Lectin histochemistry shows fucosylated glycoconjugates in the primordial germ cells of Xenopus embryos

ABO phenotype-protected reproduction based on human specific α1,2 L-fucosylation as explained by the Bombay type formation

The metabolic relationship between the formation of the ABO(H) blood group phenotype and human fertility is evident in the case of the (Oh) or Bombay blood type, which Charles Darwin would have interpreted as resulting from reduced male fertility in consanguinities, based on the history of his own family, the Darwin/Wedgwood Dynasty. The classic Bombay type occurs with the extremely rare, human-specific genotype (h/h; se/se), which (due to point mutations) does not encode fucosyltransferases 1(FUT1) and 2 (FUT2). These enzymes are the basis for ABO(H) phenotype formation on the cell surfaces and fucosylation of plasma proteins, involving neonatal immunoglobulin M (IgM). In the normal human blood group O(H), which is not protected by clonal selection with regard to environmental A/B immunization, the plasma contains a mixture of non-immune and adaptive anti-A/B reactive isoagglutinins, which in the O(h) Bombay type show extremely elevated levels, associated with decreased levels of fucosylation-dependent functional plasma proteins, suchs as the van Willebrand factor (vWF) and clotting factor VIII. In fact, while the involvement of adaptive immunoglobulins remains unknown, poor fucosylation may explain the polyreactivity in the Bombay type plasma, which exhibits pronounced complement-binding cross-reactive anti-A/Tn and anti-B IgM levels, with additional anti-H reactivity, acting over a wide range of temperatures, with an amplitude at 37 °C. This aggressive anti-glycan-reactive IgM molecule suggests the induction of ADCC (antibody-dependent) and/or complement-mediated cytotoxicity via overexpressed glycosidic bond sites against the embryogenic stem cell-to-germ cell transformation, which is characterized by fleeting appearances of A-like, developmental trans-species GalNAcα1-O-Ser/Thr-R glycan, also referred to as the Tn (T "nouvelle") antigen.

Structural characterization and biological implications of sulfated N-glycans in a serine protease from the neotropical moth Hylesia metabus (Cramer [1775]) (Lepidoptera: Saturniidae)

Contact with the urticating setae from the abdomen of adult females of the neo-tropical moth Hylesia metabus gives rise to an urticating dermatitis, characterized by intense pruritus, generalized malaise and occasionally ocular lesions (lepidopterism). The setae contain a pro-inflammatory glycosylated protease homologous to other S1A serine proteases of insects. Deglycosylation with PNGase F in the presence of a buffer prepared with 40% H2 (18)O allowed the assignment of an N-glycosylation site. Five main paucimannosidic N-glycans were identified, three of which were exclusively α(1-6)-fucosylated at the proximal GlcNAc. A considerable portion of these N-glycans are anionic species sulfated on either the 4- or the 6-position of the α(1-6)-mannose residue of the core. The application of chemically and enzymatically modified variants of the toxin in an animal model in guinea pigs showed that the pro-inflammatory and immunological reactions, e.g. disseminated fibrin deposition and activation of neutrophils, are due to the presence of sulfate-linked groups and not on disulfide bonds, as demonstrated by the reduction and S-alkylation of the toxin. On the other hand, the hemorrhagic vascular lesions observed are attributed to the proteolytic activity of the toxin. Thus, N-glycan sulfation may constitute a defense mechanism against predators.

In situ characterization of O-linked glycans of Muc2 in mouse colon

The characterization of mucus O-linked glycans in the proximal and distal mouse colon was performed by conventional histochemical methods and by lectin histochemistry in combination with enzymatic treatment (PNGase, α1,2 fucosidase, sialidase digestion), with and without prior desulfation. We demonstrated the presence of sialo- and sulfomucins in both the proximal and distal colon of the mouse. In the distal colon the sulfomucins were clearly prevalent, although there were always sialomucins with sialyl residues linked α2,6 to the subterminal galactose. Sialic acid was poorly O-acetylated, especially in the distal colon. The lectin binding pattern indicates a massive presence of fucose α1,2 linked to galactose in O-glycans and smaller quantities of fucose linked α1,6 to N-acetylglucosamine in the core of N-linked glycans. Lectin histochemistry also demonstrated the presence of glycosidic residues of N-acetylglucosamine, N-acetylgalactosamine, and galactose in oligosaccharide chains of highly sulfated mucins.

