Fig. 5. A dominant negative FGFR, XFD, suppresses phenotypes caused by Xnr3 over-expression. (A) Morphology of animal caps. Elongation movements caused by Xnr3 over-expression (Xnr3) was suppressed by co-injection of XFD (Xnr3+XFD). (B) MyoD and NCAM expression in animal caps. XFD repressed the induction of MyoD in Xnr3 over-expressing animal caps. Xnr3 (500 pg), XFD (500 pg) or Xnr3+XFD (500 pg each) were injected animally into two cells of 2-cell-stage embryos, and animal caps were dissected from stage 9 embryos. Gene expressions were analyzed by real-time RT-PCR at stage 20. In each case, ornithine decarboxylase (ODC) was used as a loading control (data not shown), and expression was normalized to the level of ODC expression. MyoD expression, but not NCAM expression was inhibited by coinjection of XFD mRNA with Xnr3 mRNA. (C) Phenotypes of Xnr3, XFD or Xnr3+XFD mRNA-injected embryos. XFD rescues both the head abnormalities and finger-like protrusions of Xnr3-injected embryos. Embryos were injected with 500 pg of each mRNA at the animal pole (2 cells at the 2-cell stage). (D) XFD blocks animal cap responses to FGF, activin and Xnr3. Animal caps from wild-type and XFD mRNA over-expressing embryos were treated with FGF (top row) or activin (middle row) as described in Materials and Methods or co-injected with Xnr3 mRNA. Caps were dissected at the late blastula stage and cultured until the late neurula stage. XFD blocked responses to all three treatments.