Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session X23: MorphogenesisFocus
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Sponsoring Units: DBIO Chair: Andrej Kosmrlj, Princeton University Room: 304 |
Friday, March 6, 2020 11:15AM - 11:51AM |
X23.00001: The role of physical forces in cortical morphogenesis Invited Speaker: Maria Holland Between individuals and across species, brain morphology is strikingly consistent in some significant ways. One example is a characteristic pattern of cortical thickness in gyrencephalic, or folded, brains - thick outer folds, or gyri, and thin inner folds, or sulci. This raises the question: which factors (genetic, biochemical, physical, and/or others) lead to this morphological consistency? In a recent combined theoretical, numerical, and experimental study, we found that the physical forces generated by buckling instabilities were sufficient to generate physiological gyral-sulcal thickness ratios. We now consider the more complex, fully three-dimensional pattern of cortical thickness in the brain, and investigate the role of physical forces in its evolution, consistency, and variability. |
Friday, March 6, 2020 11:51AM - 12:03PM |
X23.00002: New directions for the animal shape analysis Vasyl Alba, Jamie Carthew, Madhav Mani, RICHARD CARTHEW We used a new precise tool to address a question of quantitative description of the morphological traits in biological systems. |
Friday, March 6, 2020 12:03PM - 12:15PM |
X23.00003: Surface Stresses Drive Morphological Changes in Three-Dimensional Microtissues Erik Mailand, Bin Li, Jeroen Eyckmans, Nikolaos Bouklas, Mahmut Selman Sakar The formation and maintenance of tissue boundaries is vital for morphogenesis and homeostasis as groups of cells with distinct functions must often be kept physically separated. Cells organize into sheets on the tissue surfaces by forming intercellular mechanical connections directly or through the ECM. The collective dynamics of boundary regulation have been extensively studied with micropatterned epithelial monolayers, whose behavior has been captured using physical models based on nematic liquid crystals. However, less is known about surface effects in 3D fibrous tissues and their contribution to tissue architecture. We developed a high-throughput biomimetic platform for the study of morphogenesis in multilayered 3D microtissues. We performed local mechanical perturbations using a robotic microsurgery system and selective optochemical manipulations using a programmable projector. We show both experimentally and by using computer simulations that cells at the tissue boundary develop surface stresses and, together with contractile cells residing in the core, drive macroscale deformation. We demonstrate that targeted elimination of cells at the tissue surface induces a local stress gradient that leads to tissue morphogenesis. |
Friday, March 6, 2020 12:15PM - 12:51PM |
X23.00004: Mechanoregulation of Valvular Morphogenesis Invited Speaker: Jonathan Butcher Defective heart valve morphogenesis is a major cause of preterm fetal death and premature postnatal tissue failure. While much has been learned over the past 30 years regarding the genetic and molecular agents engaged in valve morphogenesis, much less is known about how these networks contribute to cellular and tissue level responses essential for sculpting initially amorphous globular cushions into elongated, thin, and striated leaflets that are competent for long term biomechanical function. Recent studies from our group and others have highlighted that the local mechanical environment within the fetal heart are essential mediators of proper, and when perturbed defective, valvular growth and maturation. We here clarify the embryonic and fetal mechanical environment and elaborate how these mechanical signals coordinate and integrate both canonical valvulogenic signaling programs and previously understudied cellular migration and traction generating programs towards maturation. As this field deepens in its understanding, new opportunities to engineer molecular therapies to harness mechanotransduction and/or mechanosensation could help rebalance disturbed valvulogenic programming, improve anatomical outcomes at birth, and ultimately extend valve performance. |
Friday, March 6, 2020 12:51PM - 1:03PM |
X23.00005: Organ Size Coordination by Chemical Signaling Ojan K Damavandi, David Lubensky A profound open question in biology is how animals ensure that their body parts have the correct relative proportions given that development is often noisy. For instance, wings of the same fruit fly do not differ in size by more than about 1% in normal conditions. More interestingly, knocking out a single gene (dilp8) responsible for a hormone secreted by the organs in fly larvae leads to increased size asymmetry of 2-3% between left and right wings. Inspired by this example, we model noisy growth of bilaterally symmetric organs and investigate different mechanisms of organ size coordination using a single coordination signal secreted by the organs. We find that generally feedback can help coordinate organs during growth, thus suppressing variability and speeding development, but that no mechanism with a single signal can robustly coordinate final organ sizes. Finally, we show that a particularly appealing mechanism is proportional feedback on growth rate, which best matches the available data on the biological signatures of dilp8 in flies. Our work suggests that while inter-organ feedback is beneficial to development, organs must additionally employ autonomous size specification mechanisms to ensure low asymmetry at the end of growth. |
Friday, March 6, 2020 1:03PM - 1:15PM |
X23.00006: Generating Cell Fate Patterns via Mechanical Stress in Stem Cell Colonies Hayden Nunley, Xufeng Xue, Jianping Fu, David Lubensky Embryonic development depends on fate specification events in which a field of initially equivalent cells differentiates in a spatially controlled manner. A key example is neural induction in which a strip of cells differentiates into the neural plate, flanked by the neural plate border (NPB). Classic studies of neural induction have confirmed the role of diffusible chemical signals from neighboring tissues; the role of mechanical signals in fate patterning events like neural induction remains poorly understood. |
