Figure 5. Loss of Sox2 affects downstream gene expression in the organ of Corti.

(a,a’,b,b’) Atoh1 expression is dramatically reduced in Sox2 CKO mice at E18.5. (a”,b”) Atoh1 ISH signal converting into a fluorescent signal shows the relative topology to the inner pillar cell marker p75. Note that the scattered HCs are found medial and lateral to p75 positive cells (white arrows; b”). However, p75 expression (arrows) is discontinuous in the base (b”,f,f’) and absent in the apex compared to prominent labeling in the inner pillar cells and the spiral ganglion neurons in control animals (e,e’). (c,d) Another supporting cell marker, Hes5, shows no expression at all in the Sox2 CKO mice at E18.5. Scale bars: 100 μm. GER, greater epithelial ridge; OC, organ of Corti; “OC”, atypical organ of Corti in the mutant; SL, spiral limbus.