Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session E50: Morphogenesis IFocus
|
Hide Abstracts |
Sponsoring Units: DBIO GSOFT GSNP Chair: Andrej Kosmrlj, Princeton Univ Room: LACC 511B |
Tuesday, March 6, 2018 8:00AM - 8:36AM |
E50.00001: Ensembles, Dynamics and Cell Types Invited Speaker: Stuart Kauffman The human genome encodes 23,000 proteins and perhaps more functional RNA sequences. Some vast genetic regulatory network couples these genes controlling their dynamical behaviors. Might the generic behaviors of some ensemble of dynamical systems predict aspects of ontogeny? Yes: Random Boolean Networks, RBN. Such anetwork has N binary variables, each with K inputs randomly chosen among the N, and governed by a randomly chosen Boolean function of K inputs. Time is discrete. The variables update synchronously. Any choice of N and K generates an ensemble. |
Tuesday, March 6, 2018 8:36AM - 8:48AM |
E50.00002: Translocation and interaction of PAR proteins explain oscillation and ratcheting mechanisms during Drosophila dorsal closure Clinton Durney, Tony Harris, Jimmy Feng We have developed a mechanochemical model that is able to recapitulate the Drosophila dorsal closure (DC) phenomenon. During DC, an opening on the dorsal side of the embryo is sealed in a great feat of coordination at the cellular and tissue scales of the embryo. The amnioserosa tissue, in the dorsal opening, exhibits three distinct phases of dynamic behavior: an early phase characterized by cellular oscillations, a late phase distinguished by dampening oscillations and loss of area, and a final late phase which is marked by rapid tissue contraction. Based on recent experimental observations, we couple the kinetics and transport of 3 key signaling proteins with cell mechanics to establish a delayed-negative feedback network that reproduces the three phases and provides a natural transition between them. In particular, the model explains the origin of the cell oscillation in the early phase, and that of the subsequent “ratcheting” action that allows the cells and tissue to shrink progressively over cycles of oscillation. |
Tuesday, March 6, 2018 8:48AM - 9:00AM |
E50.00003: Redundancy in a supracellular actomyosin networks yields robust tissue folding Hannah Yevick, Norbert Stoop, Jörn Dunkel, Adam Martin Correct tissue shape is essential proper tissue function. In many developing systems myosin-driven contractions are harnessed to fold cell monolayers and sculpt shape. For example folding forms both the vertebrate eye and the neural tube. In Drosophila, a cell monolayer on the ventral side of the embryo undergoes myosin-dependent constriction to fold the tissue internalizing presumptive mesoderm cells. The ventral furrow establishes a supracellular network of contractile actin-myosin fibers just prior to folding. While the cytoskeletal organization and mechanism of contraction in a single cell is understood, less is known about how the cytoskeleton is patterned across the tissue to achieve robust folding. We have integrated concepts from topological feature analysis to map the connectivity of the previously unquantified network spanning hundreds of cells. Our framework allows us to explore stereotypic properties of the supracellular network and investigate the need for reproducibility its of mechanical connections. We apply both mechanical and genetic perturbations to degrade the network and have identified that there exists multiple network architectures that induce folding. Additionally, we demonstrate the importance of redundant connections in ensuring the folding robustness. |
Tuesday, March 6, 2018 9:00AM - 9:12AM |
E50.00004: Tuning the mechanochemical machinery in oocytes using light. Jinghui Liu, Zackery Swartz, Tzer Han Tan, Nikta Fakhri Cellular development often involves a series of robust events that are elaborately coordinated by coupled biochemical and mechanical regulation. Surface contraction waves (SCW) in starfish oocytes post anaphase is a canonical example of such complex mechanochemical feedback. During these contraction waves, Rho-GTPase pathway dynamics and mechanical deformations mutually crosstalk, constituting the oocyte as an active biological material capable of forming self-organized spatiotemporal patterns. Though molecular players are broadly known, the detailed physical mechanisms of SCW are still unexplored due to a lack of perturbative methods in this mechanochemical system. Here, we report the implementation of a light-mediated molecular switch in the starfish Rho GTPase activation pathway that allows for versatile spatiotemporal manipulation of Rho recruitment. By precisely controlling the Rho activation sites and the resulting oocyte contraction patterns, we can explore with vast flexibility the interplay between biochemical and mechanical regulators. This framework will facilitate a quantitative understanding of the underlying physical mechanism driving SCW. |
Tuesday, March 6, 2018 9:12AM - 9:24AM |
