Revealing the anti-HRP epitope in Drosophila and Caenorhabditis

Recognition of Highly Branched N-Glycans of the Porcine Whipworm by the Immune System

Glycans are key to host-pathogen interactions, whereby recognition by the host and immunomodulation by the pathogen can be mediated by carbohydrate binding proteins, such as lectins of the innate immune system, and their glycoconjugate ligands. Previous studies have shown that excretory-secretory products of the porcine nematode parasite Trichuris suis exert immunomodulatory effects in a glycan-dependent manner. To better understand the mechanisms of these interactions, we prepared N-glycans from T. suis and both analyzed their structures and used them to generate a natural glycan microarray. With this array, we explored the interactions of glycans with C-type lectins, C-reactive protein, and sera from T. suis-infected pigs. Glycans containing LacdiNAc and phosphorylcholine-modified glycans were associated with the highest binding by most of these proteins. In-depth analysis revealed not only fucosylated LacdiNAc motifs with and without phosphorylcholine moieties but phosphorylcholine-modified mannose and N-acetylhexosamine-substituted fucose residues, in the context of maximally tetraantennary N-glycan scaffolds. Furthermore, O-glycans also contained fucosylated motifs. In summary, the glycans of T. suis are recognized by both the innate and adaptive immune systems and also exhibit species-specific features distinguishing its glycome from those of other nematodes.

Analysis of Caenorhabditis Protein Glycosylation

Glycoproteins result from post-translational modification of proteins by glycans attached to certain side chains, with possible heterogeneity due to different structures being possible at the same glycosylation site.In contrast to the mammalian systems, analysis of invertebrate glycans presents a challenge in analysis as there exist unfamiliar epitopes and a high degree of structural and isomeric variation between different species-Caenorhabditis elegans is no exception. Simple screening using lectins and antibodies can yield hints regarding which glycan epitopes are present in wild-type and mutant strains, but detailed analysis is necessary for determining more exact glycomic information. Here, our analytical approach is to analyze N- and O-glycans involving "off-line" RP-HPLC MALDI-TOF MS/MS. Enrichment and labeling steps facilitate the analysis of single structures and provide isomeric separation. Thereby, the "simple" worm expresses over 200 N-glycan structures varying depending on culture conditions or the genetic background.

Recognition of highly branched N-glycans of the porcine whipworm by the immune system

Glycans are key to host-pathogen interactions, whereby recognition by the host and immunomodulation by the pathogen can be mediated by carbohydrate binding proteins, such as lectins of the innate immune system, and their glycoconjugate ligands. Previous studies have shown that excretory-secretory products of the porcine nematode parasite Trichuris suis exert immunomodulatory effects in a glycan-dependent manner. To better understand the mechanisms of these interactions, we prepared N-glycans from T. suis and both analyzed their structures and used them to generate a natural glycan microarray. With this array we explored the interactions of glycans with C-type lectins, C-reactive protein and sera from T. suis infected pigs. Glycans containing LacdiNAc and phosphorylcholine-modified glycans were associated with the highest binding by most of these proteins. In-depth analysis revealed not only fucosylated LacdiNAc motifs with and without phosphorylcholine moieties, but phosphorylcholine-modified mannose and N-acetylhexosamine-substituted fucose residues, in the context of maximally tetraantennary N-glycan scaffolds. Furthermore, O-glycans also contained fucosylated motifs. In summary, the glycans of T. suis are recognized by both the innate and adaptive immune systems, and also exhibit species-specific features distinguishing its glycome from those of other nematodes.

Interaction of the sorting nexin 25 homologue Snazarus with Rab11 balances endocytic and secretory transport and maintains the ultrafiltration diaphragm in nephrocytes

Proper balance of exocytosis and endocytosis is important for the maintenance of plasma membrane lipid and protein homeostasis. This is especially critical in human podocytes and the podocyte-like Drosophila nephrocytes that both use a delicate diaphragm system with evolutionarily conserved components for ultrafiltration. Here, we show that the sorting nexin 25 homologue Snazarus (Snz) binds to Rab11 and localizes to Rab11-positive recycling endosomes in Drosophila nephrocytes, unlike in fat cells where it is present in plasma membrane/lipid droplet/endoplasmic reticulum contact sites. Loss of Snz leads to redistribution of Rab11 vesicles from the cell periphery and increases endocytic activity in nephrocytes. These changes are accompanied by defects in diaphragm protein distribution that resemble those seen in Rab11 gain-of-function cells. Of note, co-overexpression of Snz rescues diaphragm defects in Rab11 overexpressing cells, whereas snz knockdown in Rab11 overexpressing nephrocytes or simultaneous knockdown of snz and tbc1d8b encoding a Rab11 GTPase-activating protein (GAP) leads to massive expansion of the lacunar system that contains mislocalized diaphragm components: Sns and Pyd/ZO-1. We find that loss of Snz enhances while its overexpression impairs secretion, which, together with genetic epistasis analyses, suggest that Snz counteracts Rab11 to maintain the diaphragm via setting the proper balance of exocytosis and endocytosis.

Immunohistochemical Characterization of the Nervous System of Culex pipiens (Diptera, Culicidae)

Arthropod-borne diseases represent one of the greatest infection-related threats as a result of climate change and globalization. Repeatedly, arbovirus-infected mosquitoes show behavioral changes whose underlying mechanisms are still largely unknown, but might help to develop control strategies. However, in contrast to well-characterized insects such as fruit flies, little is known about neuroanatomy and neurotransmission in mosquitoes. To overcome this limitation, the study focuses on the immunohistochemical characterization of the nervous system of Culex pipiens biotype molestus in comparison to Drosophila melanogaster using 13 antibodies labeling nervous tissue, neurotransmitters or neurotransmitter-related enzymes. Antibodies directed against γ-aminobutyric acid, serotonin, tyrosine-hydroxylase and glutamine synthetase were suitable for investigations in Culex pipiens and Drosophila melanogaster, albeit species-specific spatial differences were observed. Likewise, similar staining results were achieved for neuronal glycoproteins, axons, dendrites and synaptic zones in both species. Interestingly, anti-phosphosynapsin and anti-gephyrin appear to represent novel markers for synapses and glial cells, respectively. In contrast, antibodies directed against acetylcholine, choline acetyltransferase, elav and repo failed to produce a signal in Culex pipiens comparable to that in Drosophila melanogaster. In summary, present results enable a detailed investigation of the nervous system of mosquitoes, facilitating further studies of behavioral mechanisms associated with arboviruses in the course of vector research.

The larval haematopoietic organs of Manduca sexta (Insecta, Lepidoptera): An insight into plasmatocyte development and larval haematopoiesis

Haematopoietic organs (HOs) in Lepidoptera are widely recognised as the source for at least two haemocyte types. With new specific markers for oenocytoids and spherule cells and a method to identify prohaemocytes, the haemocytes formed in and released by the HOs of Manduca sexta are characterised. Differentiation of HO-cells to haemocytes other than plasmatocytes and prohaemocytes neither occurs in the organ itself nor in cells released in vitro by the HOs. Differential labelling patterns evidence the existence of plasmatocyte subpopulations and prohaemocytes, which might represent a gradual differentiation of haemocytes within the organs. Prohaemocytes can be identified by PNA-labelling of the cell membrane. These prohaemocytes are found in circulation and in the HOs and are released by the organs. Circulating prohaemocytes possess characteristics for granular cells, plasmatocytes or oenocytoids while HO derived prohaemocytes share characteristics only with plasmatocytes. Ablation of the HOs diminishes the plasmatocyte and prohaemocyte number, indicating a true larval haematopoietic function.

