Figure 4

Aberrant HCs in ectopic topology and abnormal pillar cells are formed in the Sox2 CKO.

Patches of HCs in the base of the E18.5 Sox2 CKO cochlea are covered by a tectorial membrane with HCs in the topology of inner HCs displaying both large diameter (a,a’) and small diameter (a,a”) stereocilia reminiscent of inner and outer HCs, respectively. (b) Vestibular HCs show normal organization of stereocilia but many display variability in stereocilia diameter in a single HC, normally associated with either type I or type II vestibular HCs. (c-d’) Scattered Myo7a positive HCs are detected in the area corresponding topologically to the organ of Corti (OC); however, forming atypical organ of Corti (“OC”) in the mutant. Immunostaining of Myo7a reveals formation of HCs in the ectopic topologies, medial to OC, in the GER, as well as lateral to OC (in the area of Hensen/Claudius cells) (white arrows) in addition to the area of “OC” in the E18.5 Sox2 CKO. (e-f”) The combination of p75 and Myo7a immunolabeling shows an unusual configuration and distribution of p75 positive cells near the remaining Myo7a positive HCs in E18.5 Sox2 CKO compared to the single row of p75⁺ inner pillar cells in control littermates (e). Scale bars: 10 μm (a,e-f”), 1 μm (a’,a”,b), 100 μm (c-d’). GER, greater epithelial ridge; H/Cl, Hensen/Claudius cells; OC, organ of Corti; “OC”, atypical organ of Corti in the mutant; SL, spiral limbus.