A mutation altering the function of a carbohydrate binding protein blocks cell-cell cohesion in developing Dictyostelium discoideum

CarbDisMut: database on neutral and disease-causing mutations in human carbohydrate-binding proteins

Protein-carbohydrate interactions are involved in several cellular and biological functions. Integrating structure and function of carbohydrate-binding proteins with disease-causing mutations help to understand the molecular basis of diseases. Although databases are available for protein-carbohydrate complexes based on structure, binding affinity and function, no specific database for mutations in human carbohydrate-binding proteins is reported in the literature. We have developed a novel database, CarbDisMut, a comprehensive integrated resource for disease-causing mutations with sequence and structural features. It has 1.17 million disease-associated mutations and 38,636 neutral mutations from 7,187 human carbohydrate-binding proteins. The database is freely available at https://web.iitm.ac.in/bioinfo2/carbdismut. The web-site is implemented using HTML, PHP and JavaScript and supports recent versions of all major browsers, such as Firefox, Chrome and Opera.

Effects of Sludge Retention Time on the Performance of Anaerobic Ceramic Membrane Bioreactor Treating High-Strength Phenol Wastewater

Anaerobic ceramic membrane bioreactor (AnCMBR) is an attractive alternative for the treatment of high-strength phenol wastewater, but the effects of sludge retention time (SRT) on the performance and membrane fouling are still unclear. The results indicated that the AnCMBR was successfully employed to treat high-strength wastewater containing 5 g phenol L⁻¹. The removal efficiencies of phenol and chemical oxygen demand (COD) reached over 99.5% and 99%, respectively, with long SRT and short SRT. SRT had no obvious effect on the performance of the AnCMBR treating high-strength phenol wastewater with long time operation. The strong performance robustness of AnCMBR benefited from the enrichment of hydrogenotrophic methanogens and syntrophic phenol-degrading bacteria. However, the decline of SRT led to a more severe membrane fouling in the AnCMBR, which was caused by the small size of sludge flocs and high concentration of protein in the biopolymers. Therefore, this work presented a comprehensive insight to the feasibility and robustness of the AnCMBR for treating high-strength phenol wastewater.

Eat Prey, Live: Dictyostelium discoideum As a Model for Cell-Autonomous Defenses

The soil-dwelling social amoeba Dictyostelium discoideum feeds on bacteria. Each meal is a potential infection because some bacteria have evolved mechanisms to resist predation. To survive such a hostile environment, D. discoideum has in turn evolved efficient antimicrobial responses that are intertwined with phagocytosis and autophagy, its nutrient acquisition pathways. The core machinery and antimicrobial functions of these pathways are conserved in the mononuclear phagocytes of mammals, which mediate the initial, innate-immune response to infection. In this review, we discuss the advantages and relevance of D. discoideum as a model phagocyte to study cell-autonomous defenses. We cover the antimicrobial functions of phagocytosis and autophagy and describe the processes that create a microbicidal phagosome: acidification and delivery of lytic enzymes, generation of reactive oxygen species, and the regulation of Zn²⁺, Cu²⁺, and Fe²⁺ availability. High concentrations of metals poison microbes while metal sequestration inhibits their metabolic activity. We also describe microbial interference with these defenses and highlight observations made first in D. discoideum. Finally, we discuss galectins, TNF receptor-associated factors, tripartite motif-containing proteins, and signal transducers and activators of transcription, microbial restriction factors initially characterized in mammalian phagocytes that have either homologs or functional analogs in D. discoideum.

The Origin of Animal Multicellularity and Cell Differentiation

Over 600 million years ago, animals evolved from a unicellular or colonial organism whose cell(s) captured bacteria with a collar complex, a flagellum surrounded by a microvillar collar. Using principles from evolutionary cell biology, we reason that the transition to multicellularity required modification of pre-existing mechanisms for extracellular matrix synthesis and cytokinesis. We discuss two hypotheses for the origin of animal cell types: division of labor from ancient plurifunctional cells and conversion of temporally alternating phenotypes into spatially juxtaposed cell types. Mechanistic studies in diverse animals and their relatives promise to deepen our understanding of animal origins and cell biology.

Specific cell-cell contacts are essential for induction of gene expression during differentiation of Dictyostelium discoideum

Postaggregation Dictyostelium discoideum cells contain 2000-3000 mRNA species that are absent from pre-aggregation cells. These aggregation-dependent sequences compose 30% of the mass of the late mRNA and represent the transcription products of an additional 11% of the single-copy genome. By analysis of mutants that are blocked at different stages of differentiation, we show that induction of expression of these genes is correlated with the formation of tight cell-cell contacts that resist EDTA. In particular, mutants that exhibit chemotaxis and aggregate to form loose mounds but do not form cell-cell contacts that resist EDTA fail to induce these late mRNA and protein species. By contrast, mutants that form normal contacts but progress no further through development do express the late mRNA species. Thus, interactions at the cell surface are involved in developmental induction of a large group of coregulated mRNAs. We have employed two independent assays for these developmentally regulated mRNAs: hybridization of gel-separated RNAs to cloned nuclear DNAs and hybridization of mRNA to a cDNA probe specific for the population of 2000-3000 regulated sequences.

