Abstract

Active gel theory offers elegant, minimal models for active matter systems built from symmetry and conservation principles. Yet, biology rarely cooperates with our theoretical ideals. Using the actomyosin dynamics of the zebrafish embryo as a case study, a system that undergoes partial division in contrast to traditional complete cytokinesis models, I will demonstrate how systematic, biologically-motivated extensions to the canonical active gel models reveal the hidden complexity of cytoskeletal systems. While simple isotropic contractility fails to explain the observed density and velocity profiles, incorporating nematic contractility and nematic order stabilization predicts the formation of contractile actin cables and mechanically-uncoupled depletion zones observed experimentally. We then distill these insights from the mesoscale into a higher-level abstraction by treating the cable and cortex as coupled mechanical components, which yields remarkably accurate predictions of embryo shape deformations. Overall, the hierarchical modelling approach captures the essential physics of the zebrafish cleavage, illustrating an example of turning active matter theories into tractable frameworks for biology.