Galectins as tools for glycan mapping in histology: comparison of their binding profiles to the bovine zona pellucida by confocal laser scanning microscopy

A comprehensive N-glycome map of porcine sperm membrane before and after capacitation

Mapping the N-glycome of porcine sperm before and after sperm capacitation is important for understanding the rearrangement of glycoconjugates during capacitation. In this work, we characterized the N-glycome on the membranes of 18 pairs of fresh porcine sperm before capacitation and porcine sperm after capacitation by MALDI-MS (Matrix-assisted laser desorption/ionization-mass spectrometry). A total of 377 N-glycans were detected and a comprehensive N-glycome map of porcine sperm membranes before and after capacitation was generated, which presents the largest N-glycome dataset of porcine sperm cell membranes. Statistical analysis revealed a significantly higher level of high mannose glycosylation and a significantly lower level of fucosylation, galactosylation, and α-2,6-NeuAc after capacitation, which is further verified by flow cytometry and lectin blotting. This research reveals new insights into the relationship between N-glycosylation variations and sperm capacitation, including the underlying mechanisms of the capacitation process.

Lectin Histochemistry: Historical Perspectives, State of the Art, and Future Directions

Lectins, discovered more than 100 years ago and defined by their ability to selectively recognize specific carbohydrate structures, are ubiquitous in living organisms. Their precise functions are as yet under-explored and incompletely understood but they are clearly involved, through recognition of their binding partners, in a myriad of biological mechanisms involved in cell identity, adhesion, signaling, and growth regulation in health and disease. Understanding the complex "sugar code" represented by the "glycome" is a major challenge and at the forefront of current biological research. Lectins have been widely employed in histochemical studies to map glycosylation in cells and tissues. Here, a brief history of the discovery of lectins and early developments in their use is presented along with a selection of some of the most interesting and significant discoveries to emerge from the use of lectin histochemistry. Further, an evaluation of the next generation of lectin-based technologies is presented, including the potential for designing recombinant lectins with more precisely defined binding characteristics, linking lectin-based studies with other technologies to answer fundamental questions in glycobiology and approaches to exploring the interactions of lectins with their binding partners in more detail.

Galectin-1 Confers Endometrial Gene Expression and Protein Related to Maternal-Conceptus Immune Tolerance in Cattle

Conceptus secretory factors include galectins, a family of carbohydrate binding proteins that elicit cell adhesion and immune suppression by interacting with intracellular and extracellular glycans. In rodents, galectin-1 (LGALS1) promotes maternal-fetal immune tolerance in the decidua through expansion of tolerogenic CD11c+ dendritic cells, increased anti-inflammatory IL-10, and activation of FOXP3+ regulatory T cells (Treg). This study characterized galectin expression in early ruminant conceptuses and endometrium. We also tested the effect of recombinant bovine LGALS1 (rbLGALS1) and progesterone (P4) on endometrial expression of genes and protein related to maternal-fetal immune tolerance in cattle. Elongating bovine and ovine conceptuses expressed several galectins, particularly, LGALS1, LGALS3 and LGALS8. Within bovine endometrium, expression of LGALS3, LGALS7 and LGALS9 was greater on Day 16 of pregnancy compared to the estrous cycle. Within ovine endometrium, LGALS7 was greater during pregnancy compared to the estrous cycle and endometrium of pregnant sheep tended to have greater LGALS9 and LGALS15. Expression of endometrial LGALS4 was less during pregnancy in sheep. Treating bovine endometrium with rbLGALS1 increased endometrial expression of CD11c, IL-10 and FOXP3, within 24 h. Specifically, within caruncular endometrium, both rbLGALS1 and P4 increased FOXP3, suggesting that both ligands may promote Treg expansion. Using IHC, FOXP3+ cells with a leukocyte phenotype were localized to the bovine uterine stratum compactum near the uterine surface and increased in response to rbLGALS1. We hypothesize that galectins have important functions during establishment of pregnancy in ruminants and bovine conceptus LGALS1 and luteal P4 confer mechanisms of maternal-conceptus immune tolerance in cattle.

