The regulation of chemotaxis and chemokinesis in Dictyostelium amoebae by temporal signals and spatial gradients of cyclic AMP

1994 ◽  
Vol 107 (2) ◽  
pp. 659-667 ◽  
Author(s):  
M.G. Vicker
Keyword(s):  
Cyclic Amp ◽  
Molecular Diffusion ◽  
Gradient Field ◽  
Computer Assisted ◽  
Spatial Gradient ◽  
Spatial Gradients ◽  
Cell Accumulation ◽  
Initial Effect ◽  
Gradient Orientation ◽  
Infusion System

The tactic and kinetic locomotion of Dictyostelium discoideum amoebae were examined in cyclic AMP (cAMP) spatial gradient and temporal signal fields. The distributions of migrating cells were examined within 150 microns-thick micropore filters after incubation with different cAMP concentrations, [cAMP], applied in three ways across the fields: as positively or negatively developing gradients, generated either by increasing or decreasing the [cAMP] on one side of the filter, respectively, or as static, linear gradients after negative development. Chemotaxis was only induced by oriented, temporally increasing [cAMP]. Pulses propagated by molecular diffusion or mechanical flow were equally effective. Negatively developing cAMP gradients had no initial effect on cell accumulation. However, if the subsequent static spatial gradient was maintained by an infusion system, some gradients also induced cell accumulation, whose degree and direction depended on the gradient [cAMP]. The basis of this new effect was examined by tracking individual cells by computer-assisted videomicroscopy during locomotion in different [cAMP]. Cells produced a triphasic [cAMP]-dependent response, with optimal cell motility induced by 10–30 nM. The results demonstrate that cell accumulation either up-field or down-field in spatial gradients is governed by the field locations of the attractant concentrations that induce the relative locomotory maxima and minima in the gradient field. Cells perceive the ambient [cAMP], but cannot read the spatial gradient orientation in static or yet steeper regions of developing gradients. Accumulation in static spatial gradients is a function of klino- and orthokinesis, but chemotaxis requires an oriented cAMP pulse or impulse.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals RasC Plays a Role in Transduction of Temporal Gradient Information in the Cyclic-AMP Wave of Dictyostelium discoideum

2004 ◽  
Vol 3 (3) ◽  
pp. 646-662 ◽  
Author(s):  
Deborah Wessels ◽  
Rebecca Brincks ◽  
Spencer Kuhl ◽  
Vesna Stepanovic ◽  
Karla J. Daniels ◽  
...  
Keyword(s):  
Cyclic Amp ◽  
Myosin Ii ◽  
Three Dimensional ◽  
Computer Assisted ◽  
Expression Array ◽  
Temporal Gradient ◽  
Spatial Gradients ◽  
Quantitative Studies ◽  
Myosin I ◽  
The Individual

ABSTRACT To define the role that RasC plays in motility and chemotaxis, the behavior of a rasC null mutant, rasC −, in buffer and in response to the individual spatial, temporal, and concentration components of a natural cyclic AMP (cAMP) wave was analyzed by using computer-assisted two-dimensional and three-dimensional motion analysis systems. These quantitative studies revealed that rasC − cells translocate at the same velocity and exhibit chemotaxis up spatial gradients of cAMP with the same efficiency as control cells. However, rasC − cells exhibit defects in maintaining anterior-posterior polarity along the substratum and a single anterior pseudopod when translocating in buffer in the absence of an attractant. rasC − cells also exhibit defects in their responses to both the increasing and decreasing temporal gradients of cAMP in the front and the back of a wave. These defects result in the inability of rasC − cells to exhibit chemotaxis in a natural wave of cAMP. The inability to respond normally to temporal gradients of cAMP results in defects in the organization of the cytoskeleton, most notably in the failure of both F actin and myosin II to exit the cortex in response to the decreasing temporal gradient of cAMP in the back of the wave. While the behavioral defect in the front of the wave is similar to that of the myoA −/myoF − myosin I double mutant, the behavioral and cytoskeletal defects in the back of the wave are similar to those of the S13A myosin II regulatory light-chain phosphorylation mutant. Expression array data support the premise that the behavioral defects exhibited by the rasC − mutant are the immediate result of the absence of RasC function.

