Two chemoreceptors mediate developmental effects of dauer pheromone in C. elegans

Intraspecific chemical communication is mediated by signals called pheromones. Caenorhabditis elegans secretes a mixture of small molecules (collectively termed dauer pheromone) that regulates entry into the alternate dauer larval stage and also modulates adult behavior via as yet unknown receptors. Here, we identify two heterotrimeric GTP-binding protein (G protein)-coupled receptors (GPCRs) that mediate dauer formation in response to a subset of dauer pheromone components. The SRBC-64 and SRBC-66 GPCRs are members of the large Caenorhabditis-specific SRBC subfamily and are expressed in the ASK chemosensory neurons, which are required for pheromone-induced dauer formation. Expression of both, but not each receptor alone, confers pheromone-mediated effects on heterologous cells. Identification of dauer pheromone receptors will allow a better understanding of the signaling cascades that transduce the context-dependent effects of ecologically important chemical signals.

The Medicago truncatula DMI1 protein modulates cytosolic calcium signaling

In addition to establishing symbiotic relationships with arbuscular mycorrhizal fungi, legumes also enter into a nitrogen-fixing symbiosis with rhizobial bacteria that results in the formation of root nodules. Several genes involved in the development of both arbuscular mycorrhiza and legume nodulation have been cloned in model legumes. Among them, Medicago truncatula DMI1 (DOESN'T MAKE INFECTIONS1) is required for the generation of nucleus-associated calcium spikes in response to the rhizobial signaling molecule Nod factor. DMI1 encodes a membrane protein with striking similarities to the Methanobacterium thermoautotrophicum potassium channel (MthK). The cytosolic C terminus of DMI1 contains a RCK (regulator of the conductance of K(+)) domain that in MthK acts as a calcium-regulated gating ring controlling the activity of the channel. Here we show that a dmi1 mutant lacking the entire C terminus acts as a dominant-negative allele interfering with the formation of nitrogen-fixing nodules and abolishing the induction of calcium spikes by the G-protein agonist Mastoparan. Using both the full-length DMI1 and this dominant-negative mutant protein we show that DMI1 increases the sensitivity of a sodium- and lithium-hypersensitive yeast (Saccharomyces cerevisiae) mutant toward those ions and that the C-terminal domain plays a central role in regulating this response. We also show that DMI1 greatly reduces the release of calcium from internal stores in yeast, while the dominant-negative allele appears to have the opposite effect. This work suggests that DMI1 is not directly responsible for Nod factor-induced calcium changes, but does have the capacity to regulate calcium channels in both yeast and plants.

Trophic control of bud break in peach (Prunus persica) trees: a possible role of hexoses

Vegetative buds of peach (Prunus persica L. Batsch.) trees act as strong sinks and their bud break capacity can be profoundly affected by carbohydrate availability during the rest period (November-February). Analysis of xylem sap revealed seasonal changes in concentrations of sorbitol and hexoses (glucose and fructose). Sorbitol concentrations decreased and hexose concentrations increased with increasing bud break capacity. Sucrose concentration in xylem sap increased significantly but remained low. To clarify their respective roles in the early events of bud break, carbohydrate concentrations and uptake rates, and activities of NAD-dependent sorbitol dehydrogenase (SDH), sorbitol oxidase (SOX) and cell wall invertase (CWI) were determined in meristematic tissues, cushion tissues and stem segments. Only CWI activity increased in meristematic tissues shortly before bud break. In buds displaying high bud break capacity (during January and February), concentrations of sorbitol and sucrose in meristematic tissues were almost unchanged, paralleling their low rates of uptake and utilization by meristematic tissues, and indicating that sorbitol and sucrose play a negligible role in the bud break process. Hexose concentrations in meristematic tissues and glucose imported by meristematic tissues correlated positively with bud break capacity, suggesting that hexoses are involved in the early events of bud break. These findings were confirmed by data for buds that were unable to break because they had been collected from trees deprived of cold. We therefore conclude that hexoses are of greater importance than sorbitol or sucrose in the early events of bud break in peach trees.

Physicochemical characterization of influenza viral vaccine loaded surfactant vesicles

The goal of this study was to develop nonionic surfactant vesicles of influenza antigen for nasal mucosal delivery. The study describes the encapsulation of viral influenza vaccine antigen in nonionic surfactant vesicles using dehydration-rehydration technique and investigation of the influence of the varying proportion of surfactant, cholesterol, and dicetyl phosphate on the morphology, particle size, entrapment efficiency, and in vitro antigen release from surfactant vesicles. The stability of the antigen was studied using SDS-polyacrylamide gel electrophoresis and immunoblotting. The effect of cholesterol concentration and the method of lyophilization on antigen loading and in vitro release of antigen from surfactant vesicles also were studied.