Crucial role of framework with cytoskeletal actin filaments for shaping microstructure of footpad setae in the ladybird beetle, Harmonia axyridis

Insects that can walk on smooth surfaces have specialized structures, footpads, on their legs. Footpads play an important role in adhesion to the substrate surface. Although the morphology and function of footpads have been studied, the mechanism of their formation is still elusive. In the ladybird beetle (Harmonia axyridis), hairy footpads are present on the first and second tarsal segments of the legs. The footpads are covered with hundreds of hairs, i.e. setae, whose tips consist of four types: pointed, lanceolate, spatular, and discoidal. We examined the formation of the footpad during the pupal stage using immuno-staining and fluorescent-conjugated phalloidin staining. We found that a seta was composed of a shaft and a socket and some setae were accompanied by a neuron. By the mid-pupal stages, the shaft cells elongated to form a setal structure. Cytoskeletal actin bundles ramified to create a framework for the setal tip structure of the cells. We examined the effects of the application of cytochalasin D, which inhibits actin polymerization, on the formation of footpad setal structures. The results showed that the setal tips were deformed by the inhibition of actin polymerization. Our observations reveal that cytoskeletal actin filaments are involved in shaping the setae.

Transient Production of Human β-Glucocerebrosidase With Mannosidic-Type N-Glycan Structure in Glycoengineered Nicotiana benthamiana Plants

Gaucher disease is an inherited lysosomal storage disorder caused by a deficiency of functional enzyme β-glucocerebrosidase (GCase). Recombinant GCase has been used in enzyme replacement therapy to treat Gaucher disease. Importantly, the terminal mannose N-glycan structure is essential for the uptake of recombinant GCase into macrophages via the mannose receptor. In this research, recombinant GCase was produced using Agrobacterium-mediated transient expression in both wild-type (WT) and N-acetylglucosaminyltransferase I (GnTI) downregulated Nicotiana benthamiana (ΔgntI) plants, the latter of which accumulates mannosidic-type N-glycan structures. The successfully produced functional GCase exhibited GCase enzyme activity. The enzyme activity was the same as that of the conventional mammalian-derived GCase. Notably, N-glycan analysis revealed that a mannosidic-type N-glycan structure lacking plant-specific N-glycans (β1,2-xylose and α1,3-fucose residues) was predominant in all glycosylation sites of purified GCase produced from ΔgntI plants. Our research provides a promising alternative plant line as a host for the production of recombinant GCase with a mannosidic-type N-glycan structure. This glycoengineered plant might be applicable to the production of other pharmaceutical proteins, especially mannose receptor targeted protein, for therapeutic uses.

Advanced in developmental organic and inorganic nanomaterial: a review

With the unique properties such as high surface area to volume ratio, stability, inertness, ease of functionalization, as well as novel optical, electrical, and magnetic behaviors, nanomaterials have a wide range of applications in various fields with the common types including nanotubes, dendrimers, quantum dots, and fullerenes. With the aim of providing useful insights to help future development of efficient and commercially viable technology for large-scale production, this review focused on the science and applications of inorganic and organic nanomaterials, emphasizing on their synthesis, processing, characterization, and applications on different fields. The applications of nanomaterials on imaging, cell and gene delivery, biosensor, cancer treatment, therapy, and others were discussed in depth. Last but not least, the future prospects and challenges in nanoscience and nanotechnology were also explored.

Glycosylation at an evolutionary nexus: the brittle star Ophiactis savignyi expresses both vertebrate and invertebrate N-glycomic features

Echinoderms are among the most primitive deuterostomes and have been used as model organisms to understand chordate biology because of their close evolutionary relationship to this phylogenetic group. However, there are almost no data available regarding the N-glycomic capacity of echinoderms, which are otherwise known to produce a diverse set of species-specific glycoconjugates, including ones heavily modified by fucose, sulfate, and sialic acid residues. To increase the knowledge of diversity of carbohydrate structures within this phylum, here we conducted an in-depth analysis of N-glycans from a brittle star (Ophiactis savignyi) as an example member of the class Ophiuroidea. To this end, we performed a multi-step N-glycan analysis by HPLC and various exoglyosidase and chemical treatments in combination with MALDI-TOF MS and MS/MS. Using this approach, we found a wealth of hybrid and complex oligosaccharide structures reminiscent of those in higher vertebrates as well as some classical invertebrate glycan structures. 70% of these N-glycans were anionic, carrying either sialic acid, sulfate, or phosphate residues. In terms of glycophylogeny, our data position the brittle star between invertebrates and vertebrates and confirm the high diversity of N-glycosylation in lower organisms.

Tissue-specific glycosylation in the honeybee: Analysis of the N-glycomes of Apis mellifera larvae and venom

BACKGROUND

Previous glycophylogenetic comparisons of dipteran and lepidopteran species revealed variations in the anionic and zwitterionic modifications of their N-glycans; therefore, we wished to explore whether species- and order-specific glycomic variations would extend to the hymenoptera, which include the honeybee Apis mellifera, an agriculturally- and allergologically-significant social species.

METHODS

In this study, we employed an off-line liquid chromatography/mass spectrometry approach, in combination with enzymatic and chemical treatments, to analyse the N-glycans of male honeybee larvae and honeybee venom in order to facilitate definition of isomeric structures.

RESULTS

The neutral larval N-glycome was dominated by oligomannosidic and paucimannosidic structures, while the neutral venom N-glycome displayed more processed hybrid and complex forms with antennal N-acetylgalactosamine, galactose and fucose residues including Lewis-like epitopes; the anionic pools from both larvae and venom contained a wide variety of glucuronylated, sulphated and phosphoethanolamine-modified N-glycans with up to three antennae. In comparison to honeybee royal jelly, there were more fucosylated and fewer Man_4/5-based hybrid glycans in the larvae and venom samples as well as contrasting antennal lengths.

CONCLUSIONS

Combining the current data on venom and larvae with that we previously published on royal jelly, a total honeybee N-glycomic repertoire of some 150 compositions can be proposed in addition to the 20 previously identified on specific venom glycoproteins.

SIGNIFICANCE

Our data are indicative of tissue-specific modification of the core and antennal regions of N-glycans in Apis mellifera and reinforce the concept that insects are capable of extensive processing to result in rather complex anionic oligosaccharide structures.

Localization of keyhole limpet hemocyanin-like immunoreactivity in the nervous system of Biomphalaria alexandrina

Recent years have led to increased effort to describe and understand the peripheral nervous system and its influence on central mechanisms and behavior in gastropod molluscs. This study revealed that an antibody raised against keyhole limpet hemocyanin (KLH) cross-reacts with an antigen(s) found extensively in both the central and the peripheral nervous systems of Biomphalaria alexandrina. The results revealed KLH-like immunoreactive (LIR) neurons in the cerebral, pedal, buccal, left pleural, right parietal, and visceral ganglion within the CNS with fibers projecting throughout all the peripheral nerves. Numerous KLH-LIR peripheral sensory neurons located in the foot, lips, tentacles, mantle, esophagus, and penis exhibited a bipolar morphology with long tortuous dendrites. KLH-LIR cells were also present in the eye and statocyst, thus suggesting the labeling of multiple sensory modalities/cell types. KLH-LIR cells did not co-localize with tyrosine hydroxylase (TH)-LIR cells, which have previously been described in this and other gastropods. The results thus provide descriptions of thousands of peripheral sensory neurons, not previously described in detail. Future research should seek to pair sensory modalities with peripheral cell type and attempt to further elucidate the nature of KLH-like reactivity. These findings also emphasize the need for caution when analyzing results obtained through use of antibodies raised against haptens conjugated to carrier proteins, suggesting the need for stringent controls to help limit potential confounds caused by cross-reactivity. In addition, this study is the first to describe neuronal cross-reactivity with KLH in Biomphalaria, which could provide a substrate for host-parasite interactions with a parasitic trematode, Schistosoma.

