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Physical Biology

Leili Shahriyari, Ali Mahdipour Shirayeh
Studying the stem cell (SC) niche architecture is a crucial step for investigating the process of oncogenesis and obtaining an effective stem cell therapy for various cancers. Recently, it has been observed that there are two groups of SCs in the SC niche collaborating with each other to maintain tissue homeostasis: border stem cells (BSCs), which are responsible in controlling the number of non-stem cells as well as stem cells, and central stem cells (CeSCs), which regulate the SC niche. Here, we develop a bi-compartmental stochastic model for the SC niche to study the spread of mutants within the niche...
January 19, 2017: Physical Biology
Eleanor Ory, Lekhana Bhandary, Amanda Boggs, Kristi Chakrabarti, Joshua Parker, Wolfgang Losert, Stuart S Martin
The periphery of epithelial cells is shaped by opposing cytoskeletal physical forces generated predominately by two dynamic force generating systems - growing microtubule ends push against the boundary from the cell center, and the actin cortex contracts the attached plasma membrane. Here we investigate how changes to the structure and dynamics of the actin cortex alter the dynamics of microtubules. Current drugs target actin polymerization and contraction to reduce cell division and invasiveness; however, the impacts on microtubule dynamics remain incompletely understood...
January 16, 2017: Physical Biology
Mathieu Rivière, Julien Derr, Stéphane Douady
The study on aerial plant organs (leaves and stems) motions is reviewed. The history of observations and studies is put in the perspective of the ideas surrounding them, leading to a presentation of the current classification of these motions. After showing the shortcomings of such a classification, we present, following an idea of Darwin's, the various movements in a renewed and observation-based perspective of the plant development. With this perspective, the different movements fit together logically, and in particular we point out that the mature reversible movements, such as the sensitive or circadian movements, are just partial regressions of the developmental ones...
January 13, 2017: Physical Biology
Jaemin Chin, Devkumar Mustafi, Michael Poellmann, Raphael Lee
Certain amphiphilic block copolymers are known to prevent aggregation of unfolded proteins. To better understand the mechanism of this effect, the optical properties of heat-denatured and dithiothreitol (DTT) reduced lysozyme were evaluated with respect to controls using UV-Vis spectroscopy, transmission electron microscopy (TEM) and circular dichroism (CD) measurements. Then, the effects of adding Polyethylene Glycol (8000 Da), the triblock surfactant Poloxamer 188 (P188), and the tetrablock copolymer Tetronic 1107 (T1107) to the lysozyme solution were compared...
January 6, 2017: Physical Biology
Emiliano Perez Ipiña, Silvina Ponce Dawson
During early development, the establishment of gradients of transcriptional factors determines the patterning of cell fates. The case of Bicoid (Bcd) in <i>Drosophila melanogaster</i> embryos is well documented and studied. There are still controversies as to whether <i> SDD</i> models in which Bcd is <i>Synthesized</i> at one end, then <i>Diffuses</i> and is <i>Degraded</i> can explain the gradient formation within the timescale observed experimentally...
January 5, 2017: Physical Biology
Elizabeth Shtrahman, Daniel Maruyama, Eva Olariu, Christian Fink, Michal Zochowski
Astrocytes form interconnected networks in the brain and communicate via calcium signaling. We investigate how modes of coupling between astrocytes influence the spatio-temporal patterns of calcium signaling within astrocyte networks and specifically how these network interactions promote coordination within this group of cells. To investigate these complex phenomena, we study reduced cultured networks of astrocytes and neurons. We image the spatial temporal patterns of astrocyte calcium activity and quantify how perturbing the coupling between astrocytes influences astrocyte activity patterns...
