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At least 613 records · Page 34Linked to original sources
PubMed2002

Temporal and spatial expression pattern of the OSVP1 and OSEM genes during seed development in rice.

The spatial and temporal expression patterns of the rice VP1 (OSVP1) gene, as well as the OSEM gene which it controls, were studied during seed development by in situ hybridization and immuno-localization techniques. The expression of OSVP1 could be detected in embryos as early as 2-3 d after pollination (DAP) and thereafter became preferentially localized to shoot, radicle and vascular tissues during the embryo development at both the mRNA and protein levels. In the aleurone layers, OSVP1 mRNA and protein were detected after 6 DAP. OSEM mRNA was detectable after 6 DAP in the embryo and aleurone tissue. The spatial distribution within the embryo of OSEM mRNA and OSVP1 mRNA/protein was very similar after 6 DAP. Transgenic rice carrying a beta-glucuronidase (GUS) gene transcribed from a chimeric promoter consisting of the CaMV 35S minimal promoter (-46) and the 55-bp promoter fragment of OSEM, minimally required for ABA and VP1 regulation, also exhibited a spatial pattern of GUS expression similar to that of OSEM and OSVP1. These results suggest that (OS)VP1 is a major determinant not only of the seed specificity but also of the spatial pattern of OSEM expression in the developing seed.

Abscisic Acid↗
PubMed1995

Spatial distribution patterns of the sporocyst infrapopulation of Schistosoma mansoni within its mollusc host (Biomphalaria glabrata): an unusual phenotype of aggregation.

A study carried out on the intramolluscan development of the larval stages of Schistosoma mansoni from Venezuela in its intermediate host Biomphalaria glabrata shows the existence of 2 patterns for the spatial distribution of daughter sporocysts within the digestive gland of the snail. Besides the normal pattern, which is a random distribution of daughter sporocysts within the gland, 11% of the infected snails harbored an infection phenotype with daughter sporocysts strongly aggregated in only the posterior half of the digestive gland. These data suggest a possible strategy allowing a better nutritional efficiency of the infected digestive gland, a process to block the supply of hemolymph toward the gonad, resulting in castration or both.

Animals↗
PubMed1984

Generation of spatially periodic patterns by a mechanical instability: a mechanical alternative to the Turing model.

We have studied the generation of spatial patterns created by mechanical (rather than chemical) instabilities. When dissociated fibroblasts are suspended in a gel of reprecipitated collagen, and the contraction of the gel as a whole is physically restrained by attachment of its margin to a glass fibre meshwork, then the effect of the fibroblasts' traction is to break up the cell-matrix mixture into a series of clumps or aggregations of cells and compressed matrix. These aggregations are interconnected by linear tracts of collagen fibres aligned under the tensile stress exerted by fibroblast traction. The patterns generated by this mechanical instability vary depending upon cell population density and other factors. Over a certain range of cell concentrations, this mechanical instability yields geometric patterns which resemble but are usually much less regular than the patterns which develop normally in the dermis of developing bird skin. We propose that an equivalent mechanical instability, occurring during the embryonic development of this skin, could be the cause not only of the clumping of dermal fibroblasts to form the feather papillae, but also of the alignment of collagen fibres into the characteristic polygonal network of fibre bundles - which interconnect these papillae and which presage the subsequent pattern of the dermal muscles serving to control feather movements. More generally, we suggest that this type of mechanical instability can serve the morphogenetic functions for which Turing's chemical instability and other reaction-diffusion systems have been proposed. Mechanical instabilities can create physical structures directly, in one step, in contrast to the two or more steps which would be required if positional information first had to be specified by chemical gradients and then only secondarily implemented in physical form. In addition, physical forces can act more quickly and at much longer range than can diffusing chemicals and can generate a greater range of possible geometries than is possible using gradients of scalar properties. In cases (such as chondrogenesis) where cell differentiation is influenced by the local population density of cells and extracellular matrix, the physical patterns of force and distortion within this extracellular matrix should even be able to accomplish the spatial control of differentiation, usually attributed to diffusible 'morphogens'.

Animals↗
PubMed1992

From stripes to spots: prepatterns which can be produced in the skin by a reaction-diffusion system.

