Active Cell Movement Research Articles

Modelling the effect of cell motility on mixing and invasion in epithelial monolayers

Collective cell invasion underlies several biological processes such as wound healing, embryonic development, and cancerous invasion. Here, we investigate the impact of cell motility on invasion in epithelial monolayers and its coupling to cellular mechanical properties, such as cell-cell adhesion and cortex contractility. We develop a two-dimensional computational model for cells with active motility based on the cellular Potts model, which predicts that the cellular invasion speed is mainly determined by active cell motility and is independent of the biological and mechanical properties of the cells. We also find that, in general, motile cells out-compete and invade non-motile cells, however, this can be reversed by differential cell proliferation. Stable coexistence of motile and static cell types is also possible for certain parameter regimes.

LiverZap: a chemoptogenetic tool for global and locally restricted hepatocyte ablation to study cellular behaviours in liver regeneration.

The liver restores its mass and architecture after injury. Yet, investigating morphogenetic cell behaviours and signals that repair tissue architecture at high spatiotemporal resolution remains challenging. We developed LiverZap, a tuneable chemoptogenetic liver injury model in zebrafish. LiverZap employs the formation of a binary FAP-TAP photosensitiser followed by brief near-infrared illumination inducing hepatocyte-specific death and recapitulating mammalian liver injury types. The tool enables local hepatocyte ablation and extended live imaging capturing regenerative cell behaviours, which is crucial for studying cellular interactions at the interface of healthy and damaged tissue. Applying LiverZap, we show that targeted hepatocyte ablation in a small region of interest is sufficient to trigger local liver progenitor-like cell (LPC)-mediated regeneration, challenging the current understanding of liver regeneration. Surprisingly, the LPC response is also elicited in adjacent uninjured tissue, at up to 100 µm distance to the injury. Moreover, dynamic biliary network rearrangement suggests active cell movements from uninjured tissue in response to substantial hepatocyte loss as an integral step of LPC-mediated liver regeneration. This precisely targetable liver cell ablation tool will enable the discovery of key molecular and morphogenetic regeneration paradigms.

Computational methods for multiscale modelling of virus infection dynamics

Abstract Virus infection dynamics is governed by the processes on multiple scales: on the whole organism level, tissue level, and intracellular level. In this paper, we develop a multi-scale multi-compartment model of HIV infection in a simplified setting and the computational methods for numerical realization of the model. The multiscale model describes the processes from various scales and of different nature (cell motility, virus diffusion, intracellular virus replication). Intracellular replication model is based on a Markov chain with time-inhomogeneous propensities that depend on the extracellular level of virions. Reaction diffusion equations used to model free virion diffusion in the lymphoid tissue have moving sources, which are determined by the positions of the infected cells (immune cell motility model) and the rate of virion secretion from them (intracellular model). Immune cell motility model parameterizes the intercellular interaction forces, friction and the stochastic force of active cell motility. Together, this allows for a proper description of the intracellular stochasticity that propagates across multiple scales. A hybrid discrete-continuous stochastic-deterministic algorithm for simulation of the multiscale model based on the uniformization Monte Carlo method is implemented.

Is energy excess the initial trigger of carbon overflow metabolism? Transcriptional network response of carbon-limited Escherichia coli to transient carbon excess

BackgroundEscherichia coli adapted to carbon-limiting conditions is generally geared for energy-efficient carbon utilization. This includes also the efficient utilization of glucose, which serves as a source for cellular building blocks as well as energy. Thus, catabolic and anabolic functions are balanced under these conditions to minimize wasteful carbon utilization. Exposure to glucose excess interferes with the fine-tuned coupling of anabolism and catabolism leading to the so-called carbon overflow metabolism noticeable through acetate formation and eventually growth inhibition.ResultsCellular adaptations towards sudden but timely limited carbon excess conditions were analyzed by exposing slow-growing cells in steady state glucose-limited continuous culture to a single glucose pulse. Concentrations of metabolites as well as time-dependent transcriptome alterations were analyzed and a transcriptional network analysis performed to determine the most relevant transcription and sigma factor combinations which govern these adaptations. Down-regulation of genes related to carbon catabolism is observed mainly at the level of substrate uptake and downstream of pyruvate and not in between in the glycolytic pathway. It is mainly accomplished through the reduced activity of CRP-cAMP and through an increased influence of phosphorylated ArcA. The initiated transcriptomic change is directed towards down-regulation of genes, which contribute to active movement, carbon uptake and catabolic carbon processing, in particular to down-regulation of genes which contribute to efficient energy generation. Long-term changes persisting after glucose depletion and consumption of acetete encompassed reduced expression of genes related to active cell movement and enhanced expression of genes related to acid resistance, in particular acid resistance system 2 (GABA shunt) which can be also considered as an inefficient bypass of the TCA cycle.ConclusionsOur analysis revealed that the major part of the trancriptomic response towards the glucose pulse is not directed towards enhanced cell proliferation but towards protection against excessive intracellular accumulation of potentially harmful concentration of metabolites including among others energy rich compounds such as ATP. Thus, resources are mainly utilized to cope with “overfeeding” and not for growth including long-lasting changes which may compromise the cells future ability to perform optimally under carbon-limiting conditions (reduced motility and ineffective substrate utilization).

