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Institute
The avian magnetic compass was analyzed by testing migratory birds, using their orientation as an indicator. These tests revealed some remarkable properties of the avian magnetic compass: (1) It is an inclination compass’, (2) it is light-dependent, with (3) receptors located in the right eye. These characteristics are in agreement with the Radical Pair model proposed by Ritz et al. (2000). Using the same experimental set-up, we tested the model by behavioral spectroscopy’, exposing migratory birds to radiofrequency fields of different frequencies and intensities. Such fields affected the orientation only when applied at an angle to the field lines. Tests with different frequencies led to an estimate of the life time of the crucial radical pair between 2-10 μs. We also could identify an extremely sensitive resonance at the Larmor frequency, which implies specific properties of the radical pair. Cryptochromes, a blue-light absorbing photopigment, has been proposed to be the receptor-molecule; it has been found to be present in the retina of birds.
Savannas are the most important timber and non-timber forest products (NTFPs) providing ecosystems in West Africa. They have been shaped by traditional human land-use (i.e. agriculture, grazing, and harvesting) for thousands of years. In the last decades, land-use has drastically changed due to the rapid population growth and the growing production of cash-crop in West Africa and this process is still continuing. The percentage of land intensively used for agriculture has increased, while the length of fallow periods has decreased. Such changes have enormous ecological, economic, and social consequences. In the context of land-use changes, there is an urgent need to better understand and evaluate the impact of land-use on savannas. Such an understanding provides insights on appropriate management activities that ensure the maintenance of savannas and guarantee the availability of savanna products for subsistence and commercial use of rural West African people.
The major objective of the present thesis was to study the impact of land-use on savanna vegetation and diversity as well as on populations of two important NTFP-providing tree species in a semi-arid area in West Africa. The study area was located in the south-eastern part of Burkina Faso and comprised the protected W National Park and its adjacent communal area.
In the first study (chapter 2), I investigated in cooperation with a colleague from Burkina Faso (Blandine Nacoulma) the impact of land-use on the savanna vegetation. We analyzed which environmental factors determine the occurrence of the vegetation types and investigated the effect of land-use on vegetation structure and the occurrence of life forms and highly valued tree species. Furthermore, we tested whether land-use has an impact on plant diversity pattern and if this impact differed between the vegetation types and layers (woody and herb layer). Vegetation relevés were performed and the vegetation and plant diversity of the protected W National Park were compared with those of its surrounding communal area. Our results reveal five vegetation types occurring in both areas. Elevation and physical soil characteristics and thus soil water availability for plants played the most important role for the occurrence of the vegetation types. The influence of land-use on plant diversity differed between the five vegetation types and the two layers. The impact was highest on the vegetation types with the most favorable soil conditions for cultivation and lowest on rocky habitats with poor soils. While the diversity of the woody layer was increased under human land-use, the diversity of the herb layer was diminished. Overall, as land-use effects were not only negative, our findings suggest that land-use does not automatically lead to a loss of plant species and to a degradation of savanna habitats. We conclude that both protected and communal areas are of great importance for the conservation of savanna vegetation and diversity. Our study highlights furthermore the importance of different management strategies for each vegetation type.
In the following two studies (chapter 3 and 4), the impact of land-use - and in particular of harvesting - on populations of Adansonia digitata L., the baobab tree, and Anogeissus leiocarpa (DC.) Guill. & Perr. was examined. These two tree species were chosen as they provide several NTFPs for the local population and as they show different levels of human protection and opposed life histories. Thus, they may react differently to land-use. Stands of the protected W National Park were compared with those of its surrounding communal area (in fallows, croplands, and villages). I applied dendrometric methods to study the population structures and combined it with rates and patterns of NTFP-harvesting (debarking and chopping/pruning). Furthermore, the impact of land-use and harvesting on the fruit production of A. digitata and on the sprouting ability of A. leiocarpa were studied. The inverse J-shaped size class distribution curve indicates that the stands of A. digitata were in a healthy state in the park, while the low number of smaller size classes in fallows, croplands, and villages may give evidence of an ageing population. However, a high number of seedlings were recorded in villages. The stands of A. leiocarpa were also in healthy states in the park and likewise in fallows. In contrast, the absence of saplings gives evidence of a declining population in croplands. Both species were strongly harvested by local people and harvesting was tree size-specific. Pruning in interaction with tree-size had a significant impact on fruit production of A. digitata. While smaller trees were more vulnerable to pruning, bigger trees benefited from slight-pruning. A. leiocarpa had a great ability to respond to chopping by sprouting. The sprouting ability increased even with higher chopping intensity. Results suggest that despite the intense harvesting and the land-use impact, populations of both species are still well preserved. While A. digitata can withstand the harvesting and land-use pressure by its longevity, extremely low adult mortality rates, and particularly due to positive human influences, A. leiocarpa is able to withstand the use pressure by its fast growing, high recruitment, and high sprouting ability. I conclude that a none protected tree species (A. leiocarpa) might not necessarily be at higher risk to the harvesting and land-use impact than a protected tree species (A. digitata) as the adverse impact of harvesting and land-use can be compensated by its specific life history.