scholarly journals The Internal Phosphodiesterase RegA Is Essential for the Suppression of Lateral Pseudopods duringDictyosteliumChemotaxis

2000 ◽  
Vol 11 (8) ◽  
pp. 2803-2820 ◽  
Author(s):  
Deborah J. Wessels ◽  
Hui Zhang ◽  
Joshua Reynolds ◽  
Karla Daniels ◽  
Paul Heid ◽  
...  
Keyword(s):  
Mutant Cell ◽  
Computer Assisted ◽  
Spatial Gradient ◽  
Wild Type ◽  
Gene Encoding ◽  
Camp Phosphodiesterase ◽  
Temporal Gradient ◽  
Spatial Gradients ◽  
Normal Manner ◽  
Analysis System

Dictyostelium strains in which the gene encoding the cytoplasmic cAMP phosphodiesterase RegA is inactivated form small aggregates. This defect was corrected by introducing copies of the wild-type regA gene, indicating that the defect was solely the consequence of the loss of the phosphodiesterase. Using a computer-assisted motion analysis system,regA−mutant cells were found to show little sense of direction during aggregation. When labeled wild-type cells were followed in a field of aggregatingregA−cells, they also failed to move in an orderly direction, indicating that signaling was impaired in mutant cell cultures. However, when labeled regA−cells were followed in a field of aggregating wild-type cells, they again failed to move in an orderly manner, primarily in the deduced fronts of waves, indicating that the chemotactic response was also impaired. Since wild-type cells must assess both the increasing spatial gradient and the increasing temporal gradient of cAMP in the front of a natural wave, the behavior of regA−cells was motion analyzed first in simulated temporal waves in the absence of spatial gradients and then was analyzed in spatial gradients in the absence of temporal waves. Our results demonstrate that RegA is involved neither in assessing the direction of a spatial gradient of cAMP nor in distinguishing between increasing and decreasing temporal gradients of cAMP. However, RegA is essential for specifically suppressing lateral pseudopod formation during the response to an increasing temporal gradient of cAMP, a necessary component of natural chemotaxis. We discuss the possibility that RegA functions in a network that regulates myosin phosphorylation by controlling internal cAMP levels, and, in support of that hypothesis, we demonstrate that myosin II does not localize in a normal manner to the cortex ofregA−cells in an increasing temporal gradient of cAMP.

scholarly journals Chemoattraction and chemotaxis in Dictyostelium discoideum: myxamoeba cannot read spatial gradients of cyclic adenosine monophosphate.

1984 ◽  
Vol 98 (6) ◽  
pp. 2204-2214 ◽  
Author(s):  
M G Vicker ◽  
W Schill ◽  
K Drescher
Keyword(s):  
Cyclic Amp ◽  
Dictyostelium Discoideum ◽  
Random Distribution ◽  
Adenosine Monophosphate ◽  
Positional Information ◽  
Spatial Gradient ◽  
Cellular Slime Mold ◽  
Embryonic Cells ◽  
Directional Information ◽  
Spatial Gradients

Myxamoebae of the morphogenetic cellular slime mold Dictyostelium discoideum are thought to be able to accurately read and respond to directional information in spatial gradients of cyclic AMP. We examined the spatial and temporal mechanisms proposed for chemotaxis by comparing the behavior of spreading or evenly distributed cell populations after exposure to well-defined spatial gradients. The effects of gradient generation on cells were avoided by using predeveloped gradients. Qualitatively different responses were obtained using (a) isotropic, (b) static spatial, or (c) temporal (impulse) gradients in a simple chamber of penetrable micropore filters. We simulated models of chemotaxis and chemokinesis to aid our interpretations. The attractive and locomotory responses of populations were maximally stimulated by 0.05 microM cyclic AMP, provided that cellular phosphodiesterase was inhibited. But a single impulse of cyclic AMP during gradient development caused a greater and qualitatively different attraction. Attraction in spatial gradients was only transient, in that populations eventually developed a random distribution when confined to a narrow territory. Populations never accumulated nor lost their random distribution even in extremely steep spatial gradients. Attraction in spatial gradients was inducible only in spreading populations, not randomly distributed ones. Thus, spatial gradients effect biased-random locomotion: i.e., chemokinesis without adaptation. Cells cannot read gradients; the reaction of the cells is stochastic. Spatial gradients do not cause chemotaxis, which probably requires a sharp stimulant concentration increase (a temporal gradient) as a pulse or impulse. The results also bear on concepts of how embryonic cells might be able to decipher the positional information in a morphogen spatial gradient during development.

scholarly journals The unconventional myosin encoded by the myoA gene plays a role in Dictyostelium motility.

