28 research outputs found

    A simple mechanochemical model for calcium signalling in embryonic epithelial cells

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    Calcium (Ca2+) signalling is one of the most important mechanisms of information propagation in the body. In embryogenesis the interplay between Ca2+ signalling and mechanical forces is critical to the healthy development of an embryo but poorly understood. Several types of embryonic cells exhibit calcium-induced contractions and many experiments indicate that Ca2+ signals and contractions are coupled via a two-way mechanochemical coupling. We present a new analysis of experimental data that supports the existence of this coupling during Apical Constriction in Neural Tube Closure. We then propose a mechanochemical model, building on early models that couple Ca2+ dynamics to cell mechanics and replace the bistable Ca2+ release with modern, experimentally validated Ca2+ dynamics. We assume that the cell is a linear viscoelastic material and model the Ca2+-induced contraction stress with a Hill function saturating at high Ca2+ levels. We also express, for the first time, the 'stretch-activation' Ca2+ flux in the early mechanochemical models as a bottom-up contribution from stretch-sensitive Ca2+ channels on the cell membrane. We reduce the model to three ordinary differential equations and analyse its bifurcation structure semi-analytically as the IP3 concentration, and the 'strength' of stretch activation, λ vary. The Ca2+ system (λ=0, no mechanics) exhibits relaxation oscillations for a certain range of IP3 values. As λ is increased the range of IP3 values decreases, the oscillation amplitude decreases and the frequency increases. Oscillations vanish for a sufficiently high value of λ. These results agree with experiments in embryonic cells that also link the loss of Ca2+ oscillations to embryo abnormalities. The work addresses a very important and understudied question on the coupling of chemical and mechanical signalling in embryogenesis

    Quantification of signaling networks

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    Studies in living system in the past several decades have generated qualitative understanding of the molecular interactions resulting in large networks. These networks were essentially deciphered by breaking the components of a cell through a reductionist approach. Biological networks comprising of interactions between genes, proteins and metabolites co-ordinate in the regulation of cellular processes. However, understanding the cellular function also requires quantitative information including network dynamics, which results due to an inherent design principle embedded in the network. Interactions within the network are well organized to form a definite regulatory structure, which in turn exhibits different emergent properties. The property of the network helps the cell to achieve the desired phenotypic state in a controlled manner. The dynamics of the network or the relationship between network structure and cellular behavior cannot be understood intuitively from the interaction map of the network. Computational methods can now be employed to study these networks at system level. The field of systems biology looks at integrating the interaction maps obtained through molecular biological approach. Various studies at the system level have been reported for pathways namely chemotactic response in bacteria, cell cycle and osmotic signaling in yeast, growth factor stimulated signaling pathways in mammals. This review focuses on understanding signaling networks with the help of mathematical models

    Calcium signaling in fish cells

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    One basic cellular response towards a multitude of physical and chemical factors is the modulation of intracellular Ca2+ levels. There is also considerable evidence that a number of toxicants have an impact on Ca2+ signaling processes, alter them, and may induce cell death. Given the immense versatility of Ca2+ modulation due to the complex mechanisms which help to encode information, recording of the intracellular Ca2+ signal might eventually be a useful tool for the detection and identification of environmental stressors. Notwithstanding the universal character of Ca2+ signaling and the highly conserved pathways, research on Ca2+ as a second messenger has mainly been restricted to mammalian models. Much less is known about its function and mode of action in fish and only a handful of papers deal with the question whether there is a Ca2+ response to environmental toxicants or not. The present thesis aims at closing some of the remaining gaps. Therefore, after adapting the cell culture and Ca2+ imaging protocols for the needs of this study, the reaction of intracellular Ca2+ to different “classical” agonists such as phenylephrine and ATP was investigated systematically in order to find out the basic principles of Ca2+ dynamics in teleost fish cells. Two cell types were used and compared to one another: primary hepatocytes from rainbow trout (Oncorhynchus mykiss), and the permanent fish cell line RTL-W1 derived from rainbow trout liver, both established model systems in aquatic ecotoxicology. From an ecotoxicological point of view, we tried to answer the question whether Ca2+ imaging can be applied for the early detection of environmental stress with cell death as a last consequence. Therefore, selected model environmental toxicants and stressors such as 4-nitrophenol, 3,4-dichloroaniline, and hydrogen peroxide were used to elucidate possible interactions between contaminants and Ca2+ signaling in RTL-W1 cells. Ca2+ oscillations in response to several stimuli were recorded in RTL-W1 cells and to a lesser extent in primary hepatocytes. Interestingly, these Ca2+ oscillations are amplitude-encoded in contrast to their mammalian counterpart. Moreover, Ca2+ release in rat cells during oscillations is markedly faster than the uptake, whereas this relation is more symmetric in the fish cells. Bioinformatics and computational analysis were employed to identify key players of Ca2+ signaling in fish and to determine likely causes for the experimentally observed differences between the Ca2+ dynamics in fish cells compared to those in mammalian liver cells. Different binding characteristics of the IP3R, e.g. responsible for the Ca2+-induced Ca2+ release, could be the origin of the observations. The present thesis also indicates that the fish cell line RTL-W1 is a suitable tool for the investigation of Ca2+ signals in consequence of toxicant exposure. Evidence is provided that ecotoxicologically relevant substances take influence on intracellular Ca2+. Namely hydrogen peroxide and 4-nitrophenol showed a clear response and produced marked Ca2+ oscillations at sublethal concentrations. Effect intensity and threshold varied from cell to cell; however, general effects were reproducible and dose-dependent. At concentrations below those inducing elevated cytotoxicity and apoptosis rates (assessed by the neutral red assay and the apoptosis assay with Hoechst 33342), there is a lasting, unspecific increase in the intracellular Ca2+ level which might be interpreted as a precursor of apoptotic or necrotic processes in the cell. Generally, Ca2+ signals seem to be dependent on the pathway activated or non-specifically interfered by the respective substance. The question whether specific types of Ca2+ responses are specific of and may be used to characterize different types of stressors still cannot be answered at present. However, there is evidence that Ca2+ imaging might provide a highly sensitive, yet non-specific indicator of toxic impact, since, as a second messenger, intracellular Ca2+ integrates toxic effects of multiple other sublethal parameters