Comparisons of N-glycans across invertebrate phyla

Many invertebrates are either parasites themselves or vectors involved in parasite transmission; thereby, the interactions of parasites with final or intermediate hosts are often mediated by glycans. Therefore, it is of interest to compare the glycan structures or motifs present across invertebrate species. While a typical vertebrate modification such as sialic acid is rare in lower animals, antennal and core modifications of N-glycans are highly varied and range from core fucose, galactosylated fucose, fucosylated galactose, methyl groups, glucuronic acid and sulphate through to addition of zwitterionic moieties (phosphorylcholine, phosphoethanolamine and aminoethylphosphonate). Only in some cases are the enzymatic bases and the biological function of these modifications known. We are indeed still in the phase of discovering invertebrate glycomes primarily using mass spectrometry, but molecular biology and microarraying techniques are complementary to the determination of novel glycan structures and their functions.

Protein-Specific Analysis of Invertebrate Glycoproteins

N-Glycans are posttranslational modifications of proteins attached to the amide side chains of asparagine residues, with possible heterogeneity due to different structures being possible at the same glycosylation site. In contrast to the mammalian systems, invertebrate N-glycosylation presents a challenge in analysis as there exist unfamiliar epitopes and a high degree of structural and isomeric variation between different species. A simple analytical approach to analyze N-glycans on specific glycoproteins is presented, which involves a combination of tryptic peptide mass spectrometry and "off-line" RP-HPLC MALDI-TOF MS/MS complemented by blotting to recognize specific epitopes. An additional N-glycan enrichment and labeling step can facilitate the analysis of single structures and even provide isomeric separation of N-glycans from specific proteins.

Temporal and spatial order of photoreceptor and glia projections into optic lobe in Drosophila

Photoreceptor (PR) axons project from the retina to the optic lobe in brain and form a precise retinotopic map in the Drosophila visual system. Yet the role of retinal basal glia in the retinotopic map formation is not previously known. We examined the formation of the retinotopic map by marking single PR pairs and following their axonal projections. In addition to confirming previous studies that the spatial information is preserved from the retina to the optic stalk and then to the optic lamina, we found that the young PR R3/4 axons transiently overshoot and then retract to their final destination, the lamina plexus. We then examined the process of wrapping glia (WG) membrane extension in the eye disc and showed that the WG membrane extensions also follow the retinotopic map. We show that the WG is important for the proper spatial distribution of PR axons in the optic stalk and lamina, suggesting an active role of wrapping glia in the retinotopic map formation.

Isomeric Separation and Recognition of Anionic and Zwitterionic N-glycans from Royal Jelly Glycoproteins

Royal jelly has received attention because of its necessity for the development of queen honeybees as well as claims of benefits on human health; this product of the hypopharyngeal glands of worker bees contains a large number of proteins, some of which have been claimed to have various biological effects only in their glycosylated state. However, although there have been glycomic and glycoproteomic analyses in the past, none of the glycan structures previously defined would appear to have potential to trigger specific biological functions. In the current study, whole royal jelly as well as single protein bands were subject to off-line LC-MALDI-TOF MS glycomic analyses, complemented by permethylation, Western blotting and arraying data. Similarly to recent in-depth studies on other insect species, previously overlooked glucuronic acid termini, sulfation of mannose residues and core β-mannosylation of the N-glycans were found; additionally, a relatively rare zwitterionic modification with phosphoethanolamine is present, in contrast to the phosphorylcholine occurring in lepidopteran species. Indicative of tissue-specific remodelling of glycans in the Golgi apparatus of hypopharyngeal gland cells, only a low amount of fucosylated or paucimannosidic glycans were detected as compared with other insect samples or even bee venom. The unusual modifications of hybrid and multiantennary structures defined here may not only have a physiological role in honeybee development, but represent epitopes recognized by pentraxins with roles in animal innate immunity.

FM Dye Cycling at the Synapse: Comparing High Potassium Depolarization, Electrical and Channelrhodopsin Stimulation

FM dyes are used to study the synaptic vesicle (SV) cycle. These amphipathic probes have a hydrophilic head and hydrophobic tail, making them water-soluble with the ability to reversibly enter and exit membrane lipid bilayers. These styryl dyes are relatively non-fluorescent in aqueous medium, but insertion into the outer leaflet of the plasma membrane causes a >40X increase in fluorescence. In neuronal synapses, FM dyes are internalized during SV endocytosis, trafficked both within and between SV pools, and released with SV exocytosis, providing a powerful tool to visualize presynaptic stages of neurotransmission. A primary genetic model of glutamatergic synapse development and function is the Drosophila neuromuscular junction (NMJ), where FM dye imaging has been used extensively to quantify SV dynamics in a wide range of mutant conditions. The NMJ synaptic terminal is easily accessible, with a beautiful array of large synaptic boutons ideal for imaging applications. Here, we compare and contrast the three ways to stimulate the Drosophila NMJ to drive activity-dependent FM1-43 dye uptake/release: 1) bath application of high [K+] to depolarize neuromuscular tissues, 2) suction electrode motor nerve stimulation to depolarize the presynaptic nerve terminal, and 3) targeted transgenic expression of channelrhodopsin variants for light-stimulated, spatial control of depolarization. Each of these methods has benefits and disadvantages for the study of genetic mutation effects on the SV cycle at the Drosophila NMJ. We will discuss these advantages and disadvantages to assist the selection of the stimulation approach, together with the methodologies specific to each strategy. In addition to fluorescent imaging, FM dyes can be photoconverted to electron-dense signals visualized using transmission electron microscopy (TEM) to study SV cycle mechanisms at an ultrastructural level. We provide the comparisons of confocal and electron microscopy imaging from the different methods of Drosophila NMJ stimulation, to help guide the selection of future experimental paradigms.

Antigenic cross-reactivity between Schistosoma mansoni and pollen allergens from the birch tree (Betula verrucosa) and Timothy grass (Phleum pratense): involvement of shared glycan epitopes and implications for the hygiene hypothesis

Previous studies have shown that schistosome infection can protect against allergic symptoms, but the underlying mechanisms are still not fully understood. Here we have shown that rabbit IgG antibodies raised against Schistosoma mansoni soluble egg antigens (SmSEA) are cross-reactive with a wide array of molecules in Timothy grass pollen (TGP) and birch tree pollen (BTP). Five of the cross-reactive pollen molecules (two from TGP and three from BTP) were selected randomly and identified by tandem mass spectrometric (TMS) analysis to be, respectively, the TGP allergens Phl p 1 and Phl p 5b, and BTP glutathione S-transferase (GST), and the BTP allergens Bet v 1 and Bet v 6.0102. Rabbit anti-SmSEA IgG antibodies that cross-reacted with each of the five allergens were found to be reactive with three major S. mansoni egg antigens, IPSE/alpha-1, omega-1 and kappa-5. Pairwise alignment of the amino acid sequences of each of the five TMS-identified pollen allergens with each of the three egg antigens revealed a low level of amino acid sequence identity. Further experiments indicated that the schistosome antigen/allergen cross-reactivity was mostly due to similar glycans present in helminths and plants, but not in mammals: so called cross-reactive carbohydrate determinants (CCDs). Previously, CCDs have been implicated in the cross-reactivity between many plants and invertebrates. Furthermore, pollen-induced anti-CCD IgGs have been found in sera of patients undergoing allergen-specific immunotherapy (SIT) and implicated in the treatment of the allergy. Thus, our finding provides not only possible explanations for the allergy-protective effect of helminth/schistosome infections as explained by the hygiene hypothesis, but also a potential starting point for improved SIT.

