When the jellyfish Aequorea victoriais is poked or jostled, spots on its rim light up like an emerald necklace. Its mysterious glow is both bioluminescent and fluorescent. Inside its miniature light organs, a chemical reaction makes blue light, and a fluorescent molecule turns the blue light to green.
The jellyfish is best known for its fluorescent molecule—the green fluorescent protein, or GFP. By inserting the genes for GFP into other organisms, scientists have turned it into a useful biological tool. Under blue light, it fluoresces brightly, letting researchers track what is happening inside living tissues and cells.
Naturally occurring fluorescent proteins have become important tools for researchers as they investigate questions like how stem cells specialize or how brain cells communicate. GFP—green fluorescent protein—was the first to be adapted for broad scientific use. Then, red fluorescent proteins from corals were adapted. Now, fluorescent proteins of many colors can be expressed in living cells, where they literally illuminate biological processes.