Mechanistic Basis of Otolith Formation during Teleost Inner Ear Development

SummaryOtoliths, which are connected to stereociliary bundles in the inner ear, serve as inertial sensors for balance. In teleostei, otolith development is critically dependent on flow forces generated by beating cilia; however, the mechanism by which flow controls otolith formation remains unclear. Here, we have developed a noninvasive flow probe using optical tweezers and a viscous flow model in order to demonstrate how the observed hydrodynamics influence otolith assembly. We show that rotational flow stirs and suppresses precursor agglomeration in the core of the cilia-driven vortex. The velocity field correlates with the shape of the otolith and we provide evidence that hydrodynamics is actively involved in controlling otolith morphogenesis. An implication of this hydrodynamic effect is that otolith self-assembly is mediated by the balance between Brownian motion and cilia-driven flow. More generally, this flow feature highlights an alternative biological strategy for controlling particle localization in solution.

Graphical AbstractFigure optionsDownload full-size imageDownload high-quality image (294 K)Download as PowerPoint slideHighlights► Inner ear hydrodynamics control spherule deposition during otolith formation ► Motile cilia drive rotational flow that suppresses spherule aggregation basally ► The resulting hydrodynamics attract particles toward the poles of the inner ear ► The interplay of flow and diffusion controls otolith shape