Histochemical characterization of the sialic acid residues in mouse colon mucins

The mucins of colonic murine mucus are highly O-glycosilated sulfosialoglycoproteins. We have characterized the sialylation pattern of oligosaccharide chains of colonic murine mucins by conventional histochemical methods and by lectin histochemistry combined with chemical pretreatments and sialidase digestion. Oligosaccharide chains are strongly sulphated, with an increase of sulfation from the proximal toward the distal colon and a decrease of sialic acid expression and acetylation toward the distal colon. In the goblet cells of proximal colon, sialic acid bound α2,3 to Galβ1,3GalNAc subterminal dimers is diacetylated at C7,C8;C7,C9;C8,C9 or triacetylated at C7,8,9. In the distal colon, sialic acid-linked α2,3 to Galβ1,3GalNAc subterminal dimers shows reduced O-acetylation at C7 and/or C8, while acetyl substituents at C9 and at C4 are almost absent. Sialic acid is involved in different essential physiological functions; thus, alterations of its expression and acetylation in oligosaccharide chains of intestinal mucins are generally associated with diseases, such as ulcerative colitis and cancer. Mice may represent a suitable animal model to study alterations of oligosaccharidic chains in colonic mucins and lectin histochemistry combined with chemical pretreatments, and enzyme digestion may be a valuable tool for this study. Our present work may represent a landmark for further lectin histochemical studies to evaluate alterations of mouse colon mucins under different physiological, pathological, or experimental conditions, with possible translational value in humans.

Expression of H(+),K(+)-ATPase and glycopattern analysis in the gastric glands of Rana esculenta

A multidisciplinary study involving lectin histochemistry, IHC, immuno-lectin blotting, and immunogold was carried out to determine the distribution of sugar residues in the glycoproteins of Rana esculenta oxynticopeptic cells. We considered animals in two experimental conditions, fasting and fed. It is known that, in mammals, the tubulovesicular membranes are rich in proteins with several functions. The proton pump H(+),K(+)-ATPase, a heterodimeric complex with a catalytic alpha-subunit and a heavily glycosylated beta-subunit, responsible for acid secretion, is the most abundant. No data have been published regarding the localization and the structures of H(+),K(+)-ATPase in amphibians. In the water frog, the luminal membrane and tubulovesicular system of oxynticopeptic cells, which differ in morphology according to their functional stage, reacted with the primary gold-conjugated antibody against the H(+),K(+)-ATPase alpha-subunit. By lectin histochemistry and immunoblotting, in the oxynticopeptic cells of R. esculenta we detected the presence of N-linked glycans having fucosylated (poly)lactosamine chains, which could correspond to the oligosaccharide chains of the beta subunit. The latter are somewhat different from those described in mammals, and this is probably because of an adaptation to the different microenvironmental conditions in which the oxynticopeptic cells find themselves, in terms of their different habits and phylogeny.

Histochemical demonstration of two subtypes of O-linked oligosaccharides in the rat gastric glands

The gastric glands synthesize glycoproteins whose oligosaccharides are linked to the peptide core mainly by the O-glycosidic bond, specifically removed by beta-elimination procedure. Our aim was to research the possibility of the existence of two subtypes of O-linked oligosaccharides with a different behavior to the removal procedure. The lectins from peanut (PNA) and Maackia amurensis (MAA-I) were histochemically used as markers of the O-linked oligosaccharides. Sections were also pretreated with beta-elimination and/or peptide N-Glycosidase F (PNGase-F) for the specific removal of O- and N-linked oligosaccharides, respectively. The lectin GNA, which mainly labels to N-linked oligosaccharides, was used to test the correct working of PNGase-F. To test the possibility that the beta-elimination treatment could remove the terminal sialic acid residues, the lectin LFA was used. The surface epithelium was negative to PNA, while it became strongly positive when beta-elimination was performed for 1 day. This staining was resistant to PNGase-F, suggesting that PNA was labeling to O-linked oligosaccharides. However, after beta-elimination for 5 days this staining is not observed. A similar pattern appeared with MAA-I. We propose the existence of two subtypes of O-linked oligosaccharides: labile and resistant. The labile O-linked oligosaccharides are removed with beta-elimination for 1 day, unmasking the PNA-positive oligosaccharides. These oligosaccharides are resistant O-linked oligosaccharides because staining is abolished with longer treatment of beta-elimination. The results with MAA-I also support this suggestion. In summary, the labile O-linked oligosaccharides are removed with short treatment, while the resistant O-linked oligosaccharides need a stronger procedure (for 5 days).

