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Elife. 2018 Jun 19;7. pii: e37131. doi: 10.7554/eLife.37131.

Lamellar projections in the endolymphatic sac act as a relief valve to regulate inner ear pressure.

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Department of Systems Biology, Harvard Medical School, Boston, United States.
Department of Pediatrics, Harvard Medical School, Boston, United States.
Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, United States.
Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, United States.
Department of Molecular and Cellular Biology, Harvard University, Cambridge, United States.
Department of Cell Biology, Harvard Medical School, Boston, United States.


The inner ear is a fluid-filled closed-epithelial structure whose function requires maintenance of an internal hydrostatic pressure and fluid composition. The endolymphatic sac (ES) is a dead-end epithelial tube connected to the inner ear whose function is unclear. ES defects can cause distended ear tissue, a pathology often seen in hearing and balance disorders. Using live imaging of zebrafish larvae, we reveal that the ES undergoes cycles of slow pressure-driven inflation followed by rapid deflation. Absence of these cycles in lmx1bb mutants leads to distended ear tissue. Using serial-section electron microscopy and adaptive optics lattice light-sheet microscopy, we find a pressure relief valve in the ES comprised of partially separated apical junctions and dynamic overlapping basal lamellae that separate under pressure to release fluid. We propose that this lmx1-dependent pressure relief valve is required to maintain fluid homeostasis in the inner ear and other fluid-filled cavities.


cell biology; developmental biology; inner ear; lamella; pressure; stem cells; timelapse; valve; zebrafish

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