Die optische Richtungsorientierung der Roten Waldameise (Formica Ruea L.)

Zusammenfassung Alle folgenden Angaben beziehen sich auf Formica rufa L., die Rote Waldameise, und sind nur unter Vorbehalt auf andere Insektenarten übertragbar.Die Ameisen benützen zur optischen Richtungsorientierung künstliche Lichtquellen, die Sonne oder den Mond.Eine distinkte Lichtquelle kann als Orientierungsmarke durch einen diffusen Lichtschein ersetzt werden.Mit Hilfe einer Polarisationsfolie läßt sich nachweisen, daß sich die Ameisen sowohl nach der Schwingungsrichtung des blauen Himmelslichtes als auch nach der Schwingungsrichtung des Folienlichtes orientieren können.Die Orientierung nach Landmarken, wie Häusern und Bäumen, spielt eine große Rolle und ist bei bewölktem Himmel wahrscheinlich die einzige optische Orientierungsmöglichkeit.Werden Himmels- und Landmarken in Konkurrenz gesetzt, dann läuft die Ameise in einer Kompromißrichtung.Ameisen reagieren in Neststimmung vorwiegend negativ und in Exkursionsstimmung vorwiegend positiv phototaktisch.Es wird eine Methode angegeben, mit der durch Vergleich von Dreherregungen die Stärke der phototaktischen Drehreaktionen gemessen werden kann.Bei gleich großer Ablenkung vom orientierten Lauf sind die geotaktischen und die phototaktischen Dreherregungen (Drehtendenzen) quantitativ gleich.Die phototaktischen Dreherregungen (Drehtendenzen) sind helligkeitsunabhängig, ändern sich jedoch mit dem Einfallswinkel des Lichtes.Aus den experimentellen Befunden wird geschlossen, daß sich am zentralnervösen Funktionsgefüge der negativen (positiven) Phototaxis mindestens drei nervöse Instanzen (Mechanismen) beteiligen: Das Integrationszentrum, das Lagezentrum und der Koordinationsmechanismus der Beinbewegung.Wichtige Vorgänge beim Übergang von der positiven und negativen Phototaxis zur menotaktischen Hin- und Rückwegorientierung sind orientierungsfreie Suchschleifen und Lernprozesse, die zur Ermittlung der Luftlinienrichtung führen.Diese Lernprozesse finden sowohl auf dem Hin- als auch auf dem Rückweg statt.Die Ermittlung der Luftlinienrichtung geschieht über die Auswertung (Integration) der optischen Reizfolge, die kinästhetische Reizfolge ist dafür wahrscheinlich völlig bedeutungslos.Mit Hilfe der Kompensationstheorie werden eine Reihe von Reaktionen sich menotaktisch orientierender Ameisen kausal erklärt.Die Ameise kann sich eine Laufrichtung in bezug auf eine Lichtquelle mindestens 5 Tage lang merken.Die Ameise kann sich mit Hilfe von Landmarken an mindestens vier verschiedenen Plätzen im Gelände je eine bestimmte Laufrichtung merken.Erinnerungsbilder von Himmels- und Landmarken werden im Gedächtnis der Ameisen unabhängig voneinander aufbewahrt, die Erinnerungsbilder der Himmelsmarken dagegen sind im Gedächtnis der Ameisen aneinandergekoppelt.Die Ameisen haben die Fähigkeit, die Wanderung der Sonne bei der Richtungsorientierung mit einzuberechnen.     

Isolation and characterization of nitrite-reductase-deficient mutants of Chlorella sorokiniana (strain 211-8k)

 A method is presented to isolate mutants of Chlorella sorokiniana with defects in NO₃ ⁻ metabolism. Three nitrite-reductase (NIR; E.C.1.7.7.1)-deficient mutants were obtained from 500 pinpoint-colony-forming clones. The final screening was performed using NO₃ ⁻, NO₂ ⁻ or NH⁺ ₄ as N-source. The mutants isolated absorb NO₃ ⁻ with rates close to those measured for the wild type and they excrete NO₂ ⁻ into the medium. The ratio between NO₃ ⁻ uptake and NO₂ ⁻ excretion was 1:1. The sensitivity of NO₃ ⁻ uptake to NH⁺ ₄ was reduced in the mutant strains as it was in the N-starved wild type of Chlorella. Nitrate reductase (NR; EC 1.6.6.1) expression and NR activity were slightly reduced compared to the wild type due to feedback regulation in the mutant strains. No NIR protein was found in the three mutants. However, NIR activity was obtained (50% of the wild-type) for one mutant strain. The NIR-deficient mutants and the already available NR-deficient mutants will be promising tools for investigations of the nitrate assimilation pathway on the molecular level and for studies searching for signaling of C and N metabolism by inorganic N-compounds. Received: 8 October 1999 / Accepted: 25 January 2000     

