Cell Perimeter Research Articles

Effects of fiber orientation and diameter on the behavior of human dermal fibroblasts on electrospun PMMA scaffolds

We used the electrospinning technique to produce fibrous scaffolds of poly(methyl methacrylate) (PMMA). Using a rotating drum, we aligned the fibers and formed multilayered structures where both the fiber spacing and pore size could be varied. We then plated adult human dermal fibroblasts and studied the effect of fiber diameter and orientation on the cell conformation, integrin receptor expression, proliferation, and migration. We found that a critical diameter minimum diameter existed, D0 = 0.97 microm for cell orientation to occur. For D < D0, no big difference in aspect ratio was observed relative to the control samples on PMMA thin film. Hence, we could fabricate substrate patterned with fibers of different diameters where different cell conformations coexisted on the same scaffold. On the other hand, staining for vinculin proteins in the cells indicated that on large diameter fibers and on flat surfaces, the integrin receptors followed the cell perimeter. On the very small diameter surfaces, the receptors were distributed uniformly along the cell. Cell dynamics studies indicated that the proliferation and migration were also affected by the fiber orientation.

Endothelial PKCδ activation attenuates neutrophil transendothelial migration

The process of neutrophil extravasation is involved in acute and chronic inflammatory diseases; however our understanding of the role of endothelial second messengers in the regulation of leukocyte emigration is still incomplete. We investigated this using an in vitro model of neutrophil migration across human endothelial cells. Activation of endothelial protein kinase C (PKC) by either phorbol myristate acetate (PMA) or bryostatin-1 (a potent PKC delta and epsilon activator) completely abolished neutrophil migration mediated by either endothelial TNF-alpha stimulation or LTB4. Pretreatment with Gö-6983 (PKC alpha, beta, delta, inhibitor) prior to addition of bryostatin-1 restored LTB4 induced PMN migration, while pretreatment with Gö-6976 (PKC alpha and beta inhibitor) did not. PKC delta specific siRNA knockdown of PKC delta expression in endothelial cells also restored LTB4 induced PMN migration. In addition, PMA and bryostatin-1 both increased endothelial adhesion to the substratum that was also reversed using PKC delta siRNA knockdown of PKC delta expression. PMA and bryostatin-1 additionally altered the staining pattern of FAK[pY397], paxillin, and vinculin from a dot-like pattern to a dash-like pattern around the cell perimeter. While PMA reduced transendothelial resistance (TER), bryostatin-1 had no effect on TER. These observations show that endothelial PKC delta activation eliminates neutrophil transendothelial migration through a mechanism unrelated to endothelial barrier integrity. These data are consistent with PKC delta mediated increased cell substrate adhesion as a limiting factor for neutrophil transendothelial migration towards a chemoattractant.

The distribution of Voronoi cells generated by Southern California earthquake epicenters

AbstractThe cells of Voronoi diagrams generated by epicentral locations of Southern California earthquakes are inspected. The tapered Pareto distribution is shown to fit quite well to the distribution of cell areas and perimeters. This same distribution, which has been used to model the distribution of seismic moments, is also a close approximation to the empirical distributions of times and distances between successive earthquakes for the same catalog of Southern California events. Verification is performed using a variety of different windows and sub‐sampling procedures in order to confirm that the results are not an artifact of the particular parameters of the selected earthquake catalog. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Do malnutrition and fluoxetine neonatal treatment program alterations in heart morphology?

Growth and development events are observed in all organisms and can be modified by exogenous factors such as nutritional changes. Drastic morphological and functional alterations may occur during a vulnerable stage of development. The aim of this study was to investigate if malnutrition and/or fluoxetine neonatal treatment program alterations in heart morphology during the postnatal period. The sample consisted of 48 albino Wistar male rats. The rats were divided into two groups: nourished and malnourished. Pharmacologic manipulation was performed during the suckling period. The animals of each group were divided into two subgroups: saline-nourished and saline-malnourished, treated with sodium chloride solution, and fluoxetine-nourished and fluoxetine-malnourished, treated with fluoxetine. Half of the individuals in each subgroup were weighed and sacrificed on day 30 and the other half on day 71. Myocardial perfusion was performed and the heart subsequently weighed. The ventricles were cross-sectioned into two parts, which were fixed, dehydrated and sectioned. There were differences in body weight, heart weight, cross-sectional area and perimeter of the heart and in the cross-sectional area and perimeter of the cardiac cells among the groups at the different ages. Malnutrition appears to program alterations in heart morphology. However, malnourished animals that had undergone drug treatment did not exhibit the same changes.

