Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session D34: Cell Level Patterning During Embryonic Development |
Hide Abstracts |
Sponsoring Units: DBP Chair: James Glazier, Indiana University Room: Colorado Convention Center 404 |
Monday, March 5, 2007 2:30PM - 3:06PM |
D34.00001: The \textit{de novo} formation of a vascular network, in warm-blooded embryos, occurs via a self-assembly process that spans multiple length and time scales Invited Speaker: Taking advantage of wide-field, time-lapse microscopy we examined the assembly of vascular polygonal networks in whole bird embryos and in explanted embryonic mouse tissue (allantois). Primary vasculogenesis assembly steps range from cellular (1-10 $\mu $m) to tissue (100$\mu $m-1mm) level events: Individual vascular endothelial cells extend protrusions and move with respect to the extracellular matrix/surrounding tissue. Consequently, long-range, tissue-level, deformations directly influence the vascular pattern. Experimental perturbation of endothelial-specific cell-cell adhesions (VE-cadherin), during mouse vasculogenesis, permitted dissection of the cellular motion required for sprout formation. In particular, cells are shown to move actively onto vascular cords \textit{that} \textit{are subject to strain via tissue deformations}. Based on the empirical data we propose a simple model of preferential migration along stretched cells. Numerical simulations reveal that the model evolves into a quasi-stationary pattern containing linear segments, which interconnect above a critical volume fraction. In the quasi-stationary state the generation of new branches offsets the coarsening driven by surface tension. In agreement with empirical data, the characteristic size of the resulting polygonal pattern is density-independent within a wide range of volume fractions. These data underscore the potential of combining physical studies with experimental embryology as a means of studying complex morphogenetic systems. \newline In collaboration with Brenda J. Rongish$^{1}$, Andr\'{a}s Czir\'{o}k$^{1,2}$, Erica D. Perryn$^{1}$, Cheng Cui$^{1}$, and Evan A. Zamir$^{1}$ \newline \newline $^{1}$Department of Anatomy and Cell Biology, the University of Kansas Medical Center, Kansas City, KS \newline $^{2}$Department of Biological Physics, E\"{o}tv\"{o}s Lor\'{a}nd University, Budapest, Hungary. [Preview Abstract] |
Monday, March 5, 2007 3:06PM - 3:18PM |
D34.00002: Physical Mechanisms of Patterning Instabilities in the Formation of Vascular Network Abbas Shirinifard, James Glazier, Shantia Yarahmadian Endothelial cells, which line the inner walls of blood vessels, self-organize into network structures in vitro and in vivo. The physical mechanisms of network formation are a current subject of debate may be important during development, wound heeling, and tumor growth. Using Glazier and Graner's Cellular Potts Model (CPM) to model chemotactically migrating cells, we studied the patterning instabilities and scaling properties of the network in two and three-dimensions. We ran our simulations in Compucell3D, an open-source software environment based on CPM (http://simtk.org/home/compucell3d). The average characteristics of the network structure are independent of the initial configuration of cells and scale with the diffusion parameters of the chemoattractant. We have also developed an analytical PDE model to study nature of patterning instabilities. [Preview Abstract] |
Monday, March 5, 2007 3:18PM - 3:30PM |
D34.00003: Physical Mechanisms of Pattern Formation in the Early Chick Embryo Ariel Balter, James Glazier, Benji Zaitlen, Mark Chaplain, Cornelis Weijer Gastrulation marks a critical step in early embryogenesis when the first recognizable patterns are laid down. Although the genome maintains ultimate responsibility for this pattern formation, it cannot actually control the organization of individual cells. The robustness of embryogenic pattern formation suggests that a few simple, physical mechanisms are unleashed and that self-organization results. We perform numerical simulations of early chick gastrulation using an agent based method in which individual cells interact via a handful of behaviors including adhesivity, secretion and chemotaxis. Through these simulations we have identified certain behaviors as being important for various stages and morphological events. For instance, experimental results on primitive streak formation are best reproduced by a model in which the Kohler's Sickle secretes a chemo repellant for streak tip cells, and cell polarization appears to be important for initiating {\it polonaise} motion during streak elongation. [Preview Abstract] |
Monday, March 5, 2007 3:30PM - 3:42PM |
D34.00004: Interface Instabilities and Fingering in a Simulated Growing Tumor Nikodem Poplawski, Maciej Swat, James Glazier, Alexander Anderson We study the physical origin of interface instabilities, which may lead to metastasis in medical contexts, during the invasion of healthy tissue by a solid tumor. We use Glazier and Graner's Cellular Potts Model (CPM), a lattice-based stochastic framework designed to simulate cell interactions and movement. This model reduces the large molecular complexity of living cells to a few basic processes: cell-cell adhesion, cell growth, division, differentiation and death, secretion and absorption of materials, chemotaxis, and cellular deformation. We run our simulations in CompuCell3D, an open-source software environment based on the CPM (https://simtk.org/home/compucell3d). We show that cells adhesivity and growth, and rate per unit nutrient consumed, determine whether the growing tumor has a flat or fingered interface. Our results differ from those reported by Anderson (A. R. A. Anderson, Math. Med. Biol. (2005) 22:163) using a continuum model. This difference shows the importance of explicit modeling of spatially extended cells to understanding the morphologies of developing tissues. [Preview Abstract] |
