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PubMed1993

Control of vertebrate gastrulation: inducing signals and responding genes.

Recently, genes with similar expression patterns in the early gastrulae of several different vertebrate species have been identified. The remarkable conservation of these expression patterns suggests that fundamental similarities exist within the vertebrates at remarkably early stages. It has yet to be established exactly how these genes are activated in the correct spatial patterns and what their functions might be.

Animals↗
PubMedDate not supplied

Proliferation, differentiation and apoptosis in villous trophoblast at 13-41 weeks of gestation (including observations on annulate lamellae and nuclear pore complexes).

Ultrastructural, immunochemical, fluorescence and stereological studies were undertaken on human villous trophoblast from 13 weeks of gestation to term. The aim was to describe and quantify morphological changes during proliferation, differentiation and apoptosis in cytotrophoblast and syncytial regions of non-aggregated and aggregated nuclei. Numbers of trophoblast nuclei increased continuously from 13 weeks. In term placentae, intrasyncytial differentiation was characterized ultrastructurally by gradual decreases in nuclear size and packing density accompanied by nucleolar regression, and increasing heterochromatinization, envelope convolution and packing density of nuclear pore complexes. In densely packed areas, nuclear profiles resembled interlocking jigsaw pieces. Occasionally, these 'pre-apoptotic' nuclei were associated with annulate lamellae. Rarely, nuclear changes terminated in apoptosis with a characteristic pattern of condensed peripheral chromatin, a central island of euchromatin, no nucleoli and no discernible nuclear pores. Apoptotic nuclei were seen singly and within dense nuclear aggregations. Similar spatial patterns of nuclei and chromatin were seen in propidium iodide-stained sections at 13-41 weeks. Whilst the relative incidence of intensely fluorescent nuclei remained constant, absolute numbers increased linearly during gestation and correlated positively with the volume of syncytial knots. Nuclei labelled for DNA fragmentation occurred very infrequently and were also found in nuclear clusters as well as singly. We suggest that nuclear differentiation in syncytium has two phases: on entering syncytium, nuclei become committed to a long programmed pre-apoptotic phase which leads to a short apoptotic execution phase. We propose further that clustered nuclei (pre-apoptotic and apoptotic) in syncytial knots probably represent the extrusion component of normal continuous epithelial turnover.

Apoptosis↗
PubMed2005

Mechanisms for the maintenance of ventricular fibrillation: the nonuniform dispersion of refractoriness, restitution properties, or anatomic heterogeneities?

INTRODUCTION: The relative importance of nonuniform dispersion of refractoriness, steep restitution slopes, and anatomic heterogeneities in causing conduction block during ventricular fibrillation (VF) remains unknown. METHODS AND RESULTS: In six open-chest pigs, ventricular refractoriness and restitution curves were estimated from activation recovery intervals (ARIs) calculated from 504 (21 x 24) unipolar electrode recordings 2 mm apart in a plaque sutured to the left ventricular (LV) free wall. A steady-state restitution protocol was performed twice at each of two pacing sites: the LV base and near the left anterior descending artery. VF was electrically induced four times and the incidence of conduction block at each electrode during the first 20 seconds was determined by an automated algorithm. The gradient of the ARI was calculated at each electrode to estimate the spatial dispersion of refractoriness. An exponential curve was fit to the restitution plots of ARIs versus the corresponding diastolic intervals (DIs) for all pacing cycle lengths at each electrode. The locations of epicardial blood vessels were noted after the study. Spatial patterns of conduction block were significantly correlated between the four VF episodes in the same animal (r = 0.66 +/- 0.07, P < 0.05). At the shortest pacing cycle length, the spatial distribution of ARIs, ARI gradients, and restitution slopes was not random but formed clusters of similar values. However, none of these variables was significantly correlated with the incidence of conduction block, even though ARI gradients >2 msec/mm were present between many clusters and approximately 90% of restitution slopes were >1. Instead, conduction block frequently appeared to cluster along epicardial vessels. CONCLUSION: Neither the dispersion of refractoriness nor action potential duration restitution determined during rapid pacing by itself is the major determinant of the location of conduction block during early VF in normal pigs. It may be that these factors interact synergistically with each other as well as with other factors, including anatomic heterogeneities such as those caused by blood vessels, which may be particularly important for the formation of conduction block and maintenance of VF.

