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We consider a one-dimensional model of cell polarization in fission yeast consisting of a hybrid partial differential equation{delay differential equation system. The model describes bulk diffusion of the signaling molecule Rho GTPase Cdc42 in the cytoplasm, which is coupled to a pair of delay differential equations at the ends of the cell via boundary conditions. The latter represent the binding of Cdc42 to the cell membrane and rerelease into the cytoplasm via unbinding. The nontrivial nature of the dynamics arises from the fact that both the binding and unbinding rates at each end are taken to depend on the local membrane concentration of Cdc42. In particular, the association rate is regulated by positive feedback and the dissociation rate is regulated by delayed negative feedback. We use linear stability analysis and numerical simulations to investigate the onset of limit cycle oscillations at the end compartments for a cell of fixed length, distinguishing between symmetric solutions in which the mean concentration is identical at both ends and asymmetric solutions where the mean concentration at one end dominates. We find that the critical time delay for the onset of oscillations via a Hopf bifurcation increases as the diffusion coeficient D decreases. We then solve the diffusion equation on a growing domain under the additional assumption that the total amount Ctot of the signaling molecule increases as the cell length increases. We show that the system undergoes a transition from asymmetric to symmetric oscillations as the cell grows, consistent with experimental findings of \new-end-take-off" in fission yeast. (The latter refers to the switch from monopolar to bipolar growth as the cell grows.) The critical length where the switch occurs depends on D and the growth rate. [ABSTRACT FROM AUTHOR]

The formation of hierarchical structures consisting of microstripe barriers decorated with nanorough ablated materials prepared by direct laser writing is described. Linear features of circa 25 μm width and 12 μm height are achieved on amorphous and crystalline titania and graphitic carbon films deposited on silicon. Ablated protrusions build up barriers decorated by nanoscale Si-film reconstructions, as indicated by EDX maps and micro-Raman spectroscopy. Wettability tests show a dramatic change in water contact angle, which leads to almost full wetting after irradiation, irrespective of the original film composition. Fluorescence microscopy images of human mesenchymal stem cells cultured on 1D and 2D structures demonstrate the short term biocompatibility of the ablated surfaces. It is shown that cells adhere, extend and polarize on feature edges, independently of the type of surface, thus suggesting that the created nanoroughness is at the origin of the antifouling behavior. In particular, irradiated anatase and graphite surfaces demonstrate an increased performance of crystalline films for the creation of cell guiding and trapping devices. The results suggest that such laser processing of films may serve as a time-and-cost-efficient method for the design of few-cells analytical surfaces. [ABSTRACT FROM AUTHOR]

During mouse embryogenesis initial specification of the cell fates depends on the type of division during 8- to 16- and 16- to 32-cell stage transition. A conservative division of a blastomere creates two polar outer daughter cells, which are precursors of the trophectoderm (TE), whereas a differentiative division gives rise to a polar outer cell and an apolar inner (the presumptive inner cell mass – ICM) cell. We hypothesize that the type of division may depend on the interactions between blastomeres of the embryo. To investigate whether modification of these interactions influences divisions, we analyzed the pattern of blastomere division and cell lineage specification in chimeric embryos obtained by injection of a different number of mouse embryonic stem cells (ESCs) into 8-cell embryos. As the ESCs populate only the ICM of the resulting chimeric blastocysts, they emulated in our model additional inner cells. We found that introduction of ESCs decreased the number of inner, apolar blastomeres at the 8- to 16-cell stage transition and reduced the number of ICM cells of host embryo-origin during formation of the blastocyst. Moreover, we showed that the proportion of inner blastomeres and their fate (EPI or PE) in chimeric blastocysts was dependent on the number of ESCs injected. Our results suggest the existence of a regulative mechanism, which links number of inner cells with a proportion of conservative vs. differentiative blastomere divisions during the cleavage and thus dictates their developmental fate. [ABSTRACT FROM AUTHOR]

Chemotaxis, the directional migration of cells in a chemical gradient, is robust to fluctuations associated with low chemical concentrations and dynamically changing gradients as well as high saturating chemical concentrations. Although a number of reports have identified cellular behavior consistent with a directional memory that could account for behavior in these complex environments, the quantitative and molecular details of such a memory process remain unknown. Using microfluidics to confine cellular motion to a 1D channel and control chemoattractant exposure, we observed directional memory in chemotactic neutrophil-like cells. We modeled this directional memory as a long-lived intracellular asymmetry that decays slower than observed membrane phospholipid signaling. Measurements of intracellular dynamics revealed that moesin at the cell rear is a longlived element that when inhibited, results in a reduction of memory. Inhibition of ROCK (Rho-associated protein kinase), downstream of RhoA (Ras homolog gene family, member A), stabilized moesin and directional memory while depolymerization of microtubules (MTs) disoriented moesin deposition and also reduced directional memory. Our study reveals that long-lived polarized cytoskeletal structures, specifically moesin, actomyosin, and MTs, provide a directional memory in neutrophil-like cells even as they respond on short time scales to external chemical cues. [ABSTRACT FROM AUTHOR]

