Fig. 4. Continued proliferation occurs in Dll1^hyp/-Jag2^-/- mutant cochleae. (A-D) Immunohistochemistry on sections from E18.5 embryos was used to detect proliferating cells (green) in the organ of Corti after injections of BrdU from E14.5-E17.5. Hair cells are labeled with an antibody to detect myosin VIIa (red) and nuclei are stained with DAPI (blue). (A) Control section through the cochlea, demonstrating that there is normally no proliferation after E14.5 in the organ of Corti, although BrdU-labeled cells can been detected in Koelliker's organ and stromal cells beneath the organ of Corti. (B-D) Sections from Dll1^hyp/-Jag2^-/- cochleae, demonstrating examples of unexpected proliferating cells in the organ of Corti. The probable identities of these labeled cells based on the position of their nuclei are indicated. Some myosin VIIa-positive nuclei are located near the basement membrane in the position of supporting cell nuclei in the mutant cochleae (arrowheads in B and D). Asterisks indicate the tunnel of Corti in A-D. H, Hensen's cells; iPh, inner phalangeal cells; Ko, Koelliker's organ; oC, organ of Corti; OS, outer sulcus; pc, pillar cells; P/D, pillar/Deiter's cells. Scale bar: 50 µm.