Activity-Induced Fluidization and Arrested Coalescence in Fusion of Cellular Aggregates

At long time scales, tissue spheroids may flow or appear solid depending on their capacity to reorganize their internal structure. Understanding the relationship between intrinsic mechanical properties at the single cell level, and the tissue spheroids dynamics at the long-time scale is key for artificial tissue constructs, which are assembled from multiple tissue spheroids that over time fuse to form coherent structures. The dynamics of this fusion process are frequently analyzed in the framework of liquid theory, wherein the time scale of coalescence of two droplets is governed by its radius, viscosity and surface tension. In this work, we extend this framework to glassy or jammed cell behavior which can be observed in spheroid fusion. Using simulations of an individual-cell based model, we demonstrate how the spheroid fusion process can be steered from liquid to arrested by varying active cell motility and repulsive energy as established by cortical tension. The divergence of visco-elastic relaxation times indicates glassy relaxation near the transition toward arrested coalescence. Finally, we investigate the role of cell growth in spheroid fusion dynamics. We show that the presence of cell division introduces plasticity in the material and thereby increases coalescence during fusion.

Capillarity and active cell movement at mesendoderm translocation in the Xenopus gastrula.

During Xenopus gastrulation, leading edge mesendoderm (LEM) advances animally as a wedge-shaped cell mass over the vegetally moving blastocoel roof (BCR). We show that close contact across the BCR-LEM interface correlates with attenuated net advance of the LEM, which is pulled forward by tip cells while the remaining LEM frequently separates from the BCR. Nevertheless, lamellipodia persist on the detached LEM surface. They attach to adjacent LEM cells and depend on PDGF-A, cell-surface fibronectin and cadherin. We argue that active cell motility on the LEM surface prevents adverse capillary effects in the liquid LEM tissue as it moves by being pulled. It counters tissue surface-tension effects with oriented cell movement and bulges the LEM surface out to keep it close to the curved BCR without attaching to it. Proximity to the BCR is necessary, in turn, for the maintenance and orientation of lamellipodia that permit mass cell movement with minimal substratum contact. Together with a similar process in epithelial invagination, vertical telescoping, the cell movement at the LEM surface defines a novel type of cell rearrangement: vertical shearing.

Single-cell transcriptomic analysis of eutopic endometrium and ectopic lesions of adenomyosis

BackgroundAdenomyosis (AM) is a common benign chronic gynaecological disorder; however, the precise pathogenesis of adenomyosis is still poorly understood. Single-cell RNA sequencing (scRNA-seq) can uncover rare subpopulations, explore genetic and functional heterogeneity, and reveal the uniqueness of each cell. It provides us a new approach to reveal biological issues from a more detailed and microscopic perspective. Here, we utilize this revolutionary technology to identify the changes of gene expression patterns between ectopic lesions and the eutopic endometrium at the single-cell level and explore a potential novel pathogenesis of AM.MethodsA control endometrium (sample with leiomyoma excluding endometrial disorders, n = 1), eutopic endometrium and ectopic lesion (from a patient with adenomyosis, n = 1) samples were analysed by scRNA-seq, and additional leiomyoma (n = 3) and adenomyosis (n = 3) samples were used to confirm colocalization and vasculogenic mimicry (VM) formation. Protein colocalization was visualized by immunofluorescence, and CD34-periodic acid-Schiff (PAS) double staining was used to assess the formation of VM.ResultsThe scRNA-seq results suggest that cancer-, cell motility- and inflammation- (CMI) associated terms, cell proliferation and angiogenesis play important roles in the progression of AM. Moreover, the colocalization of EPCAM and PECAM1 increased significantly in the ectopic endometrium group (P < 0.05), cell subpopulation with high copy number variation (CNV) levels possessing tumour-like features existed in the ectopic lesion sample, and VNN1- and EPCAM-positive cell subcluster displayed active cell motility in endometrial epithelial cells. Furthermore, during the transformation of epithelial cells to endothelial cells, we observed the significant accumulation of VM formation (positively stained with PAS but not CD34, P < 0.05) in ectopic lesions.ConclusionsIn the present study, our results support the theory of adenomyosis derived from the invasion and migration of the endometrium. Moreover, cell subcluster with high CNV level and tumour-associated characteristics is identified. Furthermore, epithelial-endothelial transition (EET) and the formation of VM in tumours, the latter of which facilitates the blood supply and plays an important role in maintaining cell growth, were also confirmed to occur in AM. These results indicated that the inhibition of EET and VM formation may be a potential strategy for AM management.

