Selective expression of endogenous lactose-binding lectins and lactoseries glycoconjugates in subsets of rat sensory neurons

Analysis of taste bud innervation based on glycoconjugate and peptide neuronal markers

Primary gustatory neurons and their peripheral and central processes were evaluated histochemically in the geniculate and petrosal cranial nerve ganglia, lingual fungiform taste buds, and the nucleus of the solitary tract (NST) using 1) the plant lectin Griffonia simplicifolia I-B4, which binds specifically to D-galactose residues and selectively labels primarily nonpeptide-containing peripheral somatosensory neurons, and 2) calcitonin gene-related peptide immunoreactivity (CGRP-IR), which labels most peptidergic somatosensory neurons. Lectin reactivity was expressed by the vast majority of geniculate and petrosal ganglion cells, while CGRP-IR labeled very few cells. Peripherally, gustatory intragemmal axons penetrating fungiform taste buds were labeled only by the lectin and were depleted following chorda tympani transection. However, both lectin-labeled and CGRP-IR subpopulations of somatosensory perigemmal axons surrounding the taste buds were observed and were eliminated by section of the lingual nerve. The differing brainstem projection patterns of lectin-reactive vs. CGRP-IR central axons reflected their distinct ganglionic origins and the differential distributions of lectin reactivity and CGRP-IR among taste buds. Central lectin-reactive terminals were found throughout the entire rostrocaudal extent of the NST, including its rostral lateral "gustatory" zone; the extensive lectin-reactive visceral afferent projection can be presumed to have originated mainly from the large proportion of lectin-labeled neurons in the nodose ganglion. The lectin also prominently and selectively labeled the area postrema. CGRP-IR central terminals, however, was relatively sparse and restricted primarily to the caudal and medial "visceral" divisions of the NST. The results are discussed with respect to the possible functional implications of cell surface glycoconjugate expression by gustatory axons innervating taste bud receptor cells of the tongue.

Two Monoclonal Antibodies Recognizing Carbohydrate Epitopes on Neural Adhesion Molecules Interfere with Cell Interactions

We have studied two monoclonal antibodies raised against crude fractions of membrane glycoproteins from adult mouse brain and found them to react with two carbohydrate epitopes expressed on several neural cell adhesion molecules. Other identified and unidentified glycoproteins from different cell types, organs and species were also recognized by these antibodies. Both epitopes are N-glycosidically linked mannosidic or hybrid type oligosaccharides and co-expressed on all the glycoproteins so far tested. In spite of their remarkable similarities, the glycan epitopes are different as shown by ELISA competition assays. In microexplant outgrowth and cell adhesion assays, both antibodies interfere with neural cell adhesion, migration, and neurite outgrowth. These observations, together with previous studies on the L2/HNK-1 glycan (Künemund et al., 1988), indicate that adhesion molecules carry various carbohydrate epitopes mediating different cell interactions in in vitro assays.

Involvement of endogenous galactoside-binding lectin of Xenopus laevis in pattern formation of Xenopus neurites in vitro

Galactoside-binding lectin has been purified from Xenopus laevis embryos at the stage of neural crest migration. Addition of this lectin to neurite cultures correlates with the appearance of fascicles of greater diameter and shorter length compared with controls. Lectin-treated neurites are also more spread out on the substratum than their controls. The potent hapten inhibitor of the endogenous lectin, thiodigalactoside (TDG), was also added to these cultures. TDG-treated neurites are less well spread out than the controls; fascicle diameters and lengths are not altered. These results suggest that galactoside-bearing receptors and endogenous galactoside-binding lectin are present in these neurites and can participate in controlling neuronal morphogenesis in vitro, although to differing extents.

Lectins as cell recognition molecules

Lectins on cell surfaces mediate cell-cell interactions by combining with complementary carbohydrates on apposing cells. They play a key role in the control of various normal and pathological processes in living organisms.

