'Invisibility' gene discovered

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A gene has been discovered that plays a powerful role in enabling fish to change colour in order to match their surroundings, helping them to become 'invisible' to predators and prey.

Researchers from Vanderbilt University in Tennessee have discovered a new member of a group of genes that have powerful influences on pigmentation and the regulation of body weight.

The gene is catchily named agRP2 and is found only in the pineal gland of thousands of species of bony fish such as zebrafish, trout and salmon.

Roger Cone, the supervisor of the project said: "We initially thought we had found the pathway that regulates hunger diurnally; that is the mechanism that makes you hungry during the day, but not at night. However, a follow up study ultimately discovered that this agouti protein is involved in the rapid pigment changes that allow fish to adapt to their environment."

This phenomenon, called background adaptation, is also observed in mammals but is a much slower process. The coat of the arctic hare, for example, turns from brown in summer to white camouflage against the winter snow. In contrast to mammals, fish, amphibians and reptiles can change their skin colour in a matter of minutes to a changing environment.

The gene is the third member of the 'agouti' family so named due to its role in producing a striped 'agouti' pattern in mammals. Prior to this work only two other agouti genes had been discovered in humans; one which helps determine skin and hair colour, and the other which is thought may play an important role in obesity and diabetes as it stimulates the hunger reflex.

"Together, the versatile agouti proteins and melanocortin receptors are responsible for regulation of body weight, the banded patterns of mammalian coats, and even red hair in most people," Cone said. The current work shows that agouti proteins are also involved in the camouflage mechanisms used in thousands of fish species.

For further information see: C. Zhang, Y. Song, D. A. Thompson, M. A. Madonna, G. L. Millhauser, S. Toro, Z. Varga, M. Westerfield, J. Gamse, W. Chen, R. D. Cone. Inaugural Article: Pineal-specific agouti protein regulates teleost background adaptation. Proceedings of the National Academy of Sciences, 2010; DOI: 10.1073/pnas.1014941107