Morphological Perturbations Research Articles

Gefitinib-mediated Reactive Oxygen Specie (ROS) Instigates Mitochondrial Dysfunction and Drug Resistance in Lung Cancer Cells

Therapeutic benefits offered by tyrosine kinase inhibitors (TKIs), such as gefitinib (Iressa) and erlotinib (Tarceva), are limited due to the development of resistance, which contributes to treatment failure and cancer-related mortality. The aim of this study was to elucidate mechanistic insight into cellular perturbations that accompany acquired gefitinib resistance in lung cancer cells. Several lung adenocarcinoma (LAD) cell lines were screened to characterize epidermal growth factor receptor (EGFR) expression and mutation profile. To circumvent intrinsic variations between cell lines with respect to response to drug treatments, we generated gefitinib-resistant H1650 clone by long-term, chronic culture under gefitinib selection of parental cell line. Isogenic cells were analyzed by microarray, Western blot, flow cytometry, and confocal and transmission electron microscope. We observed that although chronic gefitinib treatment provided effective action against its primary target (aberrant EGFR activity), secondary effects resulted in increased cellular reactive oxygen species (ROS). Gefitinib-mediated ROS correlated with epithelial-mesenchymal transition, as well as striking perturbation of mitochondrial morphology and function. However, gefitinib treatment in the presence of ROS scavenger provided a partial rescue of mitochondrial aberrations. Furthermore, withdrawal of gefitinib from previously resistant clones correlated with normalized expression of epithelial-mesenchymal transition genes. These findings demonstrate that chronic gefitinib treatment promotes ROS and mitochondrial dysfunction in lung cancer cells. Antioxidants may alleviate ROS-mediated resistance.

Increased classical endoplasmic reticulum stress is sufficient to reduce chondrocyte proliferation rate in the growth plate and decrease bone growth.

Mutations in genes encoding cartilage oligomeric matrix protein and matrilin-3 cause a spectrum of chondrodysplasias called multiple epiphyseal dysplasia (MED) and pseudoachondroplasia (PSACH). The majority of these diseases feature classical endoplasmic reticulum (ER) stress and activation of the unfolded protein response (UPR) as a result of misfolding of the mutant protein. However, the importance and the pathological contribution of ER stress in the disease pathogenesis are unknown. The aim of this study was to investigate the generic role of ER stress and the UPR in the pathogenesis of these diseases. A transgenic mouse line (ColIITgcog) was generated using the collagen II promoter to drive expression of an ER stress-inducing protein (Tgcog) in chondrocytes. The skeletal and histological phenotypes of these ColIITgcog mice were characterised. The expression and intracellular retention of Tgcog induced ER stress and activated the UPR as characterised by increased BiP expression, phosphorylation of eIF2α and spliced Xbp1. ColIITgcog mice exhibited decreased long bone growth and decreased chondrocyte proliferation rate. However, there was no disruption of chondrocyte morphology or growth plate architecture and perturbations in apoptosis were not apparent. Our data demonstrate that the targeted induction of ER stress in chondrocytes was sufficient to reduce the rate of bone growth, a key clinical feature associated with MED and PSACH, in the absence of any growth plate dysplasia. This study establishes that classical ER stress is a pathogenic factor that contributes to the disease mechanism of MED and PSACH. However, not all the pathological features of MED and PSACH were recapitulated, suggesting that a combination of intra- and extra-cellular factors are likely to be responsible for the disease pathology as a whole.

التغيرات الشكلية الناتجة عن تعرض كريات الدم الحمراء للرايبوفلافين المعرض للضوء المرئي

