Fig 1 .

Expression patterns of Bdnf-LacZ in E18.5 (A–D, H–K), E12.5 (E–G) ears of wildtype (A, E, K), Atoh1 null mice (B, F, J), Neurog1 null mice (C, G, I) and Neurog1/Atoh1 double null mice (D, H) is shown. Note that the canal cristae (HC, AC) and the cochlear apex are strongly labeled in all cases. However, the basal turn shows no Bdnf-LacZ staining in Atoh1 null mice (B, F) and Neurog1/Atoh1 double null (D) mice. Neurog1 null and Neurog1/Atoh1 double null mice show decreased length of all sensory epithelia (C, D) with the cochlea showing only one, tightly coiled turn. The saccule (S) is almost lost in Neurog1 null mice (C) and Bdnf-LacZ positive cells appear in the ductus reuniens (DR, vertical arrow) and the GER (horizontal arrow). In E12.5 embryos, sensory neurons delaminate in wildtype (E) and Atoh1 null mice (F) from the utricle (U; arrow), the ductus reuniens (DR) leading from the saccule (S) to the cochlea (arrow), and the upper middle turn of the cochlea (arrow). No Bdnf-LacZ positive sensory neurons and no ganglion exist in Neurog1 null mutants (G; no ggl). Note that delaminating cells may upregulate Bdnf-LacZ in Atoh1 null mice de novo (F) since no Bdnf-LacZ is expressed in the utricle and saccule in Atoh1 null mutants. In contrast to the absence of Bdnf–LacZ positive cells in Atoh1 null mice (F) is the more profound expression of Bdnf-LacZ in the utricle of Neurog1 null mice (G) which have a saccule (S) formed of few cells (out of focus in G). These data suggest a differential effect of Atoh1 and Neurog1 on Bdnf-LacZ expression in hair cells, in particular in the utricle, saccule and basal turn. Direct comparison of the anterior crista in various genetic backgrounds shows the additive effect of Neurog1 and Atoh1 null mutation on the size and degree of differentiation of this sensory epithelium (H–K). AC, anterior crista; DR, ductus reuniens; Ggl, ganglion; HC, horizontal crista; PC, posterior crista; s, saccule; u, utricle. Bar indicates 100 μm.