E50.00005: Physics of epithelial folding Guillaume Salbreux Three-dimensional deformations of epithelia play a fundamental role in tissue morphogenesis. The shape of an epithelium is determined by mechanical stresses acting within the tissue cells and from the outside environment. Here we discuss how patterned force generation in an epithelium can drive biological tissue folding. We discuss the formation of folds during the growth of the Drosophila wing disc, and show that two folds with similar shapes arise by two different physical mechanisms. We use three-dimensional vertex model simulations that take into account cell shapes and balance of forces in a tissue to show how patterned cellular surface tensions can drive tissue folding. A continuum theory of active surface allows to capture generic aspects of fold formation, which can be understood from the action of internal active bending moments resulting from apico-basal asymmetric forces. |
Tuesday, March 6, 2018 9:24AM - 9:36AM |
E50.00006: Precision in Models of Epithelial Growth Alexander Golden, David Lubensky One of the key questions in the study of the control of tissue growth is the question of precision. What mechanisms do growing tissues have at their disposal to ensure that they grow to the correct size? How reliable are these different strategies? We present a study of possible mechanisms for the arrest of growth in the Drosophila wing disc epithelium, which appears to robustly arrive at a unique final size. In particular we investigate different methods by which mechanical feedback by stresses induced by nonuniform growth could halt growth. We introduce an analytic framework for comparing different feedback structures. This allows us to make precise claims about the fixed point structures of the growth models induced by these feedback structures. From this we can understand to what extent each model predicts precision in the growing disk as well as how stable these final sizes are. |
Tuesday, March 6, 2018 9:36AM - 9:48AM |
E50.00007: Smooth muscle differentiation physically sculpts domain branches during mouse lung development Katharine Goodwin, Celeste Nelson During branching morphogenesis, an epithelial tube is physically guided by the surrounding mesenchyme to proliferate and branch to generate an arborized network. In the mouse lung, the overall architecture is established by domain branching off of an existing branch, while bifurcations build a space-filling network. The developing airways are gradually encircled with smooth muscle derived from the mesenchyme, and specific spatial patterns of smooth muscle are required for bifurcation. Here, we examined smooth muscle differentiation during domain branching. We found that changes in morphology of domain branches are stereotyped, and are accompanied by an increase in smooth muscle wrapping at the base of the new branch. Perturbing the pattern of smooth muscle differentiation results in abnormal branch positioning and morphology. Loss of smooth muscle causes ectopic branching events and slows branch thinning, whereas enhanced smooth muscle differentiation suppresses branch initiation and extension. Our work shows that smooth muscle physically sculpts domain branches during mouse lung morphogenesis. |
Tuesday, March 6, 2018 9:48AM - 10:00AM |
E50.00008: Morphology of Embryonic Epidermis: An Empirical Multiscale Biophysics Approach Jesse Silverberg, Peng Yin Between nanoscale genotype and mesoscale phenotype, a cascade of physical and biological events take place that translate coded DNA into biological shape, function, and form. But how does this happen? How do we coarse grain from –omics regulation to quasi-pre-programmed anatomical patterns? Here, we use embryonic mouse epidermis as a specific test case to address these questions. Empirical measurements are acquired using the Molecular Atlas Platform – a multiscale imaging technology for visualizing proteomic data across many orders of magnitude in scale – and DNA-PAINT for highly multiplexed super-resolution imaging of immunofluorescent stained molecular targets. We focus on studying the biomechanics of pattern formation, and the sequence of events leading to stem cell fate specification. Our results lead us to a head-on collision with a fundamental chick-and-egg question: Does genetic programming pattern morphology, or do the material effects of morphology pattern gene expression? |
Tuesday, March 6, 2018 10:00AM - 10:12AM |
E50.00009: Impact of Cell Dynamics and Tissue Rheology on the Development of Zebrafish Left-right Organizer Gonca Erdemci-Tandogan, Jeffrey Amack, M Manning How do the material properties of a tissue impact biological processes such as embryonic development? In a developing embryo, individual cells undergo programmed shape changes to generate emergent macroscopic patterns that are essential for building functional organs, but the mechanisms involved in these precise changes remain less clear. Kupffer’s vesicle (KV), a transient organ that is responsible for specifying the left-right body axis of the zebrafish embryo, provides an excellent system to identify the factors that contribute to organogenesis and left-right embryo patterning. Although previous work has implicated intercellular tensions and extracellular matrix in this patterning, we conjecture that the dynamic motion of the KV through the tailbud may also play a role. Using a self-propelled Voronoi model, which incorporates both tissue rheology and cell motility, we investigate how the mechanical properties of highly dynamic cells surrounding the KV influence cell shape changes in the KV and consequently the left-right asymmetries in the embryo. |
Tuesday, March 6, 2018 10:12AM - 10:24AM |