Manning J, Abad-Rodríguez J, Gabius HJ. What Cyto- and Histochemistry Can Do to Crack the Sugar Code

As letters form the vocabulary of a language, biochemical 'symbols' (the building blocks of oligo- and polymers) make writing molecular messages possible. Compared to nucleotides and amino acids, sugars have chemical properties that facilitate to reach an unsurpassed level of oligomer diversity. These glycans are a part of the ubiquitous cellular glycoconjugates. Cyto- and histochemically, the glycans' structural complexity is mapped by glycophenotyping of cells and tissues using receptors ('readers', thus called lectins), hereby revealing its dynamic spatiotemporal regulation: these data support the concept of a sugar code. When proceeding from work with plant (haem)agglutinins as such tools to the discovery of endogenous (tissue) lectins, it became clear that a broad panel of biological meanings can indeed be derived from the sugar-based vocabulary (the natural glycome incl. post-synthetic modifications) by glycan-lectin recognition in situ. As consequence, the immunocyto- and histochemical analysis of lectin expression is building a solid basis for the steps toward tracking down functional correlations, for example in processes leading to cell adhesion, apoptosis, autophagy or growth regulation as well as targeted delivery of glycoproteins. Introduction of labeled tissue lectins to glycan profiling assists this endeavor by detecting counterreceptor(s) in situ. Combining these tools and their applications strategically will help to take the trip toward the following long-range aim: to compile a dictionary for the glycan vocabulary that translates each message (oligosaccharide) into its bioresponse(s), that is to crack the sugar code.

Eukaryotic protein glycosylation: a primer for histochemists and cell biologists

Proteins undergo co- and posttranslational modifications, and their glycosylation is the most frequent and structurally variegated type. Histochemically, the detection of glycan presence has first been performed by stains. The availability of carbohydrate-specific tools (lectins, monoclonal antibodies) has revolutionized glycophenotyping, allowing monitoring of distinct structures. The different types of protein glycosylation in Eukaryotes are described. Following this educational survey, examples where known biological function is related to the glycan structures carried by proteins are given. In particular, mucins and their glycosylation patterns are considered as instructive proof-of-principle case. The tissue and cellular location of glycoprotein biosynthesis and metabolism is reviewed, with attention to new findings in goblet cells. Finally, protein glycosylation in disease is documented, with selected examples, where aberrant glycan expression impacts on normal function to let disease pathology become manifest. The histological applications adopted in these studies are emphasized throughout the text.

Lectin Histochemistry: Historical Perspectives, State of the Art, and the Future

Lectins, discovered more than 100 years ago and defined by their ability to selectively recognize specific carbohydrate structures, are ubiquitous in living organisms. Their precise functions are as yet under-explored and incompletely understood but they are clearly involved, through recognition of their binding partners, in a myriad of biological mechanisms involved in cell identity, adhesion, signaling, growth regulation, in health and disease. Understanding the complex "sugar code" represented by the glycome is a major challenge and at the forefront of current biological research. Lectins have been widely employed in histochemical studies to map glycosylation in cells and tissues. Here, a brief history of the discovery of lectins and early developments in their use is presented along with a selection of some of the most interesting and significant discoveries to emerge from use of lectin histochemistry. Further, an evaluation of the next generation of lectin-based technologies is presented, including the potential for designing recombinant lectins with more precisely defined binding characteristics, linking lectin-based studies with other technologies to answer fundamental questions in glycobiology, and approaches to exploring the interactions of lectins with their binding partners in more detail.

Lectins: a primer for histochemists and cell biologists

An experimental observation on selecting binding partners underlies the introduction of the term 'lectin'. Agglutination of erythrocytes depending on their blood-group status revealed the presence of activities in plant extracts that act in an epitope-specific manner like antibodies. As it turned out, their binding partners on the cell surface are carbohydrates of glycoconjugates. By definition, lectins are glycan-specific (mono- or oligosaccharides presented by glycoconjugates or polysaccharides) receptors, distinguished from antibodies, from enzymes using carbohydrates as substrates and from transporters of free saccharides. They are ubiquitous in Nature and structurally widely diversified. More than a dozen types of folding pattern have evolved for proteins that bind glycans. Used as tool, this capacity facilitates versatile mapping of glycan presence so that plant/fungal and also animal/human lectins have found a broad spectrum of biomedical applications. The functional pairing with physiological counterreceptors is involved in a wide range of cellular activities from cell adhesion, glycoconjugate trafficking to growth regulation and lets lectins act as sensors/effectors in host defense.

Galectin-8 enhances adhesion of multiple myeloma cells to vascular endothelium and is an adverse prognostic factor

Multiple myeloma is characterized by abnormal infiltration of malignant plasma cells into bone marrow. Testing the hypothesis that bivalent galectin-8 (Gal-8) may influence homing of myeloma cells to vascular endothelium as a key prerequisite for infiltration, we analyzed the two Gal-8 splice variants (Gal-8S, Gal-8L). They differ in the length of their linker peptide connecting the two lectin domains. Both Gal-8 isoforms bind to cells of the myeloma lines Gal-8⁺ MOLP-8 and Gal-8^- LP-1 in a glycan-inhibitable manner. Both Gal-8 isoforms led to enhanced adhesion of myeloma cells to vascular endothelium under dynamic shear stress conditions, Gal-8L (by more than 40-fold) even stronger than Gal-8S. Additional treatment of endothelial cells with tumour necrosis factor prior to the dynamic shear stress assay entailed an almost 100-fold enhanced adhesion of myeloma cells without addition of Gal-8 variants and a further 1.5-1.7-fold enhancement by addition of Gal-8 variants. We also found that elevated expression of Gal-8 in native multiple myeloma cells is an adverse prognostic factor for overall and event-free survival using patients' gene expression profile data of the total therapy 2 and 3 myeloma studies. Also, elevated concentrations of Gal-8 were detected (45%, 19/42 patients) in sera of multiple myeloma patients compared to those of healthy, age-matched donors. Both experimental and clinical data strongly point to the significance of Gal-8 for multiple myeloma development.

