Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session Y47: Multi-cellular Processes and Development |
Hide Abstracts |
Sponsoring Units: DBIO Chair: Pushpita Ghosh, Rice University Room: 217B |
Friday, March 6, 2015 8:00AM - 8:12AM |
Y47.00001: Propagating stress waves in spreading and confined cell monolayers Kazage J Christophe Utuje, Shiladitya Banerjee, M. Cristina Marchetti Many developmental processes such as morphogenesis and wound repair, involve collective cell migration, which in turn requires long-range transmission of mechanical stresses. We consider a minimal physical model of an expanding cell monolayer described as a self-propelled elastic medium coupled to the kinetics of active contractile units. These contractile units represent actomyosin stress fibers that generate local contractile stresses through ATP hydrolysis. The model also considers the effects of time-dependent propulsion forces, arising from fluctuations in the cell polarization. Our model quantitatively reproduces many experimental findings, including propagating stress waves that are driven by a mechano-chemical feedback between mechanical strain and cell contractility. Furthermore, our model predicts that the effective material rigidity of the cell layer undergoes sustained periods of stiffening and fluidization as waves propagate in the system. Using the model, we further investigate the mechanisms of wave propagation in confined geometries, as observed in recent experiments on cell monolayers in micropatterned environments. [Preview Abstract] |
Friday, March 6, 2015 8:12AM - 8:24AM |
Y47.00002: A Combined Light Sheet Fluorescence and Differential Interference Contrast Microscope for Live Imaging of Multicellular Specimens Ryan Baker, Michael Taormina, Matthew Jemielita, Raghuveer Parthasarathy We present a microscope capable of both light sheet fluorescence microscopy (LSFM) and differential interference contrast microscopy (DICM). The two imaging modes, which to the best of our knowledge have not previously been combined, are complementary: LSFM provides high speed three-dimensional imaging of fluorescently labeled components of multicellular systems, large fields of view, and low phototoxicity, while DICM reveals the unlabeled neighborhood of tissues, organs, and other structures with high contrast and inherent optical sectioning. Use of a shared detection path for both imaging modes enables simple integration of the two techniques in one microscope. To demonstrate the instrument's utility, we provide several examples which focus on the digestive tract of the larval zebrafish. We show that DICM can sometimes circumvent the need for fluorescent based techniques, augmenting the number of parameters obtainable per experiment when used alongside LSFM, and that DICM can be used to augment each experiment by imaging complementary features, such as non-fluorescent local environments near fluorescent samples (e.g. fluorescent enteric neurons imaged alongside the non-fluorescent gut wall), interactions between fluorescent and non-fluorescent samples (e.g. bacteria), and more. [Preview Abstract] |
Friday, March 6, 2015 8:24AM - 8:36AM |
Y47.00003: Mechanical origins of rightward torsion in early chick brain development Zi Chen, Qiaohang Guo, Eric Dai, Larry Taber During early development, the neural tube of the chick embryo undergoes a combination of progressive ventral bending and rightward torsion. This torsional deformation is one of the major organ-level left-right asymmetry events in development. Previous studies suggested that bending is mainly due to differential growth, however, the mechanism for torsion remains poorly understood. Since the heart almost always loops rightwards that the brain twists, researchers have speculated that heart looping affects the direction of brain torsion. However, direct evidence is lacking, nor is the mechanical origin of such torsion understood. In our study, experimental perturbations show that the bending and torsional deformations in the brain are coupled and that the vitelline membrane applies an external load necessary for torsion to occur. Moreover, the asymmetry of the looping heart gives rise to the chirality of the twisted brain. A computational model and a 3D printed physical model are employed to help interpret these findings. Our work clarifies the mechanical origins of brain torsion and the associated left-right asymmetry, and further reveals that the asymmetric development in one organ can induce the asymmetry of another developing organ through mechanics, reminiscent of D'Arcy Thompson's view of biological form as ``diagram of forces". [Preview Abstract] |
Friday, March 6, 2015 8:36AM - 8:48AM |
Y47.00004: ABSTRACT WITHDRAWN |
Friday, March 6, 2015 8:48AM - 9:00AM |
Y47.00005: Modeling the fusion of cylindrical bioink particles in post bioprinting structure formation Matt McCune, Ashkan Shafiee, Gabor Forgacs, Ioan Kosztin Cellular Particle Dynamics (CPD) is an effective computational method to describe the shape evolution and biomechanical relaxation processes in multicellular systems. Thus, CPD is a useful tool to predict the outcome of post-printing structure formation in bioprinting. The predictive power of CPD has been demonstrated for multicellular systems composed of spherical bioink units. Experiments and computer simulations were related through an independently developed theoretical formalism based on continuum mechanics. Here we generalize the CPD formalism to (i) include cylindrical bioink particles often used in specific bioprinting applications, (ii) describe the more realistic experimental situation in which both the length and the volume of the cylindrical bioink units decrease during post-printing structure formation, and (iii) directly connect CPD simulations to the corresponding experiments without the need of the intermediate continuum theory inherently based on simplifying assumptions. [Preview Abstract] |
