An article published in the July issue of the FASEB Journal describes how graduate student Youngsup Song, working in the lab of Roger D. Cone, genetically engineered a small tropical fish — Danio rerio, or the zebrafish — to be longer and fatter than normal. At 6 months of age, the obese fish were 20% to 100% heavier than the non-engineered fish with whom they shared a tank.
The point of creating such fish is — no, not to make us all feel less self-conscious in these days of expanding waistlines — to show that zebrafish, like humans and mice, can be made obese simply through the increased activity of one of their genes, says Cone, director of the center for the study of weight regulation and associated disorders at the Oregon Health and Science University in Portland.
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It's easier to study a fish than a person — so fat fish may shed light on human obesity and help devise ways to treat it, Cone says.
The behemoth fish were engineered to produce extra amounts of a protein, AgRP, which is also naturally present in humans. In people (and mice) extra amounts of AgRP have been shown to increase appetite and slow metabolism.
A small percentage of people who are obese are that way because they have a single mutant gene, like these fish. But, Cone adds, "80 to 95% of severe obesity remains unexplained." Trawling through the zebrafish genome for genes that make fish obese may help identify some of these unknown genes in people, he says.
Cone stresses that there's a difference between the severe type of obesity created here and the increasingly prevalent type we hear about in the headlines. The latter is controlled by many genes and is influenced by factors such as a poor diet or sedentary lifestyle. Still, he adds, because common obesity is so much more complex, studying single genes with big effects is a good place to start. Enough of all this chatter: Go check out the picture of the fish.
— Chelsea Martinez