Figure 1. The structure of the auditory hair bundle. A–B: Scanning electron micrograph of hair bundles protruding from the apical surface of a P7 mouse OHC (A) and IHC (B). Mouse cochlear hair bundles are composed of 60–100 stereocilia organized in three adjacent rows. C: Transmission electron micrograph of a P2 + 1 day in culture hair bundle from a mouse OHC. Just above the apical surface, the stereocilia are interconnected by ankle links (small arrows). Shaft connectors link the lateral aspects of the stereocilia (stars). At the tip of each stereocilium are tip links (long arrows) and horizontal top connectors (arrowheads). D: High-resolution freeze-etch image of a tip link from a guinea pig cochlea hair bundle. E: Transmission electron micrograph of a P12 apical OHC. F: The tip link is formed by a PCDH15 parallel dimer interacting tip to tip with a CDH23 parallel dimer. These proteins feature 11 and 27 extracellular cadherin (EC) repeats, respectively. Inset shows possible arrangement at the junction. Scales: A, B: 1 µm. C: 200 nm. D: 100 nm. E: 200 nm.

Panel C was modified and E reprinted with permission of Journal of Comparative Neurology, by Goodyear et al. (2005). Panel D modified from Kachar et al. (2000), PNAS. Panel F reprinted with permission from Macmillan Publishers Ltd: Sotomayor et al. (2012), Nature.