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Results for “organelle interaction”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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9 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Cytoskeleton-amyloplast interactions in sweet clover

The distribution of organelles within columella cells of sweet clover was examined by transmission electron microscopy following growth under static or clinorotating conditions. A developmentally conditioned polarity was observed, with a proximal location of the nucleus and a distal accumulation of the endoplasmic reticulum. This polarity was insensitive to clinorotation. In contrast, clinorotation altered the location of amyloplasts. Application of cytoskeletal poisons (colchicine, cytochalasin D, taxol, and phalloidin), especially during clinorotation, had interesting effects on the maintenance of columella cell polarity, with a profound effect on the extent, location, and structure of the endoplasmic reticulum. The site of cytoskeletal interactions with sedimenting amyloplasts is thought to be the amyloplast envelope. An envelope fraction, having over 17 polypeptides, was isolated using immobilized antibody technology, and will provide a means of assessing the role of specific peptides in cytoskeleton/amyloplast interactions.

Non-NASA Center↗
NASA NTRS2000

Release of kinesin from vesicles by hsc70 and regulation of fast axonal transport

The nature of kinesin interactions with membrane-bound organelles and mechanisms for regulation of kinesin-based motility have both been surprisingly difficult to define. Most kinesin is recovered in supernatants with standard protocols for purification of motor proteins, but kinesin recovered on membrane-bound organelles is tightly bound. Partitioning of kinesin between vesicle and cytosolic fractions is highly sensitive to buffer composition. Addition of either N-ethylmaleimide or EDTA to homogenization buffers significantly increased the fraction of kinesin bound to organelles. Given that an antibody against kinesin light chain tandem repeats also releases kinesin from vesicles, these observations indicated that specific cytoplasmic factors may regulate kinesin release from membranes. Kinesin light tandem repeats contain DnaJ-like motifs, so the effects of hsp70 chaperones were evaluated. Hsc70 released kinesin from vesicles in an MgATP-dependent and N-ethylmaleimide-sensitive manner. Recombinant kinesin light chains inhibited kinesin release by hsc70 and stimulated the hsc70 ATPase. Hsc70 actions may provide a mechanism to regulate kinesin function by releasing kinesin from cargo in specific subcellular domains, thereby effecting delivery of axonally transported materials.

Non-NASA Center↗
NASA NTRS2000

Columella cells revisited: novel structures, novel properties, and a novel gravisensing model

A hundred years of research has not produced a clear understanding of the mechanism that transduces the energy associated with the sedimentation of starch-filled amyloplast statoliths in root cap columella cells into a growth response. Most models postulate that the statoliths interact with microfilaments (MF) to transmit signals to the plasma membrane (or ER), or that sedimentation onto these organelles produces the signals. However, no direct evidence for statolith-MF links has been reported, and no asymmetric structures of columella cells have been identified that might explain how a root turned by 90 degrees knows which side is up. To address these and other questions, we have (1) quantitatively examined the effects of microgravity on the size, number, and spatial distribution of statoliths; (2) re-evaluated the ultrastructure of columella cells in high-pressure frozen/freeze-substituted roots; and (3) followed the sedimentation dynamics of statolith movements in reoriented root tips. The findings have led to the formulation of a new model for the gravity-sensing apparatus of roots, which envisages the cytoplasm pervaded by an actin-based cytoskeletal network. This network is denser in the ER-devoid central region of the cell than in the ER-rich cell cortex and is coupled to receptors in the plasma membrane. Statolith sedimentation is postulated to disrupt the network and its links to receptors in some regions of the cell cortex, while allowing them to reform in other regions and thereby produce a directional signal.