Important additional information to such ecological findings can be provided by local people. Learning from traditional knowledge and management systems of local people will help to produce culturally and ecologically reasonable conservation and management strategies. Thus, I investigated local uses and management strategies of A. digitata and A. leiocarpa in the last two studies (chapter 5 and 6). Quantitative ethnobotanical surveys among the Gulimanceba people were conducted in the communal area in order to document uses of the different plant parts, harvesting modes, perceptions about the population status, and conservation status of both species. Hereby, differences in knowledge between gender, generations, and people from different villages were tested. Interviews reveal that both species are harvested for multipurpose and emphasize the high importance of both species for local people. Especially the leaves and fruits of A. digitata add valuable minerals and vitamins to the otherwise micronutrient-“poor” staple crops of the Gulimanceba people. In comparison with other studies in West Africa, it has turned out that people in this area could benefit even more from A. leiocarpa, e.g. for dyeing of clothes, for treatment of malaria and skin problems. Local knowledge did not differ between genders and generations, while it slightly differed between people from different villages. The lack of age differences suggests that the traditional knowledge about these two species is passed on from one generation to another. Differences between people from different villages might be explained by influences from the neighboring countries Niger and Benin. Current local harvesting modes and management strategies of both species resulted in sustainable use. However, ongoing land-use intensifications require adapted harvesting and management techniques to guarantee the persistence of these economically important species. These results provide, in combination with the ecological findings (chapter 3 and 4), appropriate management recommendations for A. digitata and A. leiocarpa that are reliable under currently practiced management strategies.
The canonical Wnt/β-catenin and the Shh pathway as well as the Notch signaling cascade
are key regulators in stem cell biology and are independently associated with the development
of cancer. Despite the knowledge of a balanced signaling for cellular maintenance, the
fundamental biochemical mechanisms of crosstalk are still poorly understood. This study
demonstrates that the outcome of interaction between Wnt and Shh is cell type specific. A
combined inhibitory mechanism of the Shh and Notch2/Jagged2 pathways on dominant
active β-catenin signaling in the adult tongue epithelium keeps Wnt/β-catenin signaling
restricted to physiological tolerable levels. In the opposite crosstalk the activation of
Wnt/β-catenin signaling in medulloblastoma (MB) of the Shh subtype, in turn inhibits the Hh
pathway.
The inhibitory mechanism of Shh and Notch2/Jagged2 on Wnt/β-catenin signaling is
independent of the degradation complex of β-catenin and takes place inside the nucleus.
Furthermore, the negative feedback on Wnt/β-catenin signaling by the Shh pathway relies
on transcriptional activity of Gli1/2A. Inhibition of Gli1/2A with the specific inhibitor GANT61
abrogated the negative impact of Shh on β-catenin signaling in vitro. Although the negative
feedback loop of Shh is still functional in human SCC25 cells, the inhibitory effect of
Notch2/Jagged2 is lost and contributes to the cancerogenic phenotype of these cells. In the
inverse situation, the activation of β−catenin signaling has a negative feedback on
constantly active Shh signaling and significantly inhibits the Hh pathway. This was shown in
Ptch+/- and Math1-Cre:SmoM2Fl/+ MB tumor spheres in vitro, in which inhibition of sphere
formation and growth was observed and Hh target gene transcription was down-regulated.
This demonstrates for the first time that the activation of canonical Wnt/β-catenin signaling
in primary MB cells with a Hh pathway over-activation has a negative effect on the growth of
these cells in vitro.