Identification and characterization of a core fucosidase from the bacterium Elizabethkingia meningoseptica

All reported α-l-fucosidases catalyze the removal of nonreducing terminal l-fucoses from oligosaccharides or their conjugates, while having no capacity to hydrolyze core fucoses in glycoproteins directly. Here, we identified an α-fucosidase from the bacterium Elizabethkingia meningoseptica with catalytic activity against core α-1,3-fucosylated substrates, and we named it core fucosidase I (cFase I). Using site-specific mutational analysis, we found that three acidic residues (Asp-242, Glu-302, and Glu-315) in the predicted active pocket are critical for cFase I activity, with Asp-242 and Glu-315 acting as a pair of classic nucleophile and acid/base residues and Glu-302 acting in an as yet undefined role. These findings suggest a catalytic mechanism for cFase I that is different from known α-fucosidase catalytic models. In summary, cFase I exhibits glycosidase activity that removes core α-1,3-fucoses from substrates, suggesting cFase I as a new tool for glycobiology, especially for studies of proteins with core fucosylation.

Diversity and functions of protein glycosylation in insects

The majority of proteins is modified with carbohydrate structures. This modification, called glycosylation, was shown to be crucial for protein folding, stability and subcellular location, as well as protein-protein interactions, recognition and signaling. Protein glycosylation is involved in multiple physiological processes, including embryonic development, growth, circadian rhythms, cell attachment as well as maintenance of organ structure, immunity and fertility. Although the general principles of glycosylation are similar among eukaryotic organisms, insects synthesize a distinct repertoire of glycan structures compared to plants and vertebrates. Consequently, a number of unique insect glycans mediate functions specific to this class of invertebrates. For instance, the core α1,3-fucosylation of N-glycans is absent in vertebrates, while in insects this modification is crucial for the development of wings and the nervous system. At present, most of the data on insect glycobiology comes from research in Drosophila. Yet, progressively more information on the glycan structures and the importance of glycosylation in other insects like beetles, caterpillars, aphids and bees is becoming available. This review gives a summary of the current knowledge and recent progress related to glycan diversity and function(s) of protein glycosylation in insects. We focus on N- and O-glycosylation, their synthesis, physiological role(s), as well as the molecular and biochemical basis of these processes.

Development of a multifunctional aminoxy-based fluorescent linker for glycan immobilization and analysis

Glycan arrays have become a technique of choice to screen glycan-protein interactions in a high-throughput manner with high sensitivity and low sample consumption. Here, the synthesis of a new multifunctional fluorescent linker for glycan labeling via aminoxy ligation and immobilization is described; the linker features a fluorescent naphthalene group suitable for highly sensitive high-performance liquid chromatography-based purification and an azido- or amino-modified pentanoyl moiety for the immobilization onto solid supports. Several glycoconjugates displaying small sugar epitopes via chemical or chemoenzymatic synthesis were covalently attached onto a microarray support and tested with lectins of known carbohydrate binding specificity. The glycan library was extended using glycosyltransferases (e.g. galactosyl-, sialyl- and fucosyltransferases); the resulting neoglycoconjugates, which are easily detected by mass spectrometry, mimic antennal elements of N- and O-glycans, including ABH blood group epitopes and sialylated structures. Furthermore, an example natural plant N-glycan containing core α1,3-fucose and β1,2-xylose was also successfully conjugated to the fluorescent linker, immobilized and probed with lectins as well as antihorseradish peroxidase. These experiments validate our linker as being a potentially valuable tool to study glycozyme and lectin specificities, sensitive enough to allow purification of natural glycans.

Sweet secrets of a therapeutic worm: mass-spectrometric N-glycomic analysis of Trichuris suis

Trichuris suis, a nematode parasite of pigs, has attracted attention as its eggs have been administered to human patients as a potential therapy for inflammatory diseases. The immunomodulatory factors remain molecularly uncharacterised, but in vitro studies suggest that glycans on the parasite's excretory/secretory proteins may play a role. Using an off-line LC-MS approach in combination with chemical and enzymatic treatments, we have examined the N-linked oligosaccharides of T. suis. In addition to the paucimannosidic and oligomannosidic N-glycans typical of many invertebrates, a number of glycans carry N,N'-diacetyllactosamine (LacdiNAc) modified by fucose and/or phosphorylcholine. Such antennal epitopes are similar to ones previously associated with immunomodulation by helminths; here we propose phosphorylcholine modifications predominantly of terminal N-acetylgalactosamine but also of subterminal α1,3-fucosylated N-acetylglucosamine. Exact knowledge of the glycome of T. suis will facilitate more targeted studies on glycan receptors in the host as well as the engineering of cell lines to produce correctly glycosylated recombinant forms of candidate proteins for future studies on immunomodulation.

Alternative NF-κB Isoforms in the Drosophila Neuromuscular Junction and Brain

The Drosophila NF-κB protein Dorsal is expressed at the larval neuromuscular junction, where its expression appears unrelated to known Dorsal functions in embryonic patterning and innate immunity. Using confocal microscopy with domain-specific antisera, we demonstrate that larval muscle expresses only the B isoform of Dorsal, which arises by intron retention. We find that Dorsal B interacts with and stabilizes Cactus at the neuromuscular junction, but exhibits Cactus independent localization and an absence of detectable nuclear translocation. We further find that the Dorsal-related immune factor Dif encodes a B isoform, reflecting a conservation of B domains across a range of insect NF-κB proteins. Carrying out mutagenesis of the Dif locus via a site-specific recombineering approach, we demonstrate that Dif B is the major, if not sole, Dif isoform in the mushroom bodies of the larval brain. The Dorsal and Dif B isoforms thus share a specific association with nervous system tissues as well as an alternative protein structure.

Miro's N-terminal GTPase domain is required for transport of mitochondria into axons and dendrites

Mitochondria are dynamically transported in and out of neuronal processes to maintain neuronal excitability and synaptic function. In higher eukaryotes, the mitochondrial GTPase Miro binds Milton/TRAK adaptor proteins linking microtubule motors to mitochondria. Here we show that Drosophila Miro (dMiro), which has previously been shown to be required for kinesin-driven axonal transport, is also critically required for the dynein-driven distribution of mitochondria into dendrites. In addition, we used the loss-of-function mutations dMiroT25N and dMiroT460N to determine the significance of dMiro's N-terminal and C-terminal GTPase domains, respectively. Expression of dMiroT25N in the absence of endogenous dMiro caused premature lethality and arrested development at a pupal stage. dMiroT25N accumulated mitochondria in the soma of larval motor and sensory neurons, and prevented their kinesin-dependent and dynein-dependent distribution into axons and dendrites, respectively. dMiroT25N mutant mitochondria also were severely fragmented and exhibited reduced kinesin and dynein motility in axons. In contrast, dMiroT460N did not impair viability, mitochondrial size, or the distribution of mitochondria. However, dMiroT460N reduced dynein motility during retrograde mitochondrial transport in axons. Finally, we show that substitutions analogous to the constitutively active Ras-G12V mutation in dMiro's N-terminal and C-terminal GTPase domains cause neomorphic phenotypic effects that are likely unrelated to the normal function of each GTPase domain. Overall, our analysis indicates that dMiro's N-terminal GTPase domain is critically required for viability, mitochondrial size, and the distribution of mitochondria out of the neuronal soma regardless of the employed motor, likely by promoting the transition from a stationary to a motile state.