Monday, March 5, 2007 3:42PM - 3:54PM |
D34.00005: Pattern formation of glioma cells: effects of adhesion Evgeniy Khain, Michal O. Nowicki, E. Antonio Chiocca, Sean E. Lawler, Leonard M. Sander \emph{Glioblastoma multiforme} is a highly malignant brain tumor. We investigate the mechanism of clustering of glioma cells \emph{in vitro}; this may shed light on clustering in the brain. Recent experiments with tumor spheroids growing in a transparent gel showed that one cell line formed clusters in a region where invasion occurs, whereas a very similar cell line does not cluster significantly. Using stochastic discrete modeling of motile adhesive and proliferative cells, we identified two important mechanisms which may lead to clustering. First, there is a critical value of the strength of cell-cell adhesion; above the threshold, large clusters grow from a homogeneous suspension of cells; below it the system remains homogeneous. Second, when several single cells form a small cluster, they may switch their phenotype from ``invasive'' to ``proliferative,'' increasing their division rate. The theoretical predictions were tested in an experiment in which we followed the clustering dynamics of glioma cells on a surface. We have successfully reproduced the experimental findings and found that both mechanisms are crucial for cluster formation and growth. [Preview Abstract] |
Monday, March 5, 2007 3:54PM - 4:06PM |
D34.00006: Role of viscosity and surface tension of zebrafish embryonic tissues in tissue flows during gastrulation. E.M. Schoetz, T. Bacarian, M.S. Steinberg, R.D. Burdine, W. Bialek, C.P. Heisenberg, R.A. Foty, F. Julicher At the onset of gastrulation in zebrafish, complex flows and cell movements occur, which are not well understood. Here, we study the material properties of zebrafish embryonic tissues which are important for the tissue dynamics. We found that these tissues behave viscoelastic and exhibit liquid-like properties on long time scales. They relax internal stress caused by compressive forces or, in the absence of external forces, round up and fuse into spheres to minimize their free surface. Quantitative differences in the adhesivity between different types of tissues result in their immiscibility and sorting behavior analogous to that of ordinary immiscible liquids. When mixed, cells segregate into discrete phases, and the position adopted correlates with differences in the aggregate surface tensions for these phases. Surface tensions were measured with a tissue surface tensiometer. Aggregates were compressed and their force response and shape were recorded as a function of time. From the analysis of the force-relaxation curves, we determined the surface tensions, relaxation times, tissue viscosities and shear moduli. Furthermore, by 4D-cell tracking, we measured kinetic parameters such as cell speed, directionality and persistence of cell movement. [Preview Abstract] |
Monday, March 5, 2007 4:06PM - 4:18PM |
D34.00007: Stochastic model of cell rearrangements in convergent extension of ascidian notochord Sharon Lubkin, Tracy Backes, Russell Latterman, Stephen Small We present a discrete stochastic cell based model of convergent extension of the ascidian notochord. Our work derives from research that clarifies the coupling of invagination and convergent extension in ascidian notochord morphogenesis (Odell and Munro, 2002). We have tested the roles of cell-cell adhesion, cell-extracellular matrix adhesion, random motion, and extension of individual cells, as well as the presence or absence of various tissue types, and determined which factors are necessary and/or sufficient for convergent extension. [Preview Abstract] |
Monday, March 5, 2007 4:18PM - 4:30PM |
D34.00008: Time markers for Drosophila morphogenesis based on cell-pattern topology. Richard Zallen, Jennifer A. Zallen Recent work on convergent extension in Drosophila has shown that the accumulation of actin-myosin networks at specific cell interfaces initiates planar polarity and the formation of multicellular rosette structures that contribute to elongation of the body axis [1]. This cell-rearrangement process takes place within a one-cell-thick layer, and the changing two-dimensional cell pattern can be characterized using topological measures such as cell-shape statistics [2]. We find that the timeline for the process contains a well-defined marker corresponding to a sharp increase in the slope of the time dependence of the variance of the cell-shape (number-of-sides) distribution. A rosette in this context is a cluster of cells enclosing high-order vertices at which 4 or 5 or more cells meet. While the cell-shape variance climbs steadily during axis elongation, the frequency of high-order vertices and large rosettes plateaus after 10 and 13 minutes, respectively. These time markers calibrate the conventional timeline descriptors referred to as stages 7 and 8 of embryonic development [3]. [1] J.T. Blankenship et al., Developmental Cell 11, 459 (2006); [2] J.A. Zallen and R. Zallen, J. Phys.: Condensed Matter 16, S5073 (2004); [3] J.A. Campos-Ortega and V. Hartenstein, The embryonic development of Drosophila melanogaster (1985). [Preview Abstract] |
Monday, March 5, 2007 4:30PM - 4:42PM |