December 22, 2016: Physical Biology
Tatiana Starkova, Alexander Polyanichko, Tatiana Artamonova, Mikhail Khodorkovskii, Elena Kostyleva, Elena Chikhirzina, Alexey Tomilin
The covalent modifications of the linker histone H1 and the core histones are thought to play an important role in the control of chromatin functioning. Histone H1 variants from K562 cell line (cH1), mouse (mH1) and calf (cH1) thymi were studied by MALDI-Q-TOF. The proteomics analysis revealed novel post-translational modifications of the histone H1, such as meK34-mH1.4, meK35-cH1.1, meK35-mH1.1, meK75-hH1.2, meK75-hH1.3, acK26-hH1.4, acK26-hH1.3- and acK17-hH1.1. The comparison of the hH1, mH1 and cH1 proteins has demonstrated that the types and positions of the post-translational modifications of the globular domains of the H1...
December 21, 2016: Physical Biology
Aaron M Prescott, Steven M Abel
The rational design of network behavior is a central goal of synthetic biology. Here, we combine in silico evolution with nonlinear dimensionality reduction to redesign the responses of fixed-topology signaling networks and to characterize sets of kinetic parameters that underlie various input-output relations. We first consider the earliest part of the T cell receptor (TCR) signaling network and demonstrate that it can produce a variety of input-output relations (quantified as the level of TCR phosphorylation as a function of the characteristic TCR binding time)...
January 13, 2017: Physical Biology
Aude Sivéry, Emmanuel Courtade, Quentin Thommen
Environmental stress, such as oxidative or heat stress, induces the activation of the heat shock response (HSR) and leads to an increase in the heat shock proteins (HSPs) level. These HSPs act as molecular chaperones to maintain cellular proteostasis. Controlled by highly intricate regulatory mechanisms, having stress-induced activation and feedback regulations with multiple partners, the HSR is still incompletely understood. In this context, we propose a minimal molecular model for the gene regulatory network of the HSR that reproduces quantitatively different heat shock experiments both on heat shock factor 1 (HSF1) and HSPs activities...
December 7, 2016: Physical Biology
Mikhail Tikhonov, William Bialek
The historical focus on network topology as a determinant of biological function is still largely maintained today, illustrated by the rise of structure-only approaches to network analysis. However, biochemical circuits and genetic regulatory networks are defined both by their topology and by a multitude of continuously adjustable parameters, such as the strength of interactions between nodes, also recognized as important. Here we present a class of simple perceptron-based Boolean models within which comparing the relative importance of topology versus interaction strengths becomes a quantitatively well-posed problem...
December 6, 2016: Physical Biology
Jacob Carroll, Matthew Raum, Kimberly Forsten-Williams, Uwe C Täuber
Surface plasmon resonance (SPR) chips are widely used to measure association and dissociation rates for the binding kinetics between two species of chemicals, e.g., cell receptors and ligands. It is commonly assumed that ligands are spatially well mixed in the SPR region, and hence a mean-field rate equation description is appropriate. This approximation however ignores the spatial fluctuations as well as temporal correlations induced by multiple local rebinding events, which become prominent for slow diffusion rates and high binding affinities...
December 6, 2016: Physical Biology
Paul François, Mathieu Hemery, Kyle A Johnson, Laura N Saunders
We consider the general problem of sensitive and specific discrimination between biochemical species. An important instance is immune discrimination between self and not-self, where it is also observed experimentally that ligands just below the discrimination threshold negatively impact response, a phenomenon called antagonism. We characterize mathematically the generic properties of such discrimination, first relating it to biochemical adaptation. Then, based on basic biochemical rules, we establish that, surprisingly, antagonism is a generic consequence of any strictly specific discrimination made independently from ligand concentration...
December 6, 2016: Physical Biology
Laura M McMillen, Dimitrios Vavylonis
Cell protrusion through polymerization of actin filaments at the leading edge of motile cells may be influenced by spatial gradients of diffuse actin and regulators. Here we study the distribution of two of the most important regulators, capping protein and Arp2/3 complex, which regulate actin polymerization in the lamellipodium through capping and nucleation of free barbed ends. We modeled their kinetics using data from prior single molecule microscopy experiments on XTC cells. These experiments have provided evidence for a broad distribution of diffusion coefficients of both capping protein and Arp2/3 complex...