PRODUCTION AND CHARACTERIZATION OF SPONGE‐DOUGH BREAD USING SCALDED RYE

ABSTRACT In this work, flatbed scanning, instrumental texture analysis, spectrophotometric color determination (L*, a*, b*), moisture and specific volume measurements were used to evaluate the effects of the addition of rye flour or rye flakes, yeast and boiling water in different amounts in sponge‐dough rye bread production. The treatments changed significantly (P &lt; 0.05) the crumb cell area (mm2), cell diameter (mm), cell perimeter (mm), texture parameters and light reflectance (L*, a*, b*). Scalding process could be used to produce new textures and color of baked products.PRACTICAL APPLICATIONSFermented foods contribute to about one‐third of the diet worldwide. Fermentation causes changes in texture, flavor, appearance, nutrition and safety of food. Many cereal products start with heat treatment to change protein and starch properties, removal of antinutrients, natural toxicants and mycotoxins, before fermentation. The study of microstructure can be used to increase understanding of the changes that occur during processing of food and the role of different ingredients, allowing a better control of the structure and regulation of texture. Designing texturally appealing foods presents a new challenge to companies.

Survey of Enterocyte Morphology and Tight Junction Formation in the Small Intestine of Avian Embryos

The developing villus in the small intestine is covered by a single cell layer epithelium where tight junctions are present between the individual enterocytes. As the incubation period proceeds, the epithelium is expanding both in area as well as replenishing epithelial cells. The formation of tight junctions was evaluated in the small intestinal segments of the chicken, duck, and turkey in the final days of incubation and the first few days posthatch. The percentage of enterocyte membrane involved in tight junctions decreased as day of hatch approached followed by an increase in the 3 d after hatch. The rapid increase of epithelial cell proliferation at day of hatch may affect the percentage of cell membrane involved in tight junctions by having enterocytes of various sizes. The microvillus length changes throughout the incubation and posthatch period with differences between the crypt and villus tip. The microvillus length on the villus tip increases after hatch, whereas the crypt microvillus length remains static. Across the intestinal segments, the microvillus length is longest on the villus tip and shortest on the crypt at day of hatch in all 3 species. The observations made in cellular structure, mitochondria and nucleus location, and lipid droplets are similar to reports by other researchers, but this is the first report of those observations in both duck and turkey. The tight junctions appear to be ensconced by day of hatch with little change in cell perimeter in the next 24 h. Potential for embryonic enterocytes exist with the appearance of a goblet cell originating along the basolateral membrane and extruding the enterocytes at day of hatch.

From Symmetry Breaking to Poisson Point Process in 2D Voronoi Tessellations: the Generic Nature of Hexagons

We bridge the properties of the regular square and honeycomb Voronoi tessellations of the plane to those of the Poisson-Voronoi case, thus analyzing in a common framework symmetry-break processes and the approach to uniformly random distributions of tessellation-generating points. We consider ensemble simulations of tessellations generated by points whose regular positions are perturbed through a Gaussian noise controlled by the parameter alpha. We study the number of sides, the area, and the perimeter of the Voronoi cells. For alpha>0, hexagons are the most common class of cells, and 2-parameter gamma distributions describe well the statistics of the geometrical characteristics. The symmetry break due to noise destroys the square tessellation, whereas the honeycomb hexagonal tessellation is very stable and all Voronoi cells are hexagon for small but finite noise with alpha<0.1. For a moderate amount of Gaussian noise, memory of the specific unperturbed tessellation is lost, because the statistics of the two perturbed tessellations is indistinguishable. When alpha>2, results converge to those of Poisson-Voronoi tessellations. The properties of n-sided cells change with alpha until the Poisson-Voronoi limit is reached for alpha>2. The Desch law for perimeters is confirmed to be not valid and a square root dependence on n is established. The ensemble mean of the cells area and perimeter restricted to the hexagonal cells coincides with the full ensemble mean; this might imply that the number of sides acts as a thermodynamic state variable fluctuating about n=6; this reinforces the idea that hexagons, beyond their ubiquitous numerical prominence, can be taken as generic polygons in 2D Voronoi tessellations.

