Ubiquitous fgf8 expression at late gastrulation stages leads to ectopic otic induction within the preotic field. (A, G) Ectopic fgf8 expression can be detected throughout the embryo after a 30 minute heat shock in transgenic hsp:fgf8 embryos in comparison to non-transgenic embryos. (B, C, H, I) Within 2 hours, expression of the two Fgf reporter genes, erm and pea3, is upregulated in cells of the transgenic embryos whereas non-transgenic siblings are unaffected. (D-F, J-L) After misexpression of fgf8 at late gastrulation stages, expression of foxi1 is reduced, whereas the preotic expression domains of pax8 and pax2a are enlarged. Dorsal views of 2–5-somite stage embryos with anterior towards the top. mhb, midbrain-hindbrain border; po, preotic region; p, pronephros. Scale bar: 100 μm for A-C, G-I; 40 μm for D-F, J-L.