1993 ◽  
Vol 4 (2) ◽  
pp. 233-246 ◽  
Author(s):  
M A Titus ◽  
D Wessels ◽  
J A Spudich ◽  
D Soll
Keyword(s):  
Cyclic Amp ◽  
Gene Targeting ◽  
Gene Product ◽  
The Other ◽  
Computer Assisted ◽  
Spatial Gradient ◽  
Unconventional Myosin ◽  
Cellular Translocation ◽  
Src Homology 3 ◽  
Src Homology

The myoA gene of Dictyostelium is a member of a gene family of unconventional myosins. The myosin Is share homologous head and basic domains, but the myoA gene product lacks the glycine-, proline-, alanine-rich and src homology 3 domains typical of several of the other myosin Is. A mutant strain of Dictyostelium lacking a functional myoA gene was produced by gene targeting, and the motility of this strain in buffer and a spatial gradient of the chemoattractant cyclic AMP was analyzed by computer-assisted methods. The myoA- cells have a normal elongate morphology in buffer but exhibit a decrease in the instantaneous velocity of cellular translocation, an increase in the frequency of lateral pseudopod formation, and an increase in turning. In a spatial gradient, in which the frequency of pseudopod formation is depressed, myoA- cells exhibit positive chemotaxis but still turn several times more frequently than control cells. These results demonstrate that the other members of the unconventional myosin family do not fully compensate for the loss of functional myoA gene product. Surprisingly, the phenotype of the myoA- strain closely resembles that of the myoB- strain, suggesting that both play a role in the frequency of pseudopod formation and turning during cellular translocation.

scholarly journals Epidermal Growth Factor Receptor Distribution during Chemotactic Responses

2000 ◽  
Vol 11 (11) ◽  
pp. 3873-3883 ◽  
Author(s):  
Maryse Bailly ◽  
Jeffrey Wyckoff ◽  
Boumediene Bouzahzah ◽  
Ross Hammerman ◽  
Vonetta Sylvestre ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Growth Factor ◽  
Epidermal Growth Factor ◽  
Egf Receptor ◽  
Fluorescent Protein ◽  
Growth Factor Receptor ◽  
Spatial Gradient ◽  
Spatial Gradients ◽  
Epidermal Growth ◽  
Green Fluorescent

To determine the distribution of the epidermal growth factor (EGF) receptor (EGFR) on the surface of cells responding to EGF as a chemoattractant, an EGFR-green fluorescent protein chimera was expressed in the MTLn3 mammary carcinoma cell line. The chimera was functional and easily visualized on the cell surface. In contrast to other studies indicating that the EGFR might be localized to certain regions of the plasma membrane, we found that the chimera is homogeneously distributed on the plasma membrane and becomes most concentrated in vesicles after endocytosis. In spatial gradients of EGF, endocytosed receptor accumulates on the upgradient side of the cell. Visualization of the binding of fluorescent EGF to cells reveals that the affinity properties of the receptor, together with its expression level on cells, can provide an initial amplification step in spatial gradient sensing.

scholarly journals Laser ultrasonic imaging of wavefield spatial gradients for damage detection

2020 ◽  
pp. 147592172095133
Author(s):  
Zihan Wu ◽  
See Yenn Chong ◽  
Michael D Todd
Keyword(s):  
Laser Scanning ◽  
Ultrasonic Imaging ◽  
Image Processing Technique ◽  
Spatial Gradient ◽  
Spatial Covariance ◽  
Laser Ultrasonic ◽  
Spatial Gradients ◽  
Orientation Map ◽  
Scanning Area ◽  
Damage Visualization

