Fig. 2. Dlx activity restricts neural plate expansion but does not induce epidermal differentiation. ß-galactosidase and either EnR-Dlx3hd, EnR-Dlx5hd or VP16-Dlx3hd mRNAs were injected into one dorsal animal blastomere of 4-cell stage embryos. The embryos were then stained for the ß-galactosidase (as a lineage label; magenta stain) and assayed for Xsox2 (stage 13), NCAM (stage 17-18) or keratin (stage 17-18) expression by whole-mount in situ hybridization (blue stain), or by EpA immunostaining (stage 17-18) to reveal neural plate or epidermal differentiation. All views are dorsal with anterior to the top except M, which is lateral with anterior to the right and H and I, which are transverse histological sections through the neural tube. Dashed lines indicate the dorsal midline. (A) Xsox2 expression is the same on the injected and uninjected sides of control embryos injected with ß-galactosidase mRNA alone. (B) Injection of VP16-Dlx3hd mRNA reduces the Xsox2 domain on the injected side. (C,D) In contrast, embryos injected with EnR-Dlx3hd (C) or EnR-Dlx5hd (D) mRNA shows expanded Xsox2 expression on the injected side. (E-G) The NCAM domain was similarly reduced by or expanded by VP16-Dlx3hd and EnR-Dlx3hd, respectively. (H,I) Transverse sections through stage 25 embryos (H) the control embryo has a symmetrical, closed neural tube. (I) An embryo expressing EnR-Dlx3hd illustrates that the neural tube closed properly but was expanded on the injected side where ß-gal-positive cells populate the neural tube. Dorsal is to the top. (J-M) keratin expression; a marker expressed throughout the non-neural ectoderm. (J) Normal expression of epidermal keratin in a control embryo injected with ß-galactosidase mRNA alone. (K) Injection of VP16-Dlx3hd mRNA did not expand epidermal keratin expression. (L) Injection of EnR-Dlx3hd mRNA inhibited epidermal keratin expression. White arrows mark the loss of keratin expression in the injected region. (M) A lateral view illustrates the loss of keratin (blue) in the injected region (magenta ß-galactosidase stain). (N-P) VP16-Dlx3hd did not affect the epidermal epitope EpA (O), whereas EnR-Dlx3hd (P) prevented normal expression (N).