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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.

Author information

1
Department of Systems Biology, Harvard Medical School, Boston, United States.
2
Department of Pediatrics, Harvard Medical School, Boston, United States.
3
Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, United States.
4
Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, United States.
5
Department of Molecular and Cellular Biology, Harvard University, Cambridge, United States.
6
Department of Cell Biology, Harvard Medical School, Boston, United States.

Abstract

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.

KEYWORDS:

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

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