Merging carbohydrate chemistry with lectin histochemistry to study inhibition of lectin binding by glycoclusters in the natural tissue context

Recognition of glycans by lectins leads to cell adhesion and growth regulation. The specificity and selectivity of this process are determined by carbohydrate structure (sequence and shape) and topology of its presentation. The synthesis of (neo)glycoconjugates with bi- to oligo-valency (glycoclusters) affords tools to delineate structure-activity relationships by blocking lectin binding to an artificial matrix, often a glycoprotein, or cultured cell lines. The drawback of these assays is that glycan presentation is different from that in tissues. In order to approach the natural context, we here introduce lectin histochemistry on fixed tissue sections to determine the susceptibility of binding of two plant lectins, i.e., GSA-II and WGA, to a series of 10 glycoclusters. Besides valency, this panel covers changes in the anomeric position (α/β) and the atom at the glycosidic linkage (O/S). Flanked by cell and solid-phase assays with human tumor lines and two mucins, respectively, staining (intensity and profile) was analyzed in sections of murine jejunum, stomach and epididymis as a function of glycocluster presence. The marked and differential sensitivity of signal generation to structural aspects of the glycoclusters proves the applicability of this method. This enables comparisons between data sets obtained by using (neo)glycoconjugates, cells and the tissue context as platforms. The special advantage of processing tissue sections is the monitoring of interference with lectin association at sites that are relevant for functionality. Testing glycoclusters in lectin histochemistry will especially be attractive in cases of multi-target recognition (glycans, proteins and lipids) by a tissue lectin.

Network monitoring of adhesion/growth-regulatory galectins: localization of the five canonical chicken proteins in embryonic and maturing bone and cartilage and their introduction as histochemical tools

Divergence from an ancestral gene leads to a family of homologous proteins. Whether they are physiologically distinct, similar, or even redundant is an open question in each case. Defining profiles of tissue localization is a step toward giving diversity a functional meaning. Due to the significance of endogenous sugar receptors (lectins) as effectors for a wide range of cellular activities we have focused on galectins. The comparatively low level of network complexity constituted by only five canonical proteins makes chicken galectins (CGs) an attractive choice to perform comprehensive analysis, here studied on bone/cartilage as organ system. Galectin expression was monitored by Western blotting and immunohistochemistry using non-cross-reactive antibodies. Overall, three galectins (CG-1B, CG-3, CG-8) were present with individual expression patterns, one was found exclusively in the mesenchyme (CG-1A), the fifth (CG-2) not being detectable. The documented extents of separation are a sign for functional divergence; in cases with overlapping stainings, as for example in the osteoprogenitor layer or periosteum, cooperation may also be possible. Recombinant production enabled the introduction of the endogenous lectins as tools for binding-site localization. Their testing revealed developmental regulation and cell-type-specific staining. Of relevance for research on mammalian galectins, this study illustrates that certain cell types can express more than one galectin, letting functional interrelationships appear likely. Thus, complete network analysis irrespective of its degree of complexity is mandatory.

Mammalian protein glycosylation--structure versus function

Carbohydrates fulfil many common as well as extremely important functions in nature. They show a variety of molecular displays--e.g., free mono-, oligo-, and polysaccharides, glycolipids, proteoglycans, glycoproteins, etc.--with particular roles and localizations in living organisms. Structure-specific peculiarities are so many and diverse that it becomes virtually impossible to cover them all from an analytical perspective. Hence this manuscript, focused on mammalian glycosylation, rather than a complete list of analytical descriptors or recognized functions for carbohydrate structures, comprehensively reviews three central issues in current glycoscience, namely (i) structural analysis of glycoprotein glycans, covering both classical and novel approaches for teasing out the structural puzzle as well as potential pitfalls of these processes; (ii) an overview of functions attributed to carbohydrates, covering from monosaccharide to complex, well-defined epitopes and full glycans, including post-glycosylational modifications, and (iii) recent technical advances allowing structural identification of glycoprotein glycans with simultaneous assignation of biological functions.

