Varying expressions of lectin receptors within embryonic cell layers of murine cerebral cortex

Fucosylated glycans in the periventricular structures and the cerebrospinal fluid of the fetal rat forebrain. An autoradiographic and lectin binding histiotopic study

Our autoradiographic 3H-fucose incorporation study of the brains of 20-day-old rat fetuses showed that the synthesis of fucosylated glycans is significantly higher in the ventricular germinative zone of the forebrain hemisphere than in the more superficial layers, including the cortical plate. Intense incorporation of 3H-fucose also occurred in the choroid plexus, both its epithelial and stromal component, in the primordial ependymal lining of the lateral ventricles, meninges and capillaries of the forebrain parenchyma. In the lateral ventricles, densely labeled microprecipitates of the cerebrospinal fluid (CSF) were occasionally observed. The histiotopic differences in 3H-fucose labeling were absent, or were much less expressed, in the autoradiograms prepared from unfixed cryostat sections containing mainly unincorporated isotope. This indicates that the blood-mediated supply of 3H-fucose to the studied brain compartments was essentially equal and our incorporation data reflect actual differences in the rate of fucosylation within the forebrain hemispheres. The cytochemical lectin-binding assay, carried out with Ulex europaeus and Lotus tetragonolobus agglutinins, showed that regions with a higher rate of 3H-fucose incorporation were also richer in fucose-bearing glycoconjugates. The study revealed that the periventricular regions and the CSF of fetal rat forebrain form a fucosylated glycan-enriched complex, which represents a new chemoarchitectonic feature that may be of importance for maintaining the germinative properties of the ventricular neuroepithelium and the growth of the hemispheric ventricles.

Specific staining of nonpyramidal cell populations of the cerebral cortex by lectin cytochemistry on semithin sections

The pattern of lectin labeling in the cerebral cortex of the cat was studied using semithin sections. The labeling produced by some lectins (Concanavalin A, Lens culinaris, Phaseolus vulgaris-L, Phaseolus vulgaris-E, Pisum sativum, wheat germ agglutinin, and succynilated-wheat germ) appeared inside every neuron as small cytoplasmic granules, probably corresponding to cisterns of endoplasmic reticulum and/or the Golgi complex. Lectins with affinity for alpha-mannosyl residues (Pisum sativum, Lens culinaris, and Concanavalin A) stained the cell surface of a subset of cortical neurons. The labeled cells were round or polygonal, medium to large neurons present in layers II-VI, exhibiting the morphological features of nonpyramidal cells. Previous lectin studies of perineuronal nets have shown that these extracellular specializations contain N-acetylgalactosamine and N-acetylglucosamine. Our results show that mannose is also a component of perineuronal nets and that lectins specific for alpha-mannose can be used as tools for the cytochemical detection of a separate class of cortical neurons, which have not yet been fully characterized. In addition, some lectins (Bandeiraea simplicifolia, Concanavalin A, Lens culinaris, Phaseolus vulgaris-L, Phaseolus vulgaris-E, Pisum sativum, and succynilated-wheat germ agglutinin) specifically labeled a population of a type of microglia-related cells known as perivascular cells. The data presented here report for the first time the selective staining of perivascular cells and further support the hypothesis that they are different from typical microglial cells.

Glycoconjugate expression during early mouse oculogenesis

The carbohydrate side-chain of glycoconjugates can show a developmentally regulated expression pattern. In order to analyse these changes during the development of the eye, 13 lectins were used to reveal glycoconjugates histochemically in 8.5- to 14-day-old mouse embryos. During this period, eyes develop from the most immature vesiculation of the neural plate neuroepithelium into a primitive stage with all structures present, such as pigment epithelium, not yet differentiated neuroretina and lens. A striking diversity of carbohydrate side-chain expression was observed in the preocular somatoectoderm and neural plate of 8.5-day-old embryos, as indicated by the binding of nine different lectins. Binding sites at the apical poles of neuroepithelium of five of these lectins (PNA, LCA, SBA, LPA and GSA-II) disappeared completely during further development. The binding sites of four other lectins, WGA, MPA, Con A and BPA, remained expressed during the course of development, being indicative for the carbohydrate side-chains beta-GlcNAc(1-4)Gluc, alpha-Gal(1-3)GalNAc, alpha-D-Man/alpha-D-Gluc and alpha-GalNAc. In contrast, binding sites for GSA-I, RCA-I (alpha-D-Gal), UEA-I (alpha-L-Fuc) and DBA (alpha-GalNAc(1-3)GalNAc) were not present at any developmental stage. The time point of gross changes of lectin binding sites correlates well with the period of neural tube formation. During later development from neuroectoderm to the ocular pigment epithelium, a sharp reduction in all lectin binding sites at the apical cell poles, except for WGA and MPA, was observed. WGA binding sites were present until embryonic day 10, while those for MPA were present until day 9. At the basal cell poles of the pigment epithelium, all lectin binding sites except for WGA were lost after embryonic day 11.5. These results indicate that there are sophisticated kinetics of glycoconjugate expression during the course of early embryonic development of ectoderm into its descendent tissues.

