Ratio control in a cascade model of cell differentiation

We propose a kind of reaction-diffusion equations for cell differentiation, which exhibits the Turing instability. If the diffusivity of some variables is set to be infinity, we get coupled competitive reaction-diffusion equations with a global feedback term. The size ratio of each cell type is controlled by a system parameter in the model. Finally, we extend the model to a cascade model of cell differentiation. A hierarchical spatial structure appears as a result of the cell differentiation. The size ratio of each cell type is also controlled by the system parameter.Comment: 13 pages, 7 figure

Turing's model for biological pattern formation and the robustness problem

One of the fundamental questions in developmental biology is how the vast range of pattern and structure we observe in nature emerges from an almost uniformly homogeneous fertilized egg. In particular, the mechanisms by which biological systems maintain robustness, despite being subject to numerous sources of noise, are shrouded in mystery. Postulating plausible theoretical models of biological heterogeneity is not only difficult, but it is also further complicated by the problem of generating robustness, i.e. once we can generate a pattern, how do we ensure that this pattern is consistently reproducible in the face of perturbations to the domain, reaction time scale, boundary conditions and so forth. In this paper, not only do we review the basic properties of Turing's theory, we highlight the successes and pitfalls of using it as a model for biological systems, and discuss emerging developments in the area

Modelling cell motility and chemotaxis with evolving surface finite elements

We present a mathematical and a computational framework for the modelling of cell motility. The cell membrane is represented by an evolving surface, with the movement of the cell determined by the interaction of various forces that act normal to the surface. We consider external forces such as those that may arise owing to inhomogeneities in the medium and a pressure that constrains the enclosed volume, as well as internal forces that arise from the reaction of the cells' surface to stretching and bending. We also consider a protrusive force associated with a reaction-diffusion system (RDS) posed on the cell membrane, with cell polarization modelled by this surface RDS. The computational method is based on an evolving surface finite-element method. The general method can account for the large deformations that arise in cell motility and allows the simulation of cell migration in three dimensions. We illustrate applications of the proposed modelling framework and numerical method by reporting on numerical simulations of a model for eukaryotic chemotaxis and a model for the persistent movement of keratocytes in two and three space dimensions. Movies of the simulated cells can be obtained from http://homepages.warwick.ac.uk/maskae/CV_Warwick/Chemotaxis.html

Effect of ethoxyformic anhydride on the Rieske iron—sulfur protein of bovine heart ubiquinol: Cytochrome c oxidoreductase

AbstractTreatment of bovine heart ubiquinol-cytochrome c oxidoreductase (complex III, bc1 complex) with ethoxyformic anhydride (EFA) inhibits electron transfer between cytochromes b and c1 [Yagi et al., Biochemistry 21 (1982) 4777–4782]. This paper shows that EFA alters the EPR lineshape of the Rieske iron—sulfur cluster in complex III and in the isolated Rieske protein without a significant decrease of spin concentration. The effect of EFA on the Rieske iron—sulfur cluster is competitive with that of Qo site inhibitors, such as stigmatellin, and is completely reversed by hydroxylamine. These results are consistent with the possible ethoxyformylation by EFA of histidine ligands of the Rieske iron—sulfur cluster at the non-iron binding imidazole nitrogens

Cell-cell contact mediated signalling — no fear of contact

Cancer research with sole focus on the cancer cell and possibly growth factors cannot faithfully reproduce the environmental interaction, such as adhesion of tumor cells to e.g. stromal cells, which may determine the response of these tumors to therapy. Methodologically cell adhesion studies are often difficult since complete but careful detachment is the prerequisite for most signal transduction assays. We describe for the first time an alternative method for the co-incubation of multiple myeloma cells on long term primary bone marrow stromal cultures using the bone marrow stromal cell line HS-5. The methods are precisely described, advantages and disadvantages are discussed, and troubleshooting advises are given.Исследования роста опухолевых клеток in vitro не отражают многих факторов (взаимодействие клеток с окружающей средой, их адгезию к клеткам стромы), которые в свою очередь могут определять чувствительность опухоли к терапии. Методологически изучение клеточной адгезии часто бывает затруднено, так как разделение клеток является основой большинства методик по изучению передачи сигнала. Впервые описан альтернативный метод ко-культивирования клеток множественной миеломы с клетками стромы линии HS-5, полученных из клеток костного мозга. Приведено подробное описание, преимущества и недостатки этого метода с детальными техническими рекомендациями

VIBRATION RESPONSE OF A DISC BRAKE: EVALUATION AND DESIGN

Noise and vibration is an increasingly important consideration in the design and study of disc brakes. Certain vibrations may only result in minor annoying squeals, while others may be severe enough to result in structural damage or failure. In either case, it is desirable to predict the conditions under which these vibrations arise, so that they may be controlled, or eliminated. This paper examines the contributions and interactions of four parameters to vibration response of a brake pad during braking: the applied load, the speed of rotation of the disc, the roughness of the disc and pad, and the Young's modulus of the disc and pad. The experiments are performed by simulating braking on a microtribometer. A statistical procedure, k 2 factorial design, is used to examine the effects and interactions of these four parameters on the vibration response of the pad in terms of the torque on the disc. Results suggested that the main effects. Disc tangential velocity, followed by Young's modulus, and applied load have the most significant influence. The model also suggested that the roughness is the least significant of the main effects, less significant than some interactions between other main effects, which indicate that the low frequency vibration at low speed is not necessarily associated with friction due to the low significance of the surface roughness

