© 2020. Published by The Company of Biologists Ltd | Journal of Experimental Biology (2020) 223, jeb222539. doi:10.1242/jeb.222539 INSIDE JEB Luciferin diet fuels brittle star glow Coubris saw the A. filiformis glow dwindle until the animals were indistinguishable from a close relative, Amphiura chiajei, which never glows. Andwhentheytestedhowmuch luciferase the coelenterazine-deprived A. filiformis were producing, they found that the enzyme activity surged briefly as coelenterazine levels declined, but then fell back to normal as the brittle stars’ spark finally fizzled out. But the real question was would the dimmed brittle stars regain their glow when coelenterazine was reintroduced into their diet? Excitingly, the gamble paid off. ‘To see the brittle stars eating the food we Bioluminescence produced by an Amphiura filiformis brittle star. Photo credit: provided was a very exciting moment’, ©J. Mallefet – FNRS, UniversitéCatholique de Louvain. says a relieved Mallefet, who wasn’tsure they would take to the change in their Instead of blending in with their Mallefet travelled to Sweden to collect the diet. And when he checked the animals’ surroundings for safety, some brittle stars delicate animals. ‘It’s an ideal place to go; coelenterazine levels, he was overjoyed advertise their presence with bright within half a day of ship time we can to see their glow returning rapidly, pinpoints of light arranged along their collect 500 specimens’, he says. He then peaking 18 days after the new diet was arms. But their ostentatious spectacle is returned to Belgium carrying the fragile initiated. more than misplaced bravado. It seems animals in a large ice box packed with likely that the brazen display is designed chilly seawater and mud to keep them Amphiura filiformis extract the key to divert predators. According to Jérôme comfortable, ‘So the animals can hide, light-giving chemical from their diet Mallefet from the Université Catholique which they do in natural conditions’,he and the researchers are now eager to de Louvain, Belgium, brittle stars shed explains. Back in the lab, Mallefet placed find out which morsels provide the the brightly illuminated tips of their arms the brittle stars on a strict coelenterazine- brittle stars with their shots of light. But with ease when under attack, allowing free diet of aquarium fish food for more that will be easier said than done; victims to crawl deeper in the mud while than a year while keeping track of their ‘Imagine searching the stomach their attacker is distracted. However, it luminosity. contents of a 3 mm diameter animal to wasn’t clear how these echinoderms come identify what is inside’, chuckles by the chemicals – known as luciferins – Mallefet extracted coelenterazine from Mallefet as he and Coubris embark on that give them light, until Mallefet brittle star arms each month to keep track the next chapter of their bioluminescent realised that captive Amphiura filiformis of their levels. However, luciferins are odyssey of discovery. seemed to lose their glow after a year only one-half of the glow-in-the-dark or two. Knowing that the luciferin equation; they emit light when triggered 10.1242/jeb.222539 coelenterazine provides the illumination by an enzyme known as luciferase. To for these brittle stars, Mallefet wondered measure the quantity of coelenterazine whether it would be possible to restore in each captive brittle star arm, Mallefet Mallefet, J., Duchatelet, L. and Coubris, C. (2020). Bioluminescence induction in the their glamour by boosting their added luciferase to the coelenterazine ophiuroid Amphiura filiformis (Echinodermata). coelenterazine levels. But first he needed samples and measured the amount of J. Exp. Biol. 223, jeb218719. do:10.1242/jeb. a new batch of the animals so he light they produced. After 5 months of 218719 could follow the decrease before captivity, Mallefet and his colleagues Kathryn Knight refuelling them. Laurent Duchatelet and Constance [email protected] Inside JEB highlights the key developments in Journal of Experimental Biology. Written by science journalists, each short report gives the inside view of the science in JEB. Journal of Experimental Biology 1.