This article describes a new damage visualization method to investigate and analyze propagating guided Lamb waves using analyses of wavefield spatial gradients. A laser ultrasonic interrogation system was used to create full-field ultrasonic data measurements for ultrasonic wavefield imaging. The laser scanning process was performed based on both a raster scan and a circle scan. From the high-resolution wavefield data, a spatial gradient–based image processing technique was developed using gradient vectors to extract features sensitive to defects. Local impedance changes at the damaged area would result in a local distortion of the waveform which was captured and quantified by the variation of the gradient vectors in the scanning area as time evolves. Such variation was accumulated over time with a statistical threshold filter to generate a gradient-orientation map for damage visualization. The proposed algorithm was capable of producing distinctive damage patterns when tested experimentally on a 3-mm aluminum plate with multiple simultaneous simulated defects. Compared to conventional techniques like local wavenumber estimation, the generation of the accumulated orientation map involves no filtering process in the frequency or wavenumber domain, at the expense of more accurate shaping of the defect. A spatial covariance analysis was adopted to locate damage from the results as well as to evaluate the correlation between different kinds of defects. Combining the proposed approach with conventional laser ultrasonic imaging techniques enables a fast and robust damage identification and characterization process which requires lower computational burden and practical operation.

Differential Gene Expression of Endothelial Cells Under High Wall Shear Stress and Spatial Gradients

2010 ◽  
Author(s):  
Jennifer Dolan ◽  
Song Liu ◽  
Hui Meng ◽  
John Kolega
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Vessel Wall ◽  
Cerebral Aneurysms ◽  
In Vivo Studies ◽  
Spatial Gradient ◽  
Flow Acceleration ◽  
Spatial Gradients ◽  
Wall Shear

In both human and animal models, cerebral aneurysms tend to develop at the apices of bifurcations in the cerebral vasculature. Due to the focal nature of aneurysm development it has long been speculated that hemodynamics are an important factor in aneurysm susceptibility. The local hemodynamics of bifurcations are complex, being characterized by flow impingement causing a high frictional force on the vessel wall known as wall shear stress (WSS) and significant flow acceleration or deceleration, manifested as the positive or negative spatial gradient of WSS (WSSG). In vivo studies have recently identified that aneurysm initiation occurs at areas of the vessel wall that experience a combination of both high WSS and positive WSSG [1,2]

scholarly journals Spatial variations in snowpack chemistry and isotopic composition of NO<sub>3</sub><sup>−</sup> along a nitrogen deposition gradient in West Greenland

2017 ◽  
Author(s):  
Chris J. Curtis ◽  
Jan Kaiser ◽  
Alina Marca ◽  
N. John Anderson ◽  
Gavin Simpson ◽  
...  
Keyword(s):  
Snow Water Equivalent ◽  
Ice Sheet ◽  
Central Area ◽  
Sea Salt ◽  
Spatial Gradient ◽  
Spatial Gradients ◽  
Free Region ◽  
Snow Water ◽  
Δ 15N ◽  
Deposition Gradient

Abstract. Snowpack chemistry, nitrate stable isotopes and net deposition fluxes for the largest ice-free region in Greenland were investigated to determine whether there are spatial gradients from the ice sheet margin to the coast linked to a gradient in precipitation. Late-season snowpack was sampled in March 2011 at 8 locations within 3 lake catchments in each of 3 regions (ice sheet margin in the east, central area near Kelly Ville and the coastal zone to the west). At the coast, snowpack accumulation averaged 181 mm snow water equivalent (SWE), compared with 36 mm SWE by the ice sheet. Coastal snowpack showed significantly greater concentrations of marine salts (Na+, Cl−, other major cations), ammonium (regional means 1.4–2.7 µmol L−1), total and non-sea salt sulfate (total 1.8–7.7, non-sea salt 1.0–1.8 µmol L−1) than the two inland regions. Nitrate (1.5–2.4 µmol L−1) showed significantly lower concentrations at the coast. Despite lower concentrations, higher precipitation at the coast results in a strong deposition gradient for NO3− as well as NH4+ and non-sea salt sulfate (nss-SO42−) increasing from the inland regions to the coast (lowest at Kelly Ville 6, 4 and 3; highest at coast 9, 17 and 11 mol ha−1 yr−1 of NO3−, NH4+ and nss-SO42− respectively). The δ(15N) of snowpack NO3− shows a significant decrease from the ice sheet margin (−7.5 ‰) to the coast (−11.3 ‰). We attribute the spatial gradient of δ(15N) in SW Greenland to post-deposition processing rather than differing sources because of (1) the climatic gradient from ice sheet margin to coast, (2) within-catchment isotopic differences between terrestrial snowpack and lake-ice snowpack, and (3) similarities between fresh snow (rather than accumulated snowpack) at Kelly Ville and the coast. Hence the δ(15N) of coastal snowpack is most representative of snowfall in SW Greenland, but after deposition the effects of photolysis, volatilization and sublimation lead to enrichment of the remaining snowpack with the greatest effect in inland areas of low precipitation and high sublimation losses.

