Figure 1.

Myosin IIIa expression lags stereocilia staircase formation. Fluorescence confocal images of whole-mount preparations of the rat organ of Corti and saccule show myosin IIIa immunofluorescence (green) in the developing stereocilia bundles. Actin filaments are counterstained with rhodamine–phalloidin (red), whereas microtubules of the kinocilia are labeled with the anti-tubulin antibody (blue; c, e). a–c, Myosin IIIa immunoreactivity is not detectable at the stereocilia in the early stages of development in the hair cells of the apical turn of the P1 rat cochlea (a) but is seen at the tips of the stereocilia of the P1 basal turn inner hair cells (b) and vestibular hair cells (c) where the staircase organization is well formed. d, e, By P3, hair cells of the apical (d) and basal (e) turns of the cochlea show clearly detectable levels of myosin IIIa immunoreactivity at the tips of their stereocilia (d). Scale bars, 5 μm.