Transgenic Zebrafish as a Novel Animal Model to Study Tauopathies and Other Neurodegenerative Disorders in vivo

Our ageing society is confronted with a dramatic increase in patients suffering from tauopathies such as Alzheimer's disease, frontotemporal dementia and others. Typical neuropathological lesions including tangles composed of hyper-phosphorylated tau protein as well as severe neuronal cell death characterize these disorders. No mechanism-based cures are available at present. Genetically modified animals are invaluable models to understand the molecular disease mechanisms and to screen for modifying compounds. We recently introduced tau-transgenic zebrafish as a novel model for tauopathies. Our model allows recapitulating key pathological features of tauopathies within an extremely short time. Moreover, life imaging of tau-dependent neuronal cell death was performed for the very first time. This demonstrated tau-dependent neuronal cell loss independent of tangle formation. Finally, we exemplified that the zebrafish frontotemporal dementia model can be used to screen for drugs that prevent abnormal tau phosphorylation and neuronal cell death. Copyright (C) 2010 S. Karger AG, Base

The Biochemical and Genetic Odyssey to the Function of a Nicastrin-Like Protein

gamma-Secretase is a high-molecular-weight protein complex required for the proteolytic processing of various transmembrane proteins including the Alzheimer's disease-associated amyloid precursor protein and the signaling receptor Notch. One of the gamma-secretase complex components is the type I transmembrane protein nicastrin. Here we review the odyssey to a cyclopic fish, which at the end allowed the functional analysis of nicalin, a novel member of the nicastrin protein family. This 60-kDa protein is part of a previously unknown membrane protein complex unrelated to gamma-secretase and binds to Nomo (Nodal modulator, previously known as pM5), a novel 130-kDa transmembrane protein. Both proteins are highly conserved in metazoans and show almost identical tissue distribution in humans. Functional studies in zebrafish embryos and cultured human cells revealed that nicalin and Nomo collaborate to antagonize the Nodal/TGF beta signaling pathway. Thus, nicastrin and nicalin are both associated with protein complexes involved in cell fate decisions during early embryonic development. Copyright (C) 2004 S. Karger AG, Base

Cellular functions of gamma-secretase-related proteins

Amyloid-beta pepticle (A beta) is generated by gamma-secretase, a membrane protein complex with an unusual aspartyl protease activity consisting of the four components presenilin, nicastrin, APH-1 and PEN-2. Presenilin is considered the catalytic subunit of this complex since it represents the prototype of the new family of intramembrane-cleaving GxGD-type aspartyl proteases. Recently, five novel members of this family and a nicastrin-like protein were identified. Whereas one of the GxGD-type proteins was shown to be identical with signal pepticle peptidase (SPP), the function of the others, now called SPP-like proteins (SPPLs), is not known. We therefore analyzed SPPL2b and SPPL3 and demonstrated that they localize to different subcellular compartments suggesting nonredundant functions. This was supported by different phenotypes obtained in knockdown studies in zebrafish embryos. In addition, these phenotypes could be phenocopied by ectopic expression of putative active site mutants, providing strong evidence for a proteolytic function of SPPL2b and SPPL3. We also identified and characterized the nicastrin-like protein nicalin which, together with the 130-kDa protein NOMO (Nodal modulator), forms a membrane protein complex different from gamma-secretase. We found that during zebrafish embryogenesis this complex is involved in the patterning of the axial mesendoderm, a process controlled by the Nodal signaling pathway. Copyright (c) 2006 S. Karger AG, Basel

Cooperative Liner Shipping Network Design by Means of a Combinatorial Auction

A liner shipping network design problem is considered which includes ship scheduling and cargo routing decisions. The question is how to enable loose cooperation of multiple liner shippers for jointly solving this profit maximizing network design problem. A variable neighborhood search matheuristic is developed to compute a network for each liner shipper. To coordinate the planning process of multiple liner shippers, a combinatorial auction is proposed. To evaluated the mechanism a computational study is performed which shows that cooperation is in many cases possible and beneficial. As the proposed joint planning mechanism requires less exchange of sensitive information compared to a centralized approach, it enables looser forms of cooperation during network design

The Nicastrin ectodomain adopts a highly thermostable structure

Nicastrin is a type I transmembrane glycoprotein, which is part of the high molecular weight gamma-secretase complex. gamma-Secretase is one of the key players associated with the generation of Alzheimer's disease pathology, since it liberates the neurotoxic amyloid beta-peptide. Four proteins Nicastrin, anterior pharynx-defective-1 (Aph-1), presenilin enhancer-2 (Pen-2) and Presenilin are essential to form the active gamma-secretase complex. Recently it has been shown, that Nicastrin has a key function in stabilizing the mature gamma-secretase complex and may also be involved in substrate recognition. So far no structural data for the Nicastrin ectodomain or any other gamma-secretase component are available. We therefore used Circular Dichroism (CD) spectroscopy to demonstrate that Nicastrin, similar to its homologues, the Streptomyces griseus aminopeptidase (SGAP) and the transferrin receptor (TfR), adopts a thermostable secondary structure. Furthermore, the Nicastrin ectodomain has an exceptionally high propensity to refold after thermal denaturation. These findings provide evidence to further support the hypothesis that Nicastrin may share evolutionary conserved properties with the aminopeptidase and the transferrin receptor family