Thermodynamic Switch in Binding of Adhesion/Growth Regulatory Human Galectin-3 to Tumor-Associated TF Antigen (CD176) and MUC1 Glycopeptides

A shift to short-chain glycans is an observed change in mucin-type O-glycosylation in premalignant and malignant epithelia. Given the evidence that human galectin-3 can interact with mucins and also weakly with free tumor-associated Thomsen-Friedenreich (TF) antigen (CD176), the study of its interaction with MUC1 (glyco)peptides is of biomedical relevance. Glycosylated MUC1 fragments that carry the TF antigen attached through either Thr or Ser side chains were synthesized using standard Fmoc-based automated solid-phase peptide chemistry. The dissociation constants (K_d) for interaction of galectin-3 and the glycosylated MUC1 fragments measured by isothermal titration calorimetry decreased up to 10 times in comparison to that of the free TF disaccharide. No binding was observed for the nonglycosylated control version of the MUC1 peptide. The most notable feature of the binding of MUC1 glycopeptides to galectin-3 was a shift from a favorable enthalpy to an entropy-driven binding process. The comparatively diminished enthalpy contribution to the free energy (ΔG) was compensated by a considerable gain in the entropic term. ¹H–¹⁵N heteronuclear single-quantum coherence spectroscopy nuclear magnetic resonance data reveal contact at the canonical site mainly by the glycan moiety of the MUC1 glycopeptide. Ligand-dependent differences in binding affinities were also confirmed by a novel assay for screening of low-affinity glycan–lectin interactions based on AlphaScreen technology. Another key finding is that the glycosylated MUC1 peptides exhibited activity in a concentration-dependent manner in cell-based assays revealing selectivity among human galectins. Thus, the presentation of this tumor-associated carbohydrate ligand by the natural peptide scaffold enhances its affinity, highlighting the significance of model studies of human lectins with synthetic glycopeptides.

A guide into glycosciences: How chemistry, biochemistry and biology cooperate to crack the sugar code

BACKGROUND

The most demanding challenge in research on molecular aspects within the flow of biological information is posed by the complex carbohydrates (glycan part of cellular glycoconjugates). How the 'message' encoded in carbohydrate 'letters' is 'read' and 'translated' can only be unraveled by interdisciplinary efforts.

SCOPE OF REVIEW

This review provides a didactic step-by-step survey of the concept of the sugar code and the way strategic combination of experimental approaches characterizes structure-function relationships, with resources for teaching.

MAJOR CONCLUSIONS

The unsurpassed coding capacity of glycans is an ideal platform for generating a broad range of molecular 'messages'. Structural and functional analyses of complex carbohydrates have been made possible by advances in chemical synthesis, rendering production of oligosaccharides, glycoclusters and neoglycoconjugates possible. This availability facilitates to test the glycans as ligands for natural sugar receptors (lectins). Their interaction is a means to turn sugar-encoded information into cellular effects. Glycan/lectin structures and their spatial modes of presentation underlie the exquisite specificity of the endogenous lectins in counterreceptor selection, that is, to home in on certain cellular glycoproteins or glycolipids.

GENERAL SIGNIFICANCE

Understanding how sugar-encoded 'messages' are 'read' and 'translated' by lectins provides insights into fundamental mechanisms of life, with potential for medical applications.

Introduction to glycopathology: the concept, the tools and the perspectives

Virtual slides

The virtual slides for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1670639891114983.

Analyzing the flow of biological information is a fundamental challenge for basic sciences. The emerging results will then lend themselves to the development of new approaches for medical applications. Toward this end, the products of protein/lipid glycosylation deserve special attention. The covalent attachment of sugars to these carriers means much more than just a change of the carriers’ physicochemical properties. In principle, the ubiquitous presence of glycoconjugates and the close inspection of the particular structural ‘talents’ of carbohydrates provide suggestive evidence for information coding by sugars. In fact, the theoretical number of ‘words’ (oligomers) formed by ‘letters’ (monosaccharides) is by far higher than by using nucleotides or amino acids. In other words, glycans harbor an unsurpassed coding capacity. The cyto- and histochemical detection of dynamic changes in the profile of cellular glycans (glycome, the equivalent of the proteome) by sugar receptors such as antibodies used as tools underscores the suitability of carbohydrates for such a task. The resulting staining patterns can be likened to a molecular fingerprint. By acting as ligand (counterreceptor) for endogenous receptors (tissue lectins), glycan epitopes become partners in a specific recognition pair, and the sugar-encoded information can then be translated into effects, e.g. in growth regulation. Of note, expression of both sides of such a pair, i.e. lectin and cognate glycan, can physiologically be orchestrated for optimal efficiency. Indeed, examples how to prevent autoimmune diseases by regulatory T cells and restrict carcinoma growth by a tumor suppressor attest occurrence of co-regulation. In consequence, these glycans have potential to establish a new class of functional biomarkers, and mapping presence of their receptors is warranted. In this review, the cyto- and histochemical methods, which contribute to explore information storage and transfer within the sugar code, are described. This introduction to the toolbox is flanked by illustrating the application of each type of tool in histopathology, with focus on adhesion/growth-regulating galectins. Together with an introduction to fundamental principles of the sugar code, the review is designed to guide into this field and to inspire respective research efforts.