Friday, March 6, 2020 1:15PM - 1:27PM |
X23.00007: How can proteins take derivatives? Manon Wigbers, Tzer Han Tan, Fridtjof Brauns, Tobias Hermann, Nikta Fakhri, Erwin A Frey Many cellular processes, such as cell division and cell motility, rely crucially on the dynamic localization of proteins in space and time. These localization patterns emerge collectively from local molecular interactions of proteins. To analyze how the interplay of diffusion and protein interactions on a nanometer scale influence the protein patterns on the cellular scale, the framework of reaction-diffusion models has proven useful. The study of such systems goes back to Turing, who showed how patterns can emerge from a homogenous steady state when two reactive components have different diffusivities. However, in nature, systems typically develop in a heterogeneous and temporally evolving environment and from one pattern into another, rather than from a homogeneous steady state into a pattern. |
Friday, March 6, 2020 1:27PM - 1:39PM |
X23.00008: Hierarchical “buckling without bending” and brain shape Jennifer Schwarz, Mahesh Chandrasekhar Gandikota, Tyler Engstrom, Teng Zhang While studies of brain shape development have focused on the cerebrum, the cerebellum, otherwise known as the little brain, typically houses more neurons than the cerebrum and has a distinct morphology with 8-10 primary lobes that subsequently branch into smaller lobes. A recent “buckling without bending” model quantifies the onset of shape change in the developing cerebellum. It consists of an inner incompressible core of cells and an outer fluid-like cortical layer of dividing cells encased by a basement membrane. Additionally, there are two types of fibrous cells---ones spanning the cerebellum and ones spanning the cortical layer. The onset of shape change is a consequence of mechanical constraints on the outer fluid-like cortical layer as it proliferates. This model is now generalized beyond the onset of shape change to predict shape development at later stages. In particular, a hierarchical version of the model is implemented to predict subsequent branching of the smaller lobes. Predictions are compared with various mammalian cerebella exhibiting varied counts of branching generations. We also explore how some aspects of “buckling without bending” may lead to a new level of detail for characterizing shape change in the developing cerebrum. |
Friday, March 6, 2020 1:39PM - 1:51PM |
X23.00009: Mechanomorphogenesis of bacterial biofilms Jing Yan Surface-attached bacterial communities called biofilms display a diversity of morphologies. Although structural and regulatory components required for biofilm formation are known, it is not understood how these essential constituents promote biofilm surface morphology. Here, using Vibrio cholerae as our model system, we combine mechanical measurements, theory and simulation, quantitative image analyses, surface energy characterizations, and mutagenesis to show that mechanical instabilities, including wrinkling and delamination, underlie the morphogenesis program of growing biofilms. We also identify interfacial energy as a key driving force for mechanomorphogenesis because it dictates the generation of new and the annihilation of existing interfaces. Finally, we discover feedback between mechanomorphogenesis and biofilm expansion, which shapes the overall biofilm contour. The morphogenesis principles that we discover in bacterial biofilms, which rely on mechanical instabilities and interfacial energies, should be generally applicable to morphogenesis processes in tissues in higher organisms. |
Friday, March 6, 2020 1:51PM - 2:03PM |
X23.00010: Quantifying mechanochemical coupling in the actomyosin cortex during early development in vivo Melis Tekant, Alexandru Bacanu, Yoon Jung, Jorn Dunkel, Nikta Fakhri Spatiotemporal symmetry-breaking transitions in biochemical patterns are essential in triggering morphological changes during the development of all life forms, both at the unicellular and multicellular level. The realization of cell and tissue-scale deformations is achieved through intra-cellular force networks that translate localized biochemical signals into effective mechanical stresses that determine the global shape dynamics. However, the mechanochemical coupling between the biochemical patterns, force network activity and the resulting stresses is not well understood. Here, we quantify the local coupling between membrane-bound Rho-GTP and the mechanical deformations of the actomyosin cortex in the starfish oocytes during meiosis. We generate various Rho-GTP dynamic patterns and map the resulting stress patterns via tracking endogenous tracer particles embedded in the cell cortex. This method provides a novel approach to probe the local coupling between biochemistry and mechanics and the resulting morphological changes. |
Friday, March 6, 2020 2:03PM - 2:15PM |
X23.00011: The role of environment, material, and function in the morphological diversity of termite mounds Tadeu Fagundes, Juan Ordonez, Neda Yaghoobian Several species of termites across the globe construct mound architectures that are of several orders of magnitude larger than themselves. These superstructures exhibit distinctive structural designs that range widely in size and shape. There are several studies exploring the function of termite mound structures, but only a few works explore reasons behind the morphological variety observed in them. To explain this diversity, the present work introduces a computational model that couples the mound’s environment, material, and thermal function to its shape. Using the fundamentals of heat transfer, the model captures the main features observed in termite mounds, such as the mound orientation and spire tilt. The influence of each environmental agent over the mound structure is analyzed, revealing a strong correlation between the mound structure and the combined effects of the environmental forces. The proposed methodology can be used in the prediction of the effect of environmental forces on the thermal performance and architecture of any natural structure for which structural and environmental information can be obtained. As such, this framework provides a broader view of the factors that are effective in the form and function of naturally made structures. |
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