Showing papers by "University of Freiburg published in 1997"

Regulation of Synaptic Efficacy by Coincidence of Postsynaptic APs and EPSPs

Abstract: Activity-driven modifications in synaptic connections between neurons in the neocortex may occur during development and learning In dual whole-cell voltage recordings from pyramidal neurons, the coincidence of postsynaptic action potentials (APs) and unitary excitatory postsynaptic potentials (EPSPs) was found to induce changes in EPSPs Their average amplitudes were differentially up- or down-regulated, depending on the precise timing of postsynaptic APs relative to EPSPs These observations suggest that APs propagating back into dendrites serve to modify single active synaptic connections, depending on the pattern of electrical activity in the pre- and postsynaptic neurons

Determination of the fold of the core protein of hepatitis B virus by electron cryomicroscopy

Abstract: Hepatitis B virus, a major human pathogen with an estimated 300 million carriers worldwide, can lead to cirrhosis and liver cancer in cases of chronic infection. The virus consists of an inner nucleocapsid or core, surrounded by a lipid envelope containing virally encoded surface proteins. The core protein, when expressed in bacteria, assembles into core shell particles, closely resembling the native core of the virus. Here we use electron cryomicroscopy to solve the structure of the core protein to 7.4 A resolution. Images of about 6,400 individual particles from 34 micrographs at different levels of defocus were combined, imposing icosahedral symmetry. The three-dimensional map reveals the complete fold of the polypeptide chain, which is quite unlike previously solved viral capsid proteins and is largely α-helical. The dimer clustering of subunits produces spikes on the surface of the shell, which consist of radial bundles of four long α-helices. Our model implies that the sequence corresponding to the immunodominant region of the core protein lies at the tip of the spike and also explains other properties of the core protein.

Degree of branching in hyperbranched polymers

Abstract: Topological considerations concerning the ratio of linear, imperfectly branched, dendritic and terminal units in hyperbranched polymers based on AB 2 , AB 3 and AB m (m ≥ 2) type monomers are summarized. The reaction of AB 2 monomers with a core molecule of the structure B f is also treated. For larger hyperbranched polymers based on AB 2 monomers the fraction of terminal units has to be equal to the number of dendritic units. A general expression for the degree ofbranching (DB) is derived for AB 2 systems, which is based on the number of dendritic and linear units. The expression is valid for low molecular weight as well as high molecular weight hyperbranched polymers in contrast to the commonly used expression based on dendritic, linear and terminal units. DB may not exceed 0.5 in hyperbranched polymers based on AB 2 systems (0.44 in AB 3 systems). Furthermore, a general expression for DB in hyperbranched polymers based on AB m monomers is derived. Consequences for signal ratios in NMR-spectra of hyperbranched polymers are discussed. The expressions presented allow verification of NMR-integration ratios obtained experimentally on the basis of model compounds.

Transcription factor NF-κB is activated in primary neurons by amyloid β peptides and in neurons surrounding early plaques from patients with Alzheimer disease

Abstract: Amyloid β peptide (Aβ)-containing plaques are a hallmark of Alzheimer disease. Here, we show that the neurotoxic Aβ, a major plaque component, is a potent activator of the transcription factor NF-κB in primary neurons. This activation required reactive oxygen intermediates as messengers because an antioxidant prevented Aβ-induced NF-κB activation. Maximal activation of NF-κB was found with 0.1 μM Aβ-(1–40) and 0.1 μM Aβ-(25–35) fragments, making a role for NF-κB in neuroprotection feasible. Using an activity-specific mAb for the p65 NF-κB subunit, activation of NF-κB also was observed in neurons and astroglia of brain sections from Alzheimer disease patients. Activated NF-κB was restricted to cells in the close vicinity of early plaques. Our data suggest that the aberrant gene expression in diseased nervous tissue is at least in part due to Aβ-induced activation of NF-κB, a potent immediate–early transcriptional regulator of numerous proinflammatory genes.

Indoor allergen exposure is a risk factor for sensitization during the first three years of life.