Serologically distinguishable alterations in the molecular specificity of cell cohesion during morphogenesis in Dictyostelium discoideum

Cells of the mutant strain JC-5 of the slime mold Dictyostelium discoideum exhibit at a specific, late developmental stage a temperature-sensitive morphogenetic defect associated with the loss of cell cohension. We show that at the restrictive temperature, the loss of cohesion and attendant dispersal of multicellular aggregates is associated with the disappearance or sequestration of a plasma membrane-bound moiety capable of reacting with and, hence, absorbing cohesion-blocking Fab. At the permissive temperature, the maintenance of cohesiveness past the critical stage or the recovery of lost cohesiveness is correlated with the presence or reappearance of the Fab-reactive moiety.This moiety is absent or sterically incapable of reaction with Fab preparations at an earlier developmental stage in either mutant or wild-type cells-i.e., at a time when they have just entered into multicellular aggregates. Conversely, a serologically distinguishable membrane-bound moiety present in the early mutant or wild-type cells, whose reaction with homologous Fab also precludes their cohesion, is absent or serologically unreactive in either mutant or wild-type cells that are at comparable late developmental stages. We conclude that the cohesive moiety responsible for initiation of cell aggregates is supplanted by or transformed into a serologically distinct, cohesive complex responsible for the maintenance of the aggregate's integrity through the later stages of development.

Adhesion properties of Entamoeba histolytica

Trophozoites of Entamoeba histolytica adhere to and phagocytize red blood cells and bacteria. Furthermore, in the initial step of the amoebic infectious process the parasite attaches to intestinal epithelial cells. A lectin (carbohydrate-binding protein) which apparently has a role in the attachment of the parasite to host cells was found in trophozoites of E. histolytica. When amoeba cells were disrupted by freeze-thawing, the lectin activity, as determined by haemagglutination of human erythrocytes, remained associated with the sedimented membrane fraction. This activity was pH dependent and heat and oxidation-sensitive, and was destroyed by proteolysis and on autoincubation. Moreover, the lectin activity was inhibited by a variety of N-acetylglucosamine-containing compounds such as chitin and chitin oligosaccharides, bacterial peptidoglycan, rabbit colonic mucus, bovine and human serum, an IgA fraction isolated from human colostrum, and IgG from sera of amoebiasis patients. These glycoconjugates also interfered with the adherence of intact radiolabelled amoeba trophozoites to human intestinal epithelial cells as well as their attachment to red blood cells. Although the lectin activity and the toxin-like activity previously found in E. histolytica seem to be two separate substances, they share a number of properties which suggest that they are related and may have a function in pathogenicity.

Studies on cellular adhesion of Xenopus laevis melanophores: modulation of cell-cell and cell-substratum adhesion in vitro by endogenous Xenopus galactoside-binding lectin

We have investigated cell-cell and cell-substratum adhesion of Xenopus laevis neural crest cells at various stages of melanophore differentiation. Single-cell suspensions were obtained by trypsinization and aggregated in a cell-cell adhesion assay. Unpigmented cells did not adhere while the rate of adhesion of melanophores correlated with the degree of melanization. Melanophore cell-cell adhesion decreased significantly in the presence of beta-galactosidase, which suggests that cell-surface galactose is involved. Beta-galactoside-binding lectin has been isolated and purified from embryos at the stage of neural crest migration. When added to aggregating cells smaller, looser clusters formed compared to controls. When lectin was added to cells in stationary culture to test cell-substratum adhesion, melanophores spread more smoothly and formed more regular spacing patterns. These results suggest that this lectin can modulate receptors used in cell-cell and cell-substratum adhesion of melanophores.

Spectroscopic studies on the structural organization of the lectin discoidin I: homologies with fibronectin

The structure of the lectin discoidin I has been studied by circular dichroism and fluorescence spectroscopy. A positive ellipticity band at 224 nm is detected in the CD spectrum of discoidin I. The fluorescence spectra show a defined shoulder at 325 nm that through acrylamide quenching has been associated with a displaced tryptophan residue partly buried in the discoidin I molecule. This tryptophan could also be responsible for the 224 nm positive band of the CD spectrum. These spectroscopic characteristics of discoidin I indicate the existence of structural homologies with fibronectin, where the optical activity of aromatic chromophores has been associated with the positive ellipticity band at 227 nm. The CD adjust parameters and theoretical secondary structure predictions show that discoidin I is a molecule with a low content of alpha-helix and beta-strand and high content of beta-turn structures, similar to other lectins.