scholarly journals Comment on Pescott & Jitlal 2020: Failure to account for measurement error undermines their conclusion of a weak impact of nitrogen deposition on plant species richness

2020 ◽  
Author(s):  
SM Smart ◽  
CJ Stevens ◽  
SJ Tomlinson ◽  
LC Maskell ◽  
PA Henrys
Keyword(s):  
Species Richness ◽  
Measurement Error ◽  
Plant Species ◽  
Large Scale ◽  
Plant Species Richness ◽  
N Deposition ◽  
Spatial Gradient ◽  
Spatial Gradients ◽  
Deposition Effect ◽  
Time Substitution

AbstractEstimation of the impacts of atmospheric nitrogen (N) deposition on ecosystems and biodiversity is a research imperative. Analyses of large-scale spatial gradients, where an observed response is correlated with measured or modelled deposition, have been an important source of evidence. A number of problems beset this approach. For example, if responses are spatially aggregated then treating each location as statistically independent can lead to biased confidence intervals and a greater probably of false positive results.Using sophisticated methods that account for residual spatial autocorrelation Pescott & Jitlal (2020) re-analysed two large-scale spatial gradient datasets from Britain where modelled N deposition at 5×5km resolution had been previously correlated with species richness in small quadrats. They found that N deposition effects were weaker than previously demonstrated leading them to conclude that “..previous estimates of Ndep impacts on richness from space-for-time substitution studies are likely to have been over-estimated”. We use a simple simulation study to show that their conclusion is flawed. They failed to recognise that an influential fraction of the residual spatially structured variation could itself be attributable to N deposition. This arises because the covariate used was modelled N deposition at 5×5km resolution leaving open the possibility that measured or modelled N deposition at finer resolutions could explain more variance in the response. Explicitly treating this as spatially auto-correlated error ignores this possibility and leads directly to their unreliable conclusion. We further demonstrate the plausibility of this scenario by showing that significant variation in N deposition at the 1km square resolution is indeed averaged at 5×5km resolution.Further analyses are required to explore whether estimation of the size of the N deposition effect on plant species richness and other measures of biodiversity is indeed dependent on the accuracy and hence measurement error of the N deposition covariate. Until then the conclusions of Pescott & Jitlal (2020) should be considered premature and not proven.

Numerical Studies of Injection Process Control With Spatial Gradients of Electrical Conductivity

2003 ◽  
Author(s):  
Liqing Ren ◽  
Dongqing Li
Keyword(s):  
Transport Phenomena ◽  
Glass Plate ◽  
Concentration Field ◽  
Lab On A Chip ◽  
Theoretical Models ◽  
Spatial Gradient ◽  
Precise Control ◽  
Spatial Gradients ◽  
Injection Process ◽  
Numerical Studies

The systematic design and precise control of the microfluidic dispenser (crossing microchannels etched into a plastic or glass plate) is key to the performance of many lab-on-a-chip devices. The fundamental understanding of the complicated electrokinetic phenomena in microfluidic dispensers therefore is necessary. In the literature, a few theoretical models studying the transport phenomena in similar crossing microchannels didn’t consider the spatial gradients of conductivity due to its complexity. A new theoretical model was developed in this paper to simulate the transport phenomena in a microfluidic dispenser with the consideration of a large range of spatial gradient of electric conductivity. This developed model was used to simulate the potential field, flow field, and concentration field of the injection processes where the conductivity of the sample-carrying buffer differs significantly from that of the driving buffer. The transport phenomena are found to be very sensitive to the conductivity difference between the sample-carrying buffer and the driving buffer. The developed model can be employed to find the optimal voltages for controlling the dispensed sample size and to provide guidance for designing such a microfluidic dispenser in lab-on-a-chip devices.

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