Fig. 1. Cells of the otic placode and vesicle express three transcription factor genes, dlx3b, dlx4b and sox9a required for inner ear development. (A,D,G) Cells of the presumptive otic placode express all three genes at the four-somite stage (4s); other cells along the lateral edge of the neural plate express dlx3b and dlx4b. (B,E,H) By the 10-somite stage (10s) cells throughout the placode express all three genes. (C,F,I) Later, by prim-5 stage (24 h), a subset of cells in the vesicle expresses dlx3b and dlx4b; other cells express sox9a. Throughout these stages, dlx4b expression is similar to but weaker than dlx3b expression. Other sites of expression are not shown. (J,L) Wild-type embryos exhibit an otic vesicle in live embryos (DIC, differential interference contrast optics) at prim-5 (24h) stage (J) and pax2a expression in the presumptive otic placode at the six-somite stage (L). (K,M) Neither the vesicle (K) nor early pax2a expression in the presumptive placode (M) is apparent in Df^b380 mutants (38/38 Df^b380 embryos). (N) The dlx3b, dlx4b and sox9a genes are closely linked on the same chromosome and are removed by the Df^b380 deficiency mutation. (Left) Schematic map of LG12 showing the region of the Df^b380 deficiency in red (not to scale). (Right) We localized dlx3b, dlx4b and sox9a to LG12 by mapping them relative to SSLP markers and other genes (as shown) using the LN54 radiation hybrid panel (Hukriede et al., 1999). We estimated the extent of the Df^b380 deficiency based on our ability to amplify flanking SSLP markers, z1176 and z1473, by PCR using Df^b380 homozygous mutant DNA. These two SSLP markers are separated by 21 cM on the HS and 24 cM on the MGH meiotic panels, and by 296 cR on the T51 radiation hybrid panel (http://zfin.org). Missing genes are shown in red. (A,B,D,E,G,H,L,M) Dorsal views, anterior towards the left; (C,F,I,J,K) side views, anterior towards the left, dorsal towards the top. Scale bar in N: 60 µm for A,D,G; 33 µm for B,E,H; 22 µm for C,F,I; 77 µm for J,K; 145 µm for L,M; 5 cM for N.

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