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Fig. 10 (A) A 16 somite control embryo probed for expression of dlx2. Anterior to the left and dorsal up. Three streams of neural crest cells can be seen on the lateral regions of the neural keel two of which lie anterior to the otic placode (op). The anteriormost stream migrates into the mandibular arch and the preotic stream into the hyoid arch (see Akimenko et al., 1994). (B) dlx2 expression in a 16-somite-staged embryo injected with Hoxa-1. Only one preotic stream of crest is now visible and it is larger than in controls. This aberrant stream of crest lies immediately anterior to the otic placode and the most anterior stream of crest is absent. (C) The positioning of the aberrant stream is confirmed in embryos probed for both dlx2 (blue) and krx-20. (red). In this 16-somite example, the single preotic stream stretches round the margin of the abnormally formed r3. Scale bar, 100 μm.