Figure 3.

Id expression is downregulating in developing hair cells. High-magnification images of Id1, Id2, Id3, and Math 1 expression in the basal cochlear turn from mid-modiolar sections at E14 and E16. Color has been removed to provide enhanced contrast. A–C, At E14, Id1 (A), Id2 (B), and Id3 (C) are broadly expressed within the developing cochlea, including progenitor cells that will develop as the organ of Corti (bracketed region). D, At the same time point, Math 1 (bracket) is also expressed as a subset of the cells that express Ids. At this stage, Math 1 expression is an indicator of the prosensory region. E, Schematic illustration of individual cell types within the developing organ of Corti at E16. A single inner hair cell (red) and three outer hair cells (green) can be identified closer to the lumenal surface of the epithelium. Specific supporting cell types, including inner phalangeal cells (blue), inner pillar cells (yellow), outer pillar cells (magenta), Deiter's cells (orange), and Hensen's cells (blue) can also be identified based on nuclear position. At E16, expression of Id1 (F), Id2 (G), and Id3 (H) persists in supporting cell types, but there is a marked decrease in the expression of all three Ids in developing hair cells. In each panel, inner and outer hair cell nuclei are indicated with red and green asterisks. Maintained expression of Id1, Id2, and Id3 can be clearly observed in pillar cells (yellow arrows), Deiter's cells (orange arrows), and Hensen's cells (blue arrows). In contrast, by this stage, expression of Math 1 is restricted to inner (red asterisk) and outer (green asterisks) hair cells. All supporting cell types (arrows as in F) are negative for Math 1. Scale bars: (in A) B, C, 25 μm; (in E) F, G, 25 μm.