The Experts below are selected from a list of 531 Experts worldwide ranked by ideXlab platform
Mary L Berbee - One of the best experts on this subject based on the ideXlab platform.
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labyrinthulomycetes phylogeny and its implications for the evolutionary loss of chloroplasts and gain of Ectoplasmic gliding
Molecular Phylogenetics and Evolution, 2009Co-Authors: Clement K. M. Tsui, Rinka Yokoyama, Daiske Honda, Wyth L Marshall, Casey J Lippmeier, Kelly D Craven, Paul D Peterson, Mary L BerbeeAbstract:Abstract The labyrinthulomycetes, also known as the ‘Labyrinthulomycota’ are saprotrophic or less frequently parasitic stramenopilan protists, usually in marine ecosystems. Their distinguishing feature is an ‘Ectoplasmic net,’ an external cytoplasmic network secreted by a specialized organelle that attaches the cell to its substrate and secretes digestive enzymes for absorptive nutrition. In this study, one of our aims was to infer the phylogenetic position of the labyrinthulomycetes relative to the non-photosynthetic bicoeceans and oomycetes and the photosynthetic ochrophytes and thereby evaluate patterns of change from photosynthesis to saprotrophism among the stramenopiles. For the labyrinthulomycetes, we determined sequences of the actin, beta-tubulin, and elongation factor 1-alpha gene fragments and where necessary, ribosomal small subunit (SSU) genes. Multilocus analysis using standard tree construction techniques not only strongly supported the oomycetes as the sister group to the phototrophic stramenopiles, but also, for the first time with moderate statistical support, showed that the labyrinthulomycetes and the bicoecean as sister groups. The paraphyly of the non-photosynthetic groups was consistent with independent loss of photosynthesis in labyrinthulomycetes and oomycetes. We also wished to develop a phylogenetically based hypothesis for the origin of the gliding cell bodies and the Ectoplasmic net found in some labyrinthulomycetes. The cells of species in Labyrinthula and Aplanochytrium share a specialized form of motility involving gliding on Ectoplasmic tracks. Before our study, only ribosomal DNA genes had been determined for these genera and their phylogenetic position in the labyrinthulomycetes was equivocal. Multilocus phylogenies applying our newly determined protein-coding sequences divided the labyrinthulomycetes between sister clades ‘A’ and ‘B’ and showed that the monophyletic group containing all of the gliding species was nested among non-gliding species in clade B. This phylogeny suggested that species that glide via an Ectoplasm evolved from species that had used the Ectoplasm mainly for anchorage and assimilation rather than motility.
James S Gates - One of the best experts on this subject based on the ideXlab platform.
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Ectoplasm and superspace integration measures for 2d supergravity with four spinorial supercurrents
Journal of Physics A, 2010Co-Authors: James S Gates, Gabriele TartaglinomazzucchelliAbstract:Building on a previous derivation of the local chiral projector for a two-dimensional superspace with eight real supercharges, we provide the complete density projection formula required for locally supersymmetrical theories in this context. The derivation of this result is shown to be very efficient using techniques based on the Ectoplasmic construction of local measures in superspace.
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Ectoplasm superspace integration measure for 2d supergravity with four spinorial supercurrents
arXiv: High Energy Physics - Theory, 2009Co-Authors: James S Gates, Gabriele TartaglinomazzucchelliAbstract:Building on a previous derivation of the local chiral projector for a two dimensional superspace with eight real supercharges, we provide the complete density projection formula required for locally supersymmetrical theories in this context. The derivation of this result is shown to be very efficient using techniques based on the Ectoplasmic construction of local measures in superspace.
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Ectoplasm has no topology the prelude
Lecture Notes in Physics, 1999Co-Authors: James S GatesAbstract:Preliminary evidence is presented that a long overlooked and critical element in the fundamental definition of a general theory of integration over curved Wess-Zumino superspace lies with the imposition of “the Ethereal Conjecture” which states the necessity of the superspace to be topologically “close” to its purely bosonic sub-manifold. As a step in proving this, a new theory of integration based on closed super p-forms is proposed.
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Ectoplasm has no topology
arXiv: High Energy Physics - Theory, 1998Co-Authors: James S GatesAbstract:In a new approach to the theory of integration over Wess-Zumino supermanifolds, we suggest that a fundamental principle is their consistency with an ``Ethereal Conjecture'' that asserts the topology of the supermanifold must be generated essentially from its bosonic submanifold. This naturally leads to a theory of ``Ectoplasmic'' integration based on super p-forms. One consequence of this approach is that the derivation of ``density projection operators'' becomes trivial in a number of supergravity theories.
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component actions from curved superspace normal coordinates and Ectoplasm
arXiv: High Energy Physics - Theory, 1997Co-Authors: James S Gates, Marcus T Grisaru, Marcia E Knuttwehlau, Warren SiegelAbstract:We give efficient superspace methods for deriving component actions for supergravity coupled to matter. One method uses normal coordinates to covariantly expand the superfield action, and can be applied straightforwardly to any superspace. The other interprets the component lagrangian as a differential form on a bosonic hypersurface in superspace, and gives a simple derivation for pertinent cases such as chiral superspace.
Joseph Novak - One of the best experts on this subject based on the ideXlab platform.
