Fig. 5. Early Irx gene requirement for pronephros development occurs at neurula stages. Embryos are shown in lateral views. Embryos were injected in a single blastomere (V2.2) at the 8- to 16-cell stage and lacZ mRNA was used as linear tracer. Late neurula-early tailbud Xenopus embryos co-injected with 500 pg of HD-E1A-GR (A-H), HD-GR (I-P) or HD-EnR-GR (I,M, inset) mRNAs and assayed for expression of Lim1. (A-H) Embryos injected with a hormone-inducible activating form of Irx (HD-E1A-GR) show expanded Lim1 only when Dex was added during mid neurula stages (arrowheads). (I-P) Embryos injected with a hormone-inducible dominant negative (HD-GR) form of Irx show reduced Lim1 expression only when Dex was added during mid neurula stages (arrowheads). The same results were found with a hormone-inducible repressing form of Irx (HD-EnR-GR) (I and M, inset and not shown).