The schematic drawings at the top of the figure depict top-down views of the saccule and the horizontal ampulla, with their different anatomical zones indicated. A,B. Representative high-magnification horizontal (xy) confocal slices of whole-mount saccules from an Atoh1 WT mouse (A) and an Atoh1 CKO mouse (B) at 3 weeks post-DT (pDT) and labeled for myosin VIIa (myo7a, green), tdTomato (red), and DAPI (blue). Arrows point to tdTomato-positive type II hair cells and the arrowhead points to a tdTomato-negative type I hair cell. A’,B’. Optical cross-section from A and B taken at the levels indicated by the yellow arrowhead (bottom left side of A). C,D. Representative high-magnification horizontal (xy) confocal slices of whole-mount lateral cristae from an Atoh1 WT mouse (C) and an Atoh1 CKO mouse (D) at 3 weeks pDT and labeled the same as A,B. Arrows point to tdTomato-labeled type II hair cells, and arrowhead points to a tdTomato-negative type I hair cell. E-H. Each graph shows the numbers of tdTomato-positive (Tom+, E, G) or tdTomato-negative (Tom-, F, H) type I and type II hair cells (HCs) per 10,000 μm2 in the saccules or lateral ampullae from Atoh1 WT and CKO mice at 3 weeks pDT. Arrows point to groups with average values of 0. Horizontal lines over bars indicate significant difference between groups (p ≤ 0.05). Error bars represent +1 standard deviation. N = 3 mice per group. Scale bar in B applies to all images.