Mechanobiological Regulation of Symmetry Breaking During Zebrafish Embryogenesis: Interplay of Myosin Activity, Mechanical Forces, and External Flows

A central challenge in developmental biology is understanding how cells and tissues undergo morphological changes via coordinated biophysical processes. We explore this using Kupffer's Vesicle (KV), the zebrafish left–right (LR) organizer, where stereotyped cell and organ shape changes support LR patterning of the embryo. While various mechanisms have been proposed, recent 3D simulations and laser ablation experiments show that KV's slow movement through tailbud tissue generates dynamic forces driving these changes. To understand molecular mechanisms controlling these changes, we investigated the role of myosin, as global downregulation of myosin activity has been shown to disrupt both shape changes and LR patterning. We locally inhibit myosin in the tailbud using an optically activated Rho-kinase (ROCK) inhibitor. To predict the impact of these perturbations, we used a 3D vertex model with dynamic forces, modeling KV as pushed by the notochord and pulled by posterior cells. The ROCK inhibitor was represented as a diffusing patch that alters both tissue mechanics and cell motion. The model predicts changes in KV motion and tissue morphology which we validate in experiments. Beyond myosin, screening experiments revealed anterior posterior asymmetric proteins and signaling pathways in KV cells, impacting cell volume and tensions. Our model also predicts how AP asymmetric changes to volumes and tensions impact KV and cell shape changes and discuss plans to validate in knockdown and mutant experiments