Human carcinoembryonic antigen (CEA) and the CEA family member CEACAM6 (formerly nonspecific crossreacting antigen [NCA]) function in vitro, at least, as homotypic intercellular adhesion molecules and, in model systems, can block the terminal differentiation and anoikis of several different cell types. We have recently demonstrated that the increased cell surface levels of CEA and CEACAM6 in purified human colonocytes from freshly excised, well to poorly differentiated colon carcinomas are inversely correlated with the degree of cellular differentiation. Thus, deregulated expression of CEA/CEACAM6 could directly contribute to colon tumorigenesis by the inhibition of terminal differentiation and anoikis. Evidence against this view includes the common observation of increased CEA/ CEACAM6 expression as normal colonocytes differentiate in their migration up colonic crypt walls. We report here the direct effects of deregulated overexpression of CEA/CEACAM6, at levels observed in colorectal carcinomas, on the differentiation of two human colonic cell lines, SW-1222 and Caco-2. Stable transfectants of both of these cell lines that constitutively express 10- to 30-fold higher cell surface levels of CEA/CEACAM6 than endogenous levels failed to polarize and differentiate into glandular structures in monolayer or 31) culture or to form colonic crypts in a tissue architecture assay in nude mice. In addition, these transfectants were found to exhibit increased tumorigenicity in nude mice. These results thus support the contention that deregulated overexpression of CEA and CEACAM6 could provide a tumorigenic contribution to colon carcinogenesis.

Fucoid zygotes use environmental vectors, including sunlight, to initiate a growth axis a few hours after fertilization. The first division is then transversely oriented by the growth axis, producing daughter cells of distinct fates. The tip growing rhizoid cell gives rise to the holdfast, anchoring the alga to the intertidal substratum, while the opposite thallus cell mainly generates the photosynthetic and reproductive stipe and fronds. Elaboration of this simple growth axis thus establishes the basic body plan of the adult; and elucidating the mechanisms responsible for formation of the growth axis is paramount to understanding fucoid morphogenesis. Recent studies have culminated in a model whereby sunlight, and perhaps other environmental cues, activate the signaling protein Rac1 at the rhizoid pole. Here it sets in motion nucleation of a patch of actin filaments that in turn, targets ions, proteins and cellular processes to the future growth site. At germination, Rac1 initiates morphogenesis by inducing transformation of the patch of actin filaments to a structure that delivers vesicles to the growing tip, and a few hours later orients the spindle and cytokinetic plate.

Cell–tissue–tissue interaction is determined by specific short range forces between cell adhesion molecules (CAMs) and ligands of the tissue, long range repulsion forces mediated by cell surface grafted macromolecules and adhesion-induced elastic stresses in the cell envelope. This interplay of forces triggers the rapid random clustering of tightly coupled linkers. By coupling of actin gel patches to the intracellular domains of the CAMs, these clusters can grow in a secondary process resulting in the formation of functional adhesion microdomains (ADs). The ADs can act as biochemical steering centers by recruiting and activating functional proteins, such as GTPases and associated regulating proteins, through electrostatic–hydrophobic forces with cationic lipid domains that act as attractive centers. First, I summarize physical concepts of cell adhesion revealed by studies of biomimetic systems. Then I describe the role of the adhesion domains as biochemical signaling platforms and force transmission centers promoting cellular protrusions, in terms of a shell string model of cells. Protrusion forces are generated by actin gelation triggered by molecular machines (focal adhesion kinase (FAK), Src-kinases and associated adaptors) which assemble around newly formed integrin clusters. They recruit and activate the GTPases Rac-1 and actin gelation promoters to charged membrane domains via electrostatic–hydrophobic forces. The cell front is pushed forward in a cyclic and stepwise manner and the step-width is determined by the dynamics antagonistic interplay between Rac-1 and RhoA. The global cell polarization in the direction of motion is mediated by the actin–microtubule (MT) crosstalk at adhesion domains. Supramolecular actin–MT assemblies at the front help to promote actin polymerization. At the rear they regulate the dismantling of the ADs through the Ca ++ -mediated activation of the protease calpain and trigger their disruption by RhoA mediated contraction via stress fibers. This article is part of a Special Issue entitled: Mechanobiology. [ABSTRACT FROM AUTHOR]

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by inflammation of the synovial lining (synovitis). The inflammation in the RA joint is associated with and driven by immune cell infiltration, synovial hyperproliferation, and excessive production of proinflammatory mediators, such as tumor necrosis factor α (TNFα), interferon γ (IFNγ), interleukin (IL)-1β, IL-6, and IL-17, eventually resulting in damage to the cartilage and underlying bone. The RA joint harbors a wide range of immune cell types, including monocytes, macrophages, and CD4+ T cells (both proinflammatory and regulatory). The interplay between CD14+ myeloid cells and CD4+ T cells can significantly influence CD4+ T cell function, and conversely, effector vs. regulatory CD4+ T cell subsets can exert profound effects on monocyte/macrophage function. In this review, we will discuss how the interplay between CD4+ T cells and monocytes/macrophages may contribute to the immunopathology of RA. [ABSTRACT FROM AUTHOR]

Pollen tubes are an excellent system for studying the cellular dynamics and complex signaling pathways that coordinate polarized tip growth. Although several signaling mechanisms acting in the tip-growing pollen tube have been described, our knowledge on the subcellular and molecular events during pollen germination and growth site selection at the pollen plasma membrane is rather scarce. To simultaneously track germinating pollen from up to 12 genetically different plants we developed an inexpensive and easy mounting technique, suitable for every standard microscope setup. We performed high magnification live-cell imaging during Arabidopsis pollen activation, germination, and the establishment of pollen tube tip growth by using fluorescent marker lines labeling either the pollen cytoplasm, vesicles, the actin cytoskeleton or the sperm cell nuclei and membranes. Our studies revealed distinctive vesicle and F-actin polarization during pollen activation and characteristic growth kinetics during pollen germination and pollen tube formation. Initially, the germinating Arabidopsis pollen tube grows slowly and forms a uniform roundish bulge, followed by a transition phase with vesicles heavily accumulating at the growth site before switching to rapid tip growth. Furthermore, we found the two sperm cells to be transported into the pollen tube after the phase of rapid tip growth has been initiated. The method presented here is suitable to quantitatively study subcellular events during Arabidopsis pollen germination and growth, and for the detailed analysis of pollen mutants with respect to pollen polarization, bulging, or growth site selection at the pollen plasma membrane. [ABSTRACT FROM AUTHOR]