Animals↗
PubMed2004

Modeling antibiotic tolerance in biofilms by accounting for nutrient limitation.

A mathematical model of biofilm dynamics was used to investigate the protection from antibiotic killing that can be afforded to microorganisms in biofilms based on a mechanism of localized nutrient limitation and slow growth. The model assumed that the rate of killing by the antibiotic was directly proportional to the local growth rate. Growth rates in the biofilm were calculated by using the local concentration of a single growth-limiting substrate with Monod kinetics. The concentration profile of this metabolic substrate was calculated by solving a reaction-diffusion problem. The model predicted the following features: stratified patterns of growth with zones of no growth in the biofilm interior, slow killing of biofilm microorganisms that was further retarded as the initial biofilm thickness increased, nonuniform spatial patterns of killing inside the biofilm, biofilm killing rates that decrease in a nonlinear way as the concentration of the growth-limiting substrate feeding the biofilm is decreased, and heightened tolerance when external mass transfer resistance is manifested. This modeling study also provides motivation for further investigation of a hypothetical cell state in which damaged cells score as nonviable but continue to consume substrate. The existence of such a cell state can further retard biofilm killing, according to the simulations. The results support the important contributions of nutrient limitation and slow growth to the antibiotic tolerance of microorganisms in biofilms.

Anti-Bacterial Agents↗
PubMed2001

Different expression of glycogen synthase kinase-3beta between young and old rat brains after transient middle cerebral artery occlusion.

Ischemia is a common stress to human brain and is difficult to cure in older individuals. To examine the differences of the response to cerebral ischemia between young and old rat brains, distributions of glycogen synthase kinase-3beta (GSK3beta) and tau proteins were analyzed after 90 min of transient middle cerebral artery occlusion (MCAO) in young (10-11 weeks) and old (15 months) rats by immunohistochemical analyses. At 4 h of reperfusion, strong cytoplasmic and nuclear immunoreactivity for GSK3beta was induced in neurons of lamina I, II, V and VI of the cerebral cortex and dorsal caudate in young brains, while the induction was not observed in lamina I and II of old cerebral cortex. The staining in lamina V and VI and dorsal caudate then gradually decreased until seven days of reperfusion in both animal groups. The staining of tau protein and terminal deoxynucleotidyl transferase-mediated dUTP-biotin in situ nick end labeling (TUNEL) did not show any positive signals in the control brain, but showed positive signals after ischemia with a peak at 24 h and 3 days, respectively. No significant difference was observed in the temporal and spatial patterns of tau and TUNEL stainings between these two groups. These data suggest that GSK3beta may have a role in ischemic neuronal cell death, and that the different spatial expression of GSK3beta between young and old rat brains may partly explain the vulnerability of older neurons after ischemia.

Aging↗
PubMed2006

Infestation of rural houses by Triatoma infestans (Hemiptera: Reduviidae) in southern area of Gran Chaco in Argentina.

The impact of control activities against Triatoma infestans (Klug) (Hemiptera: Reduviidae) in South America has a marked contrast within and outside the Gran Chaco region. Development of a geographic information system, as part of an improvement in control program activities, allowed analysis of the spatial pattern of house infestations by T. infestans before and after house spraying with deltamethrin in the San Martin Department (an arid Chaco region of central Argentina). The overall peridomestic infestation index decreased from 48.2 to 28.2% after insecticide application. House infestation was spatially clustered in regions with low or high infestation levels that were located east and southwest of the department, respectively. This pattern was detected both before and after the insecticide application. Three environmental variables calculated from a temporal series of MODIS imagery (average of night temperature, maximum of day temperature, and temporal variation of vegetation index) were capable of correctly discriminating 96% of the places belonging to either high or low house infestation observed after the insecticide application.

