How a glowing jellyfish threw much light on cells

In the last few decades, our understanding of cells has seen a monumental change. We now know about the various processes that happen inside these cells and the diseases that bother them. Did you know much of it was possible because of a jellyfish and its glow?

Crystal jelly, scientifically called Aequorea victoria, is a jellyfish species found on the coasts of the Pacific Ocean in North America. What’s unique about this colourless, transparent jellyfish is that it glows green when threatened or agitated. For a long time, we did not know what caused it. In 1961, two researchers, Osamu Shimomura and Frank Johnson, finally had an answer. They noticed that although the jellyfish had a green glow when it came in contact with calcium ions, it turned blue. Intrigued, they collected tens of thousands of jellyfish from Friday Harbour, Washington, to take a more in-depth look. They identified that a protein present in the jellyfish made it glow. The protein, called aequorin, appeared greenish under sunlight but turned into fluorescent green under ultraviolet (UV) light.

Aequorin came to be known with a modest name—‘green fluorescent protein’ or GFP. Shimomura further studied the structure of GFP and found that it contains a long chain of 238 amino acids coiled into the shape of a beer can. A group of three amino acids in this chain helped absorb UV and blue light, and emit the green fluorescent light.

Martin Chalfie, another scientist, was excited about the prospects of GFPs and in 1994, used DNA technology to create roundworms with green-glowing neurons. A similar technique was later used to develop yeast, fungi, mice, and other mammals with GFP genes to produce glowing proteins. Scientists could then track these proteins in live animals to study their genetic functions. Roger Tsien, a biochemist, modified a few amino acids in the GFP to create other colours of glow, including cyan, blue and yellow.

GFPs are today used as markers and tracers in cells to ‘look’ closer into them. In recognition of their contributions, Shimomura, Chalfie, and Tsien were awarded the Nobel Prize in Chemistry in 2008. However, the crystal jelly remains a mystery as we do not yet know why it came to have its glow in the first place!