EAAT2 density at the astrocyte plasma membrane and Ca2 + -regulated exocytosis

We studied whether regulated exocytosis affects the glutamate transporter density in cultured astrocytes, in which the expression of a fluorescently labeled excitatory amino acid transporter 2 (EAAT2-EGFP) predominantly labeled the plasma membrane. The addition of ionomycin that elevates cytosolic Ca(2+) strongly increased the fluorescence of FM 4-64 membrane area dye, confirming the presence of regulated exocytosis in transfected astrocytes. However, concomitant with Ca(2+)-dependent FM 4-64 fluorescence increase, ionomycin induced a significant steady-state decrease in EAAT2-EGFP fluorescence. This is likely due to a secondary inner filter effect since,(i) in the absence of FM 4-64, ionomycin stimulation was ineffective in changing the EAAT2-EGFP fluorescence, and (ii) fluorescence changes in FM 4-64 and EAAT2-EGFP were inversely correlated. To test whether subcellular EAAT2-EGFP structures are translocated from the cytoplasm to the plasma membrane during ionomycin stimulation, EAAT2-EGFP fluorescence was monitored locally at the plasma membrane and a few microns away in the adjacent cytoplasm. Measurements revealed sites with an increase in EAAT2-EGFP plasma membrane fluorescence correlated with a fluorescence decrease beneath the plasma membrane, and sites with plasma membrane fluorescence decrease correlated with fluorescence increase within the adjacent cytoplasm. The sites of rapid translocation/retrieval of EAAT2-EGFP structures to/from the plasma membrane appeared to be distributed in a punctuate pattern around the cell perimeter. The density of EAAT2-EGFP was regulated in a Ca(2+)-dependent manner, since in the absence of extracellular Ca(2+) local translocation/retrieval events were absent, revealing rapid surface density regulation of EAAT2 in astrocytes by regulated exo/endocytosis.

Classification and Computer Simulation of 2D Tessellations

In an analogy to the 3D tool of tessellation classification – w−s diagram, a similar graphical device is proposed for 2D tessellations. Any tessellation is represented by a point in the Cartesian coordinate system with the axes Ep (the mean cell perimeter) and CV a (the coefficient of cell area variation). Images of tessellations and p−CV a diagrams for selected tessellations with low and high values of CV a are shown as examples.

Atmospheric emissions and attenuation of non-methane organic compounds in cover soils at a French landfill

In addition to methane (CH(4)) and carbon dioxide (CO(2)), landfill gas may contain more than 200 non-methane organic compounds (NMOCs) including C(2+)-alkanes, aromatics, and halogenated hydrocarbons. Although the trace components make up less than 1% v/v of typical landfill gas, they may exert a disproportionate environmental burden. The objective of this work was to study the dynamics of CH(4) and NMOCs in the landfill cover soils overlying two types of gas collection systems: a conventional gas collection system with vertical wells and an innovative horizontal gas collection layer consisting of permeable gravel with a geomembrane above it. The 47 NMOCs quantified in the landfill gas samples included primarily alkanes (C(2)-C(10)), alkenes (C(2)-C(4)), halogenated hydrocarbons (including (hydro)chlorofluorocarbons ((H)CFCs)), and aromatic hydrocarbons (BTEXs). In general, both CH(4) and NMOC fluxes were all very small with positive and negative fluxes. The highest percentages of positive fluxes in this study (considering all quantified species) were observed at the hotspots, located mainly along cell perimeters of the conventional cell. The capacity of the cover soil for NMOC oxidation was investigated in microcosms incubated with CH(4) and oxygen (O(2)). The cover soil showed a relatively high capacity for CH(4) oxidation and simultaneous co-oxidation of the halogenated aliphatic compounds, especially at the conventional cell. Fully substituted carbons (TeCM, PCE, CFC-11, CFC-12, CFC-113, HFC-134a, and HCFC-141b) were not degraded in the presence of CH(4) and O(2). Benzene and toluene were also degraded with relative high rates. This study demonstrates that landfill soil covers show a significant potential for CH(4) oxidation and co-oxidation of NMOCs.