Morphology and distribution of primary afferent fibres expressing alpha-galactose extended oligosaccharides in the spinal cord and brainstem of the rat. Light microscopy

The light microscopic morphology and distribution of non-substance P-containing small primary afferent fibres were studied. These fibres were labelled using LD2 and LA4 monoclonal antibodies which recognize alpha-galactose extended oligosaccharides expressed by primary afferent neurons. The LD2 and LA4 antibodies immunostained small primary afferent fibres ending mainly in lamina II of the spinal cord dorsal horn and trigeminal subnucleus caudalis of the rat. The lamination pattern of both types of primary afferents was assessed using an image analysis system. The highest density of LD2-immunoreactive fibres was located in a patchy band located in lamina II outer, while LA4-immunoreactive fibres were distributed mainly through lamina II inner. In lateral regions of cervical and lumbar dorsal horn the LA4-immunoreactive band is broader and comprises almost all lamina II. In contrast to substance P-containing primary afferents, a low density of LD2- or LA4-immunoreactive fibres was found in lamina I, and no terminal fields were found in lamina V or lamina X of the spinal cord or in levels of the trigeminal system outside the subnucleus caudalis. Both antibodies also labelled the parent fibres in the white matter fasciles. LD2-immunoreactive fibres were located in the dorsal roots, medial regions of the Lissauer tract, dorsal columns of the spinal cord, outer regions of the spinal trigeminal tract and dorsal to the cuneatus and gracilis nuclei. In contrast, LA4-immunoreactive fibres were restricted to the dorsal roots, medial and lateral regions of the Lissauer tract and the outer regions of the trigeminal tract. Immunostained fibres in the rootlets of the X and IX nerves and immunoreactive terminal arborizations in various subnuclei of the nucleus tractus solitarius were seen using both antibodies. These results show that subpopulations of small primary afferents stained by LD2 and LA4 antibodies have distinct patterns of central distribution and are consistent with a subdivision of small primary afferents into peptide- and non-peptide-containing groups.

Changes in lectin binding of lumbar dorsal root ganglia neurons and peripheral axons after sciatic and spinal nerve injury in the rat

The effects of chronic lesions of rat lumbar spinal or sciatic nerves on the binding of Glycine max (soybean) agglutinin to galacto-conjugates, in small- and medium-size primary sensory neurons of the L4 and L5 dorsal root ganglia, were examined over a 580-day period. Spinal nerve section resulted in a marked decrease in the population of stained neurons within 7 days. However, despite some retrograde morphological changes triggered by axonal injury, the proportion of stained nerve cells was normalized 180 days postoperatively. This temporary decrease in perikaryal lectin reactivity was initially associated with a marked accumulation of stained material in the nerve, proximal and distal to the site of section, with similar accumulations also being noticeable at each level of injury in sciatic nerves subjected to double ligature. This may reflect the presence of glycocompounds linked to the autolysis of nerve fibers during the phase of retrograde dying-back and Wallerian degeneration. At later stages, stained deposits could be seen scattered along central and peripheral axonal processes of the dorsal root ganglion neurons in the vicinity of the cell body. They may indicate a disturbance in the peripheral turnover of glycoproteins in chronically-transected nerves, with piling up of neuronal products. Sciatic nerve injury caused similar but less severe effects which, except for the L4 ganglion cells, were rapidly reversible.

Human cytomegalovirus induces stage-specific embryonic antigen 1 in differentiating human teratocarcinoma cells and fibroblasts

Cell surface expression of stage specific embryonic antigen 1 (SSEA-1), or Lex (III3 FucnLC4), was induced in differentiated human teratocarcinoma cells and in human diploid fibroblasts 3-6 d after infection with human cytomegalovirus (HCMV). In parallel, fucosylated lactoseries glycolipids bearing the SSEA-1/Lex epitope were readily detected in the infected cells but not in the uninfected cells. HCMV infection also results in altered expression of several glycosyltransferases. SSEA-1/Lex induction is probably a consequence of both increased expression of beta 1----3N-acetylglucosaminyltransferase, which catalyzes the rate-limiting step in lactoseries core chain synthesis, and subtle alterations in the relative competition for common precursor structures at key points in the biosynthetic pathway. Since SSEA-1 has been suggested to play a role in some morphogenetic cell-cell interactions during embryonic development, the induction of this antigen at inappropriate times might provide one mechanism whereby intrauterine infection with HCMV can damage the developing fetal nervous system.

Commitment of neural crest cells to the sensory neuron lineage

Clonal cultures and monoclonal antibodies against a lineage-specific epitope, stage-specific embryonic antigen-1 (SSEA-1) were used to analyze the commitment of quail neural crest cells to the sensory neuron pathway. There were two distinct populations of sensory cells at the time of gangliogenesis. Postmitotic neuroblasts that remained in close association with the neural tube coexisted with a large number of pluripotent cells that formed the leading edge of the emigrating cells and gave rise to sensory and autonomic neuroblasts and to melanocytes. The data suggest a dual origin of spinal sensory neuroblasts and a predominantly late divergence of the autonomic and sensory lineages.

