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Fig. 6. FGF signalling is necessary for placodal Six1 induction. Embryos shown in lateral (A,B,D,E; anterior to the left), dorsal (G; anterior to the top), or frontal views (J,K; midline in panel K indicated by dotted line). Embryos were analysed at early tailbud stages (stages 206: A, K) or neural plate stages (stage 14: G). (A) Placodal Six1 expression is reduced in embryos treated with SU5402 (stages 12/130) compared to controls (B). (C) Percentage of embryos with reduced Six1 expression after SU5402 treatment during different periods. (D,E) SU5402-soaked beads inhibit Six1 expression (arrowheads) after implantation at stage 13 into the region of the prospective ear placode (D) or of prospective trigeminal, lateral line, and epibranchial placodes (E). (F) Western blot demonstrating that the FGF8 MO but not an unspecific control MO specifically blocks in vitro translation of FGF8 but not of Eya1. (G) Embryos unilaterally injected with FGF8 MO (to the left on each panel) show strong reductions (arrowheads) of placodal Six1 (G,J,K), Sox3 (H), and FGF8 (I) expression, while neural plate domains of Sox3 or FGF8 expression are not reduced (asterisks). Both posterior (G,K) and anterior (J,K) subdomains of placodal Six1 expression are reduced in embryos analysed at neural plate (G,J) or tailbud stages (K; lower and upper arrowheads indicate olfactory and otic placode, respectively). The injected side was marked by coinjection of either GFP (G; not shown) or lacZ (J,K; light blue staining).
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