The Rap GTPase Activator Drosophila PDZ-GEF Regulates Cell Shape in Epithelial Migration and Morphogenesis

Epithelial morphogenesis is characterized by an exquisite control of cell shape and position. Progression through dorsal closure in Drosophila gastrulation depends on the ability of Rap1 GTPase to signal through the adherens junctional multidomain protein Canoe. Here, we provide genetic evidence that epithelial Rap activation and Canoe effector usage are conferred by the Drosophila PDZ-GEF (dPDZ-GEF) exchange factor. We demonstrate that dPDZ-GEF/Rap/Canoe signaling modulates cell shape and apicolateral cell constriction in embryonic and wing disc epithelia. In dPDZ-GEF mutant embryos with strong dorsal closure defects, cells in the lateral ectoderm fail to properly elongate. Postembryonic dPDZ-GEF mutant cells generated in mosaic tissue display a striking extension of lateral cell perimeters in the proximity of junctional complexes, suggesting a loss of normal cell contractility. Furthermore, our data indicate that dPDZ-GEF signaling is linked to myosin II function. Both dPDZ-GEF and cno show strong genetic interactions with the myosin II-encoding gene, and myosin II distribution is severely perturbed in epithelia of both mutants. These findings provide the first insight into the molecular machinery targeted by Rap signaling to modulate epithelial plasticity. We propose that dPDZ-GEF-dependent signaling functions as a rheostat linking Rap activity to the regulation of cell shape in epithelial morphogenesis at different developmental stages.

Microstructural changes during osmotic dehydration of parenchymatic pumpkin tissue

Pumpkin ( Cucurbita pepo L.) fruit was selected to study the microstructural changes of vegetable tissue during osmotic dehydration. Cylinders (diameter: 1.5 cm; length 2.5 cm) of the parenchymatic tissue were dehydrated with 45% (w/w) sucrose solutions at 25 °C. The microstructure of fresh and processed samples was observed using light microscopy techniques. Fresh pumpkin cells showed average values of 0.015 mm 2, 0.469 mm and 0.136 mm for cell area, cell perimeter and cell equivalent diameter, respectively; and 1.288, 0.831 and 0.871 for cellular elongation, roundness and compactness, respectively. The main modifications observed during osmotic dehydration were shrinkage of cells, plasmolysis and folding of the cell walls. These changes led to the decrease of cellular area, equivalent diameter, roundness and compactness; elongation of cells increased whereas the perimeter was maintained essentially constant along the process. The observed changes were not homogeneously distributed in the material, and were dependent on cell location in the sample and on process time. Empirical quadratic functions were used to relate the average cellular shape and size parameters with the dehydration parameters water loss, weight reduction and normalized moisture content. The equations showed a good fit of the experimental data, leading to correlation coefficients ranging 0.93–0.99 and average relative deviations ranging 0.7–2.8%.

Mutants in the Dictyostelium Arp2/3 complex and chemoattractant-induced actin polymerization

We have investigated the role of the Arp2/3 complex in Dictyostelium cell chemotaxis towards cyclic-AMP and in the actin polymerization that is triggered by this chemoattractant. We confirm that the Arp2/3 complex is recruited to the cell perimeter, or into a pseudopod, after cyclic-AMP stimulation and that this is coincident with actin polymerization. This recruitment is inhibited when actin polymerization is blocked using latrunculin suggesting that the complex binds to pre-existing actin filaments, rather than to a membrane associated signaling complex. We show genetically that an intact Arp2/3 complex is essential in Dictyostelium and have produced partially active mutants in two of its subunits. In these mutants both phases of actin polymerization in response to cyclic-AMP are greatly reduced. One mutant projects pseudopodia more slowly than wild type and has impaired chemotaxis, together with slower movement. The second mutant chemotaxes poorly due to an adhesion defect, suggesting that the Arp2/3 complex plays a crucial part in adhering cells to the substratum as they move. We conclude that the Arp2/3 complex largely mediates the actin polymerization response to chemotactic stimulation and contributes to cell motility, pseudopod extension and adhesion in Dictyostelium chemotaxis.

