Fig. 4. Stereociliary bundles of vestibular hair cells of mgRb:Rb^-/- mutants at birth, as shown by espin-immunostaining. (A) Espin is localized to HC stereocilia of control utricules. (B) In mutants, espin-positive HCs are situated throughout the thickened utricular sensory epithelium. Several HCs at the surface show abnormal bundles. (C,D) High magnification views show HCs with aberrant stereocilia in the utricle and in the adjacent mesenchyme (arrow) of mutants. (E,F) In contrast to controls, mutants show espin-stained HCs at different levels of the ampullary sensory epithelium. HCs in the mesenchyme are also espin positive (arrow). (G,H) In addition to the distinct bundle abnormalities, stereociliary bundle morphologies comparable with controls are seen in some HCs of mutants, especially in ampullae. Abbreviations: wt, wild type; ut; utricle; amp, ampulla; SE, sensory epithelium; ME, mesenchyme; LU, lumen. Scale bar: 70 µm for A-F; 60 µm for G,H; 30 µm for C,D.