Lectin staining in the basal nucleus (Meynert) and the hypothalamic tuberomamillary nucleus of the developing human prosencephalon

Previous studies have demonstrated that extracellular matrix glycoconjugates, shown by lectin-histochemistry with Vicia villosa agglutinin (VVA) and peanut agglutinin (PNA) as so-called perineuronal nets, play an important role in brain maturation. Concanavalin A (ConA) binding to neuronal surface glycoconjugates may be a marker of synaptic junctions. The present study was done to demonstrate the binding sites of these lectins in two functionally related nuclei of the prosencephalon, the basal nucleus (Meynert) and the hypothalamic tuberomamillary nucleus. Fetal brains of 16-36 weeks of gestation were examined by using VVA, PNA, and ConA to determine appearance and distribution patterns of specific lectin-binding sites on glycoconjugates during fetal brain development. The basal nucleus and the tuberomamillary nucleus showed a characteristic "cellular staining" that may have been due to cytoplasmatic labeling, surface labeling, or both. Lectin-staining occurred much earlier in the basal nucleus than in the tuberomamillary nucleus. Although all three lectins were bound to neurons of the basal nucleus, only ConA-positive neurons were observed in the tuberomamillary nucleus. In conclusion, lectin-labeled cells most probably represent projection neurons that are GABAergic (tuberomamillary nucleus) or cholinergic (basal nucleus). Labeling with the three lectins demonstrated nuclear-specific staining patterns that occur early in fetal development and gradually increase. Binding sites for lectins characterizing perineuronal nets (VVA, PNA) occurred only in the basal nucleus, whereas binding sites for ConA on neuronal-surface glycoconjugates, which seem to play a role in early synaptogenesis, were present in the basal and the tuberomamillary nucleus. The basal nucleus, however, expressed ConA binding sites distinctly earlier, probably indicating early arriving afferents.

Specification of layer-specific connections in the developing cortex

One of the basic tasks of neurobiology is to understand how the precision and specificity of neuronal connections is achieved during development. In this paper we reviewed some recent in vitro studies on the developing mammalian cerebral cortex that have been made towards this end. The results of these experiments provided evidence that membrane-associated molecules are instrumental for the formation of specific afferent and efferent cortical projections. Substrate-bound molecules guide growing axons towards their target, regulate the timing of thalamocortical innervation and mediate target cell recognition. Moreover, a newly described glycoprotein, defined by a monoclonal antibody, revealed a molecular heterogeneity in the developing white matter. Since this molecule has opposite effects on thalamic and cortical axons, it might play a role in the segregation of axons running to and from the cortex. Substrate-bound cues are important during the formation of local cortical circuits. In vitro assays demonstrated that molecular components confined to individual cortical layers control the laminar specificity of cortical axon branching. This suggests that similar developmental strategies contribute to the laminar specification of extrinsic and intrinsic cortical circuits. Thus substrate-bound molecules might provide the framework for subsequent activity-dependent mechanisms that control the elaboration of precise connections between the cortical columns. A major challenge ahead is to identify the factors that mediate these processes and to determine their mode of action. Recently, two families of proteins, the netrins and the semaphorins/collapsins, have been identified as growth cone signals in the developing spinal cord (reviewed in Goodman, 1994; Colamarino and Tessier-Lavigne, 1995a; Dodd and Schuchardt, 1995; Kennedy and Tessier-Lavigne, 1995). Semaphorins/collapsins appear to regulate axonal guidance by repelling growth cones and by inhibiting axonal branching and synapse formation. Originally, netrins have been purified as diffusible chemoattractants for commissural axons of the dorsal spinal cord, but it is now well established that they can also function as chemorepellent factors for other classes of neurons. Since netrins are related to extracellular matrix components and since they can bind to the cell surface, they might also act as local guidance cues. A possible role of netrins and semaphorins/collapsins in the development of cortical connections is likely to be resolved in the near future. The identification of the factors that regulate specific branching patterns of cortical neurons might provide a better understanding of cortical development, but it might also be relevant to some aspects of plasticity and repair in the adult cortex.

