Localization of wheat germ agglutinin receptor sites on yeast cells by scanning electron microscopy

Changes in reactive oxygen species begin early during replicative aging of Saccharomyces cerevisiae cells

Increased reactive oxygen species (ROS) are a feature of aging cells, but little is known about when ROS generation begins as cells age. Here we show how ROS change in Saccharomyces cerevisiae cells throughout their early replicative life span using the fluorescent ROS indicator dihydroethidium (DHE), which has some specificity for the superoxide anion. Cells in a particular age range were heterogeneous with respect to their ROS burden. Surprisingly, some cells as young as 5-7 generations acquired a greatly increased level of ROS detected by DHE relative to virgin cells. By 12 generations 50% of cells had a substantial ROS burden despite being only halfway through their life span. In contrast to the wild type, cells of a sir2 mutant had lower levels of ROS reacting with DHE. Daughters from older mothers had low ROS levels, and this asymmetric distribution of ROS was SIR2-independent. Mitochondrial fragmentation also began to occur in cells after 4 generations and increased markedly as cells aged. Daughter cells regenerated normal tubular mitochondria despite the fragmentation of mitochondria in the mother cells, whereas daughters of the sir2 mutant had fragmented mitochondria at all ages.

Glycans with N-acetyllactosamine type 2-like residues covering adult Schistosoma mansoni, and glycomimesis as a putative mechanism of immune evasion

Glycans at the surface of adult Schistosoma mansoni were investigated with gold-labelled lectins. The fragile complex of the glycans with the outer membranes could be preserved for electron microscopy by avoiding extensive pre-fixation with aldehydes and by introducing osmium-ferrocyanide as a membrane fixative. Male and female worms were entirely covered with glycans that intensely bound lectins from Erythrina cristagalli and Datura stramonium, suggesting that galactose(beta 1-4)N-acetylglucosamine residues occur in high numbers in the surface glycans. Similar staining was obtained with lectins from Triticum vulgaris, Glycine max and Ricinus communis agglutinin I, which react with N-acetylglucosamine or terminal galactose residues and bind non-selectively with high affinity to N-acetyllactosamine. Fucose, N-acetylgalactose and sialic acid were not detected with lectins and sialidase treatment. The tegument contained an abundance of glycans with the same lectin reactivities as the surface-expressed molecules, indicating that the worms synthesize and replenish their surface glycans and do not merely adsorb host substances. Glycomimesis is discussed as a mechanism of immune evasion in view of N-acetyllactosamine being a common and weakly immunogenic component in glycans of vertebrate hosts. S. mansoni might disguise themselves with the glycans against attack by immune effectors.

Immunocytochemical demonstration of wheat germ agglutinin (WGA)-receptors on the cell surface of guinea pig peritoneal macrophages

WGA-receptors on the surface of resident guinea pig peritoneal macrophages were investigated. Macrophages were characterized by the endogenous peroxidase pattern. Two different immunogold techniques, the indirect WGA-anti WGA-protein A-gold technique and the direct WGA/BSA-gold technique were compared to evaluate their suitability for quantification of WGA binding sites on the cell surface. Because of the higher binding specificity the direct technique should be preferred for quantitative studies.

Double-staining methods at the ultrastructural level applying colloidal gold conjugates

Several double gold-labeling methods have been reviewed, and our own results of applying some of these methods have been included. Of the six double-staining methods tested, four gave satisfactory results (indirect double immunogold staining method, two-face protein A-gold staining method, two-face amplified protein A-gold staining method, and formaldehyde blockade protein A-gold staining method). The other two techniques (sequential double protein A-gold staining method and formaldehyde blockade amplified protein A-gold staining method) showed cross-reaction between the first and second staining sequence.

Isolation and characterization of a lectin from tulip bulbs, Tulipa gesneriana

A lectin, which agglutinated specifically the yeast cells of the Saccharomyces genus, was isolated from tulip bulbs (Tulipa gesneriana) using affinity chromatography on mannan-Sepharose 4B. Its relative molecular mass was determined by gel filtration to be approximately 67,000. On polyacrylamide gel electrophoresis in sodium dodecyl sulfate, a relative molecular mass of 17,000 was obtained, suggesting that the lectin is a tetramer. Binding studies performed with iodinated lectin indicated that Saccharomyces cerevisiae cells contained approximately 5.7 X 10(6) binding sites per cell, whereas little binding was observed with yeasts other than the Saccharomyces genus, bacteria and animal erythrocytes. D-Mannose, D-mannose 6-phosphate, L-fucose and L-fucosylamine were potent inhibitors of the lectin binding to S. cerevisiae cells, while, D-glucose, D-galactose and D-mannosamine were inactive, indicating that hydroxyl group at C-2 of D-mannose was essential for the lectin binding. Furthermore, inhibition experiments, using various manno-oligosaccharides, suggested that the lectin recognized (1----6)-linked manno-oligosaccharide units larger than mannobiose.