Background: Reactive oxygen species (ROS) are formed as a natural byproduct of the normal metabolism of oxygen and have important roles in cell signaling and homeostasis. However, during times of oxidative stress, ROS levels can rise dramatically. This may result in significant damage to cell structures. In this work we are interested to show the effect of different ROS on the morphology of fresh human RBCs. Methods: The RBCs were incubated with different reaction mixtures at room temperature and exposed to cool fluorescent light (800 lux). Then, cells were isolated and scanned by a scanning electron microscope. Results: When incubated with photoilluminated riboflavin, RBCs lost their biconcave shape and adopted a spherocytes shape. The formation of spherocytes is usually associated with spectrin deficiency. In the presence of Cu(II) and riboflavin, RBCs appeared with spikes of different sizes on their surface showing the formation of “acanthocytes”, which is usually prevalent in abetalipoprotienemia. Moreover, addition of NaN3 to riboflavin-Cu(II) system resulted in completely damaged RBCs. Away from the above combinations, when RBCs are incubated with riboflavin-aminophylline combination, they appeared with spikes of equal lengths and sizes on their surface “echinocytes”, which usually appear in different diseases like pyruvate kinase deficiency and uremia. Conclusion: Red blood cells undergo different morphological changes when incubated in each of the above combinations, most probably due to the formation of different ROS and these ROS could be involved in different pathological consequences. تتأثر كريات الدم الحمراء بالظروف السابقة بطرق مختلفة نتيجة لتكون انواع مختلفة من جذور الاكسجين الحرة وهذا يطرح تساؤل عن الدور التي تلعبه جذور الاكسجين الحرة في آلية حدوث الامراض المختلفة. أرضية البحث: جذور الاكسجين الحرة تتكون كنواتج جانبية لكثير من العمليات الحيوية في جسم الانسان، ولها دور اساسي في تنظيم كثير من العمليات. أثناء اوقات الاكسدة تتغلب جذور الاكسجين الحرة على موانع الاكسدة بشكل كبير، وهذا قد يؤدي الى تدمير الخلايا. في هذه الدراسة قمنا بدراسة آثار جذور الاكسجين الحرة على شكل كريات الدم الحمراء. طريقة العمل: تم تعريض كريات الدم الحمراء لعدة انواع من التفاعلات على درجة حرارة الغرفة وبوجود قوة ضوء مرئي مقداره 800 لوكس. تم عزل كريات الدم الحمراء ودراسة التغيرات باستخدام الميكروسكوب الالكتروني. النتائج: عندما تعرضت كريات الدم الحمراء ل رايبوفلافين المعرض للضوء فقدت كريات الدم الحمراء شكلها القرصي المقعر الوجهين واصبحت كروية. وهذا الشكل الكروي يحدث ايضاً كنتيجة لنقص بروتين ال "سبكترين". أما بوجود النحاس بالاضافة الى الرايبوفلافين والضوء، فأن كريات الدم الحمراء يظهر على سطحها نتوءات بأطوال مختلفة وهذا الشكل يسمى "اكانثوسايت" وعادة تظهر هذه الاشكال في حالات ابيتالايبوبروتينيميا. أما عند اضافة ازايد الصوديوم الى التفاعل الاخير نتج التكسر التام لكريات الدم الحمراء. وبعيدا عن ما ذكر، عند تعرض كريات الدم الحمراء لخليط من الرايبوفلافين و الامينوفيلين وبوجود الضوء، ظهرت اشكال جديدية لكريات الدم الحمراء تسمى "ايكاينوسايت" وهذه الاشكال تظهر في حالات مرضية كنقص البايروفيت واليوريميا.

A point mutation in Caulobacter crescentus MreB results in cells with gross morphological perturbations that nonetheless maintain a surface area to volume ratio very similar to wild‐type cells. For details, see the article by Harris et al. on pp. 988–1005 of this issue

Molecular MicrobiologyVolume 94, Issue 5 p. i-i Front CoverFree Access A point mutation in Caulobacter crescentus MreB results in cells with gross morphological perturbations that nonetheless maintain a surface area to volume ratio very similar to wild-type cells. For details, see the article by Harris et al. on pp. 988–1005 of this issue First published: 26 November 2014 https://doi.org/10.1111/mmi.12868AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume94, Issue5December 2014Pages i-i RelatedInformation

Stabilization of the surface morphology of stressed solids using simultaneously applied electric fields and thermal gradients