A lectin and synaptophysin study of developing brain

Lectins which bind to carbohydrate residues of glycoconjugates can be used as histochemical markers of these substances. A battery of lectins including peanut agglutinin, ricinus communis, wheat germ agglutinin, soybean agglutinin, concanavalin ensiformis, Ulex europaeus, and Dolichos biflorus as well as synaptophysin was used on paraffin-embedded human fetal and infant brains of varying gestation (20 weeks to term) to determine whether there were changes in the pattern of glycoconjugate staining. The findings indicate that lectin binding of several of these markers changes with gestation as does synaptophysin.

Guidance of thalamocortical axons by growth-promoting molecules in developing rat cerebral cortex

Substrate-bound guidance cues play an important role during the development of thalamocortical projections. We used time-lapse video microscopy to study the growth behaviour of thalamic axons on different substrates. On embryonic cortical membranes and on a pure laminin substrate, thalamic fibres advanced relatively slowly (approximately 15 microns/h) and on average their growth cones retracted transiently every approximately 5 h. In contrast, on membranes prepared from early postnatal cortex, thalamic fibres grew twice as fast and spontaneous growth cone collapse occurred approximately 8 times less often. Experiments in which we used the sugar-binding lectin peanut agglutinin or heat inactivation to change the membrane properties indicated that these differences are due to growth-supporting molecules on postnatal cortical membranes. When offered a choice between embryonic and postnatal cortical membranes, thalamic axons preferred the postnatal membrane substrate. Time-lapse imaging revealed that borders between these two substrates effectively guided thalamic fibres, and in most cases axons changed their direction without collapse of the growth cone. Our results suggest that thalamic axons can be guided by the spatial distribution of growth-promoting molecules in the developing cortex.

Developmentally-regulated lectin binding in the embryonic mouse telencephalon

Cell-surface carbohydrate epitopes are important determinants in cell-cell and cell-matrix interactions, and oligosaccharide groups are structural components of many growth factor receptors and cell adhesion molecules. These epitopes may participate in the regulation of stem cell proliferation and differentiation during central nervous system development. To further understand these cellular phenomena, it is important to define the changes in neuroepithelial cell-surface carbohydrate expression during development. We used a panel of fluorescein-conjugated lectins to label live, freshly dissociated cells from the embryonic day 11 to 18 (E11 to E18) mouse telencephalon. The intensity and heterogeneity of lectin labeling was assessed by flow cytometry. The lectins that we examined exhibited widely varying levels of labeling intensity. Lectins with the highest degree of binding included cholera toxin B subunit (CTB), which binds primarily to the gangliosides GM1 and GD1b, phaseolus vulgaris erythroagglutinating lectin (PHA-E), which binds to a variety of cell adhesion molecules, and wheat germ agglutinin (WGA). Many lectins showed increasing labeling intensity and cellular heterogeneity as development progressed. To determine if the observed cellular heterogeneity in lectin binding reflected biological differences in neuroepithelial cell subpopulations, cells from the E14 telencephalon were separated into two populations based on their intensity of CTB labeling using a fluorescence activated cell sorter. The population of weakly CTB labeled cells contained more than four times as many cells in S-phase of the cell cycle than the population of intensely CTB labeled cells. These observations suggest that lectin cytochemistry and flow cytometry can be useful in identifying specific cell subpopulations of neuroepithelial precursor cells during development, allowing their isolation and characterization in vitro.