Up‐Regulation of Myocardial L‐Type Ca2+ Channel in Chronic Alcoholic Subjects Without Cardiomyopathy

Excessive ethanol intake is one of the most frequent causes of acquired dilated cardiomyopathy in developed countries. L-type Ca(2+) channels, involved in excitation-contraction coupling, are disturbed in animal models of persistent ethanol consumption. This study was designed to evaluate the density and function of myocardial L-type Ca(2+) channel receptors in organ donors with chronic alcoholism and controls. The protein expression of L-type Ca(2+) channels was determined with (3)H-(+)-PN 200-110-binding experiments using a specific antibody against the alpha(1)-subunit in homogenate samples of left-ventricle apex from organ donors: healthy controls (n=11), chronic alcoholic without cardiomyopathy (n=12), and alcoholics with cardiomyopathy (n=11). Morphometric measurements of cardiomyocytes were performed. Binding experiments proved an up-regulation of L-type Ca(2+) channels expression in alcoholic patients compared with controls (B(max) 2.61 +/- 1.10 vs 1.33 +/- 0.49 fmol/mg, respectively; p<0.001). This up-regulation was present in the group of alcoholic subjects without cardiomyopathy, and was not seen in those with cardiomyopathy (3.39 +/- 2.20 vs 1.77 +/- 0.53 fmol/mg, respectively; p=0.02). The cross-sectional area and perimeter of the cells were greater in alcoholic patients with cardiomyopathy compared with controls and alcoholic patients without cardiomyopathy (500 +/- 87 vs 307 +/- 74 and 255 +/- 25 microm(2), respectively; p<0.001 both) as was the perimeter (78.7 +/- 7.7 vs 61.5 +/- 7.2 and 56.5 +/- 2.8 microm, respectively; p<0.001 both). Binding results did not change after adjusting receptor measurements for cross-sectional area and cell perimeter. Chronic alcoholism causes an up-regulation of myocardial L-type Ca(2+) channel receptors, which decreases when cardiomyopathy is present.

Evaluation of mucosal surface reduction after ethmoidal surgery in nasal polyposis

To assess the reduction of mucosal surface after total sphenoethmoidectomy. Prospective study. Twelve normal, consecutive computed tomography scans were used. Computed tomography measurements were made at two different levels: the cribriform plate, and the upper level of the maxillary antrum. The length of the lateral wall of the ethmoid sinus and the perimeter of each ethmoid cell were measured at each level and on each side. The whole perimeter of the ethmoid sinus was evaluated for each CT scan level. For each side and each level, the ratio between the ethmoid sinus perimeter and the lateral ethmoid wall length was calculated. The mean length of the lateral ethmoid sinus wall was 61.7+/-1.3 mm and 59.9+/-1.6 mm at the upper and lower parts of the ethmoid sinus, respectively. The mean ethmoid sinus perimeter was 263.2+/-11.5 mm and 250.4+/-11.1 mm at the upper and lower parts of the ethmoid sinus, respectively. No significant statistical difference was observed between measurements as a function of side (right or left) or level (upper or lower). The mean ratio between the ethmoid sinus perimeter and the lateral ethmoid wall length was 4.2. After total sphenoethmoidectomy, the mucosal surface of the ethmoid sinuses is reduced by a factor of 4.2; about 76 per cent of the mucosa is removed during total sphenoethmoidectomy.

Two-Dimensional Simulation of Red Blood Cell Deformation and Lateral Migration in Microvessels

A theoretical method is used to simulate the motion and deformation of mammalian red blood cells (RBCs) in microvessels, based on knowledge of the mechanical characteristics of RBCs. Each RBC is represented as a set of interconnected viscoelastic elements in two dimensions. The motion and deformation of the cell and the motion of the surrounding fluid are computed using a finite-element numerical method. Simulations of RBC motion in simple shear flow of a high-viscosity fluid show "tank-treading'' motion of the membrane around the cell perimeter, as observed experimentally. With appropriate choice of the parameters representing RBC mechanical properties, the tank-treading frequency and cell elongation agree closely with observations over a range of shear rates. In simulations of RBC motion in capillary-sized channels, initially circular cell shapes rapidly approach shapes typical of those seen experimentally in capillaries, convex in front and concave at the rear. An isolated RBC entering an 8-mum capillary close to the wall is predicted to migrate in the lateral direction as it traverses the capillary, achieving a position near the center-line after traveling a distance of about 60 mum. Cell trajectories agree closely with those observed in microvessels of the rat mesentery.

