Fig. 8. Enhancement of inner ear defects in Eya1/Six1 double mutants. (A-D) Medial (A-C) and lateral (D) views of paintfilled inner ears of wild-type (A), Six1^+/- (B), and Six1^+/-/Eya1^+/- compound heterozygous (C,D) embryos at E16.5. (A) All structures of the inner ear reached their mature shape at E16.5. The cochlea completed 1.75 turns by this stage (inset). aa, anterior ampulla; asc, anterior semicircular canal; cc, common crus; co, cochlea; csd, cochleosaccular duct; ed, endolymphatic duct; es, endolymphatic sac; la, lateral ampulla; lsc, lateral semicircular canal; pa, posterior ampulla; psc, posterior semicircular canal; s, saccule; u, utricle; usd, utriculosaccular duct. (B) A Six1^+/- inner ear showing a malformed saccule (asterisk), absence of the endolymphatic sac and a truncated endolymphatic duct (arrowhead). The cochlea only completed 1.5 turns (arrow and inset). (C,D) Inner ears from Six1^+/-/Eya1^+/- double heterozygotes showing severe cochlear defects (arrows), absence of posterior ampulla (asterisk) and truncated posterior semicircular canal. The cochlea only completed less than one turn and their distal tips were enlarged and mal-shaped (insets). (E-H) Frontal histological sections at comparable levels of X-gal-stained E9.5 embryos of Eya1/Six1 double heterozygous (E) and double homozygous embryos (F-H). Eya1/Six1 double heterozygote shows restricted Six1^lacZ expression in the otic vesicle (ov). In the double homozygotes, the otic vesicles appeared to be formed in the correct position but severely hypoplastic. Because Six1^lacZ is Eya1 dependent, it is not expressed in Eya1^-/-/Six1^-/- otic vesicle (arrows) but is ectopically turned on in rhombomeres 2, 4 and 6 (r4 and r6). Scale bars: 100 µm.