Abstract: Background: The purpose of the study was to investigate the influence of environmental allergen exposure on allergic sensitization in infancy and early childhood. Methods: A cohort of 1314 newborns was recruited and followed up prospectively at the ages 12, 24, and 36 months. The levels of major mite (Der p 1 and Der f 1) and cat (Fel d 1) allergens were determined from domestic carpet dust samples by sandwich ELISA. Specific serum IgE antibodies to mite and cat allergens were determined by CAP fluoroimmunoassay (Pharmacia). Logistic regression was used to assess the effects of allergen exposure, age, family history, and cord blood IgE simultaneously on the risk of sensitization. Results: Children, who had been found to be sensitized at least once during the first 3 years of life, were found to be exposed to significantly higher house dust mite (median, 868 ng/gm vs 210 ng/gm; p =0.001) and cat (median, 150 ng/gm vs 64 ng/gm; p =0.011) allergen concentrations in domestic carpet dust compared with the group without sensitization. In homes with low (≤25th percentile) dust concentrations, the risk of sensitization to mite (1.6%) and cat (2.0%) is low, compared with 6.5% for mite and 6.3% for cat if the domestic exposure is above the 75th percentile. The dose-response relationships between allergen levels and sensitization indicate that the increase in sensitization risk at low allergen levels is more pronounced in cat allergy ( p =0.002) than in mite allergy ( p =0.026). In the group with a positive family history, lower mite and cat allergen concentrations are needed to achieve specific sensitization compared with the group with a negative family history. Conclusion: Our data indicate that avoidance measures in the domestic environment aimed at the primary prevention of allergen-driven sensitization should be introduced at the earliest possible stage, if possible during infancy. (J Allergy Clin Immunol 1997;99:763–9.)

Gln 63 of Rho is deamidated by Escherichia coli cytotoxic necrotizing factor-1

Abstract: The actin cytoskeleton is regulated by GTP-hydrolysing proteins, the Rho GTPases, which act as molecular switches in diverse signal-transduction processes Various bacterial toxins can inactivate Rho GTPases by ADP-ribosylation or glucosylation Previous research has identified Rho proteins as putative targets for Escherichia coli cytotoxic necrotizing factors 1 and 2 (CNF1 and 2) These toxins induce actin assembly and multinucleation in culture cells Here we show that treatment of RhoA with CNF1 inhibits the intrinsic GTPase activity of RhoA and completely blocks GTPase activity stimulated by the Rho-GTPase-activating protein (rhoGAP) Analysis by mass spectrometry and amino-acid sequencing of proteolytic peptides derived from CNF1-treated RhoA indicate that CNF1 induces deamidation of a glutamine residue at position 63 (Gln 63) to give constitutively active Rho protein

Functional Organic Analogues of Zeolites Based on Metal–Organic Coordination Frameworks

Abstract: inner cavities and channels that are mainly surrounded by or- ganic components is attractive, since the shape, size, and func- tion of the cavity then become designable.[21 There is much interest in tailoring the geometry and the hydrophilic and hy- drophobic character of the pores.[31 However, the key feature is not only the incorporation of guest molecules but also their reversible exchange. Here the present state of research concern- ing this crucial aspect is summarized. Research on intercalation has concentrated largely on nanoporous inorganic materials such as aluminosilicates (zeo- lites), aluminophosphates, pillared clays, and graphite-all of which have been known for a long time.[41 Porous solids such as zeolites, which can now be “engineered” to some extent, are already important materials and find widespread application in adsorption (molecular sieves), shape- and size-selective hetero- geneous catalysis, and ion exchange. An important aspect of zeolites

A role for Cajal–Retzius cells and reelin in the development of hippocampal connections

Abstract: DURING development of the nervous system, specific recognition molecules provide the cues necessary for the formation of neural connections. In some regions, guiding cues for axonal pathfinding and target selection are provided by specific cells that exist only transiently during development, such as the floorplate or the cortical subplate1–4. In the hippocampus, distinct groups of fibres innervate different layers5. We have tested the hypothesis that transient neurons in the hippocampus6,7 provide positional information for the targeting of these fibres. Here we report that ablation of Cajal–Retzius cells in organotypic slice cultures of hippocampus prevented the ingrowth of entorhinal but not of commissural afferents. Experiments inhibiting Reelin (an extracellular matrix protein expressed by Cajal–Retzius cells) and analysis of reeler mutant mice showed dramatic abnormalities in the development of entorhinal afferents. Thus Cajal–Retzius cells and reelin are essential for the formation of layer-specific hippocampal connections.

Initiation and processing of signals from the B cell antigen receptor.

Abstract: Current models of signal transduction from the antigen receptors on B and T cells still resemble equations with several unknown elements. Data from recent knockout experiments in cell lines and mice contradict the assumption that Src-family kinase and tyrosine kinases of the Syk/Zap-70 family are the transducer elements that set signaling from these receptors in motion. Using a functional definition of signaling elements, we discuss the current knowledge of signaling events from the BCR and suggest the existence of an as-yet-unknown BCR transducer complex.

