectin-1 nor anti-galectin-1 antibody affected melanoma cell spreading on laminin in vitro. These data indicate that galectin-1 might participate in melanoma cell adhesion to laminin and therefore could be a modulator of invasion and metastasis.

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Soluble, dimeric, lactose-binding lectins with subunit M(r) of approximately 14-16 x 10(3), here called L-14s, are expressed in multiple tissues in all vertebrates that have been examined. L-14s have particular affinity for polylactosamine chains on laminin, co-localize with laminin in some basement membranes, and influence adhesion to laminin and proliferation for some cultured cells. In previous studies of mammals and chickens, L-14s have been found at high levels in a variety of adult tissues, such as muscle and peripheral nerve, but at much higher levels in many embryonic tissues, suggesting a special role in development. To further explore possible roles of L-14 in embryogenesis, we have studied the expression of L-14 in embryonic and adult Xenopus laevis tissues. Xenopus skin, we find that Xenopus L-14 is expressed in the same general distribution as its mammalian homologues. However, we could detect no expression of L-14 in Xenopus embryos using either a sensitive immunoassay for the protein or a sensitive RNase protection assay for its mRNA. Furthermore, use of affinity chromatography to identify other lactose-binding lectins in embryonic tissue revealed only scarce proteins with higher subunit molecular weights. These results suggest that in X.laevis L-14 functions in adult tissues and is not involved in embryogenesis.

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There is a large body of suggestions that complex carbohydrates play a role in the regulation of cell adhesion and cell proliferation. Many reports have emphasized that proteoglycans, glycoproteins or glycolipids are participating to cell adhesion mechanisms. The use of polyvalent anti-carbohydrate antibodies and plant lectins as well as the use of glycosylation inhibitors suggested that cell proliferation can be modulated by surface carbohydrates. The dating experiment of Burger and Noonan (1970) showing restoration of contact inhibition of malignant cells by monovalent concanavalin A was a determining experiment. However, in the latter as in the others, no precise mechanism was demonstrated how carbohydrates can be involved in adhesion and proliferation. New insights were opened with the discovery of vertebrate membrane-bound and soluble lectins. The latter generally display agglutinating activities in in vitro systems, suggesting that they were potential cell adhesion molecules, by forming bridges between cell surface carbohydrates. These polyvalent molecules may be also considered as clustering agents for their cell surface ligands, consequently generating signals for cell proliferation and/or differentiation.

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The role of the endogenous brain carbohydrate-binding protein R1 in muscle cell development and regeneration was analysed both in vivo and in vitro. In vivo, R1 was developmentally regulated, with an embryonic 65,00 subunit and a neonatal 67,000 subunit, being replaced progressively by a 135,000 adult form. Lectin R1 was intracellularly localized at birth and in the prenatal period. During development and at the time of myoblast fusion, the antigen was progressively found at the surface, where it remained at low levels in the adult. In vitro, in pure myoblast cultures, only the embryonic form was present. The ultrastructural studies indicated that the lectin could participate in the membrane fusion process during myoblast fusion. The specific role in myoblast fusion, derived from the ultrastructural localization of R1, was evidenced by a strong inhibitory effect of anti-R1 Fab fragments (10-100 micrograms/ml), relative to control Fab fragments. In vivo, the embryonic subunit pattern and subcellular distribution of R1 reappeared in muscle cells after lesion of the adult muscle. This suggested that, as observed in vitro, R1 participated in vivo in the phenomenon of myoblast fusion. Similar modifications in subunit expression were observed in muscles after denervation (the embryonic form of lectin R1 reappearing after lesion), suggesting that R1 could be involved in the process of neuromuscular junction formation. Thus, it is proposed that the carbohydrate-binding protein R1 is an important recognition molecule for the formation of myotubes. Its potential involvement in a recognition process between axons and muscle cells during neuromuscular junction formation is discussed.