Targeted release and fractionation reveal glucuronylated and sulphated N- and O-glycans in larvae of dipteran insects

Mosquitoes are important vectors of parasitic and viral diseases with Anopheles gambiae transmitting malaria and Aedes aegypti spreading yellow and Dengue fevers. Using two different approaches (solid-phase extraction and reversed-phase or hydrophilic interaction HPLC fractionation followed by MALDI-TOF MS or permethylation followed by NSI-MS), we examined the N-glycans of both A. gambiae and A. aegypti larvae and demonstrate the presence of a range of paucimannosidic glycans as well as bi- and tri-antennary glycans, some of which are modified with fucose or with sulphate or glucuronic acid residues; the latter anionic modifications were also found on N-glycans of larvae from another dipteran species (Drosophila melanogaster). The sulphate groups are attached primarily to core α-mannose residues (especially the α1,6-linked mannose), whereas the glucuronic acid residues are linked to non-reducing β1,3-galactose. Also, O-glycans were found to possess glucuronic acid and sulphate as well as phosphoethanolamine modifications. The presence of sulphated and glucuronylated N-glycans is a novel feature in dipteran glycomes; these structures have the potential to act as additional anionic glycan ligands involved in parasite interactions with the vector host.

Hitting the sweet spot-glycans as targets of fungal defense effector proteins

Organisms which rely solely on innate defense systems must combat a large number of antagonists with a comparably low number of defense effector molecules. As one solution of this problem, these organisms have evolved effector molecules targeting epitopes that are conserved between different antagonists of a specific taxon or, if possible, even of different taxa. In order to restrict the activity of the defense effector molecules to physiologically relevant taxa, these target epitopes should, on the other hand, be taxon-specific and easily accessible. Glycans fulfill all these requirements and are therefore a preferred target of defense effector molecules, in particular defense proteins. Here, we review this defense strategy using the example of the defense system of multicellular (filamentous) fungi against microbial competitors and animal predators.

Emergence of tissue sensitivity to Hox protein levels underlies the evolution of an adaptive morphological trait

Growth control scales morphological attributes and, therefore, provides a critical contribution to the evolution of adaptive traits. Yet, the genetic mechanisms underlying growth in the context of specific ecological adaptations are poorly understood. In water striders, adaptation to locomotion on the water surface is associated with allometric and functional changes in thoracic appendages, such that T2-legs, used as propelling oars, are longer than T3-legs, used as steering rudders. The Hox gene Ubx establishes this derived morphology by elongating T2-legs but shortening T3-legs. Using gene expression assays, RNAi knockdown, and comparative transcriptomics, we demonstrate that the evolution of water surface rowing as a novel means of locomotion is associated with the evolution of a dose-dependent promoting-repressing effect of Ubx on leg growth. In the water strider Limnoporus dissortis, T3-legs express six to seven times higher levels of Ubx compared to T2-legs. Ubx RNAi shortens T2-legs and the severity of this phenotype increases with increased depletion of Ubx protein. Conversely, Ubx RNAi lengthens T3-legs but this phenotype is partially rescued when Ubx protein is further depleted. This dose-dependent effect of Ubx on leg growth is absent in non-rowing relatives that retain the ancestral relative leg length. We also show that the spatial patterns of expression of dpp, wg, hh, egfr, dll, exd, hth, and dac are unchanged in Ubx RNAi treatments. This indicates that the dose-dependent opposite effect of Ubx on T2- and T3-legs operates without any apparent effect on the spatial expression of major leg patterning genes. Our data suggest that scaling of adaptive allometries can evolve through changes in the levels of expression of Hox proteins early during ontogeny, and in the sensitivity of the tissues that express them, without any major effects on pattern formation.

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Ubx is generally expressed at higher levels in T3- relative to T2-legs in semi-aquatic insects.

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It is only in the derived Gerridae where the high levels of Ubx result in reduced T3-leg length.

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In the Gerridae, the response of leg tissues to Ubx levels is bimodal.

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Changes in Ubx regulation and function have evolved in Limnoporus without disrupting patterning hierarchies.

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Changes in Hox protein levels and emergence of tissue sensitivity to these levels can shape adaptive morphological traits.

N-glycosylation requirements in neuromuscular synaptogenesis

Neural development requires N-glycosylation regulation of intercellular signaling, but the requirements in synaptogenesis have not been well tested. All complex and hybrid N-glycosylation requires MGAT1 (UDP-GlcNAc:α-3-D-mannoside-β1,2-N-acetylglucosaminyl-transferase I) function, and Mgat1 nulls are the most compromised N-glycosylation condition that survive long enough to permit synaptogenesis studies. At the Drosophila neuromuscular junction (NMJ), Mgat1 mutants display selective loss of lectin-defined carbohydrates in the extracellular synaptomatrix, and an accompanying accumulation of the secreted endogenous Mind the gap (MTG) lectin, a key synaptogenesis regulator. Null Mgat1 mutants exhibit strongly overelaborated synaptic structural development, consistent with inhibitory roles for complex/hybrid N-glycans in morphological synaptogenesis, and strengthened functional synapse differentiation, consistent with synaptogenic MTG functions. Synapse molecular composition is surprisingly selectively altered, with decreases in presynaptic active zone Bruchpilot (BRP) and postsynaptic Glutamate receptor subtype B (GLURIIB), but no detectable change in a wide range of other synaptic components. Synaptogenesis is driven by bidirectional trans-synaptic signals that traverse the glycan-rich synaptomatrix, and Mgat1 mutation disrupts both anterograde and retrograde signals, consistent with MTG regulation of trans-synaptic signaling. Downstream of intercellular signaling, pre- and postsynaptic scaffolds are recruited to drive synaptogenesis, and Mgat1 mutants exhibit loss of both classic Discs large 1 (DLG1) and newly defined Lethal (2) giant larvae [L(2)GL] scaffolds. We conclude that MGAT1-dependent N-glycosylation shapes the synaptomatrix carbohydrate environment and endogenous lectin localization within this domain, to modulate retention of trans-synaptic signaling ligands driving synaptic scaffold recruitment during synaptogenesis.

Gliogenesis in the embryonic brain of the grasshopper Schistocerca gregaria with particular focus on the protocerebrum prior to mid-embryogenesis

I investigate the pattern of gliogenesis in the brain of the grasshopper Schistocerca gregaria prior to mid-embryogenesis, with particular focus on the protocerebrum. Using the glia-specific marker Repo and the neuron-specific marker HRP, I identify three types of glia with respect to their respective positions in the brain: surface glia form the outmost cell layer ensheathing the brain; cortex glia are intermingled with neuronal somata forming the brain cortex; and neuropil glia are associated with brain neuropils. The ontogeny of each glial type has also been studied. At 24% of embryogenesis, a few glia are observed in each hemisphere of the proto-, deuto- and tritocerebrum. In each protocerebral hemisphere, such glia form a cluster that expands rapidly during later development. Closer examination reveals proliferative glia in such clusters at ages spanning from 24 to 36% of embryogenesis, indicating that glial proliferation may account for the expansion of the clusters. Data derived from 33-39% of embryogenesis suggest that, in the protocerebrum, each type of glia is likely to be generated by its respective progenitor-forming clusters. Moreover, the glial cluster located at the anterior end of the brain can give rise to both surface glia and cortex glia that populate the protocerebrum via subsequent migration. Proliferation is observed for all three glial types, indicating a possible source for the glia.

