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Results for “Spatial pattern formation”

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At least 127 records · Page 7Linked to original sources

PubMed2006

Dynamics of precipitation pattern formation at geothermal hot springs.

We formulate and model the dynamics of spatial patterns arising during the precipitation of calcium carbonate from a supersaturated shallow water flow. The model describes the formation of travertine deposits at geothermal hot springs and rimstone dams of calcite in caves. We find explicit solutions for travertine domes at low flow rates, identify the linear instabilities which generate dam and pond formation on sloped substrates, and present simulations of statistical landscape evolution.

Journal Article↗

PubMed2000

A series of novel mutants of Arabidopsis thaliana that are defective in the formation of continuous vascular network: calling the auxin signal flow canalization hypothesis into question.

For the genetic analysis of molecular mechanisms underlying temporal and spatial regulation of vascular pattern formation, we isolated mutants of Arabidopsis thaliana that are impaired in vascular patterning. Microscopic examination of the cotyledonary venation of 3,400 M(3) lines led to the identification of 12 mutant lines. Genetic analysis of 8 of these mutant lines indicated that vein pattern formation in these lines resulted from monogenic recessive mutations in 7 different genes, designated VAN1 through VAN7. Mutations in VAN1 through VAN6 genes caused fragmentation (disconnection or partial loss) of lateral veins of the cotyledon and tertiary veins of the rosette leaf whereas they were less injurious to the formation of major veins. Detailed characterization of the van3 mutant using pAthb8::GUS and pTED3::GUS, as molecular markers for the early stage of vascular tissue formation showed that the provascular tissue of the cotyledonary lateral veins was differentiated in fragments during late embryogenesis. These phenotypes of the van mutants are discussed in relation to the auxin signal flow canalization hypothesis and the diffusion-reaction prepattern hypothesis, with the fragility of the continuity in the minor vein formation favoring the latter hypothesis.

Arabidopsis↗

PubMed1995

Spatial organization of transport domains and subdomain formation in the plasma membrane of Chara corallina.

Pattern formation mechanisms in developing organisms determine cellular differentiation and function. However, the components that interact during the manifestation of a spatial pattern are in general unknown. Characean algae represent a model system to study pattern formation. These algae develop alternating acid and alkaline transport domains that influence the pattern of growth. In the present study, it will be demonstrated that a diffusion mechanism is implicated in acid and alkaline domain formation and this growth pattern. Experiments on the characean growth pattern were performed that resulted in pronounced, however, unpredictable modifications in the original pattern. A major component involved in this pattern-forming mechanism emerged from the nonlinear kinetics of the H(+)-ATPase that is located in the plasma membrane of these algae. Based on these kinetics, a mathematical model was developed and numerically analyzed. As a result, the contribution of a diffusional component to the characean acid/alkaline pattern appeared most likely.

Biological Transport↗

PubMed1981

Central correlates of peripheral pattern alterations in the trigeminal system of the rat. II. The effect of nerve section.

The effect of trigeminal nerve section on pattern formation in the rat central nervous system was investigated. Nerve section was found to abolish all evidence of afferent segmentation in the brain stem. At thalamic and cortical levels the pattern of afferent segmentation was affected in a time-dependent fashion. The later the procedure is performed, the less severe the resultant effect. Early section abolishes all afferent segmentation, later section only within-row segmentation, and still later section has no effect on pattern formation. The results of this experiment support the hypothesis that peripheral spatial information plays an important role in pattern formation in the central trigeminal system.

Afferent Pathways↗

PubMed2001

Self-organized dynamics in spatially structured populations.

Self-organization and pattern formation represent the emergence of order in temporal and spatial processes. Self-organization in population ecology is gaining attention due to the recent advances concerning temporal fluctuations in the population size of dispersal-linked subunits. We shall report that spatially structured models of population renewal promote the emergence of a complex power law order in spatial population dynamics. We analyse a variety of population models showing that self-organization can be identified as a temporal match in population dynamics among local units, and how the synchrony changes in time. Our theoretical results are concordant with analyses of population data on the Canada lynx.

Animals↗

PubMed2005

Turing pattern formation in coupled reaction-diffusion system with distributed delays.