Friday, March 6, 2015 9:00AM - 9:12AM |
Y47.00006: Modeling the Epithelial Morphogenesis of Germ Band Retraction in Three Dimensions W. Tyler McCleery, Jim Veldhuis, G. Wayne Brodland, Sarah M. Crews, M. Shane Hutson Embryogenesis of higher-order organisms is driven by an intricate coordination of cellular mechanics. Mechanical analysis of certain developmental events, e.g., dorsal closure in the fruit fly D. melanogaster, has been sufficiently described using two-dimensional models. Here, we present a three-dimensional modeling technique to investigate germ band retraction (GBR) -- a whole-embryo, irreducibly 3D morphogenetic event. At the start of GBR, the epithelial tissue known as the germ band is initially wrapped around the posterior end of an ellipsoidal fly embryo. This tissue then retracts as an adjacent epithelial tissue, the amnioserosa, simultaneously contracts. We hypothesize that proper GBR requires maintenance of cell-cell connectivity in the amnioserosa, as well as both cell and tissue topology on the embryo's ellipsoidal surface. The exact interfacial tensions are less important. We test the dynamic interactions between these two tissues on a 3D ellipsoidal last. To speed simulation run times and focus on the relevant tissues, epithelial cells are defined as polygons constrained to lie on the surface of the ellipsoidal last. These cells have adjustable parameters such as edge tensions and cell pressures. Tissue movements are simulated by balancing these dynamic cell-level forces with viscous resistance and allowing cells to exchange neighbors. This modeling approach helps elucidate the multicellular stress fields in normal and aberrant development, providing deeper insight into the mechanical interdependence of developing tissues. [Preview Abstract] |
Friday, March 6, 2015 9:12AM - 9:24AM |
Y47.00007: Signaling Delays Preclude Defects in Lateral Inhibition Patterning Ingmar Riedel-Kruse, David Glass, Xiaofan Jin Developmental biology is extraordinarily robust in its ability to self-organize spatiotemporal patterns despite an intrinsically noisy set of parts. Lateral inhibition is a classic example of a mechanism behind such precise emergent behavior. However, the models through which we understand lateral inhibition's capabilities usually assume that cells signal to one another without delay, a supposedly minor source of error at most. Here we explicitly investigate the effects of signaling delays as well as their relation to cis-interactions in lateral inhibition patterning. We reduce the patterning problem effectively to a two-parameter phase space (signaling delay and coupling strength), and we found that rather than being a source of error, signaling delays enable significant decrease of error rates. Together with cis-interactions, these delays lead to patterning that can be both fast and robust to noise and parameter variation. This suggests that overlooking time delays in developmental signaling does not just ignore a potential source of error, but rather ignores a knob with which evolution may tune patterning robustness in general. [Preview Abstract] |
Friday, March 6, 2015 9:24AM - 9:36AM |
Y47.00008: Waves of ratcheting cancer cells in growing tumor tissue layer Taeseok Yang, Tae Kwon, Hyun Kim, Kyoung Lee Over many years researchers have shown that the mechanical forces generated by, and acting on, tissues influence the way they grow, develop and migrate. As for cancer research goes, understanding the role of these forces may even be as influential as deciphering the relevant genetic and molecular basis. Often the key issues in the field of cancer mechanics are to understand the interplay of mechanics and chemistry. In this study, we discuss very intriguing population density waves observed in slowly proliferating of tumor cell layers. The temporal periods are around 4 hr and their wavelength is in the order of 1 mm. Tumor cell layer, which is initially plated in a small disk area, expands as a band of tumor cells is ``ratcheting'' in concert in radially outward direction. By adding Cytochalasin D and Latrunculin B, an inhibitor of actin polymerization, or Mytomycin, a chemotherapeutic agent, we could halt and modulate the wave activities reversibly. The observed waves are visually quite similar to those of chemotaxing dictyostelium discodium amoeba population, which are driven by nonlinear chemical reaction-diffusion waves of cAMP. So far, we have not been able to show any relevant chemo-attractants inducing the collective behavior of these tumor cells. Researchers have been investigating how forces from both within and outside developing cancer cells interact in intricate feedback loops. This work reports the example of periodic density waves of tumor cells with an explanation purely based on nonlinear mechanics. [Preview Abstract] |
Friday, March 6, 2015 9:36AM - 9:48AM |
