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Fig. 6 Patterned response of gata5 and ntl expression to activin; dependence of both genes on TGF-β signalling. (A-D) 50% epiboly embryo coinjected at 16-32 cell stage with activin (10 mg/ml) and nls-β-gal (100 mg/ml) RNA. β-gal detected with X-Gal (turquoise nuclear staining). The embryo was photographed after staining for ntl (red) and again after detection of gata5 (blue; B,D). (A,B) Low magnification, animal pole views of the whole embryo. (C,D) Higher magnification views of the patch of ectopic expression. (C) ntl expression overlaps with the injected cells and extends 4-8 cell diameters beyond the cells injected. (D) gata5 is induced in injected cells and up to 2-3 cell diameters beyond them. A ring of cells expressing ntl alone extends for about 4 cell diameters beyond those coexpressing ntl and gata5, mimicking the normal pattern of expression of these genes. (E-G) Blastoderm margin, 50% epiboly embryos coinjected at 2-cell stage with 1 mg/ml dnXAR and 100 ng/ml nls-β-gal RNA. (E) Stained for ntl expression (red); (F) stained for gata5 expression (blue) after staining for β-gal activity and (G) gata5 stain without staining for β-gal to show more clearly the gap in gata5 expression. Expression of both genes is eliminated by inhibiting TGF-β signalling.