Fig. 6. Eng2/Eng3 and Fgf8 act synergistically in positioning of the DMB. The positioning of the DMB is dependent on Fgf signalling in early somitogenesis. Embryos were orientated dorsal side upwards and anterior towards the left. Inhibition of Fgf signalling via the pharmaceutical Fgfr inhibitor SU5402 (8 µm) in noi mutant embryos from 90% of epiboly to 15 ss leads to a strong expansion of the anterior pax6.1 domain (A,B). A weaker expansion is visible when the treatment starts at 5 ss and lasts until 15 ss (C). After 10 ss, inhibition of Fgf signalling does not lead to a posterior shift of the forebrain expression of pax6.1 (D). (H,J) Eng2/Eng3- and Fgf-deficient embryos show a stronger expansion of the forebrain expression of pax6.1 than do single deficient embryos (F,G). (E-G) Embryos were orientated laterally and anterior is towards the left. The forebrain expression domain of pax6.1 expands in wild-type embryos (E), noi mutant embryos (F) and in MO-fgf8 morphant embryos (G). In noi mutant embryos, injected with MO-fgf8, the forebrain and hindbrain expression domain fuses (H). A comparable phenotype is observed in noi mutant embryos treated with Fgfr inhibitor SU5402 from 90% of epiboly until 15 ss (I). In ace mutant embryos injected with MO-eng2/eng3 forebrain and hindbrain domain fuses similarly (J). DMB, diencephalic-mesencephalic boundary; fb, forebrain; hb, hindbrain.