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Results for “Signal Transduction/physiology”

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Ionic signaling in plant responses to gravity and touch

Touch and gravity are two of the many stimuli that plants must integrate to generate an appropriate growth response. Due to the mechanical nature of both of these signals, shared signal transduction elements could well form the basis of the cross-talk between these two sensory systems. However, touch stimulation must elicit signaling events across the plasma membrane whereas gravity sensing is thought to represent transformation of an internal force, amyloplast sedimentation, to signal transduction events. In addition, factors such as turgor pressure and presence of the cell wall may also place unique constraints on these plant mechanosensory systems. Even so, the candidate signal transduction elements in both plant touch and gravity sensing, changes in Ca2+, pH and membrane potential, do mirror the known ionic basis of signaling in animal mechanosensory cells. Distinct spatial and temporal signatures of Ca2+ ions may encode information about the different mechanosignaling stimuli. Signals such as Ca2+ waves or action potentials may also rapidly transfer information perceived in one cell throughout a tissue or organ leading to the systemic reactions characteristic of plant touch and gravity responses. Longer-term growth responses are likely sustained via changes in gene expression and asymmetries in compounds such as inositol-1,4,5-triphosphate (IP3) and calmodulin. Thus, it seems likely that plant mechanoperception involves both spatial and temporal encoding of information at all levels, from the cell to the whole plant. Defining this patterning will be a critical step towards understanding how plants integrate information from multiple mechanical stimuli to an appropriate growth response.

Review↗
NASA NTRS2001

Cellular and molecular mechanisms for the bone response to mechanical loading

To define the cellular and molecular mechanisms for the osteogenic response of bone to increased loading, several key steps must be defined: sensing of the mechanical signal by cells in bone, transduction of the mechanical signal to a biochemical one, and transmission of that biochemical signal to effector cells. Osteocytes are likely to serve as sensors of loading, probably via interstitial fluid flow produced during loading. Evidence is presented for the role of integrins, the cell's actin cytoskeleton, G proteins, and various intracellular signaling pathways in transducing that mechanical signal to a biochemical one. Nitric oxide, prostaglandins, and insulin-like growth factors all play important roles in these pathways. There is growing evidence for modulation of these mechanotransduction steps by endocrine factors, particularly parathyroid hormone and estrogen. The efficiency of this process is also impaired in the aged animal, yet what remains undefined is at what step mechanotransduction is affected.

Review↗
NASA NTRS2002

Mechanotransduction: all signals point to cytoskeleton, matrix, and integrins

Mechanical stresses modulate cell function by either activating or tuning signal transduction pathways. Mechanotransduction, the process by which cells convert mechanical stimuli into a chemical response, occurs both in cells specialized for sensing mechanical cues and in parenchymal cells whose primary function is not mechanosensory. However, common among the various responses to mechanical stress is the importance of direct or indirect connections between the internal cytoskeleton, the extracellular matrix (ECM), and traditional signal transducing molecules. In many instances, these elements converge at focal adhesions, sites of structural attachment between the cytoskeleton and ECM that are anchored by cell surface integrin receptors. Alenghat and Ingber discuss the accumulating evidence for the central role of cytoskeleton, ECM, and integrin-anchored focal adhesions in several mechanotransduction pathways.

Review, Tutorial↗
NASA NTRS2000

Mechanisms of the early phases of plant gravitropism

Gravitropism is directed growth of a plant or plant organ in response to gravity and can be divided into the following temporal sequence: perception, transduction, and response. This article is a review of the research on the early events of gravitropism (i.e., phenomena associated with the perception and transduction phases). The two major hypotheses for graviperception are the protoplast-pressure and starch-statolith models. While most researchers support the concept of statoliths, there are suggestions that plants have multiple mechanisms of perception. Evidence supports the hypothesis that the actin cytoskeleton is involved in graviperception/transduction, but the details of these mechanisms remain elusive. A number of recent developments, such as increased use of the molecular genetic approach, magnetophoresis, and laser ablation, have facilitated research in graviperception and have allowed for refinement of the current models. In addition, the entire continuum of acceleration forces from hypo- to hyper-gravity have been useful in studying perception mechanisms. Future interdisciplinary molecular approaches and the availability of sophisticated laboratories on the International Space Station should help to develop new insights into mechanisms of gravitropism in plants.