    Mechanics of the axoneme: self-organized beating patterns and vortex arrays of spermatozoa: Selbst-organisierte Schlagmuster und Vortex Anordnungen von Spermien

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    Cilien und eukariotische Flagellen sind lange, dünne Fortsaetze von Zellen. Sie enthalten eine Struktur namens Axonem. Die wesentlichen Komponenten des Axonems sind die Filamente und Motorproteine namens Mikrotubuli und Dynein. Die Motoren forcieren die Filamente, sich in oszillierender Weise gegeneinander zu verschieben, was zu einem Schlagmuster entlang des Axonemes fuehrt. Wie diese Motoren koordiniert werden und wie dieses Phaenomen quantitativ beschrieben werden kann, ist nicht verstanden. Wir studierten die Wellenformen an Spermienschwaenzen, welche ein solches Axonem enthalten, unter verschiedenen Bedingungen mit einer Hochgeschwindigkeitskamera. Wir entwickelten eine automatisierte Bildanalyse-Software, die es erlaubt, lange Zeitreihen solcher Wellenformen von Filmen zu extrahieren. In einer anschließenden Fourieranalyse erzielten wir eine gemittelte Wellenform mit erhoehter Präzision. Ein Vergleich von unseren Daten mit den Vorhersagen einer Theorie (Camalet, Julicher et al. 1999) führte zu einer Diskrepanz. Entsprechend schlugen wir eine Erweiterung der Theorie vor, indem wir annahmen, daß an der Basis des Axonems ein viskos-elastisches Element existiert. Dies führte zu einer zufrieden stellenden Übereinstimmung zwischen Theorie und Experiment. Abschließend diskutieren wir offene Fragen und zukünftige Experimente. Als ein Nebenprodukt entdeckten wir ein neues Phaenomen, bei welchem Spermien Anordnungen von dynamischen Strudeln (Vortices) bilden. Wir beschrieben dieses Phaenomen im Detail und führten einen neuen Ordnungsparameter ein, mit dem die Ordnung zwischen vielen Objekten quantifiziert werden kann. Mittels dieses Ordnungsparameters konnten wir zeigen, daß dieses Muster sich erst ab einer kritischen Dichte herausbildet. Wir schlugen ein Model vor, um den Ursprung des Musters zu erklären. Die Simulation des Models zeigte volle Uebereinstimmung mit den wesentlichen Eigenschaften dieses Musters. Weiterhin schaetzten wir die typische Wechselwirkungskraft zwischen aktiven Axonemen mit 0.1 pN ab. Abschließend ziehen wir Schlußfolgerungen über die kollektive Wirkung von Axonemen im Allgemeinen mit Hinblick auf Spermienkooperation und metachronale Cilienwellen. - Die Druckexemplare enthalten jeweils eine CD-ROM als Anlagenteil: QuickTimeMovies (ca. 65 MB) Nutzung: PLAY32 - Übersicht über Inhalte siehe Dissertation S. 108 - 109Cilia and eukaryotic flagella are long, thin extensions of cells that contain a structure known as axoneme. The key components of the axoneme are microtubule filaments and the motor proteins dynein. These dynein motors force the microtubules to slide in an oscillatory fashion leading to a wave pattern along the axoneme. How these motors are coordinated and how this phenomenon can be described quantitatively is not understood. I therefore studied the waveforms of sperm tails that contain such an axoneme. I observed these waveforms under different conditions with a high-speed camera and developed an automated image analysis tool allowing the extraction of long time series of this waveform. In a subsequent Fourier analysis I increased the precision by obtaining an averaged waveform. I then compared the data to the predictions of a theoretical framework (Camalet, Julicher et al. 1999) and found that they do not agree. I suggested extending this theoretical framework by considering a visco-elastic element at the base of the axoneme, which leads to a satisfactory agreement. This project leaves open questions hence further work is discussed. As a side finding, I discovered a new phenomenon on how spermatozoa form dynamic vortex arrays. I described this pattern in detail and introduced a novel order parameter to quantify the order among many particles. I showed that the array only forms above a critical sperm density. I suggested a model to explain the origin of the pattern and showed by simulation that the model can account for the main features of the pattern. Finally I estimated the typical interaction force between beating axonemes to be 0.1 pN and drew conclusions about their collective action in general that might be relevant for sperm cooperation or metachronal waves of cilia

    Nonlinear dynamics of Poly(hydroxyalkanoate) production in Ralstonia eutropha and Rhodospirillum rubrum

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    Magdeburg, Univ., Fak. für Elektrotechnik und Informationstechnik, Diss., 2015von André Fran

    Biomimetic Based Applications

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    The interaction between cells, tissues and biomaterial surfaces are the highlights of the book "Biomimetic Based Applications". In this regard the effect of nanostructures and nanotopographies and their effect on the development of a new generation of biomaterials including advanced multifunctional scaffolds for tissue engineering are discussed. The 2 volumes contain articles that cover a wide spectrum of subject matter such as different aspects of the development of scaffolds and coatings with enhanced performance and bioactivity, including investigations of material surface-cell interactions
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