Fig. 6. A positive role for Dlx function in non-neural ectoderm. (A-D) Embryos were injected unilaterally with EnR-Dlx3hd and ß-galactosidase (magenta stain). Broad domains of EnR-Dlx3hd expression dorsoventrally show maximal expansion of the neural plate is limited to approximately twice its normal width, as visualized by Xsox2 expression (A,B blue stain). Arrows in B show staining for ß-gal indicative of injected mRNA outside of the Xsox2 domain. Note that in these cases of broad EnR-Dlx3hd expression, Xslug expression was not reactivated at the border of the expanded neural plate (C,D), similar to ablation of Xsix1 (Fig. 4Y) and other markers (not shown). (E) Schematic showing isochronic stage 12 transplant of fluorescent dextran (pseudo colored green stain) injected donor neural plate tissue (N) to ventral ectoderm of host embryos. Host embryos were injected ventrally to express ß-galactosidase either alone or with EnR-Dlx3hd. Control grafts showed Xslug induction at stage 25 (photo; ventral view, anterior to top). (F-I) Controls show that donor neural plate explants cultured alone express no or only minimal levels of Xslug (F) or Xsix1 (G), unless taken from a more lateral region that included prospective epidermis (H, Xslug; I, Xsix1). Therefore, marker expression is indicative of neural crest (Xslug) or placode (Xsix1) induction. (J-N) High magnification views of grafts into control hosts that had been injected with ß-gal mRNA alone. The three panels shown are light field, fluorescent and merged images. Induction (blue stain) of Xslug (J-L) and Xsix1 (M,N) was observed in areas adjacent to and overlapping both donor (green) and host tissue. In particular, note expression (arrows in J,K,M, arrowheads in L,N) within and adjacent to host tissue expressing the injected ß-galactosidase (magenta stain). Sections (L) show Xslug expression (blue) adjacent to donor tissue (green). (O-S) High magnification views of grafts into experimental hosts that had been injected with EnR-Dlx3hd and ß-gal mRNAs. Unlike controls (J-N), Xslug and Xsix1 are not induced adjacent to host tissue that had been injected with EnR-Dlx3hd and ß-galactosidase mRNAs (magenta). P shows a graft inserted adjacent to both injected and uninjected host tissue. Note that induction was prevented near cells that expressed EnR-Dlx3hd (red arrowhead) but occurred where host tissue lacked injected mRNAs (black arrowhead).