Combining glycocluster synthesis with protein engineering: an approach to probe into the significance of linker length in a tandem-repeat-type lectin (galectin-4)

Complementarity in lectin-glycan interactions in situ is assumed to involve spatial features in both the lectin and the glycan, giving a functional meaning to structural aspects of the lectin beyond its carbohydrate-binding site. In combining protein engineering with glycocluster synthesis, it is shown that the natural linker length of a tandem-repeat-type human lectin (galectin-4) determines binding properties in two binding assays (using surface-presented glycoprotein and cell surface assays). The types of glycocluster tested included bivalent lactosides based on tertiary amides of terephthalic, isophthalic, 2,6-naphthalic and oxalic acids as well as bivalent H(type 2) trisaccharides grafted on secondary/tertiary terephthalamides and two triazole-linker-containing cores. The presented data reveal a marked change in susceptibility to the test compounds when turning the tandem-repeat-type to a proto-type-like display. The testing of glycoclusters is suggested as a general strategy to help to delineate the significance of distinct structural features of lectins beyond their contact sites to the glycan.

Rho GTPase Rac1: molecular switch within the galectin network and for N-glycan α2,6-sialylation/O-glycan core 1 sialylation in colon cancer in vitro

The Rho GTPase Rac1 is a multifunctional protein working through different effector pathways. The emerging physiological significance of glycanlectin recognition gives reason to testing the possibility for an influence of modulation of Rac1 expression on these molecular aspects. Using human colon adenocarcinoma (SW620) cells genetically engineered for its up- and down-regulation (Rac1+ and Rac1- cells) along with wild-type and mock-transfected control cells, the questions are addressed whether the presence of adhesion/growth-regulatory galectins and distinct aspects of cell surface glycosylation are affected. Proceeding from RT-PCR data to Western blotting after two-dimensional gel electrophoresis and flow cytofluorimetry with non-crossreactive antibodies against six members of this lectin family (i.e. galectins-1, -3, -4, -7, -8 and -9), a reduced extent of the presence of galectins-1, -7 and -9 was revealed in the case of Rac1 cells. Application of these six galectins as probes to determination of cell reactivity for human lectins yielded relative increases in surface labelling of Rac1- cells with galectins-1, -3 and -7. Examining distinct aspects of cell surface glycosylation with a panel of 14 plant/fungal lectins disclosed a decrease in α2,6-sialylation of N-glycans and an increase in PNA-reactive sites (i.e. non-sialylated core 1 O-glycans), two alterations known to favour reactivity for galectins-1 and -3. Thus, manipulation of Rac1 expression selectively affects the expression pattern within the galectin network at the level of proteins and distinct aspects of cell surface glycosylation.

Identification of bovine embryos cultured in groups by attachment of barcodes to the zona pellucida

The low number of oocytes collected from unstimulated donors by ovum pick-up means that embryos produced from each individual female have to be cultured individually or in very small groups. However, it has been demonstrated that single-embryo culture is less efficient than embryo culture in groups. To overcome this limitation, we developed a direct embryo-tagging system, which allows the collective culture of embryos from different origins whilst preserving their pedigree. Presumptive bovine zygotes were tagged with eight wheat-germ agglutinin biofunctionalised polysilicon barcodes attached to the outer surface of the zona pellucida (ZP). Four different barcodes were used to encode groups of 20–25 embryos, which were then cultured in the same drop. Cleavage, Day-7 and Day-8 blastocysts and barcode retention rates were assessed. In addition, Day-7 blastocysts were vitrified and warmed. Barcode attachment to the ZP of bovine embryos affected neither in vitro embryo development nor post-warming survival of the tagged embryos. All the embryos maintained barcodes attached until Day 8 of culture (3.63 ± 0.37 barcodes per embryo) and could be identified. In conclusion, identification of embryos by barcodes attached to the ZP is feasible and will allow the culture of embryos from different donors in the same drop.

