Fig. 1. Six1 expression during inner ear development. E8.75 to 15.5 Six1^lacZ heterozygous embryos or inner ears were stained with X-gal for Six1^lacZ and sectioned through the inner ear region. (A) A transverse section showing Six1 expression in the otic pit (op) at E8.75. (B) A transverse section showing Six1 expression in the otic cup (oc) at E9.0. (C) A transverse section showing Six1 expression in the middle and ventral otic vesicle (ov) at E9.5. Note Six1 is excluded from the dorsal otic pit and vesicle (arrows). (D) A transverse section at E12.5 showing Six1 expression in the saccular region and the vestibuloacoustic ganglion (gVIII). For A-D, dorsal is upwards. (E) A section showing Six1 expression in the primordia of lateral (la) and anterior (aa) Crista ampullaris. Arrow indicates the origin of the anterior ampulla on the other side. (F) A section showing Six1 expression in the hair cells (hc) of the utricle (u). (G) In the cochlea, Six1 is expressed throughout the future greater and lesser epithelial ridge (GER and LER). Note its expression level is reduced in an area that will become the organ of Corti (bracket) at E12.5. (H) In E15.5 cochlea, Six1 is expressed weakly in the supporting cells and first appeared in the inner hair cell (arrowhead) in the apex. Strong Six1 expression was also observed in the cells flanking the developing organ of Corti in the GER and LER. (I) In the base of E15.5 cochlea, Six1 is expressed in the outer (arrow) and inner (arrowhead) hair cells. It is also expressed in some cells in the GER. In addition, it is expressed in the thinner part of the cochlea duct that will probably differentiate into the stria vascularis (sv). (J) A latex paintfilled E15.5 cochlea showing the apical and basal regions. Scale bars: 50 µm.

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