Wnt freely spreads the word

Cells exchange signaling proteins that help them to communicate with each other. These signals control which genes are active, and how cells grow and specialize to do different tasks. Signals can also help cells to position themselves inside a body to form new tissues and organs. For example, the so-called Wnt signaling system is important for many processes in the body, from early development to the growth and maintenance of tissues.

Signaling proteins are often thought to travel long distances between cells that produce them and the cells that respond to them. How these molecules move between cells has been challenging to study in a natural context. Signals may travel by diffusion – the random movement of molecules over time. But this had not been directly shown, and some studies suggest that thin, finger-like extensions from cells help carry the signals.

Pani and Goldstein investigated how Wnt signals travel between cells in the round worm, Caenorhabditis elegans. The Wnts were labelled with fluorescent tags inserted into the genome, which made them glow under certain lights. The results showed that Wnts can travel quickly between remote cells by using diffusion. Diffusion can create gradients of Wnt over long distances, with higher levels near the cells that produce Wnt and lower in others. When the Wnts were prevented from spreading freely across cells, they could not travel as far or act on their regular target cells. Both Wnt molecules and Wnt receptor proteins clustered on thin cell extensions in some cells, but the extensions were not necessary for helping the molecules spread.

This study helps us to understand one way that Wnt can traverse cells. A next step will be to examine if this aspect of Wnt signaling is similar between worms and humans. In humans, faulty Wnt signaling is implicated in many cancers. A better understanding of how this pathway normally works may help researchers develop ways to manipulate Wnt signaling in diseases.