Refine
Year of publication
Document Type
- Article (31128)
- Part of Periodical (11550)
- Book (8266)
- Doctoral Thesis (5713)
- Part of a Book (3967)
- Working Paper (3385)
- Review (2939)
- Contribution to a Periodical (2368)
- Preprint (2084)
- Report (1560)
Language
- German (42718)
- English (29217)
- French (1060)
- Portuguese (840)
- Spanish (309)
- Croatian (302)
- Multiple languages (258)
- Italian (198)
- mis (174)
- Turkish (168)
Has Fulltext
- yes (75568) (remove)
Keywords
- Deutsch (1076)
- Literatur (868)
- taxonomy (760)
- Deutschland (553)
- Rezension (511)
- new species (449)
- Rezeption (354)
- Frankfurt <Main> / Universität (341)
- Übersetzung (326)
- Geschichte (300)
Institute
- Medizin (7691)
- Präsidium (5170)
- Physik (4464)
- Extern (2738)
- Wirtschaftswissenschaften (2686)
- Gesellschaftswissenschaften (2369)
- Biowissenschaften (2184)
- Biochemie und Chemie (1975)
- Frankfurt Institute for Advanced Studies (FIAS) (1686)
- Center for Financial Studies (CFS) (1628)
This thesis reports on the results obtained by expression photoactivatable adenylyl cyclase from Beggiatoa spp. (bPAC) in cholinergic neurons from Caenorhabditis elegans (C. elegans) and the characterization of the role of a single neuron, RIS, during locomotion in the adult animal.
Pharmacological activation of adenylyl cyclases through Forskolin is known to induce increased neuronal output in diverse model organisms through a protein kinase A (PKA) dependent mechanism. Nevertheless, pharmacological assays are not spatially restricted, do not allow for precise and acute activation nor to cessation of the signal. Thus, an optogenetic approach for was selected trough the expression of photoactivatable adenylyl cyclase from Beggiatoa spp. (bPAC) in cholinergic neurons of Caenorhabditis elegans (C. elegans). This model organism was chosen due to its transparency, ease of maintenance, fast generation cycles as well as for being an eutelic animal. Further, its genome has been fully sequenced and the connectome of the neuronal network is known, thus allowing for precise analysis of neuronal function. Furthermore, the molecular mechanisms governing neuronal functions are well conserved up to primates. Mainly two optogenetical tools were applied, bPAC and the light gated cation channel channelrhodopsin 2 (ChR2).
Behavioral assays of bPAC photostimulation in cholinergic neurons recapitulated previous work performed with the photoactivatable adenylyl cyclase from Euglena gracilis (EuPACa), in which swimming frequency and speed on solid substrate were increased. Electrophysiological recordings of body wall muscle (BWM) cells by Dr. Jana F. Liewald showed that bPAC photoactivation led to an increase in miniature postsynaptic current (mPSC) rate and, in contrast to ChR2 invoked depolarization, also amplitude. Analysis of mutants deficient in neuropeptidergic signaling (UNC- 31) via electrophysiology performed by Dr. Jana F. Liewald showed that the increase in mPSC amplitude due to bPAC photoactivation requires neuropeptide release. This was confirmed by co-expression of bPAC with the neuropeptide marker NLP-21::Venus and subsequent fluorescence analysis of release, exploiting the fact that released neuropeptides are ultimately degraded by scavenger cells (coelomocytes). These were enriched with NLP-21::Venus after bPAC photostimulation, but no fluorescence could be observed in the UNC-31 mutants.
Additional analysis of the electrophysiological data performed by myself showed no modulation of mPSC kinetics dues to neuropeptidergic release induced by bPAC. Hence, neuropeptide release and action sites were in the cholinergic neurons, the latter including cholinergic motoneurons.
Dr. Szi-chieh Yu provided electron microscopy images of high pressure frozen, bPAC or ChR2 expressing animals. These were tagged by myself for automatic analysis of ultrastructural properties of the cholinergic presynapse, also during photoactivation of both optogenetic tools. Photoactivation of both induced a reduction of synaptic vesicles, with ChR2 showing a more severe effect. In contrast to ChR2, though, bPAC also reduced the amount of dense core vesicles (DCV), the neuropeptide transporters. Additionally, long bPAC photoactivation as well as ChR2 photoactivation led to the appearance of large vesicles (LV), presumably in response to the increased SV fusion rate. bPAC photostimulation also induced an increase in SV size, not observed after ChR2 photostimulation. In UNC-31 mutants, bPAC photostimulation could not lead to the SV size increase, a further argument for the presynaptic effect of the released neuropeptide. Additional analysis of electrophysiology paired with pharmacology, performed by Dr. Jana F. Liewald, showed that mPSC amplitude increase requires the function of the vesicular acetylcholine transporter.