Deficiency of α-glucosidase I alters glycoprotein glycosylation and lifespan in Caenorhabditis elegans

Endoplasmic reticulum (ER) α-glucosidase I is an enzyme that trims the distal α1,2-linked glucose (Glc) residue from the Glc3Man9GlcNAc2 oligosaccharide following its addition to nascent glycoproteins in the initial step of processing. This reaction is critical to the subsequent processing of N-glycans and thus defects in α-glucosidase I gene in human cause congenital disorder of glycosylation (CDG) type IIb. We identified the Caenorhabditis elegans α-glucosidase I gene (F13H10.4, designated agl-1) that encodes a polypeptide with 36% identity to human α-glucosidase I. The agl-1 cDNA restored the expression of complex-type N-glycans on the cell surface of α-glucosidase I-defective Chinese hamster ovary Lec23 cells. RNAi knockdown of agl-1 [agl-1(RNAi)] produced worms that were visibly similar to wild-type, but lifespan was reduced to about half of the control. Analyses of N-glycosylation in agl-1(RNAi) animals by western blotting and mass spectrometry showed reduction of paucimannose and complex-type glycans and dramatic increase of glucosylated oligomannose glycans. In addition, a significant amount of unusual terminally fucosylated N-glycans were found in agl-1(RNAi) animals. ER stress response was also provoked, leading to the accumulation of large amounts of triglucosylated free oligosaccharides (FOSs) (Glc3Man4-5GlcNAc1-2) in agl-1(RNAi) animals. Acceleration of ER-associated degradation in response to the accumulation of unfolded glycoproteins and insufficient interaction with calnexin/calreticulin in the ER lumen likely accounts for the increase of FOSs. Taken together, these studies in C. elegans demonstrate that decreased ER α-glucosidase I affects the entire N-glycan profile and induces chronic ER stress, which may contribute to the pathophysiology of CDG-IIb in humans.

Hemocytes and plasma of the eastern oyster (Crassostrea virginica) display a diverse repertoire of sulfated and blood group A-modified N-glycans

The eastern oyster (Crassostrea virginica) has become a useful model system for glycan-dependent host-parasite interactions due to the hijacking of the oyster galectin CvGal1 for host entry by the protozoan parasite Perkinsus marinus, the causative agent of Dermo disease. In this study, we examined the N-glycans of both the hemocytes, which via CvGal1 are the target of the parasite, and the plasma of the oyster. In combination with HPLC fractionation, exoglycosidase digestion, and fragmentation of the glycans, mass spectrometry revealed that the major N-glycans of plasma are simple hybrid structures, sometimes methylated and core α1,6-fucosylated, with terminal β1,3-linked galactose; a remarkable high degree of sulfation of such glycans was observed. Hemocytes express a larger range of glycans, including core-difucosylated paucimannosidic forms, whereas bi- and triantennary glycans were found in both sources, including structures carrying sulfated and methylated variants of the histo-blood group A epitope. The primary features of the oyster whole hemocyte N-glycome were also found in dominin, the major plasma glycoprotein, which had also been identified as a CvGal1 glycoprotein ligand associated with hemocytes. The occurrence of terminal blood group moieties on oyster dominin and on hemocyte surfaces can account in part for their affinity for the endogenous CvGal1.

Array-assisted characterization of a fucosyltransferase required for the biosynthesis of complex core modifications of nematode N-glycans

Fucose is a common monosaccharide component of cell surfaces and is involved in many biological recognition events. Therefore, definition and exploitation of the specificity of the enzymes (fucosyltransferases) involved in fucosylation is a recurrent theme in modern glycosciences. Despite various studies, the specificities of many fucosyltransferases are still unknown, so new approaches are required to study these. The model nematode Caenorhabditis elegans expresses a wide range of fucosylated glycans, including N-linked oligosaccharides with unusual complex core modifications. Up to three fucose residues can be present on the standard N,N'-diacetylchitobiose unit of these N-glycans, but only the fucosyltransferases responsible for transfer of two of these (the core α1,3-fucosyltransferase FUT-1 and the core α1,6-fucosyltransferase FUT-8) were previously characterized. By use of a glycan library in both array and solution formats, we were able to reveal that FUT-6, another C. elegans α1,3-fucosyltransferase, modifies nematode glycan cores, specifically the distal N-acetylglucosamine residue; this result is in accordance with glycomic analysis of fut-6 mutant worms. This core-modifying activity of FUT-6 in vitro and in vivo is in addition to its previously determined ability to synthesize Lewis X epitopes in vitro. A larger scale synthesis of a nematode N-glycan core in vitro using all three fucosyltransferases was performed, and the nature of the glycosidic linkages was determined by NMR. FUT-6 is probably the first eukaryotic glycosyltransferase whose specificity has been redefined with the aid of glycan microarrays and so is a paradigm for the study of other unusual glycosidic linkages in model and parasitic organisms.

Glia associated with central complex lineages in the embryonic brain of the grasshopper Schistocerca gregaria

We have investigated the pattern of glia associated with central complex lineages in the embryonic brain of the grasshopper Schistocerca gregaria. Using the glia-specific marker Repo, we identified glia associated externally with such lineages, termed lineage-extrinsic glia, and glia located internally within the lineages, termed lineage-intrinsic glia. Populations of both glial types increase up to 60 % of embryogenesis, and thereafter decrease. Extrinsic glia change their locations over time, while intrinsic ones are consistently found in the more apical part of a lineage. Apoptosis is not observed for either glial type, suggesting migration is a likely mechanism accounting for changes in glial number. Proliferative glia are present both within and without individual lineages and two glial clusters associated with the lineages, one apically and the other basally, may represent sources of glia.

Mass spectrometric analysis of neutral and anionic N-glycans from a Dictyostelium discoideum model for human congenital disorder of glycosylation CDG IL

The HL241 mutant strain of the cellular slime mold Dictyostelium discoideum is a potential model for human congenital disorder of glycosylation type IL (ALG9-CDG) and has been previously predicted to possess a lower degree of modification of its N-glycans with anionic moieties than the parental wild-type. In this study, we first showed that this strain has a premature stop codon in its alg9 mannosyltransferase gene compatible with the occurrence of truncated N-glycans. These were subject to an optimized analytical workflow, considering that the mass spectrometry of acidic glycans often presents challenges due to neutral loss and suppression effects. Therefore, the protein-bound N-glycans were first fractionated, after serial enzymatic release, by solid phase extraction. Then primarily single glycan species were isolated by mixed hydrophilic-interaction/anion-exchange or reversed-phase HPLC and analyzed using chemical and enzymatic treatments and MS/MS. We show that protein-linked N-glycans of the mutant are of reduced size as compared to those of wild-type AX3, but still contain core α1,3-fucose, intersecting N-acetylglucosamine, bisecting N-acetylglucosamine, methylphosphate, phosphate, and sulfate residues. We observe that a single N-glycan can carry up to four of these six possible modifications. Due to the improved analytical procedures, we reveal fuller details regarding the N-glycomic potential of this fascinating model organism.

