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Speaker: Max LavrentovichTitle: Strongly driven mixtures and membranes: Out of equilibrium surprisesVenue: CMSA Room G10Active Matter Seminar Speaker: Max Lavrentovich, Worcester State University Title: Strongly driven mixtures and membranes: Out of equilibrium surprises Abstract: The more prosaic cousin of active matter, driven inactive matter, is still full of unexpected phenomena. I will discuss two projects involving two seemingly mundane systems, a phase-separating colloidal mixture and a lipid membrane, which demonstrate counterintuitive properties when driven out of equilibrium. We will see that the phase separating mixture, when driven by a uniform force, develops (in simulations) an intriguing pattern with a characteristic length scale set by the magnitude of the drive. We will look at some theoretical approaches to understanding the pattern formation and possible experimental realizations. The membrane, when driven by an oscillatory electric… |
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Speaker: Herbert LevineTitle: Frustration-free states of cell fate networks: the case of the epithelial-mesenchymal transitionVenue: CMSA Room G10Active Matter Seminar Speaker: Herbert Levine (Northeastern) Title: Frustration-free states of cell fate networks: the case of the epithelial-mesenchymal transition Abstract: Cell fate decisions are made by allowing external signals to govern the steady-state pattern adopted by networks of interacting regulatory factors governing transcription and translation. One of these decisions, of importance for both developmental processes and for cancer metastasis, is the epithelial-mesenchymal transition (EMT). In this talk, we will argue that these biological networks have highly non-generic interaction structures such that they allow for phenotypic states with very low frustration, i.e. where most interactions are satisfied. This property has important consequences for the allowed dynamics of these systems. |
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Speaker: Sahand HormozTitle: Insights from single cell lineage treesVenue: Jefferson 256Active Matter Seminar Speaker: Sahand Hormoz, Harvard Medical School, Dana-Farber Cancer Institute Title: Insights from single cell lineage trees Abstract: In this talk, I will discuss two recent projects from my lab that involve lineage trees of cells (the branching diagram that represents the ancestry and division history of individual cells). In the first project, we reconstructed the lineage trees of individual cancer cells from the patterns of randomly occurring mutations in these cells. We then inferred the age at which the cancer mutation first occurred and the rate of expansion of the population of cancer cells within each patient. To our surprise, we discovered that the cancer mutation occurs decades before diagnosis. For the second project, we developed… |
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Speaker: Mehran KardarTitle: Competition at the front of expanding populationsVenue: CMSA Room G10Active Matter Seminar Speaker: Mehran Kardar, MIT Title: Competition at the front of expanding populations Abstract: When competing species grow into new territory, the population is dominated by descendants of successful ancestors at the expansion front. Successful ancestry depends on the reproductive advantage (fitness), as well as ability and opportunity to colonize new domains. (1) Based on symmetry considerations, we present a model that integrates both elements by coupling the classic description of one-dimensional competition (Fisher equation) to the minimal model of front shape (KPZ equation). Macroscopic manifestations of these equations on growth morphology are explored, providing a framework to study spatial competition, fixation, and differentiation, In particular, we find that ability to expand in space may overcome reproductive advantage in… |
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Speaker: Shane McInallyTitle: Control of actin cable length by decelerated growth and network geometryVenue: CMSA Room G10Active Matter Seminar Speaker: Shane McInally, Brandeis Title: Control of actin cable length by decelerated growth and network geometry Abstract: The sizes of many subcellular structures are coordinated with cell size to ensure that these structures meet the functional demands of the cell. In eukaryotic cells, these subcellular structures are often membrane-bound organelles, whose volume is the physiologically important aspect of their size. Scaling organelle volume with cell volume can be explained by limiting pool mechanisms, wherein a constant concentration of molecular building blocks enables subcellular structures to increase in size proportionally with cell volume. However, limiting pool mechanisms cannot explain how the size of linear subcellular structures, such as cytoskeletal filaments, scale with the linear dimensions of the… |