Posttranslational modifications of zona pellucida proteins

The zona pellucida (ZP), which surrounds the mammalian oocyte, functions in various aspects of fertilization. The ZP consists of three or four glycoproteins, which are derived from transmembrane proteins that lack the ability to self-assemble. Following posttranslational processing at specific sites, ectodomains of ZP precursor proteins are released from the membrane and begin to form a matrix. Glycosylational modification is thought to be involved in species-selective sperm recognition by ZP proteins. However, in mice, the supramolecular structure of the zona matrix is also important in sperm recognition. One ZP protein, ZP2, is processed at a specific site upon fertilization by ovastacin, which is released from cortical granules inside the oocyte. This phenomenon is involved in the block to polyspermy. The proteolysis of ubiquitinated ZP proteins by a sperm-associated proteasome is involved in penetration of the zona matrix by sperm, at least in the pigs. Thus, the posttranslational modification of ZP proteins is closely tied to ZP formation and the regulation of sperm-oocyte interactions.

Phosphorylation of multifunctional galectins by protein kinases CK1, CK2, and PKA

Phosphorylation is known to have a strong impact on protein functions. We analyzed members of the lectin family of multifunctional galectins as targets of the protein kinases CK1, CK2, and PKA. Galectins are potent growth regulators able to bind both glycan and peptide motifs at intra- and extracellular sites. Performing in vitro kinase assays, galectin phosphorylation was detected by phosphoprotein staining and autoradiography. The insertion of phosphoryl groups varied to a large extent depending on the type of kinase applied and the respective galectin substrate. Sites of phosphorylation observed in the recombinant galectins were determined by a strategic combination of phosphopeptide enrichment and nano-ultra-performance liquid chromatography tandem mass spectrometry (nanoUPLC-MS/MS). By in silico modeling, phosphorylation sites were visualized three-dimensionally. Our results reveal galectin-type-specific Ser-/Thr-dependent phosphorylation beyond the known example of galectin-3. These data are the basis for functional studies and also illustrate the analytical sensitivity of the applied methods for further work on human lectins.

Peptides derived from human galectin-3 N-terminal tail interact with its carbohydrate recognition domain in a phosphorylation-dependent manner

Galectin-3 (Gal-3) is a multi-functional effector protein that functions in the cytoplasm and the nucleus, as well as extracellularly following non-classical secretion. Structurally, Gal-3 is unique among galectins with its carbohydrate recognition domain (CRD) attached to a rather long N-terminal tail composed mostly of collagen-like repeats (nine in the human protein) and terminating in a short non-collagenous terminal peptide sequence unique in this lectin family and not yet fully explored. Although several Ser and Tyr sites within the N-terminal tail can be phosphorylated, the physiological significance of this post-translational modification remains unclear. Here, we used a series of synthetic (phospho)peptides derived from the tail to assess phosphorylation-mediated interactions with (15)N-labeled Gal-3 CRD. HSQC-derived chemical shift perturbations revealed selective interactions at the backface of the CRD that were attenuated by phosphorylation of Tyr 107 and Tyr 118, while phosphorylation of Ser 6 and Ser 12 was essential. Controls with sequence scrambling underscored inherent specificity. Our studies shed light on how phosphorylation of the N-terminal tail may impact on Gal-3 function and prompt further studies using phosphorylated full-length protein.

Glycophenotyping of osteoarthritic cartilage and chondrocytes by RT-qPCR, mass spectrometry, histochemistry with plant/human lectins and lectin localization with a glycoprotein

INTRODUCTION

This study aimed to characterize the glycophenotype of osteoarthritic cartilage and human chondrocytes.

METHODS

Articular knee cartilage was obtained from nine osteoarthritis (OA) patients. mRNA levels for 27 glycosyltransferases were analyzed in OA chondrocytes using RT-qPCR. Additionally, N- and O-glycans were quantified using mass-spectrometry. Histologically, two cartilage areas with Mankin scores (MS) either ≤ 4 or ≥ 9 were selected from each patient representing areas of mild and severe OA, respectively. Tissue sections were stained with (1) a selected panel of plant lectins for probing into the OA glycophenotype, (2) the human lectins galectins-1 and -3, and (3) the glycoprotein asialofetuin (ASF) for visualizing β-galactoside-specific endogenous lectins.

RESULTS

We found that OA chondrocytes expressed oligomannosidic structures as well as non-, mono- and disialylated complex-type N-glycans, and core 2 O-glycans. Reflecting B4GALNT3 mRNA presence in OA chondrocytes, LacdiNAc-terminated structures were detected. Staining profiles for plant and human lectins were dependent on the grade of cartilage degeneration, and ASF-positive cells were observed in significantly higher rates in areas of severe degeneration.

CONCLUSIONS

In summary, distinct aspects of the glycome in OA cartilage are altered with progressing degeneration. In particular, the alterations measured by galectin-3 and the pan-galectin sensor ASF encourage detailed studies of galectin functionality in OA.