In summary the results show that crosstalk of Wnt/β-catenin and Shh signaling has context
specific outcome on pathway activity. Elucidation of the molecular interactions will improve
our understanding of Wnt and Hh associated tumors and contribute to the development of
new therapeutic strategies.
Das maligne Gliom, auch Glioblastom multiforme (GBM) genannt, ist der häufigste und gleichzeitig auch bösartigste hirneigene Tumor und macht rund 2% aller Krebsneuerkrankungen aus. Die Weltgesundheitsorganisation (world health organisation, WHO) stuft das GBM als Grad IV Tumor ein, was es als hochmalignen Tumor auszeichnet der infiltrativ in das umliegende Hirnparenchym einwandert und mit den gegenwärtigen Behandlungsmethoden, bestehend aus Resektion des Tumors, Chemotherapie und Strahlentherapie nicht kuriert werden kann. Das aggressive Wachstum und die ausgeprägte Resistenz dieses astrozytären Tumors gegenüber den verfügbaren Therapien der Bestrahlung und Chemotherapie sind Hauptgründe für die schlechte Prognose für Patienten mit Glioblastomen, deren medianes Überleben immer noch unter der Zwei-Jahres-Grenze liegt. Daher ist es von Nöten neue therapeutische Strategien auf Grundlage der Chemotherapie zu entwickeln, die selektiv wichtige, deregulierte Signalwege der Krebszelle angreifen. Einer dieser Signalwege in Gliomen ist der Stat3-Signalweg (signal transducer and activator of transcription). Stat3, ein latenter zytoplasmatischer Transkriptionsfaktor liegt in Gliomen oftmals konstitutiv aktiv vor. Diese Deregulation des Signalweges führt zur dauerhaften Transkription proonkogener Zielgene die in transformierten Zellen zu Proliferation, Apoptoseresistenz, Neoangiogenese und Immunsupprimierung führen können. In der vorliegenden Arbeit wurde untersucht, inwiefern eine pharmakologische oder gentechnische Inhibierung von Stat3 molekulare und zelluläre Charakteristika von Gliomen beeinflusst. Dazu wurde für die in-vivo Versuche ein syngenes, murines Gliom-Transplantationsmodell verwendet dessen Pathologie der eines humanen Glioms gleicht und den Vorteil besitzt keine immunsupprimierten Tiere verwenden zu müssen. Die murinen Gliomzelllinien, gewonnen aus spontanen Gliomen von GFAP-v-Src überexprimierenden Mäusen, wurden vorher in-vitro und auch exvivo bezüglich ihres Verhaltens auf die pharmakologische oder gentechnische Inhibierung von Stat3 charakterisiert. Für die pharmakologische Inhibierung wurde Kurkumin gewählt, der biologische aktive Wirkstoff der Pflanze Curcuma longa. In der vorliegenden Arbeit konnte gezeigt werden, dass eine Behandlung mit Kurkumin konzentrationsabhängig die Phosphorylierung von Stat3 in drei murinen Gliomzelllinien hemmt. Des Weiteren zeigte sich, dass auch die Proliferation der untersuchten transformierten Zellen sowie ihre Fähigkeit zur Invasion und Migration konzentrationsabhängig durch den Einsatz von Kurkumin inhibiert werden konnte, ohne dabei allerdings die Proliferation von primären Astrozyten im gleichen Maße zu hemmen. Kurkumin induziert zusätzlich in den überaus aopotoseresistenten Gliomzellen einen G2/M Zellzyklusarrest. Diese beobachteten Effekte stehen im Zusammenhang mit der konzentrationsabhängigen transkriptionellen Beeinflussung Kurkumins der tumorpromotenden Stat3- Zielgene. Durch Einsatz einer Stat3-Mutante, Stat3C, die ohne Phosphorylierung konstitutiv aktiv in der Zelle vorliegt, konnte in der vorliegenden Arbeit gezeigt werden, dass Kurkumin seinen Einfluss auf die Invasion und Migration der murinen Gliomzelllinien auch über den Stat3-Signalweg vermittelt, zeigte sich, dass durch Einbringung dieser Mutante trotz Kurkuminbehandlung die Migrations- und Invasionsfähigkeit partiell retabliert werden konnte. Durch dietätische Gabe von Kurkumin konnte in tumortragenden Mäusen gezeigt werden, dass die invitro ermittelten Effekte an einem längeren Überleben jener Mäuse beteiligt waren, deren Futter