Motility of polymorphonuclear leukocytes in malnutrition]

Random polymorphonuclear granulocytes motility has been studied in malnourished children, aged between one month and one year. A technique, which allowed to observe trajectories of individual cells has been applied. An analysis included the measurements of cells centres position. Results have indicated, that the average cell velocity (one-minute translocation) does not differ in malnutrition from that seen during convalescence period. However, distribution of cell translocation values have been statistically significantly different.     

Influence of individual cell motility on the 2D front roughness dynamics of tumour cell colonies

The dynamics of in situ 2D HeLa cell quasi-linear and quasi-radial colony fronts in a standard culture medium is investigated. For quasi-radial colonies, as the cell population increased, a kinetic transition from an exponential to a constant front average velocity regime was observed. Special attention was paid to individual cell motility evolution under constant average colony front velocity looking for its impact on the dynamics of the 2D colony front roughness. From the directionalities and velocity components of cell trajectories in colonies with different cell populations, the influence of both local cell density and cell crowding effects on individual cell motility was determined. The average dynamic behaviour of individual cells in the colony and its dependence on both local spatio-temporal heterogeneities and growth geometry suggested that cell motion undergoes under a concerted cell migration mechanism, in which both a limiting random walk-like and a limiting ballistic-like contribution were involved. These results were interesting to infer how biased cell trajectories influenced both the 2D colony spreading dynamics and the front roughness characteristics by local biased contributions to individual cell motion. These data are consistent with previous experimental and theoretical cell colony spreading data and provide additional evidence of the validity of the Kardar-Parisi-Zhang equation, within a certain range of time and colony front size, for describing the dynamics of 2D colony front roughness.     

A cellular automaton model for the migration of glioma cells

We present a study of in vitro cell migration in two dimensions as a first step towards understanding the mechanisms governing the motility of glioma cells. Our study is based on a cellular automaton model which aims at reproducing the kinetics of a lump of glioma cells deposited on a substrate of collagen. The dynamical effects of cell attraction and motion inertia are introduced through adequate automaton rules. We compare the density profiles given by the model to those obtained experimentally. The result of the best fit indicates a substantial cell-cell attraction due to cell-cell communication through gap junctions (or chemotaxis) and negligible inertia effects during migration. Tracking of individual migrating cells indicates highly convoluted cell trajectories.     

A Computational Model for Collective Cellular Motion in Three Dimensions: General Framework and Case Study for Cell Pair Dynamics

Cell migration in healthy and diseased systems is a combination of single and collective cell motion. While single cell motion has received considerable attention, our understanding of collective cell motion remains elusive. A new computational framework for the migration of groups of cells in three dimensions is presented, which focuses on the forces acting at the microscopic scale and the interactions between cells and their extracellular matrix (ECM) environment. Cell-cell adhesion, resistance due to the ECM and the factors regulating the propulsion of each cell through the matrix are considered. In particular, our approach emphasizes the role of receptors that mediate cell-cell and cell-matrix interactions, and examines how variation in their properties induces changes in cellular motion. As an important case study, we analyze two interacting cells. Our results show that the dynamics of cell pairs depends on the magnitude and the stochastic nature of the forces. Stronger intercellular stability is generally promoted by surface receptors that move. We also demonstrate that matrix resistance, cellular stiffness and intensity of adhesion contribute to migration behaviors in different ways, with memory effects present that can alter pair motility. If adhesion weakens with time, our findings show that cell pair break-up depends strongly on the way cells interact with the matrix. Finally, the motility for cells in a larger cluster (size 50 cells) is examined to illustrate the full capabilities of the model and to stress the role of cellular pairs in complex cellular structures. Overall, our framework shows how properties of cells and their environment influence the stability and motility of cellular assemblies. This is an important step in the advancement of the understanding of collective motility, and can contribute to knowledge of complex biological processes involving migration, aggregation and detachment of cells in healthy and diseased systems.     

