Seeing the Light

Researchers discover fluorescence in important fish-like animal

In late summer of 2005, Dimitri Deheyn was going about his business inside the Experimental Aquarium at Scripps Institution of Oceanography at UC San Diego.

Deheyn, a Scripps project scientist, was screening a variety of marine animals using a blue light, a device used to evaluate which organisms emit fluorescent light.

Outside of the Experimental Aquarium, Deheyn bumped into marine biology professor Nick Holland, who was carrying a bucketful of fish-like animals called amphioxus that Holland had collected in Tampa, Fla. Curious, Deheyn decided to test the newly obtained creatures and instantly came away with spectacular results.

"Every single amphioxus had a bright area in the anterior that was fluorescent," said Deheyn.

Probing the animals further, Deheyn and his colleagues at Scripps and in Japan found green fluorescent proteins, or GFPs, as the light source.

The discovery proved important not simply because a new organism was identified with GFPs, but because of amphioxus's key position in the animal kingdom. A small invertebrate that lives mostly burrowed in coastal ocean sediment, amphioxus holds an evolutionarily significant place at the base of a large phylum of animals called chordates.

In research laboratories, GFPs have proven useful in biotechnology and biomedicine as markers to trace gene expression and probes for monitoring how molecules transfer energy. Previously the proteins had been identified mostly in corals and jellyfish, leading scientists to believe that fluorescence is limited to such primitive animals. Yet the type of GFPs in amphioxus were found to be similar to those in corals, an interesting discovery since the two animal groups are separated by hundreds of millions of years of evolution, according to Scripps professor Greg Rouse.

Project scientist Dimitri Deheyn

Deheyn says the new finding supports the idea that fluorescence may be much more prevalent across the animal kingdom, a fact that goes largely unproven simply because many animals haven't been screened for fluorescence.

As for the function of GFPs in amphioxus, Deheyn says the proteins may be a form of a "sunscreen," providing protection by absorbing ultraviolet light and redirecting it away as fluorescent light. They also may serve as antioxidants, reducing stress levels during temperature fluctuations and other changes in amphioxus's environment.

Earlier this month, Deheyn headed to the southern Pacific Ocean to search for new species of fluorescent light-producing creatures.

The amphioxus research was published in Biological Bulletin and coauthored by Deheyn, Rouse, Holland, James McCarthy, Magali Porrachia at Scripps and colleagues at the University of Tokyo and Kobe University.

—Mario C. Aguilera