Actin-Bundling Protein TRIOBP Forms Resilient Rootlets of Hair Cell Stereocilia Essential for Hearing

► TRIOBP, an actin-associated protein, localizes to hair cell stereocilia rootlets ► Purified TRIOBP protein organizes F-actin into uniquely dense rootlet-like bundles ► Stereocilia in TRIOBP-deficient mice lack rootlets and degenerate, causing deafness ► Mechanosensory stereocilia lacking rootlets are hyperflexible and fragile