Differential development of binding sites of two lectins in the vomeronasal axons of the rat accessory olfactory bulb

Binding of fluorochrome-conjugated lectins, Bandeiraea simplicifolia lectin-I (BSL-I) and Vicia villosa agglutinin (VVA), to the vomeronasal axons was investigated in the accessory olfactory bulb (AOB) of developing rats at embryonic day (E) 16, 18, and 20, and postnatal day (P) 0, 3, 7, 14, and 28. Intense fluorescence for VVA was first observed at E18, and the position-specific binding pattern observed in adults was established at P0; intense fluorescence for VVA was observed in the posterior 2/3 of the vomeronasal nerve layer (VNL) and glomerular layer (GL) and weak fluorescence was present in the anterior 1/3 of these layers. Fluorescence for BSL-I was observed in the posterior half of VNL and GL at P0; the area bound with BSL-I was expanded to the anterior area and intensity of the fluorescence increased as the development proceeded. At P28, binding of BSL-I was observed in the entire VNL and GL as identical to adults. These results indicate that the binding sites of BSL-I and VVA in the vomeronasal axons at the level of rat AOB develop differentially during ontogeny, suggesting that rat VN axons consist of two subpopulations expressing different glycoconjugates.

Immunocytochemical analysis of a novel carbohydrate differentiation antigen (CDA-3C2) associated with olfactory and otic systems during embryogenesis in the rat

Carbohydrate differentiation antigens are known to display specific patterns of expression during mammalian development and are thought to participate in significant morphogenetic events. In the present study, two monoclonal antibodies that react with a novel carbohydrate differentiation antigen (CDA-3C2) were used to analyze, by light microscopy, the spatiotemporal distribution of this unique high molecular weight antigen during embryogenesis in the rat. Correlative analysis of the development of peripheral neural structures, in which CDA-3C2 was expressed, was carried out with an anti-neurofilament antibody. Enzymatic digestion, combined with Western blots, reveal that the CDA-3C2 epitope is a carbohydrate which is carried on a high molecular weight glycoprotein with a mass of greater than 1 million Daltons. Characteristic of carbohydrate antigens, immunoreactivity was found in several distinct cellular patterns: only along the apical border of cells, along lateral and basal membranes of cells, and extracellular-like staining in the mesenchyme. During neurulation, CDA-3C2 showed differential staining in the ectoderm, distinguishing lateral from neural regions. Following closure of the neural tube, there was a striking specificity of expression of CDA-3C2 in the periphery, found almost exclusively in olfactory and otic epithelial structures. While CDA-3C2 is found in placode-derived tissues that subserve sensory transduction, it appears to be primarily associated with the supportive cells (and their secretions) in both otic and olfactory regions and less so with the sensory cells. The data suggest that a unique carbohydrate antigen on a large macromolecule may play a role in neurulation and/or morphogenesis of the placode-derived otic and olfactory structures.

Lectin binding patterns in developing canine retina

Developing canine retina, fixed in Bouin's or Tellyesnizky's acetic alcoholic formalin, was examined with a battery of biotinylated lectins. ConA and WGA consistently bound to all retinal layers including the tapetum cellulosum, retinal pigment epithelium, inner and outer segments, plexiform layers and ganglion cells. Binding became more intense with increased age. S-WGA bound to apical portions of the retinal pigment epithelium and to outer segments. Outer segments also bound ConA, WGA and RCA. DBA preferentially labelled all inner segments, while PNA bound to a subpopulation of inner segments. RCA bound intensely to retinal vessels as did PNA after neuraminidase treatment. UEA did not consistently bind to any layers. There was transient binding by some lectins at different developmental stages. This study indicates that canine retina demonstrates differential expression of glycoproteins, as indicated by lectin binding, during development and that this expression is temporally and topographically regulated.

Effects of retinoic acid on the distribution of glycoconjugates during mouse tail bud development

Retinoic acid (RA), a potent teratogen of caudal axial development in rodents, has been shown to alter glycoconjugates in a variety of embryonic tissues and teratocarcinomas. In this study, we examined its effects on the expression of cell surface and extracellular matrix glycoconjugates during tail bud development in mouse embryos by using lectin histochemistry. The lectins WGA, sWGA, and PNA showed striking differences in binding between RA-exposed and control embryos. Computer-assisted densitometry revealed a significant increase in binding of all three lectins to the extracellular material of the luminal and abluminal borders of the secondary neural tube and surrounding the notochord in RA-exposed embryos. RA-treated embryos also showed an increased binding affinity for the lectins sWGA and PNA to the cells of the notochord, while WGA showed increased binding to the neuroepithelial cells of the secondary neural tube. The results suggest that RA affects the expression of lectin binding sites during the early development of RA-induced caudal axial defects.

