Fig. 3. Irx genes are not required for the initial activation of the early kidney genes. Embryos are shown in lateral views (except A and B, which are dorsal views); red arrowheads indicate the kidney territory. Embryos were injected in a single blastomere (V2.2) at the 8- to 16-cell stage. Xenopus embryos injected with a mix of Irx1 and Irx3 MOs and lacZ mRNA were assayed for the expression of Pax8 and Lim1 genes at early (A,B) or late (C-F) neurula stages. (A,B) Impairment of Irx gene function does not affect early expression of Pax8 (A) or Lim1 (B). (C-F) By contrast, depletion of Irx activity downregulates the expression of these genes at late neurula stage. (G,H) Tadpole embryos injected with Irx1 and Irx3 MOs and triple labelled for muscle (12/101, brown), pronephric tubules (3G8, blue) and duct (4A6, purple). The injected side (H) shows strong impairment of kidney tissue (red arrowheads) and reduced number of ventral muscle fibres (blue arrowheads) when compared with the control side (G). (I) Transverse section of the embryo shown in H. (J) The same section after treatment with propidium iodide. An increased number of fibroblast-like cells in the injected right side compared with the control left side (arrowheads).