This scanning electron micrograph shows the hair bundle of a inner hair cell from a wild-type mouse cochlea. Sound-induced forces displace these mechanosensitive organelles, which comprise stereocilia organized into rows of increasing height. Hair bundle deflection tenses external filaments (called tip links) that connect stereocilia rows, and this gates mechanotransduction channels, initiating the auditory signal. A critical maturation step for hair bundle mechanotransduction that occurs between postnatal days 7 and 11 requires the integrity of the deafness gene LOXHD1. For more information, see the article by Trouillet et al. (pages 3331–3343). Cover image: Nicolas Grillet.