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Fig. 4. Induction of Xbra and Xwnt11 expression and convergent extension through inhibition of IGF signaling and Otx2 activity. (A–F) Otx2-EnR, Otx2-VP16 or dnIGFR mRNA was injected in the animal pole region at 4-cell stage. Ectodermal explants were dissected at blastula stage and cultured to early gastrula for RT-PCR analysis (A) or to late neurula stage for analysis of explant elongation (B–F). (A) RT-PCR analysis showing that Otx2-VP16 and dnIGFR induce Xbra and Xwnt11 expression in ectodermal explants similarly as bFGF. At late neurula stage, uninjected (B) or Otx2-EnR-injected (F) explants remain rounded, while Otx2-VP16-injected (C) and dnIGFR-injected (D) explants exhibit elongation similarly as bFGF-treated explants (E). (G–L) Embryos at 8-cell stage were injected with dnIGFR or Otx2-VP16 mRNA in the two dorso-animal blastomeres either alone or coinjected with Lac Z mRNA. Injected embryos at early gastrula stage were either prepared for in situ hybridization (G–I) or for ‘Keller sandwich explants’ (J–L). (G–I) Dorsal injection of dnIGFR (H) or Otx2-VP16 (I) mRNA expands the expression of Xwnt11. (J–L) Both dnIGFR (K) and Otx2-VP16 (L) potentiate elongation in ‘Keller sandwich explants’. |