E50.00010: Tissue Fracture Dynamics governs Mechanics of Morphogenesis in a Simple, Early Divergent Metazoan Vivek Nagendra Prakash, Matthew Bull, Arjun Bhargava, Manu Prakash Tissue flow mechanics dictate shape and form in all animals, and is commonly regulated by genetics. Here, we have discovered a novel case of morphogenesis regulated by tissue fracture dynamics in a simple, early divergent animal - the Trichoplax adhaerens. Live microscopy reveals that adult animals are capable of real-time extreme shape changes exhibiting both solid-like and liquid-like tissue properties. We quantitatively studied this phenomenon by developing a novel technique for long duration (~hrs) and large-scale (~mm) morphogenetic imaging and tracking of thousands of cells. We find surprising fluid-like patterns including vortices and shear zones. The ventral epithelial cells can physiologically undergo fast (~sec) and local cell rearrangements in response to internally generated forces. We find that these cellular rearrangements reflect mechanical force patterns generated by the animal’s natural movements. We further observe local micro-fracture dynamics that lead to tissue rearrangements. Remarkably, these fractures can heal over time and lead to permanent shape change. We demonstrate that micro-scale fracture and healing dynamics govern two biologically important phenomena – asexual reproduction by fission, and tissue mixing in an early divergent metazoan. |
Tuesday, March 6, 2018 10:24AM - 10:36AM |
E50.00011: Morphogenesis of growing tubes Andrej Kosmrlj, Tristan Guyomar, Katharine Goodwin, Celeste Nelson Formation, remodeling and shaping of growing tubes is a ubiquitous phenomenon observed during embryo development. Common examples include gastrulation, vascularization, and development of guts and lungs. The shaping of tubes typically occurs in response to patterned biochemical processes, which can produce mechanical forces either directly via molecular motors (e.g. the apical constriction in gastrulation) or indirectly via differential growth of connected tissues. The growth mismatch produces internal stresses, which can be released via shape transformations and mechanical instabilities, such as the formation of vili inside guts. Motivated by recent experiments, our goal is to construct a minimal mathematical model that will capture the processes involved in the branching morphogenesis of lungs. Our starting model are simple tubes constructed from an individual epithelium surrounded by the mesenchyme tissue. We investigate how patterned differential growth between the inner epithelium and the outer mesenchyme tissue can lead to formation of new branches and their subsequent development. I will also comment how stiff smooth muscles can be incorporated into our model, which will help us investigate what is the functional role of smooth muscles during the branching morphogenesis. |
Tuesday, March 6, 2018 10:36AM - 10:48AM |
E50.00012: Mechanical Feedback during Ventral Furrow Formation in Drosophila: Intercellular Coordination and Robustness Michael Holcomb, Guo-Jie Gao, Mahsa Servati, Jeffrey Thomas, Jerzy Blawzdziewicz We explore the mechanical nature of Ventral Furrow Formation (VFF) in Drosophila melanogaster using two complementary models that represent cells as mechanically excitable objects that interact through pairwise potentials. The first model focuses on the apical (outer) surface of the embryo. We represent the apical surfaces of cells as mechanically active discs and examine the initiating phase of VFF in which up to 40% of cells experience correlated stochastic constrictions, forming cellular constriction chains (CCCs). We define quantities that can be used to determine mechanical feedback mechanisms that would give rise to the observed CCC morphology, and our findings indicate that cellular sensitivity to tensile mechanical feedback is a factor in the formation of CCCs. The second model considers cells to be fully three dimensional, soft, non-spherical objects and focuses on the cross-section of the embryo. Driven by continued apical constrictions, VFF culminates in the internalization of a region of cells on the underside of the embryo. Our models show how multiple mechanisms work in concert to ensure completion of the invagination process, and we have found that mechanical feedback can allow for successful furrow closure in systems with perturbed or weakened constrictions. |
Tuesday, March 6, 2018 10:48AM - 11:00AM |
E50.00013: How does the little brain get its folds? Tyler Engstrom, Jennifer Schwarz Cerebellar foliation is "simpler" than cerebral gyrification in several important ways. All mammal species have a folded cerebellar cortex, with an underlying ten-fold motif. The cortical structure has fewer layers than that of the cerebrum, and the morphogenesis problem is effectively a two-dimensional one, resulting in rows of parallel folia. This relative simplicity makes the cerebellum an attractive problem from a physics point of view, but the mechanism by which the cusped folia are formed remains unclear. In this talk, I will describe our three-pronged investigation of cerebellum folding onset involving analysis of experimental data, computational modeling, and analytical techniques. Specifically, we map out the Bergmann glia fiber distribution to look for evidence of fold prepatterning as well as characterize localized buckling and creasing instabilities in this living matter. Informed by results from the latter two queries, we simulate cerebellum growth and morphogenesis using a two-dimensional active vertex model. |
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