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Fig. 2. IGF-I and Otx2 specifically block expression of Xbra and Xwnt-11 in vivo. Embryos at 4-cell stage were injected with synthetic mRNAs corresponding to IGF-I and Otx2 in the two dorsal blastomeres near the equatorial region. They were cultured to early gastrula (A–L) or late gastrula (M–R) stage for whole-mount in situ hybridization. (A) Xbra is expressed in the entire marginal zone mesoderm in the control embryo. (B) Dorsal injection of IGF-I blocked Xbra expression near injection sites. (C) Dorsal overexpression of Otx2 also blocked Xbra expression. Coinjection with Lac Z mRNA (red-stained cells) shows cell autonomous inhibtion of Xbra expression. (D) Xwnt-11 is expressed in the entire marginal zone in a control early gastrula. (E) Dorsal injection of IGF-I blocks Xwnt-11 expression. (F) Overexpression of Otx2 also blocked Xwnt-11 expression (red staining indicates cells coinjected with Lac Z and Otx2 mRNAs). (G–L) Dorsal injection of IGF-I or Otx2 had no effect on chordin (G–I) and Xnot (J–L) expression. (M–O) At late gastrula stage, the notochordal expression of Xbra was blocked by overexpression of IGF-I and Otx2. (P–R) Overexpression of IGF-I and Otx2 does not block Xnot expression at late gastrula stage, but prevents elongation of notochord and results in delayed gastrulation. |
