...Sir John B. Gurdon and Shinya Yamanaka for the discovery that mature cells can be reprogrammed to become pluripotent.
Gurdon's major work in this area goes back to the 1960s. In '62, in what would become a classic experiment in developmental genetics, he removed the nucleus from a Xenopus egg cell, replacing it with the mature nucleus from an intestinal cell1. This modified egg cell then developed into a fully normal tadpole, indicating that the intestinal cell, despite being fully differentated, still held all the necessary 'instrictions' to form an entire organism. This became one of the pioneering experiments in both developmental genetics and nuclear transplantation. Gurdon's work was perhaps most important because it challenged the then prevalent dogma that a cell's fate was set in stone once it became specialized. Gurdon showd that this was not the case.
Yamanaka's major contribution is much more recent. Yamanaka was studying embryonic stem cells, which are always in an immature, undifferentiated state. He was interested in identifying the genes which kept these cells immature, and after finding and identifying a number of them, he wondered whether these genes could be used in mature cells to induce them to revert back into pluripotent stem cells2. He and his team introduced four of the identified genes into mature fibroblasts, and observed that the mature cells would revert back into stem cells. These induced pluripotent stem cells (iPSC) could then go on to differentiate into many other cell types. This was a major breakthrough, and the discovery was lauded in all corners of the scientific world.
Both these discoveries have lead to research in medicine that could change the world, and many of the potential applications have yet to be realized. The use of iPS cells in effectively treating diseases or correcting genetic disorders is just on the horizon. Both the pioneering work of Gurdon and the breakthrough work of Yamanaka are definitely worthy of the Nobel Prize, indeed!
1. Gurdon, J. B.;
Elsdale, T. R.; Fischberg, M. (1958). "Sexually Mature Individuals of
Xenopus laevis from the Transplantation of Single Somatic Nuclei". Nature 182 (4627): 64–65
(Read it here!)
2. Takahashi, K.; Yamanaka, S. (2006). "Induction of Pluripotent Stem Cells from Mouse Embryonic and Adult Fibroblast Cultures by Defined Factors". Cell 126 (4): 663