We analyze the surface morphological stability of bulk conducting face-centered cubic (fcc) crystalline solids in uniaxial tension under the simultaneous action of an electric field and a temperature gradient. The analysis is based on self-consistent dynamical simulations, in conjunction with linear stability theory, according to a well validated fully nonlinear surface mass transport model that accounts for surface electromigration and thermomigration induced by the externally applied fields, surface diffusional anisotropy, and the Arrhenius temperature dependence of surface diffusivity. Our simulation results validate the findings of linear stability theory and establish that the electric field and the thermal gradient, if properly directed, can work synergistically to stabilize the planar surface morphology against the Asaro-Tiller/Grinfeld (ATG) instability when the strength of the resulting effective external field is higher than a critical level. We also show that the temperature dependence of the surface diffusivity does not change the criticality criterion for surface stabilization but only affects the rate of growth or decay of the surface morphological perturbation from its planar state. Furthermore, we establish that, in fcc crystals, the morphological response of ⟨111⟩-oriented surfaces is superior to that of differently oriented surfaces. In case of failure due to ATG instability, the super-exponential growth of the surface perturbation amplitude exhibits a logarithmic singularity as the time to failure is approached. Our study provides an effective practical solution to inhibit the surface cracking of crystalline conducting solids based on the optimal combination of the simultaneous action of externally applied electric fields and thermal gradients.

Compensations during Unsteady Locomotion.

Locomotion in a complex environment is often not steady, but the mechanisms used by animals to power and control unsteady locomotion (stability and maneuverability) are not well understood. We use behavioral, morphological, and impulsive perturbations to determine the compensations used during unsteady locomotion. At the level both of the whole-body and of joints, quasi-stiffness models are useful for describing adjustments to the functioning of legs and joints during maneuvers. However, alterations to the mechanics of legs and joints often are distinct for different phases of the step cycle or for specific joints. For example, negotiating steps involves independent changes of leg stiffness during compression and thrust phases of stance. Unsteady locomotion also involves parameters that are not part of the simplest reduced-parameter models of locomotion (e.g., the spring-loaded inverted pendulum) such as moments of the hip joint. Extensive coupling among translational and rotational parameters must be taken into account to stabilize locomotion or maneuver. For example, maneuvers with morphological perturbations (increased rotational inertial turns) involve changes to several aspects of movement, including the initial conditions of rotation and ground-reaction forces. Coupled changes to several parameters may be employed to control maneuvers on a trial-by-trial basis. Compensating for increased rotational inertia of the body during turns is facilitated by the opposing effects of several mechanical and behavioral parameters. However, the specific rules used by animals to control translation and rotation of the body to maintain stability or maneuver have not been fully characterized. We initiated direct-perturbation experiments to investigate the strategies used by humans to maintain stability following center-of-mass (COM) perturbations. When walking, humans showed more resistance to medio-lateral perturbations (lower COM displacement). However, when running, humans could recover from the point of maximum COM displacement faster than when walking. Consequently, the total time necessary for recovery was not significantly different between walking and running. Future experiments will determine the mechanisms used for compensations during unsteady locomotion at the behavioral, joint, and muscle levels. Using reduced-parameter models will allow common experimental and analytical frameworks for the study of both stability and maneuverability and the determination of general control strategies for unsteady locomotion.

Early B-cell factor 1 is an essential transcription factor for postnatal glomerular maturation

The coordination of multiple cytokines and transcription factors with their downstream signaling pathways have been shown to be integral to nephron maturation. Here we present a completely novel role for the helix-loop-helix transcription factor Early B cell Factor 1 (Ebf1), originally identified for B cell maturation, for the proper maturation of glomerular cells from mesenchymal progenitors. The expression of Ebf1 was both spatially and temporally regulated within the developing cortex and glomeruli. Using Ebf1-null mice we then identified biochemical, metabolic, and histological abnormalities in renal development that arose in the absence of this transcription factor. In the Ebf1 knockout mice the developed kidneys show thinned cortices and reduced glomerular maturation. The glomeruli showed abnormal vascularization and severely effaced podocytes. The mice exhibited early albuminuria and elevated blood urea nitrogen levels. Moreover, the GFR was reduced over 66 percent and the expression of podocyte-derived VEGF-A was decreased compared to wild type control mice. Thus, Ebf1 has a significant and novel role in glomerular development, podocyte maturation, and the maintenance of kidney integrity and function.