Biomolecule screening for efficient attachment of biofunctionalized microparticles to the zona pellucida of mammalian oocytes and embryos

Individual tagging of oocytes and embryos through the attachment of micrometer-sized polysilicon barcodes to their zona pellucida (ZP) is a promising approach to ensure their correct identification and traceability in human assisted reproduction and in animal production programs. To provide barcodes with the capacity of binding to the ZP, they must be first biofunctionalized with a biomolecule capable of binding to the ZP of both oocytes and embryos. The aim of this work was to select, among an anti-ZP2 antibody and the two lectins wheat germ agglutinin (WGA) and phytohemagglutinin-L, the most optimal biomolecule for the eventual biofunctionalization of barcodes, using mouse oocytes and embryos and commercially available microspheres as a model. Despite the anti-ZP2 antibody showed the highest number of binding sites onto the ZP surface, as determined by field emission scanning electron microscopy, the binding of anti-ZP2-biofunctionalized microspheres to the ZP of cultured oocytes and embryos was less robust and less stable than the binding of lectin-biofunctionalized ones. WGA proved to be, among the three candidates tested, the most appropriate biomolecule to biofunctionalize microparticles with the aim to attach them to the ZP of both oocytes and embryos and to maintain them attached through oocyte activation (zona reaction) and in vitro culture up to the blastocyst stage. As saccharides recognized by WGA are highly abundant in the ZP of most mammalian species, WGA-biofuncionalized microparticles would be able to attach to the ZP of oocytes/embryos of species other than the mouse, such as humans and farm animals.

The third dimension of reading the sugar code by lectins: design of glycoclusters with cyclic scaffolds as tools with the aim to define correlations between spatial presentation and activity

Coding of biological information is not confined to nucleic acids and proteins. Endowed with the highest level of structural versatility among biomolecules, the glycan chains of cellular glycoconjugates are well-suited to generate molecular messages/signals in a minimum of space. The sequence and shape of oligosaccharides as well as spatial aspects of multivalent presentation are assumed to underlie the natural specificity/selectivity that cellular glycans have for endogenous lectins. In order to eventually unravel structure-activity profiles cyclic scaffolds have been used as platforms to produce glycoclusters and afford valuable tools. Using adhesion/growth-regulatory galectins and the pan-galectin ligand lactose as a model, emerging insights into the potential of cyclodextrins, cyclic peptides, calixarenes and glycophanes for this purpose are presented herein. The systematic testing of lectin panels with spatially defined ligand presentations can be considered as a biomimetic means to help clarify the mechanisms, which lead to the exquisite accuracy at which endogenous lectins select their physiological counterreceptors from the complexity of the cellular glycome.

Direct embryo tagging and identification system by attachment of biofunctionalized polysilicon barcodes to the zona pellucida of mouse embryos

STUDY QUESTION

Is the attachment of biofunctionalized polysilicon barcodes to the outer surface of the zona pellucida an effective approach for the direct tagging and identification of cultured embryos?

SUMMARY ANSWER

The results achieved provide a proof of concept for a direct embryo tagging system using biofunctionalized polysilicon barcodes, which could help to minimize the risk of mismatching errors (mix-ups) in human assisted reproduction technologies.

WHAT IS KNOWN ALREADY

Even though the occurrence of mix-ups is rare, several cases have been reported in fertility clinics around the world. Measures to prevent the risk of mix-ups in human assisted reproduction technologies are therefore required.

STUDY DESIGN, SIZE, DURATION

Mouse embryos were tagged with 10 barcodes and the effectiveness of the tagging system was tested during fresh in vitro culture (n=140) and after embryo cryopreservation (n = 84). Finally, the full-term development of tagged embryos was evaluated (n =105).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Mouse pronuclear embryos were individually rolled over wheat germ agglutinin-biofunctionalized polysilicon barcodes to distribute them uniformly around the ZONA PELLUCIDA surface. Embryo viability and retention of barcodes were determined during 96 h of culture. The identification of tagged embryos was performed every 24 h in an inverted microscope and without embryo manipulation to simulate an automatic reading procedure. Full-term development of the tagged embryos was assessed after their transfer to pseudo-pregnant females. To test the validity of the embryo tagging system after a cryopreservation process, tagged embryos were frozen at the 2-cell stage using a slow freezing protocol, and followed in culture for 72 h after thawing.

MAIN RESULTS AND THE ROLE OF CHANCE

Neither the in vitro or in vivo development of tagged embryos was adversely affected. The tagging system also proved effective during an embryo cryopreservation process. Global identification rates higher than 96 and 92% in fresh and frozen-thawed tagged embryos, respectively, were obtained when simulating an automatic barcode reading system, although these rates could be increased to 100% by simply rotating the embryos during the reading process.

LIMITATIONS, REASONS FOR CAUTION

The direct embryo tagging developed here has exclusively been tested in mouse embryos. Its effectiveness in other species, such as the human, is currently being tested.