Collective cell migration (CCM) can be described as a large scale coordinated movement of cells that are in close proximity with each other. It is a phenomenon that is observed not only in physiological processes such as that found in embryogenesis and wound healing but also in pathophysiological processes such as cancer metastasis. Some of the factors influencing this concerted process include cell-cell adhesion, cell-substrate interaction and mechanical cues such as geometrical constraints among others. Here, we review recent research work done to investigate CCM of adherent cells. We highlight the classical example of an in vitro cell monolayer to illustrate our current understanding of the different mechanobiological mechanisms involved as these cells respond to the mechanical cues present in their environment. It is hoped that such understanding may potentially lead to better therapeutic strategies for diseases such as cancer and for tissue engineering and repair. [ABSTRACT FROM AUTHOR]

We present a stochastic model of active vesicular transport and its role in cell polarization, which takes into account positive feedback between membrane-bound signaling molecules and cytoskeletal filaments. In particular, we consider the cytoplasmic transport of vesicles on a two-dimensional cytoskeletal network, in which a vesicle containing signaling molecules can randomly switch between a diffusing state and a state of directed motion along a filament. Using a quasi-steady-state analysis, we show how the resulting stochastic hybrid system can be reduced to an advection-diffusion equation with anisotropic and space-dependent diffusivity. This equation couples to a reaction-diffusion equation for the membrane-bound transport of signaling molecules. We use linear stability analysis to derive conditions for the growth of a precursor pattern for cell polarization, and we show that the geometry of the cytoskeletal filaments plays a crucial role in determining whether the cell is capable of spontaneous cell polarization or only polarizes in response to an external chemical gradient. As previously found in a simpler deterministic model with uniform and isotropic diffusion, the former occurs if filaments are nucleated at sites on the cell membrane (cortical actin), whereas the latter applies if the filaments nucleate from organizing sites within the cytoplasm (microtubule asters). This is consistent with experimental data on cell polarization in two distinct biological systems, namely, budding yeast and neuronal growth cones. Our more biophysically detailed model of motor transport allows us to determine how the conditions for spontaneous cell polarization depend on motor parameters such as mean speed and the rate of unbinding from filament tracks. [ABSTRACT FROM AUTHOR]

Cytotoxic T lymphocytes (CTLs) lyse target cells by delivering lytic granules that contain the pore former perforin to the cytotoxic immunological synapse. Here, we establish that opposing cytoskeletal forces drive lytic granule polarization and simultaneously shape T cell synapse topography to enhance target perforation. At the cell rear, actomyosin contractility drives the anterograde movement of lytic granules toward the nucleus. At the synapse, dynein-derived forces induce negatively curved membrane pockets to which granules are transported around the nucleus. These highly concave degranulation pockets are located directly opposite positively curved bulges on the target cell membrane. We identify a curvature bias in the action of perforin, which preferentially perforates positively curved tumor cell membrane. Together, these findings demonstrate murine and human T cell-mediated cytotoxicity to be a highly tuned mechano-biochemical system, in which the forces that polarize lytic granules locally bend the synaptic membrane to favor the unidirectional perforation of the target cell. [Display omitted] • T cells contract their tail to propel lytic granules anteriorly toward the nucleus • The forces that polarize lytic granules also shape T cell synapse membrane curvature • T cell lytic granules are transported to negatively curved degranulation pockets • Perforin preferentially perforates positively curved plasma membrane Govendir and Kempe et al. employ biophysical methods and quantitative imaging to study the mechanics of individual T cells killing tumor cells. The authors show that the cellular forces that polarize lytic granules also induce highly curved membrane pockets at the synapse, where perforin preferentially perforates positively curved target membrane. [ABSTRACT FROM AUTHOR]

P-glycoprotein (P-gp), an ATP-binding cassette (ABC), is able to transport structurally and chemically unrelated substrates. Overexpression of P-gp in cancer cells significantly decreases the intercellular amount of anticancer drugs, and results in multidrug resistance in cancer cells, a major obstacle in cancer chemotherapy. P-gp is mainly localized on the plasma membrane and functions as a drug efflux pump; however, P-gp is also localized in many intracellular compartments, such as endoplasmic reticulum, Golgi, endosomes and lysosomes. P-gp moves between the intracellular compartments and the plasma membrane in a microtubule-actin dependent manner. This review highlights our current understanding of 1) the intracellular localization of P-gp; 2) the trafficking and cycling pathways among the cellular compartments as well as between these compartments and the plasma membrane; and 3) the cellular factors regulating P-gp traffic and cycling. This review also presents a potential implication in overcoming P-gp-mediated multidrug resistance by targeting P-gp traffic and cycling pathways and impairing P-gp localization on the plasma membrane.

