Inheritance pattern of RAPD markers in Melipona quadrifasciata (Hymenoptera: Apidae, Meliponinae).

Melipona quadrifasciata is an important pollinator agent in several regions of Brazil. Data concerning the genetics of this species are scarce in the literature. In this work we used the random amplified polymorphic DNA (RAPD) technique to determine the degree of polymorphism and the inheritance pattern of these molecular markers in this species. Our ultimate goal is to establish tools to be used in the study of the genomic organization of M. quadrifasciata. Genomic DNA from progenies F(1) and BC(1) were assayed with 79 different primers, yielding an average of 6.67 bands and 1.68 polymorphisms per primer. Three types of polymorphisms were detected: band presence/absence, band intensity, and fragment-length polymorphisms. Most of the observed polymorphisms were band presence/absence, typical of RAPD-dominant markers. The number of observed polymorphisms and their segregation in accordance with a Mendelian proportion confirm the importance of this technique for genome analysis of species like M. quadrifasciata that are poorly studied at the genetic level.     

Glutaric acid stimulates glutamate binding and astrocytic uptake and inhibits vesicular glutamate uptake in forebrain from young rats

Glutaric acidemia type I (GA I) is an inherited neurometabolic disorder caused by glutaryl-CoA dehydrogenase deficiency, which leads to accumulation in body fluids and in brain of predominantly glutaric acid (GA), and to a lesser extent of 3-hydroxyglutaric and glutaconic acids. Neurological presentation is common in patients with GA I. Although the mechanisms underlying brain damage in this disorder are not yet well established, there is growing evidence that excitotoxicity may play a central role in the neuropathogenesis of this disease. In the present study, preparations of synaptosomes, synaptic plasma membranes and synaptic vesicles, as well as cultured astrocytes from rat forebrain were exposed to various concentrations of GA for the determination of the basal and potassium-induced release of [(3)H]glutamate by synaptosomes, Na(+)-independent glutamate binding to synaptic membranes and vesicular glutamate uptake and Na(+)-dependent glutamate uptake into astrocytes, respectively. GA (1-100 nM) significantly stimulated [(3)H]glutamate binding to brain plasma membranes (40-70%) in the absence of extracellular Na(+) concentrations, reflecting glutamate binding to receptors. Furthermore, this stimulatory effect was totally abolished by the metabotropic glutamate ligands DHPG, DCG-IV and l-AP4, attenuated by the ionotropic non-NMDA glutamate receptor agonist AMPA and had no interference of the NMDA receptor antagonist MK-801. Moreover, [(3)H]glutamate uptake into synaptic vesicles was inhibited by approximately 50% by 10 and 100 nM GA and Na(+)-dependent [(3)H]glutamate uptake by astrocytes was significantly increased (up to 50%) in a dose-dependent manner (maximal stimulation at 100 microM GA). In contrast, synaptosomal glutamate release was not affected by the acid at concentrations as high as 1 mM. These results indicate that the inhibition of glutamate uptake into synaptic vesicles by low concentrations GA may result in elevated concentrations of the excitatory neurotransmitter in the cytosol and the stimulatory effect of this organic acid on glutamate binding may potentially cause excitotoxicity to neural cells. Finally, taken together these results and previous findings showing that GA markedly decreases synaptosomal glutamate uptake, it is possible that the stimulatory effect of GA on astrocyte glutamate uptake might indicate that astrocytes may protect neurons from excitotoxic damage caused by GA by increasing glutamate uptake and therefore reducing the concentration of this excitatory neurotransmitter in the synaptic cleft.     

Differential regulation of the release of tumor necrosis factor-alpha and of eicosanoids by mast cells in rat airways after antigen challenge