A further effect observed in the ultrastructure of bPAC photostimulated cholinergic presynapses was a shift in the distribution of SV regarding the dense projection. An analysis of cAMP pathway mutants showed that synapsin is required for bPAC induced behavior effects. Synapsin is known to mediate SV tethering to the cytoskeleton. Here, I show evidence for a new role of synapsin in controlling the availability of DCVs for fusion and thus, in neuropeptidergic signaling.
In the second part of my thesis I characterized the function of the GABAergic interneuron RIS in the neuronal network of C. elegans. RIS was shown to induce lethargus, a sleep-like state, during all larval molts, but its function in the adult animal was not yet described. Specific RIS expression of ChR2 achieved by a recombinase based system allowed to acutely depolarize the neuron during locomotion, which led to an acute behavioral stop. Diverse signal transduction pathway mutants were analyzed showing that the phenotype was induced by neuropeptidergic signaling. Through mutagenesis followed by whole genome sequencing data analysis as well as analysis of RIS specific RNA sequencing data further narrowed the signal transduction pathway to mediate the locomotion stop behavior. Since the neuropeptide and, to some extent, the neuron are conserved across nematodes, an argument is outlined in favor of the conservation of this sleep-like state.
In addition, since ChR2 could induce neuropeptidergic signaling from RIS, secretion of vesicles is regulated by variable pathways depending on the neuronal identity. Nevertheless, expression of bPAC in RIS allowed to optogenetically increase the probability of short stops, as observed by expression of a calcium sensor (GCaMP) in RIS and analysis of its intrinsic activity in the adult animal.
In the title compound, C17H18N2O, the central carbon atom with the OH substituent and one of the (E)-benzylideneamino substituents are disordered over two sets of sites with occupancies of 0.851 (4) and 0.149 (4). The relative positions of the two disorder components is equivalent to a rotation of approximately 60° about the C—N single bond. In the crystal, the molecules are held together by O—H...N hydrogen bonds, forming simple C(5) chains along the b-axis direction. In addition, pairs of the chains are further aggregated by weak C—H...π interactions.
Mathematical models of virus dynamics have not previously acknowledged spatial resolution at the intracellular level despite substantial arguments that favor the consideration of intracellular spatial dependence. The replication of the hepatitis C virus (HCV) viral RNA (vRNA) occurs within special replication complexes formed from membranes derived from endoplasmatic reticulum (ER). These regions, termed membranous webs, are generated primarily through specific interactions between nonstructural virus-encoded proteins (NSPs) and host cellular factors. The NSPs are responsible for the replication of the vRNA and their movement is restricted to the ER surface. Therefore, in this study we developed fully spatio-temporal resolved models of the vRNA replication cycle of HCV. Our simulations are performed upon realistic reconstructed cell structures—namely the ER surface and the membranous webs—based on data derived from immunostained cells replicating HCV vRNA. We visualized 3D simulations that reproduced dynamics resulting from interplay of the different components of our models (vRNA, NSPs, and a host factor), and we present an evaluation of the concentrations for the components within different regions of the cell. Thus far, our model is restricted to an internal portion of a hepatocyte and is qualitative more than quantitative. For a quantitative adaption to complete cells, various additional parameters will have to be determined through further in vitro cell biology experiments, which can be stimulated by the results deccribed in the present study.
Der 1994 in Niedersachsen gegründete Nationalpark Harz wird mit seinen Aufgaben, Zielen und Naturschutzmaßnahmen vorgestellt. Die Flora des Nationalparks weist zahlreiche Besonderheiten auf, darunter zwei Gefäßpflanzenarten und drei Flechtenarten, die innerhalb von Niedersachsen ausschließlich hier Vorkommen. Exkursionsziele im Rahmen der Tagung sind hochmontane Borstgrasrasen (Violion caninae) und Bergheiden (Vaccinio-Callunetum) mit Flachbärlapp-Vorkommen am Großen Sonnenberg, das Sonnenberger Moor als typisches Harzmoor, über große Flächen als Rasenbinsen-Hochmoor ausgeprägt, Schluchtwälder im Eckertal (Fraxino-Aceretum) mit Vorkommen von Lunaria rediviva, artenreiche Kleinseggensümpfe (u.a. mit zahlreichen Carex-Arten und Pinguicula vulgaris) entlang von Forstwegen sowie das Luchsgehege an den Rabenklippen.
