FIGURE 4. Tether cilia motility drives otolith biogenesis.

a–h, Particle tracking analysis demonstrates that cilium-dependent fluid dynamics drive precursor particle movement near the otolith. In control embryos, particle tracks (a) and displacements (b) show that particles near the otolith move by non-Brownian motion. Each track has a different colour. d, e, In gas8 morphants, particle tracks (d) and displacements (e) show decreased particle displacements in comparison with control. c, f, Mean particle displacement, r(t), plotted as a function of time. In control embryos, mean particle displacement is large and non-random, indicating diffusive transport. In gas8 morphants, mean particle displacement is small and random, indicating Brownian motion only. Error bars indicate the variance in the calculation of r(t). g, h, Particle tracking in control embryos shows that particle displacement is directly correlated with position relative to the otolith. g, particle tracks. h, Displacements of particles in regions I, II and III of g were calculated as a function of time and the average of the mean displacement, r(t), for each particle is shown. Net particle displacement decreases with increasing distance from tether cilia, indicating the reduction of the influence of ciliary beating. i–k, Diagrams depicting cilium-dependent otolith biogenesis. i, Tether cilia motility creates vortices that attract precursor particles. j, Cilia motility further serves to disperse particles locally and causes oscillation of the otolith, together facilitating uniform otolith growth. k, In gas8 morphants, absence of ciliary motility limits particles to Brownian motion. l, In wild-type embryos, the net consequence of tether cilia motility is that precursor particles are concentrated near the tethers, preferentially seeding otoliths at two poles of the otic vesicle. m, In gas8 morphants, loss of normal ciliary motility leads to formation of ectopic aggregates, non-uniform otolith growth and small particles that fail to coalesce into full-sized otoliths. Scale bars, 5 m.

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