Distribution of cell surface glycoconjugates during secondary neurulation in the chick embryo

Lectin histochemistry was used to examine the expression of cell surface glycoconjugates during secondary neurulation in chick embryos. Fourteen lectins were applied to serial sections of the caudal region of embryos at the various stages of tail bud development. The lectins Bandeiraea simplicifolia, Dolichos biflorus agglutinin, Phaseolus vulgaris leukoagglutinin, soybean agglutinin, Sophora japonica agglutinin, Ulex europaeus agglutinin and succinylated wheat germ agglutinin (sWGA) showed very light or no binding to the developing medullary cord of the tail bud. With the other lectins, staining occurred throughout the early tail bud and solid medullary cord. During cavitation, however, differential expression of cell surface glycoconjugates by different cell populations was observed. The lectins concanavalin A, Lens culinaris agglutinin, Pisum sativum agglutinin, Phaseolus vulgaris erythroagglutinin, Ricinus communis agglutinin and WGA showed basic similarities in the distribution of lectin binding. Of these, the binding pattern of WGA was the most striking. As the medullary cord cells were separating into central mesenchymal and peripheral epithelial populations, WGA bound preferentially to the epithelial cells and the notochord. The lectin PNA, however, became preferentially bound to the mesenchymal cells. Heavy staining by WGA (specific for N-acetylglucosamine and sialic acid) where sWGA staining (specific for N-acetylglucosamine only) was faint suggested that WGA binding was due to the presence of sialic acid containing glycoconjugates.

Analysis of differentiation and transformation of cells by lectins

During differentiation cells are known to change their biological behavior according to their genotype. This is thought to be accompanied by a modulation of cell surface determinants expressed on the outer cell membrane. Vice versa, cell surface molecules are suggested to mediate extracellular signals to the genome. Most of these molecules integrated in the cell membrane have been proven to be glycoconjugates. The carbohydrate moieties of these molecules can be detected by means of lectins that are characterized by their ability to react specifically with distinct terminal sugar sequences. Thus, lectins have been used as appropriate tools for studying the modulation of functionally important membrane-associated molecules during the differentiation of cells, in particular of B- and T-lymphocytes. Moreover, lectins have been proven to distinguish between differentiated cells and malignant cell clones, according to the hypothesis that transformed cells possess a glycoconjugate profile that corresponds to the stage of differentiation at which they are arrested. Since lectins, like monoclonal antibodies, make it possible to study functionally important molecules that are associated with differentiation and malignancy, they might be of value for diagnostic purposes and, moreover, for analyzing malignant transformation.

Brain lectin-mediated agglutinability of dissociated cells from embryonic and postnatal mouse brain

Brain extracts contain a soluble lectin which enables the agglutination of dissociated mouse brain cells via saccharidic receptors. The ability of the brain cells to be agglutinated depends on their stage of development in vivo. Furthermore, after birth, the mechanism of the lectin-promoted agglutination is complicated by the appearance of a self-aggregation of the dissociated cells. Lactose and galactosides are inhibitors of lectin-mediated agglutination as well as of the dissociated cells' self-aggregation.

Sulfated glucuronic acid-containing glycoconjugates are temporally and spatially regulated antigens in the developing mammalian nervous system