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The linear multiplet and Ectoplasm
Journal of High Energy Physics, 2012Co-Authors: Daniel Butter, Sergei M. Kuzenko, Joseph NovakAbstract:In the framework of the superconformal tensor calculus for 4D N = 2 super- gravity, locally supersymmetric actions are often constructed using the linear multiplet. We provide a superform formulation for the linear multiplet and derive the corresponding action functional using the Ectoplasm method (also known as the superform approach to the construction of supersymmetric invariants). We propose a new locally supersymmetric action which makes use of a deformed linear multiplet. The novel feature of this multiplet is that it corresponds to the case of a gauged central charge using a one-form potential not annihilated by the central charge (unlike the standard N = 2 vector multiplet). Such a gauge one-form can be chosen to describe a variant nonlinear vector-tensor multiplet. As a byproduct of our construction, we also find a variant realization of the tensor mul- tiplet in supergravity where one of the auxiliaries is replaced by the field strength of a gauge three-form.
Wyth L Marshall - One of the best experts on this subject based on the ideXlab platform.
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labyrinthulomycetes phylogeny and its implications for the evolutionary loss of chloroplasts and gain of Ectoplasmic gliding
Molecular Phylogenetics and Evolution, 2009Co-Authors: Clement K. M. Tsui, Rinka Yokoyama, Daiske Honda, Wyth L Marshall, Casey J Lippmeier, Kelly D Craven, Paul D Peterson, Mary L BerbeeAbstract:Abstract The labyrinthulomycetes, also known as the ‘Labyrinthulomycota’ are saprotrophic or less frequently parasitic stramenopilan protists, usually in marine ecosystems. Their distinguishing feature is an ‘Ectoplasmic net,’ an external cytoplasmic network secreted by a specialized organelle that attaches the cell to its substrate and secretes digestive enzymes for absorptive nutrition. In this study, one of our aims was to infer the phylogenetic position of the labyrinthulomycetes relative to the non-photosynthetic bicoeceans and oomycetes and the photosynthetic ochrophytes and thereby evaluate patterns of change from photosynthesis to saprotrophism among the stramenopiles. For the labyrinthulomycetes, we determined sequences of the actin, beta-tubulin, and elongation factor 1-alpha gene fragments and where necessary, ribosomal small subunit (SSU) genes. Multilocus analysis using standard tree construction techniques not only strongly supported the oomycetes as the sister group to the phototrophic stramenopiles, but also, for the first time with moderate statistical support, showed that the labyrinthulomycetes and the bicoecean as sister groups. The paraphyly of the non-photosynthetic groups was consistent with independent loss of photosynthesis in labyrinthulomycetes and oomycetes. We also wished to develop a phylogenetically based hypothesis for the origin of the gliding cell bodies and the Ectoplasmic net found in some labyrinthulomycetes. The cells of species in Labyrinthula and Aplanochytrium share a specialized form of motility involving gliding on Ectoplasmic tracks. Before our study, only ribosomal DNA genes had been determined for these genera and their phylogenetic position in the labyrinthulomycetes was equivocal. Multilocus phylogenies applying our newly determined protein-coding sequences divided the labyrinthulomycetes between sister clades ‘A’ and ‘B’ and showed that the monophyletic group containing all of the gliding species was nested among non-gliding species in clade B. This phylogeny suggested that species that glide via an Ectoplasm evolved from species that had used the Ectoplasm mainly for anchorage and assimilation rather than motility.
D L Taylor - One of the best experts on this subject based on the ideXlab platform.
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in vitro models of tail contraction and cytoplasmic streaming in amoeboid cells
Journal of Cell Biology, 1993Co-Authors: Lee W. Janson, D L TaylorAbstract:We have developed a reconstituted gel-sol and contractile model system that mimics the structure and dynamics found at the Ectoplasm/endoplasm interface in the tails of many amoeboid cells. We tested the role of gel-sol transformations of the actin-based cytoskeleton in the regulation of contraction and in the generation of endoplasm from Ectoplasm. In a model system with fully phosphorylated myosin II, we demonstrated that either decreasing the actin filament length distribution or decreasing the extent of actin filament cross-linking initiated both a weakening of the gel strength and contraction. However, streaming of the solated gel components occurred only under conditions where the length distribution of actin was decreased, causing a self-destruct process of continued solation and contraction of the gel. These results offer significant support that gel strength plays an important role in the regulation of actin/myosin II-based contractions of the tail cortex in many amoeboid cells as defined by the solation-contraction coupling hypothesis (Taylor, D. L., and M. Fechheimer. 1982. Phil. Trans. Soc. Lond. B. 299:185-197). The competing processes of solation and contraction of the gel would appear to be mutually exclusive. However, it is the temporal-spatial balance of the rate and extent of two stages of solation, coupled to contraction, that can explain the conversion of gelled Ectoplasm in the tail to a solated endoplasm within the same small volume, generation of a force for the retraction of tails, maintenance of cell polarity, and creation of a positive hydrostatic pressure to push against the newly formed endoplasm. The mechanism of solation-contraction of cortical cytoplasm may be a general component of the normal movement of a variety of amoeboid cells and may also be a component of other contractile events such as cytokinesis.
