Even flies get fat. And the overlap between insect and mammalian biology makes them a convenient model for finding genes that may be involved in human obesity. Faced with food, starved normal (left) fruit flies (Drosophila melanogaster) feast only until they’re full. But the genetically-modified flies on the right don’t know when to stop. They gorge on the red-dyed food and become bloated. Stretching of the gut normally sends nerve signals using a neurotransmitter called leucokinin to the fly’s brain, so it knows when it’s full. In the fat flies, genes that send or receive this signal have been knocked-out, and so has the message to stop eating. Leucokinin and its receptor molecule in flies are similar to the vertebrate tachykinin system, which regulates our food intake. So it’s possible that the genes that stop us from overeating have evolved from a common ancestor shared with flies.
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