FGF21 Induced by the ASK1-p38 Pathway Promotes Mechanical Cell Competition by Attracting Cells

Cell competition is a social cellular phenomenon in which unfit cells are selectively eliminated to maintain tissue homeostasis.1-3 Recent studies have revealed that mechanical forces induce competitive cell-cell interactions in Drosophila.4-6 This mechanical cell competition has also been reported to play an important role in mammalian cells, using Madin-Darby canine kidney (MDCK) cells depleted of a polarity regulator Scribble in a tetracycline-inducible manner (scribKD cells).7scribKD cells are hypersensitive to crowding due to the lower homeostatic density than wild-type (WT) cells,7,8 and in the context of cell competition, scribKD cells are compacted and eliminated by WT cells.7-10 Although p38 and p53 are involved in this process,7,10 the molecular mechanism by which WT cells recognize and mechanically eliminate scribKD cells remains unclear. Here, we report that scribKD cells secrete fibroblast growth factor 21 (FGF21) to drive cell competition. Knockdown of FGF21 in scribKD cells or loss of FGFR1 in WT cells suppresses cell competition, suggesting that WT cells recognize scribKD cells through FGF21. FGF21-containing culture medium of scribKD cells activates cell motility. Moreover, FGF21 promotes the compression and elimination of scribKD cells by attracting surrounding WT cells. We also demonstrate that activation of the apoptosis signal-regulating kinase 1 (ASK1)-p38 pathway in scribKD cells induces FGF21 to drive cell competition. Our findings reveal a mechanism whereby WT cells mechanically eliminate scribKD cells and propose a new function for FGF21 in cell-cell communication.

Advances in collective cell dynamics

<p indent="0mm">Collective cell dynamics plays significant roles in various physiological or pathological processes including embryo development, wound healing, and cancer invasion. It involves the self-organization of cytoskeleton and biochemical signaling transduction, as well as complex cell-cell interactions and cell-environment interactions. Therefore, collective cell dynamics is a hot topic in the interdisciplinary fields of biology, mechanics, physics and chemistry, attracting increasing efforts, both experimentally and theoretically, toward understanding the underlying biomechanical principles. In this review, we focus on the collective cell dynamics in cell monolayer systems and introduce the research progresses in recent years. A cell monolayer refers to a single layer of cells in which cells connect to their neighbors via cell-cell adhesions and adhere to the subjacent substrate via focal adhesions. We first introduce collective cell migration modes in cell monolayer systems under various boundary constraints. In confluent cell monolayers of large size, cells always self-organize into dynamic swirling motion patterns, as observed in various cell lines. Such motion patterns stem from active cell motility and cell-cell interactions, and can be theoretically accounted for by both continuum mechanical theory such as active gel theory and discrete models such as active vertex model. Boundary constraints affect collective cell migration modes significantly. For example, for cell monolayers in confined spaces, the persistent rotation mode, the collectively directed motion mode, and the shear flow mode have been observed. While for freely expanding cell monolayers, deformation waves emerge spontaneously and propagate toward the interior region of the cell monolayer. As a confluent cell monolayer matures, the cell density increases while cell motions gradually slow down, indicating a jamming-like behavior. Such jamming-like behavior of collective cell migration has been suggested similar to the jamming behavior of particle systems. We next introduce the statistics of cell shape and cell orientation, and discuss the relation between collective cell migration, cell fate and topological defects formed by cell orientation. Specifically, reported experiments indicated that in two-dimensional cell monolayers +1/2 topological defects trigger cell accumulation or cell extrusion while −1/2 topological defects lead to cell escape, accompanied with distinct tissue flow patterns. This topological defect-dictated cell fate has been observed in both eukaryotic cell monolayers and bacterial suspensions, revealing its potential universality. We further introduce collective cell shape oscillations and the underlying biomechanical mechanisms. Cell shape oscillation has been observed in both isolated cell systems and collective cell systems, stemming from the negative feedback between myosin activity and cell deformation. Compared with isolated cell oscillations, collective cells exhibit coordinated oscillatory morphodynamics, including aligned oscillatory patterns, polarized oscillation directions, and synchronized oscillatory amplitudes, which may help signaling transmission and synchronization among cells over large scales. In addition, collective cell dynamics on curved substrates and the role of substrate curvature is briefly introduced. This topic is in its infancy and plenty of questions remain to be explored. Finally, we introduce the cellular vertex model, an extensively used mechanical model in the study of epithelial mechanics and collective cell dynamics. In the cellular vertex model, cells are represented by interconnected polygons and vertices refer to tri-cellular junctions. The history, development, theoretical foundation, and applications of the cellular vertex model are briefly introduced.

