Fig. 3. The DMB shifts posteriorly in embryos deficient for eng2/eng3. The forebrain expression domain of pax6.1 expands posteriorly in embryos deficient for eng2/eng3 at 15 ss (A,B). noi mutants are recognized by the absence of pax5 expression (C). The normal AP extent of the forebrain is marked by a white arrow from the anterior tip of the telencephalon to the posterior border of the forebrain; this arrow is of the same length in A,B,D,E. The red arrow indicates the expansion of pax6.1 expression observed in embryos lacking eng2/eng3 or noi function. A comparable phenotype is observed in the noi mutant embryos (C,F). Diencephalic expression of efna4 is similarly expanded in eng2/eng3 morphant embryos (D,E) and noi mutant embryos (F). Proliferation of forebrain cells is unaffected, as visualized by -Phosphohistone 3 antibody and in situ hybridization with pax6.1 probe of wild-type and eng2/eng3 morphant embryos at the indicated stages (G-L). The expanded pax6.1 territory is marked by red arrows. (M,N) In eng2/eng3 morphants Engrailed protein is not detectable by the -Engrailed antibody 4D9. (O,P) The expansion is paralleled by a posterior shift of the posterior commissure (arrowheads) at 32 hours, stained with antibodies against acetylated tubulin. Asterisks mark the epiphysis. DMB, diencephalic-mesencephalic boundary; fb, forebrain; hb, hindbrain.

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