In amniotes, primitive endoderm(PrE) plays important roles not only for nutrient support but also as an inductive tissue required for embryo patterning. PrE is an epithelial monolayer that is visible shortly before embryo implantation and is one of the first three cell lineages produced by the embryo. We review here the molecular mechanisms that have been uncovered during the past 10 years on PrE and epiblast cell lineage specification within the inner cell mass of the blastocyst and on their subsequent steps of differentiation. [ABSTRACT FROM AUTHOR]

Fucoid zygotes use environmental vectors, including sunlight, to initiate a growth axis a few hours after fertilization. The first division is then transversely oriented by the growth axis, producing daughter cells of distinct fates. The tip growing rhizoid cell gives rise to the holdfast, anchoring the alga to the intertidal substratum, while the opposite thallus cell mainly generates the photosynthetic and reproductive stipe and fronds. Elaboration of this simple growth axis thus establishes the basic body plan of the adult; and elucidating the mechanisms responsible for formation of the growth axis is paramount to understanding fucoid morphogenesis. Recent studies have culminated in a model whereby sunlight, and perhaps other environmental cues, activate the signaling protein Rac1 at the rhizoid pole. Here it sets in motion nucleation of a patch of actin filaments that in turn, targets ions, proteins, and cellular processes to the future growth site. At germination, Rac1 initiates morphogenesis by inducing transformation of the patch of actin filaments to a structure that delivers vesicles to the growing tip, and a few hours later orients the spindle and cytokinetic plate. [ABSTRACT FROM AUTHOR]

The morphometric characteristics of NCTC cell clone 929 were compared before and after coming into contact with type I collagen added to cultivation medium. The cells were plated onto plastic in the form of a colony. The day after seeding, the cultivation medium was replaced by the same medium complemented with 0.1% type I collagen. The cells were incubated in this medium for 30 min more and then washed out of collagen. Using time-lapse shooting, the cell image at the colony edge was recorded for 7 h. The area of the cells and the degrees of their spreading and polarization were measured. It is shown that the contact with collagen did not affect the cell area, decreased cell spreading, and sharply reduced the portion of polarized cells. These results probably show the sensitivity of NCTC cells to the presence of type I collagen in cultivation medium and suggest that collagen plays an active role in formation by cells of long filopodia. [ABSTRACT FROM AUTHOR]

It has been well established that an aligned matrix provides structural and signaling cues to guide cell polarization and cell fate decision. However, the modulation role of cells in matrix remodeling and the feedforward effect on stem cell differentiation have not been studied extensively. In this study, we report on the concerted changes of human decidua parietalis placental stem cells (hdpPSCs) and the highly ordered collagen fibril matrix in response to cell–matrix interaction. With high-resolution imaging, we found the hdpPSCs interacted with the matrix by deforming the cell shape, harvesting the nearby collagen fibrils, and reorganizing the fibrils around the cell body to transform a 2D matrix to a localized 3D matrix. Such a unique 3D matrix prompted high expression of β-1 integrin around the cell body that mediates and facilitates the stem cell differentiation toward neural cells. The study offers insights into the coordinated, dynamic changes at the cell–matrix interface and elucidates cell modulation of its matrix to establish structural and biochemical cues for effective cell growth and differentiation. [ABSTRACT FROM AUTHOR]

Proteins are typically categorized into protein families based on their domain organization. Yet, evolutionarily unrelated proteins can also be grouped together according to their common functional roles. Sequestering proteins constitute one such functional class, acting as macromolecular buffers and serving as an intracellular reservoir ready to release large quantities of bound proteins or other molecules upon appropriate stimulation. Another functional protein class comprises effector proteins, which constitute essential components of many intracellular signal transduction pathways. For instance, effectors of small GTP-hydrolases are activated upon binding a GTP-bound GTPase and thereupon participate in downstream interactions. Here we describe a member of the IQGAP family of scaffolding proteins, DGAP1 from Dictyostelium, which unifies the roles of an effector and a sequestrator in regard to the small GTPase Rac1. Unlike classical effectors, which bind their activators transiently leading to short-lived signaling complexes, interaction between DGAP1 and Rac1-GTP is stable and induces formation of a complex with actin-bundling proteins cortexillins at the back end of the cell. An oppositely localized Rac1 effector, the Scar/WAVE complex, promotes actin polymerization at the cell front. Competition between DGAP1 and Scar/WAVE for the common activator Rac1-GTP might provide the basis for the oscillatory re-polarization typically seen in randomly migrating Dictyostelium cells. We discuss the consequences of the dual roles exerted by DGAP1 and Rac1 in the regulation of cell motility and polarity, and propose that similar signaling mechanisms may be of general importance in regulating spatiotemporal dynamics of the actin cytoskeleton by small GTPases. [ABSTRACT FROM AUTHOR]

Cell polarization, in which intracellular substances are asymmetrically distributed, enables cells to carry out specialized functions. While cell polarity is often induced by intracellular or extracellular spatial cues, spontaneous polarization (the so-called symmetry breaking) may also occur in the absence of spatial cues. Many computational models have been used to investigate the mechanisms of symmetry breaking, and it was proved that spontaneous polarization occurs when the lateral diffusion of inactive signaling molecules is much faster than that of active signaling molecules. This conclusion leaves an important question of how, as observed in many biological systems, cell polarity emerges when active and inactive membrane-bound molecules diffuse at similar rates while cycling between cytoplasm and membrane takes place. The recent studies of Rätz and Röger showed that, when the cytosolic and membrane diffusion are very different, spontaneous polarization is possible even if the membrane-bound species diffuse at the same rate. In this paper, we formulate a two-equation non-local reaction-diffusion model with general forms of positive feedback. We apply Turing stability analysis to identify parameter conditions for achieving cell polarization. Our results show that spontaneous polarization can be achieved within some parameter ranges even when active and inactive signaling molecules diffuse at similar rates. In addition, different forms of positive feedback are explored to show that a non-local molecule-mediated feedback is important for sharping the localization as well as giving rise to fast dynamics to achieve robust polarization. [ABSTRACT FROM AUTHOR]

