Fig. 2. Derrière, like activin, but unlike Xnr-2, can exert long-range effects in Xenopus tissue. (A) The experimental design. Animal pole regions dissected from embryos uniformly labelled with the cell lineage marker fluorescein-lysine-dextran (FLDx) were juxtaposed with animal pole regions derived from embryos injected with RNA encoding activin (5 pg), derrière (500 pg), or Xnr-2 (500 pg). Caps were cultured for 3 hours and then examined by whole-mount in situ hybridisation for expression of Xbra (B,D,F,H) or by fluorescence microscopy for detection of FLDx (C,E,G,I). (B,C) A control conjugate in which an FLDx-labelled animal cap was juxtaposed with an uninjected cap. Xbra is not activated. (D,E) A conjugate in which an FLDx-labelled animal cap was juxtaposed with an cap derived from an embryo injected with RNA encoding activin. Note induction of Xbra in FLDx-labelled tissue, as previously described (Gurdon et al., 1994; Jones et al., 1996). (F,G) A conjugate in which an FLDx-labelled animal cap was juxtaposed with an cap derived from an embryo injected with RNA encoding Xnr-2. Induction of Xbra is restricted to unlabelled tissue (see Jones et al., 1996). (H,I) A conjugate in which an FLDx-labelled animal cap was juxtaposed with a cap derived from an embryo injected with RNA encoding derrière. Note induction of Xbra in both unlabelled and FLDx-labelled tissue. In this respect the pattern of Xbra expression differs from that induced by activin (see text).

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