Department of Mathematics and Center for Quantitative Modeling in Biology
University of California, Riverside, CA
Novel cell-based model of the generation and maintenance of the shape and structure of the multi-layered shoot apical meristem of Arabidopsis thaliana
Abstract: One of the central problems in animal and plant developmental biology is deciphering how chemical and mechanical signals interact within a tissue to produce the final form, size, structure and function of an organ. To address this problem, a novel, multi-scale, cell-based computational model of the stem cells of the shoot apical meristem (SAM) of Arabidopsis thaliana is developed and calibrated using experimental data. Novel features of the model include separate, detailed descriptions of cell wall extensibility and mechanical stiffness, deformation of the middle lamella and increase in cytoplasmic pressure generating internal turgor pressure. The model is used to test a novel hypothesized mechanism of formation of the shape and structure of the growing, multilayered SAM. It combines contributions of mechanical properties of sub-cellular components of individual cells determining anisotropic cell expansion across three different SAM layers, and varied cell growth rates based on WUS concentrations of individual cells. This suggests a possible novel SAM growth mechanism to be tested in experiments.
MECHANICAL EFFECT ON GROWTH AND MORPHOLOGY OF EPITHELIAL CELLS DURING EARLY DEVELOPMENT
Department of Mathematics, University of California, Riverside, CA
Abstract: Uncontrolled epithelial growth and dysregulation of epithelial morphology underlie more than ninety percent of tumors. Epithelia serve a critical role as barriers between the environment and internal structures of organs. The growth and morphogenesis of epithelia must be carefully controlled through coordination of cellular properties. Mechanical properties are an important regulator during the development. However, how the mechanical properties in the cell scale contribute to growth and morphogenesis in the tissue scale is still poorly understood. Here, we introduce a subcellular element particle-based model to predict the mechanical properties of epithelial cells to investigate their contribution to the proliferation and morphology in cell and tissue scale. The developed model consists of three sets of nodes: internal nodes represent inner organelles, membrane nodes represent cortex and membrane of cells, and extra cellular nodes represent the extra cellular matrix. These three classes of nodes interact through distinct potential energy functions. Our model incorporates subcellular properties such as cytoplasmic pressure, cortical stiffness, cell adhesion and interactions between the cell membrane and nucleus. We also account for the mechanical interaction between the extracellular matrix and epithelial cells. We found that cytoplasmic pressure is the main driver of cell’s expansion in mitotic phase, while cortical stiffness and cell-cell adhesion are contributors to the roundness of cells before division. Recently, we have extended the model to predict the curvature profile of epithelial cells. Our results show that the level of contraction in the extracellular matrix significantly contributes to the curvature profile of epithelia. To validate this prediction, tissue mechanics were measured experimentally in Drosophila wing imaginal discs, an established biophysical model of epithelial organ development. Furthermore, both computational predictions and experiments establish that the relative cells’ nucleus position contributes to the curvature profile. The right curvature profile of wing disc is essential for wing eversion, the next stage of wing development. Aberrant folding and bending of epithelia can lead to cyst formation, which occurs during early cancer progression.
Tuesday, October 9, 2018 at 2:10pm to 3:00pm
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