Highlights: [•] Microfluidic chambers provide a highly quantitative means for analysis of vectorial movement of cells, including positioning of organelles within migrating cells. [•] Reduced rate of migration was observed in fibroblasts from DYT1 dystonia patients as compared to controls. [•] Abnormal feature in the relative positions of the Golgi and nucleus is more variable in DYT1, as compared to control cells in the process of migrating. [ABSTRACT FROM AUTHOR]

Cell polarization relies on small GTPases, such as Cdc42, which can break symmetry through self-organizing principles, and landmarks that define the axis of polarity. In fission yeast, microtubules deliver the Tea1-Tea4 complex to mark cell poles for growth, but how this complex activates Cdc42 is unknown. Here, we show that ectopic targeting of Tea4 to cell sides promotes the local activation of Cdc42 and cell growth. This activity requires that Tea4 binds the type I phosphatase (PP1) catalytic subunit Dis2 or Sds21, and ectopic targeting of either catalytic subunit is similarly instructive for growth. The Cdc42 guanine-nucleotide-exchange factor Gef1 and the GTPase-activating protein Rga4 are required for Tea4-PP1-dependent ectopic growth. Gef1 is recruited to ectopic Tea4 and Dis2 locations to promote Cdc42 activation. By contrast, Rga4 is locally excluded by Tea4, and its forced colocalization with Tea4 blocks ectopic growth, indicating that Rga4 must be present, but at sites distinct from Tea4. Thus, a Tea4-PP1 landmark promotes local Cdc42 activation and growth both through Cdc42 GEF recruitment and by creating a local trough in a Cdc42 GAP. [ABSTRACT FROM AUTHOR]

Adhesive interactions of cadherins induce crosstalk between adhesion complexes and the actin cytoskeleton, allowing strengthening of adhesions and cytoskeletal organization. The underlying mechanisms are not completely understood, and microtubules (MTs) might be involved, as for integrin-mediated cell -- extracellular-matrix adhesions. Therefore, we investigated the relationship between N-cadherin and MTs by analyzing the influence of N-cadherin engagement on MT distribution and dynamics. MTs progressed less, with a lower elongation rate, towards cadherin adhesions than towards focal adhesions. Increased actin treadmilling and the presence of an actomyosin contractile belt, suggested that actin relays inhibitory signals from cadherin adhesions to MTs. The reduced rate of MT elongation, associated with reduced recruitment of end-binding (EB) proteins to plus ends, was alleviated by expression of truncated N-cadherin, but was only moderately affected when actomyosin was disrupted. By contrast, destabilizing actomyosin fibers allowed MTs to enter the adhesion area, suggesting that tangential actin bundles impede MT growth independently of MT dynamics. Blocking MT penetration into the adhesion area strengthened cadherin adhesions. Taken together, these results establish a crosstalk between N-cadherin, F-actin and MTs. The opposing effects of cadherin and integrin engagement on actin organization and MT distribution might induce bias of the MT network during cell polarization. [ABSTRACT FROM AUTHOR]

Abstract: This technical note describes a method for distinguishing normal skin tissue samples from those electrically injured by Fourier transform infrared microspectroscopy (FTIR MSP). Furthermore, the infrared spectral features of electrically injured cells and tissues were evaluated to identify molecular changes in epidermal cells. In the present study, 20 human hand tissue samples were evaluated macroscopically and histopathologically. The electrically injured skin samples were subdivided into 2 regions [normal cell regions (NCRs) and polarized cell regions (PCRs)] and 14 major spectral absorption bands were selected. The spectral results showed that the band absorbance at 1080, 1126, 1172, 1242, 1307, 1403, 1456, 1541, 2852, 2925, 2957, 3075, and 3300cm−1 increased significantly both in the stratum and non-stratum corneum of the PCRs in electrically injured skin tissues samples. No significant difference was found between normal skin and the NCR of the electrically injured skin samples. The band absorbance ratios of A 1172/A 1126, A 1456/A 1403, and A 2925/A 2957 were significantly increased, whereas the A 1652/A 1541 ratio was decreased in the PCR of the stratum corneum and non-stratum corneum. Baseline changes from 4000 to near 1737cm−1 were observed in the spectra of the electrically injured skin samples, which were interpreted in terms of the pathological process involved in electrical injury. FTIR-MSP presents a useful method to provide objective spectral markers for the assisted diagnosis of electrical marks. [Copyright &y& Elsevier]

Many mathematical models have been proposed for the process of cell polarization. Some of these are 'functional models' that capture a class of dynamical behaviour, whereas others are derived from features of signalling molecules. Some mechanistic models are detailed, and therefore complex, whereas others are simplified. Each type contributes to our understanding of cell polarization. However, the huge variety at different levels of detail makes comparisons challenging. Here, we provide examples of both elementary and more detailed models for polarization. We also display how a recent mathematical method, local perturbation analysis, can provide an appropriate tool for such comparisons. This technique simplifies and speeds up the model development process by revealing the effect of model extensions, parameter variations and in silico manipulations such as knock-out or over-expression of key molecules. Finally, simulations in both one dimension and two dimensions, and particularly in deforming two-dimensional 'cells', can highlight behaviour not captured by traditional simulation methods. [ABSTRACT FROM AUTHOR]

