XB-ART-40605Development 2009 Dec 01;13624:4083-8. doi: 10.1242/dev.032524.
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Secreted Frizzled-related proteins enhance the diffusion of Wnt ligands and expand their signalling range.
Secreted Frizzled-related proteins (sFRPs) are thought to negatively modulate Wnt signalling. Although Wnt proteins are thought to diffuse extracellularly and act as morphogens, little is known about the diffusibility of either Wnts or sFRPs. Here we show that Frzb and Crescent (Cres), which are members of the sFRP family, have the ability to regulate the diffusibility and signalling areas of the Wnt ligands Wnt8 and Wnt11. We found, using the Xenopus embryo, that Wnts do not diffuse effectively, whereas Frzb and Cres spread very widely. Interestingly, Frzb and Cres substantially promoted the diffusion of Wnt8 and Wnt11 through extracellular interactions. Importantly, we show that Wnt8 conveyed by sFRPs can activate canonical Wnt signalling despite the function of sFRPs as Wnt inhibitors, suggesting a novel regulatory system for Wnts by sFRPs.
PubMed ID: 19906850
Article link: Development
Species referenced: Xenopus laevis
Genes referenced: frzb frzb2 gal.2 gpi myc otx2 szl wnt11 wnt8a
Morpholinos: frzb MO1
Article Images: [+] show captions
|Fig. 3. Cres expands the signalling area of Wnt8 through extracellular interactions. (A-C) TOP-FLASH reporter analysis. The TOP-FLASH reporter was co-injected with mRNAs for Wnt8 and Cres into one blastomere (A), or separately injected into different blastomeres (B) of four-cell stage Xenopus embryos as indicated. GPI-anchored Cres was used as an immobilised form (C). Luciferase (luc) activity was assayed at the gastrula stage. Combinations of injected mRNAs are indicated (by +). Amounts of injected mRNAs (pg/embryo) were: Wnt8, 25 in A,C; Wnt8-Myc, 33 in B; cres mRNA, 0.33, 1.0, 3.3 and 10 in A and 0.10, 0.33, 1.0, 3.3 and 10 in B,C). **P<0.01, ***P<0.001 (t-test); error bars, s.e.m.; n=10 samples, except 4 (n=9) in C. (D) Expansion of Wnt8 signalling as assayed by otx2 expression. Wnt8 was expressed by injecting a DNA expression construct (pCS2+Xwnt8, 25 pg/embryo) together with nβ-gal (pCS2+nβ-gal, 100 pg/embryo; red cells). frzb or cres mRNA (1.0 pg/embryo) was injected into the blastomere diagonal to that expressing Wnt8. otx2 expression was visualised by whole-mount in situ hybridisation. The green double-headed arrows indicate the limits of the regions of otx2 inhibition.|