Osamu Shimomura was a freshly-minted Phd from Nagoya University in Japan when he arrived in the United States to take up a research post at Princeton University. He came with excellent references having, against all odds, found a protein in a bioluminescent crustacean called Cypridina. The purified protein glowed 37,000 times more brightly than crushed samples of the animal itself.
His task at Princeton was to study another naturally luminescent material, this time the jellyfish Aequorea victoria which boasts a beautiful outer ring that glows a vivid green when the jellyfish is agitated. After collecting many samples of the jellyfish and filtering their tissues, Shimomura and his Princeton colleagues eventually found a bioluminescent protein, which they named aequorin. This protein glowed blue rather than green.
However, when they purified aequorin they discovered another protein in the jellyfish with a bright green fluorescence, which in 1961 they were also able to purify. They called it “green protein”, later to be renamed “green fluorescent protein” (GFP) — and so began a new kind of science based on the natural fluorescence of certain proteins.
Today, immunofluorescence is just one branch of this field of research, where scientists use the GFP of the jellyfish to label antibodies in order to observe them binding to specific protein markers. Other fluorescent proteins, and their genes, have been discovered in nature with different properties, emitting red or blue light for instance when activated. It has enabled immunologists to watch previously invisible interactions at the cellular and sub-cellular level — making it possible for example to automate certain tasks such as counting cells by machine using flow cytometry.
Shimoura says that when he first identified GFP in 1961, it had no obvious use, but 50 years later it is used routinely in laboratories around the world — thanks to the jellyfish Aequorea victoria.