NASA Discipline Plant Biology↗
NASA NTRS1999

Novel optical methodologies in studying mechanical signal transduction in mammalian cells

For the last 3 decades evidence has been accumulating that some types of mammalian cells respond to their mechanically active environment by altering their morphology, growth rate, and metabolism. The study of such responses is very important in understanding, physiological and pathological conditions ranging from bone formation to atherosclerosis. Obtaining this knowledge has been the goal for an active research area in bioengineering termed cell mechanotransduction. The advancement of optical methodologies used in cell biology research has given the tools to elucidate cellular mechanisms that would otherwise be impossible to visualize. Combined with molecular biology techniques, they give engineers invaluable tools in understanding the chemical pathways involved in mechanotransduction. Herein we briefly review the current knowledge on mechanical signal transduction in mammalian cells, focusing on the application of novel optical techniques in the ongoing research.

NASA Discipline Cell Biology↗
NASA NTRS2000

Ceratopteris richardii: a productive model for revealing secrets of signaling and development

Ceratopteris richardii is an aquatic fern grown in tropical and subtropical regions of the world. It is proven to be a productive model system for studies in the genetics, biochemistry, and cell biology of basic biologic processes that occur in early gametophytic development. It provides several advantages to biologists, especially those interested in gravitational biology, polarity development, and in the genetics of sexual development. It is easy to culture, has a relatively short life cycle, and offers an array of attractive features that facilitate genetic studies. The germination and early development of large populations of genetically identical spores are easy to synchronize, and both the direction of polarity development and cell-level gravity responses can be measured and readily manipulated within the first 24 h of spore development. Although there is no reliable transformation system available yet in Ceratopteris, recent studies suggest that the technique of RNA interference can be used to block translation of specific genes in a related fern, Marsilea, and current studies will soon reveal the applicability of this approach, as well as of other transformation approaches, in Ceratopteris. A recently completed expressed sequence tag (EST) sequencing project makes available the partial sequence of more than 2000 cDNAs, representing a significant percentage of the genes being expressed during the first 24 h of spore germination, when many developmentally interesting processes are occurring. A microarray of these ESTs is being constructed, so especially for those scientists interested in basic cellular phenomena that occur early in spore germination, the availability of the ESTs and of the microarray will make Ceratopteris an even more attractive model system.

NASA Discipline Plant Biology↗
NASA NTRS2001

Optimal firing rate estimation

We define a measure for evaluating the quality of a predictive model of the behavior of a spiking neuron. This measure, information gain per spike (Is), indicates how much more information is provided by the model than if the prediction were made by specifying the neuron's average firing rate over the same time period. We apply a maximum Is criterion to optimize the performance of Gaussian smoothing filters for estimating neural firing rates. With data from bullfrog vestibular semicircular canal neurons and data from simulated integrate-and-fire neurons, the optimal bandwidth for firing rate estimation is typically similar to the average firing rate. Precise timing and average rate models are limiting cases that perform poorly. We estimate that bullfrog semicircular canal sensory neurons transmit in the order of 1 bit of stimulus-related information per spike.

NASA Discipline Neuroscience↗
NASA NTRS2001

Time course of the MAPK and PI3-kinase response within 24 h of skeletal muscle overload

Knowledge of the molecular mechanisms by which skeletal muscle hypertrophies in response to increased mechanical loading may lead to the discovery of novel treatment strategies for muscle wasting and frailty. To gain insight into potential early signaling mechanisms associated with skeletal muscle hypertrophy, the temporal pattern of mitogen-activated protein kinase (MAPK) phosphorylation and phosphatidylinositol 3-kinase (PI3-kinase) activity during the first 24 h of muscle overload was determined in the rat slow-twitch soleus and fast-twitch plantaris muscles after ablation of the gastrocnemius muscle. p38alpha MAPK phosphorylation was elevated for the entire 24-h overload period in both muscles. In contrast, Erk 2 and p54 JNK phosphorylation were transiently increased by overload, returning to the levels of sham-operated controls by 24 h. PI3-kinase activity was increased by muscle overload only at 12 h of overload and only in the plantaris muscle. In summary, sustained elevation of p38alpha MAPK phosphorylation occurred early in response to muscle overload, identifying this pathway as a potential candidate for mediating early hypertrophic signals in response to skeletal muscle overload.

