Fgf signaling is required for EB placode development. hsp70::dn-fgfr1 embryos (bottom panels) were heat shocked at 10 hpf (bud stage), collected at 19, 24 and 36 hpf and processed for in-situ hybridization with foxi1, pax2a and phox2b, respectively. Top and middle panels show embryos treated with the DMSO and the Fgfr inhibitor SU5402, respectively, beginning at 10 hpf and processed in the same way as the hsp70::dn-fgfr1 embryos. All panels are lateral views, except foxi1+pax2a panels that show dorsal views. Anterior is at left. As expected, pax2a expression in the midhindbrain boundary and the otic vesicle was either absent or strongly reduced in the Fgf-depleted embryos. In the SU5402-treated and hsp70::dn-fgfr1 embryos, foxi1 expression is strongly reduced (bracket), and pax2a expression in the EB placodes is absent. phox2b was not expressed in EB placodes in SU5402-treated embryos; its expression was strongly reduced in hsp70::dn-fgfr1 embryos, but a few phox2b-positive neurons remain in the large vagal ganglion. We presume that this milder phenotype resulted from the degradation of the transgenic protein. Black arrowheads mark the phox2b+ vagal neural crest cells (not affected in Fgf-depleted embryos) on their ventral migration route just posterior to the last branchial arch. These cells can be easily identified, because they make a characteristic turn toward the gut (Shepherd et al., 2004). Scale bars: 50 μm. e, eye; f, facial placode or ganglion; g, glossopharyngeal placode or ganglion; mhb, midhindbrain boundary; nc, vagal neural crest; o, otic vesicle; v, vagal placode or ganglion.
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