Wheat germ agglutinin-gold as a novel marker for mesectoderm formation in mouse embryos cultured in vitro

The routes of movement of mesectoderm cells in mammalian embryos have not yet been investigated experimentally due to technical problems. However, the recent development of in vitro culture methods have made an experimental approach to this problem in mouse and rat embryos possible. We have used combined lectin and colloidal-gold (WGA-Au) probe as a nontraumatic, easily detectable mesectoderm marker. The probe is introduced into the amniotic cavity by microinjection. All of the cells lining the cavity, including the mesectoderm precursors, phagocytose the colloidal gold, which is then stored in membrane-bound vesicles. The probe remains inside the target mesectoderm cells after their migration into the mesoderm compartment. Vesicles containing gold are detectable in both ultrathin and semithin sections. The applicability of WGA-HRP as a probe was also assessed because of the many properties it shares with WGA-Au, but it proved to be unsatisfactory for this purpose because it is transferred between cells and also to the extracellular spaces.

Chitinase-gold complex used to localize chitin ultrastructurally in tomato root cells infected by Fusarium oxysporum f. sp. radicis-lycopersici, compared with a chitin specific gold-conjugated lectin

A cytochemical technique for the ultrastructural localization of chitin in tomato root cells infected by Fusarium oxysporum f. sp. radicis-lycopersici is reported. Chitinase was complexed to colloidal gold and thin sections were incubated with the enzyme-gold complex. This technique yielded a more uniform distribution of gold particles over the fungus wall, compared to that obtained with the lectin-gold technique. Both techniques revealed no labelling of the fungus cytoplasm, except for organelles resembling Woronin bodies. No significant labelling of either healthy or infected root cells was seen except for the secondary walls of vessels and, occasionally, that of adjoining parenchyma cells. The importance of this technique in studying the development of the pathogen within host cells is discussed.

Sedimentation Field Flow Fractionation: Applications

Sedimentation field flow fractionation is a powerful, new, high-resolution separation method for a wide variety of colloids, micelles, particulates, and soluble macromolecules of biological interest. Advances in instrumentation allow sedimentation field flow fractionation operation with rotor speeds up to 32,000 revolutions per minute ( approximately 85,000 gravities), which permits separation of materials as small as 5 x 10(5) molecular weight, depending on sample density. Compared to conventional centrifugation techniques, the gentle, mass-separating sedimentation field flow fractionation method is capable of higher resolution in shorter times.

Distribution of chitin in the yeast cell wall. An ultrastructural and chemical study

The distribution of chitin in Saccharomyces cervisiae primary septa and cell walls was studied with three methods: electron microscopy of colloidal gold particles coated either with wheat germ agglutinin or with one of two different chitinases, fluorescence microscopy with fluorescein isothiocyanate derivatives of the same markers, and enzymatic treatments of [14C]glucosamine-labeled cells. The septa were uniformly and heavily labeled with the gold-attached markers, an indication that chitin was evenly distributed throughout. To study the localization of chitin in lateral walls, alkali-extracted cell ghosts were used. Observations by electron and fluorescence microscopy suggest that lectin-binding material is uniformly distributed over the whole cell ghost wall. This material also appears to be chitin, on the basis of the analysis of the products obtained after treatment of 14C-labeled cell ghosts with lytic enzymes. The chitin of lateral walls can be specifically removed by treatment with beta-(1 leads to 6)-glucanase containing a slight amount of chitinase. During this incubation approximately 7% of the total radioactivity is solubilized, about the same amount liberated when lateral walls of cell ghosts are completely digested with snail glucanase yield primary septa. It is concluded that the remaining chitin, i.e., greater than 90% of the total, is in the septa. The facilitation of chitin removal from the cell wall by beta-(1 leads to 6)-glucanase indicates a strong association between chitin and beta-(1 leads to 6)-glucan. Covalent linkages between the two polysaccharides were not detected but cannot be excluded.

Location of mannan and chitin on thin sections of budding yeasts with gold markers

Mannan was located on thin sections of Saccharomyces cerevisiae and Candida utilis with the homologous anti-mannan antibodies or with Concanavalin A, both labelled with gold granules. Fully synthesized mannan was found in the cell walls, on the plasmalemma and within the cytoplasm sometimes associated with vesicles and vacuoles. Chitin or its oligomers were located with wheat germ agglutinin in the bud scars but also in the cell wall and the cytoplasm near the plasmalemma. Both mannan and chitin or its oligomers were found in the forming septum and are synthesized within the cytoplasm. The gold method was also suitable for marking mannan and chitin simultaneously.

Localization of alpha-Galactomannan on the surface of Schizosaccharomyces pombe cells by scanning electron microscopy

Galactomannan was localized by scanning and transmission electron microscopy on the cells and cell walls of Schizosaccharomyces pombe. The markers were prepared from colloidal gold granules labelled with an alpha-galactopyranosyl-binding lectin isolated from the seeds of Bandeiraea simplicifolia. Part or all of this alpha-galactomannan was present in the outer layer of the cell wall and was uniformly distributed even on the fission scars.