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Dev Biol
2000 Feb 15;2182:183-98. doi: 10.1006/dbio.1999.9586.
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Cloning and expression of the Wnt antagonists Sfrp-2 and Frzb during chick development.
Ladher RK
,
Church VL
,
Allen S
,
Robson L
,
Abdelfattah A
,
Brown NA
,
Hattersley G
,
Rosen V
,
Luyten FP
,
Dale L
,
Francis-West PH
.
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The Wnt genes are known to play fundamental roles during patterning and development of a number of embryonic structures. Receptors for Wnts are members of the Frizzled family of proteins containing a cysteine-rich domain (CRD) that binds the Wnt protein. Recently several secreted frizzled-related proteins (Sfrps) that also contain a CRD have been identified and some of these can both bind and antagonise Wnt proteins. In this paper we report the expression patterns of the chick homologues of Frzb, a known Wnt antagonist, and Sfrp-2. Both genes are expressed in areas where Wnts are known to play a role in development, including the neural tube, myotome, cartilage, and sites of epithelial-mesenchymal interactions. Initially, Sfrp-2 and Frzb are expressed in overlapping areas in the neural plate and neural tube, whereas later, they have distinct patterns. In particular Sfrp-2 is associated with myogenesis while Frzb is associated with chondrogenesis, suggesting that they play different roles during development. Finally, we have used the early Xenopus embryo as an in vivo assay to show that Sfrp-2, like Frzb, is a Wnt antagonist. These results suggest that Sfrp-2 and Frzb may function in the developing embryo by modulating Wnt signalling.
FIG. 8. Overexpression of Sfrp-2 and Frzb dorsalises the Xenopus embryo. One ventralblastomere of the four-cell staged Xenopus embryo was injected with 1 ng of RNA. (A) Uninjected stage 36 embryo. (B) Sfrp-2-injected embryo lacking posterior structures (e.g., tail). This embryo also has head defects, which were seen in 25% of the embryos, including poor differentiation of the eye. (C) Frzb-injected embryo lacking posterior structures (e.g., tail). In contrast to Sfrp-2-injected embryos, these embryos did not show head defects. (D) Section of a normal eye from an uninjected embryo. Note the three-layered structure of the retina. (E and F) Sections of abnormal eyes from Sfrp-2- (E) and Frzb- (F) injected embryos. Note the disrupted organisation of the retina. (G) Sections through control (G), Sfrp-2-injected (H), and Frzb-injected (I) embryos. The notochord is arrowed in (G). Note the highly enlarged notochord in the Sfrp-2-injected embryo.
FIG. 10. Sfrp-2 and Frzb can inhibit Xwnt-8-mediated dorsalisation.
Ventral marginal zone explants were taken from embryos that were injected with the indicated mRNAs, and muscle was detected by whole-mount immunolocalisation using the muscle-specific 12/101 antibody and is stained blue, whilst globin, a ventral marker, is shown by red staining. (A) Control whole embryo showing normal 12/101 localisation in the somites and globin ventrally. (B) Uninjected ventral marginal zone explants do not contain any muscle. (C) Xwnt-8-injected (20 pg) ventral marginal zones differentiate muscle. (D and E) Co-injection of either Sfrp-2 (2 ng) (D) or Frzb (2 ng) (E) blocks most muscle differentiation in Xwnt-8-injected (20 pg) ventral marginal zones.
