XB-ART-12646Mech Dev July 1, 1999; 85 (1-2): 123-31.
Antagonist activity of DWnt-4 and wingless in the Drosophila embryonic ventral ectoderm and in heterologous Xenopus assays.
Wnt genes encode secreted signalling molecules involved in a number of basic developmental processes. In Drosophila, wingless and DWnt-4 are two physically clustered Wnt genes, which are transcribed in overlapping patterns during embryogenesis and, in several instances, are controlled by the same regulatory molecules. To address the question of the functional relationship of wingless and DWnt-4, we analysed how embryonic cells respond when they are exposed, simultaneously or not, to the encoded Wnt signals. We show that DWnt-4 has the capacity to antagonise Wingless signalling both in the Drosophila ventral epidermis and in a heterologous system, the Xenopus embryo. We provide evidence that DWnt-4 inhibits the Wingless/Wnt-1 signalling pathway upstream of the activation of transcriptional targets. This is the first report that antagonising Wnt signals exist in Drosophila.
PubMed ID: 10415353
Article link: Mech Dev
Species referenced: Xenopus
Genes referenced: chdh chrd.1 gsc otx2 wnt4
Article Images: [+] show captions
|Fig. 1. DWnt-4 counteracts the axis-inducing activity of Wg in Xenopus. Control embryos (A,a) and embryos injected, into the vegetal region of ventral blastomeres at the four-cell stage, with either 5 pg wg mRNA (B,b) or with 5 pg wg mRNA and 6 ng DWnt-4 mRNA (C,c) were left to develop until the tailbud stage (A–C, ventral views) or stained for chd mRNA at the early gastrula stage (a–c). Control embryos possess a single axis and a single cement gland (A). Embryos injected with wg mRNA show fully duplicated axes and two cement glands (B). In embryos co-injected with wg and DWnt-4 mRNAs, the formation of the secondary axis is blocked and a single cement gland is seen (C). At the early gastrula stage, control embryos (a) and those co-injected with wg and DWnt-4 mRNAs (c) show a single dorsal site of chd expression, while embryos injected with wg mRNA alone display in addition a second chd expression site (b).|
|Fig. 2. Dorsal injection of DWnt-4 mRNA blocks the formation of anterior axial structures in Xenopus but does not alter the expression of Spemann Organiser genes. Control embryos (A,B) and embryos injected with 6 ng DWnt-4 mRNA into the marginal zone of dorsal blastomeres at the four-cell stage (C,D) were left to develop till tailbud (A,C) or tadpole stages (B,D). Injected embryos show de®cient dorsal axis development, resulting in the absence of cement gland and eye (C,D). Embryos were injected with 6 ng of DWnt-4 mRNA into the marginal zone of dorsal blastomeres at the four cell stage, left to develop until the early gastrula stage and stained for chd (E), gsc (F), otx2 (G) and Xnr3 (H) transcripts. Comparison with expression in non-injected embryos (not shown) indicates that the organiser genes are normally transcribed.|