A hypothesis on the dual significance of ABH, Lewis and related antigens

ABH and related antigens appeared a long time ago in the evolution of vertebrates on tissues in contact with the external environment, which suggests that the polymorphism given by these antigens might play a role in the relationships of the species with pathogens. However, they are also oncodevelopmental markers and some recent experimental data suggest that they might play a role in cell-cell recognition at some stages of development. This type of function is difficult to reconcile with the polymorphic nature of these markers unless one considers that the glycosyltransferases necessary for the synthesis of the active structures are encoded by various members of multigene families. Some non-polymorphic members of the families would have their expression limited in time and space during development, leading to the same antigenic patterns in every individual, and these could reappear in some tumours, while the expression of other polymorphic members (A/B/O, H/h, Se/se, Le/le), leading to a variety of antigenic phenotypes, would be expressed at later stages and remain so during the whole life of the individual. The corresponding antigens could disappear from some cancer cells. It is argued that the ABH and related antigens would have primarily been involved in cell-cell recognition phenomena. The polymorphism would have evolved later from gene duplication under environmental pressure, the expression on erythrocytes which occurred very late in evolutionary time probably being of very little biological significance.

Ulex europaeus agglutinin-I binding to dental primary afferent projections in the spinal trigeminal complex combined with double immunolabeling of substance P and GABA elements using peroxidase and colloidal gold

Ulex europaeus agglutinin I (UEA-I) is a plant lectin with an affinity for L-fucosyl residues in the chains of lactoseries oligosaccharides associated with medium- and smaller-diameter dorsal root ganglion neurons and their axonal processes. These enter Lissauer's tract and terminate within the superficial laminae of the spinal cord overlapping projections known to have a nociceptive function. This implies that the surface coatings of neuronal membranes may have a relationship with functional modalities. The present investigation further examined this concept by studying a neuronal projection with a nociceptive function to determine whether fucosyl-lactoseries residues were incorporated in its primary afferent terminals. Transganglionic transport of horseradish peroxidase (HRP) following injection into tooth pulp chambers was employed to demonstrate dental pulp terminals in the trigeminal spinal complex, while peroxidase and fluorescent tags were used concomitantly to stain for UEA-I. Double immunolabeling for substance P (SP) and gamma-aminobutyric acid (GABA) using peroxidase and colloidal gold allowed a comparison of the distribution of a known excitatory nociceptive transmitter with that of UEA-I binding in specific subnuclei. Synaptic interrelationships between UEA-I positive dental pulp primary afferent inputs and specific inhibitory terminals were also examined. SP immunoreactivity occurred in laminae I and outer lamina II (IIo) of subnucleus caudalis (Vc) and in the ventrolateral and lateral marginal region of the caudal half of subnucleus interpolaris (Vi), including the periobex area in which Vi is slightly overlapped on its lateral aspect by cellular elements of Vc. The adjacent interstitial nucleus (IN) also showed an intense immunoreactivity for this peptide antibody. UEA-I binding displayed a similar distribution pattern in both Vc and Vi, but extended into lamina IIi and the superficial part of Lamina III in Vc. Dental pulp terminals were found to have a comparable distribution; however, many extended into the dorsal portion of the caudal half of Vi and the ventromedial quadrant of rostral Vi. Electron-microscopic analysis showed that transganglionically labeled dental pulp terminals contained ovoid, complex membrane-bound vacuoles laden with transported HRP. The preterminal axon and synaptic membranes of those dental pulp terminals located in zones of Vc and Vi displaying an affinity for UEA-I were usually characterized by a patchy, electron-dense coating of the peroxidase tag. SP was demonstrated ultrastructurally with Protein-A colloidal gold (3-nm particles), whereas GABA immunoreactivity was revealed by the avidin-biotin-peroxidase method.(ABSTRACT TRUNCATED AT 400 WORDS)

Endogenous sugar receptor pattern in human glioblastomas and gangliocytomas studied by histochemical application of biotinylated (neo)glycoproteins and affinity chromatography

