The Royal Swedish Academy of Sciences announced the 2008 Nobel Laureates last week. The prize in medicine was awarded for the discovery of the viruses that cause cervical cancer and AIDS, the prize in physics was awarded for the discovery of the causes of broken symmetry in subatomic particles, which predicts the existence of quarks, and the prize for chemistry went to three scientists for the discovery and development of a protein found in jellyfish.
That last one might not have sounded quite like Nobel prize material.
The jellyfish protein is green fluorescent protein, or GFP. The discovery of a green protein in jellyfish may not seem to compare with the discovery of HIV or predicting the existence of new particles in nature, but the uses of GFP are far-reaching: from labeling proteins to tracking cancers.
I use GFP in my own research in frog development. In my project I inject mRNA (messenger ribonucleic acid, the instructions for building proteins) that modifies cell signaling. Since neither mRNA nor my protein of interest is visible, I inject GFP mRNA along with it, which gets translated into GFP protein. This way I can trace which cells are derived from the cell that I injected. All cells that are descendents of the injected cell are green (pictured), so I know which parts of the embryo I have modified.
But this is a very mundane use of GFP. Labeling proteins directly with GFP, however, has allowed previously invisible proteins to be visualized. GFP labeled proteins carry out their functions normally but are bright green, allowing researchers to locate where proteins are, which is crucial to understanding what proteins do. And with Tsien’s modifications, proteins can be made to fluoresce red and blue as well, meaning that multiple proteins can be labeled and imaged simultaneously.
A few years ago you may have heard about scientists creating Green Pigs. These pigs have a gene for GFP fused into their genomes; every one of their cells, including their internal organs, fluoresce green. While this may seem like mad science, the pigs were created for transplantation and stem cell research aimed at treating human diseases. Green tissues or cells from these pigs can be transplanted into other animals, and their growth and movement can be easily monitored.
The prize went to Osamu Shimomura, Martin Chalfie, and Roger Y. Tsien. Shimomura first isolated the protein and discovered that it fluoresces under ultraviolet light, Chalfie demonstrated how GFP could be used to tag and image other proteins, and Tsien modified the protein to fluoresce at different colors, which allowed researchers to follow different proteins at the same time.