Turing pattern formation in coupled two-layer system with distributed delayed is investigated. Numerical simulations prove that, when the coupling is weak, it can apparently accelerate the formation process and enhance the spatial amplitude of the pattern. When it is strong, it will prolong the formation process or even inhibit the pattern and turn the whole system into bulk oscillatory state by its influence on the transient oscillatory state. If the coupling covers only part of the system, Turing pattern can be prominently oriented according to the shape of the coupling area at tiny coupling strength. However, if the coupling is too strong, the Turing pattern may also be destroyed. This means that in coupled systems, the delay effect in the cross-layer signal transfer may significantly influence the spatial character and/or the evolution dynamics in Turing pattern formation, even to destroy the pattern. This work is of practical significance in the study of Turing pattern in biosystems, where bilayer membranes or multilayer tissues are often found.

Chemistry, Physical↗

PubMed2006

Reversible pattern formation through photolysis.

We report a photolytic method to induce spatial and temporal patterning/deposition of particles at the micron scale on a time scale of seconds. Reversible pattern formation by negatively charged particles occur around micron-sized silver features on different substrates when exposed to UV light in the presence of aqueous hydrogen peroxide. Diffusiophoretic motion due to a spatially defined ion gradient accounts for our observations. Atomic force and optical microscopy, as well as conductivity measurements, support this hypothesis.

Journal Article↗

PubMed1993

Gap junction formation during development of the mouse lens.

We have identified a 60 kDa membrane protein (MP60) as a component of the mouse cortical lens fiber gap junction and a monoclonal antibody recognizing this protein has been used to establish the temporal and spatial patterns of gap junction formation during development of the mouse lens. The initial expression of MP60 during embryonic development of the mouse lens correlates with primary fiber elongation and is first seen on the luminal aspect of the extending cells. About 2 days after birth, the relatively large, antibody-positive macular structures characteristic of late embryonic fiber cells begin to disperse into progressively smaller structures within a centrally located region of the lens. This change in the staining pattern with antibody directed against MP60 is consistent with the dispersion of gap junction plaques as confirmed by freeze fracture analysis. Around 5 days after birth, the 60 kDa gap junctional protein in this central region of the lens undergoes a modification resulting in the alteration to the epitope for the monoclonal antibody and a consequent loss of immunorecognition. Our results suggest that gap junctions in the central region of the developing mouse lens undergo sequential changes in immunoreactivity which may reflect potentially distinct functional phases of intercellular communication.

Age Factors↗

PubMed2002

Three-dimensional distribution patterns of PRL, GH and ACTH cells in the house musk shrew ( Suncus murinus).

Despite a multitude of reports on the classification and distribution of anterior pituitary cells, no previous study has attempted to obtain the three-dimensional (3D) and computer-graphic distribution pattern of each cell type in the whole pituitary. Therefore, we mapped the anterior pituitary cells of the house musk shrew ( Suncus murinus) and found a distinct cellular distribution pattern. Serial horizontal sections of whole shrew pituitaries were stained immunohistochemically for prolactin (PRL), growth hormone (GH), and adrenocorticotropic hormone (ACTH) cells. The contours of positive cells and the anterior, intermediate, and posterior lobes in each section were digitized for 3D visualization by a volume rendering method. The reconstructed images and virtual frontal and sagittal slices were examined in detail. On the 3D reconstructed images, the PRL and GH cells had similar distribution patterns, although the former were concentrated in the dorsolateral and ventrocentral portions, and the latter in the dorsocentral portions of the anterior lobe. On both sides of the pituitary stalk, there lay portions that were conspicuous by scarcity of PRL and GH cells. ACTH cells were widely scattered throughout the whole anterior lobe, but they were very few in the above portions and the dorsocentral portions where GH cells were concentrated. No sex difference in the distribution patterns of each cell type was observed. However, PRL cells in females were more numerous than in males, whereas the opposite was true for GH and ACTH cells. We discuss the relationship between the formation of the spatial distribution patterns and anterior pituitary ontogeny.

Adrenocorticotropic Hormone↗

PubMed2005

Coupled-mode theory for photonic band-gap inhibition of spatial instabilities.