Differential redistribution of lectin receptor classes on clonal rat myotubes and myoblasts

To evaluate the relative mobilities of cell surface glycoconjugates during myogenesis we have studied the redistribution of fluorescein-conjugated plant lectins on L6 rat myogenic cells. Previous experiments had demonstrated that the receptors for the lectins soybean agglutinin (SBA), wheat germ agglutinin, concanavalin A and Lens culinaris agglutinin all were relatively uniformly distributed on both myoblasts and myotubes, and that SBA receptors were capable of rapid redistribution on myotubes but not myoblasts at 4 degrees C (Sawyer & Akeson, 1983). Here we show that when SBA-labelled myoblasts are incubated at 37 degrees C, or for extended times at 4 degrees C, the lectin aggregates as on myotubes. So it appears that SBA-binding components show a quantitative rather than qualitative change in their mobility during L6 differentiation. In addition, the redistribution of the three other lectins on myoblasts and myotubes was either less prominent (i.e. showing fewer apparent surface clusters) or occurred less rapidly than with SBA. None of these three lectins showed striking differences in mobility between myoblasts and myotubes. Thus, it appears that SBA binds to a subset of surface glycoconjugates that is relatively highly mobile, and that this mobility is specifically enhanced with differentiation.

Cell surface carbohydrate involvement in controlling the adhesion and morphology of neural crest cells and melanophores of Xenopus laevis

Pieces of dorsal neural tube (stages 22-23) or late neural crest tissue (stages 24-26) of Xenopus laevis were cultured. Migratory cells moved out of explants to form an outgrowth of multipolar melanophores on the substratum. Treatment with beta-galactosidase (0.1-0.4 U/ml) to remove cell surface galactose was correlated with detachment of melanophores. In the presence of lower concentrations of this enzyme the shapes of these cells were converted to arborized, spidery morphologies and cell movement was inhibited. Unpigmented cells were affected more slowly. Neuraminidase treatment, to remove cell surface sialic acid and expose more galactose, only affected melanophores. These became increasingly spread on the substratum and cell overlap was observed. These results suggest that the relative amounts of galactose and sialic acid at the cell surface become increasingly important in controlling cell adhesion as X. laevis neural crest cells migrate and differentiate into melanophores.

Overproduction of discoidin I by a temperature-sensitive motility mutant of Dictyostelium discoideum

Dictyostelium discoideum MC2 is a temperature-sensitive motility mutant of AX3. Mutant cells are incapable of growth, phagocytosis, and migration under restrictive conditions (Kayman et al., J. Cell Biol. 92:705-711, 1982). We show here that at the restrictive temperature MC2 cells grown axenically or on bacteria synthesized excessive quantities of the lectin discoidin I. By two-dimensional gel electrophoresis and peptide mapping, the proteins overproduced by MC2 cells were indistinguishable from discoidin I synthesized at lower levels in AX3 cells. At least two of the three species of discoidin I were overproduced. This protein family constituted 9% of the total protein in cells that were incubated overnight at 27 degrees C in axenic medium. Although MC2 cells are defective in nutrient uptake under restrictive conditions, the overproduction of discoidin I did not appear to be part of a pleiotropic response to starvation. We propose that transcription of the coordinately regulated discoidin I genes is altered in mutant cells. This alteration may be related to the motility defects manifested by MC2.

Overproduction of discoidin I by a temperature-sensitive motility mutant of Dictyostelium discoideum

Dictyostelium discoideum MC2 is a temperature-sensitive motility mutant of AX3. Mutant cells are incapable of growth, phagocytosis, and migration under restrictive conditions (Kayman et al., J. Cell Biol. 92:705-711, 1982). We show here that at the restrictive temperature MC2 cells grown axenically or on bacteria synthesized excessive quantities of the lectin discoidin I. By two-dimensional gel electrophoresis and peptide mapping, the proteins overproduced by MC2 cells were indistinguishable from discoidin I synthesized at lower levels in AX3 cells. At least two of the three species of discoidin I were overproduced. This protein family constituted 9% of the total protein in cells that were incubated overnight at 27 degrees C in axenic medium. Although MC2 cells are defective in nutrient uptake under restrictive conditions, the overproduction of discoidin I did not appear to be part of a pleiotropic response to starvation. We propose that transcription of the coordinately regulated discoidin I genes is altered in mutant cells. This alteration may be related to the motility defects manifested by MC2.