Modelling Directional Guidance and Motility Regulation in Cell Migration

Although cell migration is an essential process in development, how cells reach their final destination is not well understood. Secreted molecules are known to have a migratory effect, but it remains unclear whether such molecules act as directional guidance cues or as motility regulators. There is potential to use signalling molecules in new medical therapies, so it is important to identify the exact role these molecules play. This paper focuses on distinguishing between inhibitory and repulsive effects produced by signalling molecules, based on recent experiments examining the effect of Slit, a secreted protein, on the migration of neurons from the brain. The primary role of Slit, whether it is an inhibitor or repellent of neurons, is in dispute. We present population-level continuum models and recast these in terms of transition probabilities governing individual cells. Various cell-sensing strategies are considered within this framework. The models are applied to the neuronal migration experiments. To resolve the particular role of Slit, simulations of the models characterising different cell-sensing strategies are compared at the population and individual cell level, providing two complementary perspectives on the system. Difficulties and limitations in deducing cell migration rules from time-lapse imaging are discussed.     

Quantitative morphodynamics of endothelial cells within confluent cultures in response to fluid shear stress

To evaluate shear stress-induced effects on cultured cells we have extended the mechanical setup of a multichannel in vitro rheological system and developed software allowing entire processing control and image data analysis. The values of cell motility, degree of orientation (alignment), and cell elongation were correlated as a function of time (morphodynamics). Collective and individual endothelial cells within confluent cultures displayed a shear stress-dependent characteristic phase behavior of the following time course: resting conditions (phase I), change of motility (phase II), onset of alignment (phase III), and finally cell elongation (phase IV). Especially cell motility was characterized by a randomized zigzag movement around mean trajectories (fluctuations) together with mean cell locomotion. Onset of shear stress caused a down-regulation of fluctuations of 30% within <10 min and simultaneously increased locomotion velocities preferring the flow direction (phase II). After a lag period of 10 to 20 min cells orientated in the direction of flow (phase III) without significant cell elongation, which finally occurs within hours (phase IV). These data provide first evidence that cells within confluent endothelial monolayers respond to shear stress with a characteristic phase behavior.     

带培养室的倒置显微镜下人雪旺细胞形态和运动的观察

为了显示体外培养条件下三维结构上人雪旺细胞的形态和运动方式,将引产人胎儿坐骨神经的雪旺细胞培养在聚酯纤维上,用带培养室的显微镜观察。结果显示人雪旺细胞呈梭形,绕聚酯纤维作螺旋式迁移;有的细胞同时抓住两根纤维;在相对静止期,细胞虽无位置的迁移,但有频繁的形态变化;分裂后的子细胞有形态和运动时相的不同。     

Motility is rate-limiting for invasion of bladder carcinoma cell lines

Induced migration of tumor cells is generally considered to be one critical step in cancer progression to the invasive and metastatic stage. The implicit caveat of studies that show this is that other, unknown, signaling pathways and biophysical events are actually the operative rate-limiting steps, and not motility per se. Thus, to examine the hypothesis that motility is a single, but overall rate-limiting function required for invasion, disparate motility processes need be blocked with concordant effects on tumor invasion. Recently, we and others have described two signaling pathways that are critical to growth factor-induced motility but not mitogenesis. The key molecular switches are phospholipase C-gamma (PLCgamma) and calpain for cytoskeletal reorganization and rear detachment, respectively. We examined this hypothesis in a highly invasive tumor, bladder carcinoma. Three different human tumor cell lines, 253J-B-V, UMUC and T-24, were tested for invasiveness in vitro by transmigration of a Matrigel barrier. Inhibiting PLCgamma with the pharmacologic agent U73122 or the molecular dominant-negative PLCz construct reduced both invasiveness and motility. The same was noted when calpain was blocked using calpain inhibitor I (ALLN). These results demonstrate that one interventional target for limiting invasion is not necessarily an individual motility pathway but rather cell migration per se.     

Movement of the Dictyostelium discoideum slug: models, musings, and images

The last 5 years have resulted in many advances in knowledge of the cytoskeleton and motility of individual cells. Here the problem of multicellular movement is addressed. The Dictyostelium discoideum slug is examined, and models for how approximately 100,000 cells become coordinated to move are briefly reviewed. Experiments that contributed to model building as well as those used to test models are considered. Four levels of experimentation are considered: (1) the extracellular matrix (ECM) is examined as a component of the system; (2) information obtained by examining the organisation of slug cells through sectioning is presented; (3) time, the 4th dimension, is considered, and approaches to studying the dynamics of cell interactions from the point of view of movement are outlined, and (4) cell adhesion molecules are addressed.     