BACKGROUND: Rat trachea display a differential topographical distribution of connective tissue mast cells (CTMC) and mucosal mast cells (MMC) that may imply regional differences in the release of allergic mediators such as tumor necrosis factor-alpha (TNF-alpha) and eicosanoids. AIM: To evaluate the role of CTMC and MMC for release of TNF-alpha and eicosanoids after allergenic challenge in distinct segments of rat trachea. MATERIALS AND METHODS: Proximal trachea (PT) and distal trachea (DT) from ovalbumin (OVA)-sensitized rats, treated or not with compound 48/80 (48/80) or dexamethasone, were incubated in culture medium. After OVA challenge, aliquots were collected to study release of TNF-alpha and eicosanoids. RESULTS: Release of TNF-alpha by PT upon OVA challenge peaked at 90 min and decayed at 6 and 24 h. Release from DT peaked at 30-90 min and decayed 6 and 24 h later. When CTMC were depleted with 48/80, OVA challenge exacerbated the TNF-alpha release by PT at all time intervals, while DT exacerbated TNF-alpha levels 6 and 24 h later only. Dexamethasone reduced TNF-alpha production after 90 min of OVA challenge in PT and at 3 and 6h in DT. OVA challenge increased prostaglandin D2) in DT and leukotriene B4 in both segments but did not modify prostaglandin E2 and leukotriene C4 release. CONCLUSION: OVA challenge induces TNF-alpha release from MMC, which is negatively regulated by CTMC. The profile of TNF-alpha and eicosanoids depends on the time after OVA challenge and of the tracheal segment considered.     

Effect of genetic modifications by selection for immunological tolerance on fungus infection in mice

Two strains of mice genetically selected for extreme phenotypes of immunological tolerance to ovalbumin, susceptible (TS) and resistant (TR), were experimentally infected with Sporothrix schenckii. The objective was to observe whether the genetic modifications produced by the selection might be associated with interstrain differences in adaptive immune and innate responses to infection. Therefore, we evaluated the LD(50), CFU, phagocytic index, fungicidal activity, pro-inflammatory cytokines, specific antibody titres, and the delayed-type hypersensitivity reactivity. TR mice were tenfold more susceptible to infection than TS mice, as shown by LD(50) (5 x 10(6) conidia i.v.). In TS mice, the resistance was a consequence of the tissue fungal load reduction, consistent specific T-cell-mediated immunity, and tumour necrosis factor (TNF)-alpha activity at onset of infection. In TR mice, these responses were not precociously detected. Therefore, the absence of CD4(+) T-cell response in the first week of infection might explain the non-clearance of pathogen in TR mice. However, TR mice did show an increase in TNF level and delayed-type hypersensitivity response after the first week post-infection; there was also expansion and increase in granulomatous foci and CFU in the spleen. The expansion of granulomatous foci and the increase in TNF-alpha and tissue fungal load to damaging levels induced severe tissue destruction, general failure of the organs, cachexy and death in TR mice. The results show that genetic selection for extreme phenotypes of immunological tolerance also modified the responses to S. schenckii infection.     

Utilization and transport of glucose in Olea Europaea cell suspensions

Cell suspensions of Olea europaea var. Galega Vulgar grown in batch culture with 0.5% (w/v) glucose were able to transport D-[(14)C]glucose according to Michaelis-Menten kinetics associated with a first-order kinetics. The monosaccharide carrier exhibited high affinity (K(m) approximately 50 micro M) and was able to transport D-glucose, D-fructose, D-galactose, D-xylose, 2-deoxy-D-glucose and 3-O-methyl-D-glucose, but not D-arabinose, D-mannitol or L-glucose. D-[(14)C]glucose uptake was associated with proton uptake, which also followed Michaelis-Menten kinetics. The transport of 3-O-methyl-D-glucose was accumulative (40-fold, at pH 5.0) and the protonophore carbonyl cyanide m-chlorophenylhydrazone strongly inhibited sugar accumulation. The results were consistent with the involvement of a monosaccharide: proton symporter with a stoichiometry of 1 : 1. When cells were grown with 3% (w/v) glucose, the uptake of D-[(14)C]glucose followed first-order kinetics and monosaccharide:proton symporter activity was not detected. The value obtained for the permeability coefficient of hexoses in O. europaea cells supported the hypothesis that the first-order kinetics observed in 0.5% and 3% sugar-grown cells was produced exclusively by passive diffusion of the sugar. The results indicate that in O. europaea cells sugar levels have a regulatory effect on sugar transport, because the activity for monosaccharide transport was repressed by high sugar concentrations.     

Purification and characterization of a new lectin from the red marine alga Hypnea musciformis

A lectin from the red marine alga Hypnea musciformis (HML) was purified by extraction with 20 mM PBS, precipitation with 70% saturated ammonium sulphate, ion-exchange DEAE-Cellulose chromatography and RP-HPLC. The 9.3 kDa polypeptide agglutinates erythrocytes from various sources and shows oligomerization tendencies under certain MALDI-TOF/MS conditions. Preliminary N-terminal sequencing and biological assays strongly suggest that the HML may belong to a new class of algae lectins.     