Glucose exerts a permissive effect on the regulation of the initiation factor 4E binding protein 4E-BP1

The eukaryotic initiation factor 4E (eIF4E) binding protein (4E-BP1) interacts directly with eIF4E and prevents it from forming initiation factor (eIF4F) complexes required for the initiation of cap-dependent mRNA translation. Insulin and other agents induce the phosphorylation of 4E-BP1 at multiple sites, resulting in its release from eIF4E, and this involves signalling through the mammalian target of rapamycin (mTOR). Here we show that D-glucose promotes the ability of insulin to bring about the phosphorylation of 4E-BP1 and the formation of eIF4F complexes. This appears to involve facilitation of the phosphorylation of at least three phosphorylation sites on 4E-BP1, i.e. Thr-36, Thr-45 and Thr-69. Non-metabolizable glucose analogues cannot substitute for D-glucose, but other hexoses can. This suggests that a product of hexose metabolism mediates the permissive effect of glucose. The effect of glucose was concentration-dependent within the range 1-5 mM. In contrast with the situation for 4E-BP1, glucose does not allow full activation of the 70 kDa ribosomal protein S6 kinase (p70 S6k; another target of mTOR signalling) or phosphorylation, in vivo, of its substrate, ribosomal protein S6. Taken together with earlier data showing that amino acids regulate 4E-BP1 and p70 S6k, the present findings show that 4E-BP1 in particular is regulated in response to the availability of both amino acids and sugars.

Sugars as signaling molecules

Recent studies indicate that, in a manner similar to classical plant hormones, sugars can act as signaling molecules that control gene expression and developmental processes in plants. Crucial evidence includes uncoupling glucose signaling from its metabolism, identification of glucose sensors, and isolation and characterization of mutants and other regulatory components in plant sugar signal transduction pathways. The emerging scenario points to the existence of a complex signaling network that interconnects transduction pathways from sugars and other hormone and nutrient signals.

D-Tagatose, a stereoisomer of D-fructose, increases hydrogen production in humans without affecting 24-hour energy expenditure or respiratory exchange ratio

In growth studies on rats, the ketohexose D-tagatose has been shown to contribute no net metabolizable energy, and a pronounced thermic effect of the sugar has been suggested to account for the absence of energy. In a double-blind and balanced cross-over design, we measured 24-h energy expenditure in eight normal weight humans in a respiration chamber during the consumption of 30 g D-tagatose or 30 g sucrose/d. Metabolic measurements were performed before and after a 2-wk adaptation period with a 30-g daily intake of the test sugar. Total 24-h energy expenditure and hour-by-hour profile were unaffected by the test sugar. The nonprotein respiratory exchange ratio (RERnp) was similar during consumption of D-tagatose and sucrose. However, the effect on RERnp due to CO2 produced by fermentation of D-tagatose could not be quantified in this study. A significant increase in 24-h H2 production (35%) during D-tagatose administration suggests a substantial malabsorption of the sugar. We found no effects of the 2-wk adaptation period on the measured gas exchange variables. Significantly lower fasting plasma insulin and triglyceride concentrations were observed during D-tagatose administration compared with the sucrose period. No effects of D-tagatose on body weight and composition were seen, but the perception of fullness 2.5 h after the sugar load was greater with D-tagatose. In conclusion, this study does not suggest a pronounced thermic effect of D-tagatose, and other mechanisms seem to be required to explain its lack of net energy.

Erythromycin A-derived macrolides modify the functional activities of human neutrophils by altering the phospholipase D-phosphatidate phosphohydrolase transduction pathway: L-cladinose is involved both in alterations of neutrophil functions and modulation of this transductional pathway

All erythromycin A derivatives, irrespective of the size of the lactone ring and the nature of the substituent, inhibit oxidant production by neutrophils and promote their degranulation. We demonstrate in this study that the L-cladinose at position 3 of the lactone ring is a key structure in the modulation of these two neutrophil functions, suggesting that this sugar (alone or combined with a lactone structure) interferes with cell target(s) involved in both oxidant production and exocytosis. Taking roxithromycin as an example of erythromycin A derivatives, we also found that these molecules interfered with the phospholipase D (PLD)-phosphatidate phosphohydrolase pathway in two ways. In nonstimulated neutrophils, roxithromycin and all L-cladinose-bearing molecules activated PLD, as reflected by 1-O-[3H]alkyl-2-acyl-phosphatidyl-ethanol production. In addition, these drugs induced an accumulation of 1-O-[3H]alkyl-2-acyl-phosphatidic acid (PA), but not 1-O-[3H]alkyl-2-acylglycerol. PA accumulation seems to be involved in the induction of exocytosis by macrolides, as the roxithromycin-induced release of granular enzymes was impaired strongly in the presence of ethanol. By contrast, in stimulated neutrophils, roxithromycin inhibited PLD activity and totally impaired 1-O-[3H]alkyl-2-acylglycerol production. The inhibition of diglyceride production by roxithromycin (not its descladinosyl derivative) could explain its inhibitory effect on oxidant production. The relevance of our data to the clinical situation, particularly the anti-inflammatory activity of these drugs, requires further investigation.