A key question in the area of spatial pattern formation in developmental biology is: how do groups of cells in a homogeneous tissue suddenly differentiate along entirely different developmental paths compared to neighbouring cells? Although experiments are now beginning to provide answers to this question, the mechanisms responsible for the development of repeated or periodic structures and spatial patterns, e.g., hair follicles and pigmentation patterns, are still unknown. Theoretical biologists and applied mathematicians have suggested various prepattern mechanisms as the primary cause of repeated or periodic spatial patterns. A class of biochemical reactions referred to here as reaction-diffusion (RD) systems, having the capacity to spontaneously generate stable stationary wavelike spatial patterns (Turing, 1952), has been suggested as a possible prepattern mechanisms, e.g., during hair follicle initiation and development (Nagorcka, 1989), and pigmentation patterns (Murray, 1989). Spatial patterns arising during development of the vertebrate skin are frequently complex. Spatial patterns in the skin can be seen to vary within an individual from one region of the skin to another. One pattern change commonly observed across the skin is from stripes to spots. An RD system is defined which is able to generate different spatial patterns depending on the value of a single parameter. The parameter varied controls the transport of the chemical components of the RD system across the basement membrane separating the epidermis and dermis. The patterns produced range from stripes to an irregular array of spots. Not only are different patterns produced, but a different time sequence of prepatterns is expected to arise in the different skin regions depending on whether the first prepattern in an array of spots or stripes. As a consequence it is possible to account for hair follicle initiation in the hair-bearing regions of the mammalian skin as well as the sequence of events required for the formation of dermatoglyphics in the volar regions.

Animals↗
PubMed2004

Examining localized patterns of air quality perception in Texas: a spatial and statistical analysis.

Environmental and human health issues associated with outdoor air pollution, such as ozone, sulfur dioxide, and other pollutants in metropolitan regions, are an area of growing concern for both policy officials and the general public. Increasing attention from the news media, new health data, and public debate over the effectiveness of clean air regulations have raised the importance of air quality in the public consciousness. While public perceptions of air quality have been studied thoroughly dating back to the 1960s, little empirical research has been conducted to explain the spatial aspects of these perceptions, particularly at the local level. Although recent studies suggest characteristics of local setting are important in shaping perceptions of air quality, the roles of proximity, neighborhood characteristics, and location have not been clarified. This study seeks to improve understanding of the major factors shaping public perceptions of air quality by examining the spatial pattern of local risk perception, the role of socioeconomic characteristics in forming these perceptions, and the relationship between perceived and scientifically measured air pollution. First, we map the spatial pattern of local air quality perceptions using Geographic Information Systems (GIS) across the Dallas and Houston metropolitan areas. Next, we explain these perceptions through local contextual factors using both bivariate correlations and multivariate regression analysis. Results indicate that perceptions of air quality in the study areas are not significantly correlated with air quality based on readings of air monitoring stations. Instead, perceptions appear to be influenced by setting (urban vs. rural), state identification, access to information, and socioeconomic characteristics such as age, race, and political identification. We discuss the implications of the findings and provide direction on how further research can provide a deeper understanding of the local contextual factors influencing public perceptions.

Air Pollutants↗
PubMed2000

Visual detection of spatial contrast patterns: evaluation of five simple models.

The ModelFest Phase One dataset is a collection of luminance contrast thresholds for 43 two-dimensional monochromatic spatial patterns confined to an area of approximately two by two degrees. These data were collected by a collaboration among twelve laboratories, and were designed to provide a common database for calibration and testing of spatial vision models. Here I report fits of the ModelFest data with five models: Peak Contrast, Contrast Energy, Generalized Energy, a Gabor Channels model, and a Discrete Cosine Transform model. The Gabor Channels model provides the best fit, though the other, simpler models, with the exception of Peak Contrast, provide remarkably good fits as well. Though there are clear individual differences, regularities in the data suggest the possibility of constructing a standard observer for spatial vision.

Contrast Sensitivity↗
PubMed2006

Scale-dependent inhibition drives regular tussock spacing in a freshwater marsh.

Regular spatial patterning is common in nature, and various mechanisms of self-organization have been proposed to explain regular patterning. We report on regular spatial patterning in Carex stricta in a freshwater wetland and investigate the applicability of theoretical models that explain regular patterning based on inhibition, facilitation, or interaction between the two. Spectral analysis of aerial photographs revealed that tussocks were regularly spaced at an average distance of 60 cm. Photosynthetically active radiation varied significantly with distance from the tussock and was lowest at intermediate distance from the tussock center (15-40 cm). Using transplants to assay growth conditions, we found that C. stricta grew well in all distance classes with and without natural C. stricta biomass, except at intermediate distances when buried in C. stricta wrack. Our experimental results reveal that C. stricta inhibits its growth in a scale-dependent manner: inhibition was found to peak at intermediate distance from the tussock. We compared three alternative models to examine potential mechanisms driving regularity and found that, similar to our experimental results, scale-dependent inhibition provides the best explanation for the observed regular tussock spacing. Our study underlines the importance of scale-dependent feedback in the formation of regular spatial patterning in ecosystems.