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Speaker: Mark BowickTitle: The Role of Orientational Order in DevelopmentVenue: CMSA Room G10Active Matter Seminar Speaker: Mark Bowick, Kavli Institute for Theoretical Physics, UCSB Title: The Role of Orientational Order in Development Abstract: Morphogenesis, the process through which genes generate form, establishes tissue scale order as a template for constructing the complex shapes of the body plan. The extensive growth required to build these ordered substrates is fueled by cell proliferation, which, naively, should disrupt order. Understanding how active morphogenetic mechanisms couple cellular and mechanical processes to generate order remains an outstanding question in animal development. I will review the statistical mechanics of orientational order and discuss the observation of a fourfold orientationally ordered phase (tetratic) in the model organism Parhyale hawaiensis. I will also discuss theoretical mechanisms for the formation… |
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Speaker: Jonathan BauermannTitle: Active chemical reactions in phase-separating systemsVenue: virtualActive Matter Seminar Speaker: Jonathan Bauermann, Max Planck Institute for the Physics of Complex Systems Title: Active chemical reactions in phase-separating systems Abstract: Motivated by the existence of membrane-less compartments in the chemically active environment of living cells, I will discuss the dynamics of droplets in the presence of active chemical reactions. Therefore, I will first introduce the underlying interplay between phase separation and active reactions, which can alter the droplet dynamics compared to equilibrium systems. A key feature of such systems is the emergence of concentration gradients even at steady states. In the second part of this talk, I will discuss how these gradients can trigger instabilities in the core of chemically active droplets, giving rise… |
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Speaker: Jörn DunkelTitle: Towards programmable living materials and quantitative models of active matterVenue: CMSA Room G10Active Matter Seminar Speaker: Jörn Dunkel, MIT Title: Towards programmable living materials and quantitative models of active matter Abstract: Over the last two decades, major progress has been made in understanding the self-organization principles of active matter. A wide variety of experimental model systems, from self-driven colloids to active elastic materials, has been established, and an extensive theoretical framework has been developed to explain many of the experimentally observed non-equilibrium pattern formation phenomena. Two key challenges for the coming years will be to translate this foundational knowledge into functional active materials, and to identify quantitative mathematical models that can inform and guide the design and production of such materials. Here, I will describe joint efforts with our experimental collaborators to… |
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Speaker: Amin DoostmohammadiTitle: Interacting Active MatterVenue: CMSA Room G10Active Matter Seminar Speaker: Amin Doostmohammadi, Niels Bohr Institute, University of Copenhagen Title: Interacting Active Matter Abstract: I will focus on the interaction between different active matter systems. In particular, I will describe recent experimental and modeling results that reveal how interaction forces between adhesive cells generate activity in the cell layer and lead to a potentially new mode of phase segregation. I will then discuss mechanics of how cells use finger-like protrusions, known as filopodia, to interact with their surrounding medium. First, I will present experimental and theoretical results of active mirror-symmetry breaking in subcellular skeleton of filopodia that allows for rotation, helicity, and buckling of these cellular fingers in a wide variety of cells ranging from epithelial,… |
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Speaker: Julien TailleurTitle: Self-organization of motile cells by quorum-sensing or chemotactic interactionsVenue: Lyman 330Active Matter Seminar Speaker: Julien Tailleur (MIT) Title: Self-organization of motile cells by quorum-sensing or chemotactic interactions Abstract: Equilibrium statistical mechanics tells us how to control the self-assembly of passive materials by tuning the competition between energy and entropy to achieve desired states of organization. Out of equilibrium, no such principles apply and self-organization principles are scarce. Active matter describes systems in which individual units dissipate energy to exert forces on their environment. Dissipation and injection of energy are then disconnected at the microscopic scale, hence driving the system strongly out of thermal equilibrium. This leads to a phenomenology markedly different from that of equilibrium systems, such as the emergence of dense phases in the absence of cohesive attractive… |
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Speaker: Max PrigozhinTitle: Dynamic and multicolor electron microscopyVenue: CMSA Room G10Active Matter Seminar Speaker: Max Prigozhin (Harvard) Title: Dynamic and multicolor electron microscopy Abstract: My lab is developing biophysical methods to achieve multicolor and dynamic biological imaging at the molecular scale. Our approach to capturing the dynamics of cellular processes involves cryo-vitrifying samples after known time delays following stimulation using custom cryo- plunging and high-pressure freezing instruments. To achieve multicolor electron imaging, we are exploring the property of cathodoluminescence—optical emission induced by the electron beam. We are developing nanoprobes (“cathodophores”) that will be used as luminescent protein tags in electron microscopy. We are applying these new methods to study G-protein- coupled receptor signaling and to visualize the formation of biomolecular condensates. |
