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More than a Glow: The Firefly
Sep 1, 2014

"One night, a very lonely firefly goes off in search of friends. Each time he sees a flicker of light he flies off toward it, but none of them turn out to be fireflies. He sees a lantern, an owl's eyes, even headlights shining in the darkness. Will the lonely firefly ever find creatures like himself?"

You need to read "The Very Lonely Firefly," a story book delighting children of all ages by Eric Carle (1) to get the answer. In the mean time, you can read this article to have better insight into the enchanting world of the firefly. Are they just a pleasure to our eyes, during their short lives in the summer, or do they live on in children's books?

Fireflies, or lightning bugs, belong to the Lampyridae family. There are thousands of firefly species all over the world and none of them are actually flies. Then what are they? Well, they are beetles, who get the names "firefly" and "lightning bug" because of the flashes of light emanating from their bodies, a process called bioluminescence (2). This "cold light" does not heat up or burn its producer through infrared or ultraviolet frequencies, and is formed by the action of an enzyme called luciferase in the lower abdomen of the firefly. It may be yellow, green, or pale red, with wavelengths from 510 to 670 nanometers. The enzyme luciferase acts on the luciferin, in the presence of magnesium ions, ATP, and oxygen to produce light (3). According to Vieira et al., 2012, in the Journal of Photochemistry and Photobiology, the firefly's luciferase is the most important and studied bioluminescence system in scientific research(4). The firefly luciferase was cloned and isolated for the purpose of constructing bioassay systems in the late 1980s (5). Since then, due to very interesting characteristics, this system has been used in numerous biomedical, pharmaceutical and bioanalytical applications (4).

In biomedical research, the ability to visualize a biological process is very important because it offers the most direct method to support or disprove any scientific claim (6). Therefore, firefly luciferase is very desirable as a reporter in this area. Typically, the luciferase gene is cloned with a DNA sequence of interest into cells and then the cells are assayed by measuring its bioluminescence. Fusing a protein with luciferase is like putting a reflective vest on a cyclist in the dark to be able to watch him. Because the firefly luciferase lights up, it helps screening for chemical biology and drug discovery applications in academia and the pharmaceutical industry (5). For example, the firefly luciferase gene was used as a reporter to screen tumor-specific promoters in lung cancer (7). Another example showing how beneficial the firefly is for scientific research is a rapid in vivo (Latin for within the living) assessment of drug efficacy against Mycobacterium tuberculosis, which is the causative agent of most cases of tuberculosis, using an improved firefly luciferase (8). In this study, Andreu et al., 2013, used a Mycobacterium tuberculosis strain carrying a red-shifted derivative of the firefly luciferase gene to infect mice, and they monitored disease progression in living animals by bioluminescence imaging before and after treatment with a frontline anti-tuberculosis drug. Furthermore, firefly luciferase was used in a research about anti-malaria drugs, an illness which affects about 5% of the world's population and brings a death toll of 0.5–2.5 million each year (9).

Firefly luciferase is not only used in biomedical research, but also in molecular plant biology. In the early '90s, plant scientists were already able to show the bioluminescence of a promoter fragment fused to the firefly luciferase gene and its regulation by phytochrome (a pigment that plants use to detect light) and the circadian clock (a roughly 24 hour cycle in the physiological processes of living beings) (10) in plants. Some examples for the great usage of this system among many others include a firefly luciferase complementation assay that was used to reveal the interacting partners of Open Stomata 1 protein, which is critical for plant drought responses in Brassica oleracea (cabbage) (11) and the characterization of the promoter region of an important gene encoding a copper chaperone for the copper/zinc superoxide dismutase that is involved in oxidative stress protection of the potato plant (12).

Scientists have found many ways to use the firefly light, but what is the function of it for its real owner? Marc Branham, an assistant professor in the department of entomology and nematology at the University of Florida, explains. "Fireflies seem to flash light for a variety of reasons. The larvae produce short glows and are primarily active at night, even though many species are subterranean (underground) or semi-aquatic. Fireflies produce defensive steroids in their bodies that make them unpalatable to predators. Larvae use their glows as warning displays to communicate their distastefulness. As adults, many fireflies have flash patterns distinctive to their species and use them to identify other members of their species as well as to discriminate between members of the opposite sex. Several studies have shown that female fireflies choose mates depending upon specific male flash pattern characteristics. Higher male flash rates, as well as increased flash intensity, have been shown to be more attractive to females in two different firefly species (13)."

Are there other creatures like fireflies producing light? "Besides fireflies, many other organisms, especially marine creatures, use bioluminescence for sexual selection, attracting prey and as a means of camouflage, and it has been estimated that about 90 percent of deep-sea animals are bioluminescent, according to the Scripps Institution of Oceanography," says Remy Melina, a staff writer for "Life's Little Mysteries."(14)

A firefly's glow is a theme of summer nights, romantic poems, and childhood adventures and books. However, when you enjoy a firework show done by fireflies next time, please look at them more carefully by thinking that they have more than that to offer humanity, including thrilling scientific inventions done with just a single protein from them. Who knows what else they have waiting to be discovered by us? How amazing it is that, like everything else created on earth, a firefly is also a very precious art piece decorated with intricate features, and even though it is very tiny, its service to humanity is, in many ways, enormous.

National Wildlife Federation
Vieira J, Pinto da Silva L, Esteves da Silva JC (2012) Advances in the knowledge of light emission by firefly luciferin and oxyluciferin. J Photochem Photobiol B. 117:33-9.
Thorne N, Inglese J, Auld DS (2010) Illuminating insights into firefly luciferase and other bioluminescent reporters used in chemical biology. Chem Biol. 17(6):646-57>
Brogan J, Li F, Li W, He Z, Huang Q, Li CY (2012) Imaging molecular pathways: reporter genes Radiat Res. 177(4):508-13.
Xu R, Guo LJ, Xin J, Li WM, Gao Y, Zheng YX, Guo YH, Lin YJ, Xie YH, Wu YQ, Xu RA (2013) Luciferase assay to screen tumour-specific promoters in lung cancer.Asian Pac J Cancer Prev. 14(11):6557-62.
Andreu N, Zelmer A, Sampson SL, Ikeh M, Bancroft GJ, Schaible UE, Wiles S, Robertson BD (2013) Rapid in vivo assessment of drug efficacy against Mycobacterium tuberculosis using an improved firefly luciferase. J Antimicrob Chemother. 68(9):2118-27.
Che P, Cui L, Kutsch O, Cui L, Li Q (2012) Validating a firefly luciferase-based high-throughput screening assay for antimalarial drug discovery. Assay Drug Dev Technol. 10(1):61-8.
Millar AJ, Short SR, Chua NH, Kay SA (1992) A novel circadian phenotype based on firefly luciferase expression in transgenic plants. Plant Cell.4(9):1075-87.
Wang M, Yuan F, Hao H, Zhang Y, Zhao H, Guo A, Hu J, Zhou X, Xie CG (2013) BolOST1, an ortholog of Open Stomata 1 with alternative splicing products in Brassica oleracea, positively modulates drought responses in plants. Biochem Biophys Res Commun. 442(3-4):214-20.
Trindade LM, Horvath BM, Bergervoet MJ, Visser RG (2003) Isolation of a gene encoding a copper chaperone for the copper/zinc superoxide dismutase and characterization of its promoter in potato. Plant Physiol. 133(2):618-29.