Non-NASA Center↗
NASA NTRS1997

Intracellular pH changes in human aortic smooth muscle cells in response to fluid shear stress

The smooth muscle cell (SMC) layers of human arteries may be exposed to blood flow after endothelium denudation, for example, following balloon angioplasty treatment. These SMCs are also constantly subjected to pressure driven transmural fluid flow. Flow-induced shear stress can alter SMC growth and metabolism. Signal transduction mechanisms involved in these flow effects on SMCs are still poorly understood. In this work, the hypothesis that shear stress alters the intracellular pH (pHi) of SMC is examined. When exposed to venous and arterial levels of shear stress, human aortic smooth muscle cells (hASMC) undergo alkalinization. The alkalinization plateau persisted even after 20 min of cell exposure to flow. Addition of amiloride (10 micromoles) or its 5-(N-ethyl-N-isopropyl) analog (EIPA, 10 micromoles), both Na+/H+ exchanger inhibitors, attenuated intracellular alkalinization, suggesting the involvement of the Na+/H+ exchanger in this response. The same concentrations of these inhibitors did not show an effect on pHi of hASMCs in static culture. 4-Acetamido-4'-isothio-cyanatostilbene-2,2'-disulfonic acid (SITS, 1 mM), a Cl-/HCO3- exchange inhibitor, affected the pHi of hASMCs both in static and flow conditions. Our results suggest that flow may perturb the Na+/H+ exchanger leading to an alkalinization of hASMCs, a different response from the flow-induced acidification seen with endothelial cells at the same levels of shear stress. Understanding the flow-induced signal transduction pathways in the vascular cells is of great importance in the tissue engineering of vascular grafts. In the case of SMCs, the involvement of pHi changes in nitric oxide production and proliferation regulation highlights further the significance of such studies.

NASA Discipline Cell Biology↗
NASA NTRS2000

Diversity and regulation of plant Ca2+ pumps: insights from expression in yeast

The spatial and temporal regulation of calcium concentration in plant cells depends on the coordinate activities of channels and active transporters located on different organelles and membranes. Several Ca2+ pumps have been identified and characterized by functional expression of plant genes in a yeast mutant (K616). This expression system has opened the way to a genetic and biochemical characterization of the regulatory and catalytic features of diverse Ca2+ pumps. Plant Ca(2+)-ATPases fall into two major types: AtECA1 represents one of four or more members of the type IIA (ER-type) Ca(2+)-ATPases in Arabidopsis, and AtACA2 is one of seven or more members of the type IIB (PM-type) Ca(2+)-ATPases that are regulated by a novel amino terminal domain. Type IIB pumps are widely distributed on membranes, including the PM (plasma membrane), vacuole, and ER (endoplasmic reticulum). The regulatory domain serves multiple functions, including autoinhibition, calmodulin binding, and sites for modification by phosphorylation. This domain, however, is considerably diverse among several type IIB ATPases, suggesting that the pumps are differentially regulated. Understanding of Ca2+ transporters at the molecular level is providing insights into their roles in signaling networks and in regulating fundamental processes of cell biology.

Review, Academic↗
NASA NTRS1992

Characterization of GTP binding and hydrolysis in plasma membranes of zucchini

We have investigated the possibility that G-protein-like entities may be present in the plasma membrane (PM) of zucchini (Cucurbita pepo L.) hypocotyls by examining a number of criteria common to animal and yeast G-proteins. The GTP binding and hydrolysis characteristics of purified zucchini PM are similar to the characteristics of a number of known G-proteins. Our results demonstrate GTP binding to a single PM site having a Kd value between 16-31 nM. This binding has a high specificity for guanine nucleotides, and is stimulated by Mg2+, detergents, and fluoride or aluminium ions. The GTPase activity (Km = 0.49 micromole) of zucchini PM shows a sensitivity to NaF similar to that seen for other G-proteins. Localization of GTP mu 35S binding to nitrocellulose blots of proteins separated by SDS-PAGE indicates a 30-kDa protein as the predominant GTP-binding species in zucchini PM. Taken together, these data indicate that plant PM contains proteins which are biochemically similar to previously characterized G-proteins.

NASA Discipline Plant Biology↗
NASA NTRS1993

Phytochrome regulates GTP-binding protein activity in the envelope of pea nuclei

Three GTP-binding proteins with apparent molecular masses of 27, 28 and 30 kDa have been detected in isolated nuclei of etiolated pea plumules. After LDS-PAGE and transfer to nitrocellulose these proteins bind [32P]GTP in the presence of excess ATP, suggesting that they are monomeric G proteins. When nuclei are disrupted, three proteins co-purify with the nuclear envelope fraction and are highly enriched in this fraction. The level of [32P]GTP-binding for all three protein bands is significantly increased when harvested pea plumules are irradiated by red light, and this effect is reversed by far-red light. The results indicate that GTP-binding activity associated with the nuclear envelope of plant cells is photoreversibly regulated by the pigment phytochrome.