Carex Plant↗
PubMed1997

The spatial relationship between scanning saccades and express saccades.

When monkeys interrupt their saccadic scanning of a visual scene to look at a suddenly appearing target, saccades to the target are made after an "express" latency or after a longer "regular" latency. The purpose of this study was to analyze the spatial patterns of scanning, express, and regular saccades. Scanning patterns were spatially biased. Express saccade patterns were biased, too, and were directly correlated with scanning patterns. Regular saccade patterns were more uniform and were not directly correlated with scanning patterns. Express saccades, but not regular saccades, seemed to be facilitated by preparation to scan. This study contributes to a general understanding of how monkeys examine scenes containing both unchanging and suddenly appearing stimuli.

Animals↗
PubMed2006

[Spatial distribution pattern of Pontania dolichura larvae and sampling technique].

In this paper, the spatial distribution pattern of Pontania dolichura larvae was analyzed with Taylor's power law, Iwao's distribution function, and six aggregation indexes. The results showed that the spatial distribution pattern of P. dolichura larvae was of aggregated, and the basic component of the distribution was individual colony, with the aggregation intensity increased with density. On branches, the aggregation was caused by the adult behavior of laying eggs and the spatial position of leaves, while on leaves, the aggregation was caused by the spatial position of news leaves in spring when m < 2.37, and by the spatial position of news leaves in spring and the behavior of eclosion and laying eggs when m > 2.37. By using the parameters alpha and beta in Iwao's m * -m regression equation, the optimal and sequential sampling numbers were determined.

Animals↗
PubMed1997

Multifactorial comparative study of spatial point pattern analysis methods.

A way of studying cooperative behaviour of biological entities (proteins, cells, etc.) is by using topographical analysis: the quantification of the spatial patterns formed by the entities considered as points. Five methods of topographical analysis were compared in terms of discriminant power, stability of parameters, methodological bias and algorithms. We tested five methods (nearest neighbour distribution, radial distribution, Voronoï paving, quadrat count, minimal spanning tree graph) which generated nine parameters on four simulated models (random point process, hardcore model and two cluster models) and on experimental cellular models. The method which offers the best discrimination power and stability seems to be the minimal spanning tree graph edge length distribution.

Animals↗
PubMedDate not supplied

A method for quantifying artefacts in mapping methods illustrated by application to headbanging.

Maps of disease rates (and other quantities) often must contend with variance associated with variable population sizes and low incidence within spatial units. These characteristics can lead to substantial statistical noise that can mask underlying spatial variation. As Gelman and Price illustrated, most conventional mapping methods fail to address this problem, and in fact can introduce statistical artefacts; mapped quantities can show spatial patterns even when there are no spatial patterns in the underlying parameter of interest. Kafadar evaluated the performance of the headbanging algorithm for spatial smoothing (Tukey and Tukey, Hansen) for eliminating small scale variation and preserving edge structure. Here we perform a simulation study to investigate the artefacts of maps smoothed by unweighted and weighted headbanging. We find substantial artefacts that depend on the spatial structure of the statistical variation (for example, the spatial pattern of sample sizes) and on the details of the spatial distribution of geographic units. The methods used here could readily be adapted to study other spatial smoothers; we choose headbanging because (i) it is an important method used in practice, and (ii) its heavily computational nature is naturally studied using simulation (in contrast to the analytical methods used by Gelman and Price).

Artifacts↗
PubMed1990

Prediction of apical thrombus formation in acute myocardial infarction based on left ventricular spatial flow pattern.