Abstract: Multicellular development has evolved independently on numerous occasions and there is great interest in the developmental mechanisms utilized by each of the divergent lineages. Fucoid algae, in the stramenopile lineage (distinct from metazoans, fungi and green plants) have long been used as a model for early development based on unique life cycle characteristics. The initially symmetric fucoid zygote generates a developmental axis that determines not only the site of growth, but also the orientation of the first cell division, whose products have distinct developmental fates. Establishment and maintenance of this growth axis is dependent on formation of a filamentous actin array that directs vesicular movement, depositing new membrane and wall material for development of the rhizoid. What is not well known, is how formation and placement of the actin array is regulated in fucoid algae. A candidate for this function is Rac1, a small GTPase of the highly conserved Rho family, which has been implicated in controlling the formation of actin arrays in diverse eukaryotes. We demonstrate that Rac1 is not only present during formation of the filamentous actin array, but that its localization overlaps with the array in polarizing zygotes. Pharmacologically inhibiting Rac1 activity was shown to impede formation and maintenance of the actin array, and ultimately polar growth. Evidence is provided that a requirement of Rac1 function is its ability to associate with membranes via a post-translationally added lipid tail. Taken together, the data indicate that Rac1 is a necessary participant in establishment of the growth pole, presumably by regulating the placement and formation of the actin array. A role for Rac1 and related proteins in regulating actin is shared by animals, plants, fungi and with this work, brown algae, thus a conserved mechanism for generating polarity is in operation in unique eukaryotic lineages. [Copyright &y& Elsevier]

Abstract: Electrochemical deposition from Ni2+ and Fe2+ using sulfate and nitrate solutions is carried out under galvanostatic regime. The resulting films are oxidized and examined in lithium test cells as potential anode materials for lithium-ion batteries. X-ray diffraction, XPS and SAED–TEM analyses revealed a thin film based on nanocomposite NiO and Fe2O3. Cycling studies show the smallest discharge polarization ever reported during the conversion reactions of metal oxides at ∼0.8V. Unlike typical transition metal oxides, the amorphous oxidized material exhibited low irreversibility from first to second discharge (∼15%) and a distinctive plateau on consecutive discharge branches. The changes in the film thickness on increasing deposition time and the crystallization phenomena on annealing the deposits strongly affect the electrochemical behavior. The present approach allows preparing a powder free electrode with improved coulombic efficiency directly on the current collector and opens a set of novel preparation routes in this field with intriguing results. [Copyright &y& Elsevier]

Over time we have come to appreciate that the complex regulation of Rho GTPases involves additional mechanisms beyond the activating role of RhoGEFs, the inactivating function of RhoGAPs and the sequestering activity of RhoGDIs. One class of regulatory mechanisms includes direct modifications of Rho proteins such as isoprenylation, phosphorylation and SUMOylation. Rho GTPases can also regulate each other by means of crosstalk signaling, which is again mostly mediated by GEFs, GAPs and GDIs. More complex mutual regulation ensues when and where two or more Rho proteins activate a common molecular target, i.e., share a common effector. We have recently unraveled a reciprocal mechanism wherein spatiotemporal dynamics of Rac1 activity during migration of Dictyostelium cells is apparently regulated by antagonizing interactions of Rac1-GTP with two distinct effectors. By monitoring specific fluorescent probes, activated Rac1 is simultaneously present at the leading edge, where it participates in Scar/WAVE-mediated actin polymerization, and at the trailing edge, where it induces formation of a DGAP1/ cortexillin actin-bundling complex. Strikingly, in addition to their opposed localization, the two populations of activated Rac1 also display opposite kinetics of recruitment to the plasma membrane upon stimulation by chemoattractants. These findings with respect to Rac1 in Dictyostelium suggest a novel principle for regulation of Rho GTPase activity that might also play a role in other cell types and for other Rho family members. [ABSTRACT FROM AUTHOR]

T cell uropods are enriched in specific proteins including adhesion receptors such as P-selectin glycoprotein ligand-1 (PSGL-1), lipid raft-associated proteins such as flotillins and ezrin/radixin/moesin (ERM) proteins which associate with cholesterol-rich raft domains and anchor adhesion receptors to the actin cytoskeleton. Using dominant mutants and siRNA technology we have tested the interactions among these proteins and their role in shaping the T cell uropod. Expression of wild type (WT) ezrin-EGFP failed to affect the morphology of human T cells or chemokine-induced uropod recruitment of PSGL-1 and flotillin-1 and -2. In contrast, expression of constitutively active T567D ezrin-EGFP induced a motile, polarized phenotype in some of the transfected T cells, even in the absence of chemokine. These cells featured F-actin-rich ruffles in the front and uropod enrichment of PSGL-1 and flotillins. T567D ezrin-EGFP was itself strongly enriched in the rear of the polarized T cells. Uropod for-mation induced byT567D ezrin-EGFP was actin-dependent as it was attenuated by inhibition of Rho-kinase or myosin II, and abolished by disruption of actin filaments. While expression of constitutively active ezrin enhanced cell polarity, expression of a dominant-negative deletion mutant of ezrin, 1-310 ezrin-EGFP, markedly reduced uropod formation induced by the chemokine SDF-1, T cell front-tail polarity, and capping of PSGL-1 and flotillins. Transfection of T cells with WT or T567D ezrin did not affect chemokine-mediated chemotaxis whereas 1-310 ezrin significantly impaired spontaneous 2D migration and chemotaxis. siRNA-mediated downregulation of flotillins in murine T cells attenuated moesin capping and uropod formation, indicating that ERMproteins and flotillins cooperate in uropod formation. In summary, our results indicate that activated ERM proteins function together with flotillins to promote efficient chemotaxis of T cells by structuring the uropod of migrating T cells. [ABSTRACT FROM AUTHOR]