das Kurkumin enthielt. Die Administration des Kurkumins wurde entsprechend einer für die Klinik bevorzugten Darreichugsform gewählt. Im zweiten Teil dieser Arbeit wurde Stat3 in den murinen Gliomzelllinien durch Transduktion mit shRNA gerichtet gegen die Stat3-mRNA stabil depletiert um im Folgenden untersuchen zu können, welche zellulären und molekularen Konsequenzen konstitutiv aktives Stat3 für die Gliomzellen hat. Es zeigte sich, dass der Wegfall von Stat3 das Migrations- und Invasionspotential signifikant verringerte und die Expression tumorfördernder Zielgene ebenfalls in den Stat3-defizienten Zellen auf Protein- und mRNA-Ebene signifikant reduziert war. Der Einfluss von Stat3 auf die Hif1α-Expression, ein Transkriptionsfaktor der die Anpassung der Gliomzellen an ein hypoxisches Milieu und damit verbunden auch Migration und Invasion induziert kann, macht deutlich, dass konstitutiv aktives Stat3 unter normoxischen sowie auch hypoxischen Bedingungen upstream entscheidender Transkriptionsfaktoren liegt und sich somit als Zielmolekül für eine therapeutische Intervention anbietet. Eine ex-vivo Applikation auf organotypischen Schnittkulturen zeigte, dass durch den Wegfall von Stat3 in den murinen Gliomzellen die Einzelzellinvasion unterbunden werden konnte was entscheidend für das klinisch hochrelevante Problem der Rezidive sein könnte. Transplantierte man nun Kontroll- und Stat3-defiziente Zellen orthotrop in die immunkompetenten Mäuse zeigte die Kaplan-Meier-Kurve, dass der Krankheitsbeginn so wie das mediane Überleben in den Mäusen mit Stat3-defizientem Tumor zeitlich deutlich nach hinten verschoben war. Neben den invitro und ex-vivo ermittelten Effekte des Stat3-Wegfalls ist anzunehmen, dass das verlängerte Überleben dieser Mäuse auch mit der fehlenden Immunsupprimierung der Stat3-defizienten Tumore zusammenhängt. Es zeigte sich, dass eine Intervention gegen Stat3, ob nun pharmakologisch oder gentechnisch, die malignen Charakteristika des Glioblastoms positiv beeinflussen kann. Stat3, bestätigt als onkogener Transkriptionsfaktor, stellt damit eine lohnenden Zielstruktur in Gliomen dar.
It has been estimated that about 1% of live births carry severe congenital heart defects and 20-30% among them have valve malformations. Despite its medical importance the underlying cause of many valvular diseases remains undiscovered. Thus, it is important to identify genes that play a crucial role in cardiac valve formation and maturation.
A temporal RNA expression analysis of heart development suggested that the extracellular matrix protein Nephronectin might be a novel regulator of valve development and/or trabeculation. Nephronectin is transiently expressed during rat heart development at the time of heart valve morphogenesis and trabeculation. Moreover, the extracellular matrix is known to be crucial for organogenesis. It is a complex, dynamic and critical component that regulates cell behavior by modulating the activity, bioavailability, or presentation of growth factors to cell surface receptors.
In order to verify the hypothesis that Nephronectin is a novel regulator of valve formation and/or trabeculation the zebrafish was chosen as model system. Females are able to spawn at intervals of 5 days laying hundreds of eggs in each clutch. Development progresses rapidly with precursors to all major organs appearing within 36 hours post fertilization. Zebrafish embryos develop externally, are translucent and continue to grow for several days despite developing severely malformed, non functional hearts. In addition, gene expression can be easily modulated. During the present study it has been shown that Nephronectin expression is correlated to valve development and trabeculation. Morpholinomediated knockdown of Nephronectin in zebrafish caused failure of valve formation and trabeculation resulting in > 85% lethality at 7 days post fertilization.