We study the inhibition of pattern formation in nonlinear optical systems using intracavity photonic crystals. We consider mean-field models for singly and doubly degenerate optical parametric oscillators. Analytical expressions for the new (higher) modulational thresholds and the size of the "band gap" as a function of the system and photonic crystal parameters are obtained via a coupled-mode theory. Then, by means of a nonlinear analysis, we derive amplitude equations for the unstable modes and find the stationary solutions above threshold. The form of the unstable mode is different in the lower and upper parts of the band gap. In each part there is bistability between two spatially shifted patterns. In large systems stable wall defects between the two solutions are formed and we provide analytical expressions for their shape. The analytical results are favorably compared with results obtained from the full system equations. Inhibition of pattern formation can be used to spatially control signal generation in the transverse plane.

Journal Article↗

PubMed2006

Experimental steady pattern formation in reaction-diffusion-advection systems.

We present here experimental evidence of a mechanism of a steady-chemical pattern formation called "flow-and-diffusion structures" (FDS). Experiments were performed using the photosensitive chlorine dioxide-iodine-malonic acid reaction, where the differential diffusion can be chemically controlled. Using the analogy between an advection boundary and a moving boundary, we obtain the formation of spatially periodic steady patterns, which matches all the previously theoretical predictions for FDS patterns. Numerical simulations are also reported in agreement with the experimental results.

Journal Article↗

PubMed2003

Medium scale spatial structures of Polycyclic Aromatic Hydrocarbons in the topsoil of Tianjin area.

The spatial distribution patterns of Polycyclic Aromatic Hydrocarbons (PAHs) in soil are important to regional environmental assessment. In this paper, the spatial structural features of sixteen prior PAH compounds in the topsoil of Tianjin area, as well as soil properties, were studied. Results shown that medium scale spatial autocorrelations were well revealed. Spherical models with sills could be used to fit all experimental variograms. The spatial structures of PAHs contents demonstrated significant anisotropy. Air precipitation caused by the combustion of coal was the key factor in the formation of the spatial structural patterns of PAHs in the topsoil of Tianjin area.

China↗

PubMed1986

Gene networks in development.

A model is presented for the formation of temporal and spatial patterns of cell types during the development of organisms. It is demonstrated that very simple random networks of interactions among genes that affect expression may lead to the autonomous development of patterns of cell types. It is required that the networks contain active feedback loops and that there is limited communication among cells. The only elements of the model, gene interactions, are specified by the DNA nucleotide sequences of the genes. Therefore, the model readily explains how the control of development is specified by the organism's DNA. In the context of this model, the formation of positional information and its interpretation becomes a single process.

Biological Evolution↗

PubMed2004

Wnt genes define distinct boundaries in the developing human brain: implications for human forebrain patterning.

Understanding the factors that govern human forebrain regionalization along the dorsal-ventral and left-right (L-R) axes is likely to be relevant to a wide variety of neurodevelopmental and neuropsychiatric conditions. Recent work in lower vertebrates has identified several critical signaling molecules involved in embryonic patterning along these axes. Among these are the Wingless-Int (WNT) proteins, involved in the formation of dorsal central nervous system (CNS) structures, as well as in visceral L-R asymmetry. We examined the expression of WNT2b and WNT7b in the human brain, because these genes have highly distinctive expression patterns in the embryonic mouse forebrain. In the human fetal telencephalon, WNT2b expression appears to define the cortical hem, a dorsal signaling center previously characterized in mouse, which is also confirmed by BMP7 expression. In diencephalon, WNT2b expression is restricted to medial dorsal structures, including the developing pineal gland and habenular nucleus, both implicated in CNS L-R asymmetry in lower organisms. At 5 weeks gestation, WNT7b is expressed in cerebral cortical and diencephalic progenitor cells. As the cortical plate develops, WNT7b expression shifts, demarcating deep layer neurons of the neocortex and the hippocampal formation. Spatial and temporal expression patterns show startling similarity between human and mouse, suggesting that the developmental roles of these WNT genes may be highly conserved, despite the far greater size and complexity of the human forebrain.

Animals↗

PubMed1988

Pattern formation in the facial primordia.