Rod-like bacterial shape is maintained by feedback between cell curvature and cytoskeletal localization

Cells typically maintain characteristic shapes, but the mechanisms of self-organization for robust morphological maintenance remain unclear in most systems. Precise regulation of rod-like shape in Escherichia coli cells requires the MreB actin-like cytoskeleton, but the mechanism by which MreB maintains rod-like shape is unknown. Here, we use time-lapse and 3D imaging coupled with computational analysis to map the growth, geometry, and cytoskeletal organization of single bacterial cells at subcellular resolution. Our results demonstrate that feedback between cell geometry and MreB localization maintains rod-like cell shape by targeting cell wall growth to regions of negative cell wall curvature. Pulse-chase labeling indicates that growth is heterogeneous and correlates spatially and temporally with MreB localization, whereas MreB inhibition results in more homogeneous growth, including growth in polar regions previously thought to be inert. Biophysical simulations establish that curvature feedback on the localization of cell wall growth is an effective mechanism for cell straightening and suggest that surface deformations caused by cell wall insertion could direct circumferential motion of MreB. Our work shows that MreB orchestrates persistent, heterogeneous growth at the subcellular scale, enabling robust, uniform growth at the cellular scale without requiring global organization.

Deciphering the driving forces of erosion rates on millennial to million‐year timescales in glacially impacted landscapes: An example from the Western Alps

In many regions, tectonic uplift is the main driver of erosion over million‐year (Myr) timescales, but climate changes can markedly affect the link between tectonics and erosion, causing transient variations in erosion rates. Here we study the driving forces of millennial to Myr‐scale erosion rates in the French Western Alps, as estimated from in situ produced cosmogenic 10Be and a newly developed approach integrating detrital and bedrock apatite fission‐track thermochronology. Millennial erosion rates from 10Be analyses vary between ~0.27 and ~1.33 m/kyr, similar to rates measured in adjacent areas of the Alps. Significant positive correlations of millennial erosion rates with geomorphic measures, in particular with the LGM ice thickness, reveal a strong transient morphological and erosional perturbation caused by repeated Quaternary glaciations. The perturbation appears independent of Myr‐scale uplift and erosion gradients, with the effect that millennial erosion rates exceed Myr‐scale erosion rates only in the internal Alps where the latter are low (<0.4 km/Myr). These areas, moreover, exhibit channels that clearly plot above a general linear positive relation between Myr‐scale erosion rates and normalized steepness index. Glacial erosion acts irrespective of rock uplift and thus not only leads to an overall increase in erosion rates but also regulates landscape morphology and erosion rates in regions with considerable spatial gradients in Myr‐scale tectonic uplift. Our study demonstrates that climate change, e.g., through occurrence of major glaciations, can markedly perturb landscape morphology and related millennial erosion rate patterns, even in regions where Myr‐scale erosion rates are dominantly controlled by tectonics.

Autophagy-mediated turnover of Dynamin-related Protein 1

BackgroundDrp1 is the primary protein responsible for mitochondrial fission. Perturbations of mitochondrial morphology and increased fission are seen in neurodegeneration. While Drp1 degradation induced by Parkin overexpression can be prevented by proteasome inhibition, there are numerous links between proteasomal and autophagic processes in mitochondrial protein degradation. Here we investigated the role of autophagy in Drp1 regulation.ResultsWe demonstrate that autophagy plays a major role in the control of Drp1 levels. In HEK-293T cells, inhibitors of autophagy increase total Drp1 and levels of Drp1 in the mitochondrial cellular fraction. Similarly by silencing ATG7, which is required for initiation of autophagy, there is an increased level of Drp1. Because of the role of increased Drp1 in neurodegeneration, we then examined the ability to modulate Drp1 levels in neurons by inducing autophagy. We are able to decrease Drp1 levels in a time- and dose-dependent manner with the potent neuronal autophagy inducer 10-NCP, as well as structurally related compounds. Further, 10-NCP was able increase average mitochondrial size and length verifying a functional result of Drp1 depletion in these neurons.ConclusionsThese pharmacological and genetic approaches indicate that autophagy targets Drp1 for lysosomal degradation. Additionally these data suggest a mechanism, through Drp1 downregulation, which may partly explain the ability of autophagy to have a neuroprotective effect.