NASA Discipline Cell Biology↗
NASA NTRS2002

Glycogen synthase kinase 3 phosphorylates kinesin light chains and negatively regulates kinesin-based motility

Membrane-bounded organelles (MBOs) are delivered to different domains in neurons by fast axonal transport. The importance of kinesin for fast antero grade transport is well established, but mechanisms for regulating kinesin-based motility are largely unknown. In this report, we provide biochemical and in vivo evidence that kinesin light chains (KLCs) interact with and are in vivo substrates for glycogen synthase kinase 3 (GSK3). Active GSK3 inhibited anterograde, but not retrograde, transport in squid axoplasm and reduced the amount of kinesin bound to MBOs. Kinesin microtubule binding and microtubule-stimulated ATPase activities were unaffected by GSK3 phosphorylation of KLCs. Active GSK3 was also localized preferentially to regions known to be sites of membrane delivery. These data suggest that GSK3 can regulate fast anterograde axonal transport and targeting of cargos to specific subcellular domains in neurons.

NASA Discipline Neuroscience↗
NASA NTRS1998

Simulated Microgravity Induced Cytoskeletal Rearrangements are Modulated by Protooncogenes

Microgravity is the environment living systems encounter during space flight and gravitational unloading is the effect of this environment on living systems. The cell, being a multiphasic chemical system, is a useful starting point to study the potential impact of gravity unloading on physiological function. In the absence of gravity, sedimentation of organelles including chromosomes, mitochondria, nuclei, the Golgi apparatus, vacuoles, and the endoplasmic reticulum may be affected. Most of these organelles, however, are somewhat held in place by cytoskeleton. Hansen and Igber suggest that intermediate filaments act to stabilize the nuleus against rotational movement, and integrate cell and nuclear structure. The tensegrity theory supports the idea that mechanical or physical forces alters the cytoskeletal structures of a cell resulting in the changes in cell: matrix interactions and receptor-signaling coupling. This type of stress to the cytoskeleton may be largely responsible regulating cell shape, growth, movement and metabolism. Mouse MC3T3 El cells under microgravity exhibited significant cytoskeletal changes and alterations in cell growth. The alterations in cytoskeleton architecture may be due to changes in the expression of actin related proteins or integrins. Philopott and coworkers reported on changes in the distribution of microtubule and cytoskeleton elements in the cells of heart tissue from space flight rats and those centrifuged at 1.7g. Other researchers have showed that microgravity reduced EGF-induced c-fos and c-jun expression compared to 1 g controls. Since c-fos and c-jun are known regulators of cell growth, it is likely that altered signal transduction involving protooncogenes may play a crucial role in the reduced growth and alterations in cytoskeletal arrangements found during space flight. It is clear that a microgravity environment induces a number of changes in cell shape, cell surface molecules, gene expression, and cytoskeletal reorganization. However the underlying mechanism for these cellular changes have not been clearly defined. We examined alterations in endothelial migration, and cytoskeleton architecture (microfilamentous f-actin and vimentin-rich- intermediate filaments) following wounding under simulated microgravity. We also examined the possibility that altered signal transduction pathways, involving protooncogenes, may play a crucial role in microgravity-induced retardation of cell migration and alterations in cytoskeletal organization. We hypothesize that, based on the tensegrity theory, cytoskeletal organization respond to gravitational unloading and through this response, cell behavior, function and gene expression are modified.

Melhado, C. D.↗
NASA NTRS1998

A role for cyclin-dependent kinase(s) in the modulation of fast anterograde axonal transport: effects defined by olomoucine and the APC tumor suppressor protein

Proteins that interact with both cytoskeletal and membrane components are candidates to modulate membrane trafficking. The tumor suppressor proteins neurofibromin (NF1) and adenomatous polyposis coli (APC) both bind to microtubules and interact with membrane-associated proteins. The effects of recombinant NF1 and APC fragments on vesicle motility were evaluated by measuring fast axonal transport along microtubules in axoplasm from squid giant axons. APC4 (amino acids 1034-2844) reduced only anterograde movements, whereas APC2 (aa 1034-2130) or APC3 (aa 2130-2844) reduced both anterograde and retrograde transport. NF1 had no effect on organelle movement in either direction. Because APC contains multiple cyclin-dependent kinase (CDK) consensus phosphorylation motifs, the kinase inhibitor olomoucine was examined. At concentrations in which olomoucine is specific for cyclin-dependent kinases (5 microM), it reduced only anterograde transport, whereas anterograde and retrograde movement were both affected at concentrations at which other kinases are inhibited as well (50 microM). Both anterograde and retrograde transport also were inhibited by histone H1 and KSPXK peptides, substrates for proline-directed kinases, including CDKs. Our data suggest that CDK-like axonal kinases modulate fast anterograde transport and that other axonal kinases may be involved in modulating retrograde transport. The specific effect of APC4 on anterograde transport suggests a model in which the binding of APC to microtubules may limit the activity of axonal CDK kinase or kinases in restricted domains, thereby affecting organelle transport.