Abstract: A detailed investigation is carried out to correlate configurational variation of SOFC anode with electrical characterizations. For this purpose, Ni-YSZ cermet anode (28–32vol.% Ni) having a novel core-shell microstructure (prepared by electroless technique) has been used in conjunction with conventional cermet (40vol.% Ni). Depending upon the thickness, electroless cermet is used in two configurations, viz. (i) as layered anode and (ii) as anode active layers (AAL). Thicknesses of electroless layer are varied sequentially for both these configurations for inducing functionality in the cermet. Layered anode with 140μm electroless layer (32vol.% Ni) shows maximum electrical conductivity (644Scm−1) with only 7% degradation after 20 redox cycles at 800°C. A theoretical approach is attempted to explain the overall cell polarization behavior and to quantify the polarization components. Single cells fabricated with electroless AAL show lowest polarization (~0.3Ω.cm2) with minimum contribution of charge transfer and concentration polarization. As a result, single cell having such a thin (~15μm) AAL, exhibits the highest electrochemical performance (~3.7A.cm−2) with significant low degradation rate (2.8% 1000h−1) at 800°C, 0.7V. [Copyright &y& Elsevier]

Abstract: A hemocyte primary culture system for Pomacea canaliculata in a medium mimicking hemolymphatic plasma composition was developed. Hemocytes adhered and spread onto culture dish in the first few hours after seeding but later began forming aggregates. Time-lapse video microscopy showed the dynamics of the early aggregation, with cells both entering and leaving the aggregates. During this period phagocytosis occurs and was quantified. Later (>4 h), hemocytes formed large spheroidal aggregates that increased in size and also merged with adjacent spheroids (24–96 h). Large single spheroids and spheroid aggregates detach from the bottom surface and float freely in the medium. Correlative confocal, transmission electron and phase contrast microscopy showed a peculiar organization of the spheroids, with a compact core, an intermediate zone with large extracellular lacunae and an outer zone of flattened cells; also, numerous round cells emitting cytoplasmic extensions were seen attaching to the spheroids'' smooth surface. Dual DAPI/propidium iodide staining revealed the coexistence of viable and non-viable cells within aggregates, in varying proportions. DNA concentration increased during the first 24 h of culture and stabilized afterward. BrdU incorporation also indicated proliferation. Spontaneous spheroid formation in culture bears interesting parallels with spheroidal hemocyte aggregates found in vivo in P. canaliculata, and also with spheroids formed by tumoral or non-tumoral mammalian cells in vitro. [Copyright &y& Elsevier]

The nematode (roundworm) Caenorhabditis elegans is one of the most popular animal models for the study of developmental biology, as its invariant development and transparent body enable in toto cellular-resolution fluorescence microscopy imaging of developmental processes at 1-min intervals. This has led to the development of various computational tools for the systematic and automated analysis of imaging data to delineate the molecular and cellular processes throughout the embryogenesis of C. elegans , such as those associated with cell lineage, cell migration, cell morphology, and gene activity. In this review, we first introduce C. elegans embryogenesis and the development of techniques for tracking cell lineage and reconstructing cell morphology during this process. We then contrast the developmental modes of C. elegans and the customized technologies used for studying them with the ones of other animal models, highlighting its advantage for studying embryogenesis with exceptional spatial and temporal resolution. This is followed by an examination of the physical models that have been devised-based on accurate determinations of developmental processes afforded by analyses of imaging data-to interpret the early embryonic development of C. elegans from subcellular to intercellular levels of multiple cells, which focus on two key processes: cell polarization and morphogenesis. We subsequently discuss how quantitative data-based theoretical modeling has improved our understanding of the mechanisms of C. elegans embryogenesis. We conclude by summarizing the challenges associated with the acquisition of C. elegans embryogenesis data, the construction of algorithms to analyze them, and the theoretical interpretation., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2022 The Author(s).)

Abstract: Polarized cell morphogenesis requires actin cytoskeleton rearrangement for polarized transport of proteins, organelles and secretory vesicles, which fundamentally underlies cell differentiation and behavior. During yeast mating, Saccharomyces cerevisiae responds to extracellular pheromone gradients by extending polarized projections, which are likely maintained through vesicle transport to (exocytosis) and from (endocytosis) the membrane. We experimentally demonstrate that the projection morphology is pheromone concentration-dependent, and propose the underlying mechanism through mathematical modeling. The inclusion of membrane flux and dynamically evolving cell boundary into our yeast mating signaling model shows good agreement with experimental measurements, and provides a plausible explanation for pheromone-induced cell morphology. [Copyright &y& Elsevier]