Protein synthesis during development and differentiation in the cellular slime mould Dictyostelium discoideum

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Soluble lectins: a new class of extracellular proteins

Soluble lectins of cellular slime molds and vertebrates are present at extracellular sites in the developing or adult tissues that make them. Some lectins are concentrated around cell groups, as in extracellular matrix or elastic fibers. Others are at the interface between cells and the external environment, as in mucin or slime. Specific glycoproteins, proteoglycans, or polysaccharides that bind these endogenous lectins may also be present at these sites. Interactions between the lectins and glycoconjugates appear to play a role in shaping extracellular environments.

The role of membrane lectins in Dictyostelium discoideum aggregation as ascertained by specific univalent antibodies against discoidin I

Antibodies against pure discoidin I have been used as a tool to ascertain the role of this lectin in aggregation of Dictyostelium discoideum. Discoidin I is widely expressed over the cell surface of aggregation-competent AX-2 cells, as ascertained by indirect immunofluorescence with specific (antidiscoidin I) antibodies. Univalent antidiscoidin I antibodies (Fab fragments) inhibit the aggregation-specific intercellular adhesion of D discoideum AX-2 cells in an in vitro assay. This inhibition depends on antibody concentration and cell density; a 50% inhibition of cell aggregation was obtained at antidiscoidin I Fab concentration of 4.5 mg/ml and 1 X 10(6) cells/ml. Aggregation and morphogenesis on solid support is also effectively inhibited when AX-2 cells are starved in the presence of antidiscoidin I Fab fragments. The inhibition of morphogenesis is also dose dependent and more effective than in the in vitro assay. No inhibition of aggregation either in the in vitro assay or on morphogenesis on solid support was observed with preimmune Fab fragments at any of the concentrations tested (up to 9.6 mg/ml).

Involvement of a cell-surface glycoprotein in the cell-sorting process of Dictyostelium discoideum

Cell sorting among prespore cells and prestalk cells in Dictyostelium discoideum was studied by using fluorochrome-labeled cells in an in vitro assay. Labeled prestalk cells first formed randomly mixed aggregates with unlabeled prespore cells. Then cells began to sort out from each other. About 3-4 hr later, prestalk cells became clustered at one pole of the aggregate. Aggregates deposited on an agar surface underwent morphogenesis and formed migrating slugs within 3 hr. The addition of Fab fragments directed against a cell-surface glycoprotein of Mr 150,000 (gp 150) to the cell mixture completely inhibited the cell-sorting phenomenon. Morphogenesis of such aggregates on agar was also delayed by 5 hr. However, inclusion of Fab fragments directed against the endogenous lectins, the contact site A glycoprotein, or vegetative cells had no detectable effect on cell sorting or morphogenesis of these reconstituted aggregates.

Mutants of Dictyostelium discoideum blocked in expression of all members of the developmentally regulated discoidin multigene family

Mutant strains of D. discoideum are described that can complete morphogenesis and cytodifferentiation but which express vastly reduced levels of the galactose-binding lectins discoidin I and II (less than 1% and 1%-2% respectively) compared to the wild-type control. Mutant cells proceeding through development lack lectin activity, lectin protein, and specific lectin mRNA. In contrast, the genes encoding these proteins are present in their wild-type configurations in the genome. Since these proteins are encoded by four to five discrete genes, the mutations in these strains are most likely in genes involved in the regulation of the expression of members of this multigene family. The results also indicate that the discoidin lectins may not be required for fruiting body construction in this organism. Finally, coupled with the recent ability to transform D. discoideum, these mutants open the way to identification and isolation of regulatory genes and their products.

Ion dependence of the discoidin I lectin from Dictyostelium discoideum

The lectin discoidin I from Dictyostelium discoideum requires divalent cations for binding activity. The data indicate that calcium is the preferred ion in vitro. In contrast, the lectin activity of discoidin II is independent of divalent ions.

Calcium-independent adhesion of extra-embryonic endoderm cells from the early chick blastoderm is inhibited by the blastoderm beta-D-galactoside-binding lectin and by beta-galactosidase

Extra-embryonic endoderm cells from gastrulating chick embryos possess Ca2+-dependent and Ca2+-independent adhesive mechanisms. These cells also contain an endogenous beta-D-galactoside-binding lectin and cell surface receptors bearing galactose groups. The endogenous lectin inhibits cellular adhesion. To test whether the adhesive interactions involving lectin and galactose molecules are part of the Ca2+-independent or Ca2+-dependent adhesive mechanism, dissociated cells which were preincubated in beta-galactosidase were allowed to aggregate in the presence and absence of Ca2+ ions. Significant decreases in adhesion were observed in both cases. Cells were also allowed to aggregate in the presence and absence of Ca2+ ions when blastoderm lectin was present in the medium. Adhesion was decreased in both cases. The results suggest that cell surface galactose groups and the beta-D-galactoside-binding lectin are involved in Ca2+-independent adhesion.