Non-NASA Center↗
NASA NTRS1993

Cellular polarity and interactions in plant graviperception

Presented are results of studies on the mechanisms of gravitropic sensing in higher and lower plants. Gravitropic roots of the aquatic angiosperm, Limnobium, were found to have sedimented amyloplasts in their elongation zone but not in their rootcap; nuclei were found to sediment in the elongation zone as well. Another study attempted to understand how plastid sedimentation occurs in vertical Ceratodon cells and how this sedimentation is regulated. To determine whether the cytoskeleton restricts plastid sedimentation, the effects of amiprophos-methyl (APM) and cytochalasin (CD) on plastid position were qualified. Results suggest that microtubules restrict the sedimentation of plastids along the length of the cell and that microtubules are load-bearing for all the plastids in the apical cell, demonstrating the importance of the cytoskeleton in maintaining organelle position and cell organization against the force of gravity. Physcomitrella and Funaria were also studied. Results suggest that gravitropism may be relatively common in moss protonemata and reinforce the idea that amyloplast mass functions in gravitropic sensing.

Sack, Fred D.↗
NASA NTRS2004

A Survey of Collectives

Due to the increasing sophistication and miniaturization of computational components, complex, distributed systems of interacting agents are becoming ubiquitous. Such systems, where each agent aims to optimize its own performance, but where there is a well-defined set of system-level performance criteria, are called collectives. The fundamental problem in analyzing/designing such systems is in determining how the combined actions of self-interested agents leads to 'coordinated' behavior on a iarge scale. Examples of artificial systems which exhibit such behavior include packet routing across a data network, control of an array of communication satellites, coordination of multiple deployables, and dynamic job scheduling across a distributed computer grid. Examples of natural systems include ecosystems, economies, and the organelles within a living cell. No current scientific discipline provides a thorough understanding of the relation between the structure of collectives and how well they meet their overall performance criteria. Although still very young, research on collectives has resulted in successes both in understanding and designing such systems. It is eqected that as it matures and draws upon other disciplines related to collectives, this field will greatly expand the range of computationally addressable tasks. Moreover, in addition to drawing on them, such a fully developed field of collective intelligence may provide insight into already established scientific fields, such as mechanism design, economics, game theory, and population biology. This chapter provides a survey to the emerging science of collectives.

Tumer, Kagan↗
NASA NTRS1992

Experiments with suspended cells on the Space Shuttle

Spaceflight experiments since 1981 have demonstrated that certain cell functions are altered by micro-g. Biophysical models suggest that cell membranes and organelles should not be affected directly by gravity, however, the chemical microenvironment surrounding the cell and molecular transport could be altered by reduced gravity. Most experiments have used suspended live cells in small chambers without stirring or medium exchange. Flight results include increased attachment of anchorage-dependent human cells to collagen coated microcarriers, reduced secretion of growth hormone from pituitary cells, decreased mitogenic response of lymphocytes, increased Interferon-alpha by lymphocytes, increased Interleukin-1 and Tumor Necrosis Factor secretion by macrophages. Related experiments on cells immediately postflight and on procaryotic cells have shown significant changes in secretory capacity, cell proliferation, differentiation and development. Postulated mechanism include altered cell-cell interactions, altered calcium ion transport, effects on cell cytoskeleton, transport of transmitters and interactions with receptors. The discussion includes use of new molecular methods, considerations for cell environmental control and a preview of several experiments planned for the Shuttle and Spacelab flights to study the basic effects of microgravity on cellular physiology and potential interactions of spaceflight with radiation damage and cellular repair mechanisms.

Review↗