Compaction Dynamics during Progenitor Cell Self-Assembly Reveal Granular Mechanics

Summary We study the self-assembly dynamics of human progenitor cells in agarose microwells that are used for production of chondrogenic organoids. Using image analysis on time-lapse microscopy, we estimate the aggregate area in function of time for a large number of aggregates. In control conditions, the aggregate radius follows an exponential relaxation that is consistent with the dewetting dynamics of a liquid film. Upon introducing Y-27632 Rho kinase inhibitor, the compatibility with the liquid model is lost, and slowed-down relaxation dynamics are observed. We demonstrate that these aggregates behave as granular piles undergoing compaction, with density relaxation that follows a stretched exponential. Using simulations with an individual cell-based model, we construct a phase diagram of cell aggregates that suggests that the aggregate in presence of Rho kinase inhibitor approaches glass transition.

Dynamic instability and migration modes of collective cells in channels.

Migrating cells constantly experience geometrical confinements in vivo, as exemplified by cancer invasion and embryo development. In this paper, we investigate how intrinsic cellular properties and extrinsic channel confinements jointly regulate the two-dimensional migratory dynamics of collective cells. We find that besides external confinement, active cell motility and cell crowdedness also shape the migration modes of collective cells. Furthermore, the effects of active cell motility, cell crowdedness and confinement size on collective cell migration can be integrated into a unified dimensionless parameter, defined as the cellular motility number (CMN), which mirrors the competition between active motile force and passive elastic restoring force of cells. A low CMN favours laminar-like cell flows, while a high CMN destabilizes cell motions, resulting in a series of mode transitions from a laminar phase to an ordered vortex chain, and further to a mesoscale turbulent phase. These findings not only explain recent experiments but also predict dynamic behaviours of cell collectives, such as the existence of an ordered vortex chain mode and the mode selection under non-straight confinements, which are experimentally testable across different epithelial cell lines.

Modeling Active Cell Movement With the Potts Model

In the last decade, the cellular Potts model has been extensively used to model interacting cell systems at the tissue-level. However, in {\bf early} applications of this model, cell movement was taken as a consequence of membrane fluctuations due to cell-cell interactions, or as a response to an external chemotactic gradient. Recent findings have shown that eukaryotic cells can exhibit persistent displacements across scales larger than cell size, even in the absence of external signals. Persistent cell motion has been incorporated to the cellular Potts model by many authors in the context of collective motion, chemotaxis and morphogenesis. In this paper, we use the cellular Potts model in combination with a random field applied over each cell. This field promotes a uniform cell motion in a given direction during a certain time interval, after which the movement direction changes. The dynamics of the direction is coupled to a first order autoregressive process. We investigated statistical properties, such as the mean-squared displacement and spatio-temporal correlations, associated to these self-propelled {\it in silico} cells in different conditions. The proposed model emulates many properties observed in different experimental setups. By studying low and high density cultures, we find that cell-cell interactions decrease the effective persistent time.

