Hey2 is expressed in supporting cells in the developing organ of Corti. Adjacent cochlear sections (A-D) from an E16.5 embryo were hybridized with probes against Hes6 (A), Hes5 (B), Hey2 (C) or Hey1 (D). The inner (arrows in A-D) and outer hair cell regions (brackets in A-D) are indicated. The arrows in A-D indicate the layer of supporting cells. (E) The dynamic expression of Hey2 in the developing cochlea is schematically diagramed. At E14.5, the expression domain of Hey2 (grey lines) overlaps with that of Hes1 (green lines) and p27/Kip1 (black) at its medial and lateral borders, respectively. At E16.5, Hey2 is expressed similarly to that of Hes5 (red lines) and Hey1 (yellow lines) in a subset of supporting cells, while p27/Kip1 is present in all the cells surrounding hair cells (open circles). By E17.5, the expression of Hey2 has started to be down-regulated from the organ of Corti at the basal region where the expression of Hey1 remains. Scale bar: 10 μm for A-D.