D34.00009: Different Strategies for Aggregation in Social Amoeba Colonies Carl Franck, Ryan Monaghan, Albert Bae, Duane Loh, Eberhard Bodenschatz When confronted by starvation, collections of the amoeba Dictyostelium discoideum seek to aggregate in order to form genome-preserving stalk and spore structures. We have been interested in the means by which individual cells unite for this purpose. It has long been recognized that communication by means of diffusion of small molecules affords one such strategy: periodic chemical wave signaling can direct individual cells to an aggregation site. By employing thin layer substrates that presumably alter the propagation characteristics of such waves, we have shifted the colonial aggregation strategies to modes that rely on adhesive interactions for initial stages of multicellular assembly. Besides relentless aggregation of individual cells into large scale streams, these substrates reveal remarkable structures composed of only a few cells which we call ``squads'' that search for each other in order to achieve sufficient aggregation mass in sparse populations. [Preview Abstract] |
Monday, March 5, 2007 4:42PM - 4:54PM |
D34.00010: Optimal Foraging by Zooplankton Ricardo Garcia, Frank Moss We describe experiments with several species of the zooplankton, \textit{Daphnia, }while foraging for food. They move in sequences: \textit{hop-pause-turn-hop }etc. While we have recorded hop lengths, hop times, pause times and turning angles, our focus is on histograms representing the distributions of the turning angles. We find that different species, including adults and juveniles, move with similar turning angle distributions described by exponential functions. Random walk simulations and a theory based on active Brownian particles indicate a maximum in food gathering efficiency at an optimal width of the turning angle distribution. Foraging takes place within a fixed size food patch during a fixed time. We hypothesize that the exponential distributions were selected for survival over evolutionary time scales. [Preview Abstract] |
Monday, March 5, 2007 4:54PM - 5:06PM |
D34.00011: Precision and Reproducibility in Biological Patterning Thomas Gregor, Eric F. Wieschaus, William Bialek, David W. Tank During embryonic development, information about spatial location is represented by the concentration of various morphogen molecules. The reproducibility and precision of biological pattern formation thus is limited by the accuracy with which these concentration profiles can be established and ``read out'' by their target pathways. We consider four measures of precision for the Bicoid morphogen in the Drosophila embryo: The concentration differences that distinguish neighboring cells, the limits set by the random arrival of Bcd molecules at their targets (which depends on the absolute concentration), the noise in readout of Bcd by the activation of Hunchback, and the reproducibility of Bcd concentration at corresponding positions in multiple embryos. We show, through a combination of different experiments, that all of these quantities are $\sim$10\%. This agreement among different measures of accuracy, which depend on very different molecular mechanisms, indicates that the embryo is not faced with sloppy input signals and noisy readout mechanisms; rather we have to understand how the embryo exerts precise control over absolute concentrations and responds reliably to small changes in these concentrations, down to the limits set by basic physical principles. [Preview Abstract] |
Monday, March 5, 2007 5:06PM - 5:18PM |
D34.00012: A lattice model of parasite-host population dynamics Brian Skinner, Beate Schmittmann, Royce Zia The study of simple parasite-host population models may help us advance fundamental understanding of nonequilibrium steady-states and provide insight into potential applications for controlling epidemics. Using Monte Carlo techniques, we investigate a model of interacting parasite-host populations in which parasites must come into contact with a host in order to reproduce. We treat the parasites and hosts as random walkers on a two-dimensional lattice with reflecting boundary conditions and vary the parasite death rate and the relative diffusion rates of the two species. For low death rates and slow host diffusion, steady state populations can exist and the resulting non-trivial spatial distributions are measured. We also explore the consequences of allowing the hosts to respond to local gradients in the parasite concentration. If the hosts are biased to move away from regions of high parasite concentration, an effective repulsion between hosts emerges. Both the population levels and the spatial distributions are observed to depend sensitively on the details of this response. Some aspects of these phenomena can be understood analytically. [Preview Abstract] |
Monday, March 5, 2007 5:18PM - 5:30PM |
D34.00013: Cell Assisted Cell Growth Experiments with Dictyostelium discoideum Albert Bae, Wui Ip, Carl Franck In eukaryotic cell culture, it is routinely recommended to keep the cells above a minimum cell density to maintain vigorous growth. We are investigating the basis for this prescription by viewing cell growth as a social behavior facilitated by cell-cell communication. Employing Dictyostelium discoideum, we find good evidence for a slow-fast transition in the cell growth rate vs. density in well mixed, 25 ml, cell cultures. We also use low height microfluidic chambers (four orders of magnitude smaller in volume) to find similar behavior even though the system is not well mixed and the cells are confined to substrates. A preliminary measurement at a flow rate that should strongly perturb cell-cell communication by means of diffusing signal molecules suggests that cell communication essential for growth is not accomplished by such means but possibly via direct contacts. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700