Deep reinforcement learning of cell movement in the early stage of C.elegans embryogenesis.

Cell movement in the early phase of Caenorhabditis elegans development is regulated by a highly complex process in which a set of rules and connections are formulated at distinct scales. Previous efforts have demonstrated that agent-based, multi-scale modeling systems can integrate physical and biological rules and provide new avenues to study developmental systems. However, the application of these systems to model cell movement is still challenging and requires a comprehensive understanding of regulatory networks at the right scales. Recent developments in deep learning and reinforcement learning provide an unprecedented opportunity to explore cell movement using 3D time-lapse microscopy images. We present a deep reinforcement learning approach within an agent-based modeling system to characterize cell movement in the embryonic development of C.elegans. Our modeling system captures the complexity of cell movement patterns in the embryo and overcomes the local optimization problem encountered by traditional rule-based, agent-based modeling that uses greedy algorithms. We tested our model with two real developmental processes: the anterior movement of the Cpaaa cell via intercalation and the rearrangement of the superficial left-right asymmetry. In the first case, the model results suggested that Cpaaa's intercalation is an active directional cell movement caused by the continuous effects from a longer distance (farther than the length of two adjacent cells), as opposed to a passive movement caused by neighbor cell movements. In the second case, a leader-follower mechanism well explained the collective cell movement pattern in the asymmetry rearrangement. These results showed that our approach to introduce deep reinforcement learning into agent-based modeling can test regulatory mechanisms by exploring cell migration paths in a reverse engineering perspective. This model opens new doors to explore the large datasets generated by live imaging. Source code is available at https://github.com/zwang84/drl4cellmovement. Supplementary data are available at Bioinformatics online.

Regulation of posterior body and epidermal morphogenesis in zebrafish by localized Yap1 and Wwtr1.

The vertebrate embryo undergoes a series of dramatic morphological changes as the body extends to form the complete anterior-posterior axis during the somite-forming stages. The molecular mechanisms regulating these complex processes are still largely unknown. We show that the Hippo pathway transcriptional coactivators Yap1 and Wwtr1 are specifically localized to the presumptive epidermis and notochord, and play a critical and unexpected role in posterior body extension by regulating Fibronectin assembly underneath the presumptive epidermis and surrounding the notochord. We further find that Yap1 and Wwtr1, also via Fibronectin, have an essential role in the epidermal morphogenesis necessary to form the initial dorsal and ventral fins, a process previously thought to involve bending of an epithelial sheet, but which we now show involves concerted active cell movement. Our results reveal how the Hippo pathway transcriptional program, localized to two specific tissues, acts to control essential morphological events in the vertebrate embryo.

Imaging of Wound Closure of Small Epithelial Lesions in the Mouse Trachea

Integrity of the airway epithelium is essential for normal lung function. However, studies analyzing the repair process of small epithelial lesions in pseudostratified airway epithelium are missing. To follow airway-epithelial wound closure over time, we lesioned small areas of the mouse tracheal epithelium (1to 12 cells) using a femtosecond laser and followed wound closure up to 6 hours by autofluorescence multiphoton microscopy. Selected lesions were also examined by scanning and transmission electron microscopy and by staining of filamentous actin. Most lesions with a size up to six cells closed by elongation of the surrounding epithelial cells within 6 hours, and all damaged cells were extruded from the epithelium. Electron microscopy confirmed that the surrounding epithelial cells directly closed lesions up to six cells. Most lesions larger than six cells did not close in the observation period of 6 hours, but we observed that basal cells flattened to cover the basement membrane. Delayed wound closure was, in part, attributable to damage of the basement membrane. Cells facing the lesion exhibited increased filamentous actin staining, indicating active cell movement. Not all cells initially facing the lesion participated directly in wound closure, indicating that closure is driven by movement of individual cells rather than a transepithelial coordinated process. Small wounds in the pseudostratified airway epithelium close within hours to preserve epithelial integrity.