NASA Discipline Plant Biology↗
NASA NTRS1996

Covisualization by computational optical-sectioning microscopy of integrin and associated proteins at the cell membrane of living onion protoplasts

Using higher-resolution wide-field computational optical-sectioning fluorescence microscopy, the distribution of antigens recognized by antibodies against animal beta 1 integrin, fibronectin, and vitronectin has been visualized at the outer surface of enzymatically protoplasted onion epidermis cells and in depectinated cell wall fragments. On the protoplast all three antigens are colocalized in an array of small spots, as seen in raw images, in Gaussian filtered images, and in images restored by two different algorithms. Fibronectin and vitronectin but not beta 1 integrin antigenicities colocalize as puncta in comparably prepared and processed images of the wall fragments. Several control visualizations suggest considerable specifity of antibody recognition. Affinity purification of onion cell extract with the same anti-integrin used for visualization has yielded protein that separates in SDS-PAGE into two bands of about 105-110 and 115-125 kDa. These bands are again recognized by the visualization antibody, which was raised against the extracellular domain of chicken beta 1 integrin, and are also recognized by an antibody against the intracellular domain of chicken beta 1 integrin. Because beta 1 integrin is a key protein in numerous animal adhesion sites, it appears that the punctate distribution of this protein in the cell membranes of onion epidermis represents the adhesion sites long known to occur in cells of this tissue. Because vitronectin and fibronection are matrix proteins that bind to integrin in animals, the punctate occurrence of antigenically similar proteins both in the wall (matrix) and on enzymatically prepared protoplasts reinforces the concept that onion cells have adhesion sites with some similarity to certain kinds of adhesion sites in animals.

NASA Discipline Plant Biology↗
NASA NTRS1989

The use of bioelectric currents to study gravity perception in roots

Inhibitor-based studies of gravity perception in plants have yielded ambiguous results because gravitropism consists of many steps in series. Inhibiting any step eliminates gravicurvature; it cannot be shown whether gravity perception and transduction are affected by the inhibitory treatment. The use of the vibrating probe has allowed detection of a response that is measurable independent of stimulus transmission and growth, two post-transduction steps of gravitropism. This application of the vibrating probe requires particular attention to artifacts. Calmodulin action and auxin transport are both believed to be components of gravitropism and specific roles have been proposed for them in graviperception. The perception-dependent current measured with the vibrating probe is eliminated by inhibitors of calmodulin, but not by auxin inhibitors. Thus, the vibrating probe has made it possible to offer more direct evidence for a role of calmodulin in transduction, and to reject one for auxin transport in perception and transduction.

Non-NASA Center↗
NASA NTRS1998

Mechanotransduction molecules in the plant gravisensory response: amyloplast/statolith membranes contain a beta 1 integrin-like protein

It has been hypothesized that the sedimentation of amyloplasts within root cap cells is the primary event in the plant gravisensory-signal transduction cascade. Statolith sedimentation, with its ability to generate weighty mechanical signals, is a legitimate means for organisms to discriminate the direction of the gravity vector. However, it has been demonstrated that starchless mutants with reduced statolith densities maintain some ability to sense gravity, calling into question the statolith sedimentation hypothesis. Here we report on the presence of a beta 1 integrin-like protein localized inside amyloplasts of tobacco NT-1 suspension culture, callus cells, and whole-root caps. Two different antibodies to the beta 1 integrin, one to the cytoplasmic domain and one to the extracellular domain, localize in the vicinity of the starch grains within amyloplasts of NT-1. Biochemical data reveals a 110-kDa protein immunoprecipitated from membrane fractions of NT-1 suspension culture indicating size homology to known beta 1 integrin in animals. This study provides the first direct evidence for the possibility of integrin-mediated signal transduction in the perception of gravity by higher plants. An integrin-mediated pathway, initiated by starch grain sedimentation within the amyloplast, may provide the signal amplification necessary to explain the gravitropic response in starch-depleted cultivars.

NASA Discipline Plant Biology↗