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. 2022 Sep 8;119(37):e2207433119. doi: 10.1073/pnas.2207433119

Fig. 4.

Fig. 4.

Neurons in the Isl1CKO inner ear are abnormally distributed. (A–I) Microdissected cochleae of reporter control-Ai14 and Isl1CKO-Ai14 mice were cleared (CUBIC protocol), immunolabeled, imaged, and reconstructed in 3D using light-sheet fluorescence microscopy (Movies S1–S4). (A) In the control cochlea, tdTomato+ SGNs form a coil of the SG in the Rosenthal’s canal and anti-Myo7a–labeled hair cells show the spiral shape of the organ of Corti. Parts of the VG with tdTomato+ neurons and the saccule with Myo7a+ hair cells are shown. (B and C) Anti-NeuN (a nuclear marker of differentiated neurons) colabeled tdTomato+ neurons form the SG and VG in the control cochlea; the modiolus contains the central processes, forming the auditory nerve (AN). (D–F) In Isl1CKO-Ai14, tdTomato+ neurons are mainly located in the conical central part of the cochlea, the modiolus, in contrast to the spiral of the organ of Corti with Myo7a+ hair cells. Some Isl1CKO neurons form a segment of the SG in the Rosenthal’s canal (RC) in the midbase region (arrowhead), shown in detail in F; the RC area is highlighted by dotted lines. (G and H) Abnormal and uneven distribution of cochlear tdTomato+ neurons is shown by anti-NeuN colabeling. Many neurons are misplaced in the modiolus, but some neurons are in their close-normal position in the Rosenthal’s canal (arrowhead). (J) Schematic drawing of the mouse cochlea shows the cochlear place-frequency map for four cochlear regions termed the apex (corresponding to the best encoding frequencies ∼8 kHz at the distance from the basal end of 82%), midapex (∼19 kHz at 49% length), midbase (∼32 kHz at 32% length), and basal turn (∼62 kHz at 9% length) (41). (K) Whole-mount images of the P10 inner ear show distribution of tdTomato-labeled neurons in superior (sVG) and inferior VG (iVG), and SG in the control-Ai14. (L) In the Isl1CKO-Ai14, the VG is fused and enlarged, spatial segregation between the VG and SG is diminished, forming an aberrant “spiro-vestibular” ganglion, and the SG has lost its spiral shape. (Scale bars: 200 μm in all panels, except for B and I, which are 100 μm.)