UC San Diego

Wnt signalling plays a critical role in development, producing signals that regulate stem cell self-renewal and differentiation. Wnt signalling is initiated when a Wnt ligand binds to a Frizzled (FZD) receptor on the cell surface membrane. The mammalian genome encodes 19 Wnt and 10 Fzd genes, however, relatively little is known about specific interactions between individual Wnts and FZDs. Complicating studies to investigate Wnt-FZD interactions is that Wnt ligands are highly hydrophobic, making them difficult to purify in a biologically active form. Here, we are investigating the utility of a novel Wnt agonist that simultaneously binds FZD7 and a co-receptor encoded by the LRP6 gene to activate downstream signalling. The Wnt mimetic is highly specific to FZD7, so I was able to identify a minimal epitope of 8 amino acids necessary for binding. I showed that engineering this tag onto other FZD receptors such as FZD2 and FZD9 was sufficient to force heterodimerization of these FZDs with LRP6 using the Wnt mimetic, and thus able to activate signal transduction. I also investigated the importance of different domains in FZD7 for β-catenin dependent signaling by generating several truncations and deletions in FZD7 and generating chimeric FZD receptors between FZD7 and FZD9. This revealed that transmembrane domains and c-terminal tail are critical for FZD7 function, while the cysteine rich domain of the FZD receptor dictates ability to bind with Wnt ligands but not signaling ability.