Abstract 1889: Formation and merger of H69 and H69AR small cell lung cancer (SCLC) tumor cell clusters (TCCs) in vitro

Abstract A novel manifestation of tumor cell invasiveness, termed mutual cellular pervasion (MCP), was observed in vitro. It involved TCCs formed by SCLC cells. Suspension cultures of H69 and H69AR cells were grown in flavin-free RPMI 1640 medium with 10% fetal bovine serum as the only source of flavins. Experiments and subcultivations were performed under light with wavelengths above 520 nm. TCC morphology was studied by confocal microscopy and transmission and scanning electron microscopy. Interactions of TCCs were followed by video microscopy in phase contrast and fluorescence modes. Data were analyzed using the Definiens software suite. The interaction of H69AR TCCs with confluent monolayers of human umbilical vascular endothelial cells (HUVEC) was visualized. Freshly subcultivated, singularized tumor cells rapidly formed aggregates. After two days, solid TCCs prevailed whose surface cells were connected by desmosome-like junctions. Apoptosis but not necrosis became obvious in central parts of clusters with diameters above 100 to 150 μm. TCCs enlarged through both cell proliferation and serial cluster mergers. In the course of TCC merger, four stages were distinguishable: (1) directed cluster movement leading to contact of clusters, (2) formation of a near circular, symmetric structure termed contact disc. It consists of planar surface areas to which both TCCs involved contribute equally. (3) Merger of TCCs took place in the contact disc, and was accompanied by active movement of adjacent cells. (4) Starting from the merger zone, major surface areas of newly formed clusters were mutually pervaded by cells from both participating cell clusters. After numerous merger events, only low numbers of TCCs reaching sizes of up to 2 to 3 mm were present at subcultivation. No spontaneous bursting, shrinkage, degeneration, or decay of TCCs has been observed. However, when TCCs of H69AR cells were confronted with confluent layers of HUVEC, drastic changes occurred in both formations. First, intense oscillatory cellular movements were triggered on TCC surfaces, preceding the release of cell aggregates which moved away from TCCs to the HUVEC layer. At the same time, HUVEC were disconnected from each other and started moving either randomly or in an oscillatory fashion. Individual tumor cells attached to the much larger HUVEC and spread on their surface, resulting in full covering which secluded HUVEC from the medium. To our knowledge, neither formation nor merger of malignant TCCs in vitro have been described so far. TCC merger involves mutual cellular penetration of the involved TCC surfaces, i. e. MCP. Contrary to the invasion of tumor cells into non-tumor tissue, pervasion does not lead to destruction but results in TCC growth. However, key features of tumor cell invasion in vivo, such as chemotaxis, spreading and TCC formation as well as disruption of endothelial layers, manifest under conditions in vitro, thus facilitating related experimental studies. Citation Format: Nico O. Ruprecht, Martin Hungerbuehler, Philipp Kellmann, Nathalie Harder, Günter Schmidt, Carlos Wotzkow, Beat Haenni, Fabian Blank, Hendrik Von Tengg-Kobligk, Christof Granzow. Formation and merger of H69 and H69AR small cell lung cancer (SCLC) tumor cell clusters (TCCs) in vitro [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1889. doi:10.1158/1538-7445.AM2017-1889

BIOFILM FORMATION AND MOTILITY OF BACTERIA PSEUDOMONAS AERUGINOSA WITH DIFFERENT C-DI- GMPLEVEL

Aim: Biofilm formation abilities determination in Pseudomonasaeruginosa strains with different cyclic dimeric guanosine monophosphate (c-di-GMP) level and swimming, swarming, and twitching motilities. Materials and methods. Wilde type strain P. aeruginosa PA01 and strains with low (PA01 pJN2133) and high (PA01 ΔwspF1) level of c-di-GMP were used as test-organisms. Bacteria were cultivated in 24-walls Nuclon plates in LB medium at 37 °С for 24 hours for biofilm formation. Determination of planktonic cells amount was carried out spectrophotometrically, biofilm formation – by CV-test. Cells motility was tested on Petri dishes with different agar content: swimming 0.3%, swarming 0.6%, and twitching 1.5%. Results. It was shown that P. aeruginosa PA01 pJN2133 form biofilm with impaired structure and in 3.7 and 5 times less intensive than P. aeruginosa PA01 and PA01 ΔwspF1. P. aeruginosa PA01 pJN2133 planktonic cells amount was higher than in wild type strain and PA01 ΔwspF1. According to the morphology of a biofilm of strains P. aeruginosa PA01 and PA01 ΔwspF1 were similar: they contained 3D structures, which in the case of the wild type strain were larger and more clearly separated from each other. The biofilm P. aeruginosa PA01 pJN2133 evenly covered the surface, was very thin and did not contain three-dimensional components. It is shown that cells of P. aeruginosa PA01 pJN2133 strain are the most mobile in all types of surface movement. Strains of P. aeruginosa PA01 and PA01 ΔwspF1 possessed the same activity when moving by swimming and twitching, but differed in their ability to swarm – in P. aeruginosa PA01 ΔwspF1 this process is blocked. P. aeruginosa PA01 pJN2133 swarming motility zones diameter was 62 мм and it were in 1,4 times higher than at P. aeruginosa PA01 – 43 мм. Swarming motility zones morphology was different. Conclusions. The low intracellular content of c-di-GMP interferes with the formation of a full-fledged biofilm and promotes the planktonic mode of P. aeruginosa PA01 pJN2133 and the active movement of cells across different surfaces. An increased level of c-di-GMP provides the formation of a biofilm with a larger mass compared to the control strain and inhibits the swarming process in P. aeruginosa PA01 ΔwspF1.