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Speaker: Siavash MonfaredTitle: Force transmission informs the collective behavior of active cell layersVenue: CMSA Room G10Active Matter Seminar Speaker: Siavash Monfared, Niels Bohr Institute, Copenhagen Title: Force transmission informs the collective behavior of active cell layers Abstract: Collective cell migration drives numerous physiological processes such as tissue morphogenesis, wound healing, tumor progression and cancer invasion. However, how the interplay of mechanical interactions and the modes of collective self-organization among cells informs such processes is yet to be established. In this talk, I will focus on the role of three-dimensional force transmission, from a theoretical and computational perspective, on two phenomena: (1) cell extrusion from a cellular monolayer and (2) density-independent solid-like to fluid-like transition of active cell layers. For the first topic, I will focus on how increasing cell-cell adhesion relative to cell-substrate adhesion… |
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Speaker: Sharad RamanathanTitle: Attempts at understanding human axial elongation and patterningVenue: CMSA Room G10Active Matter Seminar Speaker: Sharad Ramanathan, Harvard Title: Attempts at understanding human axial elongation and patterning Abstract: Some of the most dramatic events during human development is the axial elongation of the embryo with concomitant changes in the geometry and composition of the underlying tissues. The posterior part of the embryo gives rise to the spinal cord, vertebral column, ribcage, back muscles, and dermis. In this talk, I will present our attempts at coaxing human embryonic stem cells to form these structures of the early human embryo that closely recapitulate the geometry, relative arrangements, composition, and dynamics of development of the early spinal cord flanked progenitors of the musculoskeletal system. Our goal was to do so, such that we could… |
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Speaker: Shenshen WangTitle: Limit and potential of adaptive immunityVenue: CMSA Room G10Active Matter Seminar Speaker: Shenshen Wang, UCLA Title: Limit and potential of adaptive immunity Abstract: The adaptive immune system is able to learn from past experiences to better fit an unforeseen future. This is made possible by a diverse and dynamic repertoire of cells expressing unique antigen receptors and capable of rapid Darwinian evolution within an individual. However, naturally occurring immune responses exhibit limits in efficacy, speed and capacity to adapt to novel challenges. In this talk, I will discuss theoretical frameworks we developed to (1) explore functional impacts of non-equilibrium antigen recognition, and (2) identify conditions under which natural selection acting local in time can find adaptable solutions favorable in the long run, through exploiting environmental variations and functional constraints. |
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Speaker: Josef KäsTitle: State Diagram of Cancer Cell Unjamming Predicts Metastatic RiskVenue: CMSA, 20 Garden St, G10Speaker: Josef Käs, Leipzig University Title: State Diagram of Cancer Cell Unjamming Predicts Metastatic Risk Abstract: Distant metastasis is probably the most lethal hallmark of cancer. Due to a lack of suitable markers, cancer cell motility only has a negligible impact on current diagnosis. Based on cell unjamming we derive a cell motility marker for static histological images. This enables us to sample huge numbers of breast cancer patient data to derive a comprehensive state diagram of unjamming as a collective transition in cell clusters of solid tumors. As recently discovered, cell unjamming transitions occur in embryonic development and as pathological changes in diseases such as cancer. No consensus has been achieved on the variables and the parameter… |
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Speaker: Guillaume DuclosTitle: Building active nematic and active polar liquids out of biological machinesVenue: Lyman 425Speaker: Guillaume Duclos (Brandeis) Title: Building active nematic and active polar liquids out of biological machines Abstract: Active matter describes out-of-equilibrium materials composed of motile building blocks that convert free energy into mechanical work. The continuous input of energy at the particle scale liberates these systems from the constraints of thermodynamic equilibrium, leading to emergent collective behaviors not found in passive materials. In this talk, I will describe our recent efforts to build simple active systems composed of purified proteins and identify generic emergent behaviors in active systems. I will first discuss two distinct activity-driven instabilities in suspensions of microtubules and molecular motors. Second, I will describe a new model system for polar fluid whose collective dynamics are driven by the non-equilibrium turnover of actin filaments. Our results illustrate… |