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Results for “spatiotemporal coupling”

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PubMed2025

Spatiotemporally resolved GPCR interactome uncovers unique mediators of receptor agonism.

Cellular signaling by membrane G protein-coupled receptors (GPCRs) is governed by a complex and diverse array of mechanisms. The dynamics of a GPCR interactome, as it evolves over time and space in response to an agonist, provide a unique perspective on pleiotropic signaling decoding and functional selectivity at the cellular level. In this study, we utilized proximity-based APEX2 proteomics to investigate the interaction network of the luteinizing hormone receptor (LHR) on a minute-to-minute timescale. We developed an analytical approach that integrates quantitative multiplexed proteomics with temporal reference profiles, creating a platform to identify the proteomic environment of APEX2-tagged LHR at the nanometer scale. LHR activity is finely regulated spatially, leading to the identification of putative interactors, including the Ras-related GTPase RAP2B, which modulate both receptor signaling and post-endocytic trafficking. This work provides a valuable resource for spatiotemporal nanodomain mapping of LHR interactors across subcellular compartments.

Humans↗

PubMed2003

Perinuclear localization of cytosolic phospholipase A(2)alpha is important but not obligatory for coupling with cyclooxygenases.

In response to Ca(2+) signaling, cytosolic phospholipase A(2)alpha (cPLA(2)alpha) translocates from the cytosol to the perinuclear membrane, where downstream eicosanoid-synthetic enzymes, such as cyclooxygenase (COX), are localized. Although the spatiotemporal perinuclear colocalization of cPLA(2)alpha and COXs has been proposed to be critical for their functional coupling leading to prostanoid production, definitive evidence for this paradigm has remained elusive. To circumstantiate this issue, we took advantage of a chimeric cPLA(2)alpha mutant harboring the C2 domain of protein kinase Calpha, which translocates to the plasma membrane following cell activation. Transfection analyses of the native or chimeric cPLA(2)alpha in combination with COX-1 or COX-2 revealed that, even though the arachidonate-releasing capacities of native and mutant cPLA(2)alpha were comparable, prostaglandin production by mutant cPLA(2)alpha was markedly impaired as compared with that by native cPLA(2)alpha. We thus conclude that the perinuclear localization of cPLA(2)alpha is preferential, even if not obligatory, for efficient coupling with COXs.

Cell Line↗

PubMed1995

EMG activation patterns during force production in precision grip. II. Muscular synergies in the spatial and temporal domain.

Electromyographic (EMG) activity was analyzed for the occurrence of synergistic patterns during the steady hold periods of force in the precision grip. To establish the presence of muscle synergies in the amplitude (spatial) domain, the EMG activation levels of pairs of simultaneously active muscles were linearly correlated. Cross-correlations of EMG activity were computed to quantify muscle synergies in the spatiotemporal domain (synchronization). A muscle pair was defined to be synergistically coupled or synchronously activated when the correlation (amplitude domain) or cross-correlation (time domain) was significant for at least two of the three steady state force levels. Muscle synergies in the amplitude domain were found in one-third of the 213 muscle pairs tested, distributed among 47 of the 82 tested muscle combinations. Coactivation was the predominant synergistic pattern, whereas trade-off comprised not more than 23% of the synergies. Cross-correlation peak size varied between 5 and 39% of the autocorrelation size, with delays in the range of +/- 8 ms and base width between 12 and 20 ms. Synchronization was found in one-fourth of the 213 muscle pairs tested and among 35 of the 82 muscle combinations, i.e., less frequently than covariation of EMG activity levels. However, the interindividual prevalence was higher for synchronization than for synergies in the amplitude domain, since, for the synergistic muscle combinations, almost twice as many muscle pairs were found to be synchronized than coupled in the amplitude domain. Synergies in the two domains occurred independently in some pairs and concurrently in other cases, and were observed between muscles moving the thumb, the index finger, or both digits. Synchronization was more frequent in pairs of muscles supplied by branches of the same peripheral nerve (46%) than in those innervated by different nerves (18%). Synergies in the amplitude domain were distributed in similar proportions across intrinsic, extrinsic, and combinations of both types of muscles, whereas synchronization mainly occurred in pairs of intrinsic muscles. When the task was repeated with slightly lower target forces, there were fewer synergies in the amplitude domain (in 52 of the 213 pairs, distributed among 35 of 82 muscle combinations) and their distribution changed, indicating a flexible, force-dependent mechanism. In conclusion, no strictly coherent interindividual pattern of synergies in the spatial domain could be established.

