MS03 - CDEV-2
Suzanne M. Scharer Room (#3146) in The Ohio Union

Polarity and patterns meet biophysical and biochemical dynamics

Tuesday, July 18 at 10:30am

SMB2023 SMB2023 Follow Tuesday during the "MS03" time block.
Room assignment: Suzanne M. Scharer Room (#3146) in The Ohio Union.
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Adriana Dawes, S. Seirin-Lee


Biological systems often generate highly complex and dynamic patterns. These emergent patterns often have functional significance: protein polarization at the single cell level is required for asymmetric division and cell fate specification in development, and multicellular patterns are required for positioning of organs and structures such as teeth. These patterns rely on many features of the system, including biochemical interaction networks, morphology, and mechanical properties. In this mini-symposium, we bring together researchers who are integrating information about these different aspects of biological systems to better understand how patterns are generated, and the consequences when these patterns are disrupted.

Adriana Dawes

The Ohio State University (Department of Mathematics/Department of Molecular Genetics)
"The interplay between biochemistry and geometry in polarization of the early C. elegans embryo"
Centrosomes are nucleus-associated organelles that serve as the nucleation site for microtubule arrays. Microtubules nucleated from these arrays interact with motor proteins such as dynein at the periphery of the cell which act to transport the nucleus and position it prior to division. In polarized cells, where specific factors are segregated to opposite ends of the cell as seen in early embryos of the nematode worm C. elegans, proper centrosome positioning is particularly important, determining whether the division process is symmetric or asymmetric. Using a combination of stochastic and continuum models with experimental validation in early C. elegans embryos, we demonstrate that the geometry of the early embryo is critical for proper centrosome positioning in the polarized C. elegans embryo, and that biochemical suppression of dynein pulling forces in specific regions of the embryo ensures reliable timing of centrosome movement.
Additional authors: Andrew Cohen, The Ohio State University; David Ignacio, The Ohio State University

Sungrim Seirin-Lee

Kyoto University (Kyoto University Institute for the Advanced Study of Human Biology (ASHBi))
"Mind the gap: Space inside eggs steers first few steps of life"
In multicellular systems, cells communicate with adjacent cells to determine their positions and fates, an arrangement important for cellular development. Orientation of cell division, cell-cell interactions (i.e. attraction and repulsion) and geometric constraints are three major factors that define cell arrangement. In particular, geometric constraints are difficult to reveal in experiments, and the contribution of the local contour of the boundary has remained elusive. In this study, we developed a multicellular morphology model based on the phase-field method so that precise geometric constraints can be incorporated. Our application of the model to nematode embryos predicted that the amount of extra-embryonic space, the empty space within the eggshell that is not occupied by embryonic cells, affects cell arrangement in a manner dependent on the local contour and other factors. The prediction was validated experimentally by increasing the extra-embryonic space in the Caenorhabditis elegans embryo. Overall, our analyses characterized the roles of geometrical contributors, specifically the amount of extra- embryonic space and the local contour, on cell arrangements. These factors should be considered for multicellular systems [1]. [1] S. Seirin-Lee*, K. Yamamoto, A. Kimura*, The extra-embryonic space and the local contour are critical geometric constraints regulating cell arrangement (2022) Development. 149, dev200401.
Additional authors: Kazunori Yamamoto (Kanagawa Institute of Technology); Akatsuki Kimura (National Institute of Genetics)

Masatoshi Nishikawa

Hosei University (Department of Frontier Bioscience)
"PAR polarization in less contractile cell"
PAR polarity establishment in C. elegans zygote requires coupling between molecular interactions between PAR proteins and the flow of contractile actomyosin cortex. One of the daughter cell, P1 cell, also shows PAR polarity while its cortex exhibits low contractility, suggesting other mechanisms to establish the PAR polarity. We will show the dynamics of pattern formation and molecular interactions involved in polarity establishment, with the aim of developing mathematical description based on reaction diffusion model.

Eric Cytrynbaum

The University of British Columbia (Mathematics)
"Mechanisms and models of spatiotemporal patterns in reptile polyphyodont dentition"
For over a century, the development and replacement of reptile teeth has been of interest originally for its value in comparative anatomy and evolutionary biology due to the prevalence of teeth in the fossil record. More recently, it has been used as a model system for understanding spatiotemporal patterning in developmental biology and for delving into the mechanisms of tooth formation. In collaboration with the Richman Lab (Joy Richman, UBC Dentistry), we are using the Leopard Gecko as a model organism to address the question of the mechanisms underlying the regular and long-lasting spatiotemporal patterns of tooth replacement seen in many polyphyodonts. In this talk, I will describe the data and our implementation and analysis of several mechanisms/models that have been proposed (but not implemented in mathematical form) in the past to explain the observations. Finding shortcomings in these models, we propose a new model, the Phase Inhibition Model, which does better at explaining the data. I will conclude by discussing ideas for how this model might be integrated with existing reaction-diffusion models of early development of dentition in reptiles.

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