Adolescent↗
PubMedDate not supplied

[Decline and social inequalities of infant mortality caused by diarrhea].

This ecological study describes the temporal trend from 1977 to 1998, and spatial patterns of infant mortality from diarrhea in the city of Salvador, Bahia State, Brazil. The annual proportional of infant mortality and specific-cause mortality rate were estimated. Spatial units of geographical zones within the city's urban area were utilized for administrative purposes, which were aggregated according to quartile of living conditions indicators. Over the study period, the diarrhea-induced infant mortality rate decreased 91.9%. The mortality risk from diarrhea in the lowest living condition strata was 90% greater than in the highest conditions. Also, infant mortality due to diarrhea increases proportionally as living conditions worsen, which necessitates a review of the control policies concerning this important public health problem. Although the infant mortality rate declined during the study period, social inequalities related to infant mortality due to diarrhea persist, reflecting a continuing poor social development.

Brazil↗
PubMed1993

Patterns of visual spatial inattention and their functional significance in stroke patients.

The relationship between patterns of visual spatial inattention and activities of daily living (ADL) performance was investigated in 64 Chinese patients with right brain lesions, using the Klein-Bell ADL Scale and the Random Chinese Word Cancellation Test. The result showed that patients demonstrating hemi-inattention were significantly worse in ADL performance than patients with nonlateralized inattention or patients with normal attention, but that the latter two groups did not differ from each other. Although ADL performance was also found to be significantly related to somatosensation, motor status, and visual factors, after controlling the effects of these variables by partial correlation, hemi-inattention still was highly related to ADL performance. Independence in dressing, mobility, and elimination appeared to be more adversely affected by hemi-inattention than were bathing/hygiene, eating, and telephone use.

Activities of Daily Living↗
PubMed1996

Spatial and temporal aspects of cellular calcium signaling.

Cytosolic Ca2+ signals are often organized in complex temporal and spatial patterns, even under conditions of sustained stimulation. In this review we discuss the mechanisms and physiological significance of this behavior in nonexcitable cells, in which the primary mechanism of Ca2+ mobilization is through (1,4,5)IP3-dependent Ca2+ release from intracellular stores. Oscillations of cytosolic free Ca2+ ([Ca2+]i) are a common form of temporal organization; in the spatial domain, these [Ca2+]i oscillations may take the form of [Ca2+]i waves that propagate throughout the cell or they may be restricted to specific subcellular regions. These patterns of Ca2+ signaling result from the limited range of cytoplasmic Ca2+ diffusion and the feedback regulation of the pathways responsible for Ca2+ mobilization. In addition, the spatial organization of [Ca2+]i changes appears to depend on the strategic distribution of Ca2+ stores within the cell. One type of [Ca2+]i oscillation is baseline spiking, in which discrete [Ca2+]i spikes occur with a frequency, but not amplitude, that is determined by agonist dose. Most current evidence favors a model in which baseline [Ca2+]i spiking results from the complex interplay between [Ca2+]i and (1,4,5)IP3 in regulating the gating of (1,4,5)IP3-sensitive intracellular Ca2+ channels. Sinusoidal [Ca2+]i oscillations represent a mechanistically distinct type of temporal organization, in which agonist dose regulates the amplitude but has no effect on oscillation frequency. Sinusoidal [Ca2+]i oscillations can be explained by a negative feedback effect of protein kinase C on the generation of (1,4,5)IP3 at the level of phospholipase C or its activating G-protein. The physiological significance of [Ca2+]i oscillations and waves is becoming more established with the observation of this behavior in intact tissues and by the recognition of Ca2+-dependent processes that are adapted to respond to frequency-modulated oscillatory [Ca2+]i signals. In some cells, these [Ca2+]i signals are targeted to control processes in limited cytoplasmic domains, and in other systems [Ca2+]i waves can be propagated through gap junctions to coordinate the function of multicellular systems.