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It has been previously shown that sectioning of parallel fibers in the cerebellar molecular layer of adult rats gave rise to rapid reinnervation of the target cells, i.e., Purkinje cells. This paper reports that such a reinnervation is accompanied by reexpression (partial and total) of two developmentally regulated complementary molecules. These are an endogenous mannose-binding lectin, called R1, which reappears at the surface of the dendrites of Purkinje cells, and an endogenous glycoprotein ligand of R1, the 31 kDa glycoprotein, which seems to be neosynthetized and transported to the surface of parallel fibers. In this system, embryonic N-CAM is not reexpressed in neurons but reappears in reactive astrocytes in the vicinity of the lesion. The reexpression of recognition molecules (lectin and glycoprotein ligand) involved in normal synaptogenesis, may constitute the molecular basis for repair of nervous circuits in the adult as well.

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A 16-kDa lactose-binding lectin comprises 5% or more of the soluble protein in Xenopus laevis skin. This lectin is mainly localized in the cytoplasm of granular gland cells. In response to stress, the lectin along with a variety of toxic and antibiotic peptides are released onto the skin surface by holocrine secretion. We have purified the lectin, sequenced tryptic peptides using tandem mass spectrometry and Edman degradation, and isolated full-length cDNA using a deduced oligonucleotide. Comparison of the cDNA and peptide sequences revealed expression of at least two isolectins, which differ in sequence at only two or three amino acids. Comparison of cDNA with complementary message by ribonuclease protection confirmed expression in approximately equal abundance of two nearly identical messages. The major soluble lactose-binding lectin expressed in Xenopus muscle is composed of these same isolectins, but at 100-fold lower levels. Similarities and distinctions in sequence and carbohydrate-binding specificity indicate that this lectin is a novel member of a family of soluble lactose-binding lectins expressed in a wide range of vertebrate tissues.

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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.

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Two endogenous cerebellar mannose binding lectins have been isolated in an active form by immunoaffinity chromatography employing their respective immobilized antibodies. One of them, termed cerebellar soluble lectin (CSL), was extracted in the absence of detergents, whereas the other, called Receptor 1 (R1), was soluble only in the presence of detergents. Tests of inhibition of agglutination of erythrocytes were performed with mono-, oligo and polysaccharides, as well as glycoconjugates of known structures. On the basis of agglutinating activities these 2 lectins are different from the previously reported lectins in brain, since they were not inhibited by galactosides and lactosides and were only marginally inhibited by glycosaminoglycans. CSL and R1 were better inhibited by mannose-rich glycopeptides as compared to the corresponding oligosaccharides. The different inhibition patterns obtained with glycans of known structures indicated that these lectins are very discriminative. Although CSL and R1 have similar specificities, they differed in their binding properties towards glycopeptides of ovalbumin. Both lectins showed considerable affinity for endogenous cerebellar glycopeptides, also rich in mannose. These glycopeptides belong to a few endogenous Con A-binding cerebellar glycoprotein subunits and are not present on other endogenous Con A-binding glycoproteins. In the forebrain, where CSL and R1 were also present, at least some of the glycoproteins interacting with the lectins were different from that observed in the cerebellum. Our data overall suggest that specific cell recognition in the nervous system could be invoked via the interactions between widely distributed lectins and cell-specific glycoproteins.

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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.

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The prevalence of rheumatoid arthritis is generally estimated to be 1 per cent, despite the marked differences between the various results published according to the survey techniques and the epidemiological criteria employed. The present survey consisted of patients from the target population (the 248,009 inhabitants of Angers over the age of 15 years), who had been examined by one of the hospital or private rheumatologists working in Angers between 1960 and 1984 and who were considered to be suffering from inflammatory rheumatism. The cases of rheumatoid arthritis included in this survey were still alive and were living in Angers between January 1 and June 30 1984 and corresponded to at least two of the New York criteria. The prevalence determined according to this technique was 0.17 per cent for two criteria and 0.11 per cent for three criteria. After discussing the bias and the particular conditions of the study, it appears that these particularly low levels are essentially related to: a recruitment bias due to the limitation of the survey to patients seen by rheumatologists, to the choice of New York criteria and more especially of 3 criteria which increases the specificity of the survey at the expense of the sensitivity, to the long observation (mean of 10.4 years) which contributed to a reduction in the number of false positives. The validity of this study is supported by the comparison with the study by O'Sullivan et al. also based 2 New York criteria with a follow-up of 3 to 5 years, which concluded on a prevalence of 0.24 per cent compared with 0.17 per cent in Angers.(ABSTRACT TRUNCATED AT 250 WORDS)

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