Fig. 11. Inhibition of activin-like or FGF signalling does not interfere with activation of derrière but does prevent its maintenance. Embryos were injected at the two-cell stage with 800 pg RNA encoding the truncated activin receptor XAR (A,D), the truncated FGF receptor XFD (B,E), or the control construct d50 (C,F). RNA encoding ß-galactosidase was co-injected as a cell lineage label in all cases. Embryos were allowed to develop to stage 9.5 (A-C) or 11 (D-F) and expression of derrière was analysed by in situ hybridisation. The initial activation of derrière is not affected by inhibition of activin-like (A) or FGF (B) signalling; note the overlap of ß-galactosidase staining (blue) with the in situ hybridisation reaction product (purple), which at this early stage is largely nuclear. Continued expression of derrière, however, does require activin-like and FGF signalling; note down-regulation of expression in D and E. Vg, vegetal pole.