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NIDCD Researchers Discover Unique Protein that Appears to Control Stereocilia Length

Stereocilia sensory cells that line the inner ear
Mouse stereocilia without Eps8 (bottom) are
much shorter than normal (top).
Credit: Uri Manor and Leonardo Andrade

Stereocilia, bundles of super-sensitive fibers perched atop the sensory cells that line the inner ear, are the structures responsible for converting vibrations entering the ear into electrical signals that travel to the brain and say “sound.” The height and staircase formation of stereocilia are precise to within a nanometer (a measure of length so tiny it would take a billion of them to stretch almost the length of a yardstick) but scientists know very little about what regulates stereocilia length—how do they know when to stop growing? That question is beginning to be answered by the discovery of a protein called Eps8. Along with two other proteins, whirlin3 and myosin XVa, EPs8 appears to control stereocilia length at an extraordinary level of precision. The discovery was made in NIDCD scientist Bechara Kachar, M.D.’s Laboratory of Cell Structure and Dynamics, aided by a team of scientists in Italy. According to Dr. Kachar, the three proteins interact to make and maintain actin, the primary component of stereocilia. myosin XVa is the motor element that transports EPs8 and whirlin to the tips of stereocilia. Once they are there, whirlin has special scaffolding properties that help actin stick to the tips, while Eps8 tells the actin when to stop accumulating. Next, the team will be looking at the molecular details involved in exactly how Eps8 regulates stereocilia length.

Read more on the NIDCD website.

The findings have been published in the January 25, 2011, issue of Current Biology.