Space-Limited Mitosis in the Glazier-Graner-Hogeweg Model.

The Glazier-Graner-Hogeweg (GGH) model is a cellular automata framework for representing the time evolution of cellular systems, appealing because unlike many other individual-cell-based models it dynamically simulates changes in cell shape and size. Proliferation has seen some implementation into this modelling framework, but without consensus in the literature as to how this behaviour is best represented. Additionally, the majority of published GGH model implementations which feature proliferation do so in order to simulate a certain biological situation where mitosis is important, but without analysis of how these proliferation routines operate on a fundamental level. Here, a method of proliferation for the GGH model which uses separate cell phenotypes to differentiate cells which have entered or just left the mitotic phase of the cell cycle is presented and demonstrated to correctly predict logistic growth on a macroscopic scale (in accordance with experimental evidence). Comparisons between model simulations and the generalised logistic growth model provide an interpretation of the latter's 'shape parameter', and the proliferation routine used here is shown to offer the modeller somewhat predictable control over the proliferation rate, important for ensuring temporal consistency between different cellular behaviours in the model. All results are found to be insensitive to the inclusion of active cell motility. The implications of these simulated proliferation assays towards problems in cell biology are also discussed.

Proteolytic and non-proteolytic regulation of collective cell invasion: tuning by ECM density and organization.

Cancer cells manoeuvre through extracellular matrices (ECMs) using different invasion modes, including single cell and collective cell invasion. These modes rely on MMP-driven ECM proteolysis to make space for cells to move. How cancer-associated alterations in ECM influence the mode of invasion remains unclear. Further, the sensitivity of the two invasion modes to MMP dynamics remains unexplored. In this paper, we address these open questions using a multiscale hybrid computational model combining ECM density-dependent MMP secretion, MMP diffusion, ECM degradation by MMP and active cell motility. Our results demonstrate that in randomly aligned matrices, collective cell invasion is more efficient than single cell invasion. Although increase in MMP secretion rate enhances invasiveness independent of cell–cell adhesion, sustenance of collective invasion in dense matrices requires high MMP secretion rates. However, matrix alignment can sustain both single cell and collective cell invasion even without ECM proteolysis. Similar to our in-silico observations, increase in ECM density and MMP inhibition reduced migration of MCF-7 cells embedded in sandwich gels. Together, our results indicate that apart from cell intrinsic factors (i.e., high cell–cell adhesion and MMP secretion rates), ECM density and organization represent two important extrinsic parameters that govern collective cell invasion and invasion plasticity.

The Hurst exponents of Nitzschia sp. diatom trajectories observed by light microscopy

We present the results of an experiment with light microscopy performed to capture the trajectories of live Nitzschia sp. diatoms. The time series corresponding to the motility of this kind of cells along ninety-five circular-like trajectories have been obtained and analyzed with the scaling statistical method of detrended fluctuation analysis optimized via a wavelet transform. In this way, we determined the Hurst parameters, in two orthogonal directions, which characterize the nature of the motion of live diatoms in light microscopy experiments. We have found mean values of these directional Hurst parameters between 0.70 and 0.63 with overall standard errors below 0.15. These numerical values give evidence that the motion of Nitzschia sp. diatoms is of persistent type and suggest an active cell motility with a kind of memory associated with long-range correlations on the path of their trajectories. For the collected statistics, we also find that the values of the Hurst exponents depend on the number of abrupt turns that occur in the diatom trajectory and on the type of wavelet, although their mean values do not change much.