Cardiac valve formation is initiated at the junction of atrium and ventricle and is characterized by extracellular matrix deposition and endocardial cell differentiation. In accordance with the above-described phenotype the earliest observed abnormality in Nephronectin morphants was an extended tube like structure at the atrio-ventricular boundary. In addition, the expression of myocardial genes involved in cardiac valve formation (cspg2, fibulin1, tbx2b, bmp4) was expanded and endocardial cells along the extended tube like structure exhibited characteristics of atrio-ventricular cells (has2, notch1b and Alcam expression, cuboidal cell shape). Inhibition of has2 in Nephronectin morphants rescued the endocardial but not the myocardial expansion. In contrast, diminishment of BMP signaling in npnt morphants resulted in reduced ectopic expression of myocardial and endocardial atrio-ventricular markers. Taken together, these results identify Nephronectin as a novel upstream regulator of BMP4-HAS2 signaling playing a crucial role in atrio-ventricular canal differentiation.
Secretins are a family of large bacterial outer membrane protein complexes mediating the transport of complex structures, such as type IV pili, DNA and filamentous phage, or various proteins, such as extracellular enzymes and pathogenicity determinants. PilQ of the thermophilic bacterium Thermus thermophilus HB27 is a member of the secretin family required for natural transformation. Here we report the isolation, structural, and functional analyses of a unique PilQ from T. thermophilus. Native PAGE, gel filtration chromatography, and electrophoretic mobility shift analyses indicated that PilQ forms a macromolecular homopolymeric complex that binds dsDNA. Electron microscopy showed that the PilQ complex is 15 nm wide and 34 nm long and consists of an extraordinary stable "cone" and "cup" structure and five ring structures with a large central channel. Moreover, the electron microscopic images together with secondary structure analyses combined with structural data of type II protein secretion system and type III protein secretion system secretins suggest that the individual rings are formed by conserved domains of alternating α-helices and β-sheets. The unprecedented length of the PilQ complex correlated well with the distance between the inner and outer membrane of T. thermophilus. Indeed, PilQ was found immunologically in both membranes, indicating that the PilQ complex spans the entire cell periphery of T. thermophilus. This is consistent with the hypothesis that PilQ accommodates a PilA4 comprising pseudopilus mediating DNA transport across the outer membrane and periplasmic space in a single-step process.
Eine verzögerte und mitunter unvollständige Immunrekonstitution nach allogener Stammzelltransplantation (SZT) birgt ein erhöhtes Risiko für Infektionen und das Auftreten eines Rezidivs. Adoptive Immuntherapien können dazu beitragen, die Immunrekonstitution zu beschleunigen. Die Indikation hierzu ist jedoch streng geregelt, da eine zusätzliche Immuntherapie mit Risiken, wie z.B. dem Auftreten einer Graft-versus-Host-Disease (GvHD), verbunden ist. Im Mittelpunkt dieser Arbeit steht die Untersuchung der Immunrekonstitution im Hinblick auf das Auftreten von Komplikationen und das Überleben nach SZT. Dazu wurde ein multivariates Normwertmodell entwickelt, das die Beurteilung der Rekonstitution verschiedener Leukozytensubpopulationen ermöglicht. Der Einfluss der Regeneration spezifischer Immunzellen wie Cytomegalievirus-spezifischer T-Zellen (CMV-CTLs) und regulatorischer T-Zellen (Tregs) auf den Verlauf nach SZT wurde insbesondere hinsichtlich CMV-bedingter Komplikationen, GvHD und Rezidiv untersucht.
The anaerobic acetogenic bacterium Acetobacterium woodii employs a novel type of Na+-motive anaerobic respiration, caffeate respiration. However, this respiration is at the thermodynamic limit of energy conservation, and even worse, in the first step, caffeate is activated by caffeyl-CoA synthetase, which hydrolyzes ATP to AMP and pyrophosphate. Here, we have addressed whether or not the energy stored in the anhydride bond of pyrophosphate is conserved by A. woodii. Inverted membrane vesicles of A. woodii have a membrane-bound pyrophosphatase that catalyzes pyrophosphate hydrolysis at a rate of 70–120 milliunits/mg of protein. Pyrophosphatase activity was dependent on the divalent cation Mg2+. In addition, activity was strictly dependent on Na+ with a Km of 1.1 mm. Hydrolysis of pyrophosphate was accompanied by 22Na+ transport into the lumen of the inverted membrane vesicles. Inhibitor studies revealed that 22Na+ transport was primary and electrogenic. Next to the Na+-motive ferredoxin:NAD+ oxidoreductase (Fno or Rnf), the Na+-pyrophosphatase is the second primary Na+-translocating enzyme in A. woodii.