LITTLE by little, we are discovering more about how our complex bodies function with so few genes 鈥� around 25,000 at the last count, rather than the 100,000 once predicted. In the latest twist, a single gene has unexpectedly been found to make two rival hormones affecting appetite: one that triggers hunger, and another that suppresses it.
The discovery suggests that single genes might exert more control than expected over entire hormonal and metabolic systems. In humans, the gene in question was once thought to make only the hormone ghrelin, a known appetite stimulant. But a study in rats strongly suggests it also makes a second hormone, which would tell us we are full. 鈥淭he same gene codes for two proteins with opposing actions,鈥� says Aaron Hsueh of Stanford University in California, who led the research.
鈥淭his is something spectacular,鈥� says Matthias Tsch枚p at the University of Cincinnati in Ohio, commenting on the breakthrough published in Science (vol 310, p 996). 鈥淲hy should nature press the brake and the gas pedal at once?鈥�
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After examining sequences of the ghrelin gene from 11 mammals, Hsueh鈥檚 team concluded that, as well as ghrelin, a second short protein, or peptide, with a particular structure must also be made by the gene. Sure enough, the researchers were able to extract the peptide from the contents of a rat鈥檚 stomach.
Once they had isolated it, they created a synthetic version which they injected into the guts of different rats. 鈥淭o our surprise, it suppressed appetite,鈥� says Hsueh. Rats given the hormone, which they named obestatin, halved the amount of food they ate and lost 20 per cent of their weight over a week, whereas rats given ghrelin put on weight.
鈥淩ats given obestatin halved the amount of food they ate and lost weight, while those given ghrelin put on weight鈥�
Hsueh now plans to investigate whether the rats lost weight because obestatin made them feel nauseous or because it directly controls appetite by preventing the stomach from contracting and pushing food through the digestive system. If the latter, it might lead to new drugs to control obesity.
