Fig. 2. Proliferation and differentiation in the cochleas of mgRb:Rb^-/- embryos. Myosin VI- and phospho-histone H3 immunostaining; Math1 and Fgf10 in situ hybridization. (A,A') At birth, myosin VI is expressed in inner and outer HCs of control cochleas and also in supernumerary HCs of mutants. (B-C') At late-embryogenesis, p27- and p75NTR-positive supporting cell populations (arrows) are seen both in controls and mutants. (D) A myosin VI-stained mitotic HC (arrow) in a mutant cochlea at birth. (E,E') At birth, phospho-histone H3 staining shows ectopic mitoses in the greater epithelial ridge and the region of inner and outer HCs in mutant cochleas. These are not present in controls. (E'') Most of these mitotic HCs with strongly stained condensed chromatin are located near the lumen. (F,F') At E14.5, phospho-histone H3-stained cells are seen in the caudal wall of the cochlea of both mutants and controls. (G,G') At birth, Math1 is expressed in cochlear HCs of controls and also in supernumerary HCs of mutants. (H,H') At birth, Fgf10 is expressed in the greater epithelial ridge of control cochleas and in the thickened ridge of mutants. Abbreviations: wt, wild type; ph3, phospho-histone H3; myo, myosin VI; GER, greater epithelial ridge; IHC, inner hair cell; OHCs, outer hair cells; CN, cochlear nerve. Scale bar: 70 µm for A-C',E-F'); 30 µm for D; 80 µm for G-H').