It’s that time of the year again: the leaves begin to turn; the thick summer air crisply thins with chimney smoke; old competitors rise and reawaken with vigor…It’s Nobel Prize Season!

Last week, John B. Gurdon, of Cambridge University, and Shinya Yamanaka, of Kyoto University, won the 2012 Nobel Prize in Physiology or Medicine for “for the discovery that mature cells can be reprogrammed to become pluripotent,” i.e., for stem cells. We’ve written a lot about stem cells on the CLB Blog, but perhaps this occasion is worth revisiting their significance.

Complex organisms, like humans, are comprised of various tissues. When grouped together and arranged in a particular fashion, several tissues can become an organ. For example, the human heart, an organ, is made up of cardiac muscle tissue, nerve tissue, blood tissue, and others. How these tissues differentiate from one another–how a cell becomes a nerve tissue as opposed to blood tissue–is the core focus of developmental biology. When an egg is first fertilized, it’s “blank”; it has the potential to become any type of tissue. Developmental biologists refer to this property as “pluripotency” (like plural potential). Because pluripotent cells are the source, or stem, of all remaining cell types, biologists also refer to them as “stem cells.”

While developmental biologists have long been aware of this concept, it was previously thought that the developmental process was irreversible. That is, once a cell progressed from a pluripotent to a defined state, it could not go back to being pluripotent. John B. Gurdon’s work in 1958 demonstrated that this common wisdom was not correct. He transplanted the DNA from an adult Xenopus frog, a common model organism, into a frog egg, and the egg grew developed into a sexually mature adult frog. This demonstrated, among other things, that pluripotency was not irreversible and that tissue development did not make permanent changes to a cell’s DNA. Shinya Yamanaka’s work in 2006 showed that this process could be induced by simply adding proteins to a cell, rather than lifting DNA from one cell and transplanting it into another.

As Hank Greely has pointed out, notably absent from the Nobel announcement is James Thomson, the University of Wisconsin researcher who did similar work with human embryonic stem cells (hESCs). This may reflect the Nobel committee’s political or moral concerns with hESCs. Perhaps; this wouldn’t be the first controversy over the Nobel in medicine. And those controversies, I suppose, are one of the reasons we follow the Nobel announcements season after season.