Elmod1 Mutations Cause Inner Ear Dysfunction Figure 2. Cochlear hair cell abnormalities in rda and rda2J mutant mice. Examination of the apical surfaces of cochlear hair cells by scanning electron microscopy showed normal bundle morphology in both inner hair cells (IHC) and outer hair cells (OHC) of rda/rda mutant mice at P0 (A). At P7 the stereocilia adjacent to the kinocilium (marked by arrow in H) had degenerated in some of the OHC bundles (marked by asterisks in B, D) of rda/rda mice, compared with the fully intact bundles of wildtype (+/+) controls (C). IHC bundles of rda/rda mice retained a normal appearance at P10 (D, K), but by P15 (F, L) all IHCs of mutant mice exhibited stereocilia elongations and fusions as compared with the normal IHC bundle morphology of age-matched controls (E). IHCs at P35 illustrate the striking degree of stereocilia elongations and fusions seen in rda/rda mutants (N) compared with age-matched controls (M). In contrast to IHCs, the OHC stereocilia of rda/rda mice did not elongate or fuse, but they did degenerate over time. By P15, nearly all OHCs had lost stereocilia at the bundle peak and a few (marked by asterisks) had lost the entire bundle (F, I), as compared with the intact OHC bundles of control mice (J). The IHC and OHC bundle abnormalities of rda2J/rda2J mutant mice (G) were very similar to those of rda/rda PLoS ONE | www.plosone.org 3 April 2012 | Volume 7 | Issue 4 | e36074