Granulin Knock Out Zebrafish Lack Frontotemporal Lobar Degeneration and Neuronal Ceroid Lipofuscinosis Pathology

Loss of function mutations in granulin (GRN) are linked to two distinct neurological disorders, frontotemporal lobar degeneration (FTLD) and neuronal ceroid lipofuscinosis (NCL). It is so far unknown how a complete loss of GRN in NCL and partial loss of GRN in FTLD can result in such distinct diseases. In zebrafish, there are two GRN homologues, Granulin A (Grna) and Granulin B (Grnb). We have generated stable Grna and Grnb loss of function zebrafish mutants by zinc finger nuclease mediated genome editing. Surprisingly, the grna and grnb single and double mutants display neither spinal motor neuron axonopathies nor a reduced number of myogenic progenitor cells as previously reported for Grna and Grnb knock down embryos. Additionally, grna-/-;grnb-/- double mutants have no obvious FTLD- and NCL-related biochemical and neuropathological phenotypes. Taken together, the Grna and Grnb single and double knock out zebrafish lack any obvious morphological, pathological and biochemical phenotypes. Loss of zebrafish Grna and Grnb might therefore either be fully compensated or only become symptomatic upon additional challenge

Multilaterale Friedenssicherung in Afrika

Der Sicherheitsrat der Vereinten Nationen (VN) mandatierte 2013 zwei neue multilaterale Friedenseinsätze in afrikanischen Staaten: Im Juli begann die Mission in Mali, um das vorläufige Friedensabkommen umzusetzen und Wahlen zu sichern. Seit September operiert erstmals eine VN-Interventionsbrigade als Teil der schon bestehenden Mission in der Demokratischen Republik Kongo (DR Kongo), die auch gegen Rebellengruppen im Osten des Landes kämpfen soll. Die vor allem von afrikanischen Staaten getragenen Einsätze in Mali und der DR Kongo verdeutlichen zwei Trends der multilateralen Friedenssicherung: Erstens haben sich unbewaffnete Beobachtermissionen zu multidimensionalen Einsätzen gewandelt, die neben der Überwachung von Waffenstillständen auch die institutionellen Grundlagen für einen langfristigen Frieden sichern sollen. Zweitens übernehmen afrikanische Staaten inzwischen eine immer größere Rolle bei der Bereitstellung von Truppen für Friedenseinsätze in Afrika. Die politikwissenschaftliche Forschung zeigt, dass besonders robust mandatierte, komplexe Friedensoperationen mit ausreichender Truppenstärke zu einem Frieden nach Bürgerkriegen beitragen können. Daher ist das gestiegene Engagement afrikanischer Staaten bei der Friedenssicherung grundsätzlich begrüßenswert, denn ein stärkeres westliches Engagement in Form von Truppen für Friedensmissionen in afrikanischen Konflikten erscheint in absehbarer Zukunft nicht realistisch. Die gestiegene Einsatzbereitschaft afrikanischer Staaten ist Teil des Aufbaus einer "afrikanischen Friedens- und Sicherheitsarchitektur" seitens der Afrikanischen Union (African Union, AU). Politische Konflikte ihrer Mitgliedsstaaten, mangelnde Ressourcenausstattung und fehlende Finanzmittel erschweren allerdings nach wie vor genuin "afrikanische Lösungen für afrikanische Probleme". Eine politische, finanzielle sowie technische Stärkung dieser regionalen Sicherheitsarchitektur ist notwendig, um die friedensfördernden Effekte von Friedensoperationen weiter zu verbessern und ihre negativen gesellschaftlichen Auswirkungen zu verringern

Productivity changes across the mid-Pleistocene climate transition

We use benthic foraminiferal accumulation rates as a proxy for productivity changes during the mid-Pleistocene climate transition (MPT) (~1.2 Ma to 0.4 Ma). Our data are chosen to test the hypothesis that longer-term cooling and the onset of 100 kyr cyclicity are linked to atmospheric CO2 draw-down associated with an increase in primary productivity. To this end, we have constructed records from a global array of seven sites spanning major ocean basins and representing different hydrographic regimes (e.g., high and low latitudes, upwelling versus the deep western warm pools). We compare our data to published productivity proxy records from each site to identify limitations and uncertainties in the reconstructions. Results indicate that there is evidence for productivity increases during the onset of the MPT (1.2–1.0 Ma), but the changes are not globally synchronous and likely reflect regional hydrographic variability. On the orbital scale, productivity maxima tend to occur more closely related to glacial than interglacial intervals overall, but the relationships are not consistent. High interglacial productivity characterizes low latitude sites some of the time. In the obliquity band, high interglacial productivity in the eastern equatorial Pacific coincides with low interglacial productivity in the Southern Ocean, supporting a high to low latitude link via intermediate water circulation distribution of nutrients. On the regional scale, our records contribute new evidence for changes in Northern Hemisphere frontal systems during the MPT and for a close link between surface ocean production of organic matter and consumption on the ocean floor in the western tropical Atlantic. Pyrite counts at the two Southern Ocean sites provide supporting evidence for sluggish thermohaline overturn during the mid-point of the MPT at ~900 ka. Taken together, our records do not show a globally synchronous productivity signal that would support the biological pump as a driver for potential CO2-induced climate cooling during the MPT. Instead, we document complex regional variations in the carbon cycle, reflecting a combination of both biological and physical processes both on the longer as well as on the orbital time-scale