Accretion does not drive the turbulence in galactic discs

Rapid accretion of cold gas plays a crucial role in getting gas into galaxies. It has been suggested that this accretion proceeds along narrow streams that might also directly drive the turbulence in galactic gas, dynamical disturbances, and bulge formation. In cosmological simulations, however, it is impossible to isolate and hence disentangle the effect of accretion from internal instabilities and mergers. Moreover, in most cosmological simulations, the phase structure and turbulence in the ISM arising from stellar feedback are treated in a sub-grid manner, so that feedback cannot generate ISM turbulence. In this paper we therefore test the effects of cold streams in extremely high-resolution simulations of otherwise isolated galaxy disks using detailed models for star formation and feedback; we then include or exclude mock cold flows falling onto the galaxies with accretion rates, velocities and geometry set to maximize their effect on the disk. We find: (1) Turbulent velocity dispersions in gas disks are identical with or without the cold flow; the energy injected by the flow is dissipated where it meets the disk. (2) In runs without stellar feedback, the presence of a cold flow has essentially no effect on runaway local collapse, resulting in star formation rates (SFRs) that are far too large. (3) Disks in runs with feedback and cold flows have higher SFRs, but only insofar as they have more gas. (4) Because flows are extended relative to the disk, they do not trigger strong resonant responses and so induce weak morphological perturbation (bulge formation via instabilities is not accelerated). (5) However, flows can thicken the disk by direct contribution of out-of-plane streams. We conclude that while inflows are critical over cosmological timescales to determine the supply and angular momentum of gas disks, they have weak instantaneous dynamical effects on galaxies.

The Cell-Autonomous Role of Excitatory Synaptic Transmission in the Regulation of Neuronal Structure and Function

The cell-autonomous role of synaptic transmission in the regulation of neuronal structural and electrical properties is unclear. We have now employed a genetic approach to eliminate glutamatergic synaptic transmission onto individual CA1 pyramidal neurons in a mosaic fashion invivo. Surprisingly, while electrical properties are profoundly affected in these neurons, as well as inhibitory synaptic transmission, we found little perturbation of neuronal morphology, demonstrating a functional segregation of excitatory synaptic transmission from neuronal morphological development.

3D quantitative analyses of angiogenic sprout growth dynamics

Zebrafish intersegmental vessel (ISV) growth is widely used to study angiogenesis and to screen drugs and toxins that perturb angiogenesis. Most current ISV growth assays observe the presence or absence of ISVs or perturbation of ISV morphology but do not measure growth dynamics. We have developed a four-dimensional (4D, space plus time) quantitative analysis of angiogenic sprout growth dynamics for characterization of both normal and perturbed growth. We tracked the positions of the ISV base and tip for each ISV sprout in 4D. Despite immobilization, zebrafish embryos translocated globally and non-uniformly during development. We used displacement of the ISV base and the angle between the ISV and the dorsal aorta to correct for displacement and rotation during development. From corrected tip cell coordinates, we computed average ISV trajectories. We fitted a quadratic curve to the average ISV trajectories to produce a canonical ISV trajectory for each experimental group, arsenic treated and untreated. From the canonical ISV trajectories, we computed curvature, average directed migration speed and directionality. Canonical trajectories from treated (arsenic exposed) and untreated groups differed in curvature, average directed migration speed and angle between the ISV and dorsal aorta. 4D analysis of angiogenic sprout growth dynamics: (1) Allows quantitative assessment of ISV growth dynamics and perturbation, and (2) provides critical inputs for computational models of angiogenesis.

A perturbation in glutathione biosynthesis disrupts endoplasmic reticulum morphology and secretory membrane traffic in Arabidopsis thaliana

To identify potentially novel and essential components of plant membrane trafficking mechanisms we performed a GFP-based forward genetic screen for seedling-lethal biosynthetic membrane trafficking mutants in Arabidopsis thaliana. Amongst these mutants, four recessive alleles of GSH2, which encodes glutathione synthase (GSH2), were recovered. Each allele was characterized by loss of the typical polygonal endoplasmic reticulum (ER) network and the accumulation of swollen ER-derived bodies which accumulated a soluble secretory marker. Since GSH2 is responsible for converting γ-glutamylcysteine (γ-EC) to glutathione (GSH) in the glutathione biosynthesis pathway, gsh2 mutants exhibited γ-EC hyperaccumulation and GSH deficiency. Redox-sensitive GFP revealed that gsh2 seedlings maintained redox poise in the cytoplasm but were more sensitive to oxidative challenge. Genetic and pharmacological evidence indicated that γ-EC accumulation rather than GSH deficiency was responsible for the perturbation of ER morphology. Use of soluble and membrane-bound ER markers suggested that the swollen ER bodies were derived from ER fusiform bodies. Despite the gross perturbation of ER morphology, gsh2 seedlings did not suffer from constitutive oxidative ER stress or lack of an unfolded protein response, and homozygotes for the weakest allele could be propagated. The link between glutathione biosynthesis and ER morphology and function is discussed.

