Fig. 7. Morphological analysis of the function of fgf8 and eng2/eng3 at the DMB at late stages. In comparison with the control embryo at 26 hpf (A), the expression of eng2 is absent in fgf8-MO morphant embryos (B), in noi mutant embryos (C) and in fgf8-MO-injected noi mutant embryos (D). The expression domain of pax6.1 weakly expands in fgf8-MO embryos (B), strongly in noi mutant embryos (C) and it fuses in the double treated embryos (D). The border of the pax6.1 expression is marked by arrowheads (A-D). The position of the posterior commissure (PC) is altered in eng2/eng3- and fgf8-deficient embryos (E-L). Embryos were orientated dorsal side upwards and anterior towards the top. At 28 hpf the isl1 staining labels the neurons of the epiphysis and interneurons of the PC (E-H). In addition, acetylated tubulin is marking the outgrowing axons (I-L). The position of the neurons of the PC is shifted posteriorly in fgf8-MO-injected embryos (F,J); a stronger expansion and an increased number of neurons were found in the noi mutant embryos (arrowheads; G,K). Furthermore, the axon bundle of the PC is fanned out. The strongest phenotype was observed in embryos deficient for Engrailed and Fgf8 (H,L). The number of interneurons is strongly increased (H), and the PC is not formed at all (L). Single branches project into the territory of the misspecified hindbrain (white arrows). Red arrows indicate the most lateral position of the PC and asterisks indicate the position of the epiphysis. Number of isl1 positive epiphyseal neurons in wild-type, MO-fgf8, noi mutant embryos and noi mutants injected with MO-fgf8 (M). Values are the average of the total number of neurons of 10 embryos per treatment. Error bars show the standard deviation and asterisks indicate significant differences (*P=0.01) when compared with wild-type siblings.