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Search Results: 1 - 10 of 862 matches for " Dietmar Riedel "
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Trends of Abundance of Salton Sea Fish: A Reversible Collapse or a Permanent Condition?  [PDF]
Ralf Riedel
Natural Resources (NR) , 2016, DOI: 10.4236/nr.2016.710045
Abstract: The Salton Sea is a closed-basin, 980 km2 salt lake in the Sonoran Desert of southern California. Three marine species, bairdiella (Bairdiella icistia), orangemouth corvina (Cynoscion xanthulus), and sargo (Anisotremus davidsoni), established from introductions of over 34 species beginning in 1929. During the late 1960s and early 1970s, a hybrid tilapia (Oreochromis mossambicus × O. urolepis hornorum) invaded the Salton Sea and became dominant by number and weight. Recent surveys show a precipitous decline of all four species above starting sometime between 2001 and 2002. Declines were more evident in nearshore than in estuarine habitats. Corvina has probably declined the soonest, followed by Gulf croaker. Tilapia declines were followed by more recent increases in population numbers. The tilapia rebound observed are probably only sustainable if a curb in Salton Sea salinity levels is realized. The marine species will likely need restocking to reach historic levels, if the salinity of the lake is managed at 40 gL1 or below. Restoration alternatives for the Salton Sea must take into consideration estuarine areas as essential fish habitats and fish refuge against high salinities.
Specification of primordial germ cells in medaka (Oryzias latipes)
Amaury Herpin, Stefan Rohr, Dietmar Riedel, Nils Kluever, Erez Raz, Manfred Schartl
BMC Developmental Biology , 2007, DOI: 10.1186/1471-213x-7-3
Abstract: PGCs specification in zebrafish appears to depend on inheritance of germ plasm in which several RNA molecules such as vasa and nanos reside. Whether the specification mode of PGCs found in zebrafish is general for other fish species was brought into question upon analysis of olvas expression – the vasa homologue in another teleost, medaka (Oryzias latipes). Here, in contrast to the findings in zebrafish, the PGCs are found in a predictable position relative to a somatic structure, the embryonic shield. This finding, coupled with the fact that vasa mRNA, which is localized to the germ plasm of zebrafish but does not label a similar structure in medaka opened the possibility of fundamentally different mechanisms governing PGC specification in these two fish species.In this study we addressed the question concerning the mode of PGC specification in medaka using embryological experiments, analysis of RNA stability in the PGCs and electron microscopy observations. Dramatic alterations in the somatic environment, i.e. induction of a secondary axis or mesoderm formation alteration, did not affect the PGC number. Furthermore, the PGCs of medaka are capable of protecting specific RNA molecules from degradation and could therefore exhibit a specific mRNA expression pattern controlled by posttrancriptional mechanisms. Subsequent analysis of 4-cell stage medaka embryos using electron microscopy revealed germ plasm-like structures located at a region corresponding to that of zebrafish germ plasm.Taken together, these results are consistent with the idea that in medaka the inheritance of maternally provided asymmetrically-localized cytoplasmic determinants directs cells to assume the germ line fate similar to zebrafish PGCs.Two basic strategies for the specification of primordial germ cells (PGCs) have been described. In Drosophila, C. elegans and Xenopus the inheritance of germ plasm with associated germ cell determinants appears to be required for PGC formation [1-3]. In these
Souffle/Spastizin Controls Secretory Vesicle Maturation during Zebrafish Oogenesis
Palsamy Kanagaraj equal contributor,Amandine Gautier-Stein equal contributor,Dietmar Riedel,Christoph Schomburg,Joan Cerdà,Nadine Vollack,Roland Dosch
PLOS Genetics , 2014, DOI: doi/10.1371/journal.pgen.1004449
Abstract: During oogenesis, the egg prepares for fertilization and early embryogenesis. As a consequence, vesicle transport is very active during vitellogenesis, and oocytes are an outstanding system to study regulators of membrane trafficking. Here, we combine zebrafish genetics and the oocyte model to identify the molecular lesion underlying the zebrafish souffle (suf) mutation. We demonstrate that suf encodes the homolog of the Hereditary Spastic Paraplegia (HSP) gene SPASTIZIN (SPG15). We show that in zebrafish oocytes suf mutants accumulate Rab11b-positive vesicles, but trafficking of recycling endosomes is not affected. Instead, we detect Suf/Spastizin on cortical granules, which undergo regulated secretion. We demonstrate genetically that Suf is essential for granule maturation into secretion competent dense-core vesicles describing a novel role for Suf in vesicle maturation. Interestingly, in suf mutants immature, secretory precursors accumulate, because they fail to pinch-off Clathrin-coated buds. Moreover, pharmacological inhibition of the abscission regulator Dynamin leads to an accumulation of immature secretory granules and mimics the suf phenotype. Our results identify a novel regulator of secretory vesicle formation in the zebrafish oocyte. In addition, we describe an uncharacterized cellular mechanism for Suf/Spastizin activity during secretion, which raises the possibility of novel therapeutic avenues for HSP research.
