How the Fluorescent Proteins from Jellyfish Illuminated the Entire Biology

In a summer of 1974, if you were at the Friday Harbor in Washington, besides the magnificent Pacific Ocean, you might have seen a scientist in his 40s had gathered with his friends and family. All they were doing was catching jellyfish from the sea. They would fill their buckets with jellyfish, cut their umbrella-like ends and send those all the way to Princeton University, New Jersey, 3000 miles away. The scientist was Osamu Shimomura. He was doing this for the last 20 years or so that would eventually lead to the discovery of fluorescent protein technology.

Osamu Shimomura with his friends
Osamu Shimomura with his friends and family at the pier of Friday Harbor, Washington for catching jellyfish from North Pacific Ocean in 1974. © Osamu Shimomura

Jellyfish are not fish. They are invertebrates or animals having no backbones. In a summer day, they would float aimlessly at the surface of the sea water. A. Victoria, the jellyfish Shimomura was interested in, shows green luminescence. This bioluminescence from jellyfish would fascinate him and he would spend a good 40 years to unravel the photochemistry of it. As a result of his curiosity, green fluorescent proteins were discovered which would change the course of the way the researches in molecular biology are done. This is a classic example of how basic science leads to a major technological innovation [1].

A.Victoria has 300 photo-organs at the periphery of its umbrella-like structure. The research group of Shimomura discovered that when calcium ions bind to one of the protein in the photo-organ, aequorin, it would give off blue lights, converting chemical energy to light energy. This blue light, in turn, would excite another set of wonderful proteins, called fluorescent proteins. Deep inside of these barrel-shaped proteins, there are molecules that fluoresce green when excited with blue light. Like a mother protects her child from hostile environments, this barrel-shaped protein structure protects the fluorescent molecules (in chemical terminology they are called “chromophores”). Once the chromophores are out of the protein barrel, they would be non-fluorescent due to non-radiative energy transfer for example heat or vibrations [1, 2].

The jellyfish
The jellyfish, A. Victoria, can exhibit green fluorescence once excited with blue light due to the presence of fluorescent protein located at their photo-organs. © Wikipedia

Now can we use this protein machinery of the jellyfish to glow other organisms? For example, worms, mouse or humans? Why not? After all, we all are made of proteins. And protein can be made from DNA via mRNA or messenger RNA. All one have to do is to insert a fluorescent protein DNA into a choice of organism. That would be a stuff of science fiction movie: a green fluorescing man, engineered in a laboratory roaming around in the public. But more importantly, it would illuminate the inner working of human beings: how brain works, how cancer cells migrate invading organ by organ or how our heart rhythm occurs from the day we were born until our death. Shimomura made a cardinal mistake here. He thought only fluorescent proteins might not be sufficient for the bioluminescence in jellyfish, there might be other specific enzymes necessary for the fluorescence to occur which were only present in jellyfish. So, he continued to work on the other stuffs and forgot about the fluorescent proteins.

Science magazine
The cover of 1994 Science magazine displaying the green fluorescence in C. elegans, the round worm. © Science

But Martin Chalfie from Columbia University would doubt that other enzymes were necessary for the fluorescence in jellyfish. With the help of Douglas Prasher, a researcher from Wood Hole Oceanographic Institute, Massachusetts, he would insert the gene that encodes the fluorescent proteins into E. Coli, the bacteria. When the student working in Chalfie lab, illuminated the bacteria expressing green fluorescent proteins (GFP) with blue light in a microscope, it was a bliss! Green fluorescent proteins were scattered all over the bacteria. Chalfie attached the GFP into a touch-sensitive protein inside C. elegans, the round worm and the worm was fluorescent too. He published this ground-breaking result in 1994 Science magazine with its cover page decorating a worm expressing the fluorescent proteins. It ushered a new era in molecular biology. People from all over the world started using GFP for their research. The invisible became visible. The Roger Tsien’s lab at University of California San Diego, further changed the chromophore molecule in GFP and its surrounding proteins to produce an entire palette of color from blue to red. The red fluorescent proteins were found from coral not from jellyfish though. For their discovery of fluorescent protein technology, Osamu Shimomura, Martin Chalfie and Roger Tsien were awarded the 2008 Nobel Prize in Chemistry.

Now, fluorescent proteins technology has become inseparable for molecular biology research. Researchers from all over the world are using them to understand the basic working principle of cells, understanding the spread and cause of diseases, illuminating the neuronal networks inside brain. For example, Robert Hoffman from Anticancer Inc. is using GFP to monitor the spreading of cancer cells into the brain, lung and bone of nude (without hair) mice in a whole-body live-cell imaging technique [3]. This would help the researchers for rapid screening of chemotherapeutic drugs that would inhibit the progress of cancer or metastasis.  At the Harvard Brain Center, researches have produced the show-called transgenic “brainbow” mice with random mixing of cyan, green and yellow fluorescent proteins in individual neurons. This produces neurons with hundreds of different colors that help the scientist to map the neuronal circuits of the brain [4].

Brainbow image showing map of neuronal circuits of the mouse cerebral cortex. The method uses random combination of fluorescent proteins of different colors to target neurons. © Lichtman JW | Nature Neuroscience Reviews

New applications of fluorescent proteins are being reported regularly in the scientific literatures which ranges from sensors for heat, pH or metal ions to optical control of neurons and super-resolutions. Researchers are making the FPs brighter and more stable so that they could be imaged with more certainty. Surely, the proteins derived from jellyfish and corals illuminated the biology for decades and they continue to amaze us by unraveling the mysteries of Mother Nature.

[2] Illuminating Disease, Marc Zimmer, Oxford University Press.
[3] Whole-body optical imaging of green fluorescent protein-expressing tumors and metastases, Yang M et al., PNAS, 2000.
[4] A technicolor approach to the connectome, Lichtman JW et al., Nature Neuroscience Reviews, 2008.

The author is a Ph.D. research scholar at the University of Colorado at Boulder working in the field of biophysics. His research interests include developing new generations of fluorescent proteins and understanding their photo-physics. Premashis got his B. Sc. degree from University of Calcutta in 2010. He obtained his M. Sc. (in Chemistry) from Indian Institute of Technology Kanpur in 2012.


One thought on “How the Fluorescent Proteins from Jellyfish Illuminated the Entire Biology

  1. A great write up! The first time I read Shimomura’s Nobel lecture – I was astonished at the number of hours he spent fishing and chopping these things up 😛

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