Fig. 7. Effects of mezzo mRNA injection on ntl expression. Overexpression of mezzo induces ectopic expression of ntl in the animal hemisphere and repress endogenous ntl at the margin. (A,B,C,D,E,G,J) Side views and (F,H,I) animal pole views of embryos at the shield stage (A-D,F-I) or 60% epiboly (E,J). (A,E,F) Control uninjected embryos. (B,G) Embryos injected at the eight-cell stage with 40 pg of mezzo plus ß-Gal RNA. (B) Expansion of the territory expressing ntl caused by injection of mezzo mRNA in the non marginal region. A close examination of these embryos showed the presence of the lineage label outside the margin. (G) Repression ntl expression caused by injection of mezzo in the marginal region. Note the presence of the lineage label in the sector of cells that do not express ntl. (C,H) Two-colour in situ hybridisation showing induction of casanova (brown) and repression of ntl (red) after overexpression of mezzo in the marginal region. (D,I,J) Injection of mezzo mRNA at the same concentration as above into one central blastomere of embryos at the 16-cell stage induced patches of ntl expression in the animal hemisphere.

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