Monoclonal antibody 4F4, which was raised against a cell suspension of embryonic rat forebrain, reacts with acidic glycolipids and several high-molecular-weight glycoproteins in rodent brain. The major reactive glycolipid is maximally expressed at Embryonic Day 15 (E15) and is no longer detectable at Postnatal Day 14 (P14) in the rat. 4F4 antibody reacts with a glucuronic acid- and sulfate-containing lipid isolated from human sciatic nerve as well as with lipids from mouse and rat embryonic brain tissue. Although the glycolipid disappears postnatally, the immunoreactive glycoproteins continue to be expressed in brain until adulthood. Both sciatic nerve and embryonic brain glycolipids are hydrolyzed by glucuronidase/sulfatase treatment but are insensitive to all other glycosidases tested. In addition, the observed 4F4 reactivity with extracted glycolipids, glycoproteins, and tissue sections of embryonic brain is identical to the reactivity demonstrated by HNK-1 antibodies. Immunocytochemical studies in developing brain showed stage-specific distribution of this carbohydrate antigen. At E10 in the mouse, immunoreactivity is associated with the mantle layer of the neural tube. At E15 in the cortex, the most intense staining is associated with the molecular layer and the subplate, and weaker staining is seen in the intermediate zone and cortical plate, suggesting that the antigen is highly concentrated on postmigratory cells in the embryonic nervous system.

Biochemical characterization of the major peanut-agglutinin-binding glycoproteins in vertebrate retinae

Peanut agglutinin (PNA), a lectin that binds D-galactose-beta (1----3) N-acetyl-D-galactosamine disaccharide linkages, selectively labels cone photoreceptors in the retinae of a variety of species. PNA binds consistently to domains of the interphotoreceptor matrix associated with cone, but not rod, inner and outer segments, to cone cell body and axonal membranes, to cone synaptic pedicles, and to portions of the inner plexiform layer. In order to begin the characterization of the molecular species responsible for cone-specific PNA binding, chick, turkey, rat, dog, pig, monkey, and human retinal extracts were separated by SDS-polyacrylamide gel electrophoresis and probed with peroxidase-conjugated PNA. The results reveal the presence of six major groups of PNA-binding glycoproteins ranging from 30 to 88 kilodaltons. Most of these are shared by the seven species examined; however, some interspecies variation is present. Three groups, designated GP39/40, GP42/45, and GP60, are the most intensely labeled by PNA and are common to all species analyzed, while groups GP29/31 and GP88 are less intensely labeled and are present in most but not all of the species investigated. Labeling of the GP54 group is variable but is most consistently associated with extracts of rat and pig retinae. Trypsin treatment, which results in the loss of cone-associated PNA binding in the interphotoreceptor matrix, causes a visually detectable reduction in three of the six groups of PNA-binding glycoproteins in porcine retinal extracts. Of these, GP54 is the most sensitive, being undetectable on PNA-stained blots after only 5 minutes of enzyme exposure; GP88 and GP45 are less sensitive but both are markedly reduced after 15 minutes of trypsinization. Trypsin-sensitive molecules thus may be involved in the establishment of the cone-specific domains of interphotoreceptor matrix identified by PNA binding. These, as well as the other groups of PNA-binding molecules, are being utilized to develop more specific immunologic probes with which to further study of their distribution and function.

The use of lectins to study normal differentiation and malignant transformation

Lectins are polypeptides that specifically recognize carbohydrate residues of glycoproteins and glycolipids. They can be extracted from plants, invertebrates and vertebrates. The binding between lectins and carbohydrate moieties can be blocked by the inhibitory sugar for which the lectin is specific. In analogy to antibodies, lectins can be used to analyse cell surface determinants. Thus, differentiation of cells, in particular of immunocytes, has been studied and lectin receptors are now important markers for distinguishing different developmental stages of T-lymphocytes. In consequence, premature, but already committed, T-cells can be eliminated from human bone marrow by means of lectins prior to transplantation in order to avoid graft-versus-host reactions. Moreover, it has been shown that malignant cells can be distinguished from their non-malignant counterparts by the profile of lectin receptors on their surface. This had led to the use of lectin binding sites as tumour markers in lymphomas and carcinomas.

Epidermal fucosylation of cell surface glycoprotein

When Ulex europeus agglutinin I (UEA) conjugated with fluorescein isothiocyanate is applied to tissue sections from the cutaneous epidermis of the newborn rat, the lectin binds to the surfaces of cells in the layer immediately above the basal layer but not to the cells in the basal layer itself. The latter cells bind the isolectin I-B4, from Griffonia simplicifolia (GS I-B4). The addition of a fucosyl residue to the oligosaccharide of the glycoprotein found on the surface of the basal cell can account for the change in lectin-binding specificity which occurs as the basal cell moves toward the cutaneous surface and becomes a spinous cell. The epidermis of the newborn rat has the necessary transferase to convert a glycoprotein with binding-specificity for GS I-B4 to binding specificity for UEA by adding a fucosyl residue from GDP-L-fucose.

