Jellyfish and their relatives, the corals, have been the only animals known to produce fluorescence on their own, by synthesizing fluorescent proteins. Other light-emitting animals, like abyssal fish and squids, rely on fluorescent bacteria.

Fluorescent proteins have found a wide array of applications, from scientific research, markers for tracking molecules (for example, to see gene expression or energy transfer between molecules), to environmental quality indicators, but also in biotechnologies, biomedicine, bioengineering and even nanotechnologies.

Now, a team at Scripps Institution of Oceanography at UC San Diego have found fluorescent proteins in an animal more evolved than jellyfish, pointing that the trait could be more common than currently thought. The new green fluorescent proteins (GFPs) were found in amphioxus, a fish-like primitive chordate, reminding us of how the vertebrates' ancestors might have looked like. These GFPs resemble those encountered in corals, a surprising fact as the two clades split hundreds of millions of years ago. "The finding emphasizes the idea that evolutionary preservation of fluorescence must play an important ecological function," said lead researcher Dimitri Deheyn from the Marine Biology Research Division at Scripps.

As very few animal species have been checked for fluorescence, its presence in the animal kingdom is still an unsolved issue.

Investigations made on Amphioxus individuals from Tampa Bay, but also from France and Japan, showed how fluorescence is produced by the different parts of the animal's body and along its various developmental stages. "When I put the specimens under the blue light (used for evoking fluorescence), every single amphioxus had a bright green area in the anterior that was fluorescent," said Deheyn.

Amphioxus (lancelet) inhabits primarily shore areas, remaining mostly burrowed in ocean sand or mud, with the head out for feeding. The animal was known to react to changes in light exposure, even if it does not have eyes. "The exact role of amphioxus' fluorescence is not known.", said Deheyn.

These proteins could work as a "sunscreen" against damaging UV light and fluorescent light, or to function as protective antioxidants, reducing the negative effects of the stress in cells when the organism experiences temperature or other environmental factor variations. "There is a great deal of interest in finding new fluorescent compounds and proteins that can show different characteristics of light production.", said Deheyn, now searching for GFPs in other sea animals, but also terrestrial environments.