Animals↗
PubMed1997

Isolation and characterization of the platelet-derived growth factor beta receptor promoter.

The PDGFbeta r gene has been implicated in many physiological processes including development and wound healing. Aberrant expression of the receptor is seen in many pathological conditions such as atherosclerosis and inflammatory diseases. To study the mechanisms of PDGFbeta r regulation, we identified the regulatory regions of the gene. We have cloned and characterized the promoter region of the platelet-derived growth factor beta receptor (PDGFbeta r). We isolated a 4.5 Kb genomic fragment which confers PDGFbeta r tissue-specific promoter activity. This fragment can direct transcription of a luciferase reporter gene in a cell-specific manner which correlates well with the known pattern of expression of the PDGFbeta r. The specificity of this clone was demonstrated by its high activity in NIH 3T3 fibroblasts and lack of activity in N-MUNG epithelial cells, a pattern that parallels the expression of the endogenous PDGFbeta r. We have defined a 614 bp region encompassing the 5' untranslated region of the gene which includes the basal promoter region. We generated transgenic mice that carry the chloramphenicol acetyltransferase (CAT) reporter gene under the control of the 4.5 Kb promoter. The expression pattern of the reporter gene was compared to that of the endogenous PDGFbeta r gene. The promoter was able to direct reporter gene expression with the same temporal and spatial pattern as the endogenous PDGFbeta r. The most prominent expression was in condensing mesenchyme of developing blood vessels, bone and tissues adjacent to epithelium. We conclude that this clone contains the regulatory regions sufficient to direct expression of the PDGFbeta r. The further analysis of this promoter will help elucidate the transcriptional regulation of expression of the PDGFbeta r, and provide a useful tool for directing expression of heterologous genes.

3T3 Cells↗
PubMed1998

Homology-based control of gene expression patterns in transgenic petunia flowers.

Plant transgenes may participate in two types of homology-based gene silencing. One requires transcript homology, is post-transcriptional, and is referred to as cosuppression; the other requires promoter homology, is transcriptional, and is similar to paramutation. This paper uses flower color transgenes to address the hierarchical operation of both mechanisms in plants carrying two transgene copies. It is shown that cosuppression of homologous, endogenous flower color genes by single-copy transgenes requires that the transgene be driven by a strong promoter and that the degree of cosuppression is highly sensitive to increasing transgene dosage. Together, these observations suggest that cosuppression should be a sensitive reporter of epigenetic changes in transgene transcription, such as might be caused by paramutation-like interactions between transgene loci. Intercrosses bringing together two homologous transgene loci, one a known epimutable reporter and the other a transgene inverted repeat, result in complete loss of cosuppression in some outcross progeny and a qualitative change in morphology-based patterns of cosuppression in other outcross progeny. This paramutation-like behavior suggests that the transgenes may be altered at the transcriptional level, eliminating cosuppression altogether or changing the spatial pattern of transgene transcription to produce a new pattern of cosuppression.

Chromosome Mapping↗
PubMed2006

Nonequilibrium patterns of cholesterol-rich chemical heterogenieties within single fluid supported phospholipid bilayer membranes.