Identification of mannose moieties in N- and O-linked oligosaccharides of the primordial germ cells of Xenopus embryos

The presence of mannose (Man) in the glycoconjugates of primordial germ cells (PGCs) of Xenopus embryos was elucidated by lectin histochemistry with Concanavalin A (Con A) and snowdrop (Galanthus nivalis) bulb lectin (GNA), in combination with deglycosylative pretreatments: beta-elimination, which removes O-linked oligosaccharides, and incubation with Peptide N glycosidase F (PNGase F), which removes N-linked glycan chains. In addition, histochemistry with Con A, which binds to Man and glucose (Glc), was also performed after glucose-oxidase incubation, which converts Glc into gluconic acid, and GNA was carried out after acid hydrolysis, which removes terminal sialic acid (NeuAc) moieties. PGCs were analyzed during their migration over the mesentery until the genital ridge, and after colonization of this gonad anlage. The results showed that for both lectins: (1) the PGCs and other surrounding tissue showed a similar binding pattern, and (2) the staining in the PGCs was similar in the developmental stages studied. Labeling with Con A was due to Man, and not to Glc, as shown after incubation with glucose-oxidase, and it was assumed that Man was in N-linked oligosaccharides. However, GNA labeling was mainly due to O-linked oligosaccharides, because the pretreatment of beta-elimination turned cells negative. Moreover, acid hydrolysis pretreatment gave rise to a stronger GNA-staining, suggesting that either Man was also in subterminal position to NeuAc or some Man-containing glycans were unmasked after removal of NeuAc from other oligosaccharide chains.

Protein fucosylation regulates synapsin Ia/Ib expression and neuronal morphology in primary hippocampal neurons

Although fucose-alpha(1-2)-galactose [Fucalpha(1-2)Gal] carbohydrates have been implicated in cognitive processes such as long-term memory, the molecular mechanisms by which these sugars influence neuronal communication are not well understood. Here, we present molecular insights into the functions of Fucalpha(1-2)Gal sugars, demonstrating that they play a role in the regulation of synaptic proteins and neuronal morphology. We show that synapsins Ia and Ib, synapse-specific proteins involved in neurotransmitter release and synaptogenesis, are the major Fucalpha(1-2)Gal glycoproteins in mature cultured neurons and the adult rat hippocampus. Fucosylation has profound effects on the expression and turnover of synapsin in cells and protects synapsin from degradation by the calcium-activated protease calpain. Our studies suggest that defucosylation of synapsin has critical consequences for neuronal growth and morphology, leading to stunted neurite outgrowth and delayed synapse formation. We also demonstrate that Fucalpha(1-2)Gal carbohydrates are not limited to synapsin but are found on additional glycoproteins involved in modulating neuronal architecture. Together, our studies identify important roles for Fucalpha(1-2)Gal sugars in the regulation of neuronal proteins and morphological changes that may underlie synaptic plasticity.

A role for fucose alpha(1-2) galactose carbohydrates in neuronal growth

We report a fucose alpha(1-2) galactose-mediated pathway for the modulation of neuronal growth and morphology. Our studies provide strong evidence for the presence of Fucalpha(1-2)Gal glycoproteins and lectin receptors in hippocampal neurons. Additionally, we show that manipulation of Fucalpha(1-2)Gal-associated proteins using small-molecule and lectin probes induces dramatic changes in neuronal morphology. These findings may provide a novel pathway to stimulate neuronal growth and regeneration.