Mislocalization of neuronal mitochondria reveals regulation of Wallerian degeneration and NMNAT/WLD(S)-mediated axon protection independent of axonal mitochondria

Axon degeneration is a common and often early feature of neurodegeneration that correlates with the clinical manifestations and progression of neurological disease. Nicotinamide mononucleotide adenylytransferase (NMNAT) is a neuroprotective factor that delays axon degeneration following injury and in models of neurodegenerative diseases suggesting a converging molecular pathway of axon self-destruction. The underlying mechanisms have been under intense investigation and recent reports suggest a central role for axonal mitochondria in both degeneration and NMNAT/WLD(S) (Wallerian degeneration slow)-mediated protection. We used dorsal root ganglia (DRG) explants and Drosophila larval motor neurons (MNs) as models to address the role of mitochondria in Wallerian degeneration (WD). We find that expression of Drosophila NMNAT delays WD in human DRG neurons demonstrating evolutionary conservation of NMNAT function. Morphological comparison of mitochondria from WLD(S)-protected axons demonstrates that mitochondria shrink post-axotomy, though analysis of complex IV activity suggests that they retain their functional capacity despite this morphological change. To determine whether mitochondria are a critical site of regulation for WD, we genetically ablated mitochondria from Drosophila MN axons via the mitochondria trafficking protein milton. Milton loss-of-function did not induce axon degeneration in Drosophila larval MNs, and when axotomized WD proceeded stereotypically in milton distal axons although with a mild, but significant delay. Remarkably, the protective effects of NMNAT/WLD(S) were also maintained in axons devoid of mitochondria. These experiments unveil an axon self-destruction cascade governing WD that is not initiated by axonal mitochondria and for the first time illuminate a mitochondria-independent mechanism(s) regulating WD and NMNAT/WLD(S)-mediated axon protection.

Exploring the unique N-glycome of the opportunistic human pathogen Acanthamoeba

Glycans play key roles in host-pathogen interactions; thus, knowing the N-glycomic repertoire of a pathogen can be helpful in deciphering its methods of establishing and sustaining a disease. Therefore, we sought to elucidate the glycomic potential of the facultative amoebal parasite Acanthamoeba. This is the first study of its asparagine-linked glycans, for which we applied biochemical tools and various approaches of mass spectrometry. An initial glycomic screen of eight strains from five genotypes of this human pathogen suggested, in addition to the common eukaryotic oligomannose structures, the presence of pentose and deoxyhexose residues on their N-glycans. A more detailed analysis was performed on the N-glycans of a genotype T11 strain (4RE); fractionation by HPLC and tandem mass spectrometric analyses indicated the presence of a novel mannosylfucosyl modification of the reducing terminal core as well as phosphorylation of mannose residues, methylation of hexose and various forms of pentosylation. The largest N-glycan in the 4RE strain contained two N-acetylhexosamine, thirteen hexose, one fucose, one methyl, and two pentose residues; however, in this and most other strains analyzed, glycans with compositions of Hex(8-9)HexNAc(2)Pnt(0-1) tended to dominate in terms of abundance. Although no correlation between pathogenicity and N-glycan structure can be proposed, highly unusual structures in this facultative parasite can be found which are potential virulence factors or therapeutic targets.

The Drosophila neurally altered carbohydrate mutant has a defective Golgi GDP-fucose transporter

Studying genetic disorders in model organisms can provide insights into heritable human diseases. The Drosophila neurally altered carbohydrate (nac) mutant is deficient for neural expression of the HRP epitope, which consists of N-glycans with core α1,3-linked fucose residues. Here, we show that a conserved serine residue in the Golgi GDP-fucose transporter (GFR) is substituted by leucine in nac(1) flies, which abolishes GDP-fucose transport in vivo and in vitro. This loss of function is due to a biochemical defect, not to destabilization or mistargeting of the mutant GFR protein. Mass spectrometry and HPLC analysis showed that nac(1) mutants lack not only core α1,3-linked, but also core α1,6-linked fucose residues on their N-glycans. Thus, the nac(1) Gfr mutation produces a previously unrecognized general defect in N-glycan core fucosylation. Transgenic expression of a wild-type Gfr gene restored the HRP epitope in neural tissues, directly demonstrating that the Gfr mutation is solely responsible for the neural HRP epitope deficiency in the nac(1) mutant. These results validate the Drosophila nac(1) mutant as a model for the human congenital disorder of glycosylation, CDG-IIc (also known as LAD-II), which is also the result of a GFR deficiency.

Glial processes at the Drosophila larval neuromuscular junction match synaptic growth

Glia are integral participants in synaptic physiology, remodeling and maturation from blowflies to humans, yet how glial structure is coordinated with synaptic growth is unknown. To investigate the dynamics of glial development at the Drosophila larval neuromuscular junction (NMJ), we developed a live imaging system to establish the relationship between glia, neuronal boutons, and the muscle subsynaptic reticulum. Using this system we observed processes from two classes of peripheral glia present at the NMJ. Processes from the subperineurial glia formed a blood-nerve barrier around the axon proximal to the first bouton. Processes from the perineurial glial extended beyond the end of the blood-nerve barrier into the NMJ where they contacted synapses and extended across non-synaptic muscle. Growth of the glial processes was coordinated with NMJ growth and synaptic activity. Increasing synaptic size through elevated temperature or the highwire mutation increased the extent of glial processes at the NMJ and conversely blocking synaptic activity and size decreased the presence and size of glial processes. We found that elevated temperature was required during embryogenesis in order to increase glial expansion at the nmj. Therefore, in our live imaging system, glial processes at the NMJ are likely indirectly regulated by synaptic changes to ensure the coordinated growth of all components of the tripartite larval NMJ.

Plasticity of the β-trefoil protein fold in the recognition and control of invertebrate predators and parasites by a fungal defence system

Discrimination between self and non-self is a prerequisite for any defence mechanism; in innate defence, this discrimination is often mediated by lectins recognizing non-self carbohydrate structures and so relies on an arsenal of host lectins with different specificities towards target organism carbohydrate structures. Recently, cytoplasmic lectins isolated from fungal fruiting bodies have been shown to play a role in the defence of multicellular fungi against predators and parasites. Here, we present a novel fruiting body lectin, CCL2, from the ink cap mushroom Coprinopsis cinerea. We demonstrate the toxicity of the lectin towards Caenorhabditis elegans and Drosophila melanogaster and present its NMR solution structure in complex with the trisaccharide, GlcNAcβ1,4[Fucα1,3]GlcNAc, to which it binds with high specificity and affinity in vitro. The structure reveals that the monomeric CCL2 adopts a β-trefoil fold and recognizes the trisaccharide by a single, topologically novel carbohydrate-binding site. Site-directed mutagenesis of CCL2 and identification of C. elegans mutants resistant to this lectin show that its nematotoxicity is mediated by binding to α1,3-fucosylated N-glycan core structures of nematode glycoproteins; feeding with fluorescently labeled CCL2 demonstrates that these target glycoproteins localize to the C. elegans intestine. Since the identified glycoepitope is characteristic for invertebrates but absent from fungi, our data show that the defence function of fruiting body lectins is based on the specific recognition of non-self carbohydrate structures. The trisaccharide specifically recognized by CCL2 is a key carbohydrate determinant of pollen and insect venom allergens implying this particular glycoepitope is targeted by both fungal defence and mammalian immune systems. In summary, our results demonstrate how the plasticity of a common protein fold can contribute to the recognition and control of antagonists by an innate defence mechanism, whereby the monovalency of the lectin for its ligand implies a novel mechanism of lectin-mediated toxicity.

