Disruption of SorCS2 reveals differences in the regulation of stereociliary bundle formation between hair cell types in the inner ear
Fig 3
Stereociliary bundles and apical surfaces. A. Normal animal at P18. Basal coil. Stereociliary bundles have a consistent characteristic shape and are entirely surrounded by smooth apical surface membrane. B-F. Affected animals at P18. B. Basal coil. Stereociliary bundles in affected animals show a variety of abnormal morphologies but each bundle is entirely surrounded by smooth apical surface membrane. Some bundles are separated completely into two clusters, with smooth apical surface membrane between. The contour of the border of the apical surface of the cell matches the bundle shape: note indent at approximate mid-point of separation between two clusters; and elongated shape of cell surface in orientation matching that of elongated bundle. C. Basal coil. Bundles appear shorter than normal (compare with normal in A at same magnification) and are much less regularly organised. D. Bundle grossly mis-shapen, but shows stereocilia in 3 rows of increasing height. The contour of the surface membrane matches the shape of the bundle. E. Bundle showing apparent shortening/retraction of stereocilia (arrow). F. Two OHC in direct contact at their apical surface (arrow). Underside of the tectorial membrane. G. Normal. Impressions of the longest stereocilia of the OHC bundle (basal coil) in a single row in the shape of the normal bundle. H. Affected animal (P18). Impressions show that stereocilia of misshapen bundles reach the tectorial membrane but reveal the various morphological peculiarities of the bundles: separate clusters of impressions; and more than one row of impressions from a single bundle indicating mis-regulation of stereocilia height in individual bundles. Scale bars: A-C 1μm; D-F 0.5μm; G,H 1μm. I. Histograms displaying means of apical surface area, number of stereocilia and length and width of longest stereocilia on OHCs in normal and affected animals. Each mean was derived from pooled measurements/counts at basal, middle and apical coils in individual cochleae from at least 3 different animals aged P17-P22; n = number of cells assessed in each group. The hair bundles of OHCs in affected animals have significantly fewer and significantly shorter stereocilia than those of normal animals.