The influence of alfalfa-switchgrass intercropping on microbial community structure and function

The use of nitrogen fertilizer on bioenergy crops such as switchgrass results in increased costs, nitrogen leaching and emissions of N2O, a potent greenhouse gas. Intercropping with nitrogen-fixing alfalfa has been proposed as an environmentally sustainable alternative, but the effects of synthetic fertilizer versus intercropping on soil microbial community functionality remain uncharacterized. We analysed 24 metagenomes from the upper soil layer of agricultural fields from Prosser, WA over two growing seasons and representing three agricultural practices: unfertilized switchgrass (control), fertilized switchgrass and switchgrass intercropped with alfalfa. The synthetic fertilization and intercropping did not result in major shifts of microbial community taxonomic and functional composition compared with the control plots, but a few significant changes were noted. Most notably, mycorrhizal fungi, ammonia-oxidizing archaea and bacteria increased in abundance with intercropping and fertilization. However, only betaproteobacterial ammonia-oxidizing bacteria abundance in fertilized plots significantly correlated to N2O emission and companion qPCR data. Collectively, a short period of intercropping elicits minor but significant changes in the soil microbial community toward nitrogen preservation and that intercropping may be a viable alternative to synthetic fertilization

Immunohistochemical detection of macrophage migration inhibitory factor in fetal and adult bovine epididymis: Release by the apocrine secretion mode?

Originally defined as a lymphokine inhibiting the random migration of macrophages, the macrophage migration inhibitory factor (MIF) is an important mediator of the host response to infection. Beyond its function as a classical cytokine, MIF is currently portrayed as a multifunctional protein with growth-regulating properties present in organ systems beyond immune cells. In previous studies, we detected substantial amounts of MIF in the rat epididymis and epididymal spermatozoa, where it appears to play a role during post-testicular sperm maturation and the acquisition of fertilization ability. To explore its presence in other species not yet examined in this respect, we extended the range of studies to the bull. Using a polyclonal antibody raised against MIF purified from bovine eye lenses, we detected MIF in the epithelium of the adult bovine epididymis with the basal cells representing a prominently stained cell type. A distinct accumulation of MIF at the apical cell pole of the epithelial cells and in membranous vesicles localized in the lumen of the epididynnal duct was obvious. In the fetal bovine epididymis, we also detected MIF in the epithelium, whereas MIF accumulation was evident at the apical cell surface and in apical protrusions. By immuno-electron microscopy of the adult bovine epididymis, we localized MIF in apical protrusions of the epithelial cells and in luminal membrane-bound vesicles that were found in close proximity to sperm cells. Although the precise origin of the MIF-containing vesicles remains to be delineated, our morphological observations support the hypothesis that they become detached from the apical surface of the epididymal epithelial cells. Additionally, an association of MIF with the outer dense fibers of luminal spermatozoa was demonstrated. Data obtained in this study suggest MIF release by an apocrine secretion mode in the bovine epididymis. Furthermore, MIF localized in the basal cells of the epithelium and in the connective tissue could be responsible for regulating the migration of macrophages in order to avoid contact of immune cells with spermatozoa that carry a wide range of potent antigens. Copyright (c) 2006 S. Karger AG, Basel

Sierpinski signal generates 1/fα1/f^\alpha spectra

We investigate the row sum of the binary pattern generated by the Sierpinski automaton: Interpreted as a time series we calculate the power spectrum of this Sierpinski signal analytically and obtain a unique rugged fine structure with underlying power law decay with an exponent of approximately 1.15. Despite the simplicity of the model, it can serve as a model for $1/f^\alpha$ spectra in a certain class of experimental and natural systems like catalytic reactions and mollusc patterns.Comment: 4 pages (4 figs included). Accepted for publication in Physical Review

Sewerage tunnel leakage detection using a fibre optic moisture-detecting sensor system

The design and development of a new fibre optic sensor system for the optical detection of leakages in sewerage tunnels is reported. The system developed overcomes the disadvantages of the usually employed camera based inspection systems which are relatively complex and, in addition, require cleaning of the structures to be monitored beforehand. The sensor concept created combines a Fibre Bragg Grating (FBG)-based humidity sensor and a swellable polymeric fibre optic sensor. Both sensors are located along the sewerage tunnel so that they can response immediately to any leakages that may occur. The swellable polymeric fibre optic sensor shows a response of 34.2 dB in the presence of water, a performance which is superior to that seen form other swellable polymeric fibre optic sensors reported so far. Furthermore, the resistance of both sensors to highly alkaline environments (pH 13.4), an important feature of such sensors was verified. Consequently, when compared to the use of conventional inspection techniques, the novel fibre optic sensor system provides a robust, relatively low-cost and continuous monitoring system well suited to use in sewerage tunnels