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Fig. 1 Expression of deltaA, deltaB, deltaD and serrateB in wild-type embryos (WT, top row) and mib mutant embryos (bottom row) at placode (14 hpf) and early otocyst (18 hpf) stages of ear development, shown by whole-mount in situ hybridization. The photographs are dorsal views of the ear rudiments and the hindbrain region between them; arrows indicate sites of delta and serrate gene expression at the anterior and posterior ends of the otic placode/otocyst. Anterior is to the left. Note the intensified and expanded expression of the genes at these sites in mib mutants – most obvious for deltaD and serrateB, but evident also for deltaA and deltaB. The band of deltaD-expressing cells very strikingly seen in the 14 hpf mib specimen extending between the anterior and posterior poles of the otocyst may correspond to the region from which neuroblasts will later delaminate.