Just about any sushi-lover knows what unagi is – it’s eel, or more specifically, the Japanese freshwater eel Anguilla japonica. What those people might not know, however, is that the eel glows green in the dark. Now, it looks like the protein that allows the fish to do so could also help doctors to assess human liver function.

Led by Drs. Atsushi Miyawaki and Akiko Kumagai, a team at Japan’s Riken Brain Science Institute have dubbed the protein UnaG, standing for Unagi Green protein. The first known fluorescent protein to be found in a vertebrate, UnaG only fluoresces when combined with naturally-occurring bilirubin present in the eels’ muscles.

A fluorescence image of a transverse section of a preserved Anguilla japonica

In humans, bilirubin is produced by the breakdown of blood hemoglobin. If too much of it is present in the bloodstream (due to a problem with the liver) it can be toxic, leading to conditions such as jaundice. The measurement of bilirubin levels in the blood is commonly used to assess the condition of the liver, and also to detect the loss of red blood cells due to anemia.

In order to develop a highly sensitive, accurate and fast method of testing for bilirubin in blood samples, the RIKEN scientists started by cloning the fluorescing gene from UnaG. Having studied the process by which it’s activated, they proceeded to create a system in which UnaG binds with any bilirubin present in a sample, causing it to glow. They now hope that once perfected, that system could find wide use, particularly in developing nations.

As a side benefit, the scientists also hope that this new value for Anguilla japonica will prompt more conservation efforts – the eel currently endangered in Japan.

A paper on the research was recently published in the journal Cell.

Source: Riken