Mechanochemical symmetry breaking during morphogenesis of lateral-line sensory organs

Symmetry breaking is essential for polarization of cells and generation of left-right body asymmetry. Here the authors investigate the arrangement of hair cells in zebrafish and show that mirror-symmetric patterns arise from a combination of biochemical and mechanical symmetry-breaking events. Actively regulated symmetry breaking, which is ubiquitous in biological cells, underlies phenomena such as directed cellular movement and morphological polarization. Here, we investigate how an organ-level polarity pattern emerges through symmetry breaking at the cellular level during the formation of a mechanosensory organ. Combining theory, genetic perturbations and in vivo imaging, we study the development and regeneration of the fluid-motion sensors in the zebrafish's lateral line. We find that two interacting symmetry-breaking events-one mediated by biochemical signalling and the other by cellular mechanics-give rise to precise rotations of cell pairs, which produce a mirror-symmetric polarity pattern in the receptor organ.