Wnt signaling has important roles in proliferation, apoptosis, tissue patterning, and cell fate.1 Its misregulation has also recently been linked to several forms of cancer.2 Wnt proteins signal through Frizzled receptors, sometimes in conjunction with co-receptors LRP-5 and -6. The Wnt pathway can be antagonized by several inhibitors including the soluble extracellular portion of the Frizzled receptor, sFRPs (soluble Frizzled-related proteins), and Dkks (Dickkopf-related proteins).3
Xwnt-8 + Inhibitor
Figure 1. (A) Xenopus embryos (16-cell stage) were injected with Xwnt-8 mRNA into a ventral/vegetal blastomere. (B) At the 64-cell stage, Wnt antagonist protein was injected into the extracellular space near the Xwnt-8 injection site.
The activity of R&D Systems' Wnt inhibitors was measured in a Xenopus secondary axis bioassay (Figure 1).4 Embryos injected with Xwnt-8 mRNA (10-20 pg) in a ventral/vegetal blastomere at the 16-cell stage form a secondary axis. The ability of Wnt antagonists to inhibit secondary axis formation was assessed by targeted injection of the inhibitors to the extracellular spaces near the Xwnt-8 injection site. The embryos were scored at stages 35 through 38 for the presence of a secondary axis (Figure 2, 3).
Xwnt-8 + Inhibitor
Figure 2. (A) A representative Xenopus embryo (stage 35) injected with Xwnt-8 mRNA has a secondary axis. (B) A representative embryo injected with Xwnt-8 mRNA and then rescued by rhDkk-1 protein (Catalog # 1096-DK) does not have a secondary axis.
Figure 3. Embryos are scored as having either a full secondary axis based on the presence of an eye and/or cement gland, or a partial secondary axis based on the presence or outgrowth of the spine. Dkk-3 is not a Wnt inhibitor in this assay and is used as a negative control.
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