Possible role for cell-surface carbohydrate-binding molecules in lymphocyte recirculation

We are investigating the hypothesis that carbohydrate-binding molecules on the cell surface are involved in the recirculation of lymphocytes from the bloodstream into lymphoid organs. This phenomenon requires the specific attachment of circulating lymphocytes to the endothelial cells of postcapillary venules. Using an in vitro assay to measure the adhesive interaction between lymphocytes and postcapillary venules, we have found that L-fucose, D mannose, and the L-fucose-rich, sulfated polysaccharide fucoidin specifically inhibit this binding interaction. L-fucose shows stereo-selective inhibitory activity at concentrations greater than 18 mM while fucoidin produces 50% inhibition at approximately 1-5 X 10(-8) M. Fucoidin appears to interact with the lymphocyte, and not the postcapillary venule, to inhibit binding. These data suggest that cell surface carbohydrates (fucoselike) and carbohydrate-binding molecules (cell surface lectins) may contribute to the specific attachment of lymphocytes to postcapillary venules.

Discoidin I and discoidin II are localized differently in developing Dictyostelium discoideum

The distribution of discoidin I and discoidin II, developmentally regulated lectins in Dictyostelium discoideum, was determined immunohistochemically at various stages of development. Discoidin I was first prominent as focal clumps in aggregating cells, then accumulated on the surface of aggregates and around them. Discoidin II became prominent later and ultimately localized in what appear to be prespore vesicles. The results indicate that discoidin I and discoidin II have different and possibly multiple functions.

Isolation and characterization of peanut agglutinin-resistant embryonal carcinoma cell-surface variants

The isolation and characterization of variant embryonal carcinoma (EC) cells possessing altered cell-surface structures is described. The lectin peanut agglutinin (PNA), which binds to EC cells but not their differentiated derivatives, was used to select the variants. Clones resistant to the cytotoxic effect of PNA were isolated at a frequency of 4 X 10(-5) following mutagenesis. The resistant phenotype was stable in the absence of selection in all eight clones tested. The increased frequency of resistant clones following mutagenesis and the stability of the phenotype suggests a mutational origin. Somatic cell hybrids constructed between wild-type cells and two different PNA-resistant cell lines were sensitive to PNA; this suggests that the resistant phenotype is recessive. Binding assays demonstrated that resistant cells exhibited a twofold to fourfold reduction in the total amount of PNA bound. Together with the recessive behavior of the phenotype, this suggests that resistant cells are deficient for PNA receptors. The PNA-resistant cells also showed reduced binding of monoclonal antibody against stage-specific embryonic antigen 1 (SSEA-1) in indirect cytotoxicity tests. All eight PNA-resistant lines isolated were tumorigenic in syngeneic mice and gave rise to well-differentiated teratocarcinomas. The PNA-resistant cells behaved like their wild-type parents in a cell recognition assay; when incubated in suspension with endodermal cells, they sorted out to form simple embryoid bodies (a core of EC cells surrounded by an endodermal rind). Thus, EC cells can form tumors, differentiate, and recognize differentiated cells in a sorting assay despite a reduction in expression of the embryo-specific cell surface structures (s) that bind PNA and anti-SSEA-1 antibody.

Cell-surface discoidin in aggregating cells of Dictyostelium discoideum

Both discoidin I and discoidin II have been detected on the surface of aggregating (10 h developmental stage) cells of Dictyostelium discoideum NC4 by radioiodination of the cell-surface followed by immunoprecipitation and sodium dodecyl sulphate/polyacrylamide-gel-electrophoretic analysis. Approx. 92% of cell-surface discoidin I and 72% of cell-surface discoidin II can be eluted with 0.5 M-galactose, showing that most of each endogenous lectin is not present as integral membrane protein but rather is bound to cell-surface discoidin receptors. Two-dimensional polyacrylamide-gel-electrophoretic analysis of discoidin I suggests that the native tetramer may be a hetero-multimer composed of both Ia and Ib subunits. Cell-surface discoidin I also contains both types of subunit, but it is not clear whether both subunits have corresponding cell-surface receptors.