The role of TGF-β in the pathogenesis of primary open-angle glaucoma

Transforming growth factor-β2 (TGF-β2) is found in increasing amounts in aqueous humor and reactive optic nerve astrocytes of patients with primary open-angle glaucoma (POAG), a major cause of blindness worldwide. The available data strongly indicate that TGF-β2 is a key player contributing to the structural changes in the extracellular matrix (ECM) of the trabecular meshwork and optic nerve head as characteristically seen in POAG. The changes involve an induction in the expression of various ECM molecules and are remarkably similar in trabecular meshwork cells and optic nerve head astrocytes. The ECM changes in the trabecular meshwork most probably play a role in the increase of aqueous humor outflow resistance causing higher intraocular pressure (IOP). In the optic nerve head, TGF-β2-induced changes might contribute to deformation of the optic nerve axons causing impairment of axonal transport and neurotrophic supply and leading to their continuous degeneration. The increase in IOP further adds mechanical stress and strain to optic nerve axons and accelerates degenerative changes. In addition, high IOP might induce the expression of activated TGF-β1 in trabecular meshwork cells and optic nerve head astrocytes; this again might significantly lead to the progress of axonal degeneration. The action of TGF-β2 in POAG is largely mediated through the connective tissue growth factor, whereas the activities of TGF-β1 and -β2 are modulated by the blocking effects of bone morphogenetic protein-4 (BMP-4) and BMP-7, by gremlin that inhibits BMP signaling and by several species of microRNAs.     

Roseobacter clade bacteria are abundant in coastal sediments and encode a novel combination of sulfur oxidation genes

Roseobacter clade bacteria (RCB) are abundant in marine bacterioplankton worldwide and central to pelagic sulfur cycling. Very little is known about their abundance and function in marine sediments. We investigated the abundance, diversity and sulfur oxidation potential of RCB in surface sediments of two tidal flats. Here, RCB accounted for up to 9.6% of all cells and exceeded abundances commonly known for pelagic RCB by 1000-fold as revealed by fluorescence in situ hybridization (FISH). Phylogenetic analysis of 16S rRNA and sulfate thiohydrolase (SoxB) genes indicated diverse, possibly sulfur-oxidizing RCB related to sequences known from bacterioplankton and marine biofilms. To investigate the sulfur oxidation potential of RCB in sediments in more detail, we analyzed a metagenomic fragment from a RCB. This fragment encoded the reverse dissimilatory sulfite reductase (rDSR) pathway, which was not yet found in RCB, a novel type of sulfite dehydrogenase (SoeABC) and the Sox multi-enzyme complex including the SoxCD subunits. This was unexpected as soxCD and dsr genes were presumed to be mutually exclusive in sulfur-oxidizing prokaryotes. This unique gene arrangement would allow a metabolic flexibility beyond known sulfur-oxidizing pathways. We confirmed the presence of dsrA by geneFISH in closely related RCB from an enrichment culture. Our results show that RCB are an integral part of the microbial community in marine sediments, where they possibly oxidize inorganic and organic sulfur compounds in oxic and suboxic sediment layers.     

Quantitation of vitellogenin messenger RNA in the liver of male xenopus toads during primary and secondary stimulation by estrogen

From livers of estrogen-stimulated female Xenopus toads, large quantities of estrogen-induced, poly(A)-containing RNA could be isolated, showing the same characteristics as vitellogenin mRNA obtained from hormone-treated males.Using cDNA hybridization, vitellogenin mRNA was monitored in the cytoplasmic poly(A)-containing RNA of the liver of male toads during 13 days of primary and the initial phase of secondary stimulation with estrogen.During primary stimulation, low amounts of vitellogenin mRNA, not exceeding 0.18% of the cytoplasmic poly(A)-containing RNA, were first detected after 12 hr of hormone treatment, and vitellogenin mRNA was found to increase on the average to 34% of the cytoplasmic poly(A)-containing RNA on the seventh day of hormone treatment. After 3 days of primary stimulation, accumulation of vitellogenin mRNA leveled off, showing no significant increase in the cytoplasm up to 13 days of hormone treatment. As judged from incorporation of ³²PO₄ into blood plasma proteins of males during primary stimulation, vitellogenin was first detected after 1 day, and its synthesis was found to increase dramatically until the thirteenth day of hormone treatment. This implies that there is a coincidence between appearance and extent of synthesis of vitellogenin and the abundance of vitellogenin mRNA in the cytoplasm, but there is evidence that during later phase of primary stimulation (day 3–13), the increase in synthesis of vitellogenin cannot be attributed anymore to a significant accumulation of vitellogenin mRNA.In male Xenopus, estrogen-induced synthesis of vitellogenin is no more detectable 41 days after hormone injection, and the concentration of vitellogenin mRNA was found to be <0.03% of the cytoplasmic poly(A)-containing RNA. Secondary stimulation by estrogen of these animals results in an at least 30 fold faster accumulation of vitellogenin mRNA in the cytoplasm within the initial 12 hr of hormone treatment. This may explain the faster appearance of vitellogenin in the blood plasma.     