Cross-cascade activation of ERKs and ternary complex factors by Rho family proteins

Abstract: Mitogens promote cell growth through integrated signal transduction networks that alter cellular metabolism, gene expression and cytoskeletal organization. Many such signals are propagated through activation of MAP kinase cascades partly regulated by upstream small GTP-binding proteins. Interactions among cascades are suspected but not defined. Here we show that Rho family small G proteins such as Rac1 and Cdc42hs, which activate the JNK/SAPK pathway, cooperate with Raf-1 to activate the ERK pathway. This causes activation of ternary complex factors (TCFs), which regulate c-fos gene expression through the serum response element. Examination of ERK pathway kinases shows that neither MEK1 nor Ras will synergize with Rho-type proteins, and that only MEK1 is fully activated, indicating that MEKs are a focal point for cross-cascade regulation. Rho family proteins utilize PAKs for this effect, as expression of an active PAK1 mutant can substitute for Rho family small G proteins, and expression of an interfering PAK1 mutant blocks Rho-type protein stimulation of ERKs. PAK1 phosphorylates MEK1 on Ser298, a site important for binding of Raf-1 to MEK1 in vivo. Expression of interfering PAK1 also reduces stimulation of TCF function by serum growth factors, while expression of active PAK1 enhances EGF-stimulated MEK1 activity. This demonstrates interaction among MAP kinase pathway elements not previously recognized and suggests an explanation for the cooperative effect of Raf-1 and Rho family proteins on cellular transformation.

Interaction of Hsp70 chaperones with substrates

Abstract: Determination of the structure of the substrate binding domain of the Escherichia coli Hsp70 chaperone, DnaK, and the biochemical characterisation of the motif it recognizes within substrates provide insights into the principles governing Hsp70 interaction with polypeptide chains. DnaK recognizes extended peptide strands composed of up to five consecutive hydrophobic residues within and positively charged residues outside the substrate binding cavity.

Effective Low-Energy Theory for Correlated Carbon Nanotubes

Abstract: The low-energy theory for single-wall carbon nanotubes including Coulomb interactions is derived and analyzed. It describes two fermion chains without interchain hopping but coupled in a specific way by the interaction. The strong-coupling properties are studied by bosonization, and consequences for experiments on single armchair nanotubes are discussed.

Transgenic rice (Oryza sativa) endosperm expressing daffodil (Narcissus pseudonarcissus) phytoene synthase accumulates phytoene, a key intermediate of provitamin A biosynthesis

Abstract: Rice (Oryza sativa L.), the major food staple for more than two billion people, contains neither beta-carotene (provitamin A) nor C40 carotenoid precursors thereof in its endosperm. To improve the nutritional value of rice, genetic engineering was chosen as a means to introduce the ability to make beta-carotene into rice endosperm tissue. Investigation of the biochemical properties of immature rice endosperm using [14C]-labelled substrates revealed the presence of geranyl geranyl diphosphate, the C20 general isoprenoid precursor necessary for C40 carotenoid biosynthesis. Phytoene synthase, which condenses two molecules of geranyl geranyl diphosphate, is the first of four specific enzymes necessary for beta-carotene biosynthesis in plants. Therefore, the Japonica rice model variety Taipei 309 was transformed by microprojectile bombardment with a cDNA coding for phytoene synthase from daffodil (Narcissus pseudonarcissus) under the control of either a constitutive or an endosperm-specific promoter. In transgenic rice plants, the daffodil enzyme is active, as measured by the in vivo accumulation of phytoene in rice endosperm. Thus, it is demonstrated for the first time that it is in principle possible to engineer a critical step in provitamin A biosynthesis in a non-photosynthetic, carotenoid-lacking plant tissue. These results have important implications for long-term prospects of overcoming worldwide vitamin A deficiency.

The one-eyed pinhead gene functions in mesoderm and endoderm formation in zebrafish and interacts with no tail

Abstract: The zebrafish locus one-eyed pinhead (oep) is essential for the formation of anterior axial mesoderm, endoderm and ventral neuroectoderm. At the beginning of gastrulation anterior axial mesoderm cells form the prechordal plate and express goosecoid (gsc) in wild-type embryos. In oep mutants the prechordal plate does not form and gsc expression is not maintained. Exposure to lithium, a dorsalizing agent, leads to the ectopic induction and maintenance of gsc expression in wild-type embryos. Lithium treatment of oep mutants still leads to ectopic gsc induction but not maintenance, suggesting that oep acts downstream of inducers of dorsal mesoderm. In genetic mosaics, wild-type cells are capable of forming anterior axial mesoderm in oep embryos, suggesting that oep is required in prospective anterior axial mesoderm cells before gastrulation. The oep gene is also essential for endoderm formation and the early development of ventral neuroectoderm, including the floor plate. The loss of endoderm is already manifest during gastrulation by the absence of axial-expressing cells in the hypoblast of oep mutants. These findings suggest that oep is also required in lateral and ventral regions of the gastrula margin. The sonic hedgehog (shh).gene is expressed in the notochord of oep animals. Therefore, the impaired floor plate development in oep mutants is not caused by the absence of the floor plate inducer shh. This suggests that oep is required downstream or in parallel to shh signaling. The ventral region of the forebrain is also absent in oep mutants, leading to severe cyclopia. In contrast, anterior-posterior brain patterning appears largely unaffected, suggesting that underlying prechordal plate is not required for anterior-posterior pattern formation but might be involved in dorsoventral brain patterning. To test if oep has a wider, partially redundant role, we constructed double mutants with two other zebrafish loci essential for patterning during gastrulation. Double mutants with floating head, the zebrafish Xnot homologue, display enhanced floor plate and adaxial muscle phenotypes. Double mutants with no tail (ntl), the zebrafish homologue of the mouse Brachyury locus, display severe defects in midline and mesoderm formation including absence of most of the somitic mesoderm. These results reveal a redundant function of oep and ntl in mesoderm formation. Our data suggest that both oep and ntl act in the blastoderm margin to specify mesendodermal cell fates.

