Hydrostatic pressure shapes and canalizes semicircular canal morphology to ensure vestibular function

How tissues acquire reproducible shapes to support their function is a fundamental question in developmental biology. Zebrafish semicircular canals form when epithelial pillars partition the lumen of the otic vesicle, the embryonic precursor of the inner ear, into the tubes that sense head rotation for balance. We show that hydrostatic pressure generated by the inflating otic vesicle shapes pillar geometry. Acute vesicle deflation shortens and broadens pillars, whereas pharmacologically induced inflation elongates and narrows them, effects captured by a physical model that treats the vesicle as a pressurized viscoelastic shell. Pillars initially form with variable curvature, but continued vesicle expansion drives them toward a common, straight geometry, a process accelerated by inflation and blocked by deflation. We identify Wnt signaling as crucial for sustaining this pressure by maintaining epithelial barrier integrity. Its disruption impairs pillar geometry and vestibular-dependent swimming behavior. Together, these findings identify hydrostatic pressure as a critical physical mechanism that canalizes tissue geometry to ensure robust organ formation and function.