Stereocilia — also known as hair bundles — are mechanosensitive organelles in the inner ear that translate sounds into nervous signals by detecting displacements in the air, but the mechanisms involved in their maintenance have been unclear. In August 22 Nature, Mark Schneider and colleagues at the National Institutes of Health, Bethesda, US, show that that the auditory hair bundles are continuously remodeled by the addition of actin monomers to stereocilium tips and that the entire core of the stereocilium is renewed 50 times faster than was previously thought (Nature 2002, 418:837-838).

Schneider et al. monitored the incorporation of β-actin labeled with a green fluorescent protein (actin–GFP) into stereocilia from cultured neonate rat auditory cells. They observed that incorporation of actin–GFP into the filaments started at the tip and was progressive and uniform. Each actin-filament bundle treadmilled towards the base at a rate of 2.5 μm...