Hepatic overexpression of hormone-sensitive lipase and adipose triglyceride lipase promotes fatty acid oxidation, stimulates direct release of free fatty acids, and ameliorates steatosis

Hepatic steatosis is often associated with insulin resistance and obesity and can lead to steatohepatitis and cirrhosis. In this study, we have demonstrated that hormone-sensitive lipase (HSL) and adipose triglyceride lipase (ATGL), two enzymes critical for lipolysis in adipose tissues, also contribute to lipolysis in the liver and can mobilize hepatic triglycerides in vivo and in vitro. Adenoviral overexpression of HSL and/or ATGL reduced liver triglycerides by 40-60% in both ob/ob mice and mice with high fat diet-induced obesity. However, these enzymes did not affect fasting plasma triglyceride and free fatty acid levels or triglyceride and apolipoprotein B secretion rates. Plasma 3-beta-hydroxybutyrate levels were increased 3-5 days after infection in both HSL- and ATGL-overexpressing male mice, suggesting an increase in beta-oxidation. Expression of genes involved in fatty acid transport and synthesis, lipid storage, and mitochondrial bioenergetics was unchanged. Mechanistic studies in oleate-supplemented McA-RH7777 cells with adenoviral overexpression of HSL or ATGL showed that reduced cellular triglycerides could be attributed to increases in beta-oxidation as well as direct release of free fatty acids into the medium. In summary, hepatic overexpression of HSL or ATGL can promote fatty acid oxidation, stimulate direct release of free fatty acid, and ameliorate hepatic steatosis. This study suggests a direct functional role for both HSL and ATGL in hepatic lipid homeostasis and identifies these enzymes as potential therapeutic targets for ameliorating hepatic steatosis associated with insulin resistance and obesity.     

Structural determinants of calmodulin binding to the intracellular C-terminal domain of the metabotropic glutamate receptor 7A

Calmodulin (CaM) binds in a Ca2+-dependent manner to the intracellular C-terminal domains of most group III metabotropic glutamate receptors (mGluRs). Here we combined mutational and biophysical approaches to define the structural basis of CaM binding to mGluR 7A. Ca2+/CaM was found to interact with mGluR 7A primarily via its C-lobe at a 1:1 CaM:C-tail stoichiometry. Pulldown experiments with mutant CaM and mGluR 7A C-tail constructs and high resolution NMR with peptides corresponding to the CaM binding region of mGluR 7A allowed us to define hydrophobic and ionic interactions required for Ca2+/CaM binding and identified a 1-8-14 CaM-binding motif. The Ca2+/CaM.mGluR 7A peptide complex displays a classical wraparound structure that closely resembles that formed by Ca2+/CaM upon binding to smooth muscle myosin light chain kinase. Our data provide insight into how Ca2+/CaM regulates group III mGluR signaling via competition with intracellular proteins for receptor-binding sites.     

The influence of spermine on the structural dynamics of yeast tRNA

A tRNA^Phe derivative carrying ethidium at position 37 in the anticodon loop has been used to study the effect of spermine on conformational transitions of the tRNA. As previously reported (Ehrenberg, M., Rigler, R. and Wintermeyer, W. (1979) Biochemistry 18, 4588–4599) in the tRNA derivative the ethidium is present in three states (T₁–T₃) characterized by different fluorescence decay rates. T-jump experiments show two transitions between the states, a fast one (relaxation time 10–100 ms) between T₁ and T₂, and a slow one (100–1000 ms) between T₂ and T₃. In the presence of spermine the fast transition shows a negative temperature coefficient indicating the existence of a preequilibrium with a negative reaction enthalpy. Spermine shifts the distribution of states towards T₃, as does Mg²⁺, but the final ratio obtained with spermine is higher than with Mg²⁺, which we tentatively interpret to mean that spermine stabilizes one particular conformation of the anticodon loop.     

A novel GlcNAcalpha1-HPO3-6Gal(1-1)ceramide antigen and alkylated inositol-phosphoglycerolipids expressed by the liver fluke Fasciola hepatica

The acidic (glyco)lipids of the parasitic liver fluke Fasciola hepatica exhibited two different phosphate-containing species, designated AL-I and AL-II, which were analyzed by MALDI-TOF MS, ESI MS, NMR, methylation analysis, and combined GC-MS in conjunction with HF treatment. AL-I was structurally determined as 1-O-hexadecyl-sn-glycerol-3-phosphoinositol, an ether bond variant of lysophosphatidylinositol. The structure of AL-II was shown to be GlcNAcalpha1-HPO3-6Gal(1-1)ceramide. Ceramide analysis revealed as major components 2-hydroxyoctadecanoic acid [18:0(2-OH)] together with C18- and C20-phytosphingosines. AL-II was apparently highly antigenic and strongly recognized by both animal- and human-F. hepatica infection sera. Furthermore, inhibition ELISAs revealed that the unusual antigenic determinant GlcNAcalpha1-HPO3- phosphate might have a potential in the serodiagnosis of F. hepatica infections.