Fig. 9. Irx1 and Irx3 are positively regulated by retinoic acid signalling. Embryos are shown in lateral views and red arrowheads indicate the kidney territory. Embryos were injected in a single blastomere (V2.2) at the 8- to 16-cell stage and lacZ mRNA was used as linear tracer. All panels show Xenopus tadpole embryos. (A,B,E,F) Embryos injected with a dominant negative RA receptor mRNA (RAR-DN) showed impaired Irx1 (A,B) and Irx3 (E,F) expression. (C,D,G,H). Embryos injected with a constitutive RA receptor mRNA (RAR-VP16) showed a strong expansion of Irx1 (C,D) and Irx3 (G,H) expression. (I-Y) Embryos treated at different developmental stages (as indicated) with DMSO (I,M,Q,U), with the inhibitor of RA signalling pathway DEAB (J-L,R-T) or with RA (N-P,V-Y), and analyzed for Irx1 (I-P) or Irx3 (Q-Y) expression. Both genes negatively or positively responded to DEAB (J,R) or RA (N,V), respectively, only when the drugs were added at stage 12.5.