Specific targeting of a DNA-binding protein to the SPP1 procapsid by interaction with the portal oligomer

The icosahedral procapsid of tailed bacteriophages is composed of a large number of identical subunits and of minor proteins found in a few copies. Proteins present in a very low copy number are targeted to the viral procapsid by an unknown mechanism. Bacteriophage SPP1 procapsids and mature virions contain two copies of gp7 on average. Gp7 forms stable complexes with the SPP1 portal protein gp6. Deletion of the gp6 carboxyl-terminus and the mutation Y467-->C localized in the same region prevent gp6-gp7 complex formation. Gp7 binds double-stranded and single-stranded DNA. Gp6 competes for this interaction, and purified gp6-gp7 complexes do not bind DNA. Procapsid structures assembled in the absence of gp6 or carrying the mutant gp6 Y467-->C lack gp7. The gp6-gp7 interaction thus targets gp7 to the procapsid where the portal protein is localized asymmetrically at a single vertex of the icosahedral structure. The interaction between the two proteins is disrupted during viral assembly. Proteins homologous to gp6 and gp7 are coded by contiguous genes in a variety of phage genomes from Gram-positive bacteria, suggesting that the gp6-gp7 complex is widespread in this group of phages. Transient association with the portal protein, an essential component of tailed bacteriophages and herpes viruses, provides a novel strategy to target minor proteins to the virion structure that might be operative in a large number of viruses.     

DNase-Resistant DNA in the Extracellular and Cell Wall-Associated Fractions of Frankia Strains R43 and CcI3

DNases were shown to be present in the extracellular fraction of Frankia strains R43 and CcI3. In spite of this, DNA was found in both the extracellular and cell wall fractions of these strains, and it was shown that extracellular DNA was resistant to the DNases secreted into the culture medium of both Frankia strains. Furthermore, Southern blot analysis under high stringency conditions revealed the chromosomal origin of the cell wall-adsorbed DNA (CW-DNA). Mobility gel band shift assays suggested that the extracellular DNA and the CW-DNA are engaged in complexes with other molecules, most likely proteins, which are probably responsible for the enzymatic resistance observed against extracellular DNase activities. In addition, it was shown that lysis of a small proportion of the cells in the exponential growth phase may account for the DNA being released into the supernatant and adsorbed to the cell wall. Received: 21 July 2000 / Accepted: 21 August 2000     

Purification, characterization, and preliminary crystallographic study of copper-containing nitrous oxide reductase from Pseudomonas nautica 617

The aerobic purification of Pseudomonas nautica 617 nitrous oxide reductase yielded two forms of the enzyme exhibiting different chromatographic behaviors. The protein contains six copper atoms per monomer, arranged in two centers named Cu(A) and Cu(Z). Cu(Z) could be neither oxidized nor further reduced under our experimental conditions, and exhibits a 4-line EPR spectrum (g(x)=2.015, A(x)=1.5 mT, g(y)=2.071, A(y)=2 mT, g(z)=2.138, A(z)=7 mT) and a strong absorption at approximately 640 nm. Cu(A) can be stabilized in a reduced EPR-silent state and in an oxidized state with a typical 7-line EPR spectrum (g(x)=g(y)= 2.021, A(x) = A(y)=0 mT, g(z) = 2.178, A(z)= 4 mT) and absorption bands at 480, 540, and approximately 800 nm. The difference between the two purified forms of nitrous oxide reductase is interpreted as a difference in the oxidation state of the Cu(A) center. In form A, Cu(A) is predominantly oxidized (S = (1)/(2), Cu(1.5+)-Cu(1.5+)), while in form B it is mostly in the one-electron reduced state (S = 0, Cu(1+)-Cu(1+)). In both forms, Cu(Z) remains reduced (S = 1/2). Complete crystallographic data at 2.4 A indicate that Cu(A) is a binuclear site (similar to the site found in cytochrome c oxidase) and Cu(Z) is a novel tetracopper cluster [Brown, K., et al. (2000) Nat. Struct. Biol. (in press)]. The complete amino acid sequence of the enzyme was determined and comparisons made with sequences of other nitrous oxide reductases, emphasizing the coordination of the centers. A 10.3 kDa peptide copurified with both forms of nitrous oxide reductase shows strong homology with proteins of the heat-shock GroES chaperonin family.