We have developed a simple method to introduce cholesterol- and sphingomyelin-rich chemical heterogeneities into controlled densities and concentrations within predetermined regions of another distinct fluid phospholipid bilayer supported on a solid substrate. A contiguous primary phase--a fluid POPC bilayer displaying a well-defined array of lipid-free voids (e.g., 20-100 microm squares)--was first prepared on a clean glass surface by microcontact printing under water using a poly(dimethylsiloxane) stamp. The aqueous-phase primary bilayer pattern was subsequently incubated with secondary-phase small unilamellar vesicles composed of independent chemical compositions. Backfilling by comparable vesicles resulted in gradual mixing between the primary- and secondary-phase lipids, effacing the pattern. When the secondary vesicles consisted of phase-separating mixtures of cholesterol, sphingomyelin, and a phospholipid (2:1:1 POPC/sphingomyelin/cholesterol or 1:1:1 DOPC/sphingomyelin/cholesterol), well-defined spatial patterns of fluorescence, chemical compositions, and fluidities emerged. We conjecture that these patterns form because of the differences in the equilibration rates of the secondary liquid-ordered and liquid-disordered phases with the primary fluid POPC phase. The pattern stability depended strongly on the ambient-phase temperature, cholesterol concentration, and miscibility contrast between the two phases. When cholesterol concentration in the secondary vesicles was below 20 mol %, secondary intercalants gradually diffused within the primary POPC bilayer phase, ultimately dissolving the pattern in several minutes and presumably forming a new quasi-equilibrated lipid mixture. These phase domain micropatterns retain some properties of biological rafts including detergent resistance and phase mixing induced by selective cholesterol extraction. These patterns enable direct comparisons of cholesterol- and sphingomyelin-rich phase domains and fluid phospholipid phases for their functional preferences and may be useful for developing simple, parallelized assays for phase and chemical composition-dependent membrane functionalities.

Cholesterol↗
PubMed1999

Stripe formation in juvenile Pomacanthus explained by a generalized turing mechanism with chemotaxis.

Current interest in pattern formation can be traced to a seminal paper by Turing, who demonstrated that a system of reacting and diffusing chemicals, called morphogens, can interact so as to produce stable nonuniform concentration patterns in space. Recently, a Turing model has been suggested to explain the development of pigmentation patterns on species of growing angelfish such as Pomacanthus semicirculatus, which exhibit readily observed changes in the number, size, and orientation of colored stripes during development of juvenile and adult stages, but the model fails to predict key features of the observations on stripe formation. Here we develop a generalized Turing model incorporating cell growth and movement, we analyze the effects of these processes on patterning, and we demonstrate that the model can explain important features of pattern formation in a growing system such as Pomacanthus. The applicability of classical Turing models to biological pattern formation is limited by virtue of the sensitivity of patterns to model parameters, but here we show that the incorporation of growth results in robustly generated patterns without strict parameter control. In the model, chemotaxis in response to gradients in a morphogen distribution leads to aggregation of one type of pigment cell into a striped spatial pattern.

Animals↗
PubMedDate not supplied

Temporoparietal electrophysiological differences characterize patients with Alzheimer's disease: a split-half replication study.

One hundred and eighty nine subjects were examined by quantified EEG (qEEG) during the resting awake state. Sixty subjects had probable Alzheimer's disease (AD) and were mild to moderately impaired. There were 129 healthy controls. Differences between patients and controls by topographic mapping demonstrated a pattern of group difference maximal posteriorly, primarily in posterior temporal and/or parietal regions. Frontal regions were much less frequently involved. Long-latency evoked potential derived difference showed similar spatial patterns of difference. By EEG spectral analysis, theta was increased and beta decreased for the AD patients. In addition, the qEEG measures were significantly correlated with neuropsychological test scores related to abilities that are impaired in the early stages of disease, such as delayed recall and verbal fluency. To assess replicability the population was split in half. Regions of interest derived from the first half provided numerical measures for discriminant function analysis. A discriminant function, derived from the first half, correctly identified 86% of all second-half subjects (91% controls, 77% AD).

Aged↗
PubMed1978

The development of the pattern of growth.