December 6, 2016: Physical Biology
R Hermsen
The spatial range of a species habitat is generally determined by the ability of the species to cope with biotic and abiotic variables that vary in space. Therefore, the species range is itself an evolvable property. Indeed, environmental gradients permit a mode of evolution in which range expansion and adaptation go hand in hand. This process can contribute to rapid evolution of drug resistant bacteria and viruses, because drug concentrations in humans and livestock treated with antibiotics are far from uniform...
November 30, 2016: Physical Biology
Alan Veliz-Cuba, Chinmaya Gupta, Matthew R Bennett, Krešimir Josić, William Ott
We assess the impact of cell cycle noise on gene circuit dynamics. For bistable genetic switches and excitable circuits, we find that transitions between metastable states most likely occur just after cell division and that this concentration effect intensifies in the presence of transcriptional delay. We explain this concentration effect with a three-states stochastic model. For genetic oscillators, we quantify the temporal correlations between daughter cells induced by cell division. Temporal correlations must be captured properly in order to accurately quantify noise sources within gene networks...
November 30, 2016: Physical Biology
Aleem Syed, Neha Arora, Thomas A Bunch, Emily A Smith
Cysteine residues (Cys) in the membrane proximal region are common post-translational modification (PTM) sites in transmembrane proteins. Herein, the effects of a highly conserved membrane proximal α-subunit Cys(1368) on the diffusion properties of αPS2CβPS integrins are reported. Sequence alignment shows that this cysteine is palmitoylated in human α3 and α6 integrin subunits. Replacing Cys(1368) in wild-type integrins with valine (Val(1368)) putatively blocks a PTM site and alters integrins' ligand binding and diffusion characteristics...
November 15, 2016: Physical Biology
Nicole Meyer-Vernet, Jean-Pierre Rospars
Self-locomotion is central to animal behaviour and survival. It is generally analysed by focusing on preferred speeds and gaits under particular biological and physical constraints. In the present paper we focus instead on the maximum speed and we study its order-of-magnitude scaling with body size, from bacteria to the largest terrestrial and aquatic organisms. Using data for about 460 species of various taxonomic groups, we find a maximum relative speed of the order of magnitude of ten body lengths per second over a 10(20)-fold mass range of running and swimming animals...
November 15, 2016: Physical Biology
Anne E Hafner, Heiko Rieger
Intracellular transport is vital for the proper functioning and survival of a cell. Cargo (proteins, vesicles, organelles, etc) is transferred from its place of creation to its target locations via molecular motor assisted transport along cytoskeletal filaments. The transport efficiency is strongly affected by the spatial organization of the cytoskeleton, which constitutes an inhomogeneous, complex network. In cells with a centrosome microtubules grow radially from the central microtubule organizing center towards the cell periphery whereas actin filaments form a dense meshwork, the actin cortex, underneath the cell membrane with a broad range of orientations...
November 15, 2016: Physical Biology
Behruz Bozorg, Pawel Krupinski, Henrik Jönsson
Morphogenesis in plants and animals involves large irreversible deformations. In plants, the response of the cell wall material to internal and external forces is determined by its mechanical properties. An appropriate model for plant tissue growth must include key features such as anisotropic and heterogeneous elasticity and cell dependent evaluation of mechanical variables such as turgor pressure, stress and strain. In addition, a growth model needs to cope with cell divisions as a necessary part of the growth process...
November 15, 2016: Physical Biology
Andrea Cavagna, Daniele Conti, Irene Giardina, Tomas S Grigera, Stefania Melillo, Massimiliano Viale
Information transfer is an essential factor in determining the robustness of biological systems with distributed control. The most direct way to study the mechanisms ruling information transfer is to experimentally observe the propagation across the system of a signal triggered by some perturbation. However, this method may be inefficient for experiments in the field, as the possibilities to perturb the system are limited and empirical observations must rely on natural events. An alternative approach is to use spatio-temporal correlations to probe the information transfer mechanism directly from the spontaneous fluctuations of the system, without the need to have an actual propagating signal on record...
November 15, 2016: Physical Biology
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