Biotinylation of chemically glycosylated bovine serum albumin, yielding a panel of neoglycoproteins, and of desialylated, naturally occurring glycoproteins allowed to systematically evaluate presence and distribution of various types of endogenous sugar receptors in the sections of human glioblastomas and gangliocytomas by a routine histochemical procedure. Pronounced cytoplasmic staining with markers, carrying constituents of natural glycoconjugates, e.g. for beta-galactoside-specific receptors, contrasted with the different intensities, noticed for alpha- and beta-glucoside-specific receptors. Significant qualitative differences between the two tumor types were detected with N-acetyl-D-galactosamine- and sialic acid-carrying probes. Nuclear staining with only a part of the applied panel underscored the specificity of the protein-carbohydrate interaction. Fine structural features of the synthetic neoglycoproteins, e.g. the mode of coupling of the carbohydrate moiety to the protein, were found to exert a significant influence on their suitability as histochemical markers. On the basis of the histochemical results, exemplary biochemical analysis of certain classes of endogenous sugar receptors by affinity chromatography and subsequent gel electrophoresis, namely of beta-galactoside-, alpha-fucoside-, alpha-mannoside- and alpha-glucoside-specific proteins, revealed presence and characteristics of respective sugar receptors that can contribute to the histochemical staining. Similar extent of histochemical staining with the respective probes notwithstanding, the different tumor types exhibited qualitative differences in the expression of individual endogenous sugar receptors. The combined histochemical and biochemical analysis is supposed to be of conspicuous value for biological and clinical investigations on endogenous sugar receptors.

Lectins in cancer cells

Studies carried out over the last few years have demonstrated that tumor cells and malignant tissues contain lectins that are similar in sugar-binding specificity, molecular size, and antigenicity to the lectins found in normal cells and tissues. Lectins from tumor cells also share marked sequence homology with lectins from normal tissues. Lectins were purified from various tumor cells by affinity chromatography and monoclonal and polyclonal antilectin antibodies were prepared against them. These enabled us to establish the following: (1) Lectins are present on the surface of all the tumor cells that were examined, albeit at varying levels. (2) The level of cell surface lectins increases after normal cells are transformed by transfection with certain oncogenes or by retroviruses, or when cells transformed with a temperature-sensitive viral mutant are switched from growth at the nonpermissive to the permissive temperature. (3) Among tumor cells differing in metastatic propensity, those exhibiting a higher potential express higher levels of surface lectins. (4) Tumor cell surface lectins might be involved in cell-cell adhesion, cell attachment to substratum, the expression of the transformed phenotype (anchorage-independent growth), and blood-borne metastasis. (5) The levels of the lectins in tumor cells are modulated by agents that suppress the transformed phenotype (as represented by anchorage-independence) or enhance differentiation. Numerous studies by others have shown that cell surface carbohydrate-containing molecules are modified after transformation, and our findings demonstrate that the expression of cell surface carbohydrate-binding proteins is also altered by transformation. Obviously, any of these changes may result in alterations in cellular interactions. All the above findings implicate tumor cell lectins in cellular interactions (adhesion, attachment, possible binding of exogenous soluble glycoconjugates), cell growth and anchorage-independent growth, malignant transformation, tumor cell differentiation, and metastasis. It is clear that even if these lectins are involved in only a few of these fundamental processes, it is important to elucidate their functions and the mechanisms by which their expression is regulated during neoplastic transformation and tumor progression and the suppression of the transformed phenotype.

A molecular view of vertebrate retinal development

Immunological probes have begun to identify molecules that delineate cell layers and cell types during the formation of the retina and other parts of the optic cup. Within the developing retina, cell-type-specific monoclonal antibodies have been used to show that differentiation occurs before cells reach their final laminar position. Cell surface molecules have been found expressed in position-dependent gradients across the retina. These molecules may convey positional information to the retinal cells and their topographic connections. One such molecule is a modified carbohydrate group on a ganglioside, suggesting that such groups may play a role in neural development. A variety of molecules that are expressed by rod photoreceptors at defined stages of their differentiation have been characterized. These molecules have been used to show the development of subcellular compartments within rods. In vitro studies have suggested that photoreceptor molecules expressed at different times are under different forms of regulation. Some of these cell-specific molecules have been shown to be under transcriptional control and thus defined cell interactions seem to be linked to changes in gene expression during retinal development.