Interleukin-6-(IL-6) plasma levels in depression and schizophrenia: comparison between the acute state and after remission.

Abstract: The concentration of cytokines such as Interleukin-6 (IL-6) has been reported to be elevated in depressed and schizophrenic patients and, in healthy persons, upon stress. Interleukin-6 plasma levels were determined in depressed (n = 12) and schizophrenic (n = 32) patients during the acute state of illness and after remission at approximately 8 weeks after admission and were compared with healthy controls (n = 12). Patients were diagnosed according to DSM-III-R by the Structured Clinical Interview (SLID). Severity of illness was assessed for depression by the Montgomery Asberg Depression Rating Scale (MADRS) and for schizophrenia by the Brief Psychiatric Rating Scale (BPRS). Interleukin-6 plasma concentrations were elevated during the acute state either of depression or of schizophrenia if compared to controls. After remission, IL-6 concentrations in depressed and in schizophrenic patients had decreased and did not differ significantly from controls. We hypothesize that the elevated IL-6 levels during the acute state of depression or schizophrenia may reflect an unspecific stress response.

Anaerobic Metabolism of Aromatic Compounds

Abstract: Aromatic compounds comprise a wide variety of natural and synthetic compounds that can serve as substrates for bacterial growth. So far, four types of aromatic metabolism are known. (1) The aerobic aromatic metabolism is characterized by the extensive use of molecular oxygen as cosubstrate for oxygenases that introduce hydroxyl groups and cleave the aromatic ring. (2) In the presence of oxygen, facultative aerobes use another so-called hybrid type of aerobic metabolism of benzoate, phenylacetate, and anthranilate (2-aminobenzoate). These pathways use coenzyme A thioesters of the substrates and do not require oxygen for ring cleavage; rather they use an oxygenase/reductase to dearomatize the ring. (3) In the absence of oxygen, facultative aerobes and phototrophsuseareductivearomaticmetabolism.Reductionofthearomaticringofbenzoyl-coenzyme A is catalyzed by benzoyl-coenzyme A reductase. This Birch-like reduction is driven by the hydrolysis of 2 ATP molecules. (4) A completely different, still little characterized benzoyl-coenzyme A reductase operates in strict anaerobes, which cannot afford the costly ATP-dependent ring reduction.

Experimental Determination of the Melting Point and Heat Capacity for a Free Cluster of 139 Sodium Atoms

Abstract: The heat capacity of a free cluster has been determined from the temperature dependence of its photofragmentation mass spectrum. The data for the spherical sodium cluster ${\mathrm{Na}}_{N}^{+}$, with $N\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}139$, show a maximum at 267 K, which is interpreted as the solid-to-liquid phase transition in this finite system. The melting point lies 104 K, or 28% lower than that of bulk sodium. The latent heat of fusion is reduced by 46%.

On the Complexity of Qualitative Spatial Reasoning: A Maximal Tractable Fragment of the Region Connection Calculus.

Abstract: The computational properties of qualitative spatial reasoning have been investigated to some degree. However, the question for the boundary between polynomial and NP-hard reasoning problems has not been addressed yet. In this paper we explore this boundary in the ``Region Connection Calculus'''' RCC-8. We extend Bennett''s encoding of RCC-8 in modal logic. Based on this encoding, we prove that reasoning is NP-complete in general and identify a maximal tractable subset of the relations in RCC-8 that contains all base relations. Further, we show that for this subset path-consistency is sufficient for deciding consistency.

Factor Four: Doubling Wealth, Halving Resource Use - A Report to the Club of Rome

Abstract: This report answers the 1971 report published by the Club of Rome that argued the world was going to run out of essential resources. It offers a solution, arguing for more efficient use of resources, in ways which can already be done, and at a negative cost. Examples show how much can be acheived by combining technical resources. The authors also suggest how markets can be organised to eliminate perverse incentives and reward efficiency, thus wealth can grow while consumption does not.