Fig. 3. Wnt7a protein influences stereociliary bundle orientation. (A) Surface view of labeled stereociliary bundles in a cochlear culture established on E13 after 6 days in vitro (DIV). Stereociliary bundles on both IHC and all rows of OHC (1-4) have developed with appropriate orientation. Orientations for the outer hair cells located in the boxed region are illustrated on the right. (B) Surface view of a cochlear culture established on E13 and maintained for 6 DIV in medium conditioned with Wnt7a protein. There are marked bundle misorientations in all rows of outer hair cells (1-4). Orientations of IHC appear unaffected. Orientations for the boxed region are illustrated on the right. (C) Average stereociliary bundle orientations were determined for outer hair cells at specific positions (determined as a percent of the total length) along the basal-to-apical axis of the cochlea in control and Wnt7a-treated cultures. In control cultures, average bundle orientation decreased progressively towards the basal end of the cochlea. This pattern is consistent with in vivo data (see Fig. 2) and suggests that bundles reorient in vitro. Exposure to Wnt7a protein did not alter the orientation of stereociliary bundles located at the 45% or 37.5% positions along the cochlea; however, there were significant changes in average stereociliary bundle orientation at the 25%, 12.5% and 5% positions (asterisks; P<0.003). Results are from three pairs of control and Wnt7a-treated cochlear explants. Error bars are s.e.m. (at least 12 stereociliary bundles were measured per point per culture). Scale bar in A (same in B), 10 µm.