Amyloid Precursor Protein Is Trafficked and Secreted via Synaptic Vesicles
Teja W. Groemer,Cora S. Thiel,Matthew Holt,Dietmar Riedel,Yunfeng Hua,Jana Hüve,Benjamin G. Wilhelm,Jürgen Klingauf
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0018754
Abstract: A large body of evidence has implicated amyloid precursor protein (APP) and its proteolytic derivatives as key players in the physiological context of neuronal synaptogenesis and synapse maintenance, as well as in the pathology of Alzheimer's Disease (AD). Although APP processing and release are known to occur in response to neuronal stimulation, the exact mechanism by which APP reaches the neuronal surface is unclear. We now demonstrate that a small but relevant number of synaptic vesicles contain APP, which can be released during neuronal activity, and most likely represent the major exocytic pathway of APP. This novel finding leads us to propose a revised model of presynaptic APP trafficking that reconciles existing knowledge on APP with our present understanding of vesicular release and recycling.
Trust between Boundary-Spanning Agents: The Role of Relational Competencies  [PDF]
Isabella Hatak, Dietmar Roessl
Open Journal of Social Sciences (JSS) , 2015, DOI: 10.4236/jss.2015.33001

Against the background of principal-agent and transaction-cost theoretical considerations, this study addresses the question whether relational competencies relate to trust within cooperative relationships, taking into account also situational and personal factors. In its conclusion, the study presents an experimentally confirmed model (n = 282) that shows the strong causal relationship between relational competencies and trust allowing boundary-spanning agents to exert influence on the development and maintenance of complex cooperative relationships characterized by long-term objectives.

The spectrum of a class of almost periodic operators
Norbert Riedel
International Journal of Mathematics and Mathematical Sciences , 2003, DOI: 10.1155/s0161171203206268
Abstract: For almost Mathieu operators, it is shown that the occurrence of Cantor spectrum and the existence, for every point in the spectrum and suitable phase parameters, of at least one localized eigenfunction which decays exponentially are inconsistent properties.
Berufsverband Information Bibliothek e.V. (BIB) Enformasyon ve Kütüphane Meslek Derne i
Susanne Riedel
Türk Kütüphanecili?i , 2009,
Exponentially decaying eigenvectors for certain almost periodic operators
Norbert Riedel
Physics , 2000,
Abstract: For certain one-dimensional Schroedinger-type difference operators with a complex potential, a "complete" set of exponentially decaying eigenvectors is shown to exist. "Completeness" entails that the parameters involved are obtained through evaluation of analytic functions on a Riemann surface.
On the additivity of the minimum output entropy
Norbert Riedel
Physics , 2012,
Abstract: It is shown that for real finite dimensional Hilbert spaces the additivity property of the minimum output entropy for quantum channels is always true.
Markoff Equation and Nilpotent Matrices
Norbert Riedel
Mathematics , 2007,
Abstract: A triple (a,b,c) of positive integers is called a Markoff triple iff it satisfies the diophantine equation a2 + b2 + c2 = abc . Recasting the Markoff tree, whose vertices are Markoff triples, in the framework of intergral upper triangular 3x3 matrices, it will be shown that the largest member of such a triple determines the other two uniquely. This answers a question which has been open for almost 100 years.
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