Adult↗

PubMed2000

H19 RNA binds four molecules of insulin-like growth factor II mRNA-binding protein.

H19 RNA is a major oncofetal 2.5-kilobase untranslated RNA of unknown function. The maternally expressed H19 gene is located 90 kilobase pairs downstream from the paternally expressed insulin-like growth factor II (IGF-II) gene on human chromosome 11 and mouse chromosome 7; and due to their reciprocal imprinting and identical spatiotemporal expression, it is assumed that the two genes are functionally coupled. Here we show that human H19 RNA contains four attachment sites for the oncofetal IGF-II mRNA-binding protein (IMP) with apparent K(d) values in the 0.4-1.3 nm range. The multiple attachment sites are clustered within a 700-nucleotide segment encoded by exons 4 and 5. This 3'-terminal segment targets H19 RNA to lamellipodia and perinuclear regions in dispersed fibroblasts where IMP is also localized. The results suggest that IMP participates in H19 RNA localization and provides a link between the IGF-II and H19 genes at post-transcriptional events during mammalian development.

Animals↗

PubMed2004

Regulation of integrin-mediated cellular responses through assembly of a CAS/Crk scaffold.

The molecular coupling of CAS and Crk in response to integrin activation is an evolutionary conserved signaling module that controls cell proliferation, survival and migration. However, when deregulated, CAS/Crk signaling also contributes to cancer progression and developmental defects in humans. Here we highlight recent advances in our understanding of how CAS/Crk complexes assemble in cells to modulate the actin cytoskeleton, and the molecular mechanisms that regulate this process. We discuss in detail the spatiotemporal dynamics of CAS/Crk assembly and how this scaffold recruits specific effector proteins that couple integrin signaling networks to the migration machinery of cells. We also highlight the importance of CAS/Crk signaling in the dual regulation of cell migration and survival mechanisms that operate in invasive cells during development and pathological conditions associated with cancer metastasis.

Animals↗

PubMed2004

Quantitative imaging of single live cells reveals spatiotemporal dynamics of multistep signaling events of chemoattractant gradient sensing in Dictyostelium.

Activation of G-protein-coupled chemoattractant receptors triggers dissociation of Galpha and Gbetagamma subunits. These subunits induce intracellular responses that can be highly polarized when a cell experiences a gradient of chemoattractant. Exactly how a cell achieves this amplified signal polarization is still not well understood. Here, we quantitatively measure temporal and spatial changes of receptor occupancy, G-protein activation by FRET imaging, and PIP3 levels by monitoring the dynamics of PH(Crac)-GFP translocation in single living cells in response to different chemoattractant fields. Our results provided the first direct evidence that G-proteins are activated to different extents on the cell surface in response to asymmetrical stimulations. A stronger, uniformly applied stimulation triggers not only a stronger G-protein activation but also a faster adaptation of downstream responses. When naive cells (which have not experienced chemoattractant) were abruptly exposed to stable cAMP gradients, G-proteins were persistently activated throughout the entire cell surface, whereas the response of PH(Crac)-GFP translocation surprisingly consisted of two phases, an initial transient and asymmetrical translocation around the cell membrane, followed by a second phase producing a highly polarized distribution of PH(Crac)-GFP. We propose a revised model of gradient sensing, suggesting an important role for locally controlled components that inhibit PI3Kinase activity.

Animals↗

PubMed2002

Chaos-based secure communications in a large community.

One-way coupled map lattices are used for cryptography in secure communication, based on spatiotemporal chaos synchronization. The sensitivity of synchronization between the encryption and decryption systems can be adjusted by varying the system size. With a suitable parameter combination, the cryptosystem can reach optimal trade-off of security and performance, i.e., it shows high security (resistant against the public-structure and known-plaintext attacks) together with fast encryption (and decryption) speed. An experiment of duplex voice transmission through university network is realized, which confirms the above advantages of our approach.