Cell motility as persistent random motion: theories from experiments

Experimental time series for trajectories of motile cells may contain so much information that a systematic analysis will yield cell-type-specific motility models. Here we demonstrate how, using human keratinocytes and fibroblasts as examples. The two resulting models reflect the cells' different roles in the organism, it seems, and show that a cell has a memory of past velocities. They also suggest how to distinguish quantitatively between various surfaces' compatibility with the two cell types.     

Microelastic gradient gelatinous gels to induce cellular mechanotaxis

The understanding and realization of directional cell movement towards a harder region of a cell culture substrate surface, so-called mechanotaxis, might provide a solid basis for a functional artificial extracellular matrix, enabling manipulation and elucidation of cell motility. The photolithographic surface microelasticity patterning method was developed for fabricating a cell-adhesive hydrogel with a microelasticity gradient (MEG) surface using photocurable styrenated gelatin to investigate the condition of surface elasticity to induce mechanotaxis as a basis for such substrate-elasticity-dependent control of cell motility. Patterned MEG gels consisting of different absolute surface elasticities and elasticity jumps were prepared. Surface elasticity and its two-dimensional distribution were characterized by microindentation tests using atomic force microscopy (AFM). From analyses of trajectories of 3T3 cell movement on each prepared MEG gel, two critical criteria of the elasticity jump and the absolute elasticity to induce mechanotaxis were identified: (1) a high elasticity ratio between the hard region and the soft one, and (2) elasticity of the softer region to provide medium motility. Design of these conditions was found to be necessary for fabricating an artificial extracellular matrix to control or manipulate cell motility.     

Influence of salinomycin treatment on division and movement of individual cancer cells cultured in normoxia or hypoxia evaluated with time-lapse digital holographic microscopy

Most studies on new cancer drugs are based on population-derived data, where the absence of response of a small population may pass unnoticed. Thus, individual longitudinal tracking of cells is important for the future development of efficient cancer treatments. We have used digital holographic microscopy to track individual JIMT-1 human breast cancer cells and L929 mouse fibroblast cultivated in normoxia or hypoxia. In addition, JIMT-1 cells were treated with salinomycin, a cancer stem cell targeting compound. Three-day time-lapse movies were captured and individual cells were analysed with respect to cell division (cell cycle length) and cell movement. Comparing population-doubling time derived from population-based growth curves and individual cell cycle time data from time-lapse movies show that the former hide a sub-population of dividing cells. Salinomycin treatment increased the motility of cells, however, this motility did not result in an increased distant migration i.e. the cells increased their local movement. MCF-7 breast cancer cells showed similar motility behaviour as salinomycin-treated JIMT-1 cells. We suggest that combining features, such as motility and migration, can be used to distinguish cancer cells with mesenchymal (JIMT-1) and epithelial (MCF-7) features. The data clearly emphasize the importance of longitudinal cell tracking to understand the biology of individual cells under different conditions.     

Effects of cell motility and chemotaxis on microbial population growth.

A mathematical model is developed to elucidate the effects of biophysical transport processes (nutrient diffusion, cell motility, and chemotaxis) along with biochemical reaction processes (cell growth and death, nutrient uptake) upon steady-state bacterial population growth in a finite one-dimensional region. The particular situation considered is that of growth limitation by a nutrient diffusing from an adjacent phase not accessible to the bacteria. It is demonstrated that the cell motility and chemotaxis properties can have great influence on steady-state population size. In fact, motility effects can be as significant as growth kinetic effects, in a manner analogous to diffusion- and reaction-limited regimes in chemically reacting systems. In particular, the following conclusions can be drawn from our analysis for bacterial populations growing at steady-state in a confined, unmixed region: (a) Random motility may lead to decreased population density; (b) chemotaxis can allow increased population density if the chemotactic response is large enough; (c) a species with superior motility properties can outgrow a species with superior growth kinetic properties; (d) motility effects become greater as the size of the confined growth region increases; and (e) motility effects are diminished by significant mass-transfer limitation of the nutrient from the adjacent source phase. The relationships of these results for populations to previous conclusions for individual cells is discussed, and implications for microbial competition are suggested.     

