Live imaging of active fluorophore labelled Wnt proteins.

For almost 30 years, Wnt proteins have been known as key regulators of many developmental decisions, including the formation of the embryonic axes, patterning of the CNS, limb bud outgrowth and segment polarity. However, live cell imaging of active Wnt proteins was rarely reported. Here, we have generated a Wnt2b-EGFP fusion protein that retains functionality in bona fide Wnt activity assays, although the secreted protein is rapidly cleaved by extracellular proteases. We can show with this new tool that Wnt2b-EGFP moves along the microtubules of Wnt producing cells and that this directed movement is essential for the secretion of active Wnt protein.