New Monte Carlo method for planar Poisson–Voronoi cells

By a new Monte Carlo algorithm, we evaluate the sidedness probability pn of a planar Poisson–Voronoi cell in the range 3 ⩽ n ⩽ 1600. The algorithm is developed on the basis of earlier theoretical work; it exploits, in particular, the known asymptotic behaviour of pn as n → ∞. Our pn values all have between four and six significant digits. Accurate n dependent averages, second moments and variances are obtained for the cell area and the cell perimeter. The numerical large-n behaviour of these quantities is analysed in terms of an asymptotic power series in n−1. Snapshots are shown of typical occurrences of extremely rare events, implicating cells of up to n = 1600 sides embedded in an ordinary Poisson–Voronoi diagram. We reveal and discuss the characteristic features of such many-sided cells and their immediate environment. Their relevance for observable properties is stressed.

Analysis of Lipolytic Protein Trafficking and Interactions in Adipocytes

This work examined the colocalization, trafficking, and interactions of key proteins involved in lipolysis during brief cAMP-dependent protein kinase A (PKA) activation. Double label immunofluorescence analysis of 3T3-L1 adipocytes indicated that PKA activation increases the translocation of hormonesensitive lipase (HSL) to perilipin A (Plin)-containing droplets and increases the colocalization of adipose tissue triglyceride lipase (Atgl) with its coactivator, Abhd5. Imaging of live 3T3-L1 preadipocytes transfected with Aquorea victoria-based fluorescent reporters demonstrated that HSL rapidly and specifically translocates to lipid droplets (LDs) containing Plin, and that this translocation is partially dependent on Plin phosphorylation. HSL closely, if not directly, interacts with Plin, as indicated by fluorescence resonance energy transfer (FRET) and bimolecular fluorescence complementation (BiFC) experiments. In contrast, tagged Atgl did not support FRET or BiFC with Plin, although it did modestly translocate to LDs upon stimulation. Abhd5 strongly interacted with Plin in the basal state, as indicated by FRET and BiFC. PKA activation rapidly (within minutes) decreased FRET between Abhd5 and Plin, and this decrease depended upon Plin phosphorylation. Together, these results indicate that Plin mediates hormone-stimulated lipolysis via direct and indirect mechanisms. Plin indirectly controls Atgl activity by regulating accessibility to its coactivator, Abhd5. In contrast, Plin directly regulates the access of HSL to substrate via close, if not direct, interactions. The differential interactions of HSL and Atgl with Plin and Abhd5 also explain the findings that following stimulation, HSL and Atgl are differentially enriched at specific LDs.

The mechanism of pattern formation in the developing drosophila retina

The biological patterning of the Drosophila retina in vivo has striking resemblance to liquid bubbles, in which the surface mechanics due to N-cadherin within a sub-group of retina cells can be mimicked by surface tension. In this work, the aggregating patterns were reasonably simplified into 2D clusters consisting of 2-6 identical bubbles confined within a shrinking boundary. By using a hybrid fluid dynamics model proposed for liquid foams, the aggregating process of 2-6 retina cells was studied. Assuming the minimal perimeter for patterning cells to be the condition of stability patterns, the stable converged patterns we simulated in this work are the same as the experimental observations. More importantly, a new pattern of 6 cells was obtained which was found physically more stable than the other two reported by Hayashi and Carthew. Aggregating perimeters of cells, i.e. the surface energy, showed a good linear fit with the cell numbers.

Perimeter recombination in thin film solar cells

Surface recombination has a profound effect on the performance of a solar cell, at the illuminated surface reduces its photocurrent and along the cell's perimeter increases its dark current. The perimeter recombination current has two components; the first is due to recombination at the surface that intersects the space-charge layer while the second originates from recombination at the surface of quasi-neutral regions. The current due to recombination at the depleted layer surface is treated in a similar way to that of the bulk, using a simple model. We present an analytical form that produces results that agree well with reported experimental findings. The recombination current outside the space-charge region is of two-dimensional nature, it represents lateral diffusion of minority carriers from the boundary of the depleted layer to the perimeter. This current is calculated by solving numerically a two-dimensional continuity equation. As the ratio of perimeter to area is increased the perimeter current acquires important proportions, consequently the expected bulk recombination current becomes insignificant.