Identification and purification of an endogenous receptor for the lectin pallidin from Polysphondylium pallidum

We report the identification and purification of an endogenous carbohydrate-containing receptor of pallidin, the cell surface lectin implicated in mediating cell-cell adhesion in the cellular slime mold Polysphondylium pallidum. The receptor is identified in an aqueous extract of crude P. pallidum membranes as a potent inhibitor of the hemagglutination activity of pallidin. The inhibitor is purified to apparent homogeneity by affinity precipitation with pallidin followed by fractionation of the solubilized precipitate on Sepharose 4B. The hemagglutination inhibitor (HAI) is metabolically radiolabeled, indicating that it is a biosynthetic product of the amoebae and not an ingested food substance. The HAI is released into the extracellular medium by living, differentiated amoebae. This release is markedly facilitated by the addition of D-galactose, a specific saccharide that binds to pallidin. Hence, the HAI appears to have an in situ association with pallidin at the cell surface. Exogenously added HAI promotes the agglutination of differentiated amoebae in a gyrated suspension at very low concentrations. The results are consistent with a model of cell-cell adhesion in which the HAI is a multivalent, extracellular aggregation factor that is recognized by pallidin molecules on adjacent cells. The HAI would then be analogues to the aggregation factors identified in marine sponges.

Membrane sites regulating developmental gene expression in Dictyostelium discoideum

Postaggregative gene expression in Dictyostelium discoideum requires cell contact. Polyspecific monovalent antibodies (Fab) prepared from sera raised against membranes of aggregation- and postaggregation-stage cells were used to probe the cell interactions that induce rapid postaggregative synthesis of UDP-glucose pyrophosphorylase. When cells of strain V12M2 were dissociated after 8 hr of development and replated in the presence of immune Fab, both reaggregation and pyrophosphorylase synthesis were blocked. Fab neutralized by incubation with EDTA-high salt extracts of cells developed for 3 hr blocked pyrophosphorylase synthesis but not reaggregation. Therefore, some cell-surface components that regulate pyrophosphorylase synthesis (called E sites) are antigenically distinct from those required for reaggregation. The Fab provides a means to assay E sites during their purification. Addition of 10(-3) M cyclic AMP or cyclic GMP enabled the cells to bypass the blocking of E sites by Fab; pyrophosphorylase was synthesized in the absence of reaggregation. We hypothesize that E sites function by raising the level of intracellular cyclic AMP.

Discoidins I and II: common and unique regions on two lectins implicated in cell--cell cohesion in Dictyostelium discoideum

As Dictyostelium discoideum amoebae differentiate from the noncohesive to the mutually cohesive state, they synthesize two galactose-binding lectins--discoidins I and II--which have been implicated as obligatory components of the morphogenetic cell-cell recognition and cohesion system. These proteins have been shown to have similar amino acid compositions and subunit Mr and overlapping but distinct carbohydrate recognition specificities. We have performed extensive immunochemical and biochemical analyses to study the structural relationships between these two molecules and to eventually identify structural and functional domains. Antisera raised against highly purified preparations of discoidin I and discoidin II were tested for their reactivities against each protein by both immunoprecipitation and double diffusion analyses. The patterns of crossreactivity indicated the presence of shared as well as unique antigenic determinants. This interpretation was supported by two-dimensional thin-layer peptide map analysis and by studies with purified peptides. Of approximately 10-12 peptides observed after exhaustive tryptic digestion of each radioiodinated lectin, 3 appeared to be common to both. These putative common peptides were purified, and the corresponding peptides from discoidins I and II were found to behave identically by two-dimensional thin-layer analysis, gel filtration, and susceptibility to chymotrypsin. The finding of common and unique regions in discoidins I and II suggests analogies with other families of recognition proteins and may have important functional implications for these cell-cell recognition molecules.

Differential expression of the members of the discoidin I multigene family during growth and development of Dictyostelium discoideum

Discoidin I and II are lectins synthesized during the aggregation of Dictyostelium discoideum amoebae which may play a role in cellular cohesion. Discoidin I was thought to consist of two major polypeptides, but we show that there are three. The N-terminal amino acid sequence of the polypeptides has been predicted by determining part of the nucleotide sequence of their respective mRNAs. We obtained the nucleotide sequences by reverse transcription of the mRNAs, using as primers, fragments derived from the coding region of two cloned discoidin I sequences, and utilizing cross hybridization to the various mRNA species and differences in the length of their 5' noncoding regions to isolate fragments for DNA sequencing. We used primer extension to measure the relative concentration of the three major discoidin I mRNA sequences. We show that during development changes in the abundance of all three mRNA sequences occur coordinately. In cells growing in nutrient broth, however, only two of the three major discoidin I mRNA sequences accumulate, and if such cells are grown to a very high density, both sequences disappear. These results indicate that the coordination of discoidin I gene expression is not obligatory and that the members of this multigene family may differ in the mode of their induction during normal development.

