It was one of those ‘eureka’ moments,” says Randy Moon of the experiment in which he first laid eyes on the awesome power of Wnt. Andrew McMahon of the Department of Molecular and Cellular Biology at Harvard University—who’d been a postdoc at Caltech at the same time as Moon—had reached a roadblock in his attempts to unravel the function of this secreted protein by knocking it out in mice. He knew that the protein accumulates along the future spine of a mouse embryo’s developing nervous system, and that it could be activated by a virus to give rise to mammary tumors. “So clearly it was involved in regulating cell signaling and behavior,” says Moon. “But exactly what it did and how it worked was completely opaque.”
That’s when Moon decided to lend a hand—or, more precisely, an egg. “I said to Andy, ‘You’ve got clones, why don’t you send them ...