It is proposed that the varying patterns of growth in development can be viewed as an aspect of pattern formation, and that different growth programmes are specified at an early stage. This is illustrated largely with respect to the development and growth of the chick wing. The spatial pattern of cellular differentiation and programme for growth can be considered in terms of the concept of positional information. The lengths of the cartilaginous elements are determined by the initial length of the primordium and its later growth, involving cell multiplication enlagement and matrix secretion. It seems that tissues have a high degree of autonomy with respect to differentiation and growth after they have had their position specified. The cellular basis of programmed growth is discussed.

Animals↗
PubMed2004

Assessing cortical functional connectivity by linear inverse estimation and directed transfer function: simulations and application to real data.

OBJECTIVE: To test a technique called Directed Transfer Function (DTF) for the estimation of human cortical connectivity, by means of simulation study and human study, using high resolution EEG recordings related to finger movements. METHODS: The method of the Directed Transfer Function (DTF) is a frequency-domain approach, based on a multivariate autoregressive modeling of time series and on the concept of Granger causality. Since the spreading of the potential from the cortex to the sensors makes it difficult to infer the relation between the spatial patterns on the sensor space and those on the cortical sites, we propose the use of the DTF method on cortical signals estimated from high resolution EEG recordings, which exhibit a higher spatial resolution than conventional cerebral electromagnetic measures. The simulation study was followed by an analysis of variance (ANOVA) of the results obtained for different levels of Signal to Noise Ratio (SNR) and temporal length, as they have been systematically imposed on simulated signals. The whole methodology was then applied to high resolution EEG data recorded during a visually paced finger movement. RESULTS: The statistical analysis performed returns that during simulations, DTF is able to estimate correctly the imposed connectivity patterns under reasonable operative conditions, i.e. when data exhibit a SNR of at least 3 and a length of at least 75 s of non-consecutive recordings at 64 Hz of sampling rate, equivalent, more generally, to 4800 data samples. CONCLUSIONS: Functional connectivity patterns of cortical activity can be effectively estimated under general conditions met in any practical EEG recordings, by combining high resolution EEG techniques, linear inverse estimation and the DTF method. SIGNIFICANCE: The estimation of cortical connectivity can be performed not only with hemodynamic measurements, by using functional MRI recordings, but also with modern EEG recordings treated with advanced computational techniques.

Analysis of Variance↗
PubMed2004

Topographical pattern dynamics in passive adhesion of cell membranes.

Strong adhesion of highly active cells often nucleates focal adhesions, synapses, and related structures. Red cells lack such complex adhesion systems and are also nonmotile, but they are shown here to dynamically evolve complex spatial patterns beyond an electrostatic threshold for strong adhesion. Spreading of the cell onto a dense, homogeneous poly-L-lysine surface appears complete in <1 s with occasional blisters that form and dissipate on a similar timescale; distinct rippled or stippled patterns in fluorescently labeled membrane components emerge later, however, on timescales more typical of long-range lipid diffusion (approximately minutes). Within the contact zone, the anionic fluorescent lipid fluorescein phosphoethanolamine is seen to rearrange, forming worm-like rippled or stippled domains of <500 nm that prove independent of whether the cell is intact and sustaining a tension or ruptured. Lipid patterns are accompanied by visible perturbations in Band 3 distribution and weaker perturbations in membrane skeleton actin. Pressing down on the membrane quenches the lipid patterns, revealing a clear topographical basis for pattern formation. Counterion screening and membrane fluctuations likely contribute, but the results primarily highlight the fact that even in adhesion of a passive red cell, regions of strong contact slowly evolve to become interspersed with regions where the membrane is more distant from the surface.

Cell Adhesion↗
PubMedDate not supplied

Spatial and temporal patterns of Krüppel gene expression in early Drosophila embryos.

The Krüppel (Kr) locus is a member of the 'gap' class of segmentation genes of Drosophila melanogaster. Mutations at the Kr locus cause the deletion of contiguous segments from the embryonic body pattern. We have elucidated the spatial and temporal characteristics of Kr gene expression during early embryo development, the localization of cytoplasmic Kr+ activity and its spatial requirement for normal segmentation.

Animals↗