COMPARATIVE CYTOTOXICITY EVALUATION OF MEDICINES USED FOR PULPTHERAPY OF PRIMARY TEETH

SUMMARY: Introduction:Despite the eight decades of widespread clinical use of formocresol growing evidence from both experimental and clinical studies clearly indicates that formaldehyde is leaking out during pulpotomy and may participate in the development of non-target tissue damage of local and systemic character. Special attention has been paid to pulp-capping materials and especially mineral trioxide aggregate (MTA) as probable alternative of formocresol in vital pulpotomy in primary teeth, in line with its excellent biocompatibility and pro-dentinogenic properties. The overwhelming evidence that MTA is superior in terms of biological compatibilityand clinical success as compared to formocresol has conditioned the dramatic shift to MTA in routine pulpotomies. Objective: The aim of this study was to assess the biocompatibility of resorcinol/formalin (RF) pulpotomy preparation in comparison to mineral trioxide aggregate (MTA) and calcium hydroxide cement (CHC). Methods: Cell survival was assessed by the MTT- assay (after 48, 72 or 144 h) in five cell lines, namely: HD- MY-Z, HEK-293, SH-SY-5Y, Neuro-2A, SaOS-2. In addition treatment-induced morphological perturbations and induction of necrosis and apoptosis were assessed in HEK-293. Results: RF evoked strong, concentration-dependent cytotoxicity, which was evident even at significant dilution of the parent solution. In general the cytotoxicity of RF was not greatly influenced by the exposure period, especially at the higher concentrations under evaluation. In contrast the MTA extracts proved to be generally devoid of cytotoxic effects. MTA treatment actually increased the viability of SaOS-2 osteosarcoma cells, which could be attributed to the presence of calcium ions in the MTA-eluate which in turn stimulates the proliferation of this cell line.The CH cement extracts showed marginal cytotoxicity which was far less pronounced than that of RF and slightly superior compared to MTA. Conclusions: In contrast to RF that exerted prominent cytotoxicity, MTA and CHC were biocompatible, with no evidence for decreased mitochondrial dehydrogenase activity, morphological changes in monolayer integrity or induction of apoptosis and/or necrosis. This contribution is the first systematic in vitro evaluation of the cytotoxicity of resorcinol- formalin vs. viable pulpotomy agents. It gives further evidence for the safety advantages of viable pulp therapy products CHC and especially MTA as compared to the RF preparation, routinely used in Bulgaria for decades.

Cytotoxicity induced by exposure to natural and synthetic tremolite asbestos: An in vitro pilot study

Mineral fibers are potential carcinogens to humans. In order to help clarify the etiology of the pathological effects of asbestos, cellular reactions to natural and synthetic asbestos fibers were compared using a lung alveolar cancer cell line (A549 epithelial cells), considered the first target of inhaled micro-environmental contaminants. Natural asbestos tremolite (NAT) fibers were collected from rocks in NW Italy. Synthetic asbestos tremolite (SAT) was iron-free and therefore considered as standard tremolite. Both fibers, subjected to mineralogical characterization by X-ray powder diffractometry, electron microscopy and energy dispersive spectrometry, fell within the definition of respirable and potentially carcinogenic fibers. Several signs of functional and structural cell damage were found after treatment with both fibers, documented by viability, motility, and morphological perturbations. Phalloidin labeling showed irregular distribution of cytoskeletal F-actin, whereas immunohistochemical investigations showed abnormal expression of VEGF, Cdc42, β-catenin, assessed as risks indicators for cancer development. Both fibers caused significant loss of viability, even compared to UICC crocidolite, but, while SAT fibers exerted a more direct cytotoxic effect, survival of damaged cells expressing high VEGF levels was detected after NAT contact. This in vitro pilot study outlines potential health risks of NAT fibers in vivo related to their iron content, which could trigger signaling networks connected with cell proliferation and neoplastic transformation.