Immunocytochemical localization of wheat germ agglutinin in wheat

Immunocytological techniques were developed to localize the plant lectin, wheat germ agglutinin (WGA), in the tissues and cells of wheat plants. In a previous study we demonstrated with a radioimmunoassay that the lectin is present in wheat embryos and adult plants both in the roots and at the base of the stem. We have now found, using rhodamine, peroxidase, and ferritin-labeled secondary antibodies, that WGA is located in cells and tissues that establish direct contact with the soil during germination and growth of the plant In the embryo, WGA is found in the surface layer of the radicle, the first adventitious roots, the coleoptile, and the scutellum. Although found throughout the coleorhiza and epiblast, it is at its highest levels within the cells at the surface of these organs. In adult plants, WGA is located only in the caps and tips of adventitious roots. Reaction product for WGA was not visualized in embryonic or adult leaves or in other tissues of adult plants. At the subcellular level, WGA is located at the periphery of protein bodies, within electron-translucent regions of the cytoplasm, and at the cell wall-protoplast interface. Since WGA is found at potential infection sites and is known to have fungicidal properties, it may function in the defense against fungal pathogens.

Characterization of sequence elements at the 5' end of a discoidin I gene isolated from Dictyostelium discoideum

The discoidin I genes of Dictyostelium discoideum encode a family of three closely related developmentally regulated lectins which may play a role in cell cohesion. We have isolated a genomic clone containing the 5' half of a discoidin I gene with 12kb of flanking sequence and we have identified the discoidin I polypeptide encoded by this gene. We have determined part of the nucleotide sequence of the cloned segment and have hence determined the N-terminal amino acid sequence of the encoded polypeptide. The nucleotide sequence upstream of the AUG initiation codon was unusually AT rich, with 94% AT base pairs in the 171 nucleotides for which sequence was determined. However, having determined the start point of transcription ('cap' site) two striking features of similarity with other eukaryotic structural genes became apparent. The sequence TATAAA was present 33 nucleotides upstream from the 'cap' site and the sequence CCAAT was present a further 20 nucleotides upstream.

A biologically active receptor for the carbohydrate-binding protein(s) of Dictyostelium discoideum

Recent biochemical and genetic evidence has shown that carbohydrate-binding protein (CBP-26) is intimately involved in the cell-cell cohesion process. We have isolated a cell-surface-associated receptor molecule for CBP-26 by affinity chromatography. The receptor has a molecular weight of 80,000 daltons. The CBP receptor is constitutively expressed during development. Most significantly, the receptor, when added to aggregation-competent cells, blocks the cells' ability to reaggregate. These results suggest that CBP and its receptor play an important role in the cell cohesion and aggregation process.

Stage-specific antigens reacting with monoclonal antibodies against contact site A, a cell-surface glycoprotein of Dictyostelium discoideum

Monoclonal antibodies against a glycoprotein presumably involved in adhesion of aggregating Dictyostelium discoideum cells have been used for labeling of the antigen at the cell surface. The antigen is distributed over the whole surface of the cells, apparently in form of small clusters. The antigen appears concomitantly with the acquisition of EDTA-stable adhesiveness typical of aggregation competent cells. In contrast, discoidin I, a lectin whose accumulation during development parallels EDTA-stable adhesiveness in another strain (NC-4), is present in nearly the same amounts of growth phase and aggregating cells of AX2-214, the strain used by use. Thus, no correlation exists in this strain between the expression of discoidin I and the development of cell adhesiveness. The 80 kilodalton glycoprotein typical of aggregation competent cells has been purified by affinity chromatography on a monoclonal antibody column. The purified antigen absorbs adhesion-blocking Fab from rabbits. Another antigen strongly reacting with the same monoclonal antibodies has an apparent molecular weight of 106 000 and is not detectable before slugs are formed.

Immunochemical analysis of discoidins I and II at the cell surface in wild type and aggregation-defective mutants of Dictyostelium discoideum

The endogenous lectins discoidins I and II are believed to be primary components of the morphogenetic cell cohesion system of D discoideum. We have developed two immunochemical methods to analyze the association of the discoidins with the cell surface. One method is a two-state specific antibody binding assay in which intact cells are incubated on ice with rabbit serum (either control serum or antidiscoidin I and II), washed, then incubated with 125I-Protein A. Specific antibody binding is defined as the difference between percent radioactivity bound with antidiscoidin versus control serum during the first stage. Substantial specific binding was observed with developed A3 cells but not with vegetative cells, and nearly all of the activity could be removed by preadsorption of the antiserum with discoidin-Sepharose. As a complementary method, quantitative immunoadsorption analysis was performed in which we tested the ability of intact cells to remove antibodies reactive with purified 125I-discoidin I or II. Developed cells, but not vegetative cells, were capable of adsorbing antibodies reactive with discoidin I as well as those reactive with discoidin II. This represents the first demonstration that both lectins are present on the surface of cohesive cells. These procedures, coupled with other methods to analyze soluble discoidin in cell extracts, were used to study discoidin expression in wild type cells and in two newly isolated aggregation-defective mutants. Strain EB-32 fails to aggregate and displays little or no discoidin in cell extracts or at the cell surface. On the other hand, strain EB-18 forms loose amorphous mounds, and expresses substantial quantities of the discoidins, both in cell extracts and at the cell surface. These mutants should prove valuable in studying the organization and regulation of discoidins I and II at the surface of aggregating cells.

