Expression of Hey2 in the developing inner ear. Otocyst (A-B) or cochlear sections (C-J) from E11.5 (A-B), E14.5 (C-J) were hybridized with RNA probes for Isl1 (A,C), Hey2 (B,D,I), Hes1 (J), Hes6 (E), Hey1 (F), and Oto90 (G). Arrowheads in A-B indicate the domain for sensory and neuronal lineages in the otocyst; the bracket in B marks the expression domain of Hey2; brackets in C-J indicate the primordial organ of Corti at E14.5. (K-M) Cochlear sections from an E14.5 Math1-/- embryo were probed for Hes6 (K), Isl1 (L), and Hey2 (M). Brackets indicate the developing sensory organ that was determined by careful comparison of adjacent sections with molecular markers for the region. The sides of the cochlear duct toward the center and the periphery of the spiraled cochlea are designated as the medial and lateral sides, respectively, and are indicated. Scale bars: 10 μm for A-B, C-G, H-J, K-M.