The predictive value of the left ventricular spatial flow pattern for thrombus formation was determined in 62 patients with acute myocardial infarction. A normal flow pattern by pulsed Doppler echocardiography was characterized by 1) simultaneous onset of blood motion at the mitral valve and apical level, and 2) a discontinuous Doppler signal along the lateral wall and interventricular septum. The flow pattern was assessed by these criteria, within 24 h after the onset of complaints and after 6 and 12 weeks. In 46 of the 62 patients, a normal flow pattern was found at the first examination; none of these 46 patients developed a thrombus during the study period. An abnormal flow pattern was seen at the first examination in 16 patients; this pattern normalized during follow-up in 6 patients, none of whom developed a thrombus. In the other 10 patients the abnormal flow pattern persisted, and 7 of these developed a thrombus. These findings suggest that a normal left ventricular flow pattern in the setting of acute myocardial infarction is not associated with subsequent thrombus formation. This observation may be of importance if anticoagulation is considered.

Aged↗
PubMed2001

Spatial expression patterns of peptide transporters in the human and rat gastrointestinal tracts, Caco-2 in vitro cell culture model, and multiple human tissues.

This study sought to identify the spatial patterns of expression of peptide transporter 1 (PepT1), peptide transporter 3 (PTR3), peptide/histidine transporter 1 (PHT1), and the human peptide transporter 1 (HPT-1) mRNA in complementary DNA (cDNA) libraries of the human and rat gastrointestinal tracts (GIT), Caco-2 in vitro cell culture model, and in a human multiple tissue panel. Human PTR3 and PHT1 are putative peptide transporters recently discovered. Using sequence-specific primers designed to amplify regions of PepT1, PTR3, PHT1, and HPT-1, we were able to identify the expression of mRNA for each of these transporters in human cDNA panels (Clontech, Palo Alto, CA), the rat GIT, and in Caco-2 cDNA libraries by the polymerase chain reaction (PCR) and Southern Blot analysis. These studies suggest that in the human GIT, PepT1 appears to be localized predominantly in the duodenum, with decreasing expression in the jejunum and ileum. In contrast, PTR3 and HPT-1 were widely expressed in the human GIT, with predominant expression in the different regions of the colon. PHT1 appeared to be expressed in low levels throughout the human GI tract. Interestingly, the mRNAs for all 4 peptide transporters were expressed in Caco-2 cells throughout 30 days of culture. PepT1, PTR3, PHT1, and HPT-1 were also widely expressed in the rat GIT. Human tissue cDNA panel screening suggests that PTR3 and PHT1 are more uniformly expressed, whereas PepT1 and HPT-1 demonstrated site-specific expression. These results suggest that PepT1, PTR3, PHT1, and HPT-1 all may act to facilitate the diffusion of peptides and peptide-based pharmaceuticals in the GIT. PTR3, PHT1, and HPT-1 expressions in Caco-2 cell monolayers strongly suggest that their function needs to be further elucidated and their contribution to peptide transport not ignored. Taken together, these results demonstrate the potential for molecular biological characterization in localizing active transporter systems that can potentially be targeted for enhancing the absorption of peptide-based pharmaceuticals.

Animals↗
PubMed2004

[Dynamics of ecological landscape pattern and its affecting factors in desert-oasis in Fukang, Xinjiang].

The spatial pattern of ecological landscape during land utilization in Fukang is heavily influenced by natural difference and the scale of water and land resource development. Analyses on the spatial pattern based on different zones and indexes showed that from 1987 to 1998, the change of the spatial pattern of ecological landscape during land utilization in Fukang was mainly the increase of plantation area in pluvial fan and the decrease in alluvial plain. The case was on the contrary about badlands. The acreage of woodland decreased in lower mountains, uplands and alluvial plain, but no variety in alluvial plain. The acreage of grassland increased in lower mountains and uplands, while decreased in other fields. The acreage of town increased in each sample field, while that of water area remained uncharged. The landscape diversity and evenness was descending, the dominance was ascending in lower mountains and in pluvial fan, while it was reverse in alluvial plain. Accessorial fragmentation showed the increasing influence of human beings. The change of the spatial pattern of ecological landscape in Fukang focused on the acreage alteration of plantation and badlands in pluvial fan and alluvial plain. The key factor was the dynamic variation of water-salt in water and soil resource utilization. Terrain and land utilization were the key factors affecting water table, and the continuous changes of the water table worked on the spatial distribution of soil water-salt.

China↗
PubMedDate not supplied

Evidence for a reaction-diffusion system as a mechanism controlling mammalian hair growth.

