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Keeping their heads out of the sand

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Ashley N. Paddock

Fluorescent proteins found in nature have been used in a variety of scientific studies, in capacities including probes for testing environmental quality and markers for tracing molecules in biomedicine. Although the proteins have been found most commonly in jellyfish and corals, scientists at Scripps Institution of Oceanography in La Jolla, Calif., have encountered GFP inamphioxi, fishlike animals. The creatures are noted for their important evolutionary position at the base of the large phylum of chordates and are found primarily in coastal areas burrowed up to their heads in sand. This discovery shows that such fluorescence may be more prevalent in the animal kingdom than previously was believed.

Green fluorescent proteins, used as markers to examine gene expression and as probes for tracking how molecules transfer energy, were discovered at the anterior end of the amphioxus by Deheyn and his colleagues. Images courtesy of Scripps Institutionof Oceanography, University of California, San Diego.

According to Dimitri D. Deheyn and his colleagues at the institution and at Kobe University in Hyogo and at the University of Tokyo, both in Japan, the finding emphasizes the idea that the evolutionary preservation of fluorescence must play an important ecological function. Deheyn made this discovery while analyzing a dozen specimens of the small, slender marine animals collected in Tampa, Fla., by colleague and paper co-author Nicholas D. Holland.

Although prior studies have shown the chordates to be sensitive to alterations in light exposure, Deheyn said that the exact role of fluorescence in amphioxi is unknown. The scientists hypothesized that the proteins may be used as a form of “sunscreen,” absorbing ultraviolet light and dissipating it as fluorescence. The GFP also may act as a protective antioxidant for the animals, decreasing stress levels in cells exposed to temperature fluctuations or to other environmental changes.

The amphioxus, or lancelet, a fishlike chordate found primarily in coastal areas, burrows into the ocean sand, leaving only its head exposed.

Because GFP can absorb light, change chemical configuration and “transmit” that information to neural cells, Deheyn also believes that it could be involved in photoreception. The cirri, where the fluorescence occurs, are made of ciliated cells packed one atop the other, appearing as a part of a photoreceptive system.

Deheyn reported in the October issue of Biological Bulletin that when amphioxi were placed under blue light — used for evoking fluorescence — each animal had a fluorescent green area at its anterior end. Follow-up analyses in specimens from Florida, France and Japan have revealed details of where the fluorescence is distributed along the animal’s body and of how this changes at different stages of the creature’s development.

Two views of an amphioxus show the fluorescence along its body structure, which is thought to act as a form of “sunscreen” against harmful UV rays or as a protective antioxidant to decrease stress levels in its cells resulting from exposure to harmful environmental changes.

Although the prevalence of fluorescence in the animal kingdom is still unknown — much of the animal population has not been tested — Deheyn will continue to focus on finding GFPs in marine and terrestrial environments.

Dec 2007
Biophotonicsfluorescent proteinsmoleculesPost Scriptsprobes

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