Technical Notes Wnt Inhibitor Activity: R&D Systems

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	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.

Wnt Related Products

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	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.