A scheme is outlined for the differentiation of epithelial cells in hair follicle bulbs which requires several spatial pattern properties characteristics of a reaction-diffusion system. Spatial patterns in the reacting and diffusing substances, called morphogens , develop spontaneously depending on the size and shape of the follicle bulb. The patterns correctly predict the cross-sectional shape of several classes of fibres known as awls , auchenes and zigzags found in mice. The spatial patterns also determine the distribution of ortho- and para-cortical cells within the fibre cross-section. In order to explain the observed variation in the morphology of zigzag fibres it is necessary to use the capacity of a reaction-diffusion system to produce spatial patterns with a preferred orientation. Moving the dermal papilla of the hair follicle bulb off-centre causes a homogeneous pattern of morphogens to become unstable and a bilateral pattern to develop with a preferred orientation. This phenomenon forms the basis of a control mechanism for the formation of zigzag fibres.

Animals↗
PubMed1995

Temporal and spatial expression patterns of PHYA and PHYB genes in Arabidopsis.

Phytochromes A and B have discrete photosensory functions in Arabidopsis. To determine whether differential temporal or spatial expression patterns of the PHYA and PHYB genes contribute to this phenomenon the expression of PHYA-GUS and PHYB-GUS reporter genes has been examined in transgenic Arabidopsis. Histochemical and quantitative biochemical analyses indicate that both transgenes are expressed extensively throughout the plant, including roots, shoots and flowers, during the entire life cycle, but with strong differences between the two in expression level and photoregulation, and more limited differences in spatial expression patterns. The data indicate that regulation is at the transcriptional level. In dry seed, PHYB-GUS is expressed throughout the embryo at three-fold higher levels than PHYB-GUS, which is confined primarily to the embryonic root tip. By contrast, PHYA promoter activity, despite strong negative regulation in shoots by light, is consistently higher than PHYB (two- to 20-fold) in both the light and dark in most tissues during all subsequent developmental phases, from seedling to mature adult. At the tissue level, most cells appear to express both transgenes at some level at all stages examined, with highest apparent activity in vascular tissue and root tips. With the notable exception of pollen, where high PHYB-GUS but not PHYA-GUS expression occurs, few major differences are observed in the quantitative spatial distribution pattern between the two transgenes. The strongly similar spatial and temporal expression patterns of PHYA-GUS and PHYB-GUS transgenes suggest that the differential photosensory activity of these two phytochromes occurs largely through differences in their (i) intrinsic biochemical activities, (ii) relative abundances, and/or (iii) independent and separate reaction partners, rather than through discrete, developmentally controlled expression patterns.

Arabidopsis↗
PubMed2006

Spatial distribution pattern of oviposition in the mosquito Aedes aegypti in relation to urbanization in Buenos Aires: southern fringe bionomics of an introduced vector.

The distribution of Aedes aegypti (L) (Diptera: Culicidae) oviposition in Buenos Aires City is spatially heterogeneous. Oviposition activity was monitored for a year with a grid of 279 traps at 850-m intervals that were serviced weekly. Geostatistics were used for the spatial analysis and generalized linear regression to model oviposition as a function of demographic and environmental variables. The proportion of weeks infested and the total number of eggs showed spatial continuity and were higher in areas that had higher densities of houses and were closer to industrial sites; they were lower in areas with higher human populations or higher densities of flats. When all sites were considered, the spatial structure showed a strong trend, but after regression, the residuals presented lower spatial dependence. When only infested sites were considered, the oviposition variables were spatially autocorrelated and the regression residuals showed little or no spatial dependence. The spatial pattern of Ae. aegypti oviposition in a highly urbanized city such as Buenos Aires seems to be related to the urbanization gradient. These urban environments might present different resource availability or continuity between patches of resources.

Aedes↗
PubMed2004

[Spatial distribution pattern of Chilo suppressalis analyzed by classical method and geostatistics].

Two original samples of Chilo suppressalis and their grid, random and sequence samples were analyzed by classical method and geostatistics to characterize the spatial distribution pattern of C. suppressalis. The limitations of spatial distribution analysis with classical method, especially influenced by the original position of grid, were summarized rather completely. On the contrary, geostatistics characterized well the spatial distribution pattern, congregation intensity and spatial heterogeneity of C. suppressalis. According to geostatistics, the population was up to Poisson distribution in low density. As for higher density population, its distribution was up to aggregative, and the aggregation intensity and dependence range were 0.1056 and 193 cm, respectively. Spatial heterogeneity was also found in the higher density population. Its spatial correlativity in line direction was more closely than that in row direction, and the dependence ranges in line and row direction were 115 and 264 cm, respectively.

Algorithms↗