Andrew Callan-Jones: The physics of symmetry-breaking phenomena in biology

Abstract: The concept of symmetry breaking is well-known in physics, for instance in condensed matter, where it results from interactions in a many-body system — e.g., phase transition in a spin system. Yet, as physicists, we tend not to think of the patterned structures seen in living, many-body systems in terms of broken symmetries. Whether it is the spacing of knuckles on our hand, the collective alignment of hairs on an insect wing, or more globally the transformation of a homogeneous, isotropic embryo into a developed organism, symmetry breaking abounds in biology. What new insights can a physicist bring to understand the origin of these complex phenomena? (Click title to read full abstract below...)

Full abstract:

The concept of symmetry breaking is well-known in physics, for instance in condensed matter, where it results from interactions in a many-body system — e.g., phase transition in a spin system. Yet, as physicists, we tend not to think of the patterned structures seen in living, many-body systems in terms of broken symmetries. Whether it is the spacing of knuckles on our hand, the collective alignment of hairs on an insect wing, or more globally the transformation of a homogeneous, isotropic embryo into a developed organism, symmetry breaking abounds in biology. What new insights can a physicist bring to understand the origin of these complex phenomena?

Starting in high school biology we often think of these in terms of a deterministic program dictated by genetic regulation and protein interactions. These are certainly important but they do not alone explain the emergence of shapes and structures at the cellular and higher scales. What approach should we take, then?

We take note that the cell is composed of macromolecules that self- assemble and consume energy released by ATP hydrolysis to constitute an intrinsically out-of-equilibrium system — an active soft material. A very important component here is the actin-myosin cytoskeleton, which can spontaneously flow, advect bound proteins, and interact with neighbouring cells and the cellular environment. In this talk, I will present research that uses ideas borrowed from soft matter physics to describe symmetry-breaking events in biology. I will present a formalism known as Active Gel Theory that provides a framework to model collective behaviours in the cytoskeleton. I will illustrate the use of this theory with models of spontaneous cell polarization and motion. Finally, I will discuss how Active Gel Theory can be extended to the tissue scale, and give an overview of current work to model tissue deformation and patterning that occurs during early organism development.

This talk is part of the Mechanics Lunch Seminar series. Bring-your-own-lunch and lots of questions.

Published Oct. 7, 2021 5:14 PM - Last modified Oct. 7, 2021 5:17 PM