BUILDING A TROJAN PIG

摘要

TO THE ANCIENT GREEKS, THE CHIMERA WAS a ferocious creature—part lion, part goat, and part snake. The first chimera that Juan Carlos Izpisua Belmonte ever created, in 1992, was considerably less intimidating: It consisted of an embryonic mouse limb grafted onto the wing of an embryonic chicken. Belmonte was a young scientist at the time, working in a lab in Heidelberg, Germany. He was transfixed by the mysteries of gene expression—the biological signals that govern how an animal develops—and the pure potential that lurked in embryonic cells. Take any vertebrate: a chicken, a pig, a human. At maturity, they are dramatically different organisms, but they start out nearly identical. Belmonte began to wonder: If a mouse limb could live on a chicken's wing, what else might be possible? How else might scientists alter the signals that dictate what a creature becomes?