Atoh1b-dependent regulation of foxj1b in kinocilia differentiation. (A) Electron micrograph (transverse section) of kinocilia (arrows) from the ear of a mib mutant zebrafish embryo. The microvilli (stereocilia) of the hair cells are also visible (small arrows). (B) High-resolution image showing the 9+2 arrangement of microtubules. The central pair of microtubules is indicated (arrowheads). (C) Wild-type pattern of atoh1b expression in the otic vesicle of a foxj1b morphant (compare with Fig. 3E). (D) Normal pattern of foxj1b expression in the otic placode of an atoh1b morphant at 10 hpf (compare with Fig. 1A). (E) Loss of foxj1b expression (arrows) from the ear of an atoh1b morphant at 16 hpf (compare with Fig. 1B). (F) Expression of pou4f3 in the differentiating hair cells (arrows) of a wild-type ear. (G) Ectopic pou4f3 expression (arrows) in supernumerary hair cells in the ear of a Tg(hs::atoh1b) transgenic embryo. (H) Ectopic foxj1b expression (arrows) in supernumerary hair cells in the ear of a Tg(hs::atoh1b) transgenic embryo (compare with Fig. 1C). (I) Kinocilia (small arrows) on ectopic hair cells (long arrows) in the ear of a Tg(hs::atoh1b) transgenic embryo. The embryo was stained with antibodies to acetylated tubulin (green) and with DAPI (blue). Scale bar: 10 μm in I.