Figure 5. Morphological defects at the cuticular plate and stereociliar bundles in inner hair cells of diap3-overexpressing mice. A–J, SEM of the organ of Corti in 1-month-old (A, E), 4-month-old (B), and 2-month-old (F) WT mice, 1-month-old (C) and 4-month-old (D, I, J) Tg 924 mice, and 1-month-old (G) and 2-month-old (H) Tg 771 mice. Note the cuticular plate lump (white asterisk) in WT IHCs starting from 4 months old (B). In the Tg lines (C, D, G–J), a severe swelling of the IHC cuticular plate is observed for all ages. The alteration of the cuticular plate can be associated with disarrayed or fused stereociliar bundle. In addition, some OHCs are missing. K–P, TEM from hair cells in 1-month-old (K) and 6-month-old (N) WT mice, 1-month-old Tg 924 mice (L, M), and 2-month-old Tg 771 mice (O, P). K, In 1-month-old WT mice, the cuticular plate (CP) forms an electron-dense matrix, which is homogeneously distributed at the IHC apical pole, except at the fonticulus. Note the presence of numerous mitochondria below the CP and the well-organized stereocilia (ST) above. N, In 6-month-old WT mice, the CP still has a homogeneous distribution. Note that the CP area expands over the neighboring supporting cell (black asterisk), although TEM did not show swelling comparable to that seen in the Tg mice. L, In 1-month-old Tg 924 mice, the CP dramatically accumulated at the border of the IHC and the ST are fused. M, In 1-month-old Tg 924 mice, the apical pole of OHCs looks normal, with its CP anchoring the ST bundle. O, In 2-month-old Tg 771 mice, the ST are embedded in the IHC cytoplasm. The CP is not confined to its regular position, and the apical pole of the IHC protrudes toward the scala media. Note the discontinuous CP (arrow). P, In 2-month-old Tg 771 mice, OHCs show a normal appearance, with the CP anchoring the ST bundle. Scale bars: A–H: 20 µm, I: 10 µm, J: 2.5 µm, K–O: 500 nm, P: 2 µm.