Y47.00009: Pattern formation in a growing bacterial colony facilitated by extra-cellular polymeric substances Pushpita Ghosh, Jagannath Mondal, Eshel Ben-Jacob, Herbert Levine Self-organization in bacterial colony is quite pervasive and diverse phenomena. Bacteria are known to self-organize into multicellular communities, commonly known as biofilms, in which microbial cells live in close association with a solid surface and are embedded in a self-produced extracellular polymeric substances(EPS). In such dense systems mechanical interactions among the structural components can be expected to significantly contribute to the morphological properties. By a simple particle-based simulation model of nonmotile rod-shaped bacterial cells and EPS secreted in a growing colony, we investigate how the combined mechanical effects can give rise naturally spatial heterogeneity observed in a biofilm. In our individual-based simulation model all the components interact mechanically via repulsive forces by pushing each other away as bacterial cells grow and divide consuming diffusing nutrient and produce EPS. We show that mechanical interactions control the collective behavior of the system, particularly, we show that the presence of non-adsorbing EPS leads spontaneous aggregation of bacterial cells by depletion attraction and generates phase separated patterns in a nonequilibrium growing colony. [Preview Abstract] |
Friday, March 6, 2015 9:48AM - 10:00AM |
Y47.00010: Evaporation-driven convection observed in a suspension of non-motile bacteria Jocelyn Dunstan, Kyoung Jin Lee, Simon Park, Raymond E. Goldstein We report a novel form of convection in a suspension of non-motile bioluminescent bacteria. The patterns appear like those of conventional bioconvection driven by oxygentaxis, yet the bacteria are observed to have limited if any motility. While the phenomenon also resembles chemo-convection, in which a chemical reaction (or metabolic activity) alters the local buoyancy balance at the air-water interface, the convention actually derives from evaporation of the salty bacterial growth medium. We corroborate this through control experiments using polystyrene beads in pure and salty water, and establish that there is a threshold of salt concentration needed to observe plumes. The dynamics of the plumes is rich, with striking coalescence events and a complex internal structure. A mathematical model is formulated for the process and studied analytically and numerically, reproducing most of the observed experimental features. Evaporation-driven convection on the millimeter scale has not been studied extensively and its effect may have been underestimated in a variety of contexts. It may naturally occur in marine settings. [Preview Abstract] |
Friday, March 6, 2015 10:00AM - 10:12AM |
Y47.00011: Optoporation to deliver impermeable molecules and genes for visualization and activation of cells Kamal Dhakal, Subrata Batbyal, Young-tae Kim, Samarendra Mohanty Visualization, activation, and detection of the cell(s) and their electrical activity require delivery of exogenous impermeable molecules and targeted expression of genes encoding labeling proteins, ion-channels and voltage indicators. While genes can be delivered by viral vector to cells, delivery of other impermeable molecules into the cytoplasm of targeted cells requires microinjection by mechanical needle or microelectrodes, which pose significant challenge to the viability of the cells. Further, it will be useful to localize the expression of the targeted molecules not only in specific cell types, but to specific cells in restricted spatial regions. Here, we report use of focused near-infrared (NIR) femtosecond laser beam to transiently perforate targeted cell membrane to insert genes encoding blue light activatable channelrhodopsin-2 (ChR2) and red-shifted opsin (ReachR). Optoporation of nanomolar concentrations of rhodamine phalloidin (an impermeable dye molecule for staining filamentous actin) into targeted living mammalian cells (both HEK and primary cortical neurons) is also achieved allowing imaging of dynamics and intact morphology of cellular structures without requiring fixation. [Preview Abstract] |
Friday, March 6, 2015 10:12AM - 10:24AM |
Y47.00012: Corn-in-chip: Mesofluidic Device for Corn Root Kevin Kreis, Sangjin Ryu Plants have a collection of beneficial microorganisms in a region surrounding their roots called the rhizosphere. Although rhizosphere management could increase crop yield, little is known about the interaction between plant roots and their associated microorganisms. Thus we aim to simulate the rhizosphere and monitor root-microbe interactions in the lab environment, and have chosen corn as a model plant because of its economic significance. Here we present our preliminary study to develop a transparent mesofluidic device accommodating the root of corn seedlings into its channel and allowing further growth of the root. [Preview Abstract] |
Friday, March 6, 2015 10:24AM - 10:36AM |
Y47.00013: Excitable Pattern Formation in Inhomogeneous Systems Kaumudi Prabhakara, Azam Gholami, Vladimir Zykov, Eberhard Bodenschatz On starvation, the amoebae \textit{Dictyostelium discoideum} signal via the chemo-attractant cyclic adenosine monophosphate (cAMP). The amoebae sense cAMP through membrane receptors and produce their own cAMP. Simultaneously they produce a basal level of Phosphodiesterase, an enzyme that degrades cAMP. Soon a pattern of rotating spiral waves or circular waves is formed at the multi-cellular level. The causal reasons for the selection of one or the other pattern are still unclear. Here we report experimental and theoretical investigations of the pattern-formation of mixtures of cells starved for different times. The excitability of the amoebae depends on the starvation time due to time dependent gene expressions. Cells starved for longer times are known to exhibit increased excitability. We report phase maps of the patterns for mixtures of different combinations of excitability. Numerical simulations of a modified Kessler-Levine model allow us to explain the experimental results and provide new insights into the dynamical behavior of the system. [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