Computer-assisted sperm analysis of canine spermatozoa motility measurements

Computer-assisted sperm analysis (CASA) allows for the determination of specific motion characteristics of sperm cells in vitro. This study was designed to develop a system for the use of CASA to objectively evaluate canine sperm motility, and specifically to determine whether motility characteristics vary between individual dogs. Ejaculates from 10 dogs were collected weekly. Sperm cells were extended in a glucose-free TALP medium, placed on slides and videotaped at 200x. Videotaped samples were then analyzed by the Hamilton-Thorn Motility Analyzer, with 100 cells evaluated per slide. Two slides were made from each ejaculate. Motility characteristics that were evaluated included lateral head displacement, beat cross frequency, path velocity, path linearity, path straightness, percentage of motile cells, and percentage of progressively motile cells. Sperm cell morphology was also evaluated. Canine spermatozoa maintained good overall motility (mean +/- SD, 73 +/- 9%) during the procedure. Mean sperm motility and morphology measurements differed significantly between dogs (P<0.01). There was no difference (P>0.05) between the mean measurements of different ejaculates for an individual dog, or for different slides made from the same ejaculate. Mean motility values for the 10 dogs are reported. There was a significant but not strong correlation (r=0.44) between the percentage of progressively motile sperm cells and the percentage of sperm cells with normal morphology.     

Explicit Separation of Growth and Motility in a New Tumor Cord Model

We investigate a new model of tumor growth in which cell motility is considered an explicitly separate process from growth. Bulk tumor expansion is modeled by individual cell motility in a density-dependent diffusion process. This model is implemented in the context of an in vivo system, the tumor cord. We investigate numerically microscale density distributions of different cell classes and macroscale whole tumor growth rates as functions of the strength of transitions between classes. Our results indicate that the total tumor growth follows a classical von Bertalanffy growth profile, as many in vivo tumors are observed to do. This provides a quick validation for the model hypotheses. The microscale and macroscale properties are both sensitive to fluctuations in the transition parameters, and grossly adopt one of two phenotypic profiles based on their parameter regime. We analyze these profiles and use the observations to classify parameter regimes by their phenotypes. This classification yields a novel hypothesis for the early evolutionary selection of the metastatic phenotype by selecting against less motile cells which grow to higher densities and may therefore induce local collapse of the vascular network.     

Successive relaxation cycles during long-time cell aggregate rounding after uni-axial compression

The mean features of cell surface rearrangement during cell aggregate rounding after uni-axial compression between parallel plates are considered. This is based on long-time rheological modeling approaches in order to shed further light on collective cell migration. Many aspects of cell migration at the supra-cellular level, such as the coordination between surrounding migrating cell groups that leads to uncorrelated motility, have remained unclear. Aggregate shape changes during rounding are considered depending on the size and homogeneity of 2-D and 3-D cell aggregates. Cell aggregate shape changes that are taking place during successive relaxation cycles have various relaxation rates per cycle. Every relaxation rate is related to the corresponding cell migrating state. If most of the cells migrate per cycle, the relaxation rate is maximal. If most of the cells are in a resting state per cycle, the relaxation rate is nearing zero. If some cell groups migrate while the others, at the same time, stay in a resting state, the relaxation rate is lower than that obtained for the migrating cells. The relaxation rates per cycles are not random, but they have a tendency to gather around two or three values indicating an organized cell migrating pattern. Such behavior suggests that uncorrelated motility during collective cell migration in one cycle induces a decrease of the relaxation rate in the next cycle caused by an accumulation of cells in the resting state. However, cells have the ability to overcome these perturbations and re-establish an ordered migrating trend in the next cycle. These perturbations of the cell migrating state are more pronounced for: (1) more mobile cells, (2) a heterogeneous cell population, and (3) a larger cell population under the same experimental conditions.