Selective lectin binding of the developing mouse retina

A battery of eight lectins with different carbohydrate specificities was used to study changes in glycoconjugate expression during cell differentiation in the mouse retina. The lectins tested included concanavalin A (Con A), wheat germ agglutinin (WGA), soybean agglutinin (SBA), peanut agglutinin (PNA), Ulex europaeus agglutinin (UEA), Ricinus communis agglutinin I (RCA), Dolichos biflorus agglutinin (DBA), and Limulus polyphemus agglutinin (LPA). Unfixed frozen sections of adult and early postnatal mouse retina were treated with fluorescein isothiocyanate-conjugated lectins and examined by fluorescence microscopy. The results showed selective lectin binding in both cellular and synaptic retinal layers of the adult mouse and throughout postnatal development. In general, an increase in intensity of fluorescent lectin staining during retinal development was observed for Con A, WGA, DBA, LPA, RCA, and PNA. This suggests an increase in the expression or accessibility of carbohydrate moieties during development. SBA and UEA showed little to no binding to adult or neonatal retina. Retinal vasculature was intensely stained by RCA, both during development and in the adult. All lectins binding to adult or neonatal retinal layers showed some degree of reactivity with the inner segment region of photoreceptor cells. However, only Con A, PNA and WGA bound to photoreceptor outer segments, suggesting significant differences in the glycosylated components of inner and outer segment membranes. PNA bound specifically to a subpopulation of photoreceptor cells and to discrete regions within the outer synaptic layer. The pattern of PNA binding suggests that this lectin binds preferentially to cone photoreceptor inner and outer segments and cone synaptic pedicles rather than to rod photoreceptor cells. This marked specificity of PNA binding suggests that it may provide a basis for the physical separation of cone and rod photoreceptor cells.

Identical lectin binding patterns of human melanocytes and melanoma cells in vitro

Cell surface glycoconjugate patterns of human epidermal cells and of melanoma cells (MC) in primary culture derived from 11 primary and metastatic melanomas were investigated using fluorescent and horseradish peroxidase conjugated lectins for visualization at the light and electron microscopic level. The lectin labeling profiles of human melanocytes (M) and MC were found to be identical. According to their binding patterns, the lectins tested were grouped into three categories: (1) lectins binding to both keratinocytes (K) and M/MC, irrespective of neuraminidase pretreatment (concanavalin-A, wheatgerm agglutinin, succinylated wheatgerm agglutinin); (2) lectins binding to K but not to M/MC, irrespective of neuraminidase pretreatment (Ulex europaeus agglutinin I); (3) lectins binding to K, but to M/MC only after neuraminidase pretreatment (soybean, Helix pomatia, and peanut agglutinins). Untreated M were reactive for soybean and peanut agglutinins only at contact sites with K. Since the lectins from soybean, Helix, and peanut bind specifically to D-galactose and N-acetyl-D-galactosamine residues, we conclude that these particular glycoconjugates are normally masked by sialic acid on M/MC surfaces and can be unmasked by neuraminidase. These features, which have been previously observed in guinea pig M, appear to be interspecies surface markers of melanocytic cells which remain unaltered in the course of malignant transformation.

Modification of cell surface glycoprotein: addition of fucosyl residues during epidermal differentiation

When cutaneous sections from the newborn rat were treated with alpha-fucosidase, Ulex europeus agglutinin I (UEA) binding to the cell surface of the differentiated cells in the epidermis was diminished and there was an appearance in these cell layers of binding by Bandeiraea simplicifolia I-B4 lectin (BS I-B4), which normally is specific for the basal cells. A similar treatment with alpha-galactosidase resulted in a loss of BS I-B4 binding, but had no effect on UEA binding. Glycoproteins isolated from the membranes of epidermal cells showed a threefold increase in the ratio of binding to UEA versus BS I-B4 affinity columns as the proteins were derived from the more differentiated cell populations. These data suggest that alpha-fucosyl residues are added to the glycoproteins on the cell surfaces of differentiated cells, thus blocking alpha-galactosyl residues and changing the lectin binding specificity as epidermal cells move out of the basal cell layer.