Mechanical tension spatially restricts signals to the leading edge during neutrophil migration

Little is known about how neutrophils and other cells establish a single zone of actin assembly during migration. A widespread assumption is that the leading edge prevents formation of additional fronts by generating long‐range diffusible inhibitors or by sequestering essential polarity components. We use morphological perturbations, cell severing experiments, and computational simulations to show that diffusive‐based mechanisms are not sufficient for long‐range inhibition by the pseudopod. Instead, plasma membrane tension could serve as a long‐range inhibitor in neutrophils. We find that membrane tension doubles during leading edge protrusion, and increasing tension is sufficient for long‐range inhibition of actin assembly and Rac activation. Furthermore, reducing membrane tension results in uniform actin assembly. We suggest that tension, rather than diffusible molecules generated or sequestered at the leading edge, is the dominant source of long‐range inhibition that constrains the spread of the existing front and prevents the formation of secondary fronts.

A general framework for using the rate law to simulate morphological response to disturbance in the fluvial system

A general framework for modelling morphological responses to perturbation is proposed, based on the underpinning principle that the rates of morphological response in alluvial channels are initially high and then decrease through time as the system relaxes following disturbance. The framework includes three morphological response models, each developed from the fundamental rate law, which has the form of an exponential decay function. These models consider the possibility that characteristic behaviours of the fluvial system, such as delayed response and/or cumulative effects, may affect morphological responses, making them capable of representing relaxation paths and times for a range of morphological response variables, whatever their initial states. To test their utility, the models in the framework were applied to simulate the sequence of geomorphological responses to disruption observed in selected rivers with well-documented histories of morphological perturbation, adjustment and recovery. The results demonstrate that the models in the general framework can successfully simulate temporal and spatial patterns of morphological response in the fluvial system under a range of different circumstances, while also indicating how their reliability could be further improved.

Membrane Tension Maintains Cell Polarity by Confining Signals to the Leading Edge during Neutrophil Migration

Little is known about how neutrophils and other cells establish a single zone of actin assembly during migration. A widespread assumption is that the leading edge prevents formation of additional fronts by generating long-range diffusible inhibitors or by sequestering essential polarity components. We use morphological perturbations, cell-severing experiments, and computational simulations to show that diffusion-based mechanisms are not sufficient for long-range inhibition by the pseudopod. Instead, plasma membrane tension could serve as a long-range inhibitor in neutrophils. We find that membrane tension doubles during leading-edge protrusion, and increasing tension is sufficient for long-range inhibition of actin assembly and Rac activation. Furthermore, reducing membrane tension causes uniform actin assembly. We suggest that tension, rather than diffusible molecules generated or sequestered at the leading edge, is the dominant source of long-range inhibition that constrains the spread of the existing front and prevents the formation of secondary fronts.

The epigenetic H3S10 phosphorylation mark is required for counteracting heterochromatic spreading and gene silencing inDrosophila melanogaster

The JIL-1 kinase localizes specifically to euchromatin interband regions of polytene chromosomes and is the kinase responsible for histone H3S10 phosphorylation at interphase. Genetic interaction assays with strong JIL-1 hypomorphic loss-of-function alleles have demonstrated that the JIL-1 protein can counterbalance the effect of the major heterochromatin components on position-effect variegation (PEV) and gene silencing. However, it is unclear whether this was a causative effect of the epigenetic H3S10 phosphorylation mark, or whether the effect of the JIL-1 protein on PEV was in fact caused by other functions or structural features of the protein. By transgenically expressing various truncated versions of JIL-1, with or without kinase activity, and assessing their effect on PEV and heterochromatic spreading, we show that the gross perturbation of polytene chromosome morphology observed in JIL-1 null mutants is unrelated to gene silencing in PEV and is likely to occur as a result of faulty polytene chromosome alignment and/or organization, separate from epigenetic regulation of chromatin structure. Furthermore, the findings provide evidence that the epigenetic H3S10 phosphorylation mark itself is necessary for preventing the observed heterochromatic spreading independently of any structural contributions from the JIL-1 protein.