Regulation, perturbation, and correction of metabolic events in pancreatic islets

The physiological regulation of nutrient catabolism in islet cells, its perturbation in non-insulin-dependent diabetes mellitus, and the tools available to compensate for such a perturbation are reviewed. In terms of physiology, emphasis is placed on the relevance of glucokinase to hexose-induced insulin release, protein-to-protein interaction and enzyme-to-enzyme channelling, and the preferential stimulation of mitochondrial oxidative events in glucose-stimulated B-cells. In terms of pathology, attention is drawn to the deficiency of FAD-linked mitochondrial glycerophosphate dehydrogenase. Last, as far as therapeutic aspects are concerned, the potential usefulness of hypoglycemic sulfonylureas and meglitinide analogs, adenosine analogs, non-glucidic nutrients, and GLP-1 is underlined.

Phagocytosis in the colonial ascidian Botryllus schlosseri

Phagocytosis by Botryllus schlosseri hemocytes is influenced by temperature, pH, concentration, and physicochemical properties of the test particles and requires Ca2+ or Mg2+ ions to occur. Phagocytes recognize glucosyl or mannosyl residues on the surface of yeast cells, and a respiratory burst is associated with phagocytosis, as indicated by increased superoxide production. Factors that enhance phagocytosis of yeast, sheep red blood cells, and latex beads and reduce the uptake of yeast and sheep erythrocytes are present in the plasma.

[Solcoseryl: Ulcerostatic effect and possible mechanisms]

It is shown that the level of DNA, RNA, collagen, non-collagen proteins, hexoses and glycosaminoglycans is changed when making the experimental gastric ulcer in rats. Solcoseryl stabilises the level of DNA, RNA and collagen, stimulating the reparation processes in ulcer.

Endogenous regulation of 2-deoxyglucose uptake in C6 glioma cells correlates with cytoskeleton-mediated changes of surface morphology

The cellular basis of the membrane-limited state of glucose utilization and the mechanism of the endogenous regulation of hexose uptake in dense monolayers of C6 glioma cells were investigated. In an earlier study, it was shown that at high rates of glucose transport and phosphorylation combined with the inhibition of glycolytic adenosine triphosphate (ATP) production by iodoacetate, an endogenous regulatory response occurred that resulted in rapid, periodic variations of the glucose uptake rates (Lange et al., 1982). Similar time-dependent periodic changes of uptake rates also occurred during incubation of C6 glioma cells with 2 mM 2-deoxyglucose (2-DG) without pretreatment of the cells with iodoacetate. These changes were accompanied by variations of the intracellular ATP content, by distinct alterations of the shape and arrangement of microvilli and lamellae (lamellipodia) on the cell surface, and by changes of the cytoskeletal F-actin content. Because the changes of 2-DG uptake rates occurred independent of the intracellular 2-DG concentration, the bulk of this 2-DG pool was assumed to be localized apart from the membranal transport sites. Downregulation of 2-DG uptake appeared to be triggered by a rapid decrease of a small pool of the cellular ATP involved in the phosphorylation of transported hexose. Scanning and transmission electron microscopic observations of cells fixed in different states of the endogenous uptake regulation supported the assumption that the interior of lamellae and microvilli may represent a small entrance compartment for transported hexoses in which occurred the observed close coupling between hexose transport and phosphorylation as well as the rapid variations of ATP content. Hexose uptake is supposed to be regulated by cytoskeleton-mediated changes of volume and diffusional accessibility of this compartment, modulating the degree of its metabolic coupling with the cytoplasmic main compartment.

Pancreatic islet discrimination of hexose anomers. II. Transient computer simulation

We have previously modeled pancreatic islet glycolysis under idealized steady-state conditions where the input is a pure hexose anomer and there is no mutarotation and reproduced the known preference for the alpha-anomers of glucose and mannose as substrates. This model is here extended to simulate real experiments, where the hexoses mutarotate and measurements may be taken over time. The behavior of our model system agrees with available experimental data. The hexose diphosphate activators of phosphofructokinase, whose effect was seen as not important in the preceding steady-state analysis, are found here to have a modest (approximately 10-15%) effect on its flux. The previous conclusion that the anomeric preference of the glycolytic pathway follows from that of glucokinase continues to hold in the real experimental situation.

[Regulation of pancreatic glucagon secretion]

Intensive investigations during the last few years have shown that the regulation of the secretion of pancreatic glucagon is controlled by nerval, humoral and metabolic factors. Of decisive importance is the actually present glucose level which by inhibition modifies the effectiveness of the most different stimulators (intestinal hormones, amino acids). In addition to this the hormones insulin and somatostatin formed by the islets of Langerhans of the pancreas seem to be of importance for the local reactivity of the A-cells of the endocrine pancreas. Disturbances of the glucagon secretion of the pancreas have been found in different diseases connected with hyperglycaemia (especially in diabetes mellitus). The review tried to summarize our present knowledge of the physiology and pathophysiology in this field.