Effects of ovarian hormones on cell membranes in the rat uterus. III. The surface carbohydrates at the apex of the luminal epithelium

Histochemical techniques, including radioisotope histochemistry, have been used to investigate the nature of the surface carbohydrates at the apex of cells of the luminal epithelium of the rat uterus under various hormonal conditions. Binding of ruthenium red was quantitatively similar in ovariectomized rats without further treatment and in those given three daily injections of progesterone. Ruthenium red binding was significantly lower after 3 days treatment with estradiol, and also after 3 days treatment with progesterone with an additional dose of estradiol on day 3, a regime known to produce an epithelium receptive to the implanting blastocyst. Binding of concanavalin A (con A), whether studied by electron microscope histochemistry after incubation of tissue with con A-horseradish peroxidase, or by light microscope autoradiography after incubation with 3H-con A, was not statistically different in any of the four groups of rats. The results with ruthenium red show a reduction in net negative charge of the carbohydrates on the apical cell membrane in conditions permitting implantation: this change is not due to variations in the amounts of the neutral carbohydrates, mannose and glucose, as demonstrated by con A.

An analysis of discoidin I binding sites in Dictyostelium discoideum (NC4)

Vegetative wild-type (strain NC4) D. discoideum cells and cells at the 10h stage of development (aggregation) were harvested in the presence of 0.5 M-galactose to remove any endogenous discoidin I already bound to the cell surface, and fixed with glutaraldehyde. Affinity-purified 125I-labelled discoidin I bound to these fixed cells in a specific manner, greater than or equal to 95% of binding being inhibited by 0.5 M-galactose. Binding of 125I-labelled discoidin I was essentially complete in 90 min at 22 degrees C. Based on specific radioactivity measurements, vegetative (0h) D. discoideum (NC4) cells bind approx. 8.4 x 10(5) discoidin I tetramers/cell and aggregated (10h) cells bind 5.1 x 10(5) discoidin I tetramers/cell, each exhibiting apparent positive co-operativity of binding with highest limiting affinity constants (Ka) of approx. 1 x 10(7) and 2 x 10(7) M-1, respectively. Klebsiella aerogenes, the food source used for growth of D. discoideum NC4 amoebae, also binds 125I-labelled discoidin I and this is greater than 99% inhibited by 0.5 M-galactose. However, at the levels of bacterial contamination present, greater than 97% of 125I-labelled discoidin I binding to D. discoideum cell preparations was to the cells themselves. Confirmation of the number of discoidin I tetramers bound per D. discoideum cell was obtained by elution of bound 125I-labelled discoidin I followed by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and then quantification by scanning of stained discoidin I bands.

Purification of a high-affinity discoidin I-binding proteoglycan from axenic Dictyostelium discoideum growth medium

The axenic Dictyostelium discoideum growth medium HL-5, prepared using Difco proteose peptone No. 2, contains an extremely potent inhibitor of the binding of 125I-labeled discoidin I to glutaraldehyde-fixed, cohesive D. discoideum cells. Axenic strain A3 D. discoideum cells bind or internalize the inhibitor during growth in HL-5 medium and subsequently shed or excrete it while differentiating in suspension. The inhibitor has been purified from Difco proteose peptone No. 2 by sequential gel filtration on Sepharose 4B and affinity adsorption using discoidin I-Sepharose. The inhibitor is heterogeneous in molecular weight (4 . 10(5)--2 . 10(6)), but is relatively homogeneous in density on CsCl density gradients. The size and activity of the inhibitor are resistant to periodate, reduction and maleylation, proteases, nucleases and heating in the absence or presence of sodium dodecyl sulfate. Mild alkali causes a partial reduction in activity and converts the higher molecular weight fraction of the inhibitor to a lower molecular weight. The purified inhibitor contains neutral hexose, hexosamine and amino acid in an approximate molar ratio of 4 : 3 : 2. These and other properties suggest that the inhibitor is an unusual proteoglycan. Certain well-characterized glycosaminoglycans are relatively potent inhibitors of discoidin I binding. The proteoglycan reported here is the most potent discoidin I-binding inhibitor ever identified.