Der vorliegende Beitrag beschäftigt sich mit der Flora und Vegetation des Hohen Meißners und seines östlichen Vorlandes (Werra-Meißner-Kreis, Nordhessen). Auf dem Meißner selbst sind, neben naturnahen Bereichen mit Basaltblockhalden und Schutthangwäldern (Fraxino-Aceretum) vor allem gut ausgebildete Beispiele montaner Grünlandkomplexe erhalten geblieben. Sie gehören pflanzensoziologisch zu den Bergwiesen (Polygono-Trisetion), Feuchtwiesen (Calthion), Borstgrasrasen (Violion caninae) und Braunseggenrieden (Caricion fuscae). Im östlichen Meißnervorland sind größere Karstgebiete zu finden, die weithin von Kalkmagerrasen (Mesobromion) eingenommen werden. Daneben treten in den Magerrasenkomplexen Glatthaferwiesen (Arrhenatherion) und kleinflächig Pionierrasen (Alysso-Sedion) auf. Die Ackerflächen sind noch heute reich an gefährdeten Ackerwildkrautgesellschaften, insbesondere die an die Magerrasen angrenzenden, klein parzellierten Kalkäcker mit vielen Arten des Caucalidion. Sowohl die Ackerwildkrautvegetation als auch die Magergrünlandkomplexe sind Gegenstand von naturschutzfachlichen Pflege- und Entwicklungsmaßnahmen, die ebenfalls erläutert werden.
Am Beispiel zweier im hessisch-thüringischen Grenzgebiet gelegener Muschelkalk-Felshänge des mittleren Werratales wird dargestellt, welche Vegetationsveränderungen vom Mittelalter bis in die Gegenwart an natürlichen Waldgrenzstandorten sowie in ihrer näheren Umgebung stattgefunden haben und welche Konsequenzen für den Naturschutz sich daraus ergeben. Markante Wendepunkte der Landnutzung sind die mit der deutlich zunehmenden Besiedelung seit dem 6. Jahrhundert vorgenommenen Rodungen, die Aufgabe des Weinbaues seit Anfang des 17. Jahrhunderts sowie der Rückgang der Schafhaltung nach 1850 und nach 1990. Die wichtigsten Vegetationstypen der Felshänge (Wald-, Saum- und Rasengesellschaften) werden vorgestellt. Qualitative und quantitative Veränderungen offener Trockenstandorte infolge sekundärer Sukzessionsprozesse kennzeichnen die gegenwärtige Situation. Rasengesellschaften sind aufgrund geringer oder fehlender Nutzungsintensität vielfach von Flächenverlusten durch Gehölzausbreitung betroffen. Dies gilt in besonderem Maße für ehemals beweidete Bestände. Mit der (Rück-)Einwanderung der Rotbuche in die Baumschicht von Laub- und Nadelwäldern trockener Kalkstandorte sind qualitative Veränderungen der Strauch- und Krautschicht verbunden. Sie äußern sich insbesondere in einem Rückgang lichtliebender, zum Teil thermophiler Arten. Die aktuelle Gefährdung der betrachteten Vegetationstypen hängt stark von deren Natürlichkeitsgrad ab. Naturschutz-Pflegemaßnahmen (v. a. Beweidung) sollten in erster Linie auf halbnatürlichen anthropo-zoogenen Kalk-Halbtrockenrasen durchgeführt werden, da hier die tiefgreifendsten Veränderungen durch Sukzession zu erwarten sind. Naturnahe Blaugras-Rasen und Saumgesellschaften können weitgehend sich selbst überlassen bleiben, da eine Sukzession hier nur langsam verläuft und zu erwarten ist, dass ihre Arten im Bereich natürlicher Waldgrenzen immer geeignete Bedingungen finden werden, wenn auch auf kleinerer Fläche.