Journal Article↗

PubMed2002

Dynamic approximation of spatiotemporal receptive fields in nonlinear neural field models.

This article presents an approximation method to reduce the spatiotemporal behavior of localized activation peaks (also called "bumps") in non-linear neural field equations to a set of coupled ordinary differential equations (ODEs) for only the amplitudes and tuning widths of these peaks. This enables a simplified analysis of steady-state receptive fields and their stability, as well as spatiotemporal point spread functions and dynamic tuning properties. A lowest-order approximation for peak amplitudes alone shows that much of the well-studied behavior of small neural systems (e.g., the Wilson-Cowan oscillator) should carry over to localized solutions in neural fields. Full spatiotemporal response profiles can further be reconstructed from this low-dimensional approximation. The method is applied to two standard neural field models: a one-layer model with difference-of-gaussians connectivity kernel and a two-layer excitatory-inhibitory network. Similar models have been previously employed in numerical studies addressing orientation tuning of cortical simple cells. Explicit formulas for tuning properties, instabilities, and oscillation frequencies are given, and exemplary spatiotemporal response functions, reconstructed from the low-dimensional approximation, are compared with full network simulations.

Animals↗

PubMed2000

Coherence resonance and noise-induced synchronization in globally coupled Hodgkin-Huxley neurons.

The coherence resonance (CR) of globally coupled Hodgkin-Huxley neurons is studied. When the neurons are set in the subthreshold regime near the firing threshold, the additive noise induces limit cycles. The coherence of the system is optimized by the noise. The coupling of the network can enhance CR in two different ways. In particular, when the coupling is strong enough, the synchronization of the system is induced and optimized by the noise. This synchronization leads to a high and wide plateau in the local CR curve. A bell-shaped curve is found for the peak height of power spectra of the spike train, being significantly different from a monotonic behavior for the single neuron. The local-noise-induced limit cycle can evolve to a refined spatiotemporal order through the dynamical optimization among the autonomous oscillation of an individual neuron, the coupling of the network, and the local noise.

Animals↗

PubMed2002

The dynamics of interlip coupling in speakers with a repaired unilateral cleft-lip history.

In this paper, data are presented on individual movement characteristics of the upper and lower lip and on interlip coordination in speakers with a repaired unilateral cleft upper lip history and age-matched control participants. The data were acquired using the AG100 EMMA system while the participants produced a selection of nonspeech and speech tasks. The participants with a repaired unilateral cleft upper lip history showed reduced upper-lip movement ranges and peak velocities and a more variable spatiotemporal pattern for individual upper-lip movement cycles, in addition to a more variable interlip coupling. The latter difference also proved to be more pronounced for the younger speakers with a repaired cleft upper lip. Overall, for both groups, the linguistically more complex task showed more variability in the individual upper- and lower-lip movement cycles and their coupling. In the discussion, we address the potential relationships between the kinematic data for upper lip in the repaired-cleft-lip speakers and the findings on movement and coordination stability as they might fit within current notions of coordination dynamics theory.

Adolescent↗

PubMed1992

Nonequilibrium dynamics in lattice ecosystems: Chaotic stability and dissipative structures.

A generalized coupled map lattice (CML) model of ecosystem dynamics is presented. We consider the spatiotemporal behavior of a prey-predator map, a model of host-parasitoid interactions, and two-species competition. The latter model can show phase separation of domains (Turing-like structures) even when chaos is present. We also use this CML model to explore the time evolution and structural properties of ecological networks built with a set of N competing species. The May-Wigner criterion is applied as a measure of stability, and some regularities in the stable networks observed are discussed.

Journal Article↗

PubMed1995

Partial inhibition of Ca2+ current by methoxyverapamil (D600) reveals spatial nonuniformities in [Ca2+]i during excitation-contraction coupling in cardiac myocytes.