WIDER IMPLICATIONS OF THE FINDINGS

The direct embryo tagging system developed here, once tested in human embryos, could provide fertility clinics with a novel tool to reduce the risk of mix-ups in human assisted reproduction technologies.

Lactose binding to human galectin-7 (p53-induced gene 1) induces long-range effects through the protein resulting in increased dimer stability and evidence for positive cooperativity

The product of p53-induced gene 1 is a member of the galectin family, i.e., galectin-7 (Gal-7). To move beyond structural data by X-ray diffraction, we initiated the study of the lectin by nuclear magnetic resonance (NMR) and circular dichroism spectroscopies, and molecular dynamics (MD) simulations. In concert, our results indicate that lactose binding to human Gal-7 induces long-range effects (minor conformational shifts and changes in structural dynamics) throughout the protein that result in stabilization of the dimer state, with evidence for positive cooperativity. Monte Carlo fits of (15)N-Gal-7 HSQC titrations with lactose using a two-site model yield K1 = 0.9 ± 0.6 × 10(3) M(-1) and K2 = 3.4 ± 0.8 × 10(3) M(-1). Ligand binding-induced stabilization of the Gal-7 dimer was supported by several lines of evidence: MD-based calculations of interaction energies between ligand-loaded and ligand-free states, gel filtration data and hetero-FRET spectroscopy that indicate a highly reduced tendency for dimer dissociation in the presence of lactose, CD-based thermal denaturation showing that the transition temperature of the lectin is significantly increased in the presence of lactose, and saturation transfer difference (STD) NMR using a molecular probe of the monomer state whose presence is diminished in the presence of lactose. MD simulations with the half-loaded ligand-bound state also provided insight into how allosteric signaling may occur. Overall, our results reveal long-range effects on Gal-7 structure and dynamics, which factor into entropic contributions to ligand binding and allow further comparisons with other members of the galectin family.

Loss of adhesion/growth-regulatory galectin-9 from squamous cell epithelium in head and neck carcinomas

Galectins are potent effectors of cell adhesion and growth regulation. Their expression as comples network necessitates systematic study of each member of this family. Toward this aim, we here focus on the tandem-repeat-type galectin-9. Its presence is monitored in normal squamous epithelium of the head and neck, the surgical margin, and four types of squamous cell carcinoma. Lectin presence was detected in cells of the basal layer of the epithelium. All galectin-9-negative epithelia showed aberrant positivity for keratins 14 and 19. The surgical margin presented either a normal pattern of galectin-9 and keratin presence or a mosaic-like presence/absence of galectin-9 and aberrant expression of both keratins 14 and 19. All studied specimens of squamous cell carcinoma were negative for galectin-9. When biotinylated galectin-9, or its N-terminal domain, was tested, no significant tissue reactivity for both probes was observed. Neuraminidase treatment generated reactivity to the N-domain. In conclusion, galectin-9 is expressed in the majority of samples of normal epithelium, along with regular presence of keratins 14 or 19. This lectin can represent a potential marker of normality in the cases of the studied squamous cell epithelia.

Adhesion/growth-regulatory galectins in the human eye: localization profiles and tissue reactivities as a standard to detect disease-associated alterations

OBJECTIVES

To characterize the localization profiles of seven adhesion/growth-regulatory galectins in the normal human eye using immunodetection of endogenous galectins and binding of labeled galectins to sections, useful as a basis to detect disease-associated alterations.

METHODS

Non-cross-reactive anti-galectin antibodies and biotinylated galectins were tested on acetone-fixed cryosections of normal human donor eyes. Controls included omission of first-step reagent, testing of an antibody against a galectin specific for rat (galectin-5), and blocking of galectin binding with lactose.

RESULTS

Galectin presence was not restricted to one or few members of this family. Signal occurrence can even include all tested or most proteins (conjunctival or corneal epithelium), whereas choroid positivity is fully accounted for by galectin-9. Regional specificity and characteristic profiles for each protein, immuno- and galectin histochemically, were determined. Differences in tissue reactivity among the galectins were detected.

CONCLUSIONS

That the galectins have characteristic localization/reactivity profiles supports the concept of a network with potential for non-overlapping functions. The reported data thus prompt to proceed to the respective analysis of specimens from ocular diseases.

Recent progress in histochemistry and cell biology

Studies published in Histochemistry and Cell Biology in the year 2011 represent once more a manifest of established and newly sophisticated techniques being exploited to put tissue- and cell type-specific molecules into a functional context. The review is therefore the Histochemistry and Cell Biology's yearly intention to provide interested readers appropriate summaries of investigations touching the areas of tissue biology, developmental biology, the biology of the immune system, stem cell research, the biology of subcellular compartments, in order to put the message of such studies into natural scientific-/human- and also pathological-relevant correlations.