Fig. 3. MO1 disrupts axial development in Xenopus and exerts dose-dependent effects on gene expression in the early gastrula. (A-C) Xenopus embryos were injected at the one-cell stage with mMO1 (A; 40 ng) or MO1 (B,C; 40 ng) and allowed to develop to tadpole stage 33. MO1 causes axial defects and a disruption of anterior development. (D-G) The phenotype illustrated in B,C is presaged by disruption of expression of Xnot (D,E) and Chordin (F,G). Xnot expression persists around the blastopore of embryos injected with MO1. (E) Expression of Chordin in embryos injected with MO1 (F) is more diffuse than that in embryos injected with mMO1 (G). (H-K) Although axial morphogenesis is disrupted in embryos injected with antisense morpholino oligonucleotide MO1, notochord and muscle do nevertheless form in such embryos. (H,J) Embryos injected with mMO1 stained with monoclonal antibody MZ15 (H) or 12/101 (J). (I,K) Embryos injected with MO1 stained with MZ15 (I) or 12/101 (K). (L) Embryos were injected with the indicated amounts of MO1 and allowed to develop to early gastrula stage 10.5, when gene expression was assessed by real-time RT-PCR. Levels of gene expression are normalised to those of ornithine decarboxylase. Increasing concentrations of MO1 cause the downregulation first of dorsally expressed genes such as Goosecoid and chordin and then the downregulation of Xbra, which is expressed throughout the marginal zone. Expression of Xwnt8, which occurs in lateral and ventral tissue, is little affected.