The laser scanning confocal microscope was used in conjunction with the Ca2+ indicator fluo 3 to examine the spatiotemporal properties of free Ca2+ ([Ca2+]i) transients in isolated rat cardiac myocytes. We show that localized increases in [Ca2+]i (Ca2+ sparks) can be triggered by membrane depolarization in cardiac myocytes when the sarcolemmal Ca2+ current amplitude is reduced by methoxyverapamil (D600). These depolarization-evoked Ca2+ sparks are similar in amplitude and spatiotemporal properties to spontaneous Ca2+ sparks previously observed at rest. These observations support the idea that Ca2+ sparks are the result of the activation of functional elementary units of sarcoplasmic reticulum (SR) Ca2+ release. The synchronous activation of a large number of Ca2+ sparks can explain the increased amplitude and slower time course of the electrically evoked [Ca2+]i transient as well as the presence of spatial nonuniformities in [Ca2+]i during its rise. The data shown here suggest a model for excitation-contraction coupling in which the amplitude of the [Ca2+]i transient is regulated by variations in the probability of recruitment of elementary SR Ca2+ release units as well as the amount of Ca2+ released by each unit. Since the activation of each release unit will depend on the local amplitude of the Ca2+ current, this model can explain the regulation of the amplitude of the [Ca2+]i transient by the Ca2+ current. In addition, these data indicate that caution should be applied to the interpretation of signals obtained with nonlinear Ca2+ indicators during the rising phase of the [Ca2+]i transient, when the nonuniformities in [Ca2+]i are largest.

Animals↗

PubMed1984

A quantitative analysis of interactions between photoreceptors in the salamander (Ambystoma) retina.

A quantitative description of the electrical properties of the photoreceptor layer in the salamander retina was obtained from earlier data on the characteristics of isolated rods and cones and on rod-rod coupling, and from new data on rod-cone and cone-cone coupling and on the rod photocurrent. Injecting -1 nA current into a rod elicits hyperpolarizations of about 20 mV in an adjacent rod and 4 mV in an adjacent cone. Responses of more distant receptors are smaller. Injecting -1 nA into a cone elicits hyperpolarizations of about 4 mV in an adjacent rod and 0.4 mV in a nearby cone. Depolarizing current evokes smaller responses. Assuming, in agreement with anatomical evidence, that each rod is electrically coupled to four rods and to four cones around it, and that there is no direct electrical coupling between cones, we found these results could be predicted from the properties of isolated rods and cones if adjacent rods are coupled by a resistance of 300 M omega and adjacent rods and cones are coupled by a resistance of 5000 M omega. The small cone-cone coupling seen is due to coupling via intervening rods. The two halves of double cones are not electrically coupled. The spectral sensitivity of both halves is a maximum around 620 nm wave-length. The rod photocurrent has been characterized by voltage-clamping rods isolated from the retina. In agreement with Bader, MacLeish & Schwartz (1979) we found the time course of the photocurrent to be approximately independent of voltage between -35 and -85 mV. The voltage responses of rods, single cones and double cones isolated from the retina obey the principle of univariance. Responses of receptors in the retina do not obey univariance. The main deviations from univariance observed can be explained if adjacent rods and cones are coupled by a resistance of 5000 M omega. Our data demonstrate that rod-cone coupling is relatively weak. We simplified our description of the photoreceptor network, by omitting cones, to investigate the spatiotemporal processing that the rod network is capable of. Computer simulations predict, as is found experimentally, that the rod voltage response to a large spot of bright light should show a much more pronounced initial transient hyperpolarization than the response to a small spot of light of the same intensity. This difference is produced by the combination of electrical coupling of the rods with the existence of a voltage-gated current, IA, in the rod membrane.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗

PubMed2001

Invited review: arteriolar smooth muscle mechanotransduction: Ca(2+) signaling pathways underlying myogenic reactivity.

The smooth muscle of arterioles responds to an increase in intraluminal pressure with vasoconstriction and with vasodilation when pressure is decreased. Such myogenic vasoconstriction provides a level of basal tone that enables arterioles to appropriately adjust diameter in response to neurohumoral stimuli. Key in this process of mechanotransduction is the role of changes in intracellular Ca(2+). However, it is becoming clear that considerable complexity exists in the spatiotemporal characteristics of the Ca(2+) signal and that changes in intracellular Ca(2+) may play roles other than direct effects on the contractile process via activation of myosin light-chain phosphorylation. The involvement of Ca(2+) may extend to modulation of ion channels and release of Ca(2+) from the sarcoplasmic reticulum, alterations in Ca(2+) sensitivity, and coupling between cells within the vessel wall. The purpose of this brief review is to summarize the current literature relating to Ca(2+) and the arteriolar myogenic response. Consideration is given to coupling of Ca(2+) changes to the mechanical stimuli, sources of Ca(2+), involvement of ion channels, and spatiotemporal aspects of intracellular Ca(2+) signaling.