Objectives: Neutrophil polarization is critical for the inflammatory response. AKT is a serine/threonine protein kinase and has been implicated in cell migration. However, it is not completely clear whether AKT affects neutrophil polarization. In this study, we tested the hypothesis that AKT regulates the polarization of neutrophil-like differentiated HL-60 cells (dHL-60) in response to fMLP. Methods: HL-60 cells were differentiated into dHL-60 by incubation in medium containing 1.3 % DMSO for up to 6 days. Polarization of dHL-60 cells and primary human neutrophils were measured by Zigmond chamber. Phospho-Akt was analyzed by immunofluorescence and Western blot analysis. F-actin polymerization was detected by Rhodamine-Phalloidine staining. Rac2 activation was evaluated using GST Pull-down assay. Results: We found that changes in the rate of cell polarization were consistent with the changes in AKT phosphorylation levels during HL-60 cell differentiation in response to fMLP. Moreover, cell polarization and AKT phosphorylation were reduced in fMLP-stimulated dHL-60 cells pretreated with the PI3 kinase inhibitors or the AKT inhibitors, which was confirmed in the primary human neutrophils. The AKT inhibitors altered fMLP-induced F-actin polymerization. Rac2 GTPases was also decreased by the AKT inhibitors in fMLP-stimulated dHL-60 cells. Conclusion: This study demonstrates that AKT activation plays a crucial role in dHL-60 cell polarization. [ABSTRACT FROM AUTHOR]

The structure, distribution and possible roles of mitochondria in growing pollen tubes is reviewed. Diverse microscopical methods have been applied to the analysis of mitochondria in pollen, with a predominance in recent years on vital fluorescent probes. We review the application of different dyes to pollen tubes, with a special emphasis on the ratiometric dye JC-1. Morphometric data shows a concentration of mitochondria in the subapical area of pollen tubes, apparently with more frequency of mitochondria with membrane depolarization when compared with the rest of the tube. Remarkably, data from various species and from transcriptomics indicates that different species may have different respiratory adaptations, ranging from high oxygen consumption in the early steps of germination, to energy production and growth on almost anoxic conditions. Various studies also showed that the pollen of many species is refractory to some common respiration inhibitors, including the ones from the alternative pathway. Given the conspicuous distribution and apparent subapical accumulation of mitochondria, we speculate on their functional relationship with known apical ion gradients that seem to characterize pollen tubes. [ABSTRACT FROM AUTHOR]

IQGAP1 is an important cytoskeletal regulator, known to act at the plasma membrane to bundle and cap actin filaments, and to tether the cortical actin meshwork to microtubules via plus-end binding proteins. Here we describe the novel subcellular localization of IQGAP1 at the cytoplasmic face of the nuclear envelope, where it co-located with F-actin. The IQGAP1 and F-actin staining overlapped that of microtubules at the nuclear envelope, revealing a pattern strikingly similar to that observed at the plasma membrane. In detergent-extracted cells IQGAP1 was retained at cytoskeletal structures at the nuclear envelope. This finding has new implications for involvement of IQGAP1 in cell polarization and migration events and potentially in cell cycle-associated nuclear envelope assembly/disassembly. [ABSTRACT FROM AUTHOR]

Podosomes are actin-rich adhesion and invasion structures. Especially in macrophages, podosomes exist in two subpopulations, large precursors at the cell periphery and smaller podosomes (successors) in the cell interior. To date, the mechanisms that differentially regulate these subpopulations are largely unknown. Here, we show that the membrane-associated protein supervillin localizes preferentially to successor podosomes and becomes enriched at precursors immediately before their dissolution. Consistently, podosome numbers are inversely correlated with supervillin protein levels. Using deletion constructs, we find that the myosin II regulatory Nterminus of supervillin [SV(1-174)] is crucial for these effects. Phosphorylated myosin light chain (pMLC) localizes at supervillinpositive podosomes, and time-lapse analyses show that enrichment of GFP-supervillin at podosomes coincides with their coupling to contractile myosin-IIA-positive cables. We also show that supervillin binds only to activated myosin IIA, and a dysregulated N-terminal construct [SV(1-830)] enhances pMLC levels at podosomes. Thus, preferential recruitment of supervillin to podosome subpopulations might both require and induce actomyosin contractility. Using siRNA and pharmacological inhibition, we demonstrate that supervillin and myosin IIA cooperate to regulate podosome lifetime, podosomal matrix degradation and cell polarization. In sum, we show here that podosome subpopulations differ in their molecular composition and identify supervillin, in cooperation with myosin IIA, as a crucial factor in the regulation of podosome turnover and function. [ABSTRACT FROM AUTHOR]

In this work, we investigate the dynamics of a nonlocal model describing spontaneous cell polarization. It consists of a drift-diffusion equation set in the half-space, with the coupling involving the trace value on the boundary. We characterize the following behaviors in the onedimensional case: solutions are global if the mass is below the critical mass and they blow up in finite time above the critical mass. The higher-dimensional case is also discussed. The results are reminiscent of the classical Keller--Segel system, but critical spaces are different (LN instead of LN/2 due to the coupling on the boundary). In addition, in the one-dimensional case we prove quantitative convergence results using relative entropy techniques. This work is complemented with a more realistic model that takes into account dynamical exchange of molecular content at the boundary. In the one-dimensional case we prove that blow-up is prevented. Furthermore, density converges toward a nontrivial stationary configuration. [ABSTRACT FROM AUTHOR]

Abstract: Rho-family small GTPases regulate epithelial cell sheet migration by organizing actin and myosin during wound healing. Here, we report that Pak3, but not Pak1, is a downstream target protein for Rac1 in wound closure of the Drosophila larval epidermis. Pak3-deficient larvae failed to close a wound hole and this defect was not rescued by Pak1 expression, indicating differential functions of the two proteins. Pak3 localized to the wound margin, which selectively required Rac1. Pak3-deficient larvae showed severe defects in actin-myosin organization at the wound margin and in submarginal cells, which was reminiscent of the phenotypes of Rac1-deficient larvae. These results suggest that Pak3 specifically mediates Rac1 signaling in organizing actin and myosin during Drosophila epidermal wound healing. [Copyright &y& Elsevier]