Pattern formation is the developmental process that leads to the spatial ordering of cell differentiation. We have explored the problem of pattern formation in the development of the face of chick embryos. At early stages, the developing face consists of a series of small buds of tissue, the facial primordia that encircle the primitive mouth. The concepts of positional information provide a framework for considering how the patterns of differentiated cells are generated in the face. We suggest that the cranial neural crest cells must first be informed to which facial primordium they belong and then of their position within that primordium. The cells of the early primordia appear indistinguishable. However, when the mesenchyme cells are placed in high-density culture, cartilage differentiates. The extent and pattern of cartilage differentiation is characteristic for the cell population of each facial primordium. Myogenic cells also differentiate in the cultures, but the proportion of myogenic cells is independent of the extent of chondrogenesis. Within the facial primordia, a set of epithelial-mesenchymal interactions appears to be required for outgrowth and pattern formation along the proximodistal axis of the chick beaks. In culture, face epithelium locally inhibits cartilage differentiation and suggests that another set of epithelial-mesenchymal interactions may be involved in cell patterning. The mechanisms involved in specifying the mediolateral axis of the face, for example, the midpoint of the upper beak, are not known. Vitamin A derivatives, collectively known as retinoids, affect the development of the face of chick embryos and lead to a specific facial defect. Upper beak development is inhibited but the lower beak develops normally. The response to retinoids could be related to the specification of cells to belong to the facial primordium that will form the upper beak. Alternatively, retinoids may interfere with positional cues that operate to inform cells of their position within that primordium.

Animals↗

PubMed2004

T-box transcription factor Tbx2 represses differentiation and formation of the cardiac chambers.

Specific regions of the embryonic heart tube differentiate into atrial and ventricular chamber myocardium, whereas the inflow tract, atrioventricular canal, inner curvatures, and outflow tract do not. These regions express Tbx2, a transcriptional repressor. Here, we tested its role in chamber formation. The temporal and spatial pattern of Tbx2 mRNA and protein expression in mouse hearts was found to be complementary to that of chamber myocardium-specific genes Nppa, Cx40, Cx43, and Chisel, and was conserved in human. In vitro, Tbx2 repressed the activity of regulatory fragments of Cx40, Cx43, and Nppa. Hearts of transgenic embryos that expressed Tbx2 in the prechamber myocardium completely failed to form chambers and to express the chamber myocardium-specific genes Nppa, Cx40, and Chisel, whereas other cardiac genes were normally expressed. These findings provide the first evidence that Tbx2 is a determinant in the local repression of chamber-specific gene expression and chamber differentiation.

Animals↗

PubMed1984

Cell traction models for generating pattern and form in morphogenesis.

During early development migratory mesenchymal cells navigate to distant sites where they aggregate to form a variety of embryonic organ rudiments. We present here a new model for mesenchymal cell morphogenesis based on the mechanical interaction between motile cells and their extracellular environment. The model is based on two properties of motile cells: (a) they are capable of generating large traction forces which can deform the extracellular matrix through which they move, and (b) the deformations they produce in their environment affect the direction of their movements. We derive field equations which describe the motion of cells in an elastic extracellular matrix and show that these equations can generate a variety of spatial patterns, such as the formations of skin organ primordia, especially feather germs, cartilage condensation patterns which presage bone formation in limb development, and melanocyte density patterns which form animal coat patterns.

Animals↗

PubMed2001

On the need for another type of predictive model in structured foods.

Most of the models discussed up till now in predictive microbiology do not take into account the variability of microbial growth with respect to space. In structured (solid) foods, microbial growth can strongly depend on the position in the food and the assumption of homogeneity can thus not be accepted: space must be considered as an independent variable. Indeed, experimental evidence exists of bacteria competition on agar not showing the same behavior as the competition in a well-mixed liquid culture system. It is conjectured that this is due to the spatially structured habitat. Therefore, in the current paper, a prototype two species competition model proposed in previous work by the authors is extended to take space into account. The extended model describes two phenomena: (i) local evolution of biomass and (ii) transfer of biomass through the medium. The structure of the food product is taken into account by limiting the diffusion through the medium. The smaller mobility of the micro-organisms in solid foods allows spatial segregation which causes pattern formation. Evidence is given for the fact that taking space into account indeed has an influence on the behavior (coexistence/extinction) of the populations. Although the reported simulations are by no means to be interpreted as accurate predictions, the proposed model structure allows one to highlight (i) important characteristics of microbial growth in structured foods and (ii) future research trends in predictive microbiology.

Bacteria↗