Animals↗

PubMed1995

Interpreting photoactivated fluorescence microscopy measurements of steady-state actin dynamics.

A continuum model describing the steady-state actin dynamics of the cytoskeleton of living cells has been developed to aid in the interpretation of photoactivated fluorescence experiments. In a simplified cell geometry, the model assumes uniform concentrations of cytosolic and cytoskeletal actin throughout the cell and no net growth of either pool. The spatiotemporal evolution of the fluorescent actin population is described by a system of two coupled linear partial-differential equations. An analytical solution is found using a Fourier-Laplace transform and important limiting cases relevant to the design of experiments are discussed. The results demonstrate that, despite being a complex function of the parameters, the fluorescence decay in photoactivated fluorescence experiments has a biphasic behavior featuring a short-term decay controlled by monomer diffusion and a long-term decay governed by the monomer exchange rate between the polymerized and unpolymerized actin pools. This biphasic behavior suggests a convenient mechanism for extracting the parameters governing the fluorescence decay from data records. These parameters include the actin monomer diffusion coefficient, filament turnover rate, and ratio of polymerized to unpolymerized actin.

Actins↗

PubMed2003

Strong spatiotemporal localization in a silica nonlinear waveguide array.

We investigate the propagation of short, intense laser pulses in arrays of coupled silica waveguides, in the anomalous dispersion regime. The nonlinearity induces trapping of the pulse in a single waveguide, over a wide range of input parameters. A sharp transition is observed for single waveguide excitation, from strong diffraction at low powers to strong localization at high powers.

Journal Article↗

PubMed2002

Bimanual circle drawing in children with spastic hemiparesis: effect of coupling modes on the performance of the impaired and unimpaired arms.

The present study examined the effect of interlimb coupling on the performance of the impaired and unimpaired arm in children with spastic hemiparesis during bimanual circle drawing. The following questions were addressed: (1) does coupling positively influence the performance of the impaired arm compared to single-hand performance and (2) is such an effect dependent on mode of coordination (i.e., symmetric versus asymmetric). Twelve children with spastic hemiparesis produced circle drawings on a digitizer under different task conditions. Spatiotemporal characteristics and quality of movement of pen trajectories of the individual limbs as well as interlimb relative phase were analysed. Coupling in a symmetric coordination mode resulted in a decrease of temporal variability and an increase of smoothness of circle drawing movements in the impaired arm compared to single-handed performance. Coupling in an asymmetric coordination mode resulted in an increase of spatial and temporal variability in the unimpaired arm. It is concluded that coupling may enhance the performance of the impaired arm in children with spastic hemiparesis, but only during symmetric bimanual coordination. A possible underlying neural mechanism that might explain these findings is discussed.

Adolescent↗

PubMed2002

On the mathematical integration of the nervous tissue based on the S-propagator formalism: II. Numerical simulations for molecular-dependent activity.

In a previous article (G. A. Chauvet, 2002), presenting a theoretical approach for integrating physiological functions in nervous tissue, we showed that a specific hierarchical representation, incorporating the novel concepts of non-symmetry and non-locality, and an appropriate formalism (the S-propagator formalism) could provide a good description of a living system in general, and the nervous system in particular. We now show that, in the framework of this theory, in spite of the complexity inherent to nervous tissue and the great number of elementary mechanisms involved, the numerical resolution of the global non-local system allows us to envisage simulations that would otherwise be impossible to realize. Here, the study is limited to one physiological function, i.e., the spatiotemporal variation of membrane potential in neuronal tissue. We demonstrate that the role of the kinetic constants at the molecular level is in agreement with the observed activity of the neuronal network. The method also reveals the critical role of the maximum density of synapses along the dendritic tree in the behavior of the network. This illustrates the great advantage of the theoretical approach in studying separately any other complementary coupled function without having to modify the computational methods used here. The application of this method to the spatiotemporal variation of synaptic efficacy, which is the basis of the learning and memory function, will be treated in a forthcoming paper.

Animals↗