Integrins establish dendrite-substrate relationships that promote dendritic self-avoidance and patterning in drosophila sensory neurons

Dendrites achieve characteristic spacing patterns during development to ensure appropriate coverage of territories. Mechanisms of dendrite positioning via repulsive dendrite-dendrite interactions are beginning to be elucidated, but the control, and importance, of dendrite positioning relative to their substrate is poorly understood. We found that dendritic branches of Drosophila dendritic arborization sensory neurons can be positioned either at the basal surface of epidermal cells, or enclosed within epidermal invaginations. We show that integrins control dendrite positioning on or within the epidermis in a cell autonomous manner by promoting dendritic retention on the basal surface. Loss of integrin function in neurons resulted in excessive self-crossing and dendrite maintenance defects, the former indicating a role for substrate interactions in self-avoidance. In contrast to a contact-mediated mechanism, we find that integrins prevent crossings that are noncontacting between dendrites in different three-dimensional positions, revealing a requirement for combined dendrite-dendrite and dendrite-substrate interactions in self-avoidance.

Repertoire of human natural anti-glycan immunoglobulins. Do we have auto-antibodies?

BACKGROUND

Profiling of donor's antibodies using glycan arrays demonstrated presence of antibodies capable of binding to >100 mammalian glycans or their fragments. For example, relatively high binding to Galα1-4Galβ1-4GlcNAc (P(1)), Galα1-4Galβ1-4Glc (P(k)), Galβ1-3GlcNAc (Le(c)), 4-O-SuGalβ1-4GlcNAc, and GalNAcα1-3GalNAc (Fs) was found in all tested individuals. Affinity isolation using hapten-specific chromatography in combination with epitope mapping revealed their glycotopes. Notably, a significant part of the antibodies was capable of recognizing a fragment of larger glycans, for example, -Galβ1-4Glc of glycolipids, or Fucα1-3GlcNAc motif of Le(X)/Le(Y) antigens. Their epitope specificity did not vary between different healthy individuals. Nominally, all the mentioned immunoglobulins could be classified as auto-antibodies.

METHODS

In this work we re-evaluated results published earlier and analyzed new data to address the question why autologous antibodies found in healthy individuals do not cause severe auto-immune reactions.

RESULTS

In all cases the presumably "auto" antibodies were found to bind short fragments "subtracted" from larger glycans whereas recognition of the same fragment in the context of the whole natural chain was completely abolished. Thus, in spite of numerous formally positive signals observed on the printed glycan array, we are yet unable to identify in blood serum of healthy individuals true auto-antibodies capable of binding carbohydrate chains in their naturally occurring form.

GENERAL SIGNIFICANCE

The identified natural anti-glycan antibodies were found to be specific, high-titer and population conservative immunoglobulins - all of this suggesting as yet unknown biological role(s) of the studied proteins. This article is part of a Special Issue entitled Glycoproteomics.

The N-glycans of Trichomonas vaginalis contain variable core and antennal modifications

Trichomonad species are widespread unicellular flagellated parasites of vertebrates which interact with their hosts through carbohydrate-lectin interactions. In the past, some data have been accumulated regarding their lipo(phospho)glycans, a major glycoconjugate on their cell surfaces; on the other hand, other than biosynthetic aspects, few details about their N-linked oligosaccharides are known. In this study, we present both mass spectrometric and high-performance liquid chromatography data about the N-glycans of different strains of Trichomonas vaginalis, a parasite of the human reproductive tract. The major structure in all strains examined is a truncated oligomannose form (Man(5)GlcNAc(2)) with α1,2-mannose residues, compatible with a previous bioinformatic examination of the glycogenomic potential of T. vaginalis. In addition, dependent on the strain, N-glycans modified by pentose residues, phosphate or phosphoethanolamine and terminal N-acetyllactosamine (Galβ1,4GlcNAc) units were found. The modification of N-glycans by N-acetyllactosamine in at least some strains is shared with the lipo(phospho)glycan and may represent a further interaction partner for host galectins, thereby playing a role in binding of the parasite to host epithelia. On the other hand, the variation in glycosylation between strains may be the result of genetic diversity within this species.

Slob, a Slowpoke channel-binding protein, modulates synaptic transmission

Modulation of ion channels by regulatory proteins within the same macromolecular complex is a well-accepted concept, but the physiological consequences of such modulation are not fully understood. Slowpoke (Slo), a potassium channel critical for action potential repolarization and transmitter release, is regulated by Slo channel–binding protein (Slob), a Drosophila melanogaster Slo (dSlo) binding partner. Slob modulates the voltage dependence of dSlo channel activation in vitro and exerts similar effects on the dSlo channel in Drosophila central nervous system neurons in vivo. In addition, Slob modulates action potential duration in these neurons. Here, we investigate further the functional consequences of the modulation of the dSlo channel by Slob in vivo, by examining larval neuromuscular synaptic transmission in flies in which Slob levels have been altered. In Slob-null flies generated through P-element mutagenesis, as well as in Slob knockdown flies generated by RNA interference (RNAi), we find an enhancement of synaptic transmission but no change in the properties of the postsynaptic muscle cell. Using targeted transgenic rescue and targeted expression of Slob-RNAi, we find that Slob expression in neurons (but not in the postsynaptic muscle cell) is critical for its effects on synaptic transmission. Furthermore, inhibition of dSlo channel activity abolishes these effects of Slob. These results suggest that presynaptic Slob, by regulating dSlo channel function, participates in the modulation of synaptic transmission.

Dramatic changes in patterning gene expression during metamorphosis are associated with the formation of a feather-like antenna by the silk moth, Bombyx mori

Many moths use sex pheromones to find their mates in the dark. Their antennae are well developed with lateral branches to receive the pheromone efficiently. However, how these structures have evolved remains elusive, because the mechanism of development of these antennae has not been studied at a molecular level. To elucidate the developmental mechanism of this type of antenna, we observed morphogenesis, cell proliferation, cell death and antennal patterning gene expression in the branched antenna of the silk moth, Bombyx mori. Region-specific cell proliferation and almost ubiquitous apoptosis occur during early pupal stages and appear to shape the lateral branch cooperatively. Antennal patterning genes are expressed in a pattern largely conserved among insects with branchless antennae until the late 5th larval instar but most of them change their expression dramatically to a pattern prefiguring the lateral branch during metamorphosis. These findings imply that although antennal primordium is patterned by conserved mechanisms before metamorphosis, most of the antennal patterning genes are reused to form the lateral branch during metamorphosis. We propose that the acquisition of a new regulatory circuit of antennal patterning genes may have been an important event during evolution of the sensory antenna with lateral branches in the Lepidoptera.

Distantly related plant and nematode core α1,3-fucosyltransferases display similar trends in structure-function relationships

Here, we present a comparative structure-function study of a nematode and a plant core α1,3-fucosyltransferase based on deletion and point mutations of the coding regions of Caenorhabditis elegans FUT-1 and Arabidopsis thaliana FucTA (FUT11). In particular, our results reveal a novel "first cluster motif" shared by both core and Lewis-type α1,3-fucosyltransferases of the GT10 family. To evaluate the role of the conserved serine within this motif, this residue was replaced with alanine in FucTA (S218) and FUT-1 (S243). The S218A replacement completely abolished the enzyme activity of FucTA, while the S243A mutant of FUT-1 retained 20% of the "wild-type" activity. Based on the results of homology modeling of FucTA, other residues potentially involved in the donor substrate binding were examined, and mutations of N219 and R226 dramatically affected enzymatic activity. Finally, as both FucTA and FUT-1 were shown to be N-glycosylated, we examined the putative N-glycosylation sites. While alanine replacements at single potential N-glycosylation sites of FucTA resulted in a loss of up to 80% of the activity, a triple glycosylation site mutant still retained 5%, as compared to the control. In summary, our data indicate similar trends in structure-function relationships of distantly related enzymes which perform similar biochemical reactions and form the basis for future work aimed at understanding the structure of α1,3-fucosyltransferases in general.