Measuring CamKII activity in Xenopus embryos as a read-out for non-canonical Wnt signaling

It has been known for quite some time that not all members of the Wnt family induce the formation of a secondary body axis when ectopically expressed in Xenopus embryos. An ingenious hypothesis led to the discovery that some Wnt ligands have the capacity to elicit intracellular Ca2+ signaling. This finding has been studied in more detail in the past years, which has revealed an intriguing complexity of Wnt signaling. The significance of a Wnt-induced Ca(2+)-mediated pathway during development has been demonstrated in various model systems so far and includes processes such as dorsal-ventral patterning, regulation of the canonical Wnt/beta-catenin signaling pathway, tumor formation, bone formation, and regulation of epithelial-mesenchymal transitions. Here we describe two assays to measure the activation of the Ca2+